Tire chart width
Tire Size Chart
Tire Size Chart for 13" Wheels
21" Tire Diameter
185/60R13 = 21.7x7.3R13
215/50R13 = 21.5X8.5R13
225/45R13 = 21x8.9R13
225/50R13 = 21.9x8.9R13
255/40R13 = 21x10R13
22" Tire Diameter
155/80R13 = 22.8x6.1R13
175/70R13 = 22.6x6.9R13
205/60R13 = 22.7x8.1R13
22X8R13
23" Tire Diameter
165/80R13 = 23.4X6.5R13
185/70R13 = 23.2x7.3R13
24" Tire Diameter
175/80R13 = 24x6.9R13
185/80R13 = 24.7x7.3R13
24.5X8R13
24.5X9R13
Tire Size Chart for 14" Wheels
19" Tire Diameter
105/70R14 = 19.8X4.1R14
20" Tire Diameter
115/70R14 = 20.3X4.5R14
125/70R14 = 20.9X4.9R14
21" Tire Diameter
165/55R14 = 21.1X6.5R14
22" Tire Diameter
135/80R14 = 22.5X5.3R14
165/65R14 = 22.4x6.5R14
185/55R14 = 22x7.3R14
185/60R14 = 22.7x7.3R14
195/55R14 = 22.4x7.7R14
205/50R14 = 22.
![]()
1x8.1R14
205/55R14 = 22.9x8.1R14
225/50R14 = 22.9x8.9R14
23" Tire Diameter
175/65R14 = 23x6.9R14
175/70R14 = 23.6x6.9R14
185/65R14 = 23.5x7.3R14
195/60R14 = 23.2x7.7R14
205/60R14 = 23.7x8.1R14
24" Tire Diameter
185/70R14 = 24.2x7.3R14
185/75R14 = 24.9X7.3R14
195/65R14 = 24x7.7R14
195/70R14 = 24.7x7.7R14
215/60R14 = 24.2x8.5R14
225/60R14 = 24.6x8.9R14
25" Tire Diameter
185R14 = 25.7x7.3R14
195/75R14 = 25.5x7.7R14
205/70R14 = 25.3x8.1R14
215/70R14 = 25.9x8.5R14
235/60R14 = 25.1x9.3R14
245/60R14 = 25.6x9.6R14
26" Tire Diameter
195R14 = 26.2x7.8R14
205/75R14 = 26.1x8.1R14
215/75R14 = 26.7x8.5R14
225/70R14 = 26.4x8.9R14
26X8.5R14
27" Tire Diameter
205R14 = 27x8.2R14
27X8.5R14
27X9.5R14
28" Tire Diameter
28X10R14
30" Tire Diameter
30X10R14
Tire Size Chart for 15" Wheels
20" Tire Diameter
105/70R15 = 20.
8X4.1R15
21" Tire Diameter
115/70R15 = 21.3X4.5R15
125/70R15 = 21.9X4.9R15
165/50R15 = 21.5X6.5R15
195/45R15 = 21.9x7.7R15
22" Tire Diameter
125/80R15 = 22.9X4.9R15
145/65R15 = 22.4x5.7R15
155/60R15 = 22.3x6.1R15
165/60R15 = 22.8x6.5R15
175/55R15 = 22.6x6.9R15
195/50R15 = 22.7x7.7R15
22X8R15
22.5X4.5R15
245/40R15 = 22.7X9.6R15
275/35R15 = 22.6x10.8R15
23" Tire Diameter
135/80R15 = 23.5X5.3R15
165/65R15 = 23.4X6.5R15
175/60R15 = 23.3x6.9R15
185/55R15 = 23x7.3R15
185/60R15 = 23.7x7.3R15
195/55R15 = 23.4x7.7R15
205/50R15 = 23.1x8.1R15
205/55R15 = 23.9x8.1R15
225/45R15 = 23x8.9R15
225/50R15 = 23.9x8.9R15
295/35R15 = 23.1X11.6R15
24" Tire Diameter
135/90R15 = 24.6X5.3R15
155/80R15 = 24.8X6.1R15
175/65R15 = 24x6.9R15
185/65R15 = 24.5x7.3R15
195/60R15 = 24.2x7.7R15
205/60R15 = 24.7x8.1R15
225/55R15 = 24.7x8.
9R15
235/50R15 = 24.3x9.3R15
24X4.5R15
24X5R15
24.5X8R15
245/50R15 = 24.6x9.6R15
345/35R15 = 24.5x13.6R15
25" Tire Diameter
165/80R15 = 25.4X6.5R15
185/70R15 = 25.2x7.3R15
195/65R15 = 25x7.7R15
195/70R15 = 25.7x7.7R15
205/65R15 = 25.5x8.1R15
215/60R15 = 25.2x8.5R15
225/60R15 = 25.6x8.9R15
265/50R15 = 25.4X10.4R15
275/50R15 = 25.8x10.8R15
26" Tire Diameter
205/70R15 = 26.3x8.1R15
215/65R15 = 26x8.5R15
215/70R15 = 26.9x8.5R15
235/60R15 = 26.1x9.3R15
245/60R15 = 26.6x9.6R15
26X10R15
26X10.5R15
26X11.5R15
26X6R15
26X7.5R15
26X8R15
26X8.5R15
295/50R15 = 26.6x11.6R15
27" Tire Diameter
205/75R15 = 27.1x8.1R15
215/75R15 = 27.7x8.5R15
225/70R15 = 27.4x8.9R15
255/60R15 = 27x10R15
27X10.5R15
27X9.5R15
27.5X4.5R15
295/55R15 = 27.8X11.6R15
325/50R15 = 27.8x12.8R15
E78-15 = 27x6.5R15
28" Tire Diameter
225/75R15 = 28.
3x8.9R15
235/70R15 = 28x9.3R15
235/75R15 = 28.9x9.3R15
245/70R15 = 28.5X9.6R15
255/65R15 = 28.1x10R15
275/60R15 = 28x10.8R15
28X10.5R15
28X11.5R15
28X12.5R15
28X13.5R15
28X4.5R15
28X7.5R15
28X9R15
29" Tire Diameter
215/85R15 = 29.4X8.5R15
255/70R15 = 29.1x10R15
265/70R15 = 29.6x10.4R15
29X10.5R15
29X11.5R15
29X12.5R15
29X15.5R15
29X18R15
29X18.5R15
29X4.5R15
29X8.5R15
29.5X11.5R15
29.5X13.5R15
29.5X9R15
315/60R15 = 29.9x12.4R15
7R15 = 29.5x7.7R15
30" Tire Diameter
255/75R15 = 30.1x10R15
265/75R15 = 30.6x10.4R15
295/65R15 = 30.1x11.6R15
30X10R15
30X10.5R15
30X11.5R15
30X12.5R15
30X13.5R15
30X7R15
30X9R15
30X9.5R15
31" Tire Diameter
31X10.5R15
31X11R15
31X11.5R15
31X12.5R15
31X13R15
31X13.5R15
31X14.5R15
31X16.5R15
31X18R15
31X18.5R15
31X9.5R15
32" Tire Diameter
32X10.
5R15
32X11.5R15
32X14R15
32X16R15
32X17.5R15
32X18.5R15
32X9.5R15
33" Tire Diameter
33X10.5R15
33X11.5R15
33X12.5R15
33X13R15
33X13.5R15
33X14R15
33X14.5R15
33X15.5R15
33X16.5R15
33X19.5R15
33X21.5R15
33X9R15
33X9.5R15
34" Tire Diameter
34X10.5R15
34X12.5R15
34X9.5R15
35" Tire Diameter
35X10.5R15
35X12.5R15
35X13.5R15
35X14.5R15
35X15R15
35X15.5R15
35X16R15
36" Tire Diameter
36X12.5R15
36X13.5R15
36X14.5R15
37" Tire Diameter
37X12.5R15
37X13R15
37X13.5R15
37X14R15
37X14.5R15
38" Tire Diameter
38X12.5R15
38X13R15
38X14.5R15
38X15.5R15
38.5X11R15
38.5X13.5R15
38.5X14.5R15
38.5X15R15
38.5X16R15
39" Tire Diameter
39X13.5R15
39.5X13.5R15
39.5X15R15
39.5X18R15
40" Tire Diameter
40X16R15
42" Tire Diameter
42X14R15
42X15R15
42.
