Visit The Dirt Forum for More Information

Author Topic:   GEAR QUESTION
Speedway65
Dirt Freak

Total posts: 344
posted March 04, 2005 12:17 PM  
Here's the question.We currently run on a 3/8 high banked track with a metric car with a th350 in 2nd with 3.73 gears and about 82 roll Street tires and turn about 6200 to 6300.We are switching to Hoosiers that are about 84-86 roll and we want to turn around the same RPM ,would switching to 4.10 be the answer?

dgb
Dirt Full Roller

Total posts: 70
posted March 04, 2005 12:35 PM  
If traction was constant, which it probably isn't, you would gain rpm. starting from 82 rollout and 6250 rpm, changing tires alone would put you at about 6050 rpm - speed being constant. Changing tires and going to 4.10 gears would jump you up to about 6600. If you are spinning the tires alot now and the hoosiers hook better, it might be what you need, but looks to me like the gear jump would more than offset the rollout difference. I think my math is right on that. dgb

Speedway65
Dirt Freak

Total posts: 344
posted March 04, 2005 01:28 PM  
What if we were only turning 6100 with the old setup?How would that work out?And yes with the street tires we are very traction limited,so i think the Hoosiers will hook up alot better!

racer17j
Dirt Forum Champ
Total posts: 5390
posted March 04, 2005 04:25 PM  
So what does 1' change in tire size do to RPM?

dgb
Dirt Full Roller

Total posts: 70
posted March 07, 2005 11:51 AM  
the relationship is linear- meaning if you know by what percent you increased or decreased the rollout, you'd increase or decrease your rpm by the same percent. So if you were at 82 rollout and went to 83, just divide 82 by 83 and get .988 -multiply that by your old rpm to get your new rpm.

Speedway65
Dirt Freak

Total posts: 344
posted March 07, 2005 12:31 PM  
Thanks for the help everyone.

    

Back to the Archives