gearing on my Seeley

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
Hi there,
Its going better to ride my bike now, almost two years after my crash, but I feel that the gearing was to short, even with the TTI 5 speed.
When starting at trafic lights the engine revs very fast to 6.000 RPM, to fast, I have the feeling that a longer gearing will give me a better accelaration over a 1/4 mile
To day a change my gearing on the bike, before I use 19 X 39, now I put 21 X 39.
There was no possibility to go lower as 39 on the back and no possibility to go bigger as 21 on the front becouse of the outrigger, the outrigger is a part of the electric starter and clutch made by Jean-Noel Gindrat, the man behind the fabulous Yellow Perril racing team.
I use also a belt made by Gindrat, 40mm widht with a bigger front pulley
Tomorrow I will try out.
I plan also to rise my footrest one inch for more security in the turns.
Last year I lower the footrest almost 8 cms becouse of my broken hip, but I toutch my boots in the turns.
On september 10 I turn 70, I can believe it.
Keep you posted
 
Joined
Nov 4, 2007
Messages
971
Country flag
Hi there,
Its going better to ride my bike now, almost two years after my crash, but I feel that the gearing was to short, even with the TTI 5 speed.
When starting at trafic lights the engine revs very fast to 6.000 RPM, to fast, I have the feeling that a longer gearing will give me a better accelaration over a 1/4 mile
To day a change my gearing on the bike, before I use 19 X 39, now I put 21 X 39.
There was no possibility to go lower as 39 on the back and no possibility to go bigger as 21 on the front becouse of the outrigger, the outrigger is a part of the electric starter and clutch made by Jean-Noel Gindrat, the man behind the fabulous Yellow Perril racing team.
I use also a belt made by Gindrat, 40mm widht with a bigger front pulley
Tomorrow I will try out.
I plan also to rise my footrest one inch for more security in the turns.
Last year I lower the footrest almost 8 cms becouse of my broken hip, but I toutch my boots in the turns.
On september 10 I turn 70, I can believe it.
Keep you posted
Hi Yves , nice to hear from you ! keep on like that and enjoy your bike ! Pierre
 
Joined
Oct 16, 2016
Messages
339
Country flag
2 score year and 10 is a major milestone, just 5 years behind you. For what it is worth I believe 1 tooth on the front is worth 3 on the back. So the 21 x 39 would be the same as 19 x 45
 
Joined
Apr 27, 2015
Messages
1,640
Country flag
For what it is worth I believe 1 tooth on the front is worth 3 on the back. So the 21 x 39 would be the same as 19 x 45

I don't think that's correct... Say the given ratio was 20 on the front and 40 on the back, then wouldn't that be a "2 to 1" ratio? By rounding off you get the closest integer, but surely the nearby ratios of "19/39" or 21/39 are closer to "2 to 1" than "3 to 1".

A full rotation up front (20 teeth) means 1/2 of a rotation in the back (if it's 40 teeth)... unless I'm missing something...

On my bike I used a cast wheel with the drum brake moved to the timing side of the bike. I can change that rear sprocket since it's not integrated into the brake drum. Being able to change the rear sprocket gives smaller incriments of change per tooth. Needless to say, if Yves has a standard commando rear wheel he can't change the sprocket size on the rear.
 
Joined
Oct 16, 2016
Messages
339
Country flag
Yeah I am not 100% sure, just something I remembered as a rule of thumb from dirt biking days, as ever stand to be corrected.
 
Joined
Jun 30, 2012
Messages
10,058
Country flag
Two teeth on the engine sprocket is a big step up. You never know your bike was under- geared until you raise the overall gearing. Commando engines tend to spin up at the same rate regardless of the gearing, because of the heavy crank. If you have raised the overall gearing, your bike will probably accelerate faster. With most bikes, lowering the overall gearing helps the bike accelerate faster because the engine is pulling less load, so goes up in the power band easier - throttle response. Commando engines have poor throttle response, but nothing stops the heavy crank once it is spinning high. That crank when used with a close box is excellent, but the weak point in a Commando is usually the gearbox.
It is like a lot of things, what happens in practice is different to the theory.
 