5X13.5R15
44" Tire Diameter
44X18.5R15
44X19.5R15
44X21R15
47" Tire Diameter
47X17R15
Tire Size Chart for 16" Wheels
22" Tire Diameter
125/70R16 = 22.9X4.9R16
175/50R16 = 22.9x6.9R16
195/40R16 = 22.1x7.7R16
195/45R16 = 22.9x7.7R16
205/40R16 = 22.5x8.1R16
215/35R16 = 21.9x8.5R16
215/40R16 = 22.8x8.5R16
23" Tire Diameter
125/80R16 = 23.9X4.9R16
135/70R16 = 23.4X5.3R16
175/55R16 = 23.6x6.9R16
185/50R16 = 23.3X7.3R16
195/50R16 = 23.7x7.7R16
205/45R16 = 23.3x8.1R16
215/45R16 = 23.6x8.5R16
24" Tire Diameter
125/85R16 = 24.4X4.9R16
125/90R16 = 24.9X4.9R16
135/80R16 = 24.5X5.3R16
175/60R16 = 24.3x6.9R16
185/55R16 = 24x7.3R16
185/60R16 = 24.7X7.3R16
195/55R16 = 24.4x7.7R16
205/50R16 = 24.1x8.1R16
205/55R16 = 24.9x8.1R16
215/50R16 = 24.5X8.5R16
225/45R16 = 24x8.9R16
225/50R16 = 24.9x8.9R16
245/45R16 = 24.
7x9.6R16
25" Tire Diameter
135/90R16 = 25.6X5.3R16
145/80R16 = 25.1X5.7R16
195/60R16 = 25.2x7.7R16
205/60R16 = 25.7x8.1R16
215/55R16 = 25.3x8.5R16
225/55R16 = 25.7x8.9R16
245/50R16 = 25.6x9.6R16
265/45R16 = 25.4X10.4R16
275/45R16 = 25.7x10.8R16
315/40R16 = 25.9X12.4R16
26" Tire Diameter
145/90R16 = 26.3X5.7R16
145/90R16 = 26.3X5.7R16
195/65R16 = 26X7.7R16
205/65R16 = 26.5x8.1R16
215/60R16 = 26.2x8.5R16
225/60R16 = 26.6x8.9R16
235/55R16 = 26.2x9.3R16
255/50R16 = 26x10R16
26X11.5R16
27" Tire Diameter
155/90R16 = 27X6.1R16
195/75R16 = 27.5x7.7R16
205/70R16 = 27.3x8.1R16
215/65R16 = 27x8.5R16
215/70R16 = 27.9x8.5R16
225/65R16 = 27.5x8.9R16
235/60R16 = 27.1x9.3R16
295/50R16 = 27.6x11.6R16
355/40R16 = 27.2X14R16
28" Tire Diameter
195/80R16 = 28.3x7.7R16
205/75R16 = 28.1X8.1R16
205/80R16 = 28.9x8.1R16
215/75R16 = 28.
7x8.5R16
225/70R16 = 28.4x8.9R16
235/65R16 = 28x9.3R16
255/60R16 = 28x10R16
28X11.5R16
29" Tire Diameter
225/75R16 = 29.3x8.9R16
235/70R16 = 29x9.3R16
235/75R16 = 29.9x9.3R16
245/70R16 = 29.5x9.6R16
255/65R16 = 29.1x10R16
275/60R16 = 29X10.8R16
285/60R16 = 29.5X11.2R16
30" Tire Diameter
215/85R16 = 30.4x8.5R16
235/80R16 = 30.8x9.3R16
245/75R16 = 30.5x9.6R16
255/70R16 = 30.1x10R16
265/70R16 = 30.6x10.4R16
285/65R16 = 30.6X11.2R16
30X11.5R16
31" Tire Diameter
225/85R16 = 31.1X8.9R16
235/85R16 = 31.7x9.3R16
265/75R16 = 31.6x10.4R16
275/70R16 = 31.2x10.8R16
285/70R16 = 31.7x11.2R16
31X10.5R16
31X11R16
31X11.5R16
31X12.5R16
7.5R16 = 31.8x8.7R16
32" Tire Diameter
265/80R16 = 32.7X10.4R16
285/75R16 = 32.8x11.2R16
305/70R16 = 32.8x12R16
32X10R16
32X11.5R16
32X9R16
33" Tire Diameter
255/85R16 = 33.
1x10R16
295/75R16 = 33.4x11.6R16
33X10.5R16
33X11.5R16
33X12.5R16
33X13R16
33X13.5R16
33X14R16
33X14.5R16
33X9.5R16
33.5X16.5R16
34" Tire Diameter
315/75R16 = 34.6x12.4R16
34X10.5R16
34X12.5R16
34X13.5R16
34X9R16
34.5X17R16
35" Tire Diameter
35X10.5R16
35X12.5R16
35X14.5R16
35X15R16
35X16R16
375/65R16 = 35.2x14.8R16
36" Tire Diameter
325/80R16 = 36.5x12.8R16
345/75R16 = 36.4x13.6R16
36X12.5R16
36X13R16
36X13.5R16
36X14.5R16
37" Tire Diameter
365/75R16 = 37.6x14.4R16
37X12.5R16
37X13R16
37X13.5R16
37X14R16
37X14.5R16
385/70R16 = 37.2x15.2R16
395/70R16 = 37.8x15.6R16
38" Tire Diameter
38X13R16
38X14.5R16
38X15.5R16
38.5X11R16
38.5X13.5R16
38.5X14.5R16
38.5X15R16
39" Tire Diameter
39X13.5R16
39.5X13.5R16
39.5X15R16
40" Tire Diameter
40X16R16
41" Tire Diameter
41X14.
5R16
42" Tire Diameter
42X14R16
42X15R16
42.5X13.5R16
44" Tire Diameter
44X19.5R16
44X21R16
46" Tire Diameter
46X19.5R16
Tire Size Chart for 16.5" Wheels
29" Tire Diameter
8.75R16.5 = 29.5x8.8R16.5
30" Tire Diameter
9.5R16.5 = 30.6x9.5R16.5
32" Tire Diameter
32X12R16.5
33" Tire Diameter
33X11.5R16.5
33X12.5R16.5
33X14R16.5
33X14.5R16.5
33X15.5R16.5
35" Tire Diameter
35X12.5R16.5
35X14.5R16.5
35X15R16.5
35X15.5R16.5
35X16R16.5
35X9.5R16.5
36" Tire Diameter
36X12.5R16.5
36X13.5R16.5
36X14.5R16.5
36X16R16.5
37" Tire Diameter
37X12.5R16.5
37X13R16.5
37X14R16.5
38" Tire Diameter
38X11R16.5
38X12.5R16.5
38X15.5R16.5
38.5X11R16.5
38.5X13.5R16.5
38.5X14.5R16.5
38.5X15R16.5
38.
5X16R16.5
39" Tire Diameter
39X13.5R16.5
39.5X13.5R16.5
39.5X15R16.5
39.5X18R16.5
42" Tire Diameter
42X14R16.5
42X15R16.5
42.5X13.5R16.5
43" Tire Diameter
43X14.5R16.5
44" Tire Diameter
44X18.5R16.5
44X18.5R16.5
44X19.5R16.5
44X21R16.5
47" Tire Diameter
47X17R16.5
48" Tire Diameter
48X12.5R16.5
49" Tire Diameter
49X21R16.5
Tire Size Chart for 17" Wheels
22" Tire Diameter
22X2.5R17
23" Tire Diameter
125/70R17 = 23.9X4.9R17
195/40R17 = 23.1x7.7R17
195/45R17 = 23.9x7.7R17
205/40R17 = 23.5x8.1R17
215/35R17 = 22.9x8.5R17
215/40R17 = 23.8x8.5R17
225/35R17 = 23.2x8.9R17
245/35R17 = 23.8x9.6R17
24" Tire Diameter
125/80R17 = 24.9X4.9R17
135/70R17 = 24.4X5.3R17
205/45R17 = 24.3x8.1R17
215/45R17 = 24.6x8.5R17
225/40R17 = 24.
