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Every once in a while the discussion comes up about racing (road or autocross) and rim/tire combos. The 2 sides always seem to be those who stand by the 15" rims and their lightweight/low inertia, and those who stand behind the shorter sidewall tires on larger rims. Both have their advantages and disadvantages, but.... has anyone tried combining the 2 thoughts.
Like using a 195/50/15 tire?
Sure, its 7% too fast, but how long are you on a track for? Not very long considering how many miles you actually rack up driving. So what if a few tick off a little too fast.
If I'm thinking about this right... shorter tires give you shorter gearing... which yields better acceleration. Smaller rims (and typically lighter) give you less inertia which also gives you quicker starts. Add too that, a considerably smaller sidewall over the stock tire, and you add the handling that is afforded by stiffer shorter sidewalls. So the only thing you really can't use is larger brakes (everything has a trade off).
Sounds like a perfect combo right? Is my thinking on the money, and has anyone tried this?

 
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actually your right the smaller diameter wheel in racing will help you accelarate through increaced gearing. So by being 7% too fast means you now accelarate 7%quicker but you lost 7% of your top speed. there is another thread some where here that S2000man01 started that shows my math.(I dont feel like repeating my self and I cant seem to find it) That's one of the reasons that 15" wheels are so popular with the Autocross croud. At least in the STS class.[IMG]i/expressions/face-icon-small-tongue.gif[/IMG]


All that and the Smaller 15's are cheaper both for wheels and tires.

oh ya, the flexing a taller side wall does can be compenstated by either the tire(most Ultra High performance and Compititon tires have a very stiff side wall regardless of the size), Tire pressure(ushually when racing you run much higher pressures then on the street) and by properly settin up your camber for racing.

 
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I think the logic is a smaller, lighter tire/wheel has less rotating mass which enables it to spin up faster then a larger heavier tire/wheel.

 
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one thing i always thought about was, yes it might take less force to rotate something small but you have it rotate it more times... say you have 1" diameter tires, that wouldnt make it better then say 15" diameter tires... i think it involves a whole lot more thought then smaller the better.

 
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True true.. but if you look at it from the other extreme its just as bad also. What I mean is if you take a wheel thats say 10 feet in diameter and weighs 500lbs, well you get the picture..

 
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oh and they make forge lightweight rims right? why dont they make light weight tires? cause tires are heavy too and you know the outside part of the wheel/tire takes more force then the center of the wheel...
there just so many things to take into account...

 
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Yah... Khumo makes lightweight tires... They're called Victoracers I think. And they just came out with a new one. I forget what it's called.

 
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Khumo has 2 sets of Compititon DOT legal tires

The V700 Victoracer and the ECSTA V700
the Victoracer is the older of the two, but from what I hear its still stickyer then the ECSTA.

both can be found at The Tire Rack

of course if you want ultimate traction The Hoosier R3S03 is the only way to go.

Gearing is a big reason behind using a smaller tire.


Taller gear Ratios provide faster top speed but at the cost of slower acceleration. "Taller" gear ratios have a lower gear ratio. Lower gear ratios provide a lower mechanical advantage between the engine and the wheels resulting in less power at the wheels to accelerate the car. The lower gear ratios also act to produce a higher top speed as there is less of a reduction between engine RPM's (Rotations per minute) and the wheels RPM's. Taller gear ratios will result in lower engine RPM's at higher car speeds.

Shorter gear Ratios provide greater acceleration for the car at the cost of slower top speed. "Shorter" gear ratios have a higher gear ratio. Higher gear ratios provide a greater mechanical advantage between the engine and the wheels resulting in more power at the wheels to accelerate the car. The higher gear ratios also result in lower top speed as there is a greater reduction between engine RPM's and the wheels RPM's. Shorter gear ratios will result in greater engine RPM's at lower car speeds.

