# Help with gearing



## msave (Nov 1, 2008)

Hi everyone. I know this question is vague without knowing much about the track, but I'll do my best to describe my situation.My son was running a losi xxxt, with a castle sidewinder and 5700kv motor.Castle said use highest spur available with a small pinion. We ran a 90 spur,16 pinion. He was doing allright, even though the motor is way too much for the track, we had the transmitter on 35 out of 120. He didn't make the A yet, but couple of 2nd and 3rds in B.Track is high grip, med size,off road clay. You gotta run slicks, with wd, or goof off. Set up another roller with a GTB and a 13.5 SS with sintered rotor to run stock. We tried 90/16-then we went to an 82/18- too slow, got faster with an 86/18. But it just don't seem right. Any body got any ideas, good starting point, anything to help???
Thanks for any info.


----------



## CClay1282 (Jan 5, 2006)

I know that with 13.5 on a medium sized track i run a 78/26. Now that is with a t4 which has a 2.6 internal ratio (i think).


----------



## msave (Nov 1, 2008)

Thanks Clay, anybody else, c'mon guys give me some feedback!!


----------



## suprcop67 (Sep 12, 2006)

i agree with clay. i raced a b4 on a medium track with loose dirt and i ran a 13.5 with a 78/28 and it was pretty sporty and the motor was barely warm


----------



## msave (Nov 1, 2008)

Are you guys gettin enough torque with that 78, and is that why the pinion is so much higher. My local buddy at the hobby shop was talking like 86/19 or 20; or 88/19.When I had the 82, he wasn't clearing jumps that well. I had a 18 pinion though. My buddy said thats like starting out in 4th gear. Comments?????


----------



## CClay1282 (Jan 5, 2006)

I noticed that the motor picked up power and speed when i went up on the gearing. Wierd i know, but thats what i noticed.


----------



## nitro4294 (Oct 15, 2004)

*I am fairly new at brushless and in what little time I have had with them, I have found out that they have a wider power band. Meaning, they have more torque in lower rpm range and seam to be able to hold that power through out the full rpm range.
I am running a B4 on dirt oval and have been able to gear it 3 to 4 teeth higher that a similar brushed motor.
With a 19turn brushed I was running an 87 spur with a 25 pinion (9.04 FDR), now with a Novak 13.5 brushless, it's a 78 spur and a 25 pinion (8.11 FDR). I probaly could even go up a couple more teeth on the pinion but the thing is plenty fast enough as is.
Motor temp is the best way to figure out gearing on a brushless, with that gearing, 8.11 FDR, it comes off the track at 125 degrees after a 4 minute run.*


----------



## rccar306109 (Feb 16, 2009)

I run a 54/80 64pitch at my dirt oval with a 13.5. kranzels terminator. lighter car than most thats why I can gear it so high. its based off a b3.


----------



## CClay1282 (Jan 5, 2006)

rccar306109 said:


> I run a 54/80 64pitch at my dirt oval with a 13.5. kranzels terminator. lighter car than most thats why I can gear it so high. its based off a b3.


What is the internal ratio on the trans?


----------



## suprcop67 (Sep 12, 2006)

on my sons custom works gbx intimidator with a 2.40 trans running on a 285' runline track we started out running a 69 spur and a 33 pinion, it sounds insane but it was what it needed.


----------



## msave (Nov 1, 2008)

Well we tried an 86/20 with better results, he actually had to turn down the transmitter. Temp was about 110-120. Might try a 21 in practice, any ideas, what about 84/22. Guess I'm on my way, just gotta keep on tryin.:thumbsup:


----------



## CustomWire (Jan 12, 2009)

good thing to do and learn is this .. was told to me when i started and works great .. 

goto local store get a notebook .. form there write it all down ...

so u have it and can use it all the time .. not all go by it but its here if u wish .. 

tire Dia times 3.141 = divid that by ur spur = times that by ur pin and divid that by trany ratio .. be it 2.6 or 2.4 so on ...

