Feedback on build plans

inshanity

New Member
Sep 3, 2021
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Greetings everyone,

I'm planning my first bike build that will be used only for the following:

Mission
This bike will be used for remote, unmaintained trails that have very steep sections. Steep segments with no runway, so geared for high low end torque, slow top end speed. Many fallen logs and other features that require lifting the bike, so as lightweight as possible.

Engine
ZT Moto Phantom 85 from bicycle-engines.com. Seems to be a powerful engine with positive reviews. Looking for something that needs as little modification/upgrade as possible similar like this one.

Frame
TBD based on what engine I select, but a well equipped mountain bike frame.

Questions
What sprocket size would you recommend? I'm looking to go as big as possible. I used to do 2 stroke motocross so I'm familiar with the risks of flipping over BTW. I will be riding weight forward for sure.

Best source for aftermarket products like chains, sprokets?

Suggestions for a frame?

Thanks in advance!
 
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Dec 11, 2014
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Tucson
Oddly mountain bike frames rob a lot of power. This is going to sound very odd but without spending a ton of money a beach cruiser frame and a suspension fork with the biggest tires you can get to clear the chain (probably 26x2.5) will be the most bang for the buck. Have done over 200 builds and the exact motor will pull substantially harder in a cruiser frame as opposed to a mountain frame. It's in the engine placement and angle of the chain. When I entered the hobby I spent months not wrapping my head around why all the cost is no object race bikes were built on these horrible cruiser frames. Well the simple answer is they are not being pedaled and the power transfer is coming from a different angle. If you have the ability to cut the down tube out of a mountain bike frame and replace it with a low curved tube from a cruiser then that would work but makes less sense.
 
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Sidewinder Jerry

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Dec 19, 2011
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Oddly mountain bike frames rob a lot of power. This is going to sound very odd but without spending a ton of money a beach cruiser frame and a suspension fork with the biggest tires you can get to clear the chain (probably 26x2.5) will be the most bang for the buck. Have done over 200 builds and the exact motor will pull substantially harder in a cruiser frame as opposed to a mountain frame. It's in the engine placement and angle of the chain. When I entered the hobby I spent months not wrapping my head around why all the cost is no object race bikes were built on these horrible cruiser frames. Well the simple answer is they are not being pedaled and the power transfer is coming from a different angle. If you have the ability to cut the down tube out of a mountain bike frame and replace it with a low curved tube from a cruiser then that would work but makes less sense.
Speed is fine for those who have a need for speed. However, many are like me and have a greater need for comfort. Therefore suspension systems is a must. I personally use suspension forks and a suspension seat post.
 
Dec 11, 2014
621
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Tucson
I understand what you mean. I'm not recommending those frames for speed though. Just for power transfer. I understand many people really dislike the styling and I never liked it myself. But there is a profound difference in power transfer when you get the motor down in the position it is on a cruiser. Which will make the difference of pulling up a hill or not, difference in miles per gallon, and long term wear on the internals.
 

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
1,507
343
83
59
Rockwood, TN
I understand what you mean. I'm not recommending those frames for speed though. Just for power transfer. I understand many people really dislike the styling and I never liked it myself. But there is a profound difference in power transfer when you get the motor down in the position it is on a cruiser. Which will make the difference of pulling up a hill or not, difference in miles per gallon, and long term wear on the internals.
I use a triple chainring shift kit with a rear rack mount. Reduction range is 66.79:1 to 16.25:1; this enables me to do things with a 33cc engine that much larger engines can do.
 
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Dec 11, 2014
621
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Tucson
Oh got it. Yes you are running a much different set up. Those as you know take their own skill set to get right and you are out of my knowledge base on that one. I have done mid mount large 4 strokes with jackshafts but not the kind of build you have.