Effect of Wheel Width?

Hey all,

I'm trying to decide on a wheel/tire package for 200 treadwear street tires. I have been looking at all the tire testing data I can find, but I haven't seen a direct test of the effect of wheel width.

For example, is a 200 treadwear 205/45/17 faster on a 7",7.5",8"... wide wheel?  

The closest I have seen is this post from Hollis Racing on FB

"

Optimal wheel size

Many folks entering the ST category are refugees from Stock looking to make some performance upgrades to their car and/or reduce their tire budget.  Unfortunately, they carry with them some baggage on concepts that may work well in Stock, but not in ST.  One of these is optimal wheel/tire fitment.

Since Stock limits you to the OE wheel sizing, astute competitors have learned how to stuff increasingly wider tires onto those skinny rims.  And tire makers have been happy to make wider and wider tires, likewise charging more and more money.  But, is wider better?  In Stock, the answer is often "yes".  The sidewalls on these DOT-approved  "Not for Highway Use" R-comps are super stiff and allow for "overtiring" much in the way that a cantilever style slick works to get around wheel width limitations for formula cars.

In ST, drivers in most classes have limits on both wheel width and tire section width, both of which are much wider than OE.  The tendency is to cram the widest legal tire on the widest legal rim that will fit and go for it.  But that is not always the optimal solution, as street tires do not have the same super-stiff sidewalls as do the best R-comps.  Sometimes it makes sense to run a narrower tire for a given rim fitment.  From the testing we've done, we find that a good rule of thumb is that the optimal rim is the same size (rounded up to the nearest half-inch or so) as the tread width (not section width!).  So a 205/50-15 tire with a typical tread width of 7.5" is best on 7.5" rim.  An 8" rim will work, too, but it will be majorly stretched on a 9.  Likewise, it will lose some performance on a 7, and will lose a LOT going down to a 6 or 6.5.  Similarly, a 225/45-15 with an 8.2" tread width works best on at least an 8.5" rim and loses a fair bit on a 7.5".

A practical example of this is in STC, STF and STS where the rim limitation of 7.5" keeps the 195/50-15 Toyo R1R at the top despite it not being the widest allowed tire size.  The 225/45-15 R-S3 mounted on that same 7.5" rim is not quite as fast.  But put that same R-S3 on an 8 and it comes alive.  And it's even better on something a bit bigger.  So in STR, where wider rims are allowed, the common 225 R-S3 on 9's is a faster combo than the 195 R1R on a 7.5 (assuming nominal weather).  And putting the 195 on an 8 or wider does nothing to enhance performance and close the gap."

https://www.facebook.com/notes/hollis-racing/street-touring-and-track-day-tire-faq-utqg-140/245008598916447

What I gather from this is you want a wheel that is as wide, or slightly wider than the tread width of the tire.

So the theory is that lap times with a 205mm tire, which has a 8" tread, ought to be slowest on a 7" wheel, faster on a 7.5", fastest on a 8", and no faster on anything wider than 8". Does this match what you guys have seen? 

In reply to gencollon :

I think most of us are reading off Andy’s findings and making our best educated guess - and everyone else is probably on their way to solo nats now. 

I went with a 205 RE71R on a 7” wheel for my STS Miata. It’s somewhat of a budget build, so rather than spend money chasing the last nth(at this point) I decided to focus on things that make the most impact: springs/swaybar/camber/shocks(though not $$ ones)/tires - then focus on learning to drive it. 

It'll depend a little bit on the car, driver and tire too.  Different tire construction can affect how much wheel width will impact performance.  Depending on how the car loads up the tires or how responsive it is and the driver's style and preferences, slightly narrower than "ideal" might be faster by virtue of being easier to drive and more forgiving, for example. 

GRM has done several tests in the past, mostly (always?) conducted by Andy. Normally section width equal to wheel width seems to be roughly optimal. I think your reading is correct.

Keep in mind that is old info, he’s talking about the RS3s. From what I’ve seen lately, the trend is moving toward stuffing bigger tires on the rim. I think the fastest ES miata had 225s on 7” rims at the last event I attended. Not quite what we used to see w R comps, but anecdotally I’m seeing tire stuffing in street.

For autox I don't think it's really changed.  The general rule is that you get the widest wheels you can (based on rules and fit), pick a tire model/compound, and then use the widest tire available in that compound that can be safely mounted on the wheel.

Im running a 245 on a 10.5" wheel. Feels really nice as there is zero sidewall wiggle. Looks kinda silly though.

