One last gearing question....

[ImprezaWRC]

If I am running a 22T pinion and a 90T spur, and I dropped to an 87T spur, but kept the same pinion, what am I doing, and can't I accomplish the same thing by merely switching pinions?

[WhoKnowsWho]

By dropping teeth on the spur, you are doing the same thing as adding teeth to the pinion, so you are gearing higher. Normally, that's what you do when going from a hot motor to a bit more mild motor. Also, a spur gear change of one tooth, does not have as drastic an effect as a pinion gear change of one tooth.

[Railman]

Impreza, Some times we change spurs to move the position of the motor, for different weight distribution & handling. To know what happens to gearing do the math. I don't know what vehicle you have but lets say it's an Assoc. B3.
SPUR PINION TRANS OVER ALL
81 / 23 x 2.41 = 8.87
The over all ratio is one rev on the axle = 8.87 on the motor.
To find out how changing gears effects the overall gearing, just divide the spur by the pinion & multiply times the trans reduction.
As far as whether you gear down or up when you change to a faster motor it really depends on the motors. If you had a Paradox & went to a 19 tun mod it might be the same.
However going from a P2K to a 19 mod you would probably have to gear down (higher over all reduction number). If you went from a P2K to a 10 turn mod you would definately gear way DOWN. Low turn mods rev way higher & thats what you gear for, unless you want to run hot, with a short life, like some pros do. Does this help? :)

[ImprezaWRC]

Helps big time, guys. Thanks. But the way HPI has printed out their gear ratio chart, their numbers are very different. I believe they are doing this a different way. For example, my RS4 Rally has a 2.1 drive ratio. Running a 30T pinion with a 90T spur says my gear ratio is 3.00. But, others have told me that it would calculate to 6.9999 or something.

The reason I'm asking is because I've had troubles with motors burning up when taken off-road, so now I won't insert a pinion of any more than 25T. I was hoping that by fine tuning with some spurs, I could increase some speed. But no matter what I do, my speed change is very minimal. but awhile ago, my car was faster. Right now, I'm running an 87T spur with a 22T pinion. But when I moved to a 24T pinion, I didn't notice much of a change. Just wondering if changing my ratios are even worth the effort.

Kind regards,

Impreza

[Railman]

Impreza, HPI is only looking at the pinion to spur ratio. Thats fine when your looking at dfferent motors, tracks etc, for just one car, but you need the over all ratio for working with different vehicles. I am not familiar with the ralley car you have. Are the rear wheels comparable in diameter to Assoc. or Losi buggy wheels? If they are we can look at their over all ratios & come up with a good ratio for yours. All I need to know is the transmision reduction, the motor your running, & spur gear. You might want to re-read my last post a few times & play around with the numbers. Let me know the other info & I can probably get you close. w Akso what is the diameter of the rear tire, rubber to rubber?

[ImprezaWRC]

Okay, my current gear ratio is an 85T spur and a 22T pinion. My tires on both the front and rear are standard 26mm rally tires(touring car size), and transmission reduction, you lost me.

Kind regards,

Impreza