1x8.9R17
235/40R17 = 24.4x9.3R17
245/40R17 = 24.7x9.6R17
275/35R17 = 24.6x10.8R17
25" Tire Diameter
115/95R17 = 25.6X4.5R17
135/80R17 = 25.5X5.3R17
145/70R17 = 25X5.7R17
155/70R17 = 25.5X6.1R17
205/50R17 = 25.1x8.1R17
205/55R17 = 25.9x8.1R17
215/50R17 = 25.5X8.5R17
225/45R17 = 25x8.9R17
225/50R17 = 25.9x8.9R17
235/45R17 = 25.3x9.3R17
245/45R17 = 25.7x9.6R17
255/40R17 = 25x10R17
265/40R17 = 25.3x10.4R17
275/40R17 = 25.7x10.8R17
295/35R17 = 25.1x11.6R17
315/35R17 = 25.7x12.4R17
26" Tire Diameter
135/90R17 = 26.6X5.3R17
145/80R17 = 26.1X5.7R17
155/80R17 = 26.8X6.1R17
215/55R17 = 26.3x8.5R17
225/55R17 = 26.7x8.9R17
235/50R17 = 26.3x9.3R17
245/50R17 = 26.6x9.6R17
255/45R17 = 26x10R17
26X11.5R17
285/40R17 = 26x11.2R17
295/40R17 = 26.3x11.6R17
335/35R17 = 26.2x13.2R17
27" Tire Diameter
145/90R17 = 27.3X5.7R17
165/80R17 = 27.
4X6.5R17
215/60R17 = 27.2x8.5R17
225/60R17 = 27.6x8.9R17
235/55R17 = 27.2x9.3R17
245/55R17 = 27.6x9.6R17
255/50R17 = 27x10R17
275/50R17 = 27.8X10.8R17
305/45R17 = 27.8X12R17
345/40R17 = 27.9x13.6R17
28" Tire Diameter
155/90R17 = 28X6.1R17
165/90R17 = 28.7X6.5R17
215/65R17 = 28x8.5R17
215/70R17 = 28.9x8.5R17
225/65R17 = 28.5x8.9R17
235/60R17 = 28.1x9.3R17
245/60R17 = 28.6X9.6R17
255/55R17 = 28x10R17
275/55R17 = 28.9x10.8R17
29" Tire Diameter
175/90R17 = 29.4X6.9R17
225/70R17 = 29.4x8.9R17
235/65R17 = 29x9.3R17
245/65R17 = 29.5x9.6R17
255/60R17 = 29x10R17
265/60R17 = 29.5x10.4R17
30" Tire Diameter
225/75R17 = 30.3x8.9R17
235/70R17 = 30x9.3R17
235/75R17 = 30.9x9.3R17
245/70R17 = 30.5x9.6R17
255/65R17 = 30.1x10R17
265/65R17 = 30.6x10.4R17
275/60R17 = 30x10.8R17
285/60R17 = 30.5X11.2R17
31" Tire Diameter
235/80R17 = 31.
8x9.3R17
245/75R17 = 31.5x9.6R17
255/70R17 = 31.1x10R17
265/70R17 = 31.6x10.4R17
275/65R17 = 31.1x10.8R17
285/65R17 = 31.6x11.2R17
31X10.5R17
32" Tire Diameter
235/85R17 = 32.7X9.3R17
255/75R17 = 32.1x10R17
275/70R17 = 32.2x10.8R17
285/70R17 = 32.7x11.2R17
305/65R17 = 32.6x12R17
32X10.5R17
32X11.5R17
33" Tire Diameter
255/80R17 = 33.1x10R17
285/75R17 = 33.8x11.2R17
295/70R17 = 33.3x11.6R17
305/70R17 = 33.8x12R17
33X10.5R17
33X12.5R17
33X13R17
33X13.5R17
33X9.5R17
34" Tire Diameter
275/80R17 = 34.3X10.8R17
315/70R17 = 34.4x12.4R17
325/70R17 = 34.9x12.8R17
34X10.5R17
35" Tire Diameter
35X10.5R17
35X11.5R17
35X12.5R17
35X13.5R17
35X14.5R17
36" Tire Diameter
355/70R17 = 36.6x14R17
36X12.5R17
36X13.5R17
37" Tire Diameter
37X12.5R17
37X13R17
37X13.5R17
37X14R17
38" Tire Diameter
38X13.
5R17
38X14.5R17
38X15.5R17
38.5X13.5R17
38.5X14.5R17
39" Tire Diameter
39X13.5R17
39.5X13.5R17
39.5X15R17
40" Tire Diameter
40X13.5R17
40X14.5R17
40X16R17
41" Tire Diameter
41X14.5R17
42" Tire Diameter
42X14R17
42X14.5R17
42X15R17
42.5X13.5R17
43" Tire Diameter
43X14.5R17
44" Tire Diameter
44X19.5R17
44X21R17
47" Tire Diameter
47X17R17
49" Tire Diameter
49X21R17
54" Tire Diameter
54X19.5R17
Tire Size Chart for 18" Wheels
23" Tire Diameter
215/35R18 = 23.9x8.5R18
24" Tire Diameter
125/70R18 = 24.9X4.9R18
205/40R18 = 24.5x8.1R18
215/40R18 = 24.8x8.5R18
225/35R18 = 24.2x8.9R18
235/35R18 = 24.5x9.3R18
245/35R18 = 24.8x9.6R18
285/30R18 = 24.7x11.2R18
25" Tire Diameter
135/70R18 = 25.
4X5.3R18
155/60R18 = 25.3X6.1R18
215/45R18 = 25.6x8.5R18
225/40R18 = 25.1x8.9R18
235/40R18 = 25.4x9.3R18
245/40R18 = 25.7x9.6R18
255/35R18 = 25x10R18
265/35R18 = 25.3x10.4R18
275/35R18 = 25.6x10.8R18
285/35R18 = 25.9x11.2R18
295/30R18 = 25x11.6R18
305/30R18 = 25.2x12R18
315/30R18 = 25.4x12.4R18
335/30R18 = 25.9x13.2R18
26" Tire Diameter
135/80R18 = 26.5X5.3R18
145/70R18 = 26X5.7R18
215/50R18 = 26.5X8.5R18
225/45R18 = 26x8.9R18
225/50R18 = 26.9x8.9R18
235/45R18 = 26.3x9.3R18
245/45R18 = 26.7x9.6R18
255/40R18 = 26x10R18
26X12R18
265/40R18 = 26.3x10.4R18
275/40R18 = 26.7x10.8R18
295/35R18 = 26.1x11.6R18
305/35R18 = 26.4x12R18
315/35R18 = 26.7x12.4R18
345/30R18 = 26.1x13.6R18
27" Tire Diameter
145/80R18 = 27.1X5.7R18
145/85R18 = 27.7X5.7R18
215/55R18 = 27.3x8.5R18
225/55R18 = 27.7x8.9R18
235/50R18 = 27.3x9.3R18
245/50R18 = 27.
6x9.6R18
255/45R18 = 27x10R18
265/45R18 = 27.4x10.4R18
275/45R18 = 27.7x10.8R18
285/40R18 = 27x11.2R18
295/40R18 = 27.3x11.6R18
305/40R18 = 27.6X12R18
315/40R18 = 27.9x12.4R18
325/35R18 = 27x12.8R18
345/35R18 = 27.5x13.6R18
28" Tire Diameter
155/85R18 = 28.4X6.1R18
225/60R18 = 28.6x8.9R18
235/55R18 = 28.2x9.3R18
245/55R18 = 28.6x9.6R18
255/50R18 = 28x10R18
265/50R18 = 28.4X10.4R18
285/45R18 = 28.1x11.2R18
295/45R18 = 28.5x11.6R18
305/45R18 = 28.8X12R18
29" Tire Diameter
155/90R18 = 29X6.1R18
165/90R18 = 29.7X6.5R18
225/65R18 = 29.5X8.9R18
235/60R18 = 29.1x9.3R18
245/60R18 = 29.6x9.6R18
255/55R18 = 29x10R18
265/55R18 = 29.5X10.4R18
275/55R18 = 29.9x10.8R18
285/50R18 = 29.2x11.2R18
325/45R18 = 29.5X12.8R18
30" Tire Diameter
175/90R18 = 30.4X6.9R18
235/65R18 = 30x9.3R18
245/65R18 = 30.5x9.6R18
255/60R18 = 30x10R18
265/60R18 = 30.
