so, at the DCTC event, I found out that my 225/55ZR16 VictoRacers mounted on WRX split-fives rub on the rear trailing arms. they don't touch just sitting, but damn close (could barely see daylight, but could slide a piece of paper through). but under hard cornering, there was noticable drag, a little smoke, and smell....pulled into the "pits" and the inner sidewalls in the rear were hot to the touch, and the trailing arms were polished. point: how big a wheel spacer should I run. 3mm? 5mm?
I can't answer the spacer question, but this should illustrate how much your tyres can flex under load... [YOUTUBE]<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/v-DMkO3g2SI&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><embed src="http://www.youtube.com/v/v-DMkO3g2SI&hl=en&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" width="425" height="344"></embed></object>[/YOUTUBE] Stuart.
My V710s were within a hair of the strut perch, could fit like a thin piece of cardboard through and I had very minimal rubbing. I think 3mm would do the trick, but then some tires may flex more than others.
Here is an example of my car, but I've seen the sidewall flex a bit more than this. These are Dunlop Direzza Z1s on 17x8 wheels. Different (ie. less aggressive) tires will flex more.
Instead of spacer try some toe-out in the rear 1/8th should be not too drastic, and roughly the same as 3mm spacer.
All Tires flex, the lower the profile the stiffer the sidewall. This is on a comparable tire. Also looking at different tire manufacturers can change sidewall flex, generally the higher the Tire rating X, W, ZR should all be pretty stiff. The other choice is to run narrower tires to stretch the sidewall out, this will really change handling and will also give you more clearance. The performance you get from decreased sidewall flex should make up for the loss in surface area. Getting your car to rotate and maintain momentum in the corners will do more than adding grip for most lower power cars. The other added benefit to lower profile tires and narrower width is that you will greatly decrease rotational mass. For instance if you use Azenis 615 225-45 17 and compare it to a 215-40 17 you will save almost 5 lbs per tire. Imagine what you would spend to drop 5 lbs per wheel. You will also get a gear ratio change that will allow you to get into 2nd gear sooner. Best r, Mike
Thanks. I really don't want to get new tires. I don't AutoX nearly enough to justify it......in fact, I probably won't get out again until next year. these are extremely stiff tires, being VictoRacer V700s. the guy who mounted them said they were an enormous PITA I do need to adjust the rear alignment....but unfortunately it's not as easy as the EJ cars......in fact, it's quite difficult.
I wish I had known this a while ago. the 225/45/17 on P7s are HEAVY! like 45+lbs per corner heavy. Next time I am going for the 215/40/17s. Also thanks for all the great information in this thread. Very good stuff to know.
wonder how safe it would be to run a thin-ish washer, x5 per wheel in the rear? (kind of to simulate a spacer, but cheaper)
Probably a bad idea. Friction between the wheel and the hub would be limited to area under washer, which is really small area so to hold the wheel just as good as spacer you'd need crazy torque, so I guess studs would break pretty soon if undertorqued, and also pretty soon if you try to torque them enough to compensate for small contact area.
could work. but, I don't think it would be quite enough, and, as mentioned, probably not an excellent idea. and, considering the rarity of XT6 rear hubs (although not likely the first thing to fail.....), I don't want to risk it. also, I probably won't need them until next summer. so I think I can scare up enough for a pair of spacers in 8 months :biggrin:
^ otherwise find a friend at a machine shop and have them drill 5 holes in a round piece of metal. Spacers are kind of expensive IIRC.
