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Old 08-26-2011, 04:42 PM
Omer Omer is offline
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What size tires to use for best off the line acceleration 0-60 mph (1968 Firebird)

This is a 1968 Firebird, with no modifications to the body, a pure street driven car with all the accessories less a/c. It's got Hotchkis total vehicle system consisting of sub-frame connectors, rear leaf springs and front coil springs with Bilstein shocks and the front & rear sway bars. Also PST poly-graphite complete front end kit and body mount bushings. Overall the car is stiff and handles great around the corners.

The engine is a 350 SBC with stock 64cc #492 angle plug heads (2.02/1.6 valves), flat top pistons, around 9.5:1 compression, XE256H cam, weiand stealth manifold, 670 cfm Holley street avenger carb, 4-2-1 headers (Doug's Tri-Y) followed by a Magnaflow 2.5" dual exhaust. I happen to enjoy the wide torque band and the throttle response of this combination. It's never been on a real dyno, but desktop dyno shows about 400 torque @ 3500 rpm and 322 hp between 4500-5000 rpm. It doesn't see past 5500 rpm. I never race it. My kind of fun is the best acceleration off the line and 0-60 times. I think this setup has enough torque for me now, if I could ever manage to keep the tires planted all the time.

The driveline is kinda weak. I have a 700r-4 with no mods in it and the rear is GM 8.5" 3.23 ratio gears with a cone type limited slip. I like the 700r4 giving me a deep 1st, compensating for the low rear gear (I think going higher would give me even more wheelspin with a street tire). For now, I don't care that the 2nd gear is too far away from the 1st gear ratio since I have good low end torque.

Well, the driveline has been holding up for now, but I don't know for how much longer. I definetely need some improvements here, but first, I need to get rid of my sorry tires!

They're Kumho 712's 255/45/16 rear on 8" rims, and 225/45/16 front on a 7.5" rims. They're long overdue for a replacement and I'm trying to find out a sensible size for my setup. I'm not sure if the wide rear tires really suit my driving style. How about 225/50/16 Eagle F1's on all four corners? I know that wouldn't look anywhere near cool, but I think I will get better heat management with that size and much better adhesion over Kumho's. Also how about going down to 15" diameter wheels? Would more sidewall height give me better traction off the line? (and for the downside, hurt cornering stability?) I'd really like to see what you guys think about it.

There's huge information everywhere on how to get more horsepower, but when it comes to tires, there's a whole lot of options and even more misinformation. I think this is often overlooked but I feel this is where the biggest gain would come in, regarding 0-60 times. If I can manage to minimize wheelspin, I'll go after some cal-trac style bars, a better limited slip and a beefier 700r-4 in short term.
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