20 vs 21 sprocket tooth

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Staytite said:
Which gearbox output sprocket do people who have a belt drive fitted prefer ?
Using standard primary of triplex chain with 26T front sprocket and 57T clutch gives 2.19 ratio into gearbox
Belt drive with say 27T front and 54T clutch gives 2.00 ratio into the gearbox speeding it up
Or am I wrong ?
So which gearbox sproket is preferred for normal road riding as described in the posts above?
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If you run a 20 tooth sprocket with this belt drive ratio, it would be roughly like running a 22 tooth sprocket with a stock chain drive primary.

I have a friend with a good working 750 who runs that exact set up, and he likes it just fine.

If you wanted to replicate the same overall drive ratio with your belt drive as a chain drive with a 21 tooth sprocket, you would need to drop to a 19 on the transmission.

Hope that answers your question.
 
Staytite said:
Many people in this string have said they like a 20 or 21 tooth sprocket for normal road use of our elderly Nortons
when using the standard chain or belt drive primary giving a ratio of 2.19:1 for the front:clutch sprockets

Onder says it all depends.....

Bill says he compensates for the change from 2.19 : 1 to 2:1 by carefull choice of gearbox output sprocket

So my dodgy maths would infer to use roughly 16T as a 20T equivalent and 17T as a 21T equivalent if using a 2:1 belt drive
Am I correct ?

Does anybody have experience of using 16/17T sprockets with a 2:1 belt drive ?

Or are people still using 20/21T with a 2:1 belt drive and what's their experience ?
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Here is the math:

20 vs 21 sprocket tooth


The total overall ratio is the product of the Primary and Final Drive ratios (multiply the two together).

Hope this helps.
 
Thank you Derek for the maths - appreciated

And perhaps another consideration is the tyre size - Oh no not another tyre thread o_O

An Avon AM9 4.10 x 19 (equivalent to original ??) has a claimed diameter of 667mm so a circumference of 2093mm
An Avon Roadrider of 110/80x18 has a claimed diameter of 640mm so a circumference of 2010mm
Thus a difference of about 4% on circumference which on a gearbox sprockets of 20/22T would be nearly a tooth?
Is my theory and maths correct?

Other tyres are available and discussed at length on other threads. These are used as an example :)

Very interesting interesting to hear your friend likes his 2:1 belt with 20T gearbox sproket.

Maths is good, but experience better !

Anybody else have any experience of 2:1 belt with various gearbox sprockets ?
I think lots have been sold ?
 
I have been running Bridgestone BT-45's for nearly 20 years. I run a 100/90-19 on the front and a 110/90-18 on the rear (typically). I say typically, because I was given a 120/90-18 a few years ago and when I wore my rear tire out about a 6 weeks ago, I fitted it, and it clears!! :)

I have no experience with Avon Roadriders. I had Supervenoms on my bike at one time and was not impressed at all with the tread life - or the cost.

I see that Avon only makes a 110/80-18, and not a 110/90. That is unfortunate, as the 110/90 only gives a -1.3% difference when compared to the 4.10-19.

The 120/90 I am running right now is only +0.9% difference (slightly larger). I find that the handling is a little bit better with this tire: better straight-line stability and that the bike actually turns in a bit better (slightly decreased rake/trail?). But it could just be me.

My $0.02
 
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The change in stability with the bigger rear tire, is probably due to the difference in alignment of the sides of the front and rear tires - more than it is to the change in rake of the steering head, due to the rear of the bike being slightly higher.. As you turn, you ride up onto the edges of the tires. A bigger rear tire is more out of line with the front tire, so you feel the difference to be in the front.
 
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My 6 penny worth in reply to Derek on tyres is that I had a 110/19 x 18 on the back many years ago and it felt a bit fat !

And many years ago (decades ?) the local Norton Owners group had a talk by the then retiring Technical Manager of
Avon tyres. He said that Super Venoms were not suitable for Nortons as they did not go fast enough continuously to warm
them up and keep them hot. Only useful on a race track. Various members of the audience challenged the not going fast
enough bit !

Please let's end this tyre bit and get back to the belt drive and gearbox sprocket of the title of this thread........

Anybody else have any experience of 2:1 belt with various gearbox sprockets ?
I think lots have been sold ?
Are people reducing the gearbox sprocket to allow for the speeding up due to the 2:1 belt drives?
 
Just to confuse things a bit more, I have a 55/28 Commando belt drive here.
It looks very similar to the RGM.
I purchased it on eBay ages ago.

Glen
 
I just ride the bloody bike and if it can get over the ton pretty quick when you need to then I am happy and my hotrod Norton is set up for my play time on it, 19 tooth works well for me works great around town and out in the twisties and on the little highway riding I do it will cruise perfect between 65 to 90mph range all day if I want, but of course the fun police will keep those speeds down, I no need to do rocket speeds now and I also have a few modern bikes if I want to travel long distants at high speeds if I want to but my Norton is my play bike and the better pick up it has is what I only need and after 45 years of ownership and clocked up a lot of long distant travels in those times without any problems with the stock gearing.

