COMPOUNDING
Compounding is an extremely complex and secretive black-art in the making of a tire. Essentially the formulation of rubber, additives, and baking/curing temperatures determine the stickiness of the tire, its operating range (whether the tire works at cold temperatures but overheats on track, or cracks at freezing temperatures, requires heat to get sticky, and makes more grip when hot at the track), and even the wet weather grip and performance. It’s possible to have a tire that looks more like a slick, but has more grip in the wet (not standing water) than a tire that looks like it should work well in the wet, but has an inferior compound. Yes, compounding is pretty impressive.
Simply put, compounds determine how a tire deals with the seasons (temperature windows).
Unlike most of their competitors, Michelin often uses “bi-compounded” and even “tri-compounded” tires! Cup 2s come standard with a “bi-compound”, while bespoke applications (like for the GT350R, GT500, and Corvettes) can have as many as 3 different compounds across a single tire. Some applications may call for bi-compounded front tires and tri-compounded rears, or vice-versa. As new compounds and constructions come out, tri-compound tires can be replaced by even more advanced bi-compound tires. It’s a never-ending development process as Michelin continually pushes the boundaries of tire technology.
Compound Variation Across Tread
On a tri-compounded tire, the outermost shoulder, only 2-3 fingers wide, is often made of an aggressive but very durable compound to handle the extreme abuse, high severity wear, heat, and sliding of a tire rolling over. Inboard of that is typically the most aggressive compound to maximize dry grip on the outer 1/3-1/2 of the tire. Meanwhile the inner part of the tire (it does not have to be the inner half and can vary from car to car) uses wet-oriented compounds. Transitions from one compound to another along the surface of the tire does not have to line up with the ribs. Often compounds will change within the same tread block. It all depends on the specific load acting on the tire for a specific car.
As we learned above in the tread design section that tires act like 2 tires in 1, where the grooves of the inner half of the tire are more wet focused and the outer half acts like a slick for dry cornering performance, tread compounding follows the same principles. These wet oriented compounds are extremely good in the dry, and contrary to popular belief: a really good dry tire is really good in the wet (from a compound-grip standpoint, not a hydroplaning resistance standpoint).
When looking at a tire with a higher ‘void ratio’ like a PS4S, or a more extreme case like a Pilot All-Season tire, these tires have more open tread blocks which inherently reduces stiffness. To offset the losses in steering response and performance due to a lack of structural stiffness, a stiffer compound is required. It’s important to know that: STIFFER DOES NOT MEAN HARDER. In this context, stiffer just means rigidity and has nothing to do with the ‘stickiness’/grip of the tire.
Compound Variation for Tread Depth
Compounding can also vary based on the tread depth. Cup 2 tires can be engineered with a super-sticky outer ‘skim coating’. This race-oriented compound can be worth over a second and last 5-6 laps (depending on the track) before wearing down to the main compound of the tire.
These compounds are so aggressive that if they were used throughout the tread depth, the whole tread block structure would squirm, overheat easily, blister, and feel disconnected and vague. Let alone last and meet the requirements of the manufacturer for a street tire.
This ‘skim coating’ essentially enables a car to post amazing lap times on a streetable tire that has deeper tread for wet weather hydroplaning performance, while not wearing out and needing replacement as frequently as a race tire. Some of the fastest Michelin-shod (Non-R) Cup 2’s on production cars utilize this option.
If the compound were to be used throughout the tire, the tread depth would need to be thinner, with a different construction, and it would not meet targets for a street tire in terms of hydroplaning resistance, longevity, or cold grip. Essentially the tire will be a single (laptime) focused Cup2R:
Cup 2 R
The Cup 2 R takes compounding to another level and are actually manufactured with Michelin’s world-class motorsport racing compounds that win at LeMans and Nurburgring. On top of the construction improvements, the Cup 2 Rs are some of the most advanced road-legal tires on the planet, and their lap times are proof of that. Currently, all cup 2 Rs utilize the same compound.
