215 or 225/60 is what you're looking for for 60s to compare with the 205/70s. math indicates 220.77/60. Ken Ames Quoting farna@xxxxxxx: > A good site for gear/tire calculations: http://www.4lo.com/ > That's why I don't have 60 or 65 series tires on my Classic. I think they > would look better, but would knock me out of the cruising rpm range I want to > be in. I could drop to 3.31 gears (instead of 3.55) and stay in the same > range with a 60 series tire instead of a 70 series. That's one reason I > wanted 3.31 gears -- could use the 65 seriess and gain a few mph at my target > cruising rpm and look a bit better! > > My tire size: 205/70, 15". Diameter (avg.) is 26.3" > 205/65 15 is 25.5" (avg.) > > w/3.55 gears and 205/70 tires I'm running ~63 mph @ 2000 rpm. > Drop to 205/65 tires and speed drops to 61.1 mph @ 2000 rpm. > I'd need a 3.44 axle to maintain the same speed, or a 24.5" diameter tire > w/3.31 gears (205/60-15 is ~24.7", and would be 63.5 mph @ 2000 rpm). > > On the 4Lo site don't forget to enter 1 for the transfer case ratio (1:1) and > enter your high gear ratio. I used 0.70 for the OD gear in the AW4. High gear > in all three speed autos and most three/four speed manuals is of course 1:1. > You can figure speed in any gear if you know the ratio. I used "average" > (avg.) and "approximate" (tilde [~] means approximately) for tire sizes as > there is a little variation among manufacturers. Should be +/- about 0.125" > though. > > > On May 12, 2005 Jim Boone wrote: > > > On May 12, 2005 Jim B wrote: > > > > > A: You also have to take into account for the size of tires on your > vehicle > > > when calculating gear ratios. Too many offroaders wonder where their > power > > > went when they slap oversize tires on. I know my own power dropped a lot > > > when I put 33" on (from 26") but going to 3.73 helped that. When I switch > to > > > AW4, I'll probably have to drop down to 4.10 to keep adequate power. > > > > Great point; I did figure in for 25" tires when I posted a day or two ago. > I think that the Jeepers have more to gain/lose than we do as going from 26" > to 33" or more is quite a difference. With a passenger car, and esp an older > AMC that you're going to use 14" or 15" wheels, it's more of a fine tuning > tool. > > > > I think the rear end we're talking about in this instance (with an OD trans > aka 200R4) is right at 3.54; however, if you wanted/needed to go a little off > of that, you could change the size of the tires. > > > > Jim Boone > > Mims, FL > > > > ============================================================= > > Posted by wixList Archiver -- http://www.amxfiles.com/wixlist > > > > > > > > > > > > . > > > ============================================================= > Posted by wixList Archiver -- http://www.amxfiles.com/wixlist > > > > > >