spur gear question

[SpeedRacer]

Heres my question. I own a b3 and in the manual it talks about final drive ratios. I have a 12 t double motor and it says a good base ratio is 10.44 to 1. But the catch is it says to do that using an 87 tooth spur gear and a 20 tooth pinion. Now when i told this to an experienced racer he was shocked that they would suggest using an 87 spur gear in the b3, he said that he uses 81/17 spur to pinion and that you never use 87 tooth spur gears in the b3. Can anyone explain this to me, does it matter what size spur and pinion you use as long as it accomplishes the same final drive ratio? for instance could i get the same results by using an 81 t spur with a certain size pinion as i could get using an 87 t spur and just make the pinion the size that i need to get the same ratio??? or will this produce different results?? WHat are the effects of different size spurs? Well thanks in advance.

[XXXER]

WELL, i think that there is some slight difference, but i forget how, the pinion is a pretty heavy thing for the motor to get spinning(since it spins it first) so i say, if you can get a smaller pinion on with a larger spur, go for it

[Nairb]

You are right. The ratios are what matter. The only reason to use bigger spur gears is the possibility of having more available ratios with different pinions. The smaller the spur gear is, the larger the gap between possible ratios.

[SrSpeedy]

Actually,

It is a best to run the largest Pinion and spur possible to achive a desired ratio.

Larger pinions have truer tooth profiles, for instance, to make pinions smaller and smaller the tooth profile gets more and more distorted. Imagine what a ten tooth pinion would look like....it would be so distorted, it would probably not index with the spur in any fashion.

A larger pinion will more efficient, and transfer more power. About ten years ago Robinson had a little section in their ads that explained why they did not recomend pinions smaller than 17T(48pitch) for this reason....

See ya...