Table of Contents:
Page 1 – Intro, My Background, Developing Bespoke Tires
Page 2 – TREAD DESIGN – Tread Depth
Page 3 – TREAD DESIGN – Circumferential Grooves, Outer Shoulder Features & Sipes, Cup 2R
Page 4 – COMPOUNDING – Compound Variation Across Tread & Tread Depth, Cup 2R
Page 5 – CONSTRUCTION – Carcass Profile/Shape, Width, Ribs
Page 6 – CONSTRUCTION – Sidewall Stiffness, Run Flat Tires, Cup 2 Connect
Page 7 – How Tread Design, Compounding, and Construction Come Together
Page 8 – Conclusion
25 comments
So when someone modifies the suspension in any manner away from stock specs (ride height, alignement) can this tire to car relationship be considered to be out the window? The high level of engineering that went into that model-matched tire was meant to be applied to the factory spec model, no?
Yes and no.
For example, if you replace the super stiff factory carbon wheels on a GT350R, GT500 CFTP, Ford GT, Ferrari Pista with a lightweight (flexible) wheel, you will lose steering feel, grip, response, and will need A LOT more static negative camber. All of these degrade performance and feel from what was originally designed. You can read more about this here:
https://motoiq.com/tested-carbon-revolution-carbon-fiber-wheels/
Making the car lighter is a positive all around.
Lowering the car is a positive but if the car’s balance changes from changing the roll centers, springs/bars/damping, alignment, weight distribution, aero, power, etc…) then the car will obviously not handle the same and will ‘work’ the tires differently. If your new setup or alignment makes the car understeer more, the front tires will wear out faster and a wider front tire could be advantageous.
Overall, if an OEM bespoke tire is better than a given aftermarket tire (or wider tire of the same model, but a less aggressive compound) in stock form, it will likely continue to be better in most situations on a modified car.
Basically what I end up explaining to my clients a lot is we are setting up your suspension for the tires you are running. If you change the tires the setup will change.
The bane of our lives!
And it gets worse for older cars: Smaller diameter wheel and tire sizes are becoming rarer and rarer. So a car with a good setup can become a car with no setup as x tire becomes unavailable.
Then again: I’m only really compaining for my own cars, not the ones of clients!
Preach Big Beautiful sideWalls brother! I don’t need them skinny runflat tires, it’s those meaty black beauties that scrub my contact patch!
Beautiful article! I’ve seen so many drivers go to what they believe will be a more aggressive tire only to go back to their previous setup because the new tire “just sucks” and they have no idea why.
Thanks for updating your How to Properly Select Tires article by the way, it’s a great resource, the only thing missing is how to find tires that work with FWD, negative scrub radius cars. The new Type Rs much through their conti SC6s.
Thank you !
Great article….thanks! I have a follow up GT350R question: What would you recommend if running running a square set-up (HPDE use only) in an attempt to keep consumable cost down or is it overall best to run the the 305/315 setup regardless? Also if running the factory tire set-up I’d assume fronts would cord before the rears would heat cycle out…would fresh set of fronts dramatically effect handling if used with rears with plenty of tread/heat cycle left?
Duane
I would love an answer to this also. I am on the cusp of buying 4S to replace the cup 2s on my 2020 R, but want to go square for rotation purposes (unmount/remount F to R). Now that I see the Base 350 has a different tread depth than the R I wonder if life would be slightly higher. If so, I would consider going 305 square with the base 350 cup 2. Also, how do I determine which 305 is the R and which is the base, in case I don’t go through Ford?
The base GT350 Cup 2 is a “35” sidewall (and is a 295/305 stagger) while the “R” has a shorter “30” sidewall (and is a 305/315 stagger). If you’re going with a square setup, I would choose the rear tire all the way around. (GT350R’s 315/30-19 or the base GT350’s 305/35-19).
The base Cup 2 has more tread depth than the R’s Cup 2, but is a slower tire. When driven at the limit, it won’t really last any longer, but if driven below the limit, it will likely last a little longer. If you’re tracking your car, the base Cup 2 tire will have more grip and perform better than the PS4S in everything but deep standing water.
