Rear sprocket size??????

harry76 · Jul 23, 2011

Hi, im building this "whippet" bike into a MB. So im going to buy one of those alloy rear sprockets off EBay.

As this bike is built in a "racer" theme id like to get a decent mph out of it, or at the very least: not overrevving at cruising speeds, and i dont mind pedalling a little to get going. The engine is a 50cc.

I havent played with these motors yet so not sure of a good "high" gearing.... so any advice would be appreciated..... cheers

So how small of a rear sprocket should i go??????????????????????

2door · Jul 23, 2011

a 36T is a good all round speed sprocket as long as you aren't climbing hills. It is more of a flat landers choice but will give you the best top end speed for a 26" bike and your engine. If you really don't mind pedaling a little to assist on starts and hills go for the smaller sprocket.
Even better is a 41T which is more like driving a car around in second gear as opposed to the 36T which is closer to high gear in a car. You'll get some differing opinions here so listen to your heart

Good luck, ride safe and have fun.
Tom

biknut · Jul 23, 2011

I now have a 50, and a 80. Both have 26" wheels. The 50 has a 40T, and the 80 has a 36T. Surprisingly both bikes cruise comfortably at about the same speed. Say 28 mph. The reason is because the 50 vibrates less, so it's ok with a little higher sustained revs.

The main difference is at 28 mph, if I gas the 50, it barely has any acceleration and is all done at about 31 mph which takes a long straight to get to. The 80 otoh races from 28 up to about 36 mph. In a pinch you can cruise it at 30 no problem. From there it still has goose, but it vibrates a lot above 30, and I don't like the engine sound..

flatblack · Jul 23, 2011

I just installed a 40t on my 66cc, xchambered, hi compression head motor on a Huffy Cranbrook. She's pretty light. I wiegh in at 161. It feels great all through the power band. The pipe comes on a half throttle which is perfect as it gives you a kick in the butt right in the middle of the power band when you're cruising. A 36t around VA would be a stretch. Just a few too many inclines.

That bike would be great on something between a 36-40t. It'll be a quick one for sure! Hardly any rolling resistance and light as ****! Love it! A great and unique build!

The_Aleman · Jul 23, 2011

I ran various 66s and a 34T on a fat-tire 26" cruiser and street MTB for 3 years.
Top speed 42MPH with easy cruising anywhere from 20-34MPH. Purred at 25!
I also like to pedal, and really I had to with some headwinds and hills.

OP's bike looks fast and easy to pedal on hills. I'd go with a 36T maximum, lean towards a 32-34T.
I really dig that bike!

biknut · Jul 24, 2011

The_Aleman said:
I ran various 66s and a 34T on a fat-tire 26" cruiser and street MTB for 3 years.
Top speed 42MPH with easy cruising anywhere from 20-34MPH. Purred at 25!
I also like to pedal, and really I had to with some headwinds and hills.

OP's bike looks fast and easy to pedal on hills. I'd go with a 36T maximum, lean towards a 32-34T.
I really dig that bike!

Mr President, it sets a very bad example for the children, if the President of the 20 MPH club goes around admiting he's a frickin speed demon.

Could you at least qualify that by mentioning you gave up that evil speed after having a close call with god or something like that so no one gets the wrong idea. lol.

.ride3

The_Aleman · Jul 24, 2011

Hmm?? Did you play football when you were younger? You sure do like to take a ball and run with it lol

The bike I'm speaking of is my first MaB I built in early 2006, the original "Alehauler". I went from 44 to 39 to 34T on that thing, because I lived in North Dakota with a 12-13 mile commute in each direction to work. I needed something that could fight the crazy winds I was experiencing for the long straight 9 mile stretch that was most of the commute. Believe me, I have always spent more time under 30 than over it.

Anyone who rides bicycles for primary transportation can also see the benefit of having a bicycle that can hit the right speed to keep up with traffic at 35, 40 in areas where there are no bike lanes or the shoulder is hazardous and/or dangerous. Besides, to gear a bike to do the easy 20-29 we in the club love so much, we have to build a bike that can do over 30!

PS: I'm a Buddhist

biknut said:
Mr President, it sets a very bad example for the children, if the President of the 20 MPH club goes around admiting he's a frickin speed demon.

Could you at least qualify that by mentioning you gave up that evil speed after having a close call with god or something like that so no one gets the wrong idea. lol.

harry76 · Jul 24, 2011

Yeah it is handy, and safer to have a bike capable of decent speeds, even if you dont use it...... And there is also a massive concrete velodrome not far from where i live and it would be cool getting around that at speed. When i finish ill try and make a video of me riding it there

Thanks for the advice guys..... i might go all out for speed with this bike (not my only one) and get a 32 tooth.

