Suggested Gearing?

[markshelfer]

I plan on getting the biggest 2 stroke happy time engine availible soon, and noticed that the back sprocket is HUGE. So I plan on buying a new sprocket from kings. I want to be able to reach a top speed of 40-45 mph, but still be able to get up those hills pretty well. I was thinking a 32 tooth, is that a good size for what I want? By the way, this will be on a standard 26" wheel.

 

[mickey]

I want to be able to reach a top speed of 40-45 mph

Aiiiyee. Anything around 30 scares me. A regular bicycle has such a short wheelbase and a high center of gravity that I feel unsafe at that speed. Plus, the brakes are barely adequate with that much momentum.

I've run a 44 and a 50 sprocket on a Kings "80". I believe that if you search for ratios on this site, you will find where top speeds have been calculated for various sprockets. 45 mph may not be possible with a HT at redline even with a 32 tooth. You might have to go with a high reving goped type motor.

 

[kerf]

Mickey is giving good advice about bicycle speed. Just try a F.D.G.B. (fall down go boom) at 15 mph them imagine what a 45 mph F.D.G.B. would be like. Bicycle parts are not designed for the stress of that kind of sustained speed.

 

[dave1490]

http://motoredbikes.com/showthread.php?t=6323

 

[markshelfer]

Aiiiyee. Anything around 30 scares me. A regular bicycle has such a short wheelbase and a high center of gravity that I feel unsafe at that speed. Plus, the brakes are barely adequate with that much momentum.

I've run a 44 and a 50 sprocket on a Kings "80". I believe that if you search for ratios on this site, you will find where top speeds have been calculated for various sprockets. 45 mph may not be possible with a HT at redline even with a 32 tooth. You might have to go with a high reving goped type motor.

I tend to go fast on anything I ride. I have hit 46mph downhill without a motor on my mountain bike, you just have to be careful. Goped motors do not allow for much speed because they are very small engines, only around 23cc's. They do have larger models such as the GSR40, and Pro 60, but these are very pricey and do not mount on bikes well.

 

[kerf]

I too go fast down hill sometimes, it is fun. The biggest danger with going fast much of the time is what we share the road with. Becoming an integral part of a Buick grill could make for a bad day.

 

[mickey]

I tend to go fast on anything I ride. I have hit 46mph downhill without a motor on my mountain bike, you just have to be careful.

Vaya con Dios, my friend. I've gone fast, I just get tired of hanging my heiny out over the rear tire.

 

[markshelfer]

thanks for all the feedback, but does anyone know what size would be ideal for my purposes?

 

[Alaskavan]

A search for Calculator turned up this:
http://www.motoredbikes.com/showthread.php?t=7711&highlight=Calculator

 

[Steve Best]

Mickey has great advice.
A FDGB (Fall Down Go Boom) gets much worse at speed with impacts and body grinding slides without motorcycle riding gear.

That said, my 26" wheel bike breaks 40 mph with the 44t sprocket at about 9500 rpm.
It would not do it stock, it required some porting, head modification, port matching the exhaust, and a short pipe muffler.
Top speed with the stock motor and 44t sprocket was about 45 KPH and it would not do steep hills.

I am sticking with 44t because this region has steep hills and I do slow trails that taller gearing would make difficult.
I would suggest no taller than 40t if you have these conditions as well.
Plan on doing engine mods to make this livable.

One advantage of bicycle speed is that it reduces the closing speed of cars coming up behind you.
One problem is that even with 30mph speeds in a 30mph zone, cars still feel they HAVE to pass you.

Steve