I just scored a set of Conti DR/Hoosier R6 slicks in 245/40-18 off the $2018 forum based on Hoosier's spec sheet saying the acceptable rim width range was 8.0 to 9.5". I have 8.0" inch rims. They got here yesterday and they are frickin' wide! The tread is 9.0" and the bead in it's unmounted state is 9.5". The sidewalls are quite stiff and I imagine getting them off the rims when they're done is going to be challenging.

Anybody have any experience with running Continental Contact Extreme DR's on the bottom end of rim width range? Are they going to work? Any input is appreciated.

I remember when I was crewing on an SCCA DP Datsun 2000, we were running an 8.0" width bias-ply cantilever tire on 6 inch rims. The sidewalls rolled over a huge amount by design to give the widest tread possible on the mandated OEM plus 1.0" rim width. These aren't going to look like that but there will be some negative sidewall camber.

In reply to gencollon :

What about wheel to wheel racing?  How does that differ from Autocrossing with regard tire size?

If you could put a stupidly wide tire on the car would that slow the car down because the added drag isn’t offset by the increased cornering speed? 

In Vintage racing I came face to face with that. There was no restriction on tire width back when I started Vintage racing ( 1975 ) just so long as it looked “Vintage” 

Original was a 5&1/2 inch wide rim. On a car with 150 mph top speed.  I used rims up to 8 inches wide because the body was fiberglass and it was easy to make the fenders look right without the need to flair them.  Over 6 inches the car actually slowed down.  Only a 10th of a second at Elkhart Lake with its 3 long straights but 3/10’ths with 8 inch rims. 

Cornering speed is one part, drag is another 

frenchyd said:

What about wheel to wheel racing?  How does that differ from Autocrossing with regard tire size?

It is possible to put too-wide a tire on a car such that the drag down the straight hurts it more than the gains in the corner, but you kinda have to work at it.  The precise point where it happens will vary from track to track depending on how many corners there are and how long the straights are.

This is a subject I've been researching for a long time, but the only way to answer the question definitively would be to do a test where the same brand tire which came in a wide range of widths was tested across its available widths on the same width wheel, and then inversely, a given tire was tested with a range of wheel widths, preferably all of the same brand.  And even then, the results would only be strictly applicable to the particular car in the test, at that particular track.

I do have some data points from my own car that I can share.  My car is a track-focused Porsche 968, weighing about 2850 pounds without the driver, and putting out about 250 hp.  The suspension is basically a full race set-up with an aggressive alignment, driven on a very technical track (Driveway Austin's Level 2 configuration, if anyone here is familiar with that) where cornering speed is the dominant factor for lap times.  Here's the summary of my times (some taken from memory, the most recent ones from my Aim Evo4S data acquisition system):

With my previous 17 x 9" wheels at all four corners:

Tire size:  245/40-17.  Tire model:  BRG Rival.  Best lap time:  ~1:04.8

Tire size:  225/45-17.  Tire model:  BRG Rival S.  Best lap time:  ~1:04.5

Tire size:  225/45-17.  Tire model:  Nitto NT01.  Best lap time:  1:04.1

With my current Signature SV103 17 x 10.5" wheels at all four corners:

Tire size:  255/40-17.  Tire model:  Bridgestone RE71R.  Best lap time:  1:03.5

Tire size:  275/35-17.  Tire model:  Maxxis RC-1.  Best lap time:  TBD

Based on what I had read, including a very good tire test in the December 2013 issue of GRM, I was very much in the put-the-widest-wheel-under-a-given-tire camp.  In other words, wheel width is what's really important - you can put pretty much any width tire on a given wheel, and it won't make much difference.  My results with my 9" wide wheels pretty much supported that, as I actually saw faster times with narrower tires, although these conclusions are tempered by the fact the the 225's were stickier than the 245 BFG Rivals.  But my results with my 10.5" wheels have  been, to be honest, very disappointing.  I had expected to see at least a 1.5s reduction in lap times, given how grip-limited my car felt with the 9" wheels, but I've barely been able to eek out 0.6s.  I think there are two possible reasons for this.  Either the 255's are just not a good match for the 10.5" wheels (they look really stretched, much more than I had expected), or the extra drag from the wider wheels and tires negates the improvement in grip.  So, I'm very anxious to see how my car performs with the 275/35-17's, as those should be a better fit for my wheels, and they're actually 0.4" smaller in diameter than my current RE71R's.  This should answer the grip-vs-drag question, at least on a car with my setup and weight-to-power ratio.  Unfortunately, they're on backorder, and won't ship till September 17, but I'll let everyone know how they perform.

