Theory about M-specific Michelin PSS

[JoeFromPA]

So....been thinking alot about the straight line traction on the M3 and wanted to posit a "theory thread" on what BMW and Michelin did to tweak this tire.

Let's establish a few background items to agree upon:

1. This is not the highest powered, highest torque RWD sedan or coupe on the planet made in the last decade.
2. Michelin PSS, historically, is one of the absolute best street tires for traction
3. The M seems to suffer more tire slip from a straight line acceleration standpoint than most historical comparatives, despite having some of the most advanced tire compound, suspension, and differential technology available.

Now....here are a few observations:

1. I owned Michelin PSS on my e39 m5 in 245/40/18 and 275/35/18 tire sizing. These tires have a more rounded shoulder profile....I think there is less contact patch pressure on the shoulders of these tires than the standard michelin PSS. This may be for wet traction or for handling purposes. This is based upon eyesight alone - I literally can see that these tires fall away more from than mid-point than my past experience with this tire.

2. These appear to be very slow wearing, even by PSS standards. Member Suave, rocking 19's and having done a good amount of track time in Europe, has 5k miles on his. I just checked them out and I think he'll get 15k out of them. Easy. On the rear with 19" wheels.

Member Karussell has done a ton of track time on his 18s, including lots of drifting, and was reporting barely visible wear (i.e. it was visible, but not by much) at 6k miles.

3. The M3 may have straight line traction problems but it's cornering prowess is amazing. Look at the reviews from modified e9x owners running similar tires who have tracked the f80/f82 stock....now the suspension tech and diff are new, and the chassis is lighter, but perhaps the PSS have been optimized for lateral traction at the expense of some straight line capability?

4. Owners, including me, have commented that these tires appear a bit louder than regular Michelin PSS. This is confounded by the solid mounted rear diff and obviously different platform, but it's a pretty consistent theme.

5. BMW/Michelin have said that they changed the contact patch shape of the tires, even front to back, in order to benefit things like steering and slip angle traction. I believe they elongated the contact patch in the front (which might be why I can visibly see a height difference from center to shoulder)

So here goes my theory:

I think the M-specific Michelin PSS had their compounds tweaked to provide longer life, greater lateral traction, possibly slightly improved wet traction (or hydroplaning resistance possibly), and took a slight penalty in noise and a penalty in straight line traction.

Therefore if you go back to regular PSS, my theory would be those would be the things you are giving up....as well as possibly some unique tuning related to the chassis and suspension and steering feel and performance.

I'm over-caffeinated and needing a distraction, so I'm giving theories here.

[robbo mcs]

I think most of what you say makes sense. All tire characteristics are trading off one thing against another

I would add one thing. This tire is one of the ones that is most pressure sensitive for straight line traction I have used. If the pressure is only slightly above recommended it loses a lot of traction. If it is around 38-40 (which is what a lot of cars seem to be delivered with) then it is quite diabolical for straight line traction.

[gthal]

Makes a lot of sense Joe. I believe Michelin modifies the PSS significantly for various vehicle applications depending on what the manufacturer wants.

One difference I have noticed (which you also commented on above) is wear. My PSS on the C7 Corvette were noticeably more worn after 2 track days. My PSS on the M4 were less so after the same usage which surprises me considering the M4 had less camber and weighs more.

I like the PSS but will soon be swapping out for RE-11 or AD-08R to hopefully improve on traction in all circumstances while knowing I'll sacrifice wear but that's OK in my books.

[Black Gold]

Originally Posted by JoeFromPA

So....been thinking alot about the straight line traction on the M3 and wanted to posit a "theory thread" on what BMW and Michelin did to tweak this tire.

Let's establish a few background items to agree upon:

1. This is not the highest powered, highest torque RWD sedan or coupe on the planet made in the last decade.
2. Michelin PSS, historically, is one of the absolute best street tires for traction
3. The M seems to suffer more tire slip from a straight line acceleration standpoint than most historical comparatives, despite having some of the most advanced tire compound, suspension, and differential technology available.

Now....here are a few observations:

1. I owned Michelin PSS on my e39 m5 in 245/40/18 and 275/35/18 tire sizing. These tires have a more rounded shoulder profile....I think there is less contact patch pressure on the shoulders of these tires than the standard michelin PSS. This may be for wet traction or for handling purposes. This is based upon eyesight alone - I literally can see that these tires fall away more from than mid-point than my past experience with this tire.

2. These appear to be very slow wearing, even by PSS standards. Member Suave, rocking 19's and having done a good amount of track time in Europe, has 5k miles on his. I just checked them out and I think he'll get 15k out of them. Easy. On the rear with 19" wheels.

