That doesn't sound very hot for an inrunner, since the main heat source, the copper windings, are attached via a good thermal pathway directly to the shell.
The best way to reduce temperature is to make less heat, and with heat in the copper increasing by the square of current, a relatively small reduction can pay big temperature dividends. Your can reduce the phase current the motor sees with a simple reduction in gearing, made more simple if your motor runs through the gears (ie accelerate using a lower gear). The motor draws current up to the controller limits based on load, and it sees a lower load pushing the same weight using a lower gear ratio. If your controller is programmable, then lowering just the phase current limit can be very effective in heat reduction.
To be sure that the heat isn't being caused by going to too high rpm (the iron side of the heat equation), go for a ride accelerating softly and then cruise for a while at high speed. If the motor still gets hot, then it's either not getting enough ventilation or you're running at an rpm that's too high. Using something to deflect more air toward the motor can be effective. What you want at the motor shell is maximum air velocity and turbulence. Also check the temp of the motor shaft relative to the motor shell. On an inrunner the most temperature sensitive thing (the magnets) are attached to the output shaft via a good themal connection, so if it's as as hot or hotter than the shell, then you're running in risky territory.
As mentioned above, attaching cooling fins with a good thermal connection to the motor shell will help cool the motor better, because it increases the effective surface area of the motor shell, and the more surface area you have, the more heat can be dissipated at a given temperature differential between the motor surface and the outside air.