Help With Rear Gears
Moderator: John_Heard
Help With Rear Gears
I'm currently running 4.57 gears in a Ford 9" in my 68 Camaro. Last year I was running 32 X 14 slicks and in the 1/4 mile I would go through the traps at 6300rpm. I switched to 31 X 13 slicks this year and ran in an 1/8 mile race today. As I went through the traps in 3rd gear, my shift light was on telling me I was at 6300rpm. I wouldn't think 1" less tire diameter would make that much difference. If I was to run 1/4 mile, what gear ratio would I need to keep from red lining my engine?
Re: Help With Rear Gears
You cant go by the size of the tire on the sidewall (32" or 31" ) you have to measure the actual rollout and divide that by 3.14 this will give you the real diameter of each tire. What mph were you going in the 1/8th and in the 1/4 .I dont see how you could run the same rpm at half track with the same gear as you ran in the 1/4 something else must have changed?? Did you cahnge anything else? Also your 32 might grow a lot and your 31 might not.
Re: Help With Rear Gears
The only thing I changed were the tires.
Re: Help With Rear Gears
Yeah, I found out the hard way that 31x18.50 doesn't mean 31x18.50. It's the actual runout on the tires / slicks that matter, not what the vendor labels them... Simplest way I found to check / measure runout is to use a piece of string and run it around the center of the mounted tire circumference, mark where it meets the end and then measure. That'll give a pretty good idea of the runout and will let you more precisely calculate mph, gears, shift points, etc. etc.
Hope this help
Hope this help
1969 ProStreet Camaro RS Best 9.75@139 1.46 60'
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline
http://www.marsh-racing.com/harrys_camaro-1.htm
Blown 427 BBC, TH400 w/Brake, Back-Half Ladderbar
Narrowed 12-Bolt, 4.10 Gears, Spool, Moser 33 Spline
http://www.marsh-racing.com/harrys_camaro-1.htm
Re: Help With Rear Gears
My wife's cloth sewing tape measure works great for measuring roll out.
{As long as I get it back in her sewing basket before she knows it's gone}
I've since bought one of those 100' cloth tape measures from the box store.
{Safer}
{As long as I get it back in her sewing basket before she knows it's gone}
I've since bought one of those 100' cloth tape measures from the box store.
{Safer}
Re: Help With Rear Gears
Hey, that's a great idea !!! I'll pick one of those up :)pro70z28 wrote:My wife's cloth sewing tape measure works great for measuring roll out.
{As long as I get it back in her sewing basket before she knows it's gone}
I've since bought one of those 100' cloth tape measures from the box store.
{Safer}
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