Tire question

[VA 330Ci]

I wasnt sure where to post this, but her goes the question. I currently run my factory 18" wheels with the factory installed Bridgestone potenza tires (255/35/18 in the rear) for track use. Car is a 2004 330Ci. The tires are more or less worn out. I want to replace with something a little more agreesive for the track. I was looking at the Falken Azenis RT-615 (not sure if I should jump all the way to RA1's), but the closest size to factory in these tires is a 245/40/18 (same goes for the RA1's). The question is, can I run a 245/40 in the rear on factory wheels without rubbing? The car is lowered on a coilover suspension.

Also, any input on using the RT-615 on the track? I have a completely different set of wheels and tires for daily use, so these are more or less dedicated to track use.

Any help would be greatly appreciated!!!

[lax01]

First off, if 255/35/18 don't rub, neither will 245/40/18 as the "40" is not an actual measurement but more of an aspect.

Second, you mentioned two very different tires. While the RT-615s are dubbed as a "motorsport tire" they are still made of street tire compound and not are a true R-compound (as far as I know). RA1s are true R-compounds and may not be allowed in some novice HPDEs.

I suggest you do a little bit more research around the web.

[VA 330Ci]

First off, if 255/35/18 don't rub, neither will 245/40/18 as the "40" is not an actual measurement but more of an aspect.

Second, you mentioned two very different tires. While the RT-615s are dubbed as a "motorsport tire" they are still made of street tire compound and not are a true R-compound (as far as I know). RA1s are true R-compounds and may not be allowed in some novice HPDEs.

I suggest you do a little bit more research around the web.

Not sure I understand your coment with regard to "aspect". theoretically a tire with 40 aspect ratio has a larger overall diameter than the same size tire with a 35 aspect ratio, right?????

Also, yes i know that these two tires are completely different compounds. I am wrestling with the idea of going to a true track only tire versus a tire that I could still potentially drive to and from the track on (plus the RT-615 are a ton cheaper). But, both are much more agressive than the tires I use now. And, most clubs allow R compounds for HPDE's (even though most discourage it because of the learning factor).

[AG]

Someone correct me if I'm wrong, but the two way's you can get rubbing is if the section width or the diameter becomes too large. Going from a 255 to a 245 gives you a smaller width. With the ratios you specified, an online tire calculator show the diameter of the tire increasing by ~.7 inches. This translates to a ~2.7% difference in speedometer readings. There's a certain max percentage difference recommended when changing ratios.

Anyway, I doubt .35" difference in radius will make a difference unless the car is slammed. If you're running these on the street, I think you also need to watch out for front to rear differences. I believe too much variation will cause excessive DSC intervention.

[jhm5]

I think you want to stick closer to factory diameter. Realize increasing the tire diameter effectively changes your rear gear ratio... the wrong way for acceleration.
I think the best setup for this car (unless you have outrageious non-stock power) is with 17 inch wheels -- 235/40 tires front and rear.
It's more balanced. It's a slightly smaller diameter than stock, slightly better rear ratio equivalent.
Of course I haven't tried that. I use 225/45/17s on my 330Ci, which i rarely use on the track. But I like my concept.
If you want to use the 18s... I would suggest finding the best performance tire you can in the factory size. And consider that the stock staggered setup favors understeer which many of us find annoying on the track.

[VA 330Ci]

I think you want to stick closer to factory diameter. Realize increasing the tire diameter effectively changes your rear gear ratio... the wrong way for acceleration.
I think the best setup for this car (unless you have outrageious non-stock power) is with 17 inch wheels -- 235/40 tires front and rear.
It's more balanced. It's a slightly smaller diameter than stock, slightly better rear ratio equivalent.
Of course I haven't tried that. I use 225/45/17s on my 330Ci, which i rarely use on the track. But I like my concept.
If you want to use the 18s... I would suggest finding the best performance tire you can in the factory size. And consider that the stock staggered setup favors understeer which many of us find annoying on the track.

I would like to stick with the 18's since I really didnt want the added expense of having to buy new wheels as well. Good point about the acceleration...I didnt think of that. A stagered set-up is ok with me right now. I am taking care of the push with some adjustable sway bars (plus I adjust my tire pressures accordingly to reduce the understeer as well). I guess I will have spend some extra cash to get the factory size.

...Unless anyone has experience running the 245/40/18's in the rears?????

[profbooty]

I've run 615's on the track for 4 events/ 8 track days, they aren't greasy like the older 215's and grip quite well. For a street tire they have excellent grip, give good feedback (feel/audible). They may get quite hard though if you heat cycle them a lot, so be sure to warm them up gently with a few laps before driving them hard if you have taken them on track before.

They are lousy when the temps fall below 50 degrees and in the wet (had a whole weekend on them at shenandoah last march like that).


For the price they are an outstanding value for your dollar. You can pick them up at vulcantire.com pretty cheap and they ship out of PA. They are a good bet to run on for a while until you feel you "need" r-comps.

[FT]

I've run 215s and 615s in the past; they loose about 50-60% of their grip on the track after about 20 mins. So, the last few laps, are your cool down laps and frankly, I don't use them anymore.

If you are going to stick with street tires, I'd highly recommend Potenza 050A Pole Positions, nearly the same grip as 615s but they last over 30 mins at the track. Or, if you can find sizes, RE01s. Otherwise, Nitto 01s or R888s are the way to go IMHO.

[Nick325xiT 5spd]

I've got a set of ugly ass 17" borbets that you can have for the cost of however much gas you burn on the way to my parents' garage.