I went to buy one off EBay but they say they dont send internationally until Friday. So i didnt buy one yet. I wonder if i can just buy a motorcycle Renthal sprocket and drill holes in it to suit a MB or is the inside hole too large? .... The advantage of buying a motorcycle sprocket is it would save me a few weeks wait for shipping.

harry76 · Jul 24, 2011

Or maybe because mine is a 50cc i would be better off with the 34 tooth? Maybe ill flip a coin lol

Off the hook performance · Aug 15, 2011

38T Mmmm I'm thinking of using it,,

DuctTapedGoat · Aug 15, 2011

I'd love to go 31T - 36 t I still get high RPMs screaming.

madwolf33 · Jan 1, 2013

i myself just bought two of the 66cc skyhawks. and still have the 44th sprockets. both bikes are huffy 7 speeds. i'm 190 pounds. one will run a easy 26 mph all day long and if i push it it will get to 30. the othere will run 31 all day long and if i push it it will hit 37mph i dont know what the differnts is. where i live we dont have lots of hills but we have wind that blows 35 to 50 mph sometimes and it will stop the bikes in there tracks. i was thinking of going to a 40 tooth on the one bike that runs slower for some reason and see what it does.

Frogster · Feb 22, 2013

If I get a sprocket larger then the stock 44 tooth one, say 48t or 56t. Will I get enough torque to pull a wheelie? Will I get a faster hole shot and acceleration?

My understanding is this:
Lower rear sprocket gears the bikes drive train higher resulting in a higher top speed at the loss of torque and acceleration.
Higher rear sprocket gears the bike lower resulting in a higher torque which means faster acceleration and better hill climbing at the sacrafice of top end speed.

Is this correct?

maniac57 · Feb 22, 2013

I just recently switched to a 41 from the stock 44 (26" NEXT mtb) and it now cruises right in the sweetspot in the powerband. I average about 18-22 and can max out to about 35 (depending on how brave I feel!) It's also flat here and that matters since I'm fat. (and old and lazy)

2door · Feb 22, 2013

Have you ever driven a car with a manual transmission? Think of your bike like that. If you run a bigger rear sprocket it is like driving a car in first or second gear. You have good off the line acceleration but the engine will rev too high for top speed. If on the other hand you run a small rear sprocket, like a 36, it's like leaving a dead stop in second or third gear. It will take some time for the engine to reach its power band which might might require some pedaling on your part but the RPMs will be lower at your top speed which will be higher than if you have a larger rear sprocket.
I hope that explains it for you.

If you've never driven a car with a manual transmission think of putting your gear selector in low range (bigger rear sprocket) and driving the car. The engine will rev high but it won't go as fast as if you put it in drive where it can shift to a higher gear (small rear sprocket).

Tom

The_Aleman · Feb 23, 2013

I've always shifted a pedal bike like a car, in lieu of the clutch I'd just back off about 20 pedal RPM to shift. Every stop, I'd be in first or second gear ready to pedal back up to speed, which for me was 12-28 depending on wind on semi-loaded 7-speed Schwinn cruisers and street-tired MTBs. Road bikes for a weekend blast, 30+ easily.

I found with my 2nd chinagirl (on an aluminum Schwinn 7-speed, Megarange 34T-11T) that gearing em high and pedaling all the way as far as you can will get you to 20+ quite quickly. I ran several rear engine sprockets and settled with a 34T. I personally saw another member with a single-speed pedal bike run sub-29T sprockets and get going just fine by pedaling, then easily cruising 40+!

Pedaling does wonders!

fargokevin · Jun 4, 2016

I also have a question on rear sprocket size how can I get max out put on my bike its a 700c fixie with a 80cc 2stroke . I have the sprocket that came with the bike I think im upward about 40mph . I thought of changing the sprocket to a 10 speed shift sprocket which in theory would give me start power at low speed and also allow me to shift to adifferent gear to increase speed.would this work? I want a higher top end. .trlrl.

sbest · Jun 5, 2016

Until you go shifter, read carefully what was said previously.
If you sprocket tall for speed, you will suffer terrible acceleration and suffer on hills.

It is hard to beat the stock 44t spocket for the best of all worlds.
If your engine is working well, you should see 40mph (I do) and still pull the steepest hill.

40mph is darned fast on a bicycle, faster then your guardian angel flies.
Faster then bike brakes were designed for.
Faster than skin was designed to abrade if the tensioner twists into the spokes.
If things go wrong beyond that speed, we probably won't hear about it from you.
Unless it is bad enough to make the papers.

Steve

Joel Richard Myers · Jan 25, 2019

harry76 said:
Hi, im building this "whippet" bike into a MB. So im going to buy one of those alloy rear sprockets off EBay.

As this bike is built in a "racer" theme id like to get a decent mph out of it, or at the very least: not overrevving at cruising speeds, and i dont mind pedalling a little to get going. The engine is a 50cc.

I havent played with these motors yet so not sure of a good "high" gearing.... so any advice would be appreciated..... cheers

So how small of a rear sprocket should i go??????????????????????

I just recently bought and what I'm guessing is an 80cc Chinese I was thinking of going down to the 28 tooth rear sprocket

curtisfox · Jan 26, 2019

Do you realize this was started back in 2011? LOL! Actual cc of a 80 is 66cc China rating is different.

If it is a 26" wheel 28 tooth will not work, unless it's a shift kit drive. If not a 40 tooth would the smallest you want to start with........Curt

Rear sprocket size??????

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