5x10.4R18
285/55R18 = 30.3x11.2R18
31" Tire Diameter
235/70R18 = 31X9.3R18
255/65R18 = 31.1x10R18
265/65R18 = 31.6x10.4R18
275/60R18 = 31x10.8R18
285/60R18 = 31.5x11.2R18
32" Tire Diameter
255/70R18 = 32.1x10R18
265/70R18 = 32.6x10.4R18
275/65R18 = 32.1x10.8R18
285/65R18 = 32.6x11.2R18
305/60R18 = 32.4x12R18
33" Tire Diameter
275/70R18 = 33.2x10.8R18
285/70R18 = 33.7x11.2R18
295/65R18 = 33.1x11.6R18
305/65R18 = 33.6x12R18
325/60R18 = 33.4x12.8R18
33X10.5R18
33X11.5R18
33X12.5R18
33X13R18
33X13.5R18
34" Tire Diameter
285/75R18 = 34.8x11.2R18
295/70R18 = 34.3X11.6R18
305/70R18 = 34.8x12R18
325/65R18 = 34.6x12.8R18
34X12.5R18
35" Tire Diameter
315/70R18 = 35.4x12.4R18
35X11.5R18
35X12.5R18
35X13R18
35X13.5R18
35X14.5R18
36" Tire Diameter
355/65R18 = 36.2x14R18
36X13.
5R18
37" Tire Diameter
37X11.5R18
37X12.5R18
37X13.5R18
38" Tire Diameter
38X13.5R18
38X14.5R18
38X15R18
38X15.5R18
38.5X14.5R18
40" Tire Diameter
40X13.5R18
40X14.5R18
41" Tire Diameter
41X14.5R18
Tire Size Chart for 19" Wheels
24" Tire Diameter
215/35R19 = 24.9x8.5R19
235/30R19 = 24.6x9.3R19
245/30R19 = 24.8x9.6R19
295/25R19 = 24.8X11.6R19
25" Tire Diameter
115/70R19 = 25.3X4.5R19
125/70R19 = 25.9X4.9R19
225/35R19 = 25.2x8.9R19
235/35R19 = 25.5x9.3R19
245/35R19 = 25.8x9.6R19
255/30R19 = 25x10R19
265/30R19 = 25.3x10.4R19
275/30R19 = 25.5x10.8R19
285/30R19 = 25.7x11.2R19
315/25R19 = 25.2x12.4R19
26" Tire Diameter
135/70R19 = 26.4X5.3R19
225/40R19 = 26.1x8.9R19
235/40R19 = 26.4x9.3R19
245/40R19 = 26.7x9.6R19
255/35R19 = 26x10R19
265/35R19 = 26.3x10.
4R19
275/35R19 = 26.6x10.8R19
285/35R19 = 26.9x11.2R19
295/30R19 = 26x11.6R19
305/30R19 = 26.2x12R19
315/30R19 = 26.4x12.4R19
325/30R19 = 26.7x12.8R19
335/30R19 = 26.9x13.2R19
27" Tire Diameter
155/70R19 = 27.5x6.1R19
175/60R19 = 27.3x6.9R19
225/45R19 = 27x8.9R19
235/45R19 = 27.3x9.3R19
245/45R19 = 27.7x9.6R19
255/40R19 = 27x10R19
265/40R19 = 27.3x10.4R19
275/40R19 = 27.7x10.8R19
295/35R19 = 27.1x11.6R19
305/35R19 = 27.4X12R19
315/35R19 = 27.7x12.4R19
345/30R19 = 27.1x13.6R19
355/30R19 = 27.4x14R19
28" Tire Diameter
145/80R19 = 28.1X5.7R19
155/80R19 = 28.8X6.1R19
225/55R19 = 28.7x8.9R19
235/50R19 = 28.3x9.3R19
245/50R19 = 28.6x9.6R19
255/45R19 = 28x10R19
265/45R19 = 28.4X10.4R19
275/45R19 = 28.7x10.8R19
285/40R19 = 28x11.2R19
295/40R19 = 28.3X11.6R19
315/40R19 = 28.9x12.4R19
345/35R19 = 28.5x13.6R19
29" Tire Diameter
235/55R19 = 29.
![]()
2x9.3R19
245/55R19 = 29.6x9.6R19
255/50R19 = 29x10R19
265/50R19 = 29.4x10.4R19
275/50R19 = 29.8X10.8R19
285/45R19 = 29.1x11.2R19
295/45R19 = 29.5x11.6R19
30" Tire Diameter
165/90R19 = 30.7X6.5R19
175/80R19 = 30X6.9R19
255/55R19 = 30x10R19
265/55R19 = 30.5x10.4R19
275/55R19 = 30.9x10.8R19
31" Tire Diameter
235/65R19 = 31X9.3R19
255/60R19 = 31x10R19
Tire Size Chart for 20" Wheels
25" Tire Diameter
215/30R20 = 25.1X8.5R20
225/30R20 = 25.3x8.9R20
235/30R20 = 25.6x9.3R20
245/30R20 = 25.8x9.6R20
275/25R20 = 25.4X10.8R20
285/25R20 = 25.6x11.2R20
295/25R20 = 25.8x11.6R20
26" Tire Diameter
145/60R20 = 26.9X5.7R20
225/35R20 = 26.2x8.9R20
235/35R20 = 26.5x9.3R20
245/35R20 = 26.8x9.6R20
255/30R20 = 26x10R20
265/30R20 = 26.3x10.4R20
275/30R20 = 26.5x10.8R20
285/30R20 = 26.7x11.2R20
305/25R20 = 26x12R20
315/25R20 = 26.
![]()
2x12.4R20
325/25R20 = 26.4x12.8R20
335/25R20 = 26.6x13.2R20
345/25R20 = 26.8X13.6R20
27" Tire Diameter
155/60R20 = 27.3x6.1R20
155/65R20 = 27.9X6.1R20
165/60R20 = 27.8X6.5R20
175/55R20 = 27.6x6.9R20
195/50R20 = 27.7x7.7R20
215/45R20 = 27.6x8.5R20
225/40R20 = 27.1X8.9R20
235/40R20 = 27.4x9.3R20
245/40R20 = 27.7x9.6R20
255/35R20 = 27x10R20
265/35R20 = 27.3x10.4R20
275/35R20 = 27.6x10.8R20
285/35R20 = 27.9x11.2R20
295/30R20 = 27x11.6R20
305/30R20 = 27.2x12R20
315/30R20 = 27.4x12.4R20
325/30R20 = 27.7x12.8R20
335/30R20 = 27.9x13.2R20
28" Tire Diameter
225/45R20 = 28X8.9R20
235/45R20 = 28.3x9.3R20
245/45R20 = 28.7x9.6R20
255/40R20 = 28x10R20
265/40R20 = 28.3x10.4R20
275/40R20 = 28.7x10.8R20
295/35R20 = 28.1x11.6R20
305/35R20 = 28.4x12R20
315/35R20 = 28.7x12.4R20
345/30R20 = 28.1x13.6R20
29" Tire Diameter
235/50R20 = 29.
