Did I change my gearbox for no good reason?

[dansuper]

As part of my engine build, I replaced the original (and seemingly perfect) early S3 LI125 box for a new, late-Indian GP200. This, along with a new sprocket combo of 19/46 and 82 link chain, was basically done to bring the final drive down from 5.65 to 4.84. I'm running a Casa 185, and being a low revving, torquey kit, it seemed to be a good idea. All of the above was pretty much based on the gear tables in Sticky's book.

The set up works pretty well but the gap between 3rd and 4th is just too close - a 19% jump. Having only recently bothered to understand how gearboxes actually work, I thought I'd have a look at Tony Cassidy's 'gearbox visualiser'. It is brilliant. But I've now discovered that I could run the original box with my new sprocket set up and have a much better ratio spread, with a 4.46 final drive.

1st would be pretty short and the jump to 2nd is 62% but the engine would gobble that up. The big improvement is that the gap between 3rd and 4th is much more suited to the kit - a 32% ratio jump. If I can pull 5500rpm in fourth, I should be able to hit about 100kph with this spec, compared to about 93kph with the GP200 set up. Damn it!

Sorry for the long post - my short question is, do any of you experts see any issue with what I'm thinking above? Running the old box with the new sprocket set up?

Cheers,

Dan

[Muttley McLadd]

I think you'll struggle to pull that gearbox. Is there anything wrong with the GP combination?

When you say the gap is too small, how is that bad?

[fred]

personally i'd have just fitted 18/47 to the li125 box.

[dansuper]

I think you'll struggle to pull that gearbox. Is there anything wrong with the GP combination?

When you say the gap is too small, how is that bad?

Basically, when shifting from 3rd to 4th the revs barely drop - it accelerates really hard but it feels like it's running out of legs too quickly. 4th in the LI125 box is taller and I think the kit would still pull it happily, but I guess I'll have to just swap them and see.

Cheers,

Dan

[drunkmunkey6969]

As i understand it..if you scooter pulls 4th gear OK with your new 4.84 set up, then surely you are better off with this gearbox than your old one? Think about when you are twos up, or loaded with luggage....or what about when you hit a headwind, or go up a big hill......?

With the new 'close ratio' gearbox surely your 3rd/4th gear ratios will come into play, where as on the old set up.......you hit the hill in 4th and then half way up you run out of steam, drop into 3rd......but the gap between 3rd and 4th is too big, and so now the engine is screaming its pants off in 3rd and not going anywhere....not good.

[battlam]

the SIL 200 gear box is pretty good on most things. the gap between 3rd and 4th is short like a close ratio, however the jump between 2nd and 3rd is larger due to this. I'd stick with what you have, great tourer for rallying imo

[ScooterLoopyJohn]

personally i'd have just fitted 18/47 to the li125 box.

This is my box of choise on all my scooters. easy to play with the gear and chains

[dansuper]

Thanks for the replies. I appreciate that the current set up will be strong if the scoot is under load in 4th, but it feels SO strong that I think it would still pull a taller 4th. Some more testing with the GP box will come first, then based on the results, we'll see what happens.

Cheers,

Dan

[soullad]

Dansuper please listen to the advice given, as they speak from experience. You seem determined to give it a go. Do not fall into the classic overgearing Lammy trap. You will defo struggle to pull 4.46 with a casa 185 kit. You haven't mentioned what pipe you running but if its a Clubman type, and you want to go faster then may I suggest you first try a different pipe that allows you to rev on a little more...it will need to be a torquey one, like a JL3 thou.??

Just think for a minute what you've actually created - you've already been able to drop from 5.6ish to 4.8ish thanks to the torquey nature of the kit / pipe etc and got a lovely small gap between 3rd and 4th, ideal for cruising / touring etc. Compared to modern bikes and cars Lambrettas will rarely be as fast .. sure they'll be nippy and fun, but be happy with your all day 60 mph crusing, its foolish to expect more tbh.

How do you think going to a 4.46 with a 30% gap between 3rd and 4th will be any better? Sure on the rare occassion you might pull this gearing, like down a long slope, but for 90% of your riding you'll be thrashing it in 3rd, drop into 4th and then gradually slowing down only to drop back into 3rd and repeat the whole thing over and over for your whole journey. Like Dan (drunkbaboon) says add luggage, hills, 2 up into this equation and it'll be useless.
That said, if you are determined, go ahead and try it. Trust me if it works I'll be the first in the queue to buy a Casa 185 kit.

[sydduckett]

the SIL 200 gear box is pretty good on most things. the gap between 3rd and 4th is short like a close ratio, however the jump between 2nd and 3rd is larger due to this. I'd stick with what you have, great tourer for rallying imo

Is this not down to the indian having one less tooth than the italian GP box?