I'm considering this, but not sure.... I'll have to do some research. As is mentioned in the other comments I believe the rolling diameter is roughly the same. I also don't really want to reduce my size down from a 255 to 225 or 205. I'd imagine the 255 tire helps me grip and offset the weight at least a little.

Interesting! I'm going to have to check this out.

Hmmm, didn't the American bumpers have bumper shocks and such? Also the black rubber thingys protrude more on the American spec. Aside from switching to fiberglass there isn't much to do?

Oh, also I have Koni reds up front and I'm not sure in the rear, but they're in good shape. Might pick up a set of Bilsteins. The Quickchange bars are 23 in the front and 28 in the rear.... pretty aggressive. Original sway bars with new bushings. Fair amount of front camber.

I know 2 years isn't much racing, and I probably exacerbated the "nut behind the steering wheel" problem, but if I'm beating other more seasoned drivers using the same 3.2 Carrera with my crappy tires then who can blame me for being a bit ambitious aiming my sights on the 964? We also generally get about 12 runs a day on average at our autoX.

Thanks for the vote of confidence. I believe he has done some modest engine tuning though. But I'm definitely asking because I think with some changes I'll find myself in direct competition with him. My crappy craigslist RE050's and his good RE71R's are definitely an Apples to Oranges comparison

I'm all about seat time, and can guarantee I'll be maxing out next year. Still not sure about the wheels though. I'm a big fan of empirical data so I'm going to pursue that. I have some RS-3's NT01's and RT615K's for my Scirocco but I've heard they don't hold a candle to the RE-71R's (well....the NT01's do but are technically R Compound)

I can weigh and measure my fronts which will give an idea for a comparable Fuchs setup....but again....like I said, I'd be scrapping width for weight.

Also, I'm bouncing off redline in 2nd gear at points which is about par for the course. I'd have a hard time conceiving wanting to be geared even lower. The autocross track we have is an airport that tends to be a quick mile+.

Buddy, put plastic lid, hood and front and rear bumpers to save weight. Caveat, will not hold up to impact. He even got rid of the bumper struts. Crazy but his car is dedicated track car. Damn Cheater :-P

Miata battery or the AGM 25lbs battery will work.

After all the weight removal do the corner balancing.

I have to redo mine because of lighter starter and muffler.

Hehehe, I'd definitely do the bumpers, but that's pretty big money. Lol I just put bumper struts in....they weigh nothing! But they'd probably rip that hood to shreds though.

The updated starter is lighter? Which one is this??

For my Scirocco I got a Featherweight lithium ion battery. Thing is suuuuuuper light. Very expensive though to get more CCA.

I agree 100% that the corner balance is the first step, This could make a HUGE difference. Yes, stock brakes are fine. Weight reduction is important next. Lower effective gearing is almost always a good thing so smaller diameter tires are good. They also lower the cg without messing up suspension geometry. Get the spindles raised 19mm and make sure you have good adjustable sway bars front and rear.

What torsion bars are in your car now?

Quickchange 23 Front/ 28 Rear

Sway bars are stock for the moment. Raise the spindles? You mean cut and Fab them? Sounds dicey. I also installed Weltmeister steering rack spacers. Cheap and does the trick.

For weight reduction, have you guys seen this??
Wps Featherweight Lithium Battery 500 Cca Hjtx30L-Fp-Il Hjtx30L-Fp-Il

I bought a 200 CCA one for my Scirocco which does the trick.....but with these batteries you're talking ounces....not pounds.

There's a lot more to it than side grip. You'll maybe get more of that with the wider tires, if you keep them flat on the ground enough, etc. You've lowered your car, that increases the amount of roll it has as the roll center height has changed, so you might be wasting some of that width. I doubt you are running enough camber to compensate for the body roll.

Those big fat tires hurt you in three other ways. One, they're probably 50 pounds heavier, as a set, than what I suggest you run. Two, they will have a much higher rotational moment of inertia, which kills your acceleration. Three, they are taller, so you effectively have taller gearing.

Yes, the US cars had heavier bumper mounts. Yes, the rear bumper pads are wider and heavier. Altogether, you're talking maybe 10 pounds. Removing all of that and installing fiberglass bumpers might save you 40-50 pounds, if you do it right.