Cloud9...68 said:

So, I'm very anxious to see how my car performs with the 275/35-17's, as those should be a better fit for my wheels, and they're actually 0.4" smaller in diameter than my current RE71R's.  This should answer the grip-vs-drag question, at least on a car with my setup and weight-to-power ratio.  Unfortunately, they're on backorder, and won't ship till September 17, but I'll let everyone know how they perform.

Comparing RC-1s in 275 to RE-71Rs in 255 isn't going to tell you anything useful about grip-vs-drag because the differences in grip between the compounds dwarf the differences in grip due to tire or wheel width.

Not so sure about that - from what I've read, the RC-1 is comparable to the Nitto NT01, which, at least in my experience, was pretty comparable to the BFG Rival S, which the RE71R has consistently, if narrowly, beaten in most tire tests.  In other words, it looks to me like you can pretty much throw a blanket (more like a neckerchief) over the differences in capability between all of these tires.   I do agree that the comparison would be more valid if Bridgestone made the RE71R in a 275/35-17, but I still think the lap times I'll see with the RC-1's will be a meaningful data point.

I was also under the impression, from the reading I have done, that the RC1 and NT01 are very well matched in terms of lap times, and both are slightly faster than rivals or RE71. I have also read, but not confirmed, that the 200 treadwear tires' lap time potential falls off faster, as they wear and heat cycle. Does that sound right to you guys?

If that's the case, Cloud's 275mm tire experiment will indeed be interesting. If it does prove to be slower than the narrower tire, it is likely because of the added rolling, and air resistance... You'll let us know, right?

Also, Cloud 968 is exactly right about the test that would need to be done: Swap the same tire  onto different width wheels, then pick a wheel size, and swap different widths of the same tire onto that wheel. It's rather expensive to do though... so, at this point, If nobody here has seen the experiment done... I don't think anyone has tried it and written up the results.

Fitzauto: do you have any data with your 1" stretch? Did it make you faster than you were before?

Frenchyd: You're definitely right about wider wheels/tires producing more air resistance as well as more rolling resistance. You can go too wide.

I have no wheel to wheel experience, but I think that with continuous lapping, it's all about keeping the tires at their optimum temperature. Wider tires cool down faster than narrower ones. If you have trouble getting the tires up to temp, they are probably too wide. If the tires get overheated and greasy, they are too narrow. In autocross or time attack, where it's just one hotlap, tire heat doesn't play as big of a role. 

Another thing that usually isn't controlled is track width. When people add width to their wheel/tire package, they usually stay around the factory offset. The extra track increases lateral G capability. Narrower wheels/tires with a different offset or extended control arms might be just as fast?

In reply to gencollon :

On the track width thing, wider wheels / tires with the same offset doesn't change track width.  It's measured based on the centerline of the wheel, not the outer edges.  

In reply to Cloud9...68 :

Another factor to take into consideration that you didn’t mention is weight.  (Generally) the wider wheels and tires are heavier which is more gyroscopic weight to be spun up (acceleration time).  So without data logging the entire lap it’s impossible to say but i’d guess your car is losing a step on the straights and carrying a bit more through the corners.

From the Miata guys: (which I used to be one)

205 = 8"

225 = 9"

245 = 10"

275 = 11"

z31maniac said:

From the Miata guys: (which I used to be one)

205 = 8"

225 = 9"

245 = 10"

275 = 11"

Or, back in the "stock" days, you could put Hoosier 275s on factory 15x6s and still be faster than any other tire available.  I've run 205s on 14x5.5s and 225s on 15x7s, they were all faster than having the "right" tire width for that wheel.

Not sure if this link is any use whatsoever but I came across it last night when googling uses for Volvo wheels.  Apparently Volvo and Ferrari are the answer but I think just from scanning the link/article it might have some good general info. 

https://www.ipdusa.com/techtips/10010/wheel-and-tire-fitment-guide-for-1994-2008-fwd-awd-volvo-models

In reply to KyAllroad (Jeremy) :

That's a good point I forgot to mention.  My new wheels are forged, and weigh just under 18 lbs, vs 21 lbs for my old cast wheels.  But of course the tires are a few pounds heavier, so the total weight of the wheel/tire combo is about the same.  However, tire weight matters more than wheel weight, since it's situated at the periphery of the rotating mass, so I've probably added a bit of rolling resistance with my new package.  This is another reason I'm chomping at the bit to receive my new tires - while I'm sure their heavier than my current RE71R's (Maxxis doesn't list their weight), they're also 0.4" less in overall diameter, which should at least partially offset the extra weight in terms of resistance to acceleration.

