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Old 02-27-2005, 06:51 AM
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Default Mixing Front and Rear Axle Ratios

[img]images/graemlins/tongue.gif[/img] If you Gearheads can possibly stand yet another post on mixed front/rear axle ratios, let me add this one: [img]images/graemlins/crazy.gif[/img] IF the tire sizes are different front to rear, you CAN mix the axle ratios. What you do is use this formula: TURNS PER MILE X AXLE RATIO(rear) = TURNS PER MILE X AXLE RATIO(front). If you go to the tire shop and stick your nose in the catalogs it will show the TURNS PER MILE of each tire. If you multiply the turns per mile by the axle ratio you will actually get the driveline RPM at 60 Miles Per Hour. Obviously, the RPM of the driveline (front) must equal the RPM of the driveline (rear)
[img]images/graemlins/crazy.gif[/img] [img]images/graemlins/smile.gif[/img] [img]images/graemlins/tongue.gif[/img] You can also use this to determine what gear ratio you must go to in order to compensate for going to a larger tire diameter all way around. If you had tires that were 627 TURNS PER MILE and went to tires that were 583 TURNS PER MILE you would just take 627 X Original Axle Ratio (say 3.54) and THAT would need to equal 583 X New Axle Ratio...call it x. [img]images/graemlins/smile.gif[/img] So......627 X 3.54 = 583(x) [img]images/graemlins/crazy.gif[/img] You solve for (x) just like the teacher taught you to do in Algebra. By doing it that way, you put the engine RPM back where it belongs after the big tire/gear swap. [img]images/graemlins/tongue.gif[/img] The little-used TURNS PER MILE info is a HUGE help in working out new ratios, yet I see so few people actually use it. Tire shops.....good ones that is.....use it to prevent shredding the differential if they have to replace just one tire on a customer's car. Of course they have to estimate what effect existing wear might have on the TURNS PER MILE of the remaining tires. [img]images/graemlins/tongue.gif[/img]
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Old 02-27-2005, 09:20 AM
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Default Re: Mixing Front and Rear Axle Ratios

[img]images/graemlins/goodpost.gif[/img] Dave. I also remember a couple guys here over the years that went different ratios because they ran different tire heights. It's also very popular in the mud drag crowd. From what I've read they want the front wheels spinning faster to help "pull the steering". But thats a whole different story.
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