Your torsion bar choice is a very poor one for autocross usage. You've increased the stiffness of the front way more than the rear, so you now have a ton more understeer than stock, which is the opposite of what you want. Who knows what shock valving you have? Don't just go out and buy more parts. Work with someone that knows how to set up 911 suspension, like Chuck at Elephant Racing. Tell him what you have, tell him what kind of courses you run and let him guide you. Listen to what he says. Better yet, have him do the work.

So, each day you get about 15 minutes of seat time. That's nothing, but it is what you get with autocross. Plan on spending a lot more time to get good. The really fast guys, the ones that win national titles, may have been doing this for 20 years or more and they'll tell you they are still learning. You should be able to run circles around that 964. You have a better power to weight ratio, a much stiffer tub, and that generation of Porsche AWD was terrible. The coupes understeered like pigs and the open cars were even worse.

You need to fix the problems your car now has, and it is far from optimum for autocrossing-trust me on this, and you need more seat time.

Have fun,
JR

In my very limited experience (though I've done lots of watching, listening, and asking), tires alone can be worth 3 seconds on a course that long! And if you've never experimented with lighter vs heavier wheels + tires, it's crazy how noticeable that difference is. Shorter diameter is even better for acceleration, though in certain situations that could just set you up to lose time on an extra shift.

Either way, the 964 driver clearly knows how to throw that floppy 'vert around the cones. I absolutely agree that a 3.2 coupe should be quicker given the same driver (and equal tires).

One common thing all of the quickest autocross 911s seem to have are custom-valved shocks. I'm not sure anything off-the-shelf aside from coilovers (which probably class you out of competition) is ideally valved for autocross.

Your old RE050s are clearly at least 3-5 sec off new RE71Rs. That's the first thing you should change. 225 and 255s on the 17s should be good. Set your alignment to at least -2.0 camber f, 2.5 rear, with 0 toe front, proper corner balance and you should fly.

A good rule of thumb is that each 100-110 lb weight reduction is good for a 1.0 sec reduction on a 1:30 track lap, or 75 sec AX course. You can see that on AX lap times when a passenger rides along. The subject of weight reduction is a long one. The first 150 lbs are the cheap and easy ones.

Regarding HP, a good rule of thumb is each additional 10 HP is good for a 1.0 sec lap time reduction on a 1:30 lap. So a 15 HP mod is good for a 1.5 sec reduction. Make sure you are getting full throttle at the throttle body and that the full throttle microswitch is working and activating.

I used to run 22mm sway bars front and rear on my 3.2, but on the advice of Rich Walton of JWE, changed to Smart Racing 31f/27r and the car was instantly 1-2 seconds faster. You could literally dive head on at a cone, heel toe into first, and throttle steer the rear end 180 degrees around it and power out.

Brakes do get hot in AX. Good ventilation, a set of Raybestos ST-43 pads, and Endless RF650 brake fluid are a good start.

Fair... Something to chew on. I'm usually the one making your argument advocating for smaller wheels so I do see where you're coming from (and many other people)

The fronts are hollow BTW. I can tell you I don't have much understeer :P In fact managing my oversteer is what I spend most of my time doing. I should contact Elephant but their price tags scare me. I usually do a ton of research on there and other places and find cheaper or used options.


Yeah, I'm definitely sounding eager, but I'm pretty addicted and yeah autocross isn't the best for seat time, but I'm not doing DE with it, but that is why I'm building a more disposable VW track car. I agree I'm completely still learning, but there are handicaps we can afford ourselves to gain speed even if our skill level still needs much improvement. A mediocre driver with a fast car will run circles around a Model T....just don't act like it's all driver's skill. My buddies 964 doesn't understeer too much either. In fact I spun it when we swapped cars at the end of the day. It's no slouch with the KW V2's

Lol, yes, I feel the tires are not getting enough credit in this thread. That's really all anyone talks about at the track....and AFAIK the RE71R's are the ONLY way to go. Right about the extra shift. Our tracks are set up for 2nd gear. Some people (on Hoosiers) get to 3rd gear, but street tires nope.

