High tension

Belt drive vs cog drive in a live axle application

- MARK ORTIZ

I was looking at the pic of the DSR racer in your column in the February 2020 issue of Racecar Engineering and one thing about it struck me – they were using a cog belt drive. Cog belt drives are seven to 10 per cent more efficient than a chain drive, so at first this appears to be a pretty good way to improve power without adding engine stress.

However, when I contacted Gates Application Engineering with my specifications for the small lakester my son and I race at Bonneville that uses a motorcycle engine with chain drive, they recommended a belt tension of over 700lbs to ensure it stays engaged!

That level of tension almost surely requires some sort of swing arm suspension be used at least on the drive side of the engine, as seen in the photo of the DSR suspension, or some way that ensures the belt is maintained under constant tension (and alignment) regardless of suspension travel.

I think the belt drive is probably the main reason the illustrated DSR is using trailing arm suspension and not a more sophisticated suspension design.

The thing I was concerned about with using, say, a pair of equal length trailing links is their length has to be exactly the same length as the belt pulley centres as even a slight difference could change the belt tension considerably. A very substantial idler pulley would be an absolute requirement to compensate for any possible change due to suspension travel, and also some sort of lateral location control to keep the pulleys vertically in line to keep the belt flat across them.

THE CONSULTANT