Member Karussell has done a ton of track time on his 18s, including lots of drifting, and was reporting barely visible wear (i.e. it was visible, but not by much) at 6k miles.

3. The M3 may have straight line traction problems but it's cornering prowess is amazing. Look at the reviews from modified e9x owners running similar tires who have tracked the f80/f82 stock....now the suspension tech and diff are new, and the chassis is lighter, but perhaps the PSS have been optimized for lateral traction at the expense of some straight line capability?

4. Owners, including me, have commented that these tires appear a bit louder than regular Michelin PSS. This is confounded by the solid mounted rear diff and obviously different platform, but it's a pretty consistent theme.

5. BMW/Michelin have said that they changed the contact patch shape of the tires, even front to back, in order to benefit things like steering and slip angle traction. I believe they elongated the contact patch in the front (which might be why I can visibly see a height difference from center to shoulder)

So here goes my theory:

I think the M-specific Michelin PSS had their compounds tweaked to provide longer life, greater lateral traction, possibly slightly improved wet traction (or hydroplaning resistance possibly), and took a slight penalty in noise and a penalty in straight line traction.

Therefore if you go back to regular PSS, my theory would be those would be the things you are giving up....as well as possibly some unique tuning related to the chassis and suspension and steering feel and performance.

I'm over-caffeinated and needing a distraction, so I'm giving theories here.

1) the reason the contact patch and shape looks different is because you had a 9.5 inch wheel on the m5 and a 10" wheel on the m3. The wider wheel will be more stretched and force the tire to look more square

2) I have noticed no wear difference with these tires over past pss. My tires wore down extremely quickly on the outer edges during track time, and are not wearing especially slow of note.

3) The tires have less to do with cornering prowess than the chassis and car itself. I will test this myself with different tires more suited to track use, but there is nothing special about the cornering abilities of these vs other pss imo.

4) the m3/4 transmits more road noise in general than past cars. this includes wind noise. based on the fact that the wind noise is increased as is tire roar, I would say this is a car issue, not a tire compound issue.

I do not think there is any tradeoffs here with this tire vs normal pss. they are a good street tire that are not suitable for regular track use. There is no evidence IMO of greater wear, and imo the lack of traction is because you have 400 wtq on a 3500 lb rwd car with only 275 width street tires.

[JoeFromPA]

Kenny,

Regarding point #1 of yours above, if a wider wheel forced the tire to look more square then it would only reinforce my point. The m3's wider wheel is visibly more of a rounded (less square) tire tread - so wouldn't that then reinforce my thoughts on how the tire carcass appears to have been reshaped?

Regarding your observation of wear: Can you provide some context as to your observation? Number of track days/type of track days, total miles, 18s or 19s, etc.?

Regarding #3: Considering BMW and Michelin specifically stated that these PSS had been optimized to the handling and steering characteristics of the m3 (at least on the front end), I'm surprised you say that. I agree that the suspension and chassis are the primary drivers - which was in my original post?

#4 - Road noise - I can't really agree here. Yes, this car transmits more noise due to the way it's setup. But while past PSS created no noise for me when brand new, these did. This appears to be what others have reported too - and across different car platforms. My point was I think this is a difference, perhaps one of the tradeoffs agreed upon.

Lastly, your point seems to be that these are in essence the same as regular PSS by all noticeable characteristics. Would that not defeat the probably millions invested by BMW and Michelin in customizing this tire? Why do it then?

And regarding traction, there are plenty of RWD 400tq cars that have been around for 10+ years and have similar weight profiles that have less straight line traction issues. Now, don't get me wrong, they all do have WOT traction issues. My point is it appears exacerbated in the M3 and is mentioned by just about every owner and every reviewer as something worth noting. And most of those reviews were on the heaviest m3s - ~3,600-3,650 models. And PSS are commonly considered just about the best everyday summer tire on the market...so this is at one of the pinnacles of everyday driver tire technology. So what's your theory here Kenny?

[CanAutM3]

Good thread.

I had installed 275/35R19 PSS on my E92 on the stock 220M wheels. Looking at my old E92 side by side with my new F82 (on of my track buddies bought my E92, so I still see it often ), I have to agree that it is clear that the 275 PSS sit much squarer on the E92 than on the F82 despite the F82 having a wider rim.

Further, the standard PSS in 275/35R19 offers much more "rubber on the road" compared to the specific F8X 275/35R19 PSS. The grooves on the F8X PSS are much wider than on the standard PSS, similar to the 255 and 265 PSS. See my thread on the topic when I was podering going to the 275 PSS on my E92. This was likely done to improve wet traction through better water evacuation.



My comparative analysis of the 265 vs 275 PSS:

Originally Posted by CanAutM3

OK, so I have done a little extrapolation based on the picture provided by Denk and some math to figure the difference between the 265 and 275.

