Building a motorized bike from the frame up?


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12:14 AM
Jul 24, 2008
Alright guys, so I just picked up a new mountain bike frame (really nice GT frame) and am going to transfer most of the hardware from my working mountain bike (Royce Union) onto it. Basically the silver GT frame is much lighter so its going to be a road bike, and the white bike is going to be the frame for the motorbike.

Is there anything I should buy that needs to be beefed up before installing everything? I'm going to run a jack-shaft from the get-go, so I'm thinking maybe 3-5 speeds on the back casette with some trigger shifters instead of the grip shifters that are on the bike already. Are there any beefier rear derailleurs I should look into getting? Should I keep the front suspension fork, or transfer that to the other frame?


My MB experience is only a month or so long with only 2 days riding my new ride. I am pretty experienced with road bikes and in the last 2 years, single speed and fixed gears. With that, my experience has shown me that on a MB, I'm busy enough with the clutch and throttle and I don't have no time for gears. I'm running a 42x16 which is good for getting my 58lbs going before I let out the clutch and it would be a low enough gear to limp home if I had to (that day is gonna suck). get some nice wide Nitto bars-with shifters it's gonna be busy.

btw. I am using the single speed conversion kit from Performance bike-it has a nice tensioner and the spacers and cog fit on the common freehub.

edit: I guess the jackshaft changes everything eh, you have to have gears then
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I would keep the front suspension. Your rear derailleur should be fine as long as you shift gently. Due to the multiple chains and freewheels there is a little slack in the drive train. When you shift and get back on the throttle too quickly the engine can free rev for a split second gaining some momentum and then all the slack is taken up and it can jerk your rear cassette causing bent axles and damaged rear freewheels.
It looks like you have a pretty good quality GT Mountain Bike frame that will need almost all new parts on it. You can make a great bike set up for the road but it will never be a real road bike compared to what is sold as a road bike. 26X1.5" tires on light rims will be quick but I would stay with a mountain bike 26X2" tire maybe a slick. Do you have any parts for the GT? The bars and seat post are definitely not stock for that frame.
Nope the GT was given to me for free (we've got a really great bicycle salvage yard in Atlanta that runs off donations and volunteer labor) since its too big for 99% of the population. I'm 6'9" and they're both huge bikes but I dont have the funds to go buy a nice road bike. Trust me, I really want my friend's massive Cannondale road bike that fits me like a glove (he's 6'7") but that one's too much money.

Thanks for the input guys. The only reason I was thinking of swapping the entire 21spd setup onto the GT is just that 7 gears in the back seems like a little overkill for the motor. I'm trying hard to be able to complete both bikes for under $500 after all's said and done and have a nice road bike to ride too and from school and a motorbike to ride around town and to work.
So what are the MB laws like in ATL? Around here I have to constantly watch my six at anything over 15 mph. It'll push my 265 lbs up to 30 mph or so and still take me up a short 3-4% grade at 10 mph, so to me it doesn't seem worth the hassle of getting it to shift.