FDR - How to work out

[zackmitchell]

Hi Guys,

Trying to work out final drive ratio's for an MI3.5 and thought it was a combination of motor pinion and spur gear divided, but when looking at the provided set up sheets and using this formula its a very different answer to what the set up sheets are saying the FDR is.

Can anyone shed some light on my blonde moment?

Thanks in advance

Zack

[coolcars782]

Spur gear / Pinnion Gear * Internel Ratio (Gearbox/Transmission Ratio) = Final Drive Ratio

e.g.

For a b4 which i only know

81/19*2.6= 11.08


Schumacher Mi3.5 PRO transmission/gearbox ratio is 1.8

so will be

Spur/Pinnion*1.8 = FDR

[zackmitchell]

Cheers for the quick reply,

That seams to make the FDR come out right from the set up sheets.

Zack

[jono83]

You also need to consider rollout( wheel and tyre diameter)

[discostu]

roll out isn't so important on a tc running rubber tyres foam tyre racing is a little different as tyre diamters change so the roll out will change.

stu rand

[zackmitchell]

Where does the rollout come into it?

Will be running schumacher yellow minipins indoor on carpet.

[discostu]

roll out is a way of working out gear ratios by the amount of times the transmission rotates to how many times the wheels rotate. but dont even bother just use the interal ratio to work out gearing your best bet is to find out what the quick guys are using and start from there and fine tune. ive never used roll out to aid gear ratios with rubber tyres and 3 carpet wars the vega cup 2 stcc championships and numaruse natinal a finals says i must have been doing somthing correct.

stu rand

[jono83]

If you imagine if you had to cars indentical in everyway including the gearing the only difference being the overall diameter of the wheel and tyres. The one with bigger wheels would travel further than the other one with one full rotation of the wheels. Like said above it's not a major detail with rubber tyres only foams as you can change the diameter to suit.

[discostu]

to work out internal ratios of a car you divide the layshaft pully into the diff pully for example 39/16=2.4375-1 hara edition cyclone 40/20=2.0-1 or if its shaft drive divide the gearbox pininon with the crown wheel. once you know this calculation you can very easily compare gear ratios between differnt manufactures.

stu

[zackmitchell]

Cheers for all your advice, will put it to good use, unlike a former member

Cheers for that link Dazzler, your a legend!!!

Zack