I'm sure I'll be corrected if I'm wrong, but I think the 1:1 ratio really only comes into play if you are trying to figure out your current gears and don't know where to start. Then you drive down the road with your tranny in the correct gear for a 1:1 ratio (normally 4th in a 5spd -- manual or auto, 3rd in a 4spd auto, 5th in our JK 6 spd, etc) and observe your rpms. Note those rpms and use it on the chart.

For us, since we (normally) are sure of our axle ratios, we can just go look at the current ratio and find our tire size to find the rpm that we're looking for.

For instance, 4.11 (closest to the 4.10 of our axles) on 32's shows 2805 rpm. So, go to the new tire size, 35's, and go across until you find the closest rpm to 2805 to maintain the "same" feel, acceleration, etc (4.56 shows 2845... that's the closest you'll get to 2805). If you want a little more power, acceleration, etc., then go for 4.88's or even 5.13's.

Does that muddy up the water a bit?

 

With 5.13's and 35's my speedometer is about 4 MPH off accorging to my GPS

 

4mph at what speed?

10mph?

20mph?

60mph?

 

in the 55-60 range. Never really took exact note as I used the GPS as my speedometer but it is close enough to keep you out of trouble with the man

 

Brent,
I got the Accupro if you ever want to have your speedo dead on. Worked great for me.

 

Doing some quick calculations (I may be slightly off here)

If you had 4.10's and stock 32's you should be about 2368RPM at 55MPH
If you swap to 5.13's and 35's at the same RPM of 2368 your going 48MPH

That is a difference of 7MPH at 55.

To actually go 55 with the 5.13's and 35's you would have an RPM of 2709.

That's not too much of a difference but it's more then 4MPH, you also have to consider that the factory speedo is off by up to 10%, so in reality your indicated speed is probably even further off.

 

Chris, Thanks for the offer......but I actually like it being off. As time goes by, my odometer logs less miles than I have actually accumulated.

I believe it is close to 4 mph off, really don't think it is 7 as you stated the speedo may not have been right in the 1st place. But none the less I just use my GPS if I am wanting to hit an exact speed and the speedo has been close enough to keep me out of trouble so far.