Thoughts on wheels and tires - basic technical discussion

[JoeFromPA]

Hi all,

So in the natural order of things, we see lots of new M owners starting their investments with wheels and tires as a time-honored favorite modification and something that's becoming widely available and highly customizable.

My basic question is this: Does anyone know of any documented testing of a well balanced platform improving in braking, slalom, track times, or acceleration simply from going to a wider set of wheels + wider tires (assume same tire/tire compound)?

From what I've read over the years, we have a few examples of instrumented testing:

- http://www.caranddriver.com/features...d-tires-tested
- http://www.popularmechanics.com/cars...omparison-test (look at the michelin tire results)

From what I can tell, upsizing wheels and tires is a really risky proposition. You are potentially moving the centerline of the tire outside of the optimum design of the suspension - you are moving a fulcrum point.

You may also be altering the weight and distribution of weight, affecting the ability of the suspension to operate as it was originally designed.

Now, suspension have play in them. New tires weigh more than worn out tires and have different heights. Some tires are wider/narrower than others. So this isn't a super sensitive thing.

Secondly, you aren't increasing contact patch UNLESS the tire gets taller overall. It may (or may not) be possible to increase contact patch because the wheel is wider and the sidewall is stiffer, but an increased contact patch on the same weight vehicle means the contact patch pressure changes...which changes traction.

...

So all of this being my main point: Do we have any objective information in documented testing that an "optimized" performance vehicle like an m3 will improve in total performance, such as a track time environment, from wider wheels and tires AND NOT because the tire compound was changed?

I ask this because I'm wondering if it's worthwhile to invest in wider wheels and tires or if I should simply plan on changing the stock tires to new compound. And because I want to stimulate a little discussion and sharing.

[JeffM-Houston]

Just my opinion, but the vast majority of owners have zero interest in performance when it comes to tires and wheels. A few of us are interested in autocross or track days but for most (95%?) it's just about how they look.

[dmk08]

Originally Posted by JeffM-Houston

Just my opinion, but the vast majority of owners have zero interest in performance when it comes to tires and wheels. A few of us are interested in autocross or track days but for most (95%?) it's just about how they look.

I for one want better traction and a better more unique look. So its 50/50.

[consolidated]

Other things to keep in mind are as the tire gets wider, taller, and stickier the rolling resistance usually goes up, gearing gets slightly taller, and likely more aerodynamic drag.

Offset by higher cornering speed, more exit speed, less wheelspin, higher braking G's, stiffer tire construction allowing lower pressures and a larger contact patch.

Grassroots Motorsports had a great test using a E90 a few years back tackling just this topic. I recall diminishing then declining returns as wheel/tire combos got larger.

Maybe call Vorsteiner, surely their widebody is backed with data and engineering.

[m4pewpew]

I don't have any data to backup, and I'm not a mechanic or engineer or race car driver or whatever. But my impression is good tires > wider wheels. I mean, yeah in theory wider wheels provide more contact patch, and more contact should mean more traction. But my experience is during a race there are a lot more variables you need to control for max traction when competing against someone with bigger wheels: especially tire pressure and temperature control. Of course, there are other things you can do (sway bars, shocks, etc) to get more traction, but hey we're talking about tires and wheels right?

Generally speaking, if I had to bet, race tires with stock wheels vs stock tires with wider wheels, I would bet on the guy with the race tires because in the past many cars were equipped with crappy tires. But in the case of the F82 & F80, I can't even place my bet because I have no idea how the stock tires perform. I just read somewhere that they pull close to 1G, and I think that's pretty good compare to older cars.

Like you, I would be curious about data too.

[FogCityM3]

Nice research and I came to similar conclusions. What I ultimately decided on was based on lap time performance of German tuned vehicles (the SportAuto Tuner GP competition) and what BMW did for the M3GTS (ran spacers which can give you an indication of max offset). Unfortunately, you might have to wait until they test various combinations. I would try to contact a-workx (Wieth Racing) as they participate in a lot of these Tuner GP competitions, have worked wonders on the E90 platform, and have worked closely with various wheel manufacturers (BBS, OZ, ATS) in developing the right wheels for their tuner cars. They are pretty responsive (in English as well)!

[gthal]

This is a great topic.

What I believe is this...

1. The OEM PSS are "OK" for the street but don't provide enough traction or heat management at the track.

2. Historically, I have not been pleased with the feel of upsizing tires on OEM wheels. Anytime I have done this I have been disappointed by how it seems to reduce feel and precision and does not seem to make a meaningful difference in traction.

3. Any time you increase weight of the wheels by more than a couple of pounds, it can be felt in driving dynamics IMO. So, bigger wheels and tires are only an "upgrade" if the weight does not increase as well.

