Roy Ritchie
From the October 2016 issue
Your vehicle’s tires are rolling kick drums. Keith Moon played two; your car plays four. Expansion joints, potholes, and heaves pound the rubber, which compresses the air inside and transmits hollow thuds to the cabin.
As cars get quieter, engineers are working to stifle the drumbeat of tire impacts. Their current favored method is polyurethane insulation glued around the tire’s inner liner. These acoustically insulated tires have stealthily spread through the market to the point that they are now offered by all the major tire manufacturers and come installed from the factory on several high-end luxury vehicles, including those hallmarks of tranquility, the Mercedes-Maybach S600 and the Tesla Model S.
Roy Ritchie
001: Yes, it really is that simple. Acoustically insulated tires use a ring of polyurethane foam bonded to the inner liner to quiet the resonant ping of tire impacts. Or at least that’s the theory.
Tire manufacturers see big potential for the technology as electrification silences powertrains, making tires one of the most obvious sources of sound intrusion. The main function of inner tire insulation is to improve the tire sound quality, specifically by absorbing impact noise. In actuality, it reduces overall cabin volumes only slightly. It has the greatest effect on frequencies near 200 hertz (Hz), a sound that is low in pitch, relative to what the human ear can register, but is at the high end of the frequencies a tire generates. Think of the deep ping of a bouncing basketball. “You hear it if the tire goes over an expansion joint,” says Scott Pajtas, technical sales director of Michelin. “It can also be a constant tone if there’s a road-surface irregularity or a uniformity irregularity in the tire.”
| Insulated tires | Standard tires | |
| Concrete with expansion joints, 70 mph | 69 dBA | 70 dBA |
| Concrete with expansion joints, 45 mph | 64 dBA | 64 dBA |
| Smooth asphalt, 70 mph | 64 dBA | 64 dBA |
| Smooth asphalt, 45 mph | 58 dBA | 57 dBA |
We put the technology to the test with two sets of Continental ContiSportContact 5 tires delivered from Tire Rack.
The tires were identical save for the ContiSilent label etched into the sidewall and the polyurethane insulation glued to the insides of one set. We mounted them on a Tesla Model S, both to minimize the influence of powertrain noise and because the insulated version is a factory fitment on the Tesla.
Roy Ritchie
For our first test, we averaged the cabin sound level over 15-second samples, driving on both a freshly paved, perfectly smooth asphalt road and an older, coarser concrete road with expansion joints, taking data at both 45 and 70 mph. In all conditions, the insulated tires had a negligible effect on the overall loudness.
Subtle differences did appear when we recorded laps on the ride road of Fiat Chrysler’s Chelsea, Michigan, proving grounds. As the chart above shows, the insulated tires performed better through the first half of the 4.3-mile loop. Over various imperfect surfaces—including expansion joints, rumble strips, and sine-wave ripples in the pavement that repeat at increasingly greater frequency—there’s a small but noticeable difference in overall loudness.
However, we saw a more pronounced difference when looking specifically at the one-third-octave band centered on 200 Hz, which covers frequencies from 178 to 224 Hz. Even if the overall loudness hasn’t dropped much, it indicates that the tone of the sound has changed.
That advantage narrows in the second half of the ride road, which includes more features you would expect to encounter in the real world. Several stretches are replicas of actual Michigan roads with lumpy, cracked, and pocked asphalt. Other sections include concrete slabs with slight vertical offsets—a condition that seems tailor-made for these tires—and yet there’s only a marginal difference between the two sets.
If the effect appears small by our sound-meter measurements, it seemed even smaller when measured with our eardrums.
We struggled to discern any significant improvement, although it probably didn’t help that our back-to-back drives were separated by a half-hour tire swap. If you really strain to hear it—squint hard, cock your head, and clench your teeth—you just might notice the slight change in the tone of tire impacts. But if you can’t tolerate the uneven drumming of tires, your best option is still drowning it out with The Who.
