Effect of Wheel Width?

I’ve tried it both ways:

(1) same tire brand/size on narrower and wider wheels. Example 225/45/15 tires on 15x6.5, 15x7, and 15x8 wheels.

(2) narrower and wider versions of the same tire on the same wheel. Example 205/55/15 and 225/45/15 sizes of the same tire on 15x7” wheels.

My conclusion has been that wider wheels are pretty much always better. Putting super wide tires on narrow wheels such that the sidewalls are visibly “pinched” doesn’t yield any more grip than using a narrower tire that fits better to begin with. Moreover, the steering feel gets noticeably sloppier. Ideally, the sidewalls should be straight or even slightly stretched.

As an extreme example, I‘ve run Hankook Z214 medium compounds in 205/50/16 on a 16x8.5” Fuchs wheel at VIR and NJMP. That’s much greater wheel width than what’s recommended for this tire, but they held up great. It was very easy to maintain even tire pressures and temps.

In reply to Cloud9...68 :

Oh yeah, if you haven’t driven on R comps before the lack of tire squeal can be a bit disconcerting.  Thank goodness they don’t though, imagine how obnoxious most Motorsports would be if everyone’s tires howled like a set of all seasons??!

LanEvo said:

I’ve tried it both ways:

(1) same tire brand/size on narrower and wider wheels. Example 225/45/15 tires on 15x6.5, 15x7, and 15x8 wheels.

(2) narrower and wider versions of the same tire on the same wheel. Example 205/55/15 and 225/45/15 sizes of the same tire on 15x7” wheels.

My conclusion has been that wider wheels are pretty much always better. Putting super wide tires on narrow wheels such that the sidewalls are visibly “pinched” doesn’t yield any more grip than using a narrower tire that fits better to begin with. Moreover, the steering feel gets noticeably sloppier. Ideally, the sidewalls should be straight or even slightly stretched.

As an extreme example, I‘ve run Hankook Z214 medium compounds in 205/50/16 on a 16x8.5” Fuchs wheel at VIR and NJMP. That’s much greater wheel width than what’s recommended for this tire, but they held up great. It was very easy to maintain even tire pressures and temps.

That's very good information, and it backs up what I've been led to believe since reading the December 2013 tire test in GRM.  In my case, I think the 255/40-17 RE71R's were just a little too stretched, seeing as the tread width shown for those tires on Tire Rack is only 8.9", and the section width is 10.2".  They were visibly very stretched.  In contrast, the 275/35-17 RC-1's are visually a perfect fit.  But I suspect that if even wider tires were available (they're not), the car wouldn't corner any faster.  I've found my go-to tire.  I just hope Maxxis never stops making it in this oddball size!

In reply to KyAllroad (Jeremy) :

None of the last few sets of tires I've run (BFG Rival, Rival S, Nitto NT01, Bridgestone RE71R, and now the Maxxis RC-1) made significant noise under even the hardest cornering, which seems to indicate the compounds used on all modern, aggressive, streetable track-oriented track tires are pretty similar.

In reply to Cloud9...68 :

I’ve never tried the Maxxis RC1 so I can’t really comment on them. But the increase in grip and high-speed stability when you go from street tires to r-comps is pretty shocking. Then it’s another huge leap when you go from regular r-comps to the top performers (like Hoosier). Once you get spoiled, it’s hard to go back down the ladder!

But the interesting thing is that I've run R-Comps before (Nitto NT01's, in 225/45-17 when I had 9" wide wheels), and while they were good, they were no faster than the Rival S's I had in the same size before.  So there are a lot of factors involved - not only do the RC-1's fit my 10.5" wide wheels better than the 255/4-17 RE71R's I had before, they're also 0.4" smaller in overall diameter, which makes for a slightly lower center of gravity without increasing the roll couple, which translates to less lateral weight transfer, and therefore better grip.  Also, the (admittedly slightly) smaller diameter will keep the revs farther up in the power band across a lap.  I guess an interesting head-to-head comparison would be the RC-1 vs. the NT01 in the same size on the same car, which would tell me if the RC-1's compound is simply stickier than any tire I've had before.

