Contradiction
Contradiction Reader
6/6/16 2:51 p.m.

Hi everyone,

I'm getting ready to order tires for my autocross wheels but I'm debating the tire size a bit.

It's an 84 VW Rabbit GTI and I'll be running it in STS.

For sake of brevity take a look at my build thread to give you a better idea of my modifications:

Build Thread

It is slightly lowered (but control arms are still parallel) and I have the following camber specs:

Front: -2 deg. Camber 1/8" toe out Rear: -1.5 Camber 1/8" Toe In.

So I have a set of 15 x 6.5" Jax Light Racing wheels for it and I want to put Dunlop Direzza ZII Star Specs on it.

I bought these wheels off of another MK1 GTI that was used for autocross and they had some old Falken Azenis on them that are toast.

I want to run 205/50/15s but the Azenis bring up a couple of concerns for me.

I'm wondering if there appears to be too much sidewall on these, and if so, would that have contributed to the tire wear on them?

Here's a pic of the old Azenis on the wheel. It looks like Falken may have molded in something similar to a "rim protector" into the middle of the sidewall and that could restrict bulge some?:

And some shots of the rest of the tire:

I realize that camber and other alignment specs could have caused the tire wear on the previous car, but does anyone think the tire wear on these could have been caused by being too wide?

That concerns me most of all because it isn't true edge wear like you'd normally see from negative camber.

Based on what you guys are seeing would 205/50/15s still be a safe bet or should I go down to 195/50/15s? I'd like to do 205s because frankly there are a lot more tire options in that size.

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
6/6/16 2:57 p.m.

Yes I think the amount of squeeze you're running contributed to increased wear in the center of the tread, and you should look into 195/50/15s. There is a bit less selection in that size, but you'll get an effectively stiffer sidewall through reduced squeeze and longer life.

Edit: The smaller tires should also heat up faster, which is good for autocross. And of course the reduced squeeze will improve grip by distributing the car's weight more evenly across the tread.

rustysteel
rustysteel Reader
6/6/16 3:25 p.m.

I use the same size rims on my MINI and I've had tires from as big as 225 (way too big) to 195's and I've always found the 195's work the best. My favourites so far have been the Toyo R1R's and my old Bridgestone RE01R's. 195/50/15 seems to be just right, sounds like a story I've told the kids, there was once 3 bears...

wvumtnbkr
wvumtnbkr GRM+ Memberand SuperDork
6/6/16 3:59 p.m.

We roadraced on 225 45 15 on a 6 inch wheel.

No issues like that.

How did you determine tire pressures? It seems too high by the pic of the tire....

Knurled
Knurled MegaDork
6/6/16 4:25 p.m.

205/50 on 15x6s was OE on some cars.

rslifkin
rslifkin HalfDork
6/6/16 4:45 p.m.

The 205s should work alright. The little bit of extra pinch can make them a bit more picky about pressure (especially for even wear), so it's worth experimenting a bit to see what they like.

ggarrard
ggarrard GRM+ Memberand Reader
6/6/16 4:48 p.m.

As Knurled notes, 205s on 6 inch rims are/were fairly common. 205/60/15 is the stock size on a 83 Datsun 280ZX Turbo with 15x6 rims. I have 225/50/15s on 15x7 rims on my 77 280z and on 15x8 rims on the ZX Turbo.

jimbob_racing
jimbob_racing Dork
6/6/16 5:06 p.m.
ggarrard wrote: As Knurled notes, 205s on 6 inch rims are/were fairly common. 205/60/15 is the stock size on a 83 Datsun 280ZX Turbo with 15x6 rims. I have 225/50/15s on 15x7 rims on my 77 280z and on 15x8 rims on the ZX Turbo.

Not to threadjack but,

What was tthe offset on your wheels? I ask because I have 15x7 0 offset wheels for my 280z and have been pondering tire sizes.

Bobzilla
Bobzilla UltimaDork
6/6/16 5:50 p.m.

I ran a 205/50 on a 5.5" steel wheel. That was a little tight. OK, that was a lot tight. on a 6.5 a 205 would be perfectly happy.

Gearheadotaku
Gearheadotaku GRM+ Memberand PowerDork
6/6/16 8:21 p.m.

I think you're fine. I ran 205 on 6" several times. Note however, some manufactures "205" was larger than others. (sneaking past some rule perhaps?)

ggarrard
ggarrard GRM+ Memberand Reader
6/6/16 10:01 p.m.

Jimbob.... Both rim sets are 0 offset... 225/50 tires on rims wider than 7 inches will not fit the 280z without coilovers. The 8 inch rims on the 280zxt just barely fit. Both cars have lowering springs with tokico shocks. I also have a set of 215/60/15 on 15x7 0 offset that fit both cars.

