13x6 vs 14x6

[itbgti]

I run an ITB Golf GTI in the Northeast. The question is whether or not a 13x6 inch wheel or 14x6 inch is "faster" (aka turn better lap times). I know there is plenty of scientific data to back either opinion, but is there someone with LOADS of experience with both wheels on a similiar car that can give some help. Also, please include the scientific "stuff" to back opinion.

Thanks
Alan

[racerdrew43]

Im not sure which is "faster" but I can tell you you'll have more 14 x 6 whels available to you than 13 x 6

[Dave Ebersole]

If tire diameters are the same, then the 14X6 should corner better because you have less tire sidewall to flex in the turns, I think.
Dave

[racer14itc]

But...the 225/45-13 Hoosiers I run are only 21" in diameter. I don't know of any 14" race tire that is even close to that. So, a 13" wheel/tire would lower the car more than a 14" wheel/tire combo could. Lower CG should improve ultimate cornering capability.

MC
#14 ITC VW Scirocco

[RSTPerformance]

Originally posted by racer14itc:
But...the 225/45-13 Hoosiers I run are only 21" in diameter. I don't know of any 14" race tire that is even close to that. So, a 13" wheel/tire would lower the car more than a 14" wheel/tire combo could. Lower CG should improve ultimate cornering capability.

MC
#14 ITC VW Scirocco

and give better acceleration but less top end. Don't know if it will be noticable but mathimatically with a smaller size diameter acceleration would be faster but top end slower.

[itbgti]

Stephen,

So would it be reasonable that depending upon the track, a Lime Rock vs a Pocono, a 13 or a 14 may prove to be a greater advantage??? (14 at Pocono, longer straights, 13 at lime rock or even NHIS, quicker exits???)

[RSTPerformance]

Originally posted by itbgti:
Stephen,

So would it be reasonable that depending upon the track, a Lime Rock vs a Pocono, a 13 or a 14 may prove to be a greater advantage??? (14 at Pocono, longer straights, 13 at lime rock or even NHIS, quicker exits???)

Mathamatically i would say yes but before I bought them I would try to ask around and see if anyone noticed any differences. I'm not sure that with less than an inch would have a huge effect. there must be someone on this forum that has tried it, isn't there, anyone?? you have to remember that your looking at buying rims more tires paying for more mounting and balancing, ect ect. this could get to become an expensive trial and error if you think about it!!! And besides you went faster at lime rock so you need to slow down anyway eventhough I beat you in the race you still had a faster lap time I think??

Stephen

[This message has been edited by RSTPerformance (edited August 21, 2001).]

[SamITC85]

Alan,
It is true 13x6 wheels are hard to come by but there is even a smaller choice of 14" tires. You may want to talk to the guys at SRS they ran a golf until it was wrecked at NHIS and they were running 13" wheels.

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Sam Rolfe
TBR Motorsports
#85 VW Rabbit

[joeg]

I've seen an inch in total circumfirance make a 4 second difference in lap times. This was on a ITC Honda. Had to drop to a 185x60 13 instead of a 205x 60 13 because of gearing.
Regards.

[itbgti]

Stephen: You did beat me in the race (because God placed his foot on the back of your car and gave you that INCREDIBLE start, six positions by turn 1?). Once again, compliments on that. My lap times were coming down. Since this is my first REAL year (I did enough last year just to gain a license with a real POS car), I am adjusting to the car. I ran a 1:06.17, i think you had 06.14??? But a lap time is not racing, I still am working on the racing part

SamITC85: According to Dick and the gang (no pun intended Mr. Shine) my car #78 is the rebirth of SRS's old 98 (the one that got wrecked). I have its motor, gearbox, header, computer, wiring, passenger door panel, etc. I built the car in 2.5 months, and let SRS button up the motor and gauge panel. I run their full suspension setup, and Dick built the cage. Back to rims, Dick has mixed opinions, his setup with the 13x6 inch rim and tire was the fastest, and they have run A LOT of setups, HOWEVER, 13x6 inch wheels are hard to come by, AND I have heard that tire companies are leaning out these 13 inch sizes, true or not I don't know, when I called around to get tires (only 2 seperate occasions), 14's gallore, 13's On-A-Backorder. Maybe it was my timing, but 13's were hard to find.

Another question: Currently, I am on the 14x6 gti wheels with 205/55/14 Kumhos. Would a 225 tire on the same rim perform better? Once again, this may be personal preference, but it can't hurt to ask.

Also, a great Thank You and compliments to SRS for helping me so much this season. I always had plenty of questions, and they always had the time to sit and discuss anything.

Thanks to everyone for the input
Alan

[Bill Miller]

Alan,

Check w/ the ITC guys as most of them run 13x6 wheels and should be able to put you on to good sources. That being said, I don't think 13" competition DOT tires will be going away any time soon.

A 225 tread width tire will fit on a 6" rim. What you need to be aware of is that not all tires are created equal. I used to run 205/55/14 Kumhos, and have subsequently switched to Hoosiers, in the same size. I can tell you that the Hoosiers are signficantly wider (~3/4") than the Kumhos. A stack of 4 Hoosiers standing next to a stack of 4 Kumhos (all on the same rims) is almost a full 3" taller.

I haven't actually put a 205/55/14 Hoosier next to a 225/50/13 Hoosier, but I did hear someone say that they are the same width. This is just one person's comment and I haven't confirmed it.

