What Size PSS for OEM 19" Wheels?

[CanAutM3]

I have been pondering on which Michelin Pilot Sport sizes to go with. I find that the F8X in stock form lacks grip and I would like to increase the contact patch width. I also would like to stick with the PSS since I like the tire a lot for DD and have had an excellent experience with it on my E92. It strikes the right balance from me between performance, durability, wet grip and comfort.

See the table below for the summary of my findings.
(F c.p. and R c.p. for Front and Rear contact patch width according to Tire Rack)
(R % dia and R % dia Front and Rear rolling diameter change in % according to Tire Rack)
(TR$ Price for the set before shipping and taxes according to Tire Rack)

Simply keeping the stock sizes but going with the standard XL tire instead of the F8X specific tire provides the best bang for the buck. It is the cheapest option, yet provides a 0.7" wider contact patch front and rear. This is the combo I had on my E92 and really loved it. Further, the rear generic 275 has thinner longitudinal grooves in the thread compared to the F8X specific 275, which translates to more rubber in contact with the road.

The 275/295 /30R19 combo provides the greatest increase in contact patch width (+1.7" front and +2.0" rear) for a reasonable increase in cost (+$120). The disadvantage is the quite smaller rolling radius (-1.5%/-2.3%). I am also concerned that the 275/30R19 is a rear specific tire with thin grooves and would not be the best in the rain for front tires.

The last option consist of moving the rear tires to the front wheels and fitting M5 rear tires in the rear. This option is the most costly when all 4 tires need to be replaced (+$308). However, it can be a relatively cheap upgrade when only replacing the rears. The rolling radius is also quite larger than stock (+2.3%/+1.9%). What is interesting with this setup is that the 295/35 rear is specifically designed to run on the 10" wide wheel of the M5.

I added another option to the table: 265-295/35R19. After having driven the 275-295/35R19 combo for a full season, I find the 295/35R19 M5 rear tire to be a perfect fit for the car with improved traction. However, I find the 275/35R19 rear not to be the best fit for the the front. The fact that it is designed as rear tire to be fitted on a 10" wide wheel makes not the best suited in the front on a 9" wide wheel. It is more prone to aquaplaning and tram-lining and loses a bit in sharpness. The bite is strong, but the response is a bit more sluggish where there is a noticeable delay before it takes a set. For those reasons, I will be likely going with a 265/35R19 M0 spec from the AMG GT-S. Since the M0 spec is designed as front tire to be mounted on a 9" wide wheel, it should be a very good fit on the front 437M wheels. With this setup, I will have PSS tires designed optimally for those front and rear positions and wheel widths. I am eager to try it out.

What would you guys and gal do?

EDIT May 2015

275(*)-295(*)/35R19 REVIEW:

OK, so I decided to go with the fifth option and finally made the switch to the 275-295/35 setup last week. I wanted to wait a little before posting a review because I wanted to ensure that the tires were broken in to share proper perspective.

I could not be happier . The car seems much more planted with the wider tires. There is much less wiggle from the rear under hard acceleration. Taking on-ramps at high speed (very high speed ), the car feels more stable with seemingly more grip to be had. The car is still very well balanced even with high slip angles and is very easy to position with the throttle. In low speed corners, the wider front tires bite with assertiveness yielding a sharp turn-in.

Steering feel and feedback is much improved and the steering has become much more alive, better communicating the pavement surface changes. The drawback is little more tramlining on the highway where trucks left big grooves in the asphalt.

Another drawback is that there is a perceptible longer delay before the car takes a set, probably due to the sidewalls of the wider tires ballooning more on the same wheel width.

The tires also improved the looks of the car too. I run a stock EDC suspension without spacers (I don't believe in changing the stock offset). The bigger and wider tires fill the wheel wells well.

Overall, it seems to me that this 275-295/35R19 setup on the OEM wheels is very well suited to the car .

Update June 2015:

Just found out about a non-negligible drawback to the 275-295/35R19 setup: aquaplaning .

I just drove back home from work in a heavy downpour, and the car aquaplaned much more than it used to on the stock 255-275/35R19 setup. I expected a little more floating, but not that much. The car now gets skittish running through very mild puddles.

Update March 2016:

I just discovered another drawback of the 275-295/35R19 combo: uneven wear on the front tire inner shoulder.

I pulled my summer wheels out of storage today and discovered that the inner shoulder of the 275/35R19 (OE rear tire) installed in the front was significantly worn down. I guess it will cord quite soon. Note that I am running a completely stock suspension with stock alignment.

I can only assume this comes from the shape of the contact patch, extra width of the tread and/or stiffer sidewall.