OK, I was finally able to get out to the track (after it was under 8 feet of water for weeks after the November floods here in Central Texas!) with my 275/35-17 Maxxis RC1's on my 17 x 10.5" forged alloys on my Porsche 968 track car.  The car has a full race suspension (too many upgrades to list), which has been well sorted by a knowledgeable alignment specialist.  The engine is close to stock, and I've removed about 220 pounds from the car.  The verdict on the tires:  Meh.  I did beat my best time on the very technical ~1 mile track, but only by 0.2s compared to the very stretched 255/40-17 RE71R's that were on the car before.  Taking the average of my lap times among the four sessions I've done on the new tires so far, my times are no faster overall than with the RE71R's.  The sessions were all done under absolutely ideal weather conditions - mid 60's to mid 70 degrees, low humidity - gorgeous weather.  This is disappointing, especially considering that the RC1's utilize what should be a stickier compound than the RE71R's, but adds another data point to the proposition that tire width is practically irrelevant - wheel width is what really matters.  On my former 17 x 9" wheels, I similarly saw no difference in lap times between 225/45 and 245/40 tires, and the switch to the 10.5" wheels has lowered my lap times by about 0.9s.  Still not very impressive, but larger than the impact of going to wider tires on the same wheel.

The most obvious possible cause of my disappointing results is that heavier tires will increase the rolling resistance, as has been pointed out in an article in GRM about a year and a half ago.  In a momentum car like mine, it appears that the extra drag canceled any benefits from additional grip from the wider tires.  A more powerful car may see larger benefit from wider tires on the same wheel.  But I sure haven't seen it.

Despite being in Texas it has got to be cooler than ideal for R comps.   Track time is less sensitive to temp than autox but anything under the ~50’s you’ll find the R comps to be far worse than streets.   

This thread is a reminder that I need to get something wider under the V.  10.4” section width on 8” wheels is less than ideal.

It was sunny and in the 60s and 70s during my sessions on the RC1's.

Interesting - wonder what you would see out of the next level tires like hoosiers.

If the rc1 is the max is 200 headwear tires, I can tell you they are about 1 to 2 seconds slower than re71.

They are a little slower than the rs4 as well.  

They don't like heat and get greasy fairly easily.

We tested these tires at a few champcar weekends and came away feeling meh.

The re71 were the E36 M3, but wear too quickly.

The rs4 were the best compromise.

For tire temps, we have found 205 on an 8, 225 on a 9, and 245 on a 10 is the ideal setup.

Even with only 150rwhp and 2400# vehicle weight, the car was faster everywhere with the 245 on 10s.  We carried more speed through the corners which made for higher straightaway speeds as well.

Thanks for the inputs.  I took a look at the data from my fastest lap on the RC1s, overlaid against my best lap on the RE71Rs (something I should have done before posting the above post), and it was pretty interesting.  In the most challenging, interesting series of corners of the track, I was vastly (by up to 6 mph!) faster on the RC1's, but inexplicably, I was a little slower in a few other parts, so the net was very little difference (only 0.2s) in lap times.  If I can be that much faster on that one sector, I should be able to be faster everywhere else.  I think it's just a matter of building my confidence that the car really is capable of going much faster than my subconscious mind thinks it is.  So, I'm not giving up on the RC1's just yet, but I may give the Hankook RS4's a try next time, since they have about the widest tread and section width (per tirerack.com) of any 255/40-17 tire, and they're a little cheaper than any of the competitive tires.

In reply to Cloud9...68 :

Actually, from what I have read, the "super 200" tires are faster than anything between 200 and 40 treadwear. So that's RE71R, Rival S 1.5, & maybe Advan A052, though I can't find much info about that last one. I have heard the Rival S 1.5 is faster than the RE71R in dry warm conditions, and the RE71R is faster in the cold and wet.. All heresay from time attackers. 

Ryan Passey recently won limited class at the Buttonwillow Super Lap Battle on Rival S 1.5s, when he could have used any tire 60 treadwear or higher. He is convinced the super 200 is the fastest. I think I'll try a set this year.

In reply to wvumtnbkr :

The Maxxis RC1 tire is a 100 treadwear DOT R comp tire. Takes time to come up to temperature, but lasts a long time. Used for endurance racing.

Now for more heresay: The RS4 appears to be as fast as the RC1 (maybe faster, it is newer after all, and each new tire is a step up from an older model) and is rumored to take continuous lapping better than the other 200 tw tires, and is the tire of choice for budget endurance racing where 200tw is required.

The RE71R and Rival S 1.5 are faster on a single hot lap than either of the previous 2 tires mentioned.

...Supposedly. Would love some confirmation of these rankings, or better info.