This is the industries' specification for metric timing belts.
Notice the shape of the belts. And this is the SP belt from the nitro Spider touring car.
There are many forums that said the belts are HTD spec. But as I have noticed in the sp belt, the teeth are not rounded and there are no groove in the middle of the teeth. Therefore, I conclude that the SP belts are actually RPD Spec.
Furthermore, the tough racing belts are STD specs, hence the S3M letters on their belts. Their belts seem soft for a high torque application and the thickness is around 2.0mm and not 2.2mm as in the industries' STD spec. Thus, Welshy, this might be the reason why your rear belt shredded in a 5 minute race.
I am trying to get a quote for these belts from another supplier. Hopefully, their MOQ (minimum order quantity) is lower then the previous ones.