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Author Topic:   gearing with tires?
rickb33
Dirt Full Roller

Total posts: 46
posted January 20, 2003 11:06 PM
i'm currently running 225/60/15 all the way around on car.3.73 rear with 1.76 trans gear.it runs out of power in the straights(too many rpms).what size should i go up to the change rpms,so i'll have something at the end of the straights.

DMS CEO
Dirt Freak

Total posts: 212
posted January 21, 2003 10:23 AM
I had a printout from summit racing about this very same subject and I lost it. It gave an equation to figure this up...Maybe Jammin can find that and post it in the toolbox...He's probably not doing anything anyway...lol.

Darcy
Dirt Full Roller

Total posts: 54
posted January 21, 2003 05:04 PM
try running a 245/60/15 or 255 on the same rim your roll out will go from say 81 inch to around 84 to 86 inch roll out or just change your ratio

dean_7585
Dirt Forum Racer

Total posts: 88
posted January 22, 2003 06:23 AM
I think changing the tire size is a small adjustment. You need to get close with a different gear and then tweek it with tires.

Smitty77
Dirt Roller

Total posts: 9
posted January 22, 2003 11:29 AM
1" tire size equals approximately 100 RPMs of change on a 1/4 mile track. Larger tire = less RPMs.

c21
Dirt Freak

Total posts: 346
posted January 22, 2003 12:43 PM
If you could make the gearing change by changing tire size alone, this would be the formula to use:


current Rpm devided by desired Rpm
X current tire size = desired tire size.

c21

doubletrouble
Dirt Full Roller

Total posts: 37
posted January 22, 2003 04:47 PM
Hey guys this brings up a question,what about running 14" tires and wheels over 15"?
Wont this help with gearing and 14's are alot cheaper! What is the deal with tire roll sill have not quite figured this one out.I have learned more from this web site then working on pit crews for years.

justin
Dirt Maniac

Total posts: 167
posted January 22, 2003 07:10 PM
doubletrouble, tire roll or "roll out" is the circumference (distance around) of the tire. It is used for stagger measurements and, in this case gear choice. It can also be used when trying to add/lose wedge in the car by trying different tire sizes at the RF or LR (this would be in classes that don't allow weight jacks). When you swap your rear tires out for ones with more roll out it is the equivalent of running a lower gear (numerically) and vice versa. Hope I've helped.

Justin

[This message has been edited by justin (edited January 22, 2003).]

[This message has been edited by justin (edited January 22, 2003).]

fastrack1
Dirt Full Roller

Total posts: 73
posted January 22, 2003 07:40 PM
HEY JUST GO TO THE TOOLBOX ON THIS WEBSITE IT WILL HELP MORE THAN U THINK ALL TH INFO IS RIGHT THERE

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