Hard core physics

[autxr]

OK, we all know that in general, a lighter wheel is better...

But, it could be that a 15 pound wheel with 90% of the mass near the hub will have a much lower moment of inertia than a 15 pound wheel with 90% of the mass concentrated near the outer edge.

So, you suppose discount tire will be able to give me the relevant force numbers...

That being said, I'm still struggling with the 7 vs 7.5 inch wide wheels. I prefer 7.5 inch, but the options tend to be heavy... Also, you KNOW that the 7.5 inch will have a higher moment of inertia, it has to, the extra weight is basically all going to be at the outside of the wheel vs a 7 inch.

The 7.5 will allow better use of a 225 series tire, the 7 inch will favor the 215 width...


Hmmm, the whole STS thing is looking to be a pain in the ass.

I need to start saving for a set of SSR Competitions in 16x7 with 215/45-16 Falkens... Of course the Kosei's are a much better value.

Oh well, the first order of business is to give Uncle Sam all of my wheel money, so it doesn't matter.

Scott

[brothermaynard]

It is hard to find competition rubber in our diameter. If you go with the 7.5 width perhaps you can go with 235's. Your physics look good but sometimes when you add in one place you lose in another. I personally went with 17x7.5 SSR competitions for a compromise of speed and vanity. Next upgrade will probably be 235 AO32r's. We will see though the 215's aren't done yet.

[Unity112]

Yes Scott you will encounter more rotational inertia with a wider wheel, as well as experience more drag at higher speeds. And weighing out this vs. power available and traction is a tough ass decision. If you are going to time trial this car and participate in some events on road courses however, I think the 7.5's will benefit quite a bit more.

Right now I'm having the same problem choosing between 7 and 7.5. I'll be getting the falkens in 215's so 7's will be good but so will the 7.5's which will allow me to fit 225's better down the line.

[afghan]

Scott, if I could compete with 17x7.5s which were 22 plus lbs (43lbs) per wheel sporting so so 215 rubber in a pretty stock GT.....

I would just say; "Drive the freakin car!!!!"

PS Send some warm air up here!

[scapamouche]

Don't forget, DDT doesn't carry Kosei, and I'm not sure they carry SSRs. Oh, and Tire rack doesn't carry Falken. Ain't it great?

[GTS LAID]

your physics looks good... just dont count on your topspeed going up.. but thats something that i dont think you're worrying about. since inertia is I/mr^2 and you'd have to integrate over the whole diameter of the tire then sticking to the center will give you a MUCH lower inertia... actually i've never thought about this.. but instead of looking into reducing the mass.. people should think about reducing the effective radius instead. But then again when you reduce the effective radius of the tire (ie concentrate the mass inside the wheel) you'd probably run into stability issues. I hate give and take situations...

[ishido]

awesome, I just decided on getting the SSR competitions. If any of you have pics I'd love to see 'em. I was looking at RH CP035s and somehow overlooked the competitions which are just as light. Is there a much better selections of 225 tires vs. 205-215? I think in either case having a lot less weight will still offer a solid improvement even if you did go 7.5