Main two reasons for straight cut gears:

1) Less side loadings, which means they can take higher loads without punching the shaft out the of the case etc (pulsars do that a lot on helicals for example)

2) MUCH cheaper to produce, especially in small numbers, so when you are racing and want loads of different ratios, you wouldnt be able to tool up for helicals even if you wanted to.


I only ever use straight cut cogs when helicals wont handle the power if its a roadcar.