911 sc 3.6 conversion -15 inch Buckley wheels, will it work?

[-Levi-]

I'm building a stock body 911 sc track car with a 3.6 vram engine.


A lot of the 911 e and d spec racers run 15 inch Buckley race wheels to get wider tires all around (and -I believe- it changes the gearing) I think with my cars engine and suspension work it woukdent be a bad idea to fit wider rubber all around.
My question is- with a stock lsd tranny- will the smaller wheels with my engulf make the gearing to short? Will it make first and second gear useless?

Does anyone have aby advise if info on thus? I hate to drop $4000 plus on wheels and tires to have a bad setup- thanks!

[Walt Fricke]

Levi - the reason that the PCA 911 SC guys running in a stock class (D or E) run the Buckleys (or other 8x15 fronts and 9x15 rears) is to get the benefit of lower effective gearing due to a smaller diameter tire than you get with 16s or 17s or larger. Stock transmissions for these cars don't suffer from too little top end, so the effect is a slightly lower rear end ratio. Nobody uses 1st on a race track unless you stopped for some reason, so forget that. And second with these short diameter tires works fine on most "2d gear" corners. Their offsets are just about perfect for wide tires. 245s will fit up front, and 275s in the rear, although that is very tight (tightly rolled lips, ground down spring plate adjustment hardware, and maybe a very thin spacer). They are fairly light rims, too. And another advantage of shorter diameter tires is ride height - the car rides lower at optimum suspension settings, and getting a car on taller tires that low means you have to use suspension settings which result in adverse geometry. In front you can raise the spindle to offset that where you aren't building to a set of rules, but not really in the rear.

But you are not planning to race in a PCA Stock class. And you have all that extra torque and horsepower with your 993 motor. And I bet you hanker for bigger brakes, and 15" rims, while you can get bigger brakes which fit with 15s, will limit your choices (for instance, I don't think Boxster brakes will fit 15s, and overkill like Big Reds certainly won't).

Unless you drive on actual go kart tracks, you won't find any 1st gear corners on race tracks (autocross is different). You should be able to get 245s in the rear on 16s, and for sure on 17s. I've seen 275s on 17s in the rear on SCs, but when I tried 17s I couldn't make that fit. In fact, I couldn't get 255s to fit. Maybe I didn't have just the right tire. Maybe I just didn't get the rims I had spaced just right. Maybe if I could have gotten more negative camber they would have fit. All that goes to squeezing rubber which fills the width of the fender to the max.

At least one fast SC racer is thinking of running 245s on 15s all the way around, because you can have too much rubber for your engine, and if it doesn't heat up into its optimum operating range you don't come out ahead with too wide a tire. Not likely to be a problem with your motor, though.

Besides, if you want wider rubber, you can flare your fenders. Us stock class racers can't do that.

What about considering running suitable rubber on the rims you have (even though it will mount, you don't want a tire which is too wide for the rim, as that makes the sidewall effectively softer and the tire squirms around more, which doesn't help)? Then, if you start thinking that tire size is limiting your performance (as opposed to the driver being the limiting factor), then you make the financial decisions on rims?

[Bill Verburg]

Originally Posted by -Levi-

I'm building a stock body 911 sc track car with a 3.6 vram engine.


A lot of the 911 e and d spec racers run 15 inch Buckley race wheels to get wider tires all around (and -I believe- it changes the gearing) I think with my cars engine and suspension work it woukdent be a bad idea to fit wider rubber all around.
My question is- with a stock lsd tranny- will the smaller wheels with my engulf make the gearing to short? Will it make first and second gear useless?

Does anyone have aby advise if info on thus? I hate to drop $4000 plus on wheels and tires to have a bad setup- thanks!

The guys i see running the 15s are 3.0 SCs and maybe a 3.2 Carrera or two. The reason is the relatively low torque available.

A 993 3.6 is a very torqey motor, any ~25" tire(or under) w/ stock gears will work very well, the shorter the tire the less suitable for street use because the gearing gets too short.

Look at whats available in tires that you want to use

if Hoosiers are on the table the 275/35 x15 R7 @23" is a great short rear 245/40 would be the tire to match it in front. you'd want 8 & 9(or 9.5) x15

if Hoosiers aren't on the table there are no other similarly sized 15s.

there is a dearth of appropriate 16" sizes

in 17s you could use 255/40 @24.8" or 275/40 @25.5" or again R7 275/35@24.7" again 245/40 fronts and again on 8 & 9(or 9.5)

[arrivederci]

Exactly what Walt said - 15s are lighter, lower the gear ratio and lower the center of gravity while keeping the suspension geometry closer to optimal. Any idea if people are still breaking the bolts on the buckley rims? I remember everyone used to check them and had spares on hand.

I didn't make the switch to Buckley's...invested in 17" Fikses (two sets) and am fine with them. I managed to fit 275s in the rear. If I had a limited slip diff I might be fine with 245s.

That's on the Euro SC E stock of course - not the '72 street car with the 3.6. On that I run 245s on 16s.

[Bill Verburg]

Here's some comparisons I did for a friend that was racing an SC in PCA
stock, w/ 245/45 x16


Change tires to 275/35 X15


change tires to either 275/35 x18 or 275/40 x17


change cwp to 7:31 and change tires to 275/35 x18


some issues found w/ the 275/35 x15 tires sway bars hitting the ground when suspension compressed, additional shifting required, sometimes at inauspicious places, high revs in street use cruise, lack of a matching front, 225/50 was a bit narrow