I believe moving from the OEM PSS to an AD-08R in OEM sizes would give meaningful improvements in both traction and heat management. I also believe that a Potenza RE-11 in a 285/35 rear would be meaningfully better (as it is still a great size for a 10" rear wheel).

However, if someone buys a very light wheel that is wider (say, 10/11) and puts wider and better compound tires on will get even better results especially in corners and on corner exits.

In order of best to worst...

1. Lightweight 19x10/19x11 wheels with 265/305 RE-11 or AD-08 tires
2. OEM wheels with 255/275 or 255/285 RE-11 or AD-08 tires
3. OEM wheels/tires
4. OEM wheels with over sized tires but a better compound (#4 because of negative impact on feel/responsiveness)
5. OEM wheels with over sized tires

I have nothing to support any of this other than my personal experience.

[TahoeM3]

I'd be very surprised if BMW didn't offer a comp pack soon with larger tires...I'd guess 285/35 or 295/35 rears. I'm going to wait a bit and see what they do, but I'm sure you will see an improvement in off-the-line traction with larger diameter rear tires. TPG had great results with the Mickeys in 305/35...of course a lot of this was the compound, but the size helps, too.

[MaynardZed]

Originally Posted by gthal

This is a great topic.

In order of best to worst...

1. Lightweight 19x10/19x11 wheels with 265/305 RE-11 or AD-08 tires
2. OEM wheels with 255/275 or 255/285 RE-11 or AD-08 tires
3. OEM wheels/tires
4. OEM wheels with over sized tires but a better compound (#4 because of negative impact on feel/responsiveness)
5. OEM wheels with over sized tires

I have nothing to support any of this other than my personal experience.

Compound trumps all though. I agree with your order accept #4, OEM wheels with better compound, say Toyo R888 will be faster around a track than all your options including #1.

[gthal]

Originally Posted by MaynardZed

Compound trumps all though. I agree with your order accept #4, OEM wheels with better compound, say Toyo R888 will be faster around a track than all your options including #1.

Agreed... the reason my #4 was that low is I find oversized tires on narrower wheels results in more sloppy feel. That's subjective, however, and just my opinion. Agreed that, regardless of "feel", it would provide better grip.

[solstice]

For fastest laps I'd spend all my wheel budget on compound given that it's a dedicated track set where you're not limited to street legal stuff.

[jewels]

I for one will be looking for a new set of wheels and tires for the track.
Better traction, bigger print, ect. try to get more power to the ground before it goes into over steer.
One of my concerns is to not change the overall diameter of the wheel tire combo we have from the factory....stagger is all part of it and ABS is a factor.

[Black Gold]

Originally Posted by consolidated

Maybe call Vorsteiner, surely their widebody is backed with data and engineering.

Lmfao

[neo871]

Great thread!

Originally Posted by TahoeM3

I'd be very surprised if BMW didn't offer a comp pack soon with larger tires...I'd guess 285/35 or 295/35 rears. I'm going to wait a bit and see what they do, but I'm sure you will see an improvement in off-the-line traction with larger diameter rear tires. TPG had great results with the Mickeys in 305/35...of course a lot of this was the compound, but the size helps, too.

+1 on the competition pack

Wider tires may not give you a larger contact patch if the sidewall is not taller.
See my 'traction issues' thread.

[JoeFromPA]

So here's the thing with these comments. We see comments by very educated members like above, "TPG had great results with the Mickeys in 305/35...of course a lot of this was the compound, but the size helps, too."

Meaning no disrespect to such commenters, the problem here is a lack of actual metrics. How much was the compound and how much was the size difference? Or even a GOOD estimate?

I can tell you that if I put Mickey's on my stock m3, in stock sizes, I will see enormous performance gains and dry traction increase. Extremely noticeable.

But my guess - and it is a guess - is that I were to go from drag radials or R-compound tires in stock sizes and simply upsized the wheels and tires...while sticking with the same exact compound....I would probably barely notice a difference.

My stance - short of additional data - is this:

- The F80 forum likes to think of itself as a more educated and track oriented forum given the vehicle + price tag + buying population.
- Buying bigger wheels/tires for look/preference makes total sense
- Buying bigger wheels/tires for predominantly performance reasons appears to be a questionable proposition unless the specific wheel and tire was somehow tested extensively as offering an increase in the total performance envelope (dry straight and lateral traction, braking, etc.). And if the offsets aren't right to maintain suspension geometry, if the wheel/tire weight and moment of inertia are significantly different from stock, or if the tread pattern/compound is not well matched to the suspension design, you could actually see a decrease in performance compared to the same compound in stock tire sizes in some situations.

Let me state again: I'm not claiming to be an authority here. I'm stating what I understand from reading and trying to understand this matter.

There is a reason BMW and Porsche and many others invest thousands of man hours and probably millions of dollars in developing a tire specifically catered to the vehicle - because minute changes can add up to make big differences in the total vehicle experience.

