TheAverageEngineer
TheAverageEngineer New Reader
4/29/17 9:20 p.m.

So I autocross my Fiat 500 Abarth (SCCA H Street), and I've been pondering other options for tires that would be good for autocross, maybe if there is something better than what I use currently.

Current choice: 215/40-17 Dunlop Direzza ZII Star Spec, on 17x7 wheels

At the time I originally selected these there were a few folks on Fiat forums who commented on using them with good results... it helped that my first set was actually free (used) from a guy in my region who ran them on his E Street Miata. After these were toast last September I bought another set. I have been doing well with these so far, and I probably don't need new tires until later this year, but I'm pondering if there might be anything better for my application.

I've narrowed down to a few possible options:

-225/45-16 Dunlop Direzza ZII Star Spec on 16x7

-215/45-16 BFGoodrich g-Force Rival S 1.5 on 16x7

-205/45-16 Bridgestone Potenza RE71R on 16x7

And a few general notes for these:

-The 225-width ZIIs are somewhat questionable on if they will actually fit without interference. Some comments I got from Fiat folks indicate it is possible but requires very careful selection of wheels, and this might not be a practical option in the end.

-The specs for the Rivals indicate that the max inflation pressure is 44 psi. I've generally run 45-50 psi in my ZIIs with good results for roll, so I'd be worried I might get excessive rollover on the sidewalls like that which I incurred when I was a noob (well, more of a noob than now) and didn't yet know how to tire pressure. Also, it appears that the Rivals are not a symmetrical tire and I'm curious if this also eliminates the possibility to flip on the wheel and wear both shoulders.

-Generally I've seen comments that the RE71 is the easy option to go fast, which is why it is quite frustrating that there are so few sizes that actually fit my car. All of the close sizes are 205s, and the 205/45-16 appears to be the only one that fits without either being questionable for clearance or requiring wheel offsets that would bump me out of H Street.

I guess my general question is: Would there be enough of an advantage with the alternatives I have listed that they would be worth pursuing, or do I already have the best setup given my size and class limits?

Also, if there any subtle details I have gotten wrong or missed, be sure to let me know, I'm still learning!

I've posed this question elsewhere but not had a great deal of specific feedback. Hoping there might be some good folks here with knowledge and/or experience that might be able to help.

Thanks!

Ransom
Ransom PowerDork
4/30/17 12:10 a.m.

I have it in my head that you should be careful about wedging a tire onto less wheel than it wants; also of course HS limits pretty tightly what wheels you can use (I don't recall off the top of my head, but I think it's stock width and very close to stock offset?)

Also, those pressures sound high to me for these tires. But I also just put a set of RE-71Rs on my Mini, and haven't yet actually run an autocross on them...

There are at least one or two people autocrossing Abarths on here; hopefully one of them chimes in. If a mod happens to wander in here, you might ask them to alter your thread title to pitch to them? Tires are indeed an eternal and vast topic, and street-class autocross tires for an Abarth is a much more specific question.

Ransom
Ransom PowerDork
4/30/17 12:13 a.m.

As an aside, I was actually asking about autocrossing Abarths myself a little while back, and Star Specs were mentioned in the context of success, but no sizes were mentioned.

https://grassrootsmotorsports.com/forum/grm/anybody-here-autocrossing-a-500-abarth/126910/page1/

red_stapler
red_stapler Dork
4/30/17 12:36 a.m.

If you're still a noob, the Rival 1.5s are supposed to be a lot more tolerant of slip angles, and are generally easier to drive fast than the RE71s.

Source: A guy with a WRX in Huntsville has run them back to back over the past few events.

Also. Don't buy Star Specs for autocross if you're trying to win or climb up the PAX.

KyAllroad
KyAllroad PowerDork
4/30/17 4:42 a.m.
red_stapler wrote: If you're still a noob, the Rival 1.5s are supposed to be a lot more tolerant of slip angles, and are generally easier to drive fast than the RE71s. Also. Don't buy Star Specs for autocross if you're trying to win or climb up the PAX.

I came to say this. Consider it seconded. Avoid Dunflops until they get their act together.

wvumtnbkr
wvumtnbkr UltraDork
4/30/17 6:23 a.m.

Instead of really high tire pressure, can you run more camber?

iceracer
iceracer UltimaDork
4/30/17 9:43 a.m.

Read the GRM tire tests.

TheAverageEngineer
TheAverageEngineer New Reader
4/30/17 3:50 p.m.

I'm going to try and do a mass reply to the comments so far, hopefully this will make it simpler for tracking posts.

Ransom wrote: I have it in my head that you should be careful about wedging a tire onto less wheel than it wants; also of course HS limits pretty tightly what wheels you can use (I don't recall off the top of my head, but I think it's stock width and very close to stock offset?)

Indeed, stock wheel width and +/-7mm offset. Your point about squeezing the tires is also something that I was thinking of, for sure the 225 ZIIs would be at the limit of what Dunlop recommends.

Ransom wrote: Also, those pressures sound high to me for these tires. But I also *just* put a set of RE-71Rs on my Mini, and haven't yet actually run an autocross on them...

I agree, the pressure does seem high. I know it's within the safe limits for the ZII (51 psi max), and some friends with other cars and other tires have run similar pressures with good results. A question that comes up here, perhaps relating to wvumtnbkr's commment, might it be because of my current (stock) alignment that I am needing to run such high pressures, or is there something in the behavior of the ZIIs on my car that require it?