If you are running the stock wheels and tires and track alignment, and aren’t driving with bad technique, the tires will wear out pretty evenly front and rear. If you’re running lightweight aftermarket wheels, you’ll need more camber than the Ford recommendation.
Billy,
This was a great and educational article! I have a 2020 GT350R that I currently do not track. I am going to be replacing the factory MPSC2 tires and will not be getting the same tires again because I mainly street drive and for me, these tires are not ideal in the rain. I am considering getting the MPS4S tires as a replacement. I see that you recommend going with 315’s all around for a square set-up in the GT350R. I do plan, however, to continue to use my factory CF wheels and do not like the idea of unmounting and remounting for tire rotations with these specific wheels. With the information in your article that you provided, would I be ok with using a 295/30/19 in the front and 305/30/19 in the rear with the MPS4S on my CF wheels? Thank you in advance!
Loved the article, thought it was well done!
Thanks for the feedback!
Loved this article!
I currently have a 2018 GT350 with PSS.
When I upgrade the tires, should I get the original bespoke PSS, or would I get better performance if I switch to PS4S?
Luis,
I’m in the same boat, but my guess would be going to the bespoke Ford Sport Cup 2s on the 2019 generation and later GT350. However, 2019 models did have a change in shocks and sway bars, ABS settings, etc to use the more sticky compound.
The 2019 bespoke Cup 2 has the best wet and dry grip. An off the shelf PS4S has the best hydroplaning resistance for deep water. The 2015-2018 bespoke PSS has similar/marginally better hydro than the newer Cup 2, but it’s not as sticky in the wet or dry than the Cup 2, but sticker than the PS4S.
Absolutely superb article! This is the kind of semi-technical info that all track day enthusiasts need and is hard to find out there, that you very much!
Thank you 🙂
What a fantastic article (so much info I wish it was a video). I’m presently looking for a Cup2 Connect tire I saw that is wider than normal for its spec, but no one at Michelin has been able to help me with it. Keep up the good work sir.
Thank you for the compliment. Will do!
Thank you for your excellent and most informative article. I have a 2019 Shelby GT350 with the bespoke Cup 2 tires. Given that the GT350 is designed for more daily road use and less track use than the GT350R, are the GT350 bespoke Cup 2 tires also better able to handle the occasional standing water that occurs on roads and freeways than those designed for the GT350R? My primary interest is in being able to keep the original Cup 2 tires while also using the car as a possible daily driver in rainy winter weather without being excessively concerned about hydroplaning. Having read your article, I have greater confidence that I don’t need to rush out and replace the Cup 2s with Michelin PS4Ss or Pirelli P Zero Sports. But if I have misunderstood your article, and shouldn’t keep the Cup 2s for daily all winter (no snow) use, please let me know. Your thoughts on this would be most appreciated.
Excellent article, thank you. I’ve been researching tires for my GT3 RS, which comes with Sport Cup 2s. Your article taught me much more than I expected and showed me how much more there is to know than I imagined.
Thank you for the feedback. I’m glad to hear it was informative 🙂
I just discovered your site and am in awe at both the high level and quantity of useful information you and your team have built up.
I’ve been in analysis paralysis choosing tires for my 2016 M235i coupe for a month now and need some help. (God I hate that they reused M235i for the new “Gran Coupe”) I’m thinking of moving to 235/40 PS4S on some sweet BimmerWorld 18×8.5″ TA5R wheels and see that there’s both a standard and a Ford OE DT1 version of the PS4S. I think the DT1 was OE on the Ford Focus ST or a Mustang, but it is really hard to get information.
This excellent article and the great article and video by TyreReviews on BMW’s custom PS4S tires for the new G80 M3 and G82 M4 have vastly improved my education on OE vs off-the-shelf tires, but unfortunately has increased my purchasing anxiety…
https://www.tyrereviews.com/Article/Should-I-Fit-OE-Tyres.htm
S the only differences in specs on the DT1 version I’ve found are 0.5/32″ shallower and 0.3″ narrower tread as well as a HUGE 1.9 lbs weight savings. By my calculations, the narrower tread width would account for only about 1/3 lb weight savings so it leaves me wondering where the rest of the weight savings came from. That relatively large weight savings is fairly attractive, more for handling feel and comfort than raw lap times, but I’m worried that Ford/Michelin may have optimized the DT1 for something that I care less about.