On long tracks like superspeedways, taller gears are used to create more top speed. On short tracks with tighter turns the race requires a lot of braking and accelerating, top speed is not as important as the cars rarely get the opportunity to reach it. In these situations short gears are used in order to accelerate the car as quickly as possible out of the turns.
taken from here

They are talking about actual transmisino gearing, but your wheels/tires are similar. If you put a smaller then stock Diameter wheel/tire on your car, you end up Shortining your gearing. making you accelarate quicker then the same car would on a larger/stock wheel. But you Now have a lower topspeed then the stock/larger wheeled car would. [IMG]i/expressions/beer_yum.gif[/IMG]

 
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damn, didnt even know they made lightweight tires.. i was half joking too...

 
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I wouldn't really call them light weight tires. But they are 10 Times better then standard street tires.

 
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I read a while back (I think it was Car & Driver)... They tested wheel widths for cornering and they found a big difference betwean 15" wheels and 16" wheels. They also compared 16" wheels to 17" wheels and they said there was a small difference in cornering. The next size up (18") yielded no perceivable difference. I forgot what car this was on, but overall 17" wheels are as big as you should consider IMO. If you're going for all out autocrossing, then I'de get a nice set of light 16" wheels and a tire sidewall that makes the overall diameter of the wheel and tire a bit larger than stock. At least for LX's. My LX has some really nice gearing in 2nd and 3rd, but 4th and 5th are just so weak...

That's why I went with 215/45-17. I think I need even lighter wheels though. I might sell my current wheels (15.5lbs each) and get some of those Velox ones. The five spoke that weigh 12lbs and change. Those are nice. Although my wheels are tough. They survive big hits. They're good for doing a bit of rough driving. Especially if there's something sticking up under the snow and you can't see it. I hit several big ole things like that, not knowing what they were, and my wheels survived. I guess I should keep these wheels for winter and get some winter tires put on them. Anyway, I think they're so tough since they have a pretty big load rating. Forget what it is now, but it surprised me when I first saw it.

 
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depends on what you are racing. if its autocross best is a tire with a low sidewall. if its drag racing, you want a big sidewall which allows for the tires to scrunch on take off (traction). thats why you always see cars w/ big slicks and 13" rims at the track.

 
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<font color=white style="background-color: 3E3E3E;">spin up</font ft>is that like spool up [IMG]i/expressions/laugh2.gif[/IMG]

 
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Lighter tire/wheel combo has less inertia. However, it also depends on how much weight of the tire/wheel combo is farthest from center. Like a very light wheel that has a very heavy tire....*coughs* 17" wheels *cough*

Lightening the tire should theoretically have the greatest effect. However, I do not believe that it is significantly more than the effect of using a lighter wheel. A weight reduction in either is going to help.

Anyhow, I have 15" rotas and am more than pleased with everything except for the looks...The stock tires are on them and I feel like the nascar pit guy that mounts the wheels everytime I take mine off and put them on. They are so light that it literally shocks me everytime. Of course this feeling is relative to the stock steel wheel/tire combo. They are light as a feather though. ~30lbs each per whee/tire.

When ever someone sees my car they say it looks pimp but has small wheels...lol...I don't meet many that are more concerned with performance than looks. I strive for a little extra pep for the daily commute and in pretty much straight lines...I had too many wrecks thinking I was driving an indy car... [IMG]i/expressions/face-icon-small-wink.gif[/IMG]

And hey, I know its just an econo civic but that's what I drive, love, and have to modify.

 
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This is one of the tricks we used on SpoonFedEG's Hatchback last fall to make him the quickest car at his high school

[IMG]i/expressions/demon.gif[/IMG] We took the little 13" steelies and put 195/60-13 Sumitomo's on the front and he turned some 9.7 (1/8th mile) times at the track (Knoxville Dragway). After they had 5-6 thousand road miles, we went to I-40 Dragway in Crossville Tenn late in the season and they wouldn't hook at all. But now we have two 215/50-13 Sumitomo's all ready for springtime [IMG]i/expressions/laugh2.gif[/IMG]

"Short tires, the poor man's Type-R Tranny" lol (if the tires could just improve the spacing between the gears...)