Safe Autocross rim and tire package?

[Suba_Roo]

I'm trying to get some passable AutoX rubber on the car... as cheap as possible.

I'm considering the Federal 595RS-RR 235/40/17. I'm looking to put them on some SSR type C 17 x 7.5" rims I have.

Federal says their approved rim width is 8 to 9.5.

Two questions. 1) Am I still in the safe amount of grey area to Autocross this tire on this rim and occasional street use? 2) Is a normal tire guy going to balk at mounting this tire on this rim? How much beer do I need to bring my tire guy when I pick up the mounted rims?

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[speedyHAM]

1. you are safely in the grey area with only being 0.5" out on a 40 series sidewall. 2. No tire guy is going to balk at that combo.

Running an '01 RS on 235's might be a tight fit though depending on your alignment and fender situation.

[Suba_Roo]

Hey SpeedyHAM,

Thanks for the quick reply. I thought it ought to work, but I needed a Suby enabler to confirm.

I'm already on rolled fenders, camber plates/crash bolts (doing the in/out thing) so it shouldn't rub too much.....

[littledrummerboy]

OP, on 7.5" wide wheels you should be generally looking at a 215 or at most 225 width tire. If you look at the manufacturer's site for the tire you're looking at you should see the "rim width range" and you generally want to fall within it, not out of it.

There is also the "rim width" or "stardard rim width" or "measuring rim width" -- this is the sweet spot for a certain size and for 215 or 225 that's where you'll get the most out of the tire.

With 235 on a 7.5" wide wheel you'll get a lot of sidewall bulge and flex. You can run it, but you'll have steering response delay and more bounce than you should, and it will cancel out any additional grip you could get on a wider tire, imo. Not exactly the best for autocross. Going down to 215/45/17 or 225/45/17 will save you some money too.

[Suba_Roo]

That's a good perspective on the narrower might be faster.

I'm in a weird situation, my class will allow a wider rim, but budgets dictate I cant change rims this season.

I've always been under the impression that for AutoX wider rubber is always better. I'm running 225s right now (RS3 and Z214).

I'll definitely consider sticking with the narrower rubber, saving a few $ and running a more optimized tire and tim package

[littledrummerboy]

Wider rubber is beneficial only within the design specs of the tire and what size wheel it's meant to be on.

On the min and max of the tire's wheel width range and beyond them, you'll experience more negatives than positives. If the wheel width is at the tire's max wheel width or more, expect tire stretch, and rim curbing to be more likely. If the wheel width is at the tire's min wheel width and smaller expect sidewall bulge/flex, and reduced steering response.

Good luck in your hunt.

Edit: I've ran a few sizes of tires and have felt those effects back in my old 06 wrx, and on my current sti in autox. Right now I've gone from 265 to 275 on a 9.5" wide wheel both spec'd for 9.5 and the 275 does have more a soft, less dart-like? feeling than 265... not sure if I'm liking it yet. My brother had a similar experience too in his mustang (yes he autox's that lol). He down sized the tire width so his wheel width is at the sweet spot.

[WhiteZombie]

Get 225's and send it. Tire will feel less floppy/slow to respond to input/numb and require a little less pressure to maintain a good contact patch.

Max out your camber as much as tolerable on the street. Mine is set at -2ish front, -1ish rear.

You'll learn more on narrow, slightly less grippy tires that give a lot better feedback. They'll be lighter, and probably put end up putting the exact same amount of rubber on the ground.

Save your money and spend it on seat time. Driver mod = best mod.

[speedyHAM]

The difference between 225's and 235's will be nothing. 235's will have slightly more contact patch(grip), 225's will respond slightly faster in turns. If you are able to differentiate between the two in an autox- go to nationals, win, and enjoy.

[littledrummerboy]

^ No difference, but you just pointed out the difference lol.

That 7.5" wide wheel is out of the spec range for that 235 federal tire. Why would anyone pay more money to run a tire that's out of the spec range that the manufacturer says it should run on, especially in a drving extreme scenario like auto-x? Those "nothing" differences will be pronounced the further out of spec range you go.

Edit: OP, stay 225 or the right aspect ratio 215 for a 7.5" wide wheel. Be in spec of the tire you're running -- you'll learn faster, be faster, actually equip your car with what its supposed to be riding on, and save a little more cash to enter into more auto-x's... or to put towards 8.5" wide wheels for 235s or even 245s.

[WhiteZombie]

Originally Posted by littledrummerboy

^ No difference, but you just pointed out the difference lol.

I'm thinking what they meant was that there would be no discernible difference in overall speed or time between them, just feel and feedback differences. So yeah, still 'some' difference, but probably none where it matters - the run time

[littledrummerboy]

Originally Posted by WhiteZombie

I'm thinking what they meant was that there would be no discernible difference in overall speed or time between them, just feel and feedback differences. So yeah, still 'some' difference, but probably none where it matters - the run time

Yeah, i understand what was meant by that, but feel/feedback does a lot to time too, so I do think it matters especially when its getting out of wheel width range.

But yes, people can run what they want to try out

[speedyHAM]

Originally Posted by littledrummerboy

Yeah, i understand what was meant by that, but feel/feedback does a lot to time too, so I do think it matters especially when its getting out of wheel width range.