Here are the results for thread block width in mm

265/35R19 (Total thread width 254mm)
47+32+32+32+47 = 191mm (75%)
275/35R19 (Total thread width 259mm)
58+38+38+38+58 = 230mm (89%)

So even if the 275 total contact patch width is only 5mm wider than the 265 contact patch, it offers 39mm more rubber contacting the road because of the narrower grooves. This is 20% more. This could justify the 2.9lb of extra weight (+12%).

[CanAutM3]

Originally Posted by KennyPowers

1) the reason the contact patch and shape looks different is because you had a 9.5 inch wheel on the m5 and a 10" wheel on the m3. The wider wheel will be more stretched and force the tire to look more square

2) I have noticed no wear difference with these tires over past pss. My tires wore down extremely quickly on the outer edges during track time, and are not wearing especially slow of note.

3) The tires have less to do with cornering prowess than the chassis and car itself. I will test this myself with different tires more suited to track use, but there is nothing special about the cornering abilities of these vs other pss imo.

4) the m3/4 transmits more road noise in general than past cars. this includes wind noise. based on the fact that the wind noise is increased as is tire roar, I would say this is a car issue, not a tire compound issue.

I do not think there is any tradeoffs here with this tire vs normal pss. they are a good street tire that are not suitable for regular track use. There is no evidence IMO of greater wear, and imo the lack of traction is because you have 400 wtq on a 3500 lb rwd car with only 275 width street tires.

See my post above. There is clearly a difference between the regular PSS and the F8X specific PSS.

Further, I do not believe that either PSS are suitable for dry track use.

[AMPowerJ]

Gosh darn these tires are loud! Maybe I'm just getting old.

[SakhirM4]

Originally Posted by AMPowerJ

Gosh darn these tires are loud! Maybe I'm just getting old.

I must be getting old because I don't think they are loud at all. Guess I need to have my hearing checked.

My E46 M3 with PS2s was much louder on the highway.

[FogCityM3]

Was thinking about getting the F80 PSS for the E90, but now not so sure. Too risky a proposition? Was thinking same weight distribution, very similar suspension designs, same goals (reducing understeer), traction less of an issue in E90 in a straight line, in addition to my wheels having a lower offset +10mm F and +5mm rear (same as GTS which has spacers). Interested in your opinion thx in advance.

Originally Posted by CanAutM3

Good thread.

I had installed 275/35R19 PSS on my E92 on the stock 220M wheels. Looking at my old E92 side by side with my new F82 (on of my track buddies bought my E92, so I still see it often ), I have to agree that it is clear that the 275 PSS sit much squarer on the E92 than on the F82 despite the F82 having a wider rim.

Further, the standard PSS in 275/35R19 offers much more "rubber on the road" compared to the specific F8X 275/35R19 PSS. The grooves on the F8X PSS are much wider than on the standard PSS, similar to the 255 and 265 PSS. See my thread on the topic when I was podering going to the 275 PSS on my E92. This was likely done to improve wet traction through better water evacuation.



My comparative analysis of the 265 vs 275 PSS:

[TahoeM3]

I am in the minority here, but I haven't had any traction issue. I always drive in M-mode, but I'm still in the break-in period. Still, even when I've punched it, it hooks up very well.

[JoeFromPA]

Originally Posted by TahoeM3

I am in the minority here, but I haven't had any traction issue. I always drive in M-mode, but I'm still in the break-in period. Still, even when I've punched it, it hooks up very well.

At 60 degrees fahrenheit, I was breaking traction when I went WOT in 4th gear when I hit 4000rpms. And definitely in 3rd gear from 4000-5000 rpms. In MDM mode.

[CanAutM3]

Originally Posted by FogCityM3

Was thinking about getting the F80 PSS for the E90, but now not so sure. Too risky a proposition? Was thinking same weight distribution, very similar suspension designs, same goals (reducing understeer), traction less of an issue in E90 in a straight line, in addition to my wheels having a lower offset +10mm F and +5mm rear (same as GTS which has spacers). Interested in your opinion thx in advance.

When I switched from the stock PS2 to the PSS on my E92, I had not other choice than going 255/275 as the rear 265 were not yet available. The PSS made a huge improvement on the E92 in all aspects: Dry grip, responsivness, wet grip, noise, rolling comfort. Since I changed size at the same time I switch tire type, I cannot comment how much comes from the size.

I however seriously doubt that changing the tires from 245/265 to 255/275 will have any impact on the overall balance, ie will not reduce understeer much. That being said, the PSS will provide a crisper turn-in, but I think it has more to do with better grip they provide. For me, going with -2.5deg front camber and running square 275 tires all around made the car nice an neutral at the track. On the street, I very rarely push the car close enough to its limits to feel a need to alter the balance provided by the staggered setup.