Roy Ritchie
Chasing the same 200-Hz tire-impact noise as tiremakers, Honda engineers developed injection-molded plastic chambers that wrap around the barrel of the Acura RLX’s wheels. They are tuned so that sound waves reflecting in the tire cavity cancel out the undesired frequencies. Mounting the noise-canceling device to the wheel, rather than the tire, presents a particular challenge. The same centrifugal force that presses acoustic insulation against the tire liner pulls the plastic chambers away from the wheel.
At 186 mph, the forces can be as great as 1500 g’s. Honda’s solution involves minimizing the weight and maximizing the rigidity of the resonators, which are then press fit under metal ridges cast into the wheel.
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#1
I purchased a spare wheel & tire and TPMS so I can have a full-service spare if I ever have a catastrophic flat or severe wheel damage to minimize downtime.
The tire is a Michelin Primacy, and as far as I can tell, almost identical to the OEM-spec tires on the SR+ models except that it doesn't have the acoustical liner in it that Tesla tires have from the factory. Seeing as it's a spare, and not a primary wheel/tire, it's kind of a secondary concern.
What I'm wondering is if this is something that an independent tire shop can add before they mount it, or if this is a proprietary product that you can only get through Tesla? It would be nice to have a full-fledged spare that I can get mounted and just leave on there. There's really no reason I couldn't, except for slightly higher noise (in theory). Any info or experience appreciated. TIA.
#2
It really doesn't help that much, I wouldn't even bother.
Reactions:
SammichLover
#3
igotzzoom said:
I purchased a spare wheel & tire and TPMS so I can have a full-service spare if I ever have a catastrophic flat or severe wheel damage to minimize downtime. The tire is a Michelin Primacy, and as far as I can tell, almost identical to the OEM-spec tires on the SR+ models except that it doesn't have the acoustical liner in it that Tesla tires have from the factory.
Seeing as it's a spare, and not a primary wheel/tire, it's kind of a secondary concern.
What I'm wondering is if this is something that an independent tire shop can add before they mount it, or if this is a proprietary product that you can only get through Tesla? It would be nice to have a full-fledged spare that I can get mounted and just leave on there. There's really no reason I couldn't, except for slightly higher noise (in theory). Any info or experience appreciated. TIA.
Click to expand...
Acoustic foam in tires is not something added by Tesla it's something added by the tire manufacturer, in this case mostly Michelin in the Pilot Sport 4S but also some brands of Continental Tire. It would be extremely foolish to attempt to add foam to the inside of a tire unless you knew exactly what kind of foam and exactly how to ensure it's adhesion to the inside of the tread. The Tesla specific tires however at least the Michelin Pilot Sport 4S it's also a different tire in terms of tread.
The tread itself is wider and we suspect uses a slightly softer compound on the outside edge to increase cornering bite. If you're skeptical about this pull up the properties and spec page on the Tire Rack website and you will see that the Tesla specific 235/35 is wider in tread but not section width than any 245 / 35, and is about as wide as an average of three different 255 / 35 tires. In other words it's not just acoustic foam, it's tread compounding and tread design. So no in a word you can't duplicate this by putting in your own acoustic foam. It's unclear whether or not the Michelin Primacy also has tread changes beneficial for their functioning on heavy electric vehicles, but you could probably tell this by comparing specifications for that tire on the Tire Rack website and seeing if there is a Tesla specific version. All that being said, it's entirely possible that if you're using this as a spare the modest differences in tread compounding and acoustic foam are functionally and acoustically modest, so in terms of your intended application all this may be somewhat academic unless you're really concerned about the nuances.
#4
Search these forums---artsci tried to glue foam inside his tires...abject failure.
Reactions:
SammichLover
#5
igotzzoom said:
I purchased a spare wheel & tire and TPMS so I can have a full-service spare if I ever have a catastrophic flat or severe wheel damage to minimize downtime.