Ashley
 
I can agree with that. My old motor is far too long in the tooth for hot rodding and the original reduction gives me adequate thrills enough..... No need to encourage oil consumption at any higher rate, eh?.... I did goose her up to 90 for a few last week before the wing ate my leg in the backyard. 20T does well for me.
 
I run 23 on a tuned 850 , you need that on a freeway in CA or you will be run over by Kenworths and everyone else, 19 is a joke on a Commando unless you just drive around town!....or want to be fast between traffic lights......
 
As I said previously your choice will be what fits your style of riding, area of riding, size of the rider and perhaps your pillion person as well as the state of tune of your engine. There can be a general all around gearing that fits most "average"
rider but you know how 'one size fits all' never seems to fit anybody.
 
manx850 said:
I run 23 on a tuned 850 , you need that on a freeway in CA or you will be run over by Kenworths and everyone else, 19 is a joke on a Commando unless you just drive around town!....or want to be fast between traffic lights......
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Isn't the speed limit on CA freeqways 65 mph or less?
I recall those freeways being crowded but pretty slow compared to Texas or Utah, both with 80 mph freeways, also very crowded around major cities.
Even our highways here go to 120 kmh , which is 75 mph.
That's not a problem with 20 teeth when needed, can't see 65 or 70 being too much for 19, unless you are stuck on freeways most of the time.

Glen
 
worntorn said:
Isn't the speed limit on CA freeqways 65 mph or less?


Glen
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Yup, 65 for general use, 55 for trucks/vehicles with trailers.
However, 75-80 is the norm, under 70 will get you run over... Including the big rigs....
 
We're 65 mph almost everywhere with 75 on interstates & major highways.... I really only take my Norton above 65 for short periods, although I'd do more were she not so old...... I've got the old wing for when the need arises for more lengthy highways speeds above 65-75. Old but can still do that all day without sweating and tossing pricey things out the crankcase.
 
jbruney said:
We're 65 mph almost everywhere with 75 on interstates & major highways.... I really only take my Norton above 65 for short periods, although I'd do more were she not so old......
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I avoid the 80 mph roads. 65-70, about 4000 RPM is comfortable for both me and the Norton (20 tooth). 55 or 65 is the legal limit here, and you can do 65 without getting run over if you stay in the "slow" lane. The Commando has plenty of oomph to go around the pansy's doing 50.

It's not the bike's age that holds me back, it's mine.
 
In road racing, you change the gearing to suit the circuit. However what you see is not necessarily what you get. How you use the bike alters the gearing requirement. Sometimes it is better to be over-geared and work towards being faster at the ends of the straights. At other times it is better to be geared lower and ride faster around the corners. However the quicker you get around the corner, the faster you might be at the end of the next straight, because you don't have to add as much speed. On public roads, you are usually only cruising, not competing in a speed event. So it is probably what makes you comfortable which counts. If your local roads are tight and twisty, I would probably gear lower than if they are long and open. If you ride on both types of road - gear high.
 
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manx850 said:
I run 23 on a tuned 850 , you need that on a freeway in CA or you will be run over by Kenworths and everyone else, 19 is a joke on a Commando unless you just drive around town!....or want to be fast between traffic lights......
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There is an article on restoration of a Fastback 750 in the latest Classic Bike magazine. I presume it was written by an American. I mentions that this Commando had a 19 tooth counter-shaft sprocket fitted, which the restorer replaced with a 23 tooth sprocket. He said Commandos were under-geared in America to get more acceleration. I've never found that raising ther gearing on my Seelery 850 has made irt accelerate slower. Going up 4 teeth on the counter-shaft, sprocket is like going up 5 teeth on the engine sprocket.
This current topic is only talking about going up on tooth on the engine sprocket. The difference would be almost nothing.
 
manx850 said:
I run 23 on a tuned 850 , you need that on a freeway in CA or you will be run over by Kenworths and everyone else, 19 is a joke on a Commando unless you just drive around town!....or want to be fast between traffic lights......
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How fast are you going on the freeway? I run on I5 northbound out of Stockton without issue on my combat with 21 tooth sprocket. The wind against my neck hurts after a bit so 70 is my fastest cruising speed. In the past with my JPN’s 22T when tucked behind the fairing I could cruise 90 pretty easily.
 
illf8ed said:
How fast are you going on the freeway? I run on I5 northbound out of Stockton without issue on my combat with 21 tooth sprocket. The wind against my neck hurts after a bit so 70 is my fastest cruising speed. In the past with my JPN’s 22T when tucked behind the fairing I could cruise 90 pretty easily.
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Sorry for anyone who rides a Commando on a freeway/carrageway. Why? What a waste.
 
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