For obvious reasons, I sure hope the wider tires are substantially faster than m current size - right-sizing my tires to my wheels is a heck of a lot cheaper that adding horsepower, especially to my oddball car.

Oh, and I do have a very nice data logger (Aim Evo4S, GS Dash, and Smartycam HD, plus analog sensors for throttle position, steering angle, and brake pressure), but unfortunately I didn't have it when I had my 9" wheels, so I can't make a direct comparison.  I will be able to compare data between my current and new tires, however, and will be happy to share.

In reply to rslifkin :

You're right. That's how track is measured. But correct me if I'm wrong: The wider wheel/tire package, at the same offset does increase the effective track width in a corner, which is the only place it really matters. That'll reduce load transfer, and better utilize the tires. 

Not having any tire load curves (lateral force vs slip angle) for 200 treadwear tires, I can't say how much faster it will make any given car... But it will make that car some amount faster around a skidpad.

If you know of some good representative 200 treadwear data, I'd like to see it! It would let me have a hack at the gains I could see by going widebody, with custom control arms... or even see how much gain there is to be had in lowering the car more.

In reply to gencollon :

One point missed, assuming a effective enough brake package to allow front wheel lock-up is a wider tire will afford slightly superior braking too!  

Cloud9...68 said:

In reply to KyAllroad (Jeremy) :

That's a good point I forgot to mention.  My new wheels are forged, and weigh just under 18 lbs, vs 21 lbs for my old cast wheels.  But of course the tires are a few pounds heavier, so the total weight of the wheel/tire combo is about the same.  However, tire weight matters more than wheel weight, since it's situated at the periphery of the rotating mass, so I've probably added a bit of rolling resistance with my new package.  This is another reason I'm chomping at the bit to receive my new tires - while I'm sure their heavier than my current RE71R's (Maxxis doesn't list their weight), they're also 0.4" less in overall diameter, which should at least partially offset the extra weight in terms of resistance to acceleration.

For obvious reasons, I sure hope the wider tires are substantially faster than m current size - right-sizing my tires to my wheels is a heck of a lot cheaper that adding horsepower, especially to my oddball car.

Oh, and I do have a very nice data logger (Aim Evo4S, GS Dash, and Smartycam HD, plus analog sensors for throttle position, steering angle, and brake pressure), but unfortunately I didn't have it when I had my 9" wheels, so I can't make a direct comparison.  I will be able to compare data between my current and new tires, however, and will be happy to share.

Don’t forget the Brakes.  Wider tire will give better braking before lock up ( assuming an effective enough braking system to lock up the tire ) 

codrus said:

Comparing RC-1s in 275 to RE-71Rs in 255 isn't going to tell you anything useful about grip-vs-drag because the differences in grip between the compounds dwarf the differences in grip due to tire or wheel width.

Agreed, but in the real world I think 949 basically proved that there's almost no tracks/Miatas in which an increase in wheel and tire size does not lead to faster times. It's almost always an improvement. 

I finally got my Maxxis RC-1's in 275/35-17 for my 17 x 10.5" wheels for my Porsche 968 mostly-track car, and did my first track session on them today.  They are fantastic!  First of all, they are (obviously) a MUCH better fit for my wheels than the 255/40-17 RE71R's I had before.  The advanced configuration of the track I drive has been flooded due to the recent torrential rain here in central Texas, so I was only able to drive on the "beginner's" section, which is a highly technical 0.7 mile configuration.  The grip of these tires is amazing - I was faster everywhere, beat my best lap time despite not having been on the track for over two months, and easily passed cars I could barely keep up with before.  I'm able to get on the power much sooner, and they respond very crisply to fast transitions.  And on top of that, these tires are very communicative and controllable.  They're even quiet, and have a fairly comfortable ride!  By far the best performance-oriented tires I've ever owned.  The only downside is that they don't have any actual tread, so they can't be driven if there's standing water on the road, but I never drive my car in the rain, anyway.

Oh, and by the way, these tires were manufactured in 2014.  I was a little concerned about this, but some research revealed the concern over "aged" tires seems to be more emotional than fact-based, and my experience definitely backs that up.