sjfehr

What's the best size 17" street tires for autocross for an 04 Boxster S? I've heard several people recommend 245s all around, but always when talking about R-comps. I can get 225 up front and 255 in the back while staying within manufacturer recommended wheel sizes, but haven't seen any 245s that are specced to fit on 7" rims, at least not of this year's hot tires. Is it worth stretching 245s up front? Would 245/45-17s rub?

I guess what I'm really asking is what's been sorted out for this car?

Thanks!

KenJ

If you're planning on competing in a stock class, the 225/255 combo can work. It's not bad. Get as much camber as you can in front... ~-1 degrees? 245s up front might seem a little squishy with a typical softer street tire sidewall on 7" rims... it's doable, but you may not like the 'feel'. It can also rub on the inside well at full steering lock (a 1/4" spacer may minimize and still be stock legal?) - I used to run 8x17 Fikse fronts with 245s and that's what happened (with stock offsets).

Sorted (for me) street tires: 8x17 fronts with 245s (38-40 lbs), 8.5x17 rears w/255s (37-39 lbs) on Neovas. Sticky tires:8x18 w/245, 9.5x18 w/245 Hoosiers all around (or) 245/285 V710s on same rims.... but, my suspension is very adjustable.

Good luck,

kj

racer

245s on a 7 look pretty silly imho. The sidewall is too ballooned to offer its true benefit of being stiff. If you aren't running Rs then you've already come with a compromised set up (depending upon class rules).

sjfehr

Thanks, guys I was planning on 225 up front and 255 in the rear, but 245 kept popping up and I wanted a reality check.

MechanicalEng

I have seen 986s with 245's on all 4 corners. It seems to work great, no more understeer..

KenJ

The Spec Boxster guys (track) are lobbying the rules committee for 255s all around on 8.5 rims.... they really like it.

kj

sjfehr

So long as I'm in SCCA AS, I'm stuck with stock wheels. Which is rather moot, as I'm too poor to afford new wheels anyhow, lol...

KenJ

Oh... SCCA. Then you can use R compounds, right? Used Porsche wheels can be had for ~$400... 7&8.5x17s. And, you've got the stock struts - unfortunately, when I tried the Kumho 245s up front with a stock set-up, I rubbed the underside of the spring perch on the left side.... other guys didn't.

Seems a shame you'll probably be the only one competing on street rubber.


kj

sjfehr

My club has a street tire class, where I'm still subject to AS PAX and won't be getting FTD on street rubber, but there's a good 20 people racing street tire class, so it's still competitive. Meanwhile, there are only 2 people actually in AS. I'm bone stock with 0 points and could go r-comps for NASAcross without bumping into the next class, as well. Shoot, NASA might even let me take out the Bose subwoofer that SCCA makes me leave in!

Believe me, I'm very tempted to move on up to r-comps, but this is only my second season so I'm still a bit reluctant to drop a grand for 18" rims (want to get the nice wide ones for racing!) and $1000/year in tires, knowing full well I still won't be competitive for the club title this year. Not to mention, my wife co-drives with me, which doubles tire wear. And now we have to tote extra tires to the track, too. I really love autocross as a "race your DD" kinda sport Maybe if I do really good this year, I'll treat myself next year!

Grantsfo

I ran my first AX in my Boxster this past weekend with 225/45/17 and 255/40/17's. My car has plenty of negative camber and I did find some push but it wasnt terrible. You could go with a 235/40/17 in front dependending on tires you are thinking about. One thing I will say is that with this setup you know when you have blown a turn by early apexing a turn as you will be rewarded with a front end that slides slowly into the cones on exit. My front end caugt its share of cones my first couple times out.

I'm making a change because I have to chase fast guys like Ken. I have ordered spacers and nice long BBS wheel studs and I'm planning to go 255 on all 4 corners with 17x8.5" wheels. Problem is that Hoosier doesnt make the proper size in A6 to do that so I may go with 245 for AX tires.

cretinx

I have gone as big as 245/45/17 front 285/40/17 rear with D.O.T. Rs on 17x7/17x9 - no issues.

DOUGLAP1

I faced the same dilemma as the OP, and decided to move to 18" wheels on my 986S, as there seemed to be better tire selection, and you can keep the OD about the same with 35 series aspect ratio tires.

I went with OZ Racing wheels with 18 x 8.5" front 18 x 9" rear and 255 front / 265 rear tires. OZ offests are perfect with no spacers needed. Still sorting suspension to make the most use of this tire, but it looks like a good combo so far.

sjfehr

This thread's rather old and OBE for me (I was the OP), but certainly still relevant for others on Rennlist. As an update, I ran 3 autocross seasons with 225/45ZR17 Star Specs up front (20mm wider than OEM) and 255/40ZR17 (OEM) in the rear. That, plus increasing front pressure to 1psi more than rear (37/36) really dialed out a lot of the chronic understeer I had with stock tire/wheel combos. I never ran wider tires on these rims because I didn't want to cantilever the rubber that badly for fear it would actually decrease performance. This tire combo served me very well; I was street tire champion every year in my local region.

I bought 18" track wheels two months ago (OZ Alleggerita HLT) and am running 245/35R18 front and 285/30R18 rear Kumho V710s. I'm still bone stock except for the wheels/tires and a GT3 front swaybar.

robthenailer

We put 225/50/17 tires on the front on stock 17" Boxster S wheels. Wheels are rubbing the bottom of the spring guard/spring even when just sitting still in the driveway.

Do I need spacers or is there some other simpler fix or ...?

Advice please?

sjfehr

50 is too tall, you need to go lower aspect than with 205; 225/45-17 fit on 17" Boxster S wheels without issue. 225/45-17 is within 1mm of 205/50-17.