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So I'm thinking of getting 18 inch wheels with falkon 225/40.. I know these would be good for autocrossing but what about drag racing? any suggestions on this would be helpfull..

 

Well, I'm sorry to tell you this but they own't really be good for anything other than looks. Having a very small sidewall height actually takes away from the contact patch. I'm really no good at explaining this in words, but basically the tire can't squat down and spread out agains the road. You would actually be better staying with a 16" wheel on the WRX for the best traction. This goes for both auto-x and drag. You may want to check out the motorsports forum over at http://www.nasioc.com There is far more collective experience in that realm with that car over there.

 

Keith

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sad.. ok.. I was told different info... but thanks. I will definately check out that website..
If a top-fueler gets to 100mph in .9 sec using big ol' squishy sidewall slicks ...well right there, that's gotta tell you just a little something about the requirements for an optimal acceleration tire. :grin:
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If a top-fueler gets to 100mph in .9 sec using big ol' squishy sidewall slicks ...well right there, that's gotta tell you just a little something about the requirements for an optimal acceleration tire. :grin:

 

yeah.. you got a point there...

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Another thing to think about is what is called unsprung weight. Any additional weight added to the wheels and tires has a greater effect on power than the same weight added to the car elsewhere. Typically an 18" wheel will weight more than a 16" wheel. Also, the 18" tire will have a very small side wall and they have to add material to help stiffen it or else you would bend the rims every time you hit a bump. So basically the big 18" will make your car accelerate slower than the stock tire. This was very evident when I put 17" wheels on a honda that normally wore 14" wheels.

 

Keith

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Another thing to think about is what is called unsprung weight. Any additional weight added to the wheels and tires has a greater effect on power than the same weight added to the car elsewhere...

Ummm... nit pick coming:

First, RallyKeith is basically right. Added tire/rim mass, especially further out from the center of rotation, has a much greater effect on a vehicle's ability to accelerate than if the weight was merely sitting in the vehicle. An old bicycle saying is, "an once on the wheel is worth a pound on the bike".

 

The nit is this is not "unsprung weight" per se, but a problem with rotating mass and its Polar Moment of Inertia (PMI). Unsprung weight more properly applies to that mass which must be moved up and down each time a tire moves vertically. A car with chassis bolted directly to the wheel's axles (no springs) has the entire car's weight (mass, really) as unsprung weight (mass). Sprung solid axles have less unsprung weight, and independent suspension (usually) has even less.

 

Sorry for the nit picking.

 

But the inceased PMI is significant. You should also consider whether the increased height (if any) and the increased peripheral mass will be too much for your suspension to handle.

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