![]()
3X9.3R20
245/50R20 = 29.6x9.6R20
255/45R20 = 29x10R20
265/45R20 = 29.4x10.4R20
275/45R20 = 29.7x10.8R20
285/40R20 = 29x11.2R20
295/40R20 = 29.3x11.6R20
305/40R20 = 29.6X12R20
325/35R20 = 29X12.8R20
30" Tire Diameter
235/55R20 = 30.2x9.3R20
255/50R20 = 30x10R20
265/50R20 = 30.4x10.4R20
275/50R20 = 30.8x10.8R20
285/45R20 = 30.1X11.2R20
295/45R20 = 30.5x11.6R20
305/45R20 = 30.8x12R20
31" Tire Diameter
245/60R20 = 31.6x9.6R20
255/55R20 = 31x10R20
275/55R20 = 31.9x10.8R20
285/50R20 = 31.2x11.2R20
295/50R20 = 31.6x11.6R20
31X18R20
32" Tire Diameter
265/60R20 = 32.5x10.4R20
285/55R20 = 32.3x11.2R20
295/55R20 = 32.8X11.6R20
305/50R20 = 32x12R20
315/50R20 = 32.4x12.4R20
325/50R20 = 32.8x12.8R20
33" Tire Diameter
275/60R20 = 33x10.8R20
285/60R20 = 33.5x11.2R20
295/60R20 = 33.9X11.6R20
305/55R20 = 33.2x12R20
33X11.
![]()
5R20
33X12R20
33X12.5R20
33X13.5R20
34" Tire Diameter
275/65R20 = 34.1x10.8R20
285/65R20 = 34.6x11.2R20
305/60R20 = 34.4x12R20
315/60R20 = 34.9x12.4R20
355/50R20 = 34X14R20
35" Tire Diameter
295/65R20 = 35.1X11.6R20
325/60R20 = 35.4x12.8R20
35X11.5R20
35X12.5R20
35X13R20
35X13.5R20
35X14.5R20
36" Tire Diameter
355/60R20 = 36.8x14R20
36X13.5R20
36X15.5R20
37" Tire Diameter
37X11.5R20
37X12.5R20
37X13.5R20
37X14.5R20
38" Tire Diameter
38X13.5R20
38X14.5R20
38X15.5R20
38.5X13.5R20
38.5X14.5R20
39" Tire Diameter
39X13.5R20
39.5X13.5R20
39.5X15R20
40" Tire Diameter
40X13.5R20
40X14.5R20
40X15.5R20
41" Tire Diameter
41X14.5R20
42" Tire Diameter
42X14.5R20
42X15R20
42.5X13.5R20
43" Tire Diameter
43X14.
![]()
5R20
44" Tire Diameter
44X19.5R20
44X19.5R20
44X21R20
45" Tire Diameter
45X14.5R20
46" Tire Diameter
46X19.5R20
49" Tire Diameter
49X21R20
54" Tire Diameter
54X19.5R20
Tire Size Chart for 21" Wheels
26" Tire Diameter
245/30R21 = 26.8x9.6R21
295/25R21 = 26.8x11.6R21
27" Tire Diameter
245/35R21 = 27.8x9.6R21
255/30R21 = 27x10R21
265/30R21 = 27.3x10.4R21
275/30R21 = 27.5x10.8R21
285/30R21 = 27.7x11.2R21
305/25R21 = 27x12R21
325/25R21 = 27.4x12.8R21
28" Tire Diameter
245/40R21 = 28.7x9.6R21
255/35R21 = 28X10R21
265/35R21 = 28.3x10.4R21
275/35R21 = 28.6x10.8R21
285/35R21 = 28.9x11.2R21
295/30R21 = 28x11.6R21
305/30R21 = 28.2x12R21
315/30R21 = 28.4X12.4R21
325/30R21 = 28.7x12.8R21
355/25R21 = 28x14R21
29" Tire Diameter
245/45R21 = 29.7X9.
![]()
6R21
255/40R21 = 29X10R21
265/40R21 = 29.3x10.4R21
275/40R21 = 29.7x10.8R21
295/35R21 = 29.1x11.6R21
305/35R21 = 29.4X12R21
315/35R21 = 29.7X12.4R21
30" Tire Diameter
265/45R21 = 30.4x10.4R21
275/45R21 = 30.7x10.8R21
285/40R21 = 30X11.2R21
295/40R21 = 30.3x11.6R21
315/40R21 = 30.9X12.4R21
31" Tire Diameter
255/50R21 = 31x10R21
275/50R21 = 31.8X10.8R21
285/45R21 = 31.1x11.2R21
325/40R21 = 31.2X12.8R21
Tire Size Chart for 22" Wheels
27" Tire Diameter
235/30R22 = 27.6x9.3R22
245/30R22 = 27.8x9.6R22
275/25R22 = 27.4x10.8R22
285/25R22 = 27.6x11.2R22
295/25R22 = 27.8x11.6R22
28" Tire Diameter
255/30R22 = 28x10R22
265/30R22 = 28.3x10.4R22
275/30R22 = 28.5X10.8R22
285/30R22 = 28.7x11.2R22
305/25R22 = 28x12R22
315/25R22 = 28.2x12.4R22
335/25R22 = 28.6x13.2R22
29" Tire Diameter
255/35R22 = 29x10R22
265/35R22 = 29.
![]()
3x10.4R22
275/35R22 = 29.6X10.8R22
285/35R22 = 29.9x11.2R22
295/30R22 = 29x11.6R22
305/30R22 = 29.2x12R22
315/30R22 = 29.4X12.4R22
30" Tire Diameter
255/40R22 = 30X10R22
265/40R22 = 30.3x10.4R22
275/40R22 = 30.7x10.8R22
295/35R22 = 30.1X11.6R22
305/35R22 = 30.4X12R22
315/35R22 = 30.7X12.4R22
31" Tire Diameter
255/45R22 = 31X10R22
265/45R22 = 31.4X10.4R22
275/45R22 = 31.7x10.8R22
285/40R22 = 31x11.2R22
295/40R22 = 31.3x11.6R22
305/40R22 = 31.6x12R22
325/35R22 = 31X12.8R22
32" Tire Diameter
275/50R22 = 32.8x10.8R22
285/45R22 = 32.1x11.2R22
305/45R22 = 32.8x12R22
33" Tire Diameter
285/50R22 = 33.2x11.2R22
33X12.5R22
33X14.5R22
355/40R22 = 33.2X14R22
34" Tire Diameter
285/55R22 = 34.3X11.2R22
295/55R22 = 34.8X11.6R22
305/50R22 = 34x12R22
325/50R22 = 34.8x12.8R22
35" Tire Diameter
35X12.
![]()
5R22
35X14.5R22
35X15.5R22
375/45R22 = 35.3X14.8R22
36" Tire Diameter
325/55R22 = 36.1x12.8R22
335/55R22 = 36.5X13.2R22
37" Tire Diameter
325/60R22 = 37.4x12.8R22
37X12.5R22
37X13.5R22
38" Tire Diameter
355/60R22 = 38.8x14R22
38X13.5R22
38X15.5R22
40" Tire Diameter
40X14.5R22
40X15.5R22
41" Tire Diameter
41X14.5R22
42" Tire Diameter
42.5X13.5R22
Tire Size Chart for 23" Wheels
28" Tire Diameter
265/25R23 = 28.2X10.4R23
30" Tire Diameter
285/35R23 = 30.9x11.2R23
325/30R23 = 30.7X12.8R23
31" Tire Diameter
275/40R23 = 31.7X10.8R23
32" Tire Diameter
285/40R23 = 32x11.2R23
305/40R23 = 32.6x12R23
325/35R23 = 32X12.8R23
Tire Size Chart for 24" Wheels
29" Tire Diameter
275/25R24 = 29.4x10.8R24
30" Tire Diameter
255/30R24 = 30x10R24
275/30R24 = 30.
