question about gearing

[inphiniti]

sup guys.. alright well im just starting to learn how to do things myself by experimenting.. i know it sounds weird, but i just completed my first motor swap... i had a 19x2 Team Orion Havoc in my HPI Sprint.. i just finished putting in the same style motor, just a 17x2..

question is, i want to possibly change or adjust some gearing in my car, how would i go about this and what would i need to do? i know teh guy who used to work at the LHS that i was friendly with said that all i have to do is change the pinion? this true, if so please explain

also, could i possibly have some suggestions as to how to gear it and to what specifications? thanks guys!

[rocknbil]

Very broad questions. :D So here's a broad answer.

The gearing is altered by the pinion gear OR the spur. It's the mathematical ratio between the two combined with the gearing in your transmission (which is set and can only be changed with major transmission revisions) that determines the final drive ratio.

But you don't care about this. All you need to know is that smaller pinions or larger spurs equal more low-end punch and a lower top speed, and larger pinions or smaller spurs equal less low-end punch and higher top speed.

There is a link to a calculator on the front page of RCZ if the numbers DO interest you.

The advantages and drawbacks of gearing affect several important things. Lower gearing will get you out of corners faster and make you overall faster on a concourse type track, and higher gearing will give you the top speed you require of high-speed racing, such as ovals. If your gearing is too high on a concourse, you'll be slower out of corners; if it's too low on an oval, you'll top out too soon and be left far behind.

This also affects the stress and strain on a motor. If you are geared too high for a particular motor, it's going to put a lot of strain on it and overheat. While most people don't care whether they toast a motor if it means winning a race, when a motor gets TOO hot, it loses a lot of power. The lower the turns on a motor, the higher the RPM, but it has progressively less torque with less turns, which is what you need for getting out of corners.

That's really a VERY general description and leaves a lot to be explained, but for the purpose of your move from a 19 to a 17 turn, it should tell you that you probably want to gear down a tooth or two on your pinion, unless you're not going to be doing a lot of slowing down and speeding up, as in an oval race.

The way you change the pinion should be self-explanatory, remove the pinion with a allen driver (allen wrenches are horrible for this, they don't get it tight enough) and slip a new one on, aligning the set screw with the flat side of the motor output shaft, then loosen the motor bolts to adjust the pinion against against the spur, leaving just a little "looseness" to the gear lash. You can fiddle with a piece of paper between the two to get the gear lash set right, but I find that frustrating. You should have just a little "wiggle" between the pinion gear and spur, just enough to tell it's not locked tight against it.

Generally you won't have to change your spur size to change gearing unless it won't reach the pinion.