pinion/spur gear question about 4S Lipo converted Revo 3.3

[corneileous]

Hey guys, just to take out a lot of the guess-work of figuring out what a good spur/pinion combination is now that I have a new motor mount that allows for more options, what's a good combo? What do you guys use?

I started out with a base 2.5:1 ratio using a 15T pinion and a 38T spur and although its good, my converted Revo 3.3 on 4S just doesn't seem to have the speed as my pretty much stock Maxx running the same battery and it feels like it has a little bit too much torque because without the wheelie bar and even with 500K weight diff oil in the center diff, it will flip itself over on it's top if you're not careful. Plus, even with fairly hard running in warmer weather, my motor, which doesn't yet have a heatsink or a cooling fan, will only get up to barely 115 degrees so I'm pretty sure the motor can handle a lot more higher-gear tuning to get some more speed out of it because you would think that even though this truck is heavier, with the Hobbywing Max8 G2 ESC and larger 1/8th scale 2550Kv motor, it should run circles around my Maxx.

I haven't yet ran it yet after doing this because its over a hundred degrees yesterday and today and will be for the next week but yesterday after I put on my new motor mount, I had a 16T pinion that replaced the 15T pinion so according to my math, the 16T/38T combo brought my ratio up to a 2.37:1 ratio from the 2.53:1 ratio it was at with the 15/38T.

If I can find one on Amazon, I'm kinda thinking I'd like to try a 17T pinion with the 38T spur that would raise it even higher to a 2.23:1 ratio. Or, I could buy the 18T pinion I did find, and put that on with my 40T spur and get almost the same ratio which would be 2.22:1. Thoughts?


Oh, and I might add that I run the bigger and heavier 6.4 or 6.5 inch Traxxas Talon EXT tires as well. The transmission is virtually the same as stock except for that it has been converted to forward only and has first gear deleted.

 

[Jerold]

I would stay away from Amazon generic gears, you get what you pay for. It won't hurt your car, but cheap gears break and then you have to buy more and replace them again, and again.

If I can find one on Amazon, I'm kinda thinking I'd like to try a 17T pinion with the 38T spur that would raise it even higher to a 2.23:1 ratio. Or, I could buy the 18T pinion I did find, and put that on with my 40T spur and get almost the same ratio which would be 2.22:1. Thoughts?

Don't over think this, that's my job. It's easy to get caught up in the numbers, but the theoretical numbers and the real world are different and I would use them as an estimate only.

If it's 2.23 or 2.22 it's probably not going to be noticeable. You also have a differential gearing so your final drive ratio with tires is going to complete the picture. The math isn't hard, but there are a bunch of gear calcs out there that include your diffs and tire size already. It's easier than building out a spreadsheet and it will give you the ideal top speed. I say "ideal" because it's in a perfect frictionless, weightless world with perfect batteries. I would dock the speed by like 20% and it should be in the ball park.

For the actual gearing you choose, depends on how you drive and your temps. Or to put it another way I don't know that there is a recipe for it. If it's running cool add more pinion and see how it goes. At some point the motor will start getting too warm or you will start dropping performance.

If it's super cool, you might try 3-4 teeth on the pinion. Then evaluate it again, maybe add a few teeth.

 

[corneileous]

I would stay away from Amazon generic gears, you get what you pay for. It won't hurt your car, but cheap gears break and then you have to buy more and replace them again, and again.

So far, I’ve had wonderful luck with gears from Robinson Racing Products and I can get them on Amazon. I’ve talked to guy on the phone so hopefully whenever he gets some more 39T 2nd gears in stock, I’ll be able to upgrade my second gear, my forward only kit and top shaft gears to his steel ones.

Don't over think this, that's my job. It's easy to get caught up in the numbers, but the theoretical numbers and the real world are different and I would use them as an estimate only.

If it's 2.23 or 2.22 it's probably not going to be noticeable. You also have a differential gearing so your final drive ratio with tires is going to complete the picture. The math isn't hard, but there are a bunch of gear calcs out there that include your diffs and tire size already. It's easier than building out a spreadsheet and it will give you the ideal top speed. I say "ideal" because it's in a perfect frictionless, weightless world with perfect batteries. I would dock the speed by like 20% and it should be in the ball park.

For the actual gearing you choose, depends on how you drive and your temps. Or to put it another way I don't know that there is a recipe for it. If it's running cool add more pinion and see how it goes. At some point the motor will start getting too warm or you will start dropping performance.

If it's super cool, you might try 3-4 teeth on the pinion. Then evaluate it again, maybe add a few teeth.

Since I made this thread, I put on a 17T pinion to spin my 38T spur and after doing a test run last weekend with it, that’s probably where I’m gonna leave it at. Although, I may some day try an 18T pinion just for grins and giggles and see how it likes a 2.11:1 ratio over the 2.23 to 1 it has now.

But as it is now with the 18T pinion/38T spur, I got 48 miles an out of it last weekend but being that I blew my right front tire, I had to abort. I think it had a little more to go but I didn’t feel like wiping out that hard on concrete so I backed out of it.

The next day after that tire (and a couple others that had minor bead separation) had time for the real tire glue to dry- I guess I cleared that argument up about regular super glue vs actual tire glue and after I took out the center diff in the trans, I ran it pretty hard on some rough and little rocky dirt kinda hard and with that combo, I got the motor up to 140° so now that with the new heatsink and dual fans I got, that running it exactly the same, it hit 125° now that it has adequate cooling capabilities so who knows, I might be at my sweet spot because it’s still pretty torque-y and it’s plenty fast for me at 48, probably 53, 54mph max speed. But now I have even taller and wider tires with the 3.8 Duratrax Six Pack MT’s and it still spins them no problem.

 

[Jerold]

So far, I’ve had wonderful luck with gears from Robinson Racing Products and I can get them on Amazon. I’ve talked to guy on the phone so hopefully whenever he gets some more 39T 2nd gears in stock, I’ll be able to upgrade my second gear, my forward only kit and top shaft gears to his steel ones.

Robinson Racing is legit.

It's not to say you can't get good stuff on Amazon, you absolutely can. I would stay away from the generic gears made from monkey metal.

 

[corneileous]

Robinson Racing is legit.

It's not to say you can't get good stuff on Amazon, you absolutely can. I would stay away from the generic gears made from monkey metal.

Oh I know, I didn’t perceive that at all, I was just saying I can get sometimes good stuff- on Amazon….lol.