for exammple ... 3 * 3.141 = 9.423 dived by spur 9.423 / 88 = 0.1070 times by ur pin 0.1070 * 21 = 2.24 now divied that by ur trany ratio say 2.6 ... 2.24 / 2.6 = 0.86 
this is your roll out meanin the in inchs how far it goes to go one round on tire to the motor .. if i remember i just do the math lol ... but gives u ideas and write them down and you knwo what works or what way your goin 
and for gear ratio pin and spur ratios only spur divied pin = so 88 / 21 = 4.19 pin spur ratio 

Bigger pin = more Top end 
Smaller pin = more Low end

Top is Speed .. how Fast ... Low is Torque .. how Quick 

Bigger spur = more Low end 
Smaller spur = more Top end

i could be wrong .. please let me know if so ty 
good luck and happy Rc'ing


----------



## msave (Nov 1, 2008)

I think your right, that I know for sure about the pinion and spur, I heard higher spur+more torque: higher pinion=more speed. But, I am gonna right down the formula for rollout. What I need to understand is rollout itself, and what effect turning and what about offroad. I know they use rollout alot in oval, but I guess I just need that part explained by someone. Like, what if it is .86 and what does that actually mean and do for you. Thanks guys, you've really been helping me grasp this, just need a little more.
Thanks


----------



## CClay1282 (Jan 5, 2006)

Rollout is how far the car moves forward for each revolution of the motor. So if it is a 2.1 rollout then when the motor turns one revolution the car would move forward 2.1 inches. We use it alot in oval. Mostly on dirt you use FDR which is final drive ratio. To find that you divide the spur by the pinion and then multiply by the trans ratio.

(spur / pinion) X Trans

So i run a 78 spur and 28 pinion with a 13.5 on my local track with a t4.

So 78 / 28 = 2.786 X 2.6 = 7.243 FDR


----------



## msave (Nov 1, 2008)

I guess that the FDR would be like in Nascar, a final gear ratio of 3.5 would be faster in the top end, as a 4.10 would have more torque and less top end. Is that correct, or am I assuming wrong???

So with your formulation with my 86spur and 20 pinion in a losi xxx-t, my FDR is 11.18, from previous posts that seems higher, than what everyone else is running.


----------



## CClay1282 (Jan 5, 2006)

You are correct. The lower the FDR number is, the more speed. The higher it is and the more torque you get.

I dont know what the trans internal ratio is on the xxx, the t4's have a 2.6 tranny. If you were to put those gears on a t4 then the number you came up with is correct.

That sounds awfully undergeared. I would at least try a 24 pinion.


----------



## msave (Nov 1, 2008)

Maybe I'll try that, or should I jump down to an 84 spur?? Looked up my losi and it has a 2.43 diff. gear and idler gear. Would that mean a 2.43 internal gear ratio??


----------



## CClay1282 (Jan 5, 2006)

2.43 sounds about right for the losi's. I would try like an 84/25 if you have it and see what that does. You may be able to gear up from there after running and checking motor temp.


----------



## msave (Nov 1, 2008)

Thanks Clay, I'm gonna try that in practice this week, along with a couple other things.:thumbsup:


----------



## CClay1282 (Jan 5, 2006)

Sounds good. Post back on what you find out! Just watch the motor temp, try not to go over 140 or 150.


----------



## CustomWire (Jan 12, 2009)

know its a few days old .. but dont forget the notebook .. notebook .. notebook.. keep them notes no mater how good we think we can remember .. we also forget things .. when you start learning more as you go along your mind overloads on gear ratios and such and you will forget a lot ..


----------



## msave (Nov 1, 2008)

Thanks, gotta get that notebook, he ran his fastest time and lowest cons with a 86/21. 20 was 2 jumpy, 22 was too slow for him. He felt comfy at 86/21. Still gonna keep playin'. Bought about 10 pinions in the last 2 wks. LOL!!!


----------



## CClay1282 (Jan 5, 2006)

Glad you are getting it worked out!


----------



## msave (Nov 1, 2008)

Yeah, thanks to some help from some unknown friends on hobbytalk!!!!!!:thumbsup: Thanks everyone will keep u posted!!!


----------

