Scooterotica

I swapped to an italian series 3 LI150 gearbox with 16/46 sprockets from an SX200 gearbox with 15/46 sprockets. The bike definitely revs higher and feels a good 4-5mph slower on long flat roads. There is no hint of clutch slip in any gear. I am just wanting to confirm that this is because of the gearbox change, and not the sign of another problem. Looking on scooter help gearing clalculator seems to show almost identical speed to rpm between the two gearboxes.

Instead of the scooterhelp calculator, I used the lambretta specific calculator in excel. This allows a side by side visual comparison.
You are right in your guess, higher revs for the same speeds with the 16/46 setup than the 15/46 from the sx200 gears. Not by much, but as you described, 3-4 mph slower for the same rpm in 4th gear.

At 7,000 rpm theres only 1 to 2 mph difference with the SX200 being higher, overall ratio is 4.89 on LI150 16/46 and 4.81 on SX200 15/46

Hmm, I have definitely lost a approx 3-4 mph in speed and am doing a fair bit more rpm to hit top speed. You really notice it on dual carridge ways, can't really over take muh now... Makes me wonder if I should have fitted the 17t front sprocket...

hi,
i have just done what you did took out my sx box and replaced with li150 box but with a 17 x47 sprockets not tried it out yet awaiting my side casing machining to take my af surflex clutch.was told it should fly i hope it does

He jump from 3rd to 4th is slightly better on the Li150 box setup you quoted, but Gp200 19/46 would be better.

Same ratio near as damit, but gives you a longer 3rd and a much shorter jump to 4th.

servetakid wrote:Hmm, I have definitely lost a approx 3-4 mph in speed and am doing a fair bit more rpm to hit top speed. You really notice it on dual carridge ways, can't really over take muh now... Makes me wonder if I should have fitted the 17t front sprocket...

Yes