The tire is a Michelin Primacy, and as far as I can tell, almost identical to the OEM-spec tires on the SR+ models except that it doesn't have the acoustical liner in it that Tesla tires have from the factory. Seeing as it's a spare, and not a primary wheel/tire, it's kind of a secondary concern.
What I'm wondering is if this is something that an independent tire shop can add before they mount it, or if this is a proprietary product that you can only get through Tesla? It would be nice to have a full-fledged spare that I can get mounted and just leave on there. There's really no reason I couldn't, except for slightly higher noise (in theory). Any info or experience appreciated. TIA.
Click to expand...
I did this as an experiment. See this thread. I spent a ton of money and it was definitely not worth it as there was no noticeable improvement in sound deadening. I concluded that the foam thing is a gimmick so tire manufacturers can charge hundreds more for tires that are lined with a few dollars worth of foam.
In other words it's a marketing gimmick. Don't waste your money.
Reactions:
igotzzoom and raptor5244
#6
artsci said:
I did this as an experiment. See this thread. I spent a ton of money and it was definitely not worth it as there was no noticeable improvement in sound deadening.
I concluded that the foam thing is a gimmick so tire manufacturers can charge hundreds more for tires that are lined with a few dollars worth of foam. In other words it's a marketing gimmick. Don't waste your money.
Click to expand...
When those of us who like to tweak our cars confront technology that is more advanced than our understanding the clear temptation is to dismiss that as some kind of gimmick or as a way of hosing the customer.
Here are some facts: First of all, the Tesla specific acoustic foam Michelin Pilot Sport 4S tire costs a whopping $12 more than the Porsche Tire of the same size. Secondly, that tire is wider than any other 235/35 by 1/4 inch. It's wider than any available 245 / 35 and it's as wide as an average of the three different available 255 / 35 tires.
We don't know exactly what Michelin did to the tread compounding but most of us believe that the changes are non-trivial, and may include a softer compounding on the outside edge and a harder compounding on the central portion of the tread.
Whether those changes are truly functionally significant or simply modest tweaks has never been empirically revealed. In other words no one's ever done a direct A / B comparison of the Tesla specific Tire with more generic alternatives. However unless you believe the Tesla has no idea what they're doing I have to believe that the tweaks that they did to the tire are probably functionally significant, even if they only yield modest margins of improvement in cornering and braking.
Then there's the question of whether the acoustic foam makes any difference in terms of noise. This on the other hand has been empirically tested and it looks as though from Tire Rack testing that you're talking about 1 DB of reduction of road/tire noise. This is not something that you can hear except in a direct A / B comparison, which of course is physically impossible in this case. However when you add it to other bits of noise reduction discussed in other threads on this form, it starts to add up. We've reduced our Highway Noise by 5 DB in 2 model 3 performance cars.
The fact that you can't hear 1db of noise reduction without a direct A / B comparison if in fact you even achieved that by gluing your own version of foam into the tire does not mean that Michelin acoustic foam is either a gimmick or a way of soaking people for hundreds of dollars.
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Reactions:
Nine2Five, SammichLover and Zoomit
#7
In my experience, I noticed a significant difference going from acoustically foam-lined OEM Michelin Pilot Sport 4S to regular non-OEM Michelin Pilot Sport 4S.
The presence of the basketball bouncing-like noise is much more present right now with these non-OEM Michelins that I'm running.
#8
Orwell said:
In my experience, I noticed a significant difference going from acoustically foam-lined OEM Michelin Pilot Sport 4S to regular non-OEM Michelin Pilot Sport 4S.
The presence of the basketball bouncing-like noise is much more present right now with these non-OEM Michelins that I'm running.
Click to expand...
I have to agree with this statement, i have also tried both tires w and w/o and there is a noticeable difference
#9
The basketball bouncing noise described in this article is what I'm talking about.