I hope this helps

[TahoeM3]

Originally Posted by JoeFromPA

At 60 degrees fahrenheit, I was breaking traction when I went WOT in 4th gear when I hit 4000rpms. And definitely in 3rd gear from 4000-5000 rpms. In MDM mode.

What is this 60 degrees Fahrenheit that you mention? I live in South Florida.

Seriously, we had a rare cold snap a couple of days ago and it got down into the 50s...I drove the car and punched it in 2nd coming around a turn onto a entry ramp and it didn't break traction at all. Were your tires warmed up?

On the other hand, I took the GTR out yesterday (70 degree temps) and the tires, which were still cold...and also PSSs...were slipping and sliding all over the place in 1st-3rd until they warmed up.

[JoeFromPA]

You punched the car in 2nd in a turn....presumably above 2500 rpms....and didn't break traction? (I.e. DSC intervened, MDM mode or normal full DSC)

There is no situation in which I can do that. None whatsoever. DSC will intervene if I punch it in 2nd gear at any speed above 3000 rpms in a straight line and definitely in a turn.

[FogCityM3]

Yes, I meant I currently run 245/265 PSS for the standard E90M3 application, wondering whether running the 255/275 F80 spec on my E90M3 would mess up with the dynamics too much given the contact patch changes? Less about the size (which won't change much) but worried about the F80 compound change on an E90 M3. thx!

Originally Posted by CanAutM3

When I switched from the stock PS2 to the PSS on my E92, I had not other choice than going 255/275 as the rear 265 were not yet available. The PSS made a huge improvement on the E92 in all aspects: Dry grip, responsivness, wet grip, noise, rolling comfort. Since I changed size at the same time I switch tire type, I cannot comment how much comes from the size.

I however seriously doubt that changing the tires from 245/265 to 255/275 will have any impact on the overall balance, ie will not reduce understeer much. That being said, the PSS will provide a crisper turn-in, but I think it has more to do with better grip they provide. For me, going with -2.5deg front camber and running square 275 tires all around made the car nice an neutral at the track. On the street, I very rarely push the car close enough to its limits to feel a need to alter the balance provided by the staggered setup.

I hope this helps

[CanAutM3]

Originally Posted by FogCityM3

Yes, I meant I currently run 245/265 PSS for the standard E90M3 application, wondering whether running the 255/275 F80 spec on my E90M3 would mess up with the dynamics too much given the contact patch changes? Less about the size (which won't change much) but worried about the F80 compound change on an E90 M3. thx!

I can confirm that the standard PSS (not the the F8X PSS) in 255/275 in /35R19 work great on the E9X

[TahoeM3]

Originally Posted by JoeFromPA

You punched the car in 2nd in a turn....presumably above 2500 rpms....and didn't break traction? (I.e. DSC intervened, MDM mode or normal full DSC)

There is no situation in which I can do that. None whatsoever. DSC will intervene if I punch it in 2nd gear at any speed above 3000 rpms in a straight line and definitely in a turn.

Correct...2nd gear around 4000 in MDM mode up to around 5500 when I went to 3rd and continued accelerating. Granted, I'm still in break-in with around 600 miles on the car so I didn't go to redline, but I was at WOT. That said, I'm still planning on going to 295/35 rear tires in advance of a plan to get a tune.

Are you sure you didn't put Armor All on your tread or drive through some oil? It sounds like you're having more trouble than most, and it doesn't seem normal. Cold weather and cold tires definitely don't help.

[CanAutM3]

Originally Posted by TahoeM3

Correct...2nd gear around 4000 in MDM mode up to around 5500 when I went to 3rd and continued accelerating. Granted, I'm still in break-in with around 600 miles on the car so I didn't go to redline, but I was at WOT. That said, I'm still planning on going to 295/35 rear tires in advance of a plan to get a tune.

Are you sure you didn't put Armor All on your tread or drive through some oil? It sounds like you're having more trouble than most, and it doesn't seem normal. Cold weather and cold tires definitely don't help.

WOT in 2nd gear with DSC off, the tires will light up every time

[gthal]

Originally Posted by CanAutM3

WOT in 2nd gear with DSC off, the tires will light up every time

Yep... 1st, 2nd and even 3rd sometimes will slip without traction on.

[CanAutM3]

Originally Posted by gthal

Yep... 1st, 2nd and even 3rd sometimes will slip without traction on.

Proof is in the pudding (at 0:35) :

[TahoeM3]

Mine must be defective, then...it just accelerates forward. Maybe that's what they mean by break-in. Of course, you can't just stomp on the gas like a monkey, you have to ease into the throttle. This isn't a torqueless E92, after all!