With your direct experience testing Michelin tires on Ford performance cars, and maybe even directly on this DT1 variant of the PS4S, what insight do you have on what differences the DT1 may have and whether it would be a better fitment for my M235i?
Should I also worry about the narrower 7.8″ DT1 vs 8.1″ ‘normal’ tread width? Would 7.8″ tread width be too stretched on a 8.5″ wheel?
For reference, my M235i is my DD and is stock so far but I will be getting back into some autocross once I replace my aging run-flats and have aspirations to do a few track days. Boyish dreams of drifting too, but that may never actually happen with my budget, wife approval factor, and lack of an LSD 😉
Sorry about the double/triple post, my formatting was totally lost on my other post attempts and I’m trying to make my huge block of text more readable. Hopefully this one comes through better.
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I just discovered your site and am in awe at both the high level and quantity of useful information you and your team have built up. I’ve been in analysis paralysis choosing tires for my 2016 M235i coupe for a month now and need some help. (God I hate that they reused M235i for the new “Gran Coupe”)
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I’m thinking of moving to 235/40 PS4S on some sweet BimmerWorld 18×8.5″ ET38 TA5R wheels and see that there’s both a standard and a Ford OE DT1 version of the PS4S. I think the DT1 was OE on the Ford Focus ST or a Mustang, but it is really hard to get information. I currently have 225/40R18 and 245/35R18 P-Zero run-flats on the stock 18×7.5/8″ wheels.
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This excellent article and the great article and video by TyreReviews on BMW’s custom PS4S tires for the new G80 M3 and G82 M4 have vastly improved my education on OE vs off-the-shelf tires, but unfortunately has increased my purchasing anxiety… ——– https://www.tyrereviews.com/Article/Should-I-Fit-OE-Tyres.htm
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So the only differences in specs on the DT1 version I’ve found are 0.5/32″ shallower and 0.3″ narrower tread as well as a HUGE 1.9 lbs weight savings. By my calculations, the narrower tread width would account for only about 1/3 lb weight savings so it leaves me wondering where the rest of the weight savings came from. That relatively large weight savings is fairly attractive, more for handling feel and comfort than raw lap times, but I’m worried that Ford/Michelin may have optimized the DT1 for something that I care less about.
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With your direct experience testing Michelin tires on Ford performance cars, and maybe even directly on this DT1 variant of the PS4S, what insight do you have on what differences the DT1 may have and whether it would be a better fitment for my M235i? Should I also worry about the narrower 7.8″ DT1 vs 8.1″ ‘normal’ tread width? Would 7.8″ tread width be too stretched on a 8.5″ wheel? What about the ~6mm increase in scrub radius according to — https://www.wheel-size.com/calc/?wheel1=225-40-18X7.5ET45&wheel2=235-40-18X8.5ET38&fcl=11mm&scl=15mm&wcl=57mm&sr=0mm ? Sorry about all the questions and thanks in advance for your help!!!
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For reference, my M235i is my DD and is stock so far but I will be getting back into some autocross once I replace my aging run-flats and have aspirations to do a few track days. Boyish dreams of drifting too, but that may never actually happen with my budget, wife approval factor, and lack of an LSD 😉
Thanks for this great article. Somehow I missed it over the past few years. I thought I was losing my mind as the Sport Cup 2 groove depth was much deeper on my friends Ferrari than my 2017 Z06 (with Z07). We all know SC2,s are very pricy. I’ve gone through a few sets over the years, changing the alignment to track settings a few years ago (per owners manual track setting recommendations). I primarily only use the car for the track. The hope with the track alignment (pretty much -2 all around), was to get the best track performance possible but also to gain tire life. My question is should I seek a set of SC2s that have the deeper grooves (to gain some tire life, even at the risk of losing a bit of track performance), or do you recommend I stay with the ones GM recommends?
Many thanks.