EDIT May 2016

265(M0)-295(*)/35R19 REVIEW:

I just came back from 2 track days at LCMT in semi-dry semi-wet (including snow ) conditions. So I mostly lapped with the PSS on the car. This exhausted whatever life was remaining on my front 275/35R19 PSS (the original rears). Interestingly, they corded on the inside first. I had already observed the inner shoulder wearing faster. Maybe this comes from the fact that these are intended as rear tires and have a squarer contact patch. So I have decided to install new 265/35R19 M0 spec PSS in the front.

After a fair bit of research, I concluded that the 265/35R19(M0) is probably the best option to pair with the 295/35R19(*). I liked the M5's 295/35R19 tire because it was specifically designed as a rear tire to be mounted on a 10" wide wheel, so a perfect fit for the F8X. I really liked the additional grip and stability it provided. So I went on a quest to find the best PSS to mount on the front 9" wheels that would keep the front-to-rear diameter stagger as close to stock as possible when combine with the 295/35R19. There were no 275 PSS that fit that bill, so I looked at the 265. Of the 5 different PSS offerings in the 265/35R19 size, the AMG GT-S' (M0) was the only one designed as front tire for a 9" wide wheel, hence why I stopped my choice on it.

First observation from the 265 is the the longitudinal channels in the tread are much wider than the 275/35R19 BMW star spec I had up front. This should reduce the increased aquaplaning sensitivity I had with the 275. The tire is also quite meaty, filling the fenders well. First impression from the short drive from the shop to my house is that there is less feedback coming through the steering wheel compared to the 275, I however cannot recall how it felt with the OE 255 though. There is also much less tram-lining going on, which is a good thing.

Update September 2016:

Having run the 265(M0)-295(*)/35R19 PSS for the summer, I can attest it is the best combo I have tried thus far. The sensitivity to aqua-planning that experienced with the OE 275 in front is completely gone and there is much less tram-lining. The 265(M0) provide ample grip up front and the car remains quite neutral with only a slight hint of understeer at the limit (which is perfectly fine for a street setup). Due to the rounder contact patches of the 265(M0), there is a bit less steering feel than with the squarer OE 275, but having recently driven an 2016 M4 mounted on the stock tires, the steering on my car with the 265(M0) is a bit more alive. For those wanting to stick with the PSS, the 265(M0)-295(*)/35R19 is definitely the one I would recommend.


PICTURES:
275(*)-295(*)/35R19 without spacers
275(*)-295(*)/35R19 with 5mm rear spacers
265(M0)-295(*)/35R19 on Eibach springs without spacers

[FTS]

I am not sure I fully understand the differences in Fcp and Rcp; are they different due to measured rim width?

[CanAutM3]

No, same rim width were used most of the time when comparing same tire width. My guess is that the different contact patch width have to do with different tire construction.

[gthal]

I voted but another option would be 255/35 front and 285/35 rear. I like the idea of staying OEM size in the front as I never found the car lacking in grip there. Yes, it changes the stagger a bit but not enough to matter and probably retains slightly better steering response. I would go that route before the choices above.

[CanAutM3]

Originally Posted by gthal

I voted but another option would be 255/35 front and 285/35 rear. I like the idea of staying OEM size in the front as I never found the car lacking in grip there. Yes, it changes the stagger a bit but not enough to matter and probably retains slightly better steering response. I would go that route before the choices above.

Interresting proposition. Definitely worth exploring.

Maybe going with the generic 255/35R19 XL instead of the F8X specific one in combination with the 285 rear could be another alternative.

[FTS]

Originally Posted by CanAutM3

No, same rim width were used most of the time when comparing same tire width. My guess is that the different contact patch sizes have to do with different tire construction.

I am having hard time figuring how same tire size from same manufacturer would have that much contact patch area difference on same width rim. Tires should have similar/close to same contact patch area, provide same side wall height, on same rim width, there are exceptions of course. In my experience, the best way to increase contact patch is to widen the wheel width if original tire was put on optimum wheel width already, but even then the results are marginal. The best method would be to increase wheel width with larger tires for optimum result; and I know you are well aware of this. So, my point is that these numbers may not yield the results you are looking for, or at least I'd be surprised if they do.

Another point I made in other posts that I'll repeat here is the 2-3% difference you are calculating in rolling diameter from original maybe misleading. The cars' stability electronics work not per wheel or axle, but based on rolling differences between front and rear. So if you select tires that have -1.5% difference in the front, for example, and +2% difference in the rear, your overall impact may actually be 3.5%, which may or may not negatively impact the electronics. I say this because with Porsche the difference between front and rear tire diameters had to be between 0.3"-0.6" per spec, it was not based on % or per axle, they pointed out to me 8 specific dangerous accidents (at the track) in their records that were caused because that tolerance was exceeded.

