Gearing

[gautrek]

Hi guys first post on here.

After starting to ride my old trial bike again after a break of about 30 odd years i have a question.At the moment its geared with an 18 tooth engine,40 tooth clutch,17 tooth gearbox and 60 tooth rear sprocket.

But due to me being rather crap and the bike seeming much to fast for my very limited skill level((but i don't know if this is in the mind or not(i managed to get round 2 sections on Sunday out of about the 30 i tried before i broke the bike)).I have a 17 tooth engine sprocket which i could use .But my question is is a drop of 1 tooth on the engine a massive drop in the ratio.

[old trials fanatic]

Hi guys first post on here.

After starting to ride my old trial bike again after a break of about 30 odd years i have a question.At the moment its geared with an 18 tooth engine,40 tooth clutch,17 tooth gearbox and 60 tooth rear sprocket.

But due to me being rather crap and the bike seeming much to fast for my very limited skill level((but i don't know if this is in the mind or not(i managed to get round 2 sections on Sunday out of about the 30 i tried before i broke the bike)).I have a 17 tooth engine sprocket which i could use .But my question is is a drop of 1 tooth on the engine a massive drop in the ratio.

Might help if you told us what bike you are talking about ?

[chewy]

Hi guys first post on here.

After starting to ride my old trial bike again after a break of about 30 odd years i have a question.At the moment its geared with an 18 tooth engine,40 tooth clutch,17 tooth gearbox and 60 tooth rear sprocket.

But due to me being rather crap and the bike seeming much to fast for my very limited skill level((but i don't know if this is in the mind or not(i managed to get round 2 sections on Sunday out of about the 30 i tried before i broke the bike)).I have a 17 tooth engine sprocket which i could use .But my question is is a drop of 1 tooth on the engine a massive drop in the ratio.

I wouldn't think 18 /40 to 17 '40 was too big a change in ratios, you would have a job (probably ) to change clutch basket /?teeth so why not ry it?

[alan]

it equates to an overall reduction of just over 5%.

if it is currently geared to do say 5 mph at 1000 rpm, changing the engine sprocket would only drop the speed to 4.75 mph at 1000 rpm.

Depends how much difference you are trying to make, but 2 teeth off the gearbox sprocket would make a 10% reduction, if you then went up 5 on the rear wheel you would get 18% overall.

[charlie prescott]

Hi Guy's

Well if it is a Panther, well done for getting it back out of the shed. I would gear it down as much as I could. If it has a Burman box you could probably go down a couple of teeth on that, I would use the 17 engine sprocket and even think about a bigger back wheel sprocket. Well done again for getting the old bike back out.

Regards Charlie.

[trickymicky]

Your overall bottom gear ratio at the moment is 21.9:1 assuming you have a road box fitted with an internal bottom gear ratio of about 2.8:1.

Using a 17T engine sprocket instead will give an overall bottom gear ratio of 23.25:1

Assuming its a 350cc,you really need a ratio nearer 32:1- some may disagree it needs to be that low,but its certainly overgeared even with a 17T sprocket.

Calculating bottom gear ratio is quite easy- the drive train comprises 3 ratios, Primary,Gearbox internal and final drive. The overall ratio is arrived at by multiplying all 3 together.

In your case-40/18=2.22:1(primary)x 2.8 (g/box internal)x 60/17=3.53:1 (Final Drive)= 21.95:1Overall

With the above,you can substitute different teeth numbers,then re calculate to check the effect.

[gautrek]

Your overall bottom gear ratio at the moment is 21.9:1 assuming you have a road box fitted with an internal bottom gear ratio of about 2.8:1.

Using a 17T engine sprocket instead will give an overall bottom gear ratio of 23.25:1

Assuming its a 350cc,you really need a ratio nearer 32:1- some may disagree it needs to be that low,but its certainly overgeared even with a 17T sprocket.

Calculating bottom gear ratio is quite easy- the drive train comprises 3 ratios, Primary,Gearbox internal and final drive. The overall ratio is arrived at by multiplying all 3 together.

In your case-40/18=2.22:1(primary)x 2.8 (g/box internal)x 60/17=3.53:1 (Final Drive)= 21.95:1Overall

With the above,you can substitute different teeth numbers,then re calculate to check the effect.

Thanks for all the replies guys.I will go ahead with the 17 tooth sprocket.

I had also heard about need to be close to 30:1 on the gearing but was unsure how to work this out.

I will need a bigger rear sprocket next as i don't think i can go much smaller on the gearbox.But i will try the 17 tooth at the next trial and see how i get on.

As too what bike i am riding.

Here it is. I have named it the "Ground Gripper"(i chose the name after reading about the nick name the pilots called the old trident airliner when operating it in hot climes as they were a bit marginal on the power in warm air) but it fits perfectly with my bike as its slightly too low to the ground.

Its my old 1937 350CC red panther.Which i last rode around the mid 70's when i was a lot younger and hadn't discovered beer and wimin.

I am just in the process if fitting some lifter plates to the bottom of the forks which will give me about 1 1/2 " more height at the front.But now i need a longer brake arm and cable.

I have also phoned about a new coil spring for the girder forks as the one fitted is 70 years old so sags a lot.But i can't get a lightweight spring so will order a medium weight one which is slightly longer and heavier so i may need to make some different spring mounts up but hopefully that will lift the front even more.

But all in all i enjoyed my first run out and have no illusions that i am any good at trial riding.

Edited October 13, 2010 by gautrek

[gautrek]

Well i have gone with the 14 tooth front sprocket and a 66 tooth dinner plate on the back.According to people who know that works out at around 29/1.Which is near enough to 30/1 for me.I must admit that the bike felt too slow when i blatted up and down the road on it.But after competing in a trial today i must say i am impressed.I was under a lot more control than i have ever been this season.

So cheers of the replys