The 964 driver is very very good. He does know how to "throw that floppy 'vert" :) I have dampening adjust on the front but non-adjustable rears. Probably on my to do list. Coilovers would throw me into another class I'm pretty sure...yeah.

Thanks Steve! I emailed you back in the day about the chip. I'll look into those HP figures..... seems a chip and throttle body enlargement might get me something. I'll have to look into the full throttle microswitch.

I feel I don't have the rear grip right now to throttle out like you said hehehe, maybe with the new RE71R's.

Also, thanks for the Camber specs!! I am probably running too much front camber and not enough rear at the moment. Eager to get that alignment and corner balance.

your car looks like it is doing pretty well I the pic, no excessive body roll.
if you can get the 225/255 in a 15 with the same profile spend the money on the rims.
that is like adding HP, it lowers the CG by 2 inches which is a lot which is also a BIG improvement without changing the suspension geometry.
your looking for 3 sec out of 75sec on a low speed course, that's a lot of time.
you need the acceleration.
trying to increase your cornering speed takes a lot of $$$ + you have to be able to utilize it in your driving skills. getting from one turn to the next is easier to improve.

say you have a 30 turn course. that's .1 sec per turn or .1 for accel for 3sec improvement. keeping one or the other the same, which would be easier to improve.

Leaving aside all of the other factors for a moment, you've more than doubled the front spring rate but only increased the rear by about 50%. That is significant, especially considering a stock 911 already understeers a bunch in low speed corners.

Oversteer can occur on the entry into a corner, through the corner and exiting the corner. Don't confuse the basic balance of the car with oversteer that arises from driver inputs.

Maybe he's changed the car a bunch, I don't know. All I know is that when it rolled out of the factory, it wasn't any good in low speed corners.

In my area, the fast guy is fast in his car, or in any other car he sets his butt in. He'll beat anybody's best time, in their own car, the first time he runs it. It doesn't matter if it's a 100hp 914-4, or a 600hp uber-Porsche. He's that good.

Modifying these cars isn't cheap. I'd rather have one car that was set up well than two that were set up poorly, so maybe my priorities aren't in line with yours. I will say that any advice I get from people that have spent a lot of time learning it usually get my business. I'm working on a car now that I've talked to Chuck about. When I get to the point of buying parts, he'll get my business as a reward.

Good luck to you,
JR

By the way, in several of the photos you've posted of your car, I see a lot of tire smoke. Your corner balance is probably a mile off and your tires may be long past their useful life. Swapping tires and re-aligning the car will help a bunch, but I'd do all the other work first, so you don't have to corner balance the thing more than once.

JR

I have an 86 Carerra that I've autocrossed for years.
-Fully agree with everyone suggesting 15s. I run 225/45Hoosiers on Fuchs 7/8X15s
Running a square tire setup lets me move the tires around as needed to equalize the uneven wear. There is still a bit of tire footprint difference (maybe 1/2 inch) front to rear because of the different width wheels.

-Get the car as low and stiff as possible. Adjustable sway bars enable fine-tuning the front/rear balance to suit your handling taste.

-I run SSIs and a SW chip. The car pulls very quickly from 2-5000rpm in 2nd gear, where you will be most of the time.

-Aggressive weight reduction with FG bumpers would be the next step for me.

Torsion bars are too stiff out front and too soft out back. You will want something like 21/31.

You need adjustable sway bars to get the most out of the car. It has way too much understeer now.

Yes, cutting and welding is required to raise the spindles. Not dicey at all. It is done all the time.

Thanks! Yeah, not too much body roll and the fronts don't seeeeem excessive. I actually got my torsion bars from my buddy who does DE. Honestly, yeah, I'd love to find 15" wheels that accommodate big tires, but then again Bridgestone doesn't make such tires :(

I did some math and I think my setup is 17lbs heavier. I think ideally I'd find lighter 17" wheels. Our courses are a lot of corners and slaloms.

I also feel like 205's would look stupid on the rear of my 911. Maybe it's a negligible concern and I'm being prideful, but I like having big meaty tires in the rear.
https://c8.staticflickr.com/9/8274/2...4d10d310_b.jpg
https://c6.staticflickr.com/9/8135/3...ced887bf_b.jpg

100% true :)