![]()
5x10.8R24
285/30R24 = 30.7x11.2R24
31" Tire Diameter
285/35R24 = 31.9x11.2R24
295/30R24 = 31X11.6R24
32" Tire Diameter
295/35R24 = 32.1x11.6R24
305/35R24 = 32.4x12R24
315/35R24 = 32.7x12.4R24
405/25R24 = 32x15.9R24
33" Tire Diameter
285/40R24 = 33x11.2R24
295/40R24 = 33.3x11.6R24
34" Tire Diameter
385/35R24 = 34.6x15.2R24
35" Tire Diameter
325/45R24 = 35.5x12.8R24
35X12.5R24
35X13.5R24
375/40R24 = 35.8X14.8R24
36" Tire Diameter
315/50R24 = 36.4X12.4R24
37" Tire Diameter
37X13.5R24
37X14.5R24
38" Tire Diameter
38X13.5R24
38X14R24
38X15.5R24
40" Tire Diameter
40X13.5R24
40X14.5R24
40X15.5R24
42" Tire Diameter
42X15.5R24
Tire Size Chart for 26" Wheels
31" Tire Diameter
275/25R26 = 31.4x10.8R26
295/25R26 = 31.
![]()
8x11.6R26
33" Tire Diameter
295/30R26 = 33x11.6R26
305/30R26 = 33.2x12R26
35" Tire Diameter
315/40R26 = 35.9x12.4R26
37" Tire Diameter
37X13.5R26
38" Tire Diameter
38X15.5R26
40" Tire Diameter
40X13.5R26
40X15.5R26
42" Tire Diameter
42X15.5R26
Tire Size Chart for 28" Wheels
33" Tire Diameter
295/25R28 = 33.8x11.6R28
37" Tire Diameter
325/35R28 = 37x12.8R28
40" Tire Diameter
40X15.5R28
42" Tire Diameter
42X15.5R28
Tire Size Chart for 30" Wheels
37" Tire Diameter
315/30R30 = 37.4x12.4R30
Tire Size Explained: What the Numbers Mean
Tire size can be confusing. Some numbers on the sidewall are listed in millimeters while others are inches. Plus, the right size for your car, truck, or trailer can differ depending on where and how you drive.![]()
You can see your original equipment tire size in your owner’s manual or on the placard generally located on the driver’s side door jam. This is the sizing recommended by the vehicle manufacturer.
If you’re interested in switching out your tires for a different look or performance, a good place to start is the numbers and other indicators on your existing tires’ sidewall. Next, have a tire professional help you determine a tire size range that will fit your vehicle and driving needs.
Tire Size Meanings
Here’s what those numbers and indicators on the sidewall indicate and how to understand them:
A: TIRE TYPE The first letter in the code tells you what class of tire it is.
P stands for passenger vehicle tire. P-class tires include cars, SUVs, crossovers, minivans and smaller pickup trucks.
LT means light truck tire, designed for vehicles that are capable of carrying heavy loads, towing trailers, or for those looking for an extra heavy duty option.![]()
These are often equipped on three-quarter or 1 ton trucks and SUVs.
ST stands for Special Trailer. These tire sizes are meant for trailers, including fifth wheels and other travel trailers, as well as boat and utility trailers.
If there’s no letter before the first number, you have a metric tire most commonly referred to as European size. It’s also measured in millimeters but may have a different load capacity than a P or LT tire.
B: TIRE WIDTH The three-digit number following the letter is the tire’s width (from side to side, looking at the tire head on) in millimeters. This may also be referred to as the section width.
C: ASPECT RATIO The forward slash separates the tire width number from the two-digit aspect ratio. The bigger the aspect ratio, the higher/taller the tire’s sidewall, or “profile” as it’s sometimes called.
The aspect ratio is indicated on the tire sidewall as a percentage. It’s the height of the sidewall measured from wheel rim to top of the tread, expressed as a percentage of tire width.![]()
In this example, the aspect ratio is 65, meaning the sidewall is 65 percent as high as the tire is wide. To get the sidewall height, take the tire width of 215 mm and convert it to inches (8.46). Then multiply this by 65% (.65). This gives you an answer of 5.5, the sidewall height in inches.
D: CONSTRUCTION TYPE This single letter tells you about the internal construction of the tire.
R is for radial tires, the industry standard for most tires today. They have better road grip, lower rolling resistance for better gas mileage, ride comfort and durability than previous generations of tires. In a radial tire, the plies — layers of strong cords made of a blend of polyester, steel and fabric and coated with rubber — are laid perpendicular to the direction of travel.
D is for tires built with diagonal (crisscrossed) plies, called bias-constructed tires. They are also called conventional, x-ply, or cross-ply tires.![]()
Some motorcycle and trailer tires still use this internal construction.
Some run-flat tires are identified with an F followed by the type of internal construction.
E: WHEEL DIAMETER This two-digit number specifies wheel diameter in inches. It’s the distance between the two bead seat areas (where a tire gets tightly sealed onto the wheel).
F: LOAD INDEX The two-digit or three-digit number that follows the gap specifies tire load index. The load index symbol indicates how much weight a tire can support, based on the following standard chart. In our example, the load index is 89, which indicates the tire has a load capacity of 1,279 pounds, when inflated to the tire’s maximum air pressure rating.
G: SPEED RATING The last letter is the tire speed rating. This indicates the top speed it’s safe to travel at for a sustained amount of time. A tire with a higher speed rating can handle heat better and provide more control at faster speeds.![]()
The maximum operating speed of a vehicle is no more than the lowest speed rating of all tires mounted on the vehicle. (Of course, you should always abide by speed limits for safer driving.) Speed rating is usually, but not always, a single letter (see the chart).
Tire Size Charts
Below you will find several charts that will help you understand tire sizing numbers, including a load index chart and speed rating chart.
Buying New Wheels or Changing Your Tire Size?
A tire size calculator is a quick way to see whether the tire size you’re considering will likely fit your car, SUV, sports car, light truck or crossover.
But remember that is only an estimate. It’s important to stay within the sizing tolerances of your vehicle. Tires that are the wrong size could cause some pull in the steering wheel, rub against the suspension or body of your vehicle, reduce clearance on hills, or result in a stiffer or noisier ride.
If you’re considering mounting a different tire size on your vehicle, check with a tire expert.![]()
Find out whether the tires and wheels you have your eye on are the right fit for your vehicle’s suspension, gearing, and bodywork. And ask how any differences in revolutions per mile, tire speed, load index, and speed rating will affect your ride quality and vehicle performance.
See how new tires and rims will look on your car or truck using our Virtual Wheels simulator, available at any Les Schwab.
Find Your Store
ISA Bus Timing Diagrams
41
The tables in this chapter show the timings for all cycles explained in the previous chapter. All times are given for SYSCLK = 8 MHz, therefore, if the designed external board must work in computers with a SYSCLK frequency up to 16 MHz, then the requirements for the speed of the external board should be at least twice as tough as those given. For resources, all times are measured at the access resource connector. Time in the range of 0...11 ns has been added to account for the propagation time of the signal along the bus.![]()
In some cases, the signal is returned from the resource that was the source of the signal, synchronized with the one returned, in which case 0...22 ns is added. Time "0" means the theoretical minimum possible time and is used only as an estimate when determining the cycle time.
NOTE: Only the -MEMR and -MEMW signals are shown in the tables and timing diagrams, not -SMEMR and -SMEMW. The -SMEMR and -SMEMW signals are generated with a delay of 0 to 10 ns relative to the -MEMR and -MEMW signals in cases where the CPU, DMA controller, or regeneration controller is the master on the bus. If the master on the bus is an external board, then the delay can be increased to 22 ns.
NOTE: In all timing tables, TCLK denotes the bus clock period.