Ransom wrote: There are at least one or two people autocrossing Abarths on here; hopefully one of them chimes in. If a mod happens to wander in here, you might ask them to alter your thread title to pitch to them? Tires are indeed an eternal and vast topic, and street-class autocross tires for an Abarth is a much more specific question.

Certainly I would welcome this.

red_stapler wrote: If you're still a noob, the Rival 1.5s are supposed to be a lot more tolerant of slip angles, and are generally easier to drive fast than the RE71s.
iceracer wrote: Read the GRM tire tests.

What I've searched through so far indicates the Rival S being highly-rated for their particular tests from 2016. The comment about high slip angle capability with the Rival S was something that jumped out at me as being being quite attractive, partly due to my FWD car and also as noted with me being a noob still.

wvumtnbkr wrote: Instead of really high tire pressure, can you run more camber?

Possibly. From the reading I did this morning, the Abarth is supposed to be set to -1.5 degrees nominal from the factory, with adjustment between -1 to -2.5 degrees possible. However, I have also seen comments that the actual factory setting can vary quite a bit within this possible range. I would probably need to get a check to confirm what my current alignment is to see if I can get more camber.

My only concern here is that, since I also use this as my daily driver, I want to make sure that any alignment changes won't make it annoying to drive normally. I'm quite happy with how nicely it tracks on the highway for such a small/short wheelbase car.

Toebra
Toebra Reader
4/30/17 4:22 p.m.

I talked to a guy today who is running the Falken Azenis 615K+ and ran the old compound 615K last year. He reported the new compound is significantly better than last year, picked up about a second and a half running cones.

They are available in 215-40-17. Tire Rack has a sale on them that is ending today. I am going to buy some when I get home.

Hankook Ventus RS3V2 is available in the 16" sizes you see, also on sale at TR

red_stapler
red_stapler Dork
4/30/17 4:33 p.m.
Toebra wrote: I talked to a guy today who is running the Falken Azenis 615K+ and ran the old compound 615K last year. He reported the new compound is significantly better than last year, picked up about a second and a half running cones.

The RT615K+ are the same compound as the ZIIs, which he already has.

iceracer
iceracer UltimaDork
4/30/17 5:53 p.m.

In most of the GRM tests, the best pressures were in the mid 30's. The pressure on the side wall is for max load and not good for traction.

Many FWDrs, will run the max pressure in the rear to decrease under steer while running the fronts around 34 or so.

rslifkin
rslifkin Dork
4/30/17 5:55 p.m.

In reply to iceracer:

And on top of that, ideal pressure can vary widely between different car / tire combos. And sometimes the ideal pressures end up being very different for front vs rear, even on a car that's not too far from 50/50.

wvumtnbkr
wvumtnbkr UltraDork
4/30/17 6:22 p.m.

If it's easy to change camber, get an alignment with Max camber and caster and mark that spot on the adjusters. Get a street alignment done and mark that as well.

When autoxing, run the aggressive setting. When street, dial the adjusters back.

This only works if it's easy to do.

It should give you way more front grip as well.

TheAverageEngineer
TheAverageEngineer New Reader
4/30/17 9:52 p.m.
iceracer wrote: In most of the GRM tests, the best pressures were in the mid 30's. The pressure on the side wall is for max load and not good for traction. Many FWDrs, will run the max pressure in the rear to decrease under steer while running the fronts around 34 or so.

I had been thinking about this direction somewhat previously, and of course logically this makes sense.

Many of my events last year I was fussing around just with the front tire pressures to keep from rolling the sidewalls, and I for the most part I didn't mess with the rears. The couple of events I've run this year I've run with square pressures (all four tires the same), and in retrospect I feel this had a noticeable improvement in the car's behavior over what I had done most of last year. I have an event this coming weekend, and I think I will try maxing the rears and see how that performs for me.

Would it be likely that I can help address the roll issue on the front tires by decreasing understeer just using higher tire pressure in the rears? If I can dial back the front tire pressures certainly that makes the Rival S a more attractive option.

Toebra
Toebra Reader
4/30/17 10:55 p.m.
red_stapler wrote: The RT615K+ are the same compound as the ZIIs, which he already has.

News to me. If he ordered them today, it would save about $300 over the Dunlops for the set

Guy with an Abarth in our local group did very well on his Dunlops

rslifkin
rslifkin Dork
5/1/17 7:47 a.m.
TheAverageEngineer wrote: Would it be likely that I can help address the roll issue on the front tires by decreasing understeer just using higher tire pressure in the rears? If I can dial back the front tire pressures certainly that makes the Rival S a more attractive option.

The roll may be less of an issue with different tires anyway (different sidewalls will behave differently). And the tread on the Rivals wraps around onto the sidewalls a bit and the shoulders are pretty round, so a bit of roll will hurt feel but probably won't have a big effect on grip.

fanfoy
fanfoy Dork
5/1/17 8:49 a.m.

I ran RE71R's for two seasons and I found them incredibly easy to drive fast. And I ran them at stock pressures. I tried higher, and what it did was make the breakaway snappier but my times remained constant as long as I was clean. Like the Rivals, they are "rounded" tires that are pretty tolerant to camber challenged FWD cars.

No experience with the Rivals but locally they are very polarizing tires. Some love them, other hate them.

The Dunlops are not competitive and are harder to drive than the Dunlops (and I'm guessing Rivals)

iceracer
iceracer UltimaDork
5/1/17 10:27 a.m.

Adding caster will help the camber problem

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