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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
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
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
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.Quote:
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
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 http://Forums.ImprovedTouring.com/it/biggrin.gif eventhough I beat you in the race http://Forums.ImprovedTouring.com/it/tongue.gif you still had a faster lap time I think?? http://Forums.ImprovedTouring.com/it/frown.gifQuote:
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???)
Stephen
[This message has been edited by RSTPerformance (edited August 21, 2001).]
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
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.
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 http://Forums.ImprovedTouring.com/it/smile.gif
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
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
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 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!! http://Forums.ImprovedTouring.com/it/biggrin.gif
See you at NHIS
Stephen
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
I just bought a set of those Momos... Ugly wheels but nice a light and fit the VW perfectly.Quote:
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
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!)
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]
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.
I don't have any empirical data to support it but I agree with Don that it is enTIREly http://Forums.ImprovedTouring.com/it/smile.gif possible to "overtire" a low-HP car.
Kirk
With out a doubt!
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MARRS #25 ITB Rabbit GTI
SCCA 279608
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.
Don, good observation...the cars were early eighties RX-7 GSLs , the drivers were Paul Kozlak (sp?) and myself, and the tire was the legend in it's own time Yokohama A001R.Quote:
Originally posted by hornerdon:
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.
OK, so lets recap....
If your rules limit your rim width, you must find and use a tire that is the proper section width for that rim.
Between two tires, the one with the smaller outside diameter will always accelaerate faster, as it's another way of changing the final drive ratio.
On tracks with long straights, the narrower tire with less aero and rolling resistance will be superior if the car is horsepower challenged.
And finally, the issue of "traction" or "stiction" .....If the car is light, going to a 30% larger contact patch will lessen the load the tire sees, (in pounds per square inch), and a subtle effect can occur. Much like a narrower tire gets through the snow better, and a wide flat tire is more likely to hydroplane (on the same vehicle), a lightly loaded tire may not actually have enough load to generate it's maximum cornering grip. keep in mind that a switch to a softer compound should be able to overcome that, but, if such a choice isn't available, perversely, a switch to a smaller tire may make the car faster!
And the point of the tire being a rotating mass is well taken, but if the outside diameter is the same, often the larger rim diameter combination will have superior acceleration deltas, due to it's lighter weight. (Generally, an inch (in dia.) of aluminum wheel is lighter than the same inch of a rubber tire.
In the end, there are so many variables, often conflicting, that actual testing is the way to go. Which brings to the original question....sorry Alan, I've got no first hand Golf wheel choice definative answers!
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Jake Gulick
ITA 57 RX-7
New England Region
[email protected]
Jake, nice summary. That's the kind of stuff that makes racing so interesting for me (I should repeat for those who don't know it, I have zero driving talent and no eye-hand coordination, so my son does the driving - building the car and thinking about details like this is my race).
This sort of thing is most often the difference between winning and losing, and is what makes a car "fully developed" without spending a lot of money. Testing, which involves buying all the different sizes and paying for the track rental, is one way to confirm it, but a cheaper way is to think it through, ignore conventional wisdom, examine the logic of threads like this one, and apply your best thinking - if the car wins, or if it exceeds all expectations (a Trabant is not supposed to be that fast!), you can be satisfied.
Yes, there are more 13 inch tires than 14s, but the stickiest 13 seems to be the Hoosier, and the size is either too wide or too narrow for the 13x6" rims on an ITB car. The C cars can get away with the 185s, but B cars cook them. The 225s seem to be faster in many cases, but they sure don't look right on a 6" rim. Some ITA cars make them work very well, but they're using 7" wide rims! So, until someone offers a sticky 205/55-13, I don't think any 13" solution is optimal for a B car.
There's a much better SIZE selection offered for sticky 14s. Note that I'm disregarding many perfectly good race tires (Kumhos, Toyos, etc.) b/c they're just not fastest, even if they are better bargains for longevity. I sure miss the old bias-ply Hoosiers (where 225/45-D13 actually worked on a 6" rim)!
Joe--Regarding those MOMO wheels, I think that I would be real careful using them. I mounted a new set of tires on a set of them this week,and checked them real carefully for cracks. I mounted them myself so there was no machine damage and I have had these wheels for a long time so I know that they hadn't been beaten up. Starting into the esses today at lime rock, the center came right apart from the outside of the rim..luckily it happened in one of the best places to run off with no control---there's a lot of other places at LRP where it probably would have been below average.. Anyway please really think over use of these as most are at least 15 years old(mine are stamped 84) and they had no visible cracks. There is a picture I took tonite at www.msnusers.com/hoosers
jerry monaghan
itb99
Eric,
I've seen some ITC guys at Summit Point run the 225/50/13 Hoosiers on 13x6 rims. I've also seen them run the 225's up front and the 185/60's in the back. Supposedly it helps the car rotate better, and especially w/ cars like Rabbits/Sciroccos/Golfs, the inside wheel is off the ground in a corner anyway.
For an ITB car, I think the 14" wheels are the way to go. There's still a decent supply of wheels out there that can be had for $75 - $100 / each.
The Hoosier specs confuse me though. Going from a 195/55/14 to a 205/55/14 goes from a 6.8" tread width to an 8.0" tread width (on a 6" vs. a 6.5" rim). Yet a 205/60/14 has a tread width of 7.3" on a 6" rim. What's even stranger is that they list a rim width of 7" - 8" for both of the 205/xx/14 tires, but the 205/60/14 is ~3/4" taller that the other two (which are essentially the same diameter). What's also interesting is that the 195/55's are $18/tire cheaper than the 205/55's, which are only $1/tire cheaper than the 205/60's.
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MARRS #25 ITB Rabbit GTI
SCCA 279608
Jerry, thanks for the warning. I spoke to my friend who I bought the MOMOs from and he tells me that he used them a lot on his Honda with Toyo RA1 tires. I noticed that you had Hoosiers mounted on yours which are stickier and would put a higher load on the wheels. Tire technology continues to improve and perhaps these wheels weren't designed for the potential side loads that tires like Hoosiers can generate. Of course, they are old and aluminum continues to weaken with each stress cycle. There can be quite a few stress cycles in 15 years.
Perhaps I'll just use them for rains with full treads. Are you interested in selling 1 or 2 of yours?
Joe