XXX-T: starting point for gearing?

[Big Wig]

I just finished building my new XXX-T and it's almost time for the track test!

BUT, I don't know what pinion size to start with. I am running a Speed Gems 14 turn double and my track is fairly tight with a lot of jumps and bumps. Some suggestions on pinion gear size would be very appreciated :D

thanks
Jay

[BadRacer]

If your running it with the kit spur (88 tooth) id put a Losi 18 tooth 48 pitch pinion on there. Get a Losi pinion to match up with the Losi spur.....they work really good and you can hardly hear any noise at all!

Take a piece of paper and put it in between the spur and pinion and tighten the motor down.....the paper should come out easy.....this works well when wanting the right gear mesh. Take your finger and put it on the spur and move it back and forward, there should be a tiny amount of play and i do mean tiny.

[Gutter Ball]

I'm running 88/22 in one and 84/18 in another. I dunno which one is faster though :) Race day starts in 10 hours too...can't wait!!!

[SirSpeedy]

18

[Nairb]

I would personally start with a 17, but gearing tends to be on the conservative (low) side at my track.

[Gutter Ball]

Okay, on the straight aways..the 88/22 is faster! But, going over the bumps and through the S turns, the 84/18 is waaaay faster. I'm gonna try 87/23 next weekend. I need more speed in my buggy though. I do okay through the turns and stuff, but once we hit the straight aways..I get burned :/ For a B2, is 81/19 okay with a Reedy Firehawk? I thought it was slow, so I swapped the Reedy for a Green Machine 2.

[Nairb]

Dude, you're geared WAY too high for any motor in that truck. Go down to 18/88 or 17/84 or risk burning up your motor.

[BadRacer]

Nairb is right.....you are way over geared! Losi says to use a 18 with a 14 turn mod, and i think 21 with a stocker. Show me up if im wrong.

Right now im running a 19p/84s with my GM3. It seems to be working really well and im happy with the gearing.

With that kind of gearing you will sooner or later burn up your motor. Thats some stress on the motor id try and avoid.

Keepin it Real
BadRacer

:cool:

[Nairb]

Just a fair warning, BadRacer, I burned up my second GM3 with 17/84 gearing, which is lower than what you're currently at.

[Gutter Ball]

Whew, thanks for the warning guys!! Okay, I'm running totally spec on my Losi trucks. 88/22 and 87/23 are too high? Yah, you're right...88/18 is the recommended gearing for the XXXT. However, for my XXT the recommended gearing is 88/22. So, I should leave my XXT at 88/22...and gear down my XXXT to 88/18? Now if I want more top speed in my XXXT, is it okay to use a 19 or 20 pinion, or is that pushing it? I know the formula for drive ratios, what's a good one for a track with a VERY long straight away, 2 hair pin turns, 2 moguls, 2 table tops and built on grey/yellow clay? Thanks for all the help!

[Railman]

Gutterball, I sense that there's a little confusion on why the buggy is geared taller(higher, lower reduction number)) than the truck. It's the difference in diameter and circumferance of the tires, along with the truck weighing more, & more friction in the truck tires than in buggy tires. There's ABOUT a 2 point difference in final ratio between truck & buggy. Hope this helps.

[nsane]

Really gearing isn't magical. What it comes down to is running a lot of practice laps changing gears after every couple of laps to find what is working best for you, your driving style, the track etc.. Basically as long as the motor isn't cooking, if it runs and has the power you want when you want it.. life is good :)

[Railman]

Gutterball, & All else: This is a perfect example of why it's important (less confusing) to use the overall ratio when gearing. We're looking at 3 different vehicles with 3 different transmisions & trying to draw a conclusion on what gear to run. Gotta use the trany reduction to evaluate! The B2 trans is a 2.41, & the XX is a 2.19. They take different pinion spur sets for the same final ratio, even though they are both buggys.

These are for a med rpm 24' stock motors such as a Paradox:
For a B2, B3, or XXX buggy (2.41 trany):
Overall ratio should be around 9.40
Example:
81/21 x 2.41=9.30 (close enough!)

For XX (2.19 trany):
86/20 x 2.19 = 9.41

For a XXT, XXXT, & T3 you need somewhere around a 11.40 with a Paradox type motor.
XXT (2.60 trany):
84/19 x 2.60 = 11.49

XXXT & T3 (2.41 trany):
86/18 x 2.41 = 11.51

Bottom line is it's better to use the final ratio when trying to compare diferent vehicles & motors.
A P2k will pull 1 to 1 1/2 teeth more on the pinion than a Paradox.
A Rage or GM3 will need to drop 2 teeth from
a Parodox.
A Firehawk is fairly close in gearing to a Paradox, but won't be as fast.
An MVP's gearing depends on how it's brushes are cut. From what I've read they run somewhere around a Paradox's gearing with stock brushes & more like a P2K with square cut brushes. Does any of this make sense, or is it just complicating things more? Please add your opinions :rolleyes: :)

[ 05-22-2001: Message edited by: Railman ]

[Gutter Ball]

Yep, I'm a BIT confused :) Thanks railman! I did a bit of searching and found the recommended gearing for a stock motor in a B2 is 81/27!! I was getting smoked on the straights using an 81/19. I'm using 81/25 now. Thanks for all the input, I race with 3 other guys and I'm the one that knows the most(scary eh?) so I wanna learn!! I'm gonna try 87/18 in the XXXT(don't have another 88 at the moment.) Later all!

[Gutter Ball]

Okay, that makes waaaaaaay more sense!!! We've just been asking people "What spur/pinion do you recommend?" and they just tell us. No one mentions final drive ratio! BUT, I'm not 100% sure what the drive ratio is. Is it how many times the pinion has to turn to get the tires to make 1 full rotation? If that's correct, a higher drive ratio = more top speed and a lower one = more acceleration, right? Just to rearrange your formula...if I know the spur I want to use, I can say "88/Desired Drive Ratio = X, X * trany ratio = pinion size" From my basic (very basic) knowledge, the closer the spur/pinion sizes are, the greater the top speed. All else being the same 88/18 will accelerate faster than 88/22, but 88/22 will have an overall better top speed. Am I getting yet? :) The ratios you recommend, are those for equal accel and speed? Whew, a crash course in gearing! Thanks for your replies, I'm sure they're helping lots of us newbies!

[Railman]

Gutter Ball, I think you got it! One of the things that confuses people is that a bigger ratio number is refered to as a lower gearing.... and a smaller ratio number is refered to higher gearing. Just think of it as the number of times the motor revolves for 1 wheel revolution, & it's easier to remember. Or another way to look at it is as the reduction number...a big reduction number = less rpm at the wheel. Whatever works for you to keep it straight. Yes you can just solve for a different gear, it's just simple multiplication & division.

Those ratios worked well for me & my 3 boys & were tracked on a spreadsheet printout that we kept updating with performance notes from racing different motors on different tracks & cars/trucks. Worked well for us, but I would still say they are just good starting points because of so many other variables. We rarely run a motor hot as some fast guys will, but we were always competetive on power just the same.

[BadRacer]

Hey Niarb i don't know why everyone is blowing their GM3's. Iv put this GM3 through heck and back and its still kickin strong. I changed the brushes and springs when i frist got it and never ran the ones that it came with.

People at my track think im plum out of my mind for running a GM3 in the stock pro class. Oh well they may think im crazy but im always atleast a lap ahead of em. Iv heard all the stories about the GM3 and untill the day mine blows up you will see me turning tho's lap times likes its a walk through the park. :D

Later