RielTime Racing

Does anyone here change their gearbox ratio for particular tracks or racing conditions? (Not to be confused with Spur/Pinion Gear Ratio or Final Drive Ratio). If so, what gearbox ratio have you settled on most of the time and why? I've figured I can change mine pretty much anywhere between 2.25-1.88. What seems to be most efficient for you? I know there are tons of factors to consider but I thought it would be an interesting, fun topic to discuss.

Currently running 107/36 Spur/Pinion, 2.0 gearbox with FDR of 5.94

a_main_attendee

iTrader: (2)

I wouldn't think it would be an efficiency issue but instead an issue that deals with getting an appropriate FDR for higher turn brushless motors.

I've never changed nor would consider changing my vehicle's internal drive ratio.

RielTime Racing

If you compared a gearbox 36/18 to 34/17 the ratio would be the same, 2.0. Depending on a given course one combo has to have an advantage over the other.

a_main_attendee

iTrader: (2)

Why should there be an advantage?

RielTime Racing

I would think that one ratio would be more efficient on the motor, or better on acceleration, or holding speed for certain parts of the course.

Superkarter

iTrader: (2)

In theory the bigger pulleys will give a slight increase in efficiency due to less belt wrap.

How much of a difference not really sure, probably not enough to notice.

Trips

iTrader: (16)

The 2.0 ratio would have a clear and noticeable advantage.

jbmx4life

iTrader: (2)

I think that you misunderstood.... both examples he gave were a 2.0 ratio, he was just asking which one would be more beneficial for particular applications.

RielTime Racing

Yes, and if you compared Tamiya, Xray, Associated ... they all use different Gearbox/Internal drive ratios.

Trips

iTrader: (16)

I understood completely. He said an 18/36 set of pulleys and a 17/34 set of pulleys both have a 2:1 ratio, but one would have to have an advantage over the other.

I responded that I thought the 2:1 ratio would be the better of the two.

jbmx4life

iTrader: (2)

Trips

iTrader: (16)

All kidding aside now, some might say the 18/36 set of pulleys might have a slight efficiency advantage over the 17/34 due to the belts making bigger radius turns, but there might be a loss of efficiency with the bigger pulleys due to increased friction having more belt teeth engaged than with the smaller set. I have no idea which would work better.

If we're comparing different ratios in the same car, then there are situations where one might prove better. I can think of two cases off the top of my head... You might find that you can't achieve the final ratio you want given pinion/spur availability unless you use a certain transmission ratio, in which case the choice is made for you. In other cases, you might be able to get to your ideal final ratio with either of several pulley ratios, but depending on pulley ratio you might find a spur piniono combo that moves the motor slightly forward or rearward in the car to optimize front/rear weight bias without having to add ballast to the car.

I've never actually gone so far as to change pulley ratio in a TC to tune weight bias, but I suspect some might go that far. I will say that I HAVE at times changed spur/pinion combos in a pan car to keep the same gear ratio, but move the motor further or closer to the rear axle.

RielTime Racing

Wow! That's awesome. Never thought of changing pulley ratio to effect the positioning of where the motor mounts for weight ditribution too. Highly doubt I'd go that far. Keep the posts coming!

Yeah, I'd think smaller pulley would be and advantage for tight, twisty tracks or a need for quik accelerations and the larger pulley for long high speed flow tracks.