Sprocket ?'s (does size really matter?)

Ravenshurst

New Member
Oct 8, 2008
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Tucson
Some friends of mine got me interested in building a MB, so I bought a frame & an engine & some other bits & pieces, and now before I have even really gotten started, they are both telling me how much better their bikes run with their new 36T sprockets. I am not interested in being the fastest MB, but they both tell me that the vibration is so much less with a smaller sprocket. True or false? What about torque? There Are a lot of hills here in Tucson. Also, does the smaller sprocket adversly effect engine life? All remedial ?'s I know, but this is my first MB.
Thanx
Gonzo
 

Dave31

Moderator
Staff member
Mar 1, 2008
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Aztlán, Arizona
Hello my fellow Tucsonan, Welcome to the forum :)

Yes a 36t will have less vibration...I have never had a problem with vibration on my bike.

I ran a 36t and then went with a 44t. I figured with a 20mph speed limit, I might as well have a little torque to get up some of Tucson hills and mountains. With a 44t sprocket I can hit around 33mph but usually ride around between 20-23 mph.

I have been everywhere with both 36 & 44t sprocket....I like the 44t sprocket better.
 

Saddletramp1200

Custom MB Buiilder
May 7, 2008
1,439
40
48
Houston, Texas
Welcome to the forum! The smaller the sprocket the faster you go. I am playing with the idea of a drag bike. Yea 0 to 40 in about 20 yards. A fuel tank the size of a beer can. Wheelie bar? rotfl (c) With Fairracing as a neighbor, you have it made!
 

Finfan

New Member
Aug 29, 2008
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Tucson, AZ USA
Another Tucsonan. Yeah! Were getting the makins' of an outlaw motorized bike gang together here! ^5 Anyway so far I have had no problem with the 44 tooth gear although I haven't tried any of those killer peaks like the 22nd St. overpass. :rolleyes:
 

saetta

New Member
Jul 29, 2008
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Central Missouri
I run a 44T with my 49cc. I briefly used a 40T. I noticed some lost of pep on the low side so I went back to the 44T were I max at 29MPH on a level road. The 40T maxed at 31.
 

Ravenshurst

New Member
Oct 8, 2008
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Tucson
Thanks for all of the responses, guys! I really appreciate the input. This is my first MB, so I am really a tyro. My fellow Tucsonans will know the hills I am talking about when I say I work @ River & La Cholla. 15 miles 1 way. And now it's c-c-c-colddddddd! I don't really care about top speed (although I have been day-dreaming about a dragbike, Saddletramp) but I do wonder about the smaller sprocket and engine longevity. Any input? Thanks again, everyone.
 

Dave31

Moderator
Staff member
Mar 1, 2008
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Aztlán, Arizona
What the heck happened? One day the low is in the 70's the next it's in the 40's...us Desert Rats don't like that rotfl

I have gone up Mt. Lemon, and A Mt. with the 36 & 44 and many other hill's. The 44t does much better.

As far as longevity, I've got 5 years and well over 4,000 miles on my China girl. I think more has to do with how hard you ride and push your motor. If you are running wide open all the time your motor just won't last as long.
 

Ravenshurst

New Member
Oct 8, 2008
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Tucson
well, those are some SERIOUS hills! In some states, they would be considered real mountains, lol. Yeah, this 4 months of winter s**ks, but at least the temp is going back up a little next week. Thanks for the input on longevity. I will probably just use the 44T that comes with the kit for awhile.
 

corpuscruiseking

New Member
Dec 5, 2008
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Corpus Christi
Just a theory...but as the smaller sprocket should indeed turn at a higher rpm, one could conclude that the increased rpm's may shorten the life of the engine; however, if you simply avoid the top end, there should be no difference at all. That being said, why not stick with the 44 and utilize the better tourqe value? I run a 49cc with a 44 tooth sprocket and I top out at 33-34 mph. Just as a thought............once you have gone 30mph on a bicycle......and want more!!!??? It might be time to look at another hobby? Be safe, my fellow brethren of bicycles!!!!
 

jasonh

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Jun 23, 2008
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Longmont, CO
Just a theory...but as the smaller sprocket should indeed turn at a higher rpm, one could conclude that the increased rpm's may shorten the life of the engine; however, if you simply avoid the top end, there should be no difference at all. That being said, why not stick with the 44 and utilize the better tourqe value? I run a 49cc with a 44 tooth sprocket and I top out at 33-34 mph. Just as a thought............once you have gone 30mph on a bicycle......and want more!!!??? It might be time to look at another hobby? Be safe, my fellow brethren of bicycles!!!!
You will get a lower motor rpm with a smaller sprocket at any speed compared to a larger sprocket. This theoretically would help out motor life as the rpms won't be so high all the time. However, you do lose torque. I'd stick with the 44T since AZ has that 20mph limit.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
The motor rpm will drop for any given road speed with a smaller (less teeth) sprocket.

The top speed may or may not increase due to several factors...these engines only make so much HP, ad that's where you get the mph from.

Most bikes (if you are lucky) will hit a top speed somewhere in the mid 30's no matter what sprocket you use.
 

offroad

New Member
Dec 31, 2008
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Connecticut
Someone had theorized that a slower engine lasts longer as RPM wears out the engine. In theory true. Why?:

1) Each revolution is a microscopic wear cycle. So more revolutions on friction bearing surfaces equals more wear.
2) The chemicals of combustian build up and will corrode the components. More revolutions causes more chemical exposure cycles, and more wear.
3) Metal fategue stress, as the engine is pushed faster, the stress on the metal increases proportionally. psuh to the limit and eventually physical stress will break a component through warping, that increases friction, thus heat.

****

One thing no one mentions is that you can increase or decrease both your front and rear sprokets. Right?
 

jasonh

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Jun 23, 2008
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Longmont, CO
One thing no one mentions is that you can increase or decrease both your front and rear sprokets. Right?
You can, but I don't think I've seen any drive sprockets available in different sizes. I know Dax has one, but it's the same amount of teeth I believe...it just allows you to run a different size chain. So you could do it, you would just have to source a new sprocket.