Table 6.1. Timing relationships for cycles with 0 wait cycles, normal and extended, for 16- and 8-bit memory resources and
bits.
| N | Designation | Master | Resource |
| pair | | on tire | Access |
| m- | | (ns) | (ns) |
| Etra | | Min Max Min Max |
| | | | | with |
| 1 | LA<23.![]() ..17> set before BALE | 61 | | 50 |
| 2 | BALE pulse width | 61 | | 50 |
| 3 | LA<23...17> saved after BALE | 26 | | 15 |
| 4 | LA<23...17> set before command for 16-bit | 120 | | 109 |
| | memory [1] | | | |
| 5 | -MEM CS16 true from LA<23...17> | | 102 | 66 |
| 6 | -MEM CS16 held after LA<23...17> | 0 | 0 | |
| 7a | SA<19.![]() ..0> is set before command for 16-bit | 39 | | 28 |
| | memory | | | |
| 7b | SA<19...0> is set before the command for 16 or 8- | | 102 | 91 |
| | bit UHV | | | |
| 7c | -SBHE set before instruction for 16-bit memory | 49 | | 38 |
| 7d | -SBHE set before command for 16 or 8 bit | 112 | | 101 |
| | UVV | | | |
| 8a | Duration of write/read commands when accessing 16- | 250 | | 239 |
| | bit memory (normal or extended cycle) | | | |
| 8b | Duration of write/read commands when accessing 16- | 187 | | 176 |
| | discharge air blower (normal or extended cycle) | | | |
| 8c | Duration of write/read commands when accessing 16- | 125 | | 114 |
| | bit memory (0 cycle wait cycle) | | | |
| 8d | Duration of write / read commands when accessing 8- | 530 | | 519 |
| | 42 | | | |
| | bit resources (normal or extended cycle) | | | |
| 9 | SA<19.![]() ..0> set before BALE | 40 | | 29 |
| 10a | Data settling time after read signal 16- | | 209 | 187 |
| | bit memory | | | |
| 10b | Data settling time after read signal 16- | | 132 | 110 |
| | bit UHV | | | |
| 10c | Data settling time after read signal 16- | | 132 | 110 |
| | bit memory for cycle with 0 wait cycles | | | |
| 10d | Data settling time after read signal 8- | | 489 | 467 |
| | bit UHV | | | |
| 11a | Data settling time in write cycle to 16-bit | 29 | | 40 |
| | memory | | | |
| 11b | Data settling time in write cycle to 16-bit | 33 | | 22 |
| | UVV | | | |
| 11c | Data settling time in 8-bit write cycle | 33 | | 22 |
| | resource | | | |
| 12 | SA<19.![]() ..0>, -SBHE removed after command signal | 22 | | 11 |
| 13a | Command shutdown time when accessing 16-bit | 125 | | 114 |
| | resource | | | |
| 13b | Command shutdown time when accessing 8-bit | 187 | | 176 |
| | resource | | | |
| 14 | Read data settling time until command is removed | 40 | | 62 |
| 15a | Data hold while reading | 0 | | 0 |
| 15b | Write Hold | 30 | | 30 |
| 16 | Transition of SD<15.![]() ..0> signals to the third state after | 32 | | 32 |
| | removal team | | | |
| 17 | -0WS true from command | 40 | | 18 |
| 18 | -I/O CS16 true from SA<19...0> | | 126 | 90 |
| 19 | -I/O CS16 held after SA<19...0> removed | 0 | | 0 |
| 20a | I/O CH RDY to "0" from 16-bit instruction | | 66 | 44 |
| 20b | I/O CH RDY to "0" from 8-bit instruction | | 378 | 356 |
| 21 | I/O CH RDY duration in log.![]() "0" TCLK | 1560 TCL 1560 |
| | | 0 | K | 0 |
| 22 | Remove command signal after enabling I/O CH RDY | TCL | | TCL |
| | | K | | K |
| 23 | Enable BALE after removing command | 50 | | 61 |
| 24 | Clock period (TCLK) | 125 | 167 | 125 167 |
| 25 | Data set before I/O CH RDY enabled | | | 63 |
| 26 | LA<23...17> held after command 9 enabled0003 | 41 | | 30 |
| | memory accesses | | | |
| 27 | Duration -0WS | 125 | | 125 |
| 28 | -0WS set to falloff SYSCLK | | | 10 |
| | 43 | | | | |
| 29 -0WS held after SYSCLK fall | | | 20 |
| | NOTE: (1) LA<23.![]() ..17> are generated in the same way as SA<19...0> if the master is set to |
| bus is not the CPU. | | | Tab. 6.2. |
| | Timing for the memory refresh cycle. |
| | | |
| N | Designation | Controller | External |
| pair | | regeneration | board (ns) |
| m- | | (ns) | | |
| Etra | | Min | Max | Min | Max |
| 1 | Duration -MEMR/-SMEMR | 250 | | 239 | |
| 2 | SA<19.![]() ..0> set to -MEMR | 125 | | 114 | |
| 3 | SA<19...0> held after completion | 10 | | 21 | |
| | teams | | | | |
| 4 | I/O CH RDY to log."0" from -MEMR/-SMEMR | | 81 | | 59 |
| 5 | -MEMR removed after I/O CH RDY permission | 125 | 250 | 125 | 261 |
| 6 | -REFRESH set to -MEMR | 250 | | 239 | |
| 7 | -REFRESH held after inhibition -MEMR | 125 | 250 | 125 | 211 |
| | (1) | | | | |
| 8 | SA<19.![]() ..0> and -MEMR held in third | | TCL | | |
| | state after inhibition -MEMR | | K | | |
| 9 | Duration log. "0" I/O CH RDY | TCLK | | TCLK | |
| 10 | Bus control return delay after | 2TCLK | | 2TCL | |
| | prohibitions - REFRESH | | | K | |
NOTE: (1) The -REFRESH signal can be held for a long time to perform multiple memory refresh cycles.
44
| | Timing ratios for RAP cycles | | Table 6.![]() 3. |
| | | | |
| N | Designation | External | External |
| par | | board as | board as |
| -etra | | source | receiver |
| | | | or | (ns) |
| | | controller | | |
| | | MAP (ns) | | |
| | | Min | Max | Min | Mac |
| | | | | | with |
| 1 | -DACK, AEN set to -I/OR, -I/OW | 145 | | 134 | |
| 2 | Address set before command | 102 | | 91 | |
| 3a | -I/OR installed before -MEMW | 235 | | 224 | |
| 3b | -MEMR installed before -I/OW | 30 | | 19 | |
| 4a | Data set from -I/OR(1) | | 230 | | 241 |
| 4b | Data set from -MEMR(1) | | 261 | 272 | |
| 5a | Data set before permission -MEMW | | | -21 | |
| 5b | Data set before permission -I/OW | | | -214 | |
| 6 | Read command held after inhibition | 50 | | 39 | |
| | write commands | | | | |
| 7 | Address held after commands disabled | 50 | | 39 | |
| 8 | Data held after inhibition | 50 | | 39 | |
| | teams(1) | | | | |
| 9 | I / O CH RDY to log.![]() "0" from the access command to | | 125 | | 90 |
| | memory (1) | | | | |
| 10 | T/C set before command | -60 | 60 | -49 | 49 |
| 11 | T/C held after command disabled | -60 | 60 | -49 | 49 |
| 12a | Duration -I/OR | 700 | | 689 | |
| 12b | Duration -MEMR | 450 | | 439 | |
| 13a | Duration -I/OW | 400 | | 389 | |
| 13b | Duration -MEMW | 650 | 639 | | |
| 14 | -DACK held after command disabled | 60 | | 49 | |
| 15 | AEN held after command disabled | 60 | | 49 | |
| 16 | DRQ active from command enable | | 119 | | 141 |
| 17 | Duration log.![]() "0" I/O CH RDY | TCLK | TCLK | |
NOTE: (1) Not for RMA controller, but for external board.
Table 6.4.
Tire capture cycle timings
| | 45 | | | |
| N | Designation | CPU, | | External |
| par | | controller | fee (ns) |
| -etra | | RAP, | | |
| | | controller | |
| | | regeneration | |
| | | (ns) | | |
| | | Min | Max | Min Mak |
| | | | | with |
| 1 | DACK enabled after DRQ (1) enabled | | | |
| 2 | Delay -MASTER from -DACK 0 | | | |
| 3 | PMA controller sets its outputs to third | 0 | 49 | |
| | state | | | |
| 4 | AEN withheld after authorization -MASTER | 0 | 49 | |
| 5 | External board starts generating signals | | | 60 |
| | addresses, data and command signals | | | |
| 6 | -MASTER signal held after inhibition | | | 100 |
| | DRQ | | | |
| 7 | -DACK signal held after inhibition | 0 | | 0 |
| | DRQ (2) | | | |
| 8 | External board transfers its outputs to the third | | | 0 |
| | state before signal inhibition -MASTER | | | |
| 9 | CPU starts generating its signals after | 0 | | |
| | inhibit signal -MASTER | | | |
| 10 | DRQ held inhibited after | | | 0 |
| | prohibition -DACK | | | |
NOTES: (1) The exact time intervals are determined by the DMA controller.![]()
(2) The DRQ signal shall remain disabled while the -DACK signal is enabled.
