DC Motor, Torque vs RPM
A motor comparsion chart like below would give you a rough idea of the torque vs speed characteristic.





The above chart is from the following Q&amp;A where you can find more useful info:
How to control DC motor speed by motor driver with PWM input? Asked 9 months ago Active 3 days ago Viewed 915 times




You might also find the above post's Appendix B - PWM Controlling Speed of JB37 Geared Motor particularly useful.



BTW, geared motor is usually much slower, but much more powerful, which I think is what your need for your bike.  In other words, the gears are worth your extra bucks. :)