Joined
Jun 30, 2012
Messages
10,058
Country flag
If you use the big engine sprocket the gearbox spins faster, so the loads on the internal gears are smaller.
 

storm42

VIP MEMBER
Joined
Jul 20, 2011
Messages
852
Country flag
Hi there,
Its going better to ride my bike now, almost two years after my crash, but I feel that the gearing was to short, even with the TTI 5 speed.
When starting at trafic lights the engine revs very fast to 6.000 RPM, to fast, I have the feeling that a longer gearing will give me a better accelaration over a 1/4 mile
To day a change my gearing on the bike, before I use 19 X 39, now I put 21 X 39.
There was no possibility to go lower as 39 on the back and no possibility to go bigger as 21 on the front becouse of the outrigger, the outrigger is a part of the electric starter and clutch made by Jean-Noel Gindrat, the man behind the fabulous Yellow Perril racing team.
I use also a belt made by Gindrat, 40mm widht with a bigger front pulley
Tomorrow I will try out.
I plan also to rise my footrest one inch for more security in the turns.
Last year I lower the footrest almost 8 cms becouse of my broken hip, but I toutch my boots in the turns.
On september 10 I turn 70, I can believe it.
Keep you posted

I think going from 19 to 21 will make about 7kph more in first gear and about 18kph more in top.

How many teeth on your engine and clutch sprockets?
 
Last edited:

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
I don't think that's correct... Say the given ratio was 20 on the front and 40 on the back, then wouldn't that be a "2 to 1" ratio? By rounding off you get the closest integer, but surely the nearby ratios of "19/39" or 21/39 are closer to "2 to 1" than "3 to 1".

A full rotation up front (20 teeth) means 1/2 of a rotation in the back (if it's 40 teeth)... unless I'm missing something...

On my bike I used a cast wheel with the drum brake moved to the timing side of the bike. I can change that rear sprocket since it's not integrated into the brake drum. Being able to change the rear sprocket gives smaller incriments of change per tooth. Needless to say, if Yves has a standard commando rear wheel he can't change the sprocket size on the rear.
My back weel is a Steve Maney 18 inches, now for sale at Minnovation.
I can change the sprocket, but lower as 39 will bring the chain in contact with the swing arm.
 
Joined
Apr 27, 2015
Messages
1,640
Country flag
My back weel is a Steve Maney 18 inches, now for sale at Minnovation.
I can change the sprocket, but lower as 39 will bring the chain in contact with the swing arm.

The stock commando rear sprocket is 42 teeth. The 39 teeth of your rear wheel would be similar to adding another 1.5 teeth to the front sprocket if you used a stock 42 tooth rear wheel. So by comparison to a stock norton your front sprocket would feel like a "22.5" size. Of course you can't have a ".5" of a tooth, so the number is only to get an idea of how far off the stock ratio you will be with your 21/39 sprockets. Your 18" tire diameter helps to reduce the ratio slightly but I would still bet your 21/39 ratio is greater than a 22/42 which is a very high ratio. I wonder how you will like such a high geared ratio. It should cruise along quickly at a low rpm...

I do the RPM/MPH calculations for my bike on https://www.gearingcommander.com/
 
Last edited:

lcrken

VIP MEMBER
Joined
Mar 15, 2009
Messages
4,150
Country flag
Glad to see you still riding, Yves. I keep telling myself, "You don't stop riding because you get too old. You get too old because you stop riding." Some days, I even believe myself:).

Going from the 19T countershaft sprocket to the 21T without changing the rear sprocket will give you a 10.5% lower rpm for the same speed (or 10.5% higher speed for the same rpm, depending on which end you want to look at it from). That's a significant amount, and you will certainly notice the difference when you ride it. If it's too much change, you can always try a 20T. We can calculate gear ratios and speeds all day, but all that really counts is how well it works for you when you ride it. My guess is with such a light bike and plenty of horsepower, you'll be happy with the 21T. Let us know if it works for you.

Ken
 

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
2 score year and 10 is a major milestone, just 5 years behind you. For what it is worth I believe 1 tooth on the front is worth 3 on the back. So the 21 x 39 would be the same as 19 x 45
I wish I was still 65, the difference between 65 and 70 is big, I need 3 time more time to do the same work as when I was 65 and with my broken hip I still need help to put my leg over the bike.
Yves
 

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
Glad to see you still riding, Yves. I keep telling myself, "You don't stop riding because you get too old. You get too old because you stop riding." Some days, I even believe myself:).

Going from the 19T countershaft sprocket to the 21T without changing the rear sprocket will give you a 10.5% lower rpm for the same speed (or 10.5% higher speed for the same rpm, depending on which end you want to look at it from). That's a significant amount, and you will certainly notice the difference when you ride it. If it's too much change, you can always try a 20T. We can calculate gear ratios and speeds all day, but all that really counts is how well it works for you when you ride it. My guess is with such a light bike and plenty of horsepower, you'll be happy with the 21T. Let us know if it works for you.