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MARRS #25 ITB Rabbit GTI

[Knestis]

The old IMSA Renault Cup cars, Alliance and Encore, (yes, I keep coming back to them but they were coooooool!) ran on 13x6 MOMOs, most of which probably outlived the cars that they were bolted to! They are the ones that have circles of circular holes, are pretty light, and are the same bolt pattern as a Rabbit/Golf. I wouldn't be surprised if Archer Racing didn't still have a train car full of them somewhere...

Kirk

[RSTPerformance]

I ran a 1:06.17, i think you had 06.14???

Ahh got you by .03!!!! Gonna be close at NHIS!!! I think you'll have an advantage out of turn 6 because my car is geared very poorly for it. Do you have a quaffe or locker if so big plus for you coming out of turn 3!!

Another question: Currently, I am on the 14x6 gti wheels with 205/55/14 Kumhos.

Ohh bad mistake!!! If you don't have major tire wear problems go to the Hoosiers. At least 1 sec a lap maybe even 2!!! They don't last as long but they are much faster!!! It took us a long time to get our car set up so we didn't burn them off but we are finally there with 4 degrees of neg camber!! In my opinion the 225 would be to large and wouldn't allow the car to slide at all a little loose seems to be faster. I think you would be so sticky you'd scrub more speed than if you could let it slide a little with a bit of oversteer. I know a lot of SSb and c cars a few years ago tried to go up to a 225 but actually went almost a sec a lap slower, but that could have been some driving style as well.

here is my advise get some wicked old hard kumhos that are 195 50 14. That way you go way slower and I don't have to worry about you!!

See you at NHIS

Stephen

[mogren]

We went 11 mph slower on 14 than 13s at Pocono. The infield was lame but we went faster times. The rollout was 3" different. ( 1 in taller)MM

[Joe Craven]

Originally posted by Knestis:
The old IMSA Renault Cup cars, Alliance and Encore, (yes, I keep coming back to them but they were coooooool!) ran on 13x6 MOMOs, most of which probably outlived the cars that they were bolted to! They are the ones that have circles of circular holes, are pretty light, and are the same bolt pattern as a Rabbit/Golf. I wouldn't be surprised if Archer Racing didn't still have a train car full of them somewhere...

Kirk

I just bought a set of those Momos... Ugly wheels but nice a light and fit the VW perfectly.

In any case, I will be running 13x6 in the Enduro races and 14x6 stock wheels in most of the sprint races on a 77 Rabbit with GTI running gear.

#41 VW GTI Cup
#26 ITB Capri
PS3 Capri (I forget the number but it will race again next year!)

[lateapex911]

My .02.....

225s are getting pretty wide for a 6" rim.
Quite awhile ago, we did a little back to back testing, comparing 175/70 13s to 185/60 13s on 5.5" rims. Two of us autocrossed two cars and swapped back and forth. The other driver won the national championship in the same class that year, (and won again just a week ago!) and I was 5th, so the driving should have been decent! Same model tire, same prep, both tire pressures were fiddled with until they were optimum, and no matter what, the smaller tires were faster. Significantly and consistantly. For both drivers.

We were a little puzzled, and surprised by the .5 second difference, and could only surmise that, at a section of 60, the tire was very sensitive to rim width, and the 185s wound up too round, or bowed at the contact patch as the rims were "pinching" them.

Point being that the rim is a very important part of getting the tire to perform optimally.

The only way to know of course, is back to back testing, but that's really hard to do.

Maybe you can team up with a buddy and borrow some rims and do a little mini test?

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Jake Gulick
ITA 57 RX-7
New England Region
[email protected]

[hornerdon]

Jake, interesting test, and the results bear out what I've always believed. Now, bear with me as I try to use layman's terms to describe what is undoubtably a very technical thing -- I'll try to get my meaning across.

The fact that you were testing 185 and 195 x 13 on 5.5" wheels tells me these were not exactly the most powerful cars in the world - certainly not a surplus of power. I believe there is a point of diminishing returns on increased tire size beyond which larger tires can hurt more than they can help. Larger, heavier tires must have much the same effect on performance as a heavier flywheel. Larger contact patches may provide more resistance to slip on cornering, but it seems to me that they are also harder to get moving and keep moving. Then, there is a point in which that contact patch is "good enough" to handle to cornering ability of the car, and any more is at best a waste, and at worst a detriment.

When we were running the Toyota Starlet in ITC, and also autocrossing it, 185/60x13 was about the smallest tire we could get. If we could have found a smaller tire with a decent cross section, such as a 165/60, we would have used it in a heartbeat. The car only had 54 HP stock, and in IT trim weighs only 1670 w/o driver. It just doesn't need any more tire, and more tire just hurts.

[Knestis]

I don't have any empirical data to support it but I agree with Don that it is enTIREly possible to "overtire" a low-HP car.

Kirk

[Bill Miller]

With out a doubt!

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MARRS #25 ITB Rabbit GTI
SCCA 279608

[JohnRW]

About 10 years ago we collected some data at Watkins Glen that showed that 13's were faster than 14's, and a skinnier tire was faster than a fat one on a long, fast "horsepower" track , on horsepower-limited cars (i.e. Golf & Rabbit and Sciroc's). You didn't spend too much time turning there, but you spent a loooong time pushing that tire down straights, so rolling resistance was an issue. Skinnier and shorter was better, if you didn't run out of gears due to diameter.