2k7AlloyGT

Alright, so the Mustang is 1-2wks out from coming in and I'm trying to decide on which size tires to go with.

OEM is 235/55-17 Pirelli PZero Nero M+S, which I had on my WRX when I 1st got it and those tires suck for autocross/lapping days. Plus that's so much sidewall to flex and again the Pirelli's have weak sidewalls.

So to solve this I'm going to a tire that I know and trust, Falken Azenis RT615. I've been running the Azenis now for about 5yrs now w/out fail.

So here's the the dilema, 235/40-17 or 245/45-17.

Stock final drive is 3.55, and from what I've been reading on the Stang forums that the Ford Racing Perf. Parts FD gear sets come in 3.73, 3.90, and 4.10 and that any of them is a good improvement over stock. Granted the higher the FD the lower the top speed, but who sees 150+ top speed @ an autocross?

The Pirelli's in 235/55 are ~28lbs and overall diameter is 27.1"
The Falken's in 245/45 are ~28lbs and overall diameter is 25.6"
The Falken's in 235/40 are ~24lbs and overall diameter is 24.4"

So anyways, going from a 235/55 to a 245/45 is equal to changing from a 3.55 to a 3.75 final drive. And should drop the car about ~1.5"
And going from a 235/55 to a 235/40 is equal to changing from a 3.55 to a 3.96 final drive. And should drop the car about ~2.7", plus it would drop ~4lbs per corner (16lbs total).

So the 245/45 are wider and cheaper. And the 235/40 are same width, is $10 more than the 245/45, and lighter.

So do I go with a wider, cheaper tire, lowers the car some, and equals to a higher final drive. Or with something that's the same width, but is a little more expensive, is lighter in weight, lowers the car more and equals to a even higher final drive.

Well now that I lay it all out there, it's pretty easy to see what I think I'm going with. But I would still like others input.

Thanks,

Jay

PS- Don't worry about how these tires will affect the cars speedo, etc, I have a SCT tuner to reset it to whatever tire I decide to go with.

callahan

255/50/17 is the widest you can safely go on the stock wheel and keep the same rolling diameter.

howarmat

You can fit wider on the 17s. 275 I think has been run before. It might not be the best But I am sure you can get 265 on there.

I would go with 40 series in 255 or 265 unless you dont want wider. I couldnt stand the look of 235s just to skinny for me.

2k7AlloyGT

Having the stock rolling diameter doesn't matter to me, I know how to do tire math and figure out what I'd need to keep the same diameter as stock.

That's not what I'm looking for, that's alot of sidewall, I don't want that. Ford did that for comfort, I want performance. Plus if you didn't read I can reset the tire size for the speedo via my SCT tuner. I'm looking to eliminate the excess weak Pirelli sidewall, get a stickier tire and at the same time basically change out the final drive by changing tire sizes.

Also, to me 255, 265, or 275width on a 8" rim doesn't look good, 245 is the widest I would do on a 8" rim.

Later,

Jay

2k7AlloyGT

Almost 50 views and only 2 posts and 1 vote? C'mon now, you guys can do better than that.

howarmat

Honestly you are asking a question that is opposite of most poeples desires. Most want wider setups and lower profile on bigger rims too. Not many are looking to increase that small amount with that lower profile on the stock 17s....

2k7AlloyGT

I guess so, I'm looking at it from a racing point of view. Based on my classing, I can't do anything but a stock sized rim, thus sticking w/ a 17x8. Anything over 245 width on a 8" rim is just not going to have the sidewall support that only an 8" wide rim can give. I'm looking to kill to birds with one stone here, better/stickier tire + the equalivalent to doing higher final drives by doing lower profile sidewalls.

Most people seem more interested in a wider tire for more contact patch for straightline performance. Considering this car won't be pushing much over an extra 10-20whp over stock, I don't need monster meats and bigger rims just add weight. Again, also going back to limitations of stock sized rims.

Thanks for the help anyways.

Later,

Jay

northy_polk

did you ever hit the track with your azenis and new mustang? what did you think? i think the feedback you're seeking is rarely if ever found on this forum. not many autocrossers or high speed driving event enthusiasts, mostly drag racers and street racers I guess. i'm just getting into autox/hpde, so i'm very interested in what you're setup is and the success you're having. i'm trying to figure out what i want for next year wheel/tire wise. keep the fanblades and just get oem sized sticky tires? something lighter? something 17"? wider? endless permutations it seems.. . and FUN!!!

StantheMan

If you go to 35's, it would also change your gear ratios. Also if your looking at racing then wouldn't you want something wider so you can hook up on the line?

RodeoFlyer

Nobody f'n reads!!!!!

He has to stick to a stock wheel width for his class. He is asking about 2 SPECIFIC sizes of a SPECIFIC tire because of this.

Jay - The 245/45 Falken RT-615 works great - I have those exact tireson my street wheels right now. Your math is off however - they lower the car 3/4 of an inch. They lower the car HALF the diameter difference. Try 36f/34r for pressures. The 235/40 will look absolutely ridiculous. Without lowering the 245/45's look ooooookay, but not great. You will have quite a bit of wheelwell showing.