Road Speed and Ratios

[Shane Noone]

Hey guys, Just looking for a rough idea based on others experience with known ratios.

If I say I run a 205/70/15 rear tyre but I am unsure of my 4th gear ratio ( close ratio ) and unsure of my Ring and Pinion ( most likely 4.125 or 3.875 ) but my road speed at 3500 RPM's in 4th gear is 55 mph ( on the speedometer driven by 145/80/15 front tyre ) then has anyone run close to this road speed in 4th with a 205/70/15,  that knows their ratios's..??

Thanks

Shane.

[adrian]

4.125 and 1.21 gives you close to 55 mph, a 3.875 would be about 58mph. Its all pretty close though... and there are probably a ton of combos that will get you close to that mph

[Shane Noone]

Ok, thanks. Yeah found a gear ratio calculator programme that I can plug my " knowns" into now to get some idea on my ratios :-)

Cheers.

[ALB]

You're speed is fast by about 4% (a 145/80 is approx 24" tall vs a 155R at about 25") so don't forget to factor that in.