Diff ratio and drops ratio
Turbo Mini Forums

A fella at work who used to be in a drag bike team told me that they used to make the gearbox run faster than the engine. This made it easier to turn which freed up power and there was less chance of it breaking.
Its the equivalent of running a lower diff in a Mini with 1.04 or 1.08 drop gears to achieve the desired diff ratio.
What are your thoughts guys?

Paul

I seriously doubt it!

yes, except i think you'd be looking at 0.9 ratio drops (can't be arsed to find calculator)

I read that they used this trick on the focus WRC car too.

Ive got .9 drops fitted now which slows the gearbox. Its only turning .9 of a revolution to the engines 1 revolution.

Paul

Edited by paul wiginton on 3rd Mar, 2008.

I seriously doubt it!

Ahhh im thinking the wrong way then, been a looong day...

This 'freeing up power' is 110%, pure classic BS unfortunately...

The advantages to overdriving the transmission are that the torques are lower. This means (for example) that the loads on gear teeth are less, the dynamic rating on bearings is lower, and synchroniser loads are less.

Of course, it does mean that you need bearings happy at the higher speed, that the gear flanks retain an adequate film of oil (assuming dry sump) and that the synchroniser PV (pressure / velocity) values aren't exceeded.

The dry-sump reference above, is used becuase you (we) aren't actually dry sump. Churning losses of the gears in the oil are pretty significant, and the faster gears are spun, the more the losses. If you overdrive them, this is even worse, as you are losing mechanical advantage to turn them at this higher speed...



All said and done - the advantegs to overdriving an A-series are more than likelly to outweigh the negatives - but only as far as reducing the bearing loads NOT in making it 'easier' to turn...

I thought you'd be the man to know TD. I also knew that you'd baffle me with science.lol.
Is it worth it then if your changing diff ratio anyway then?

Paul

I seriously doubt it!

I'd say no - unless you are breaking gears and bearings.
Why change somet that is working fine?

Fair enough cheers

Paul

I seriously doubt it!

ive knoewn about the slowing the box down same as bikes have, supposedly reduces losses as dave pointed out,

does anyone know if the minispares centre do overdrive idlers for there timkin roller drops.

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

What ratio Carl?

Paul

I seriously doubt it!