Honda Global | Noise-reducing Wheels - Picture Book
#10
I think people are focused on the wrong type of noise reduction and therefore don't notice the difference.
If you know what type of noise is being eliminated then it quickly becomes apparent between the acoustic and non-acoustic tire.
#11
According to Car and Driver, they measured an ear pounding 1db difference between an acoustic tire and a regular tire (see below). So is 1 db worth the added cost over a conventional tire?
Tested: Do Acoustically Insulated Tires Really Hush Road Noise? – Feature – Car and Driver
Just some information from TireRack:
https://www.
tirerack.com/tires/tiretech/techpage.jsp?techid=336
Here's a different approach from Honda. They apply the sound deadening material to the wheel and not the tire:
Honda Global | Noise-reducing Wheels - Picture Book
Here's a cute little youtube on the tire itself:
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#12
Thanks for the information.
I got a spare tire (without the foam) with a spare wheel. When it comes time to replace them, I'll probably replace them with the OE-spec tires, but for a spare, I just wanted one that would get me far enough down the road to get the tire replaced.
Reactions:
dfwatt
#13
I must say that having read many of the tire threads on this forum, I've entered a state of tire overwhelm.
The idea of researching alternative tires for my M3 MR with 18" aero wheels is just too daunting. However not wanting to be at the mercy of the OEM, my question is simply do the Michelin MX4M's OEM tires I have come with the foam as well? And how did those that achieved a 5db highway noise reduction accomplish that? Thanks in advance.
#14
Schroeder0202 said:
I have to agree with this statement, i have also tried both tires w and w/o and there is a noticeable difference
Click to expand.
..
cfichuck said:
I must say that having read many of the tire threads on this forum, I've entered a state of tire overwhelm. The idea of researching alternative tires for my M3 MR with 18" aero wheels is just too daunting. However not wanting to be at the mercy of the OEM, my question is simply do the Michelin MX4M's OEM tires I have come with the foam as well? And how did those that achieved a 5db highway noise reduction accomplish that? Thanks in advance.
Click to expand...
Yes, there's a lot of information and a lot of conflicting claims to sort out. But don't get discouraged, keep learning and asking questions and it will eventually become clear what your best options are. I believe the 18 inch OEM tires are acoustically foamed.
We got the 5db of reduced highway noise through a whole lot of different stuff.
A lot of owners probably aren't willing to do all this, but it really was pretty easy if you have above-average technical skills and you've worked on your cars before.
Our modifications included dynamating all four doors, the trunk area, and the front strut towers. In addition we got the RPM Tesla wind noise reduction kit, and did the extra set of door seals as outlined by BradHS. And then the last and non-trivial modification was to get the clipin interior Tesla cloth sunscreens. I'm not sure I can unpack each of those in terms of their relative contributions, but the difference pre and post is pretty significant. It used to be that about 65 miles an hour and up, wind and road noise would become really intrusive and you had to turn the stereo up quite a bit. Now we just don't have to do that. If you don't want to get into taking apart your doors get the RPM wind noise reduction kit, do the door seals and get the interior cloth sunscreens. Those are probably worth at least 3 - 4 DB.
Reactions:
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To advance the use of next-generation automotive tires featuring effective noise suppression and enhanced sensor technology, Henkel introduced LOCTITE SI 5930 FIT, a room temperature vulcanizing rubber adhesive-sealant for use as a tire adhesive.
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The continuous reduction of driving noise in the automotive industry has led designers to pay more attention to noise resonating from tire cavities. Tire manufacturers are increasingly using new acoustic foam materials that adhere to the inside surface of the tread material to minimize noise transmission. At the same time, there is a growing demand for embedded sensors to measure characteristics such as tire pressure, tread height or contact area. nine0069
“A critical requirement for these functional tire designs is the long-term reliable adhesive strength exhibited by the adhesive even under severe road and weather conditions,” says Wim Boone, Senior Sales Engineer Henkel company.
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