Question about sprocket tooth count - first build

[cheesegeese]

The bike I'm planning to mod is the Gravity BaseCamp 29 DLX24 from bikesdirect. It has 29 inch wheels and a 21 inch frame. I've heard conflicting answers from people online about whether a 36 or 44 tooth sprocket (the only options that come with the kit) is gonna be better for my needs. The kit I'm planning on getting is a BT100. Its essentially gonna be purely for fun and fooling around, so I just want to go as fast as I can. I am 6'2 and 185 lbs. Which sprocket should I get if my only goal is fun? Also, what speeds would I be expecting?

 

[DAMIEN1307]

Your barking up the wrong tree if that is an aluminum frame bike...MB's are not that user friendly to aluminum frames, that is why you will see experienced builders going with steel frames for their builds.

 

[Sidewinder Jerry]

What's more important than going fast is being able to stop. Make sure you have a good braking system before being concerned with investing into getting more speed.

At 185 lbs you aren't considered a heavy rider for these engines. So the next question is do you have steep hills to contend with 20%+ grade?

Running a 44t on a 29" tire would be similar to running a 40t on a 26" tire. Running a 36t on a 29" tire would be similar to running a 32t on a 26" tire.

To use a 32t on 26" tires usually requires engine mods be done to improve performance and no steep hills. So unless you're also wanting to do engine mods I suggest using the 44t if you're a flat lander and possibly getting a 48t-52t if you have steep hills to contend with.

Last of all, many of us here aren't big fans of aluminum framed bicycles. When it comes to motorized bicycles most of the old timers like myself prefer steel frames.

 

[Chainlube]

Have some 50cc fun.

 

[francisjohn]

The bike I'm planning to mod is the Gravity BaseCamp 29 DLX24 from bikesdirect. It has 29 inch wheels and a 21 inch frame. I've heard conflicting answers from people online about whether a 36 or 44 tooth sprocket (the only options that come with the kit) is gonna be better for my needs. The kit I'm planning on getting is a BT100. Its essentially gonna be purely for fun and fooling around, so I just want to go as fast as I can. I am 6'2 and 185 lbs. Which sprocket should I get if my only goal is fun? Also, what speeds would I be expecting?

@Sidewinder Jerry - hit the nail on the head

You don't want to run smaller than a 36T on a 26" as 1) Due to gear ratio and 2) These engines don't have the torque to pull a 32T or 28T. Using a 32T on 20" is different than 10/32 on a 26"

I understand wanting to go fast, but it isn't what you want to base the build off of. When I first started, I wanted something fast. You only get torque or speed. I would rather have torque than speed because it doesn't matter when it takes awhile to get to that higher speed. I run 10/40 and tried 11/40 which is similar to 10/36 and it was awful. I had no low-end, and couldn't ride at lower speeds. I had to go over 4,500RPMs just to make the ride comfortable.

I'd suggest going with a 40T. 36T isn't great unless you have wide and open roads. I live in a city and 11/40 wasn't sustainable. I sold the 11T front sprocket to a buddy after four miles.

You can't calculate speed correlated to sprocket size. You can only figure out how many RPMs you need to hit a certain speed based on front/rear sprocket and wheel size (not including riders weight and flat ground/up hill. You can expect 6,000-7,000 RPMs out of box. Don't believe the people who swear on a 66cc/69cc they're turning over 10k RPMs.

I would not suggest a 36T. I'd run a 40T if I were you. You don't want to lose your low end. I was a speed demon and realized the value in low end torque especially up hills.

 

[Sidewinder Jerry]

You can't calculate speed correlated to sprocket size. You can only figure out how many RPMs you need to hit a certain speed based on front/rear sprocket and wheel size (not including riders weight and flat ground/up hill. You can expect 6,000-7,000 RPMs out of box. Don't believe the people who swear on a 66cc/69cc they're turning over 10k RPMs.

Did you say calculate???

Speed Formula:

(RPM × Wheel Diameter × π)÷(1056 × Total Reduction) = MPH

RPM Formula:

(MPH × Total Reduction × 1056)÷(Wheel Diameter × π) = RPM

 

[Heavyload]

Yea, those Fred Flintstone
stops are ruff at high speed.