pinions
I had the same problem in the Uk, 17.5 is not a class we run so had to tool up with spurs and pinions.
72 and 74 spurs are not easy to buy.Anything smaller wont fit. Also pinons 58 60 and 62 are like hens teeth.
The largest cobination i can fit on my car is 72 spur 62 pinion 64dp. Any thing larger and the motor wont fit.
43.5 tyres 72 spur and 58 pinion is rollout of 110mm even that isnt enough on limited profile. Drove the car full throttle and steered round. Motor came off at 32c.
Pinions and spurs were available from stormer hobbies. HTH