911 Track Width

jluetjen · jluetjen's Garage

OK - here's the question. As I go through my daily life daydreaming about (aka: planning out) the conversion of the '69E to SCCA E-Prod spec's I started thinking about the track width.

The SCCA E-Prod spec's limit the 911 to a maximum track of 54.1 inches F / 53.3 inches rear (that's 1374 / 1354 mm for you metrically inclined)

From the factory with the original skinny wheels the car's track is 53.6 / 52.8 inc F/R (1362 / 1343 mm), but no one's going to run with those wheels.

The maximum wheel size for the car in the class is 7x15. Looking through my documentation I noticed that the '78 SC's with the 6 and 7 inch ATS Cookie cutters had a track of 53.6/52.8. I've got a set of those wheels and so it looks like I'm good to go.

By 1980 an SC with 6 and 7 inch Fuchs looked like it still had the same track measurements.

But looking at the 2.4 S with 15x6's, it looks like with the track was 54.1 x 53.3 and would just squeek by.

The 2.7 Carrera (US) had 15x6's and 15x7's and the track was 54 x 54.9 which would be over the top and make my car illegal.

Does anyone have any information regarding the offsets of the the different variants of Fuch's compared to the ATS. BA's book suggests that all of the 7x15s had the same offset excepting the 911R's (and I don't want to go there -- too much $$$). Or did some of the cars use spacers? Has anyone ever had the inside face of their wheels flycut down to increase the offset?

911pcars · 04-25-2003, 10:51 AM

John,
To maximize the regs, I'd use the 15x7 ATS wheels, then use spacers (if permitted) to sneak right up to the max. track width.

BTW, I assume SCCA defines "track width" as sidewall-to-sidewall. If so, your tire choice will have a bearing on this measurement.

I wouldn't take any material off of a wheel. The center is a high-stress area.

Sherwood Lee
http://members.rennlist.org/911pcars

jluetjen · jluetjen's Garage

GCR Glossory P194 -- "Track: The distance between the center of the rims of two wheels at one of a car, with any angular adjustments at normal settings and steered wheels in the straight ahead position."

GCR 17.17 Track:
Track is the distance betweenthe centerlines of the wheels as raced, without driver, measured at a horizontal plane through the wheel hub centerline. Alternatively, it may be measured from the inside of one wheel at the hub centerline height to the outside of the other wheel, then conversely from the outside of the first wheel at hub centerline to the inside of the second wheel. The two (2) dimensions obtained are to be added together anddivided by two to obtain the average. Measurements are to be taken at both front and rear of the wheels and averaged to compensate for toe in/out. Under certain circumstances it may be preferable to measure from the outside of one wheel to the outside of another and from this dimension deduct the thickness of one wheel. This should be repeated 180 degrees opposite to the first measurement and the two dimensions averaged.

911pcars · 04-25-2003, 12:32 PM

It seems like you would have to mount the wheels (only) on your car, measure the track, then go from there. The rules say 7" is the max. You could use spacers to maximize the track to regs. In lieu of the pricey R wheels, I'd use the ATS 7" wheels as they would be lighter and wider than the available Fuchs.

Sherwood

jluetjen · jluetjen's Garage

Sherwood, you and are coming to the same conclusion. I even like the looks of the ATS wheels and plan to use them at least for the rain tires.

But I'm hoping that I can use some Fuchs with the dry tires since they are a little tougher being forged. Since this will be wheel-to-wheel racing, they will most likely get banged-on some while cutting across the curbing or while being nudged by a competitor. I just don't want to end up buying upteen wheels until I find the set that works. I'd rather have it figured out ahead of time.

It would be interesting to see if anyone else turns up with some information.

911pcars · 04-25-2003, 01:07 PM

They say it's wise to budget periodic xray, Zyglo or Magnaflux inspections on things that can break and cause havoc with your personal well being. Even Fuchs wheels break.

Best wishes on your racing,
Sherwood

Bill Verburg · Bill Verburg's Garage

An easy way to measure the track as defined above is to measure the distance between the hub faces and subtract 2 x o/s for the 2 wheels(assuming + o/s, add 2x o/s if its negative which isn't likely)

Don't understand how the double post got here, sorry!

Bill Verburg · Bill Verburg's Garage

An easy way to measure the track as defined above is to measure the distance between the hub faces and subtract 2 x o/s for the 2 wheels(assuming + o/s, add 2x o/s if its negative which isn't likely)

6" Fuchs are +36mm
7" Fuchs are +23.3mm
7R Fuchs +49mm
ATS ????

For track use I would stick w/ Fuchs, I vaguely remember hearing horror stories about the ATS wheels. maybe not