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DRR Trophy
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How much if any difference will it change the gear ratio form a 108 1/4 tire to a 109 3/4 tire?


PMWLLC
 
Posts: 7 | Location: At the track | Registered: December 23, 2016Reply With QuoteReport This Post
DRR Pro
Picture of 67TSCHEVY2
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.o1783%
 
Posts: 1231 | Location: middle georgia | Registered: July 20, 2003Reply With QuoteReport This Post
DRR Pro
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The revolutions per mile will change. You can't actually change the gear ratio without physically changing the ring and pinion. I know that you meant what effective change, but it just bugs me when it is referred to as "changing the ratio". Take care. Tom Worthington


If it seems that bracket racing has gotten too expensive for you, maybe you are just doing it wrong.
 
Posts: 1221 | Location: Rocky Mount, NC | Registered: December 01, 1999Reply With QuoteReport This Post
DRR S/Pro
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The difference between those two numbers is all you need to know.

109 3/4 is about 1.4% larger, so you will get about 1.4% more distance traveled for each rotation of the driveshaft.


Tony Leonard
 
Posts: 3138 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
DRR Top Comp
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Hypothetically, if you have a 4.10 gear and went from a 34.5 tire to a 35, the effective gear would be 4.03.
 
Posts: 9398 | Location: Madeira Beach Fl. | Registered: June 12, 2018Reply With QuoteReport This Post
DRR Sportsman
Picture of FootbrakeJim
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What are you trying to figure out with tire rollout difference? RPM change at stripe, or?
You might want to check out this site:
Wallace Racing Calculators


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1029 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
DRR Trophy
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trying to see if it will slow the car down on 60 foot. sorry for any confusion


PMWLLC
 
Posts: 7 | Location: At the track | Registered: December 23, 2016Reply With QuoteReport This Post



DRR Sportsman
Picture of FootbrakeJim
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IMHO, the amount of change in your 60' is usually not going to be a lot for that difference in rollout. But it depends a lot on the converter, and the camshaft/torque curve of your engine. Even tire pressure will affect how much difference you'll see. If you've got a broad flat torque curve, and a loose converter, it may not change a bit. I made a 2" difference in tire height and it didn't change my short times at all, though it did affect RPM at stripe.


Dan "Jim" Moore
Much too young to feel this damn old!!
 
Posts: 1029 | Location: Farmersville, TX  | Registered: December 05, 2002Reply With QuoteReport This Post
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