6.1 - 6.8 shows the timing diagrams of the ISA bus in various modes.
46
Fig. 6.1. 16-bit memory access cycle with 0 wait cycle.
47
Fig. 6.2. Normal and extended write/read cycle of 16-bit memory.
48
Fig. 6.3. Normal and extended write/read cycle of a 16-bit I/O device.
49
Fig. 6.4. Normal and extended write/read cycle of 8-bit memory.
50
Fig. 6.5. Normal and extended write/read cycle of an 8-bit I/O device.
51
Fig. 6.6. Normal and extended refresh cycles: 1 - The -REFRESH signal resolution time can be extended to allow for multiple refresh cycles; 2 - The current master on the bus must triage the address and command signals before the -REFRESH signal is enabled.
52
Fig. 6.7. Normal and extended RAP cycles: 1 - DRQ can go negative at any time after -DACK; 2 - -IO/CH RDY is disabled for inserting additional wait clocks.![]()
Each additional wait cycle consists of two SYSCLK cycles; 3 - The DMA controller activates the TC signal during the last data transfer.
53
Fig. 6.8. Bus capture cycle: (1) - PDP controller; (2) - External board.
Experience of another engineering investigation / Sudo Null IT News0001
We had the opportunity to conduct another small but extremely instructive tactical lesson
The theme of this post was inspired by a mailing list from Sherlock Ohms - stories about non-trivial engineering problems that arose during the diagnosis of various electronic devices are periodically posted there. So I thought, why not? Although I understand perfectly well that the topic is quite specific, it requires very specific highly specialized knowledge and is unlikely to be of interest to a wide range of readers, but it can deliver a few pleasant minutes to a narrow circle of connoisseurs of hardware puzzles. So, for those who know what a data bus is and how it works - a story in which there will be ships, shoes, sealing wax, and cabbage palms.![]()
In the process of designing a device based on the MK 1986BE1T, which I already wrote about, it became necessary to interact with external FLASH memory chips through a fairly fast interface, preferably a parallel one. Fortunately, in the MC under consideration, such an opportunity is present, and to organize access to devices mapped to memory, but not included in the MC itself, you can use the full (32 bit address, 32 bit data, 2 control signals, 4 tracking signals) external bus, and the exchange for the user program looks absolutely transparent. As always, thanks to the developers for including such an option, and, as always, dissatisfaction with the apparently insufficient documentation, although the post is not about that. Due to a number of design features and the controller, not the entire width of the data bus was used, but only 8 bits, starting from 03, which is absolutely insignificant for describing the detected problem. Mk, together with all output buffers, is powered by +3.![]()
3, in addition, to ensure the operation of other devices, pull-up resistors of 2 kΩ were connected to a voltage of +5 on the data bus. After assembling a prototype of the device, debugging began and the first test cases (of course, or, as they say, of course) did not work, after which they took (hereinafter, the plural is used, since we carried out this work with a young colleague who, for some reason, categorically does not want to write posts on Habré) an oscilloscope and climbed to look at the makeshift. And here an interesting phenomenon was discovered. The expected oscillogram of signals on the data bus should look like this (red and green colors - I didn’t come up with it, it just happened when uploading to Habr):
The fragment of the waveform marked with the number 2 is the expected behavior of the bus in the absence of an addressed external device (achieved by setting the sample input to an inactive state). The MK removes data from the bus (black line in the upper diagram) and the voltage on it begins to be pulled up to power through the supply resistor.![]()
After some time, the MC generates an active level (zero) of the read signal (green signal in the lower diagram) and at this moment the external device must transmit data (since it is inactive, the pull-up continues), then after a certain time the active level of the read signal is removed, the external device releases the bus, the further state on the bus is indefinite, in our case, the tightening continues. Everything is logical and understandable, but the fact is that the diagrams shown in section 1 were initially detected. In this case, before the read signal was given, the MK gave the bus a high level and continued to hold it during the reading time and even beyond, only after a significant time (on the order of milliseconds) the data bus went into a disabled state. Somewhat unexpectedly, but at first I reacted to the situation without due attention - I decided that somewhere there was an error in the pin settings and I had to look for it (since the program was written by a young colleague, it was easy for me to assume the presence of possible errors in it, now if I wrote it , then the situation would not be so unambiguous :) ).![]()
The strong belief in the presence of a configuration error disappeared after it was established that ALL 16 data lines (out of 32) were configured the same, and there were failures on only 4 of them, and these are bits 4,5, 8 and 11.
Thinking further and experimenting. An idea arises that it is impossible to read immediately after writing (this is not reflected in the documentation, but when working with Milandrom we are already used to guessing something), so we do 2 consecutive readings, in the hope that the second one will pass correctly.
data=*buffaddr; data=*buffaddr;
And here the most interesting thing begins - the second reading really goes right, BUT the first one also becomes right - a very interesting phenomenon - I can’t imagine its mechanism at all - that is, I can’t imagine a reasonable mechanism for the influence of the subsequent command on the previous one. A quick look at the generated assembler code gives a hint - the location address of the first reading command has changed due to the peculiarities of the linker - it's already better, it's easier to come up with a mechanism for influencing the address on command execution.![]()
In order to investigate the behavior of the MC, we select the fragment related to the exchange with the external bus from the general program by removing everything unnecessary. And we get another surprise - incorrect reading is not observed even with a single access, although the command address remains unchanged. By inserting the deleted fragments back, we find out that when the CRC16 calculation function is connected, an incorrect reading is observed, and if it is absent, it is not, and this function obviously does not interact with the external bus in any way and cannot influence the reading in reasonable ways. Further experiments showed that it is not the CRC16 calculation function as such that is important, but the presence of a subtotal data block in it, moreover, the size of this block, that is, with the code:
static CRC16Buff[256]; an error is observed when static CRC16Buff[215]; (and less than 215) - no access error
How can this fragment affect the code executed in a completely different place? We find that the only change is in the value of the stack, since the required space for global variables has changed.![]()
That is, it turns out that mishandling occurs when a command is executed from certain places with certain stack values, and the number of erroneous bits in a word is small? It's time to remember the first rule of an engineer - "There are no miracles in the world." It can be assumed that this is a remnant of some kind of VHDL debugging function, which signaled certain situations and was not removed from the release. It looks like the thought of a heavily stoned developer, but so far there is no other hypothesis, since we reject divine intervention. Another thought - "here you are, reindeer" - we found a BOOKMARK, however, quite meaningless, but who can understand them, the guys from the NSA.
We continue our research and discover with amazement that moving the command to different addresses (by adding NOP) does not lead to anything - the error does not appear, or, accordingly, does not disappear for different stack values, that is, the hypothesis with the address should be rejected.![]()
But how then does the addition of the second command affect the first? We look at the assembler code more carefully and find more changes, namely, with a single read, the compiler generates
mov r0, sp ldrh r1,[r4] strh r1,[r0]
And with two readings in a row, he performed optimization:
mov r2, sp ldrh r1,[r4] strh r1,{r2] ldrh r1,[r4] strh r1,[r2] It was hard to believe, but we really further establish that an incorrect reading takes place if, and only if, a very specific value lies in the register r0, and it does not matter whether this register will be used in the future. Compared to the previous completely crazy hypothesis about the connection between the stack pointer and the program counter, we observe clear progress. Further experiments establish that the forced erroneous high level is observed on data bits that were written to in the last cycle, and in which register r0 was written to, moreover, the phenomenon is clearly triggered - it occurs during the first reading after recording and is retained for a certain time, and this time is in no way related to the frequency of the MC (within the observation error), but has a clearly pronounced relationship with the temperature of the crystal (as the temperature rises, the retention time increases) .![]()
