Need a math check for Tire/Gear/RPM calculation

I am trying to decide on gear ratio to tire size combinations. I put some numbers in a spreadsheet and calculated RPM for 26 and 28 inch tires at 55 and 120 MPH for a few gear ratios.

If anyone has one of these gear ratios and tire sizes, please let me know if my numbers are good.

Here is the table:
Tire Dia. Gear ratio Speed RPM
in inches (MPH)
26 3.8 55 2702
26 3.91 55 2780
26 4.11 55 2922
26 4.56 55 3242
26 3.80 120 5895
26 3.91 120 6066
26 4.11 120 6376
26 4.56 120 7074


28 3.80 55 2509
28 3.91 55 2582
28 4.11 55 2714
28 4.56 55 3011
28 3.8 120 5474
28 3.91 120 5633
28 4.11 120 5921
28 4.56 120 6569

Thanks,
Jamie

 

Rpms will probably be a hundred or two higher with an automatic transmission due to convertor slippage. Might be a little higher than that with a high stall convertor.

 

http://www.ringpinion.com/content/calculators/RPM.asp

this might help

 

RegL404 thanks for the auto comment that is what I was trying to figure out.

mercgt73 Thanks for the link.

Looks like 4.11 wins out over 3.80.

 

Here's the one I use:
http://www.f-body.org/gears/

I run 4.11 with a 26" tire and enjoy it.

 

courier11sec - Thanks for the confirmation. That was the combo I was thinking of. If RPM is'nt tolerable for the street I will use 28 inch radials for to and from the track and occasional cruising and swap on the grippy 26 inch tires at the track.