why Grandma, what a big pulley you have

I have been looking at a lot of pictures of pre-war bikes, Monarchs, Whizzers, etc. & I really like that style of bike. I was wondering though, why all belt drive bikes have such large rear pulleys. Good torque, I suppose, but it cuts waaaaaay down on top speed, correct? Not that I really care so much about top speed with a cruiser bike, but I am curious about the size of that rear pulley. If I decided to build a belt drive bike with a chinese engine, would I need a gigundous pulley? Also, I am sure that a belt is quieter than a chain, but it would almost have to be a smoother ride too, right? Any info would be appreciated. Thanks

Ride Safe!

Gonzo

You should look into a "Gilmer Belt Drive", toothed belt like Harley-Davidson uses. Walter F.

Chains can get away with smaller sprockets because of gearing. The HT for example is way geared down. Friction drives are a good example. With no gearing they need the whole wheel to act like a pulley.

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The overall "gearing" depends on both front and rear pulley sizes.

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Don't forget that the Happy Times have internal gear reduction so they need that smaller rear sprocket to get decent speed. I'm not sure if the older bikes you speak of have that internal gear reduction. If they don't have internal reduction, they can get away with a larger rear pulley and still have a good top speed.

As others have indicated its all about the total gear reduction. The target overall reduction seems to fall in the range of 18:1 - 22:1 depending upon motor type and its powerband. The Chinese motor you mention has a primary reduction of I believe 4.2:1 built into it. The older/early motorcycles achieved this total reduction in one shot, hince the need for a large dia. rear sheave/pulley. The Whizzer that you mention uses V-belts and use a jackshaft mounted on the frame so there is a primary reduction to the jackshaft and then final reduction to the rear wheel. The V type belt won't wrap around a very small pulley so to get the same amount of total reduction larger pulleys are needed. The biggest draw back to using belts is the fact that they don't come apart like a chain and there for comming up with a driveline that dosen't hit the chainstays and seatstays of the bicycle can be difficult. This problem is really challengeing with a frame mounted motor, less so with a rack mounted motor. The other area you will find challenging is converting the output driver of the chinese motor from its 11t sprocket to a driver for a belt. If the Gilmer Style Belt Drive is what interests you you might have better luck looking into the world of Metric Timing Belts. Pfeifer Industries :: Metric Timing Belts and Pulleys Pfeifer Industries in Naperville Ill. Is a leader in the field of metric Timing Belt Drive Trains and their web site has lots of tech information on the various parts of this type of drive train. Another source of parts for this type of drivtrain is Viza Motors in Scottsdale AZ. V2 Belt Drive Parts Viza Motors - Push Scooters - Gas Motorized scooters - Electric Generators - Water Pumps - Viza Motors LLC They have 3 different sizes of 5mm metric timing belt pulleys. They have a 20t driver and two different driven pulleys a 70t and a 102t.

ocscully

Hi Everyone,

As some already know we [EZM] have been looking into rear belt drive for some time, but for different reasons than most. During my extensive research many advantages & dis-advantages of belt drive have surfaced. I have learned that many experts don't have a clue about what works and what doesn't.

Our new 4 stroke kit is supplied with a standard ratio of 16.03 X 1, whereas most on the market are approx 23 X 1. A very large portion of the power is wasted in the gear boxes, and must be geared with such high numbers to overcome the exessive drag.

The Whizzer [original] was a ratio of 9.148616914893617021276595 X 1. The flywheel pulley was 2.5", the clutch primary pulley was 5", the secondary clutch drive pulley was 3.5" and the belt sheave was 15". Quick math would indicate a ratio of 8.57142857142857 X 1, however the belt seating areas of the pulleys must be considered. The Whizzer has a clutch pulley that is mounted on the cluth arm, and the arm rotates to loosen or tighten the belts. The belts are kept tight via a spring.



Have fun,
Quenton

Good answers & info. I am still building my chain drive, but I was just curious. Thanks everyone.

The engine and clutch pulley on the whizzer is relatively large, so the rear wheel sheave pulley has to be way larger. Way back when, I converted a whizzer Pacemaker to chain drive, but the gear ratio was way too high. For the power a Whizzer engine has, the big pulley is pretty necessary. Some of the new bike engines now use chain drive, and have a smaller bolt-on rear wheel pulley and small engine pulley. The existing pulley setup on a whizzer should get you between 25 and 40 MPH, and is still marginal for climbing moderate uphill grades. A smaller rear pulley would produce more top end, but the engine would certainly stall going uphill.

Traveler

Ravernshurst, Have You Looked At The "golden Eagle Belt Drive" Mab? They Run A 1" Dia 14 Tooth Htd Gear Direct Drive On The Engine (no Gear Reduction) And A Large Cogged Nylon Pulley That Just Snaps Onto The Spokes. The Kevlar Belt Is About 3/8" Wide. Someone Posted Pic Montage Today (two Of Them) Of Recent Ride In S Florida. One Fellow Has The Belt Drive With Pocket Bike Motor With Exspansion Chamber, Turns The Engine 17,000 Rpm. Imho All The Drive Systems Are Great, We All Should Have One Of Each!! Ron.

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