Diff ratio help

[Niva]

car is currently getting different diffs put in it, lower ratio ones

trying to calculate the difference its going to make but all the online calculators I can find want gearbox ratios etc. and this im not too sure about

car had 4.9 and now has 4.1

[eaglesfandavid]

4.1/4.9 = 84% therefore revs will be 84% of what they were for the same speed?

[Niva]

buitifull, thankyou :)