Triumph Tiger Cub Gearing/sprockets

[trialsrfun]

What size of sprockets are you fellow Triumph Tiger Cub riders running on the crank, gearbox and rear wheel also rear chain size.

My bike is 199cc currently fitted with a 420 chain.

Edited April 13, 2016 by trialsrfun

[trialsrfun]

Does anyone know if the smaller crank sprocket is essential to obtain trials gearing or just a way of reducing the diameter of the one fitted to the rear wheel?

I think the standard crank sprocket is 19t but I have seen both 16t and 17t crank sprockets, would these require a half link or cause clutch slip problems.

[trialsrfun]

Just found an American Triumph Cub website which says the 16t engine sprocket is to enable a 14t gearbox sprocket to be fitted for greater swing arm clerance, with this info the options/confusion list just gets longer, what do you use on your Cub.

Edited April 13, 2016 by trialsrfun

[stanmet]

I run a 16 engine.sprocket 13 gearbox and 52 rear wheel on 420 chain you need a chain tensioner on front chain

[laird387]

On a comparative test way back when, which involved an ex-works Triumph rider, we proved that using combinations of crankshaft, gearbox and rear wheel sprockets that gave very similar final overall gear ratios, it was much easier to break traction on slippery going with a larger rear wheel sprocket - in every gear.

 

It took a lot of doing, a lot of rapid spanner work to keep the comparison valid, in case the surface conditions were changing - but we had received a challenging question from an engineering student who felt, as a result of purely mathematical calculations, that the radius at which the driving effort to the wheel was applied had a significant effect.  And our test supported his maths, the bigger the rear wheel sprocket, the more difficult to find grip.

 

So the answer must be fit the smallest crank and gearbox sprockets, that will give you the smaller rear wheel sprocket and you should find grip better............unless you can prove different.

[davetom]

I remember this being discussed before ( quote below), was this the same experiment or a different one ? I notice the one involved 2 bikes and the other lots of spannering..

Hi,

 

There was a lot of discussion at one stage that the larger the diameter of the rear sprocket, the easier it was to lose traction under slippery section conditions, the argument resting on the point of the diameter of the rear wheel at which the tractive effort of the chain pull was exerted.

 

To settle the argument two machines were chosen one with a larger gearbox sprocket and huge rear sprocket, the other with a minute gearbox sprocket and a smaller rear sprocket - but both with exactly the same overall gearing.

 

Then a multitude of riders compared the two bikes in an afternoon of various sections.

 

Realising it wasn't a genuine comparison, one of the rear tyres might have had better grip - one of the footrest positions could be affecting the result, etc., etc., but the overall view at the end of the day was universal, every single rider was convinced the bike with the smaller sprocket gave far better grip.  It was universally agreed that the minute gearbox sprockets would wear quickly - but ever one of the riders involved gradually modified their own bikes over the following season to get the smallest diameter rear sprocket that they could.

 

Proof - several riders went down a chain size because that gave them an even smaller sprocket...............

[laird387]

I remember this being discussed before ( quote below), was this the same experiment or a different one ? I notice the one involved 2 bikes and the other lots of spannering..

 

No,

 

That was a second session as a follow on when someone realised that a further reduction in sprocket diameter could be achieved by using the smaller chain sizes but wanted to check the theory.

Edited April 15, 2016 by laird387

[davetom]

Ok thanks. If larger sprockets are acting as torque multipliers then, it sounds like a good mod for low powered, low torque bikes, like the smaller two strokes ?

[trialsrfun]

Hi Deryk an interesting comparison, do you recall the sprockt sizes please.

Are we talking sizes that are used for trials with maybe a six or eight tooth size difference which would be simiar to possibly two at the gearbox or a much greater difference.

[laird387]

Ok thanks. If larger sprockets are acting as torque multipliers then, it sounds like a good mod for low powered, low torque bikes, like the smaller two strokes ?

 

Sorry, Dave, I feel that the traction break effect applies to all bikes - I feel that what you describe as the torque multiplier effect would more accurately describe being in too low a gear.  I was riding Ariels at the same time as Sammy Miller was on GOV, and I particularly noted that he often selected second to enter a slithery uphill where most would automatically have selected bottom.........

[laird387]

Hi trialsrfun,

 

Sorry I never owned a Cub so I can't recall the sprocket sizes used on our test - but I do remember having sprockets made for my Ariel by Roger Maughfling at Knighton to enable a smaller rear sprocket - but we cheated because I had fitted an AMC mainshaft and clutch, so we were able to make a new sprocket with an extra couple of teeth to fit the clutch basket which helped to keep the overall gearing right......

Edited April 15, 2016 by laird387

[davetom]

I thought Sammy went to smaller chain sizes for weight reasons rather than sprocket diameter? I bet that maths student was grateful that you carried out all this work to validate his calculations ? It's a shame that no numbers were kept on the test examples

[laird387]

Hi Deryk an interesting comparison, do you recall the sprockt sizes please.

Are we talking sizes that are used for trials with maybe a six or eight tooth size difference which would be simiar to possibly two at the gearbox or a much greater difference.

Trials only,  my road machines very early on meant putting a sidecar on, our eldest child was five days old when she went for her first ride in a sidecar.  Prior to that we had done many thousands of miles on the solo Matchless G80CS, put together for me by Hugh Viney's team in Plumstead and supplied by Stan Hailwood through his Oxford shop.

 

I do remember we were aiming for a rear sprocket reduction of ten teeth on the Cub - but remember there were not many genuine Trials Cubs supplied, a lot were sort of cobbled-up Sports Cubs, I suspect because the Triumph ordering system for dealers was not the simplest maybe?

 

 

Edited April 16, 2016 by laird387

[laird387]

Hi davetom,

 

Weight was also a consideration - the sprocket Roger made for my Ariel clutch basket was in alloy!

 

Interestingly Sammy needed a dished rear sprocket for GOV 132 and made one out of, I believe a Hiduminium billet, whereas his 'practice' machine, GON,  had a heavier steel unit, which obviously supports the weight reduction theory.

[trialsrfun]

Some interesting observations here, many small capacity modern trials bikes (those ridden by youngsters) have sprockets the size of a frying pan but the 199a and 199b Bultaco bikes had smaller rear sprockets than previous models.

The post was started because I think I may have my bike a little overgeared and wondered what ratios others were using but it has become very thought provoking which is positive, it just goes to show that motorcycle trials is actually a branch of physic's.