But yes, people can run what they want to try out

What I meant was that for the time difference on course there will be pretty much no difference for 99.999% of drivers. Neal Tovsen could tell me which was better- along with Jeff Cashmore, Annie Gill, Sam Strano, Billy Banks, and a bunch of other drivers who are better than we are.

[Suba_Roo]

So... I pulled the trigger on the 225s. I know that those will fit without rubbing and it sounds like the consensus is that the extra 10mm of tread width will be lost in the noise of stuffing a wider tire on a rim that's really too narrow.

[WhiteZombie]

Originally Posted by Suba_Roo

So... I pulled the trigger on the 225s. I know that those will fit without rubbing and it sounds like the consensus is that the extra 10mm of tread width will be lost in the noise of stuffing a wider tire on a rim that's really too narrow.

The Federal tires you were looking at?

[Suba_Roo]

Yep Federal 595RS-RR. Cheapest fastish tire I could find

[WhiteZombie]

Originally Posted by Suba_Roo

Yep Federal 595RS-RR. Cheapest fastish tire I could find

Nice! Let me know how you like them. Attending any events soon?

[nemos_black_wrx]

what year impreza and is it a rs or is it turbo, and what class will you be running in. if stock under 13.4 wheels of the solo hand book. you can only go down or up a inch . so if 16 stocks you can only use a 15, stock 16, or a 17. and have to run the same width as what comes on the car.

[Suba_Roo]

nemos_black_wrx - thanks, I have an 01 RS. I run in SM because I have an STI steering rack and rear lateral links with heim joints. Like I said, I could run a much wider rim, but cash flows mean, I need to stick with the rims I have (17x7.5 SSR type C)

WhiteZombie - I'm instructing at the Fresno SCCA autocross school on the 25th and racing on the 26th. Will report back on how it goes. Might rain, so probably not going to be the best feedback.

On another note, I've been driving on my stock 01 RS rims with some M&S tires. I had been thinking that the M&S tires just sucked, then I discovered a broken rear swaybar endlink. Now I'm second guessing myself that my old Hankook slicks werent truely dead and that my ****ty driving at the last two events was because of no rear swaybar. I had some spare Kartboy endlinks so I just threw those on. Did a quick hoon around and car feels much much better.

[Breezio]

225 is a good size for 7.5" width.
My own experience:
I ran 225/45 RE71's on a 7.5" wheel for a couple years. Switched to 235/45 for most of the season before last. I did this because they would fit, a taller tire would help with my gearing, and they were cheaper (bigger is not always more expensive).
I enjoyed the setup with 235's, I couldn't feel any difference in feedback and feel. I didn't appear to be any faster or slower versus the rest of the people in my region.
Went back to 225's late that season when they wore out and a buddy gave me some 225's with only a few runs on them.
The only difference I noticed was the slight change in speed before hitting rev limit.

[WhiteZombie]

A busted endlink could do that, haha. Plastic stocker?

Jealous you guys get to run year round out there. I miss it. Have fun!

[Suba_Roo]

White zombie
You can see the broken KLC19 whiteline steel endlink in the picture I attached. Second time I've sheared one of those in half

[WhiteZombie]

Originally Posted by Suba_Roo

White zombie
You can see the broken KLC19 whiteline steel endlink in the picture I attached. Second time I've sheared one of those in half

Ahh, for whatever reason the photo isn't showing up for me.

[Suba_Roo]

So an update.

I got the 225 Federal 595RS-RRs. Mounted them on the 17x7.5 SSR type-c.

We autocrossed on Saturday and Sunday in Fresno. Saturday was the Fresno Autocross school and Sunday was our 1st event of the season. The weather was mixed. Sunny and cold on Saturday. It rained Saturday night, was damp on Sunday morning, but we ran Sunday afternoon in the dry. Asphalt surface, relatively low grip.

Girlfriend driving the car in Novice class


I really had no idea where to start on tire pressure. I was racing SM and my girlfriend (her 1st autocross) was racing novice-SM. I expected that tire pressure would build fast with two drivers, but since she was about 4-seconds off my pace, she might not have been getting that much heat in the tires. I started with a much lower pressure than I would normally, hoping that this would help build heat on a 50* day, but we only gained about 2lbs over starting pressure.

Long story long. The Federals suck compared to Hankook slicks (duh). I preferred my Hankook RS-3s, but I think that I just didn't have the tire pressure's right. The Hankooks, both Z214 and RS-3's really loved hot temps. I'm looking forward to trying the 595s in warm temps.

Overall results were good. I won SM (against weak competition) and my girlfriend drove her face off and came in 4th in Novice based on PAX. She now understands why I think PAX sucks.

The competition (notice, covering eyes, because embarrassed about getting smoked by a 20 year old Japanese car.)

[WhiteZombie]

Anybody else having trouble seeing the pics or just me?

[Breezio]

They appear to be links to their googledocs. The links don't work.

BTW, I've been told that if you are trying to warm up tires quicker in autox, run a higher pressure. I believe this is because higher pressure = less traction, more sliding, more heat getting built up.