Ken
Hi Ken,
to me you need to find a gearing according to you riding style, the level of tuning from the engine, the waight of the rider and more.
I should do a test ride to day and keep you posted.
Yves
 
  • Like
Reactions: baz
Joined
Nov 15, 2010
Messages
411
Country flag
I wish I was still 65, the difference between 65 and 70 is big, I need 3 time more time to do the same work as when I was 65 and with my broken hip I still need help to put my leg over the bike.
Yves
Yes, but getting older, with all the problems, is still better than the only other alternative....
 
Joined
Mar 7, 2020
Messages
1,020
Country flag
I wish I was still 65, the difference between 65 and 70 is big, I need 3 time more time to do the same work as when I was 65 and with my broken hip I still need help to put my leg over the bike.
Yves
As I approach 64 that's comforting to know..... Thank you :)
 

MichaelB

"Sons of Arthritus"
VIP MEMBER
Joined
Jan 14, 2004
Messages
1,359
Country flag
Yes, as I approach 67, I'm taking notes.

Back when I was a youngster in my 50's, I was skiing and shared a chair lift with a guy in his 80's.
I commented how I hope I'm able to do what he's doing when I get there.
His response was ...'Well, Sonny, let me tell you something. Take care of yourself, cause every that ever happened to you, every broken bone, sprain, tear
cut, bruise, whatever will come back to hurt.' as that was setting in my mind, he receached down to his stomach and said. 'and when he feel this coming on,
run, go for a walk, do something to keep it off.' As he's looking over at mine...And then he skiied off........
 

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
Hi There,
I did the test ride to day on a road W/O radars.
The longer gearing give me full satisfaction, I even have the feeling that the Seeley have beter accelaration with the longer gearing.
Difficult to explain in my poor english, but it's like the engine breathe better.
I did 120 KPH at 3.800 RPM in fift gear, and when go WOT from there, the engine pull like the Toraka Express to 6.500 RPM with the concerto for two cylinders and Maney exhaust.
Here are some numbers:
Former gearing: 19 X 39, ratio 2.052
To day gearing: 21 X 39, ratio 1.857
Primary gearing:
Front pulley 38 toots, clutch basket 70 toots ratio 1.842 ( I use a belt with 8mm between the toots)
Original Codo gearing with triplex chain 26 X 57 ratio 2.192
As you see my belt primary is longer as the original.

I am a mistery for the Doctors, I am a smoker, I am 1.70 and weight 90kgs, 3 hart infarct behind me, more broken bones as Evel Knievel.
No doctors understand how I turn 70, It must be good luck, my familly Doctor says already 30 years " you will die one of this days" well he pass away and I am still there riding my Seeley.
Yves
 
Joined
Jun 30, 2012
Messages
10,058
Country flag
It is interesting that you feel your bike is accelerating faster. Every time I have raised the overall gearing on my Seeley 850, the corners have arrived faster. It is very deceptive. You can ride the bike and believe it is accelerating as fast as it can. But if you don't make the engine pull hard, you might not use all the available torque. The give-away is the amount of revs you lose on the up-changes. If I use low gearing, the drop is almost nothing. Currently I lose 1500 revs on every up-change through the close ratio box, and the revs come back very quickly. So my latest change is up one more tooth on the engine sprocket (single row primary). Eventually I must reach a point where the bike stops accelerating faster.
 

yves norton seeley

VIP MEMBER
Joined
Feb 13, 2014
Messages
631
Country flag
Hi There,
Last saturday I did a long ride with two friends (Luc and Johan) it was very hot and we take different kind of roads and some traffic lights.
As you remember I change the final gearing from 19 X 39 to 21 X 39, I did a short test ride and was satisfed.
Saturday I feel that the gearing was to long on the traffic lights, must use the clutch more as usual, so I decide to go to 19 X 41, I dont test it so far becouse of raining, but this will be not far from perfection I hope.
I also change the main Jets on the FCR: from 175 to 180, this must give more cooling to the engine.
The oil pressure was good but as you maybe know on the Seeley there is a gap in the seat to fill the oil, wel saturday we spend some time in the traffic, stop and go, you know with as result that my family jewellery that are on the top of the gap in the seat, almost burn.
I find the solution: fill the gap with a piece of wood with the same hupholstry as on the seat, I can stiil take this piece away to fill the oil.
Keep you posted
Yves
 
Top