FDR question
 

hi! i have a question about FDR for touring car. internal ratio is 2.0 and i have 96 spur and 48 pitch pinion final drive ratio is 4.0 and i have 98spur and 49pitch pinion final is 4.0. both has the same FDR whats the difference for both or is it the same? thanks!

Although the FDR is the same the feeling is little different on low speed. You need to check it at the track.

edit: deleted my post to avoid confusion... I noticed I have misunderstood the question :)

There is such a small difference between those spurs that you'll most likely never notice any real difference on the track. Big V. Small spur gears with same FDR has been debated for years and it comes down to several things: slight handing changes because of changed CG of the car by moving the location of the motor (but usually it is noticed with really big differences in the size of the spur sort of a "Duncan" sized SPUR and a "Parker" Sized SPUR) and some efficiencies in better gear mesh with bigger gears. There are some valid arguments about changes in rotating mass that would affect acceleration, but in a touring car the pinion and spur are a relatively small proportion of the total rotating mass of the car so that the effect would be very very minimal at best. IMO most other claimed effects are just placebos. (Sorry I'm from San Antonio and couldn't resist the NBA pun). GO SPURS GO!!!

+1 for Thomsva re mixing pitch and the number of teeth, but bornox in his question is changing both the spur and the pinion (98 sized spur gear and a 49 pinion) to keep the same FDR so that the only different is the size of the gears being used.

From a mechanical standpoint the ratio is the ratio. As stated it is easier to set the mesh. From a pure mechanical side the larger the gear the closer it comes to a straight line and this increases efficiency. The step we can take in our cars is small and the location of the motor is probably the biggest change.

+1 on the ratio is the ratio

+1 on the motor and even that amount of change is limited by the design of the motor mount to just a few mms in most touring cars (or at least the ones I'm familiar with) and in some cases further restricted by the motor itself (and I'm thinking of my ORCA motor with that big flange around the motor shaft that protrudes into the motor mount).

thanks guys! one last thing the temp of my motor is gonna be the same if i use 96/48 or 98/49?

Outside of a labratory any meaningful measurment in difference is motor temp is tough due to the number of variables that are bound to change such as ambient temp, grip level, gear mesh, etc. Assuming you are using the same FDR the temps should remain stable but if they are off a few degrees be careful attributing that to a change in gear sizes.

What he just said plus how you drive the car and how much you brake. My motor temps vary by 10 -20 degrees throughout the race day and I don't change anything on the car.

There is theoretical differences and practical differences, in this case there will be very little of the former and none of the latter!

If you were comparing a light weight 64p set of gears vs a heavy 32p set with the same ratio you *might* notice the difference! but not with what you are looking at.

The comments about motor positioning and balance are valid, but not in this case either - you motor would be moving by about a millimetre. Picking up tyre debris and dirt will make more of a difference.

Having the gears you do means you have a set of spares in case you strip them at the track essentially :)

thanks guys! i appreciate ur opinions about FDR.

But your comments about confusing pitch and the number of teeth were totally correct.

All great answers guys.

Wow, this sure got technical. I would have just said everything would be the same, lol