Boost_Crazy
Boost_Crazy Reader
6/6/16 10:02 p.m.

I've run 205/50R15's on 6" rims on my Miata for years. Falken 615's and Khumo XS's, both of which run wide. They sit pretty square, no wear issues. The wear in the pics looks like it's more from burn outs than cornering. Maybe the previous owner had a little fun before he retired them?

Stefan (Not Bruce)
Stefan (Not Bruce) MegaDork
6/6/16 10:08 p.m.

Factory fitment in the eighties on many Chrysler FWD cars were 205/50 on 6" wide wheels.

They stuffed 225/50's on 6.5" rims.

So run them and enjoy.

codrus
codrus GRM+ Memberand Dork
6/7/16 1:24 a.m.

AFAICT, the rule for autox is that you run the widest wheel that your budget, rules, and fender clearance will allow, and then you run the widest tires that match those same criteria and that it's also possible to physically mount on the wheel. So while 205s would probably be faster on 15x8s than 15x6.5s, it's unlikely that 195s would be faster on 15x6.5s than 205s on the same wheel. This is all assuming the same tire compound, of course.

Wider tires do mean more drag from air resistance, but that's unlikely to be an issue at autox speeds. Road courses may be another matter.

GameboyRMH
GameboyRMH GRM+ Memberand MegaDork
6/7/16 9:27 a.m.
codrus wrote: AFAICT, the rule for autox is that you run the widest wheel that your budget, rules, and fender clearance will allow, and then you run the widest tires that match those same criteria and that it's also possible to physically mount on the wheel.

Running the widest you can physically fit on a wheel only makes sense if you're using cantilevered tires. Squeezing the widest possible (non-cantilevered) tire onto a wheel is going to leave you with squishy-feeling sidewalls, no matter how stiff the sidewalls actually are, and the outer edges of your tread hardly ever touching the pavement...and that's not even getting into the worst potential downsides.

So running a squeezed setup is sub-optimal and a waste of rubber at best.

I will be shocked if 195/50/15 is not faster than 205/50/15 on a 6.5" wide wheel.

jimbbski
jimbbski Dork
6/7/16 10:05 a.m.

I road race a Scriocco 16V and I use 205/50X15 tires but I use 15X7 inch rims and wouldn't use anything narrower! My car is an IT prep car and SCCA says it should run in ITB. It used to be classed in ITA and the group I race with has not updated their rules to reflect this and since I'm the only one racing a Scriocco in the class I haven't asked for the change and won't. A change in class from ITA to ITB would required me to change wheel size from 15X7 to 15X6. The expense of buying new wheels and the poorer handling I can expect, as well as higher tire wear keeps me from even considering asking for the change. Plus I am having my butt kicked now and that wouldn't change in "B" as the fastest car there is still faster then I am now.

My success or current lack of is more related to the car and not my driving skills. If I wanted to "win" I could always go with the universal answer, Miata! But I like going my own way so I'll stay with my VW for now.

fireball123
fireball123 New Reader
6/7/16 12:05 p.m.

When it comes to tires their is no such thing as too big

chandlerGTi
chandlerGTi UberDork
6/7/16 3:16 p.m.

Wow! He sold my old wheels to you? I put those tires on in 2005 I can't believe they are still on, they fit well and were enough tire for my car.

 photo SU1HMDAwMDUtMjAxMDAxMTUtMTYxMy5qcGc.jpg

Edit: As for the burn out comments, that car was difficult to not slide sideways away from the lights. It had horrible wheel hop if you tried to smoke them though. I must have made four years worth of auto-X in those tires.

Contradiction
Contradiction Reader
6/7/16 3:34 p.m.
chandlerGTi wrote: Wow! He sold my old wheels to you? I put those tires on in 2005 I can't believe they are still on, they fit well and were enough tire for my car.  photo SU1HMDAwMDUtMjAxMDAxMTUtMTYxMy5qcGc.jpg Edit: As for the burn out comments, that car was difficult to not slide sideways away from the lights. It had horrible wheel hop if you tried to smoke them though. I must have made four years worth of auto-X in those tires.

Yup! It's sitting in storage doing nothing still. :( If I had more money and ambition I would go rescue it and put a Berg Cup kit and a 1.8T in it.

At least the wheels are getting put to use though. Those old Azenis are ROCK HARD NOW! I put them on the car only to get it aligned with the wider wheels and they were like driving on Matchbox Car wheels. LOL

chandlerGTi
chandlerGTi UberDork
6/7/16 3:56 p.m.

I want the drivetrain back to put in a pickup.

Contradiction
Contradiction Reader
6/7/16 3:56 p.m.

Thanks for the input everyone. After mulling over it more I decided to go with 205s. Should have them on the car this weekend for an autocross too.

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