Final Gear ratio?

[JJJ]

I might be crazy but I was thinking if I mark a tooth on my clutch bell and a spot on one of my wheels and then line them both up at the top, can I find my final gear ratio this way by comparing clutch bell revolutions to one revolution of the wheel?

[Adanmtxt1]

Not really. That measurement would take into account tire rollout, and there is a chance that the differential would allocate different torque to one wheel or the other when rolling the car. Drivetrain slop / slack would also be a factor that would throw off your measurement even if you wanted to consider rollout.

RCCaraction has an on-line calculator for determining all the gear ratios (including final drive) that you would want, but I didn't immediately find it. Perhaps someone else could help! :)

Welcome to RCZ, though! :D :wave:

[Duster_360]

Don't know why this is hard to find, took me a little to find it.

http://www.radiocontrolzone.com/cars/calculator.asp

Need a lot of infor to fill it out, should be able to find it in your manual. May have to chase data online. Basically FDR is (spur/pinion)*(diff ring gear/diff pinion)*(trans driven gear/trans drive gear) = FDR. If you have a 2 speed (or 3 for that matter), you'll have a fdr in each gear, but the FDR in top gear is considered "the" FDR.

For a stock Emaxx in 2nd gear, this works out like this (66tspur/18tpinion)*(37t diff ring gear/13t diff pinion)*(31t 2nd driven trans gear/18t 2nd drive transgear) = (3.67)*(2.85)*(1.72) = 17.99 ~18 FDR

There is a lot of room for error to try to do it on the vehicle, had to be precise with angles and portions of turns. Calculating it is easy if you can find the gear sizes involved.

[JJJ]

Thanks for the help guys.

[Grant Tokumi]

I might be crazy but I was thinking if I mark a tooth on my clutch bell and a spot on one of my wheels and then line them both up at the top, can I find my final gear ratio this way by comparing clutch bell revolutions to one revolution of the wheel?
That is a perfectly valid way to get an idea of your final gear ratio or FDR. It does not consider rollout. And I assume you're aware that it would be an approximate method.

Its also a very good method to validate FDR calculations made with the linked calculator. Numbers are just numbers. Anytime you can validate numbers with real life checks, it gives you a lot more confidence in your answers.

[JJJ]

I feel like such a dummy. I went back and looked in my manual and there is a section with all of the clutch and gear combos giving you FDR. I am using a 14 T clutch bell with a 54 T spur on my MGT and I came up with an approximate FDR of 30:1 (30 being my clutch and 1 being my wheel) in first gear. I looked in the book and they have a result of 30.1 etc. for FDR using a 14T and 52T. So I figure my guess might be sloppy but close. I don't know how to lock it into second gear to try the same test but what do you know they gave me those #s to. Thanks for the help guys really appreciate it. I love this hobby.