The max. cadence depends on the max. rpm.
A 36V 4000rpm or a 48V 4000rpm handle a max. cadence of about 90
If you run a 36V 4000rpm with 48V battery the max. cadence rises to about 120
If you run the 48V tsdz2 with 36V battery the max. cadence drops to about 70
With OSF and fieldweakening you can rise that max. cadence a bit, but less effective and not as high you want.
So for a higher cadence it would be better to use a >52V battery with 48V 4000rpm Tsdz2
Your options are:
- Replace battery (48V-52V)
- Replace bare motor (36V)
- Ad a DC-DC boostconverter
Imho the most clean and cost effective solution is the advice from
@Blacklite to replace the bare motor and reflash the firmware for a 36V motor.
A DC-DC boostconverter is maybe cheaper but need to be wired and packed in a waterproof case with cooling.