Sometimes I have to shake my head when different drive systems are proposed. I shake my head because a drive system is designed to transfer the drive torque of the engine to the wheels, yes that is true, but how much torque is the clincher.
Very often we think that just routing a system together and getting the two to join in rotation is sufficient. In a large number of cases, it isn’t just a slap and go system.
The reason is that the engine output must be matched to the rear wheels with the correct overall output ratio. If not the engine will do the following:
1. Smoke the clutch
2. Smoke a belt
3. Stall the engine
4. Won’t Climb Hills
If you recall from some previous articles, the rule of thumb for sprocket or belt drive sizing is that the size of the sprocket or pulley for the driven section must be at least 85% of the diameter of the wheel size. Secondly, the drive sprocket on the engine must be at least 10 to 12 teeth (or in the case of the pulley) 1 ¾ diameter at a max. This rule of thumb will give you the needed ratio for good overall performance.
Unfortunately with a vertical drive engine, using a twisted belt requires a couple of things:
– Center Line-Pulley Line Up
– Sufficient Space Or CC distance between Engine Shaft and the Final Drive
What this often requires is that the engine be dropped so that the pulley is in line with the rear axel. Additionally, the engine needs to be brought back or in front of the axel a large distance (12 to 20 inches in some cases).
This presents a problem because on two accounts, it either eats up valuable real-estate and crowds the drive, making a long and unwieldy go kart, or it puts the engine back too far on the go kart causing it to have very poor CG placement which redounds to very poor steering performance.
In case you think I am against twisted belt drives, I am not, what I am against is a twisted belt drive that doesn’t perform, that is ill-designed, or not matched well to the go kart. A properly designed twisted belt drive will work just fine, if the ratios are set up correctly.
Getting the set up so that it fits into a go kart and does not cause other problems, like CG placement, steering problems (insufficient weight on the front wheels), tracking problems, clutch engagement problems and so on….that can be a very large challenge to get all those ducks in a row.
The twisted belt drive is a viable system, it just depends on how you set it up.
For more information on vertical engine drives visit the Go Kart Building 202 series.