[CanAutM3]

Originally Posted by FTS

I am having hard time figuring how same tire size from same manufacturer would have that much contact patch area difference on same width rim. Tires should have similar/close to same contact patch area, provide same side wall height, on same rim width, there are exceptions of course. In my experience, the best way to increase contact patch is to widen the wheel width if original tire was put on optimum wheel width already, but even then the results are marginal. The best method would be to increase wheel width with larger tires for optimum result; and I know you are well aware of this. So, my point is that these numbers may not yield the results you are looking for, or at least I'd be surprised if they do.

I don't see it that difficult to understand. A different construction of the tire carcass and a different mold for the rubber thread can yield a different contact patch size for the same tire standard dimensions (Width/Ratio-Dia). BMW has been vocal to the fact that specific PSS were developped for the F8X.

See the chart below taken from Tire Rack. For three different 275/35R19 PSS, with three different contact patch widths. I corroborated the missing data with the Michelin.ca website and can confirm that all 3 tires have the same 10.9" section width and 26.6" diameter as measured on 9.5" rims. However, the rim width for the F8X specific tire is not specified. If we assume it was also measured on a 10" rim (OEM size), why would it make the contact patch smaller?

This also corroborates my experience. Looking at them side by side, the 275/35R19 on my E92 sat much squarer on the road with more rubber on the road compared to the 275/35R19 on my F82

Originally Posted by FTS

Another point I made in other posts that I'll repeat here is the 2-3% difference you are calculating in rolling diameter from original maybe misleading. The cars' stability electronics work not per wheel or axle, but based on rolling differences between front and rear. So if you select tires that have -1.5% difference in the front, for example, and +2% difference in the rear, your overall impact may actually be 3.5%, which may or may not negatively impact the electronics. I say this because with Porsche the difference between front and rear tire diameters had to be between 0.3"-0.6" per spec, it was not based on % or per axle, they pointed out to me 8 specific dangerous accidents (at the track) in their records that were caused because that tolerance was exceeded.

I fully agree. That is why I specified front and rear ratio changes for each proposed combo. If both are close enough (which is the case in all options presented), the front to rear stagger ratio is maintained close to stock.

I can attest that when running a sqaure setup on my E92, the DSC became much more intrusive.

Further, BMW does recommend a square setup for winter driving. So, IMO, the electronics should be able to "safely" support the difference between stock stagger and no stagger. All proposed combos essentially reduce the front to rear stagger bringing them closer to square.

[gthal]

Originally Posted by CanAutM3

Interresting proposition. Definitely worth exploring.

Maybe going with the generic 255/35R19 XL instead of the F8X specific one in combination with the 285 rear could be another alternative.

That's what I would likely try... or should I say that is what I will try when the time comes.

[CanAutM3]

Originally Posted by gthal

That's what I would likely try... or should I say that is what I will try when the time comes.

The time will come faster than later for me since I corded my fronts at the track last fall

[Palomequet]

Originally Posted by CanAutM3

The time will come faster than later for me since I corded my fronts at the track last fall

Do what I did, I'm prep a full report before and after H&R springs, 'till now my M4 improves a lot in handling and looks and I had to buy just a pair of OEM rear tires for it.

[CanAutM3]

Originally Posted by Palomequet

Do what I did, I'm prep a full report before and after H&R springs, 'till now my M4 improves a lot in handling and looks and I had to buy just a pair of OEM rear tires for it.

Agreed, the drop and stiffer rates will help with better camber control.

However, my car is also my 4 season DD. I am concerned that the H&R will lower the car too much for winter driving. I am waiting to see what comes out of Eibach.

[FTS]

Originally Posted by CanAutM3

I don't see it that difficult to understand. A different construction of the tire carcass and a different mold for the rubber thread can yield a different contact patch size for the same tire standard dimensions (Width/Ratio-Dia). BMW has been vocal to the fact that specific PSS were developped for the F8X.

You should know by now, nothing comes easy to me

I do not think, but do not know for sure, a tire company will change the carcass construction for any specific car, that is too expensive to do. When a car company says the tires were specifically developed for their model, I believe what they really mean is the car company has some not-so-specific targets in terms of tires' hysteresis and modulus, and the tire company probably only changes the vulcanization time and/or temp, or possibly modify accelerants or softener levels on one or few layers to come up with something close to that target. Then again, you may be right, who knows.

[CanAutM3]

Originally Posted by FTS

You should know by now, nothing comes easy to me

I do not think, but do not know for sure, a tire company will change the carcass construction for any specific car, that is too expensive to do. When a car company says the tires were specifically developed for their model, I believe what they really mean is the car company has some not-so-specific targets in terms of tires' hysteresis and modulus, and the tire company probably only changes the vulcanization time and/or temp, or possibly modify accelerants or softener levels on one or few layers to come up with something close to that target. Then again, you may be right, who knows.

