Hello All, I was wondering what your opinions are on this question, and a few others.

Is running say a Spur/Pinion combination of 60/18, 75/20, and 88/27 all the same thing? These all come out to around 8 for a final drive ratio using my present set up. I run a Novak 4300/10.5 and according to Novaks web site they recommend starting out around 8 when using a 10.5 on a 2WD buggy.

Specifics:

I run a Losi 2WD buggy as an EDM with a 2.43 transmission. We are running custom works street trac tires which are around 3 inches in diameter. I am running a 4300/10.5 with a sintered rotor and a GTB speed controller. I use 5000 MAH lipo batteries. The track we run on is a banked outdoor dirt oval with about 5 to 6 second laps to give you an idea of the size.

My current set up is not close to the recommended Novak starting point for a 10.5, which is not the real factor because my car is reasonably fast. I attempted to go smaller on the spur, and use whatever pinion I needed to maintain my current FDR and first time out it thermaled. I went down on the pinion with the same spur and it thermaled again. Needless to say I went back to my original set up, and it was fine and the motor came in after a 5 minute run at around 130 degree.

Any ideas why changing the spur/pinion set up while not changing the actual ratio would cause this when I had no problems with the original set up?

Can you go too small on the spur gear? My belief was the smaller the spur even with the same ratio, you would get a slight amount of increased acceleration because you were rotating slightly less mass, and it would take less revolutions of the spur to get one revolution for the tire.

I have overheated the motor a few times and it has a permanent STANK smell to it although it still seems to run OK. I recently purchased a new bullet and would appreciate anyones suggestions they might have on what would be the best starting point to gear my car.

I am not extremely knowledgeable about this kind of thing, and could be way off from where I should be for best performance. I am open to any ideas, and would appreciate any comments.

Fabian

Fabian - your ratios are not quite the same and the resulting rollout (distance traveled per motor revolution) is significantly different. The 75/20 is the lowest but the others are not that high either.

The fact that the motor thermaled may just be a coincidence - if the motor is an older 4300 with the sintered rotor upgrade and it smells after it thermaled, it may have fried something inside. I had one that acted that way and there wasn't anything that would bring it back - but it still ran ok as long as I didn't push it.

I was running 81/28 (2.8 internal) with a 13.5 (black rotor) when I was down to Silvis a week or so ago and the motor didn't even get warm.

The bottom line is to watch the temp and keep it down below 140.

Jim

Way undergeared
170ft. dirt oval outwest the gear ratio with cw.rubber tires, novak 10.5,sintered rotor is 4.6 to 4.75,has'nt matter direct drive or gbx thats the ratio however you get there,btw. spur \pinion size have no effect on power\speed\etc.. gear ratio is a gear ratio period,only difference beeing location of motor in car or ability to get proper rollout\ratio in a given car,be it dd or gearbox
motors come off 140 after a good clean 5 minute run lap time 4.7's to 5.2's, surface bite,weather,time of day alters overall run. but thats the number that we have found works well at our track.
i run a 4 cell version gtb,no fan,heatsink,etc.. speedo never hits 100*

I worked out your numbers SLOTS and it was around 8 for a FDR. KOZ is suggesting I should be in the 4.6 to 4.75 range as best as I can tell for a FDR. I tell you I never get this undergeared/overgeared. Taller/shorter gear stuff right as far as what it actually means to my question.

What specific FDR should I be looking for to maximize the 10.5 with my set up?

Thanks.

Fabian

The info on novaks website that you got you info is for suggested offroad gear ratio,which doesn't apply to your application-dirt oval.

Thank you for the input guys. A big Thank You to you KOZ as you have helped me understand things a little better.

Fabian

60/18X2.43= 8.099 FDR - Middle Ratio - 1.116 Rollout (CW Tires)
75/20X2.43= 9.113 - FDR - Lowest Ratio - 1.034 Rollout
88/27X2.43= 7.920 - FDR - Highest Ratio - 1.190 Rollout

I agree with KOZ too - we were both undergeared but that was the best I could do that night. The middle of his FDR range (4.7 - 5.2) on rollout would be about 1.88. I would have a hard time getting there and still use a gear cover - the biggest pinion that will fit under mine is 28 so it would need a 56 to 65 spur and I'm not sure I can go that small either.

I'm not sure there is enough bite at Silvis to carry enough speed through the corners to use that kind of ratio but it is the right direction to go.

See ya in a couple of weeks.

64 pitch guy's ,on one of my gearbox cars i only needed 2 pinions and 3 spur gears to get the ratio from 4.20-5.30when i was testing to find the correct gearing for our track with the 10.5 stuff. we ended up with 4.60-4.75 depending on where the timing was set
Btw-undergeared can build to much heat as well..

Slots, That 75/20 was a mistake on my part. I was attempting to put out 3 ratios which were all fairly close using extremely different gears to get to around 8 as a FDR.

Thank you KOZ and SLOTS for your input. It has been greatly appreciated.

I will be off this Saturday July 5th. My next Wednesday off with be July 16th. Hopefully I will see you at the track slots.

Fabian