that was post #1000

What is the gear tooth difference between 23" tires and 26" to maintain the same ground speed?

3 in. of circumfrence is about 1 tooth is gearing. you really can't go by the tire size on the tire. you need to measure the tires with the correct air psi to find out what the actuall circumfrence is or as some call it roll out

Been thinking about your 15-17 gearset recommendation. Watched a few pulls on youtube. One in particular caught my eye. The guy was all over the place spinning tires. He about ran off the track a couple of times and really didn't get that far. After thinking about it, it seems his gearset was too high and a lower gear would give him more control and get him farther down the track. Am I correct in this assumption?

The traction of a tire spinning in dirt should be like a riverboat paddle wheel. A paddle wheel cavitates if you spin it too fast and actually results in a lower speed and less power. A tire should do the same thing in dirt. Or am I having a brain fart.

Wheel speed gives you the ability to get a new bite more rapidly. The down side is it stacks dirt up in front of the sled. There is a Delicate balance between to much gear and not enough gear.

Which is why the 15/17 combo works. Not much difference, but it makes all the difference.


Pulling is probably 40%-50% experience. You just can't be taught that. You have to be able to read the track, know the ability of your tractor...... Racing is the same way. FWIW, I've seen guys with good machines on the track who just didn't know how to drive them. Consequently I've seen guys with lesser machines win just because they were better at what they did, not because they had the better machine. It's a game. The only way to learn how to play is to do it..... Just because you have a good built machine, doesn't mean you'll win.

here's some pulls to watch
https://www.youtube.com/watch?v=MoRzSHiKyN0

usually guys that go all over the place have more issues than gearing

That was great but way past anything am planning. The local competition is running Bosh coils, #30 carburetors, and maybe an 18hp cam and shaved heads but I doubt it. They only beat me by 4 feet, and I was running a 10" hitch height and had the timing set at 16 instead of 22. The engine dropped about 600 rpm at about 50 feet and kept going like the little engine that could out to 100 feet, then the tires dug a hole.

This year was the tire year. Next year I will buy a transmission from Midwest super cubs with a locking shifter and a 15-17 gear set. The following year I'll get the engine built if I haven't won a couple of trophies.

One thing I noticed about the videos is that they backed off on the throttle at the start until they got the sled moving.

4 feet is a LOT.

The tractors in the vid don't have a governor. There are few reasons they don't hold it wide open.....

they are WOT the whole run. We let them free rev at the starting line. they will hit 10,000. but there's no power there so when the tires start to hook it pulls the motor down to where there's enough hp and torque and then it builds RPM back up again.