I cannot attest if the carcass is different for the different PSS variants of the 275/35R19 PSS. But I can confirm that mold used for the thread is different. The "generic" 275/35R19XL PSS on my E92 has much thinner longitudinal "grooves" in the thread pattern than the "F8X specific" 275/35R19 PSS. The generic PSS also sits wider and squarer on the road. See my old thread here on the topic.

[gthal]

Originally Posted by CanAutM3

I cannot attest if the carcass is different for the different PSS options in 275/35R19. But I can confirm that mold used for the thread is different. The "generic" 275/35R19XL PSS on my E92 has much thinner longitudinal "grooves" in the thread pattern than the "F8X specific" 275/35R19 PSS. The generic PSS also sits wider and squarer on the road. See me old thread here on the topic.

Interesting... I missed your other thread but there are very meaningful difference in the tread of the tires. The M specific PSS looks far less aggressive (tread) for dry grip and more rain oriented with wider grooves and more pronounced siping. The difference is much bigger than I expected.

[Racer20]

Originally Posted by FTS

You should know by now, nothing comes easy to me

I do not think, but do not know for sure, a tire company will change the carcass construction for any specific car, that is too expensive to do. When a car company says the tires were specifically developed for their model, I believe what they really mean is the car company has some not-so-specific targets in terms of tires' hysteresis and modulus, and the tire company probably only changes the vulcanization time and/or temp, or possibly modify accelerants or softener levels on one or few layers to come up with something close to that target. Then again, you may be right, who knows.

Most cars use a custom carcass construction and rubber compound. This is nothing special . . . Even basic cars like the Ford Fusion and Jeep Cherokee typically have tires that are specifically developed for them.

[FTS]

Originally Posted by CanAutM3

I cannot attest if the carcass is different for the different PSS variants of the 275/35R19 PSS. But I can confirm that mold used for the thread is different. The "generic" 275/35R19XL PSS on my E92 has much thinner longitudinal "grooves" in the thread pattern than the "F8X specific" 275/35R19 PSS. The generic PSS also sits wider and squarer on the road. See my old thread here on the topic.

I agree that probably the thread compound and grooving might be different, I am with you on that. However, those would not change contact patch area as much as the data in the table you listed, or at least I don't think they would.

Originally Posted by Racer20

Most cars use a custom carcass construction and rubber compound. This is nothing special . . . Even basic cars like the Ford Fusion and Jeep Cherokee typically have tires that are specifically developed for them.

Are you saying that Michelin (or other) would actually change the carcass construction for a specific model car within a specific model tire? What I am asking specifically is do you find it feasible for a tire manufacturer to change the compound, Carbon Black levels, number of fiber strands and angles, within the PSS model line for different model cars? If you seriously think that, I'd believe you, but please state some background on this so I can understand it better. TIA.

[CanAutM3]

Originally Posted by FTS

I agree that probably the thread compound and grooving might be different, I am with you on that. However, those would not change contact patch area as much as the data in the table you listed, or at least I don't think they would.

Do note that the "contact patch width" ("c.p." in my table) obtained from the Tire Rack site is the thread WIDTH, not contact patch AREA .

The shape of the thread cross section as it is molded (straight or angled inward) can have a drastic impact on the width of the thread in contact with the road (contact patch width).

[FTS]

I give you that, I'd agree. May be I have to rethink this, but that much difference? Still not computing in my head

[CanAutM3]

In an attempt to get more voters

[M4TW]

Thank you for your work on this CAM3! For the stupid like me, are you saying that simply switching to the regular PSS tires should improve dry forward grip?

[CanAutM3]

Originally Posted by M4TW

Thank you for your work on this CAM3! For the stupid like me, are you saying that simply switching to the regular PSS tires should improve dry forward grip?

I am pretty sure it would.

[Racer20]

Originally Posted by FTS

I agree that probably the thread compound and grooving might be different, I am with you on that. However, those would not change contact patch area as much as the data in the table you listed, or at least I don't think they would.


Are you saying that Michelin (or other) would actually change the carcass construction for a specific model car within a specific model tire? What I am asking specifically is do you find it feasible for a tire manufacturer to change the compound, Carbon Black levels, number of fiber strands and angles, within the PSS model line for different model cars? If you seriously think that, I'd believe you, but please state some background on this so I can understand it better. TIA.

Yes, that's exactly what I'm saying. It's not a matter of what I think . . . My background is that I'm a ride and handling engineer and I have done this exact type of tire development in the past at the OEM level. Even something as mundane as a Grand Cherokee has one-off tires. Typically tread design is kept common across a tire model line, but everything else you mentioned is fair game. There are SOME cases where off the shelf tires are used, but overall it's the exception, not the rule.

Automakers make a big deal about "specifically developed" tires because the public doesn't know any better. Just like "low pressure Nitrogen filled gas shocks" . . . EVERY shock made today is filled with Nitrogen. It's just fancy words for marketing.