Opportunity to change my gear ratio - GT186 thoughts?

[Donnie]

OK, setup is TSR Evo, GT186 triple port, 30mm PHBH on a Series 2, pilot is 16.5 stone, never any pillions.
Gearing is LI150 box, 16 tooth front and 46 tooth rear sprockets giving final drive ratio of 4.89 according to scooterhelp

So, on the way home this happened!


Details here viewtopic.php?f=10&t=6375

Anyway, I have the opportunity now to change my final gear ratio as I keep having to drop to 3rd more often than I like when riding with others (usually about the 55mph mark) so am wondering about changing from 16/46 (final drive 4.89) to either 16/47 (final drive 4.99) or even 15/46 (final drive 5.21) but wonder if the latter on my setup would be too much strain on the top end?

Any opinions welcome as well as other gt186 owner setups and drives too?

[Adam_Winstone]

15/46 as 5.2 was good enough for Innocenti GP200 and SIL tuned Stg IV version. Throw in an expansion and 5.2 should be fine. You certainly wouldn't need to be dropping it to 3rd, as you are now.

If you look at AF's TS1 gearing recommendations you'll see that they often quote 5.2 for bikes running revvy pipes and they cope with the slightly shorter gearing and higher revs.

The one driving force behind me saying this is that you can use genuine Innocenti 15 tooth front sprocket and not have to worry too much about sprocket wear

Adam

[Stevepshipley]

Ooops!!

Think I've got a spare 15 front you can have if you need one if you need one

[Donnie]

Thanks Steve and Adam, got a genuine 15t right here so might give that a whirl. I've seen through my googling though that Rich Taylor himself doesn't recommend a 15 in any of his engines.

[burnside]

I'm running the same gearing as you in my GT186 with 60/110 crank and Franspeed Race, was 17/46 initially but that was too tall, mine can handle 55 in 4th but any lower and I have to change down to get it back into the power band, but it seems fine on long runs when we tend to sit at around the 60-65 mark.

I did start of with 16/47 with my GT200 with BGM clubman, but changed that to 17/46 which is handles with ease, but guess that the pipe help loads in that respect, I'd have thought 16/47 would work well with your setup.

[Stevepshipley]

I have 16 46 on my Spanish S2 with TSR evo and 198 muggy with 12.5 stone pilot. Runs good.

[Donnie]

I have 16 46 on my Spanish S2 with TSR evo and 198 muggy with 12.5 stone pilot. Runs good.

I've an extra 4 stone to carry Steve

[dickie]

You could try either lower gearing or the slimfast plan.

[Donnie]

feck slimfast They don't do a real ale

[johnnyXS]

thats a crazy dilemma isn't it
Having a powerful engine yet struggling to match the slow speed of others on a run
You could almost do with a 5x speed and have a close ratio 1-4 and high speed cruise in the 5th gear.

If you change your gearing to something like the pacemaker set with 16T 46t (5.3 ratio ) you would be right on the money for 45mph in 4th at 5000rpm and 55mph at 6000rpm but you're gonna be screaming 8000rpm at 70mph
Beedspeed have produced a really handy 'at-a-glance' spreadsheet for instant comparisons of various combos
http://beedspeed.com/html-pages/LambrettaGearBoxOverallGearRatioChart.htm

[Donnie]

heh heh yeah, thats the thing im not sure i wanna be screaming at 70 on a cast iron setup.

Seen that beedspeed chart already and confirms the scooterhelp gear calculators numbers too.
Think im going to try the 16 47 giving me 4.99 ratio and see what that does.

[johnnyXS]

16 x 47 with a 4.99 final drive ratio sounds like a cunning plan !

i'll probably go with the same when I rebuild my 200cc smallblock with S3 gearbox

[Adam_Winstone]

"changing from 16/46 (final drive 4.89) = I keep having to drop to 3rd more often than I like when riding with others (usually about the 55mph mark)."

"Think im going to try the 16 47 giving me 4.99 ratio and see what that does."

It is certainly a step in the right direction, however, whether 0.1 of a change will be enough to make any change whatsoever has yet to be seen. Then again, 4.8 to 5.2 is enough of a change to make a big difference in ability to pull 4th so 0.4 is a very noticeable change... suck it and see, I guess. Not sure that you're not missing the opportunity to change the final ratio though as I doubt 0.1 will do much.

Good luck with it though.

Adam

[johnnyXS]

thats the problem isn't it. Most of us need two widely different gear ratios for different uses.
When i'm toolin around the lanes and villages in the Countryside I can rarely get an opportunity to hit 55mph and then its usually only for a couple of minutes at most before you have to change down for a corner or road junction.
For that you need a closer ratio box to get back up to speed quickly without any large gear ratio jumps

Yet when we occasionally need to do long high speed runs for club runs and rallies etc you need a high speed cruising top gear .

What would be nice is a crankcase with a simple drop-in final ratio cog like you can quickly and easily change your wheel sprocket on a motorcycle

Just thinking out loud here I wonder what sort of difference to gear ratios you could achieve by fitting a larger wheel with a lower profile tyre like the Ve*pa Lx50 has a 11" wheel rim with 110-70-11 tyre . Clearance to the frame is very minimal as it is though....barely an inch. Not sure how to work out a final ratio or speed

If you fit a wide rear rim with a 4" wide tyre theoretically you'd get an extra 4mph @ 6000rpm ignoring wind resistance http://scooterhelp.com/tuning/lam.gear.calc.html
conversley... fitting a 3" wide tyre on a standard rim gives a 4mph reduction at 6000rpm

[Donnie]

I see what you are saying Adam, and I know you are right, id certainly get a more noticable change going to 5.2, but to do that on the li150 box will mean the 15 tooth sprocket and while i have no doubt it would mean a decent top speed quicker, im not sure im happy that it would be revving a lot higher for the same speed on a motoryway or dual carraigeway. It just worries me.

[Adam_Winstone]

^... I totally relate to that

[Donnie]