nile13

Of course. But we are talking about choosing a size for a specific tire model that OP has already decided on. Granted, even there the same mfg will fudge the numbers a bit on the same tire model in different sizes (I've seen it with Hoosiers, for example). But we are talking calculations for a mfg's given markings on a given tire model.

nile13

Steven, thanks! This is about my understanding as well. I've seen numerous reports of about 30mm difference front to rear tires on 1.5-2" different width rims.

My own 993 is currently on 225/265 18s on 8ET50 and 10ET65. If I go with RE71s (tires I really like on a Miata) for the next set, they will probably be the same sizes as I don't see putting 235s on 8" rim as an advantage. On the other hand, my own 993 is mostly a street car with an occasional autocross for GF and rarely for me, so it doesn't much matter. On a previous 993 I've ran 225/255 17s after running original 205/255. As much as I'm dull and insensitive to the car setup, there was a perceptible difference to me.

PS. RE-71Rs are pretty magic for a street tire, no?

trophy

It seems the 30 to 40 is the magic number, any more and you end up with the understeer issue. I think the 30mm difference for a 255/285 didn't work as well as I would have expected, and I would only use a 255 on a 9" rim. the 30mm number has always had me thinking to try a 255/35r18 and 295/30r18... Though I will probably stick with the 245/285 Hoosier combo...

I think if i autocross the car more I will try a 255/285 combo, which is available in a RE71r. Need to build some new wheels though... Which I need to do anyway with the new brakes.

The RE71r's are the performance bargain of the decade... I have been very impressed, now if they would only do a 245/35 I would be as happy as a pig in mud.....

Bill Verburg

great track tire too!!

nile13

You are a brave man, sir! I would not dare go with a 255 upfront, though curious what it would be like. On the other hand, my front autocross tires are 275s. on a Miata

Oh, and as I've mentioned before, it turns out that Costco sells RE-71Rs and periodically runs $70 off on Bridgestones (and new another $60 off, from what i understand). And only $15 for mounting and balancing each. Which makes it a complete bargain beyond believe. I wish I wasn't in CSP. A7s are great, but god, $13 a minute...

Bill Verburg

Your spring, sway, shock and alignment have a lot to do w/ tire choice too

Me too, I don't under stand why there are so few 245/35 x18 choices, 285/30 as well for that matter but at least RE71 comes in that size

nile13

Bill, what are you guys getting out of them, longevity-wise? Say, compare to R7s and R888s? I've put a set on my Florida street car which is autocrossed very occasionally. Longevity is the only question, I'm curious how it stands up to the track work.

trophy

The 255 provided incredible grip when I ran them on 9" wheels for the track, however the balance was out. It may have been that they were r888's but have only ever tried them once. I still think it would be a good combo in the RE71r as an autocross combo..

Very true on the Suspension setup.... It really sucks with any normal street tires

I think we need to petition Bridgestone to start making 245's in the RE71r... I am sure there would be a ton of guys that would jump on that band wagon.

Bill Verburg

Can't say, I only used them for 3 days at WGI this summer when my regular wheels were being rebuilt. A very impressive 3 days though!!

Bill Verburg

Especially when you consider the alternatives.

I'm not unhappy w/ NT01 235/40 & 275/35 or w/ RE71R 225/40 & 265/35 but
either NT01 or RE71R in 245/35 & 285/30 would be fantastic

nile13

Would be very interesting to hear the impressions. I just think that 255s could make for a bit of a hard initial turn-in on an autocross course.

trophy

The RE71r is available in a 235/40r18 Which works very well with the 265 rear. I ran that with the Dunlop Direzza's with great success... But an NT01 or RE71r in 245/285 would be fantastic...

That is the only concern I have, however from an input perspective, the 997 Cup power steering I have does lighten the steering load over the stock PS pump.

nile13

This might sound weird, but here goes. I find that on an autocross course, I pretty much drive the 993 with my right foot. Unlike the CSP Miata that I've been intimate with for teh last 13 years (hey ) the 993 rack is so long that trying to steer precisely in low speed, constantly changing environment is pretty much impossible. 964 is even worse. The older a 911 is, the more it is so, in my experience. It seem to have changed with 996 and 997s that are completely different in this respect, they seem to have modern steering that gives me an ability to control it well with both the right foot and hands.

So, what do I do with a 993 at autocross? Kinda bluntly chuck it into the turn, trying to get it upset and off the straight line. Then, instead of doing small adjustments with steering wheel, do them with my right foot. I think at higher speed, on the track, this behaviour would lead into the nearest wall But on the autocross course it seems to work better.

With wider front tires, though, the initial steerng wheel yank to change directions and turn in would have to be even harder And this is where I'm concerned that the car will step out too much. So would be very curious how it behaves and whether above makes any sense. And whether the 997 steering would help (are you using the 997 rack or the long 993 rack?)

Here's a little illustration (notice where I'm looking):

trophy

That makes sense to me, I am new to autocross, and I have found I have to drive the car with my right foot more that steering. I have found that I steer in the general direction and keep it there with the right foot... Lots of fun, but a challenge to be fast.

I will see where my plans go for the year and if I end up doing more AX as the car is with the RE71r's and not getting what I want out of the front grip, I may as an experiment try some 255;s and report back.

No 997 rack Just the PS Pump.

nile13

Well, good luck at autocross courses next year, Steven! Such a frustrating addiction. I just completed my 18th season and will continue to throw money out the window