[gthal]

Originally Posted by JoeFromPA

There is a reason BMW and Porsche and many others invest thousands of man hours and probably millions of dollars in developing a tire specifically catered to the vehicle - because minute changes can add up to make big differences in the total vehicle experience.

Although I generally agree, when BMW decides on wheels and tires, they are are also managing compromises in addition to pure performance. We are starting from a place of inherent compromise.

For example, they could design the suspension to have the wheels pushed out more to the fenders and increase track width but they don't as they need to accommodate real life considerations (tire chains, debris spray, safe fender clearance, etc). On any mass produced car, design decisions are inherently compromises regardless of the millions of dollars in development. I am certain that if BMW engineers were given a mandate of giving the F82 the best possible performance and traction from the wheel/tire set up on a track (and ignore other competing demands) that we would have a different result in offset, size, compound, geometry, etc.

Originally Posted by JoeFromPA

Meaning no disrespect to such commenters, the problem here is a lack of actual metrics. How much was the compound and how much was the size difference? Or even a GOOD estimate?

I don't know if you will get the hard data you are seeking as I don't know that there are clear answers anywhere. What you will get is what you have gotten .... some objective info and some subjective/anecdotal info based on experience. How much someone can improve the result from after market changes is hard to confirm unless someone has tested the configurations back to back and I suspect few, if any, have done so. Subjectively, however, I am a firm believer that improvements are possible and can be meaningful if done correctly.

From an objective view, I was running about 1.0 - 1.5 seconds faster on a 1:20 lap with RE-11 vs. PSS on my E92 M3. Also, I was able to get more consistent lap times over a longer period. Same size tire so the variable is sidewall construction and compound. I suspect the delta is larger for the F82 given the benefit of extra traction would have on managing torque. If I used a similar compound RE-11 tire but wider and on appropriate wheels, it would have to provide even further benefit in corner entry, corner navigation and exit but I can't quantify how much.

[Black Gold]

I have to believe that wider wheels with relatively conservative offsets with appropriately wider wheels will help this car

I plan to run 9.5/10.5 wheels with 265/285 re11. That's a standard plus 1 size, and will provide

-higher than stock traction due to slightly greater contact patch (based on increased wheel width) and superior compound
-higher tjan stock lateral grip due to stickier compound and more lateral support based on more support from the wheel and a stiffer sidewall on the tire.

The lateral stability will increase due to wider wheels having more contact with the road, more of a stretch fitnent allowing more wheel sidewall support and a much stiffer tire.

A cup tire is great in theory, but is useless on the road every day in real world conditions. This is my do everything car, and extreme summer tires walk that line between dd and track perfectly. They are the m3 of tires haha

[Iceman9591]

Originally Posted by FogCityM3

Nice research and I came to similar conclusions. What I ultimately decided on was based on lap time performance of German tuned vehicles (the SportAuto Tuner GP competition) and what BMW did for the M3GTS (ran spacers which can give you an indication of max offset). Unfortunately, you might have to wait until they test various combinations. I would try to contact a-workx (Wieth Racing) as they participate in a lot of these Tuner GP competitions, have worked wonders on the E90 platform, and have worked closely with various wheel manufacturers (BBS, OZ, ATS) in developing the right wheels for their tuner cars. They are pretty responsive (in English as well)!

I have had longer discussion with Mr. Wieth concerning the traction topic on the new F82 with the following output:
-Key issue concerning traction is the setup of the suspension - he said with his setup on the new KW Clubsport you will not see any blinking lights in the dashboard any more
-He will stick to the tire setup of BMW, meaning 255/275 stating that this setup of tires is specifically designed for the BMW M4 and upgrading it to 285/295 would be nearly impossible to gather any difference
-The Pirelli TrofeoR is the better tyre on dry conditions - however lacks in the wet, meaning the PSS is the better all-day driving tyre

[neo871]

What about BMW starred PSS tires vs. regular PSS?! Would the latter be better in terms of grip? Or is there any difference?! I am seriously considering replacing the stock PSS tires with non-starred ones, when they wear out.

[JoeFromPA]

By the way, I'm not attempting to address how a wider wheel/tire combo with a stiffer sidewall will better handle heat build-up over a harder driving environment. That's a factor that I believe would lead to greater track times but again, I can't quantify it, yet I know it's more of a PROVEN aspect of going with a wider wheel/tire.

[Iceman9591]

Originally Posted by neo871

What about BMW starred PSS tires vs. regular PSS?! Would the latter be better in terms of grip? Or is there any difference?! I am seriously considering replacing the stock PSS tires with non-starred ones, when they wear out.

If I remember correctly, the outer rubber is in some way different (I assume softer) than the one from the regular PSS. Also the "wall"(flank) of the tire are stiffer than the ones from the regular PSS. So i assume the grip is supposed to be better with the specific M4 PSS tyres.