Very possibly thick gearing question

[stoneislandv8]

Had a couple of people recentlymention that I'd be better running my Casa 185 kit with a standard Indian GP200 box and 18/47 sprockets.

Currently its running Spanish Li125 gearbox, 16/46 sprocket and stretched 80 chain. Pulls well through all the gears, 4th pulls ok from low revs, if changing into 4th at high revs in 3rd the pick-uup in 4th is gradual which I guess is the power tailing off at higher revs on the casa kit. Did run the kit originally on Li125 box with 17/46 and it wouldn't pull 4th.

I've gone through the gearbox visualiser but can anyone tell me,in the real world, when riding the scoot, what effect swapping to the GP box would have?

John

PS apologies in advance if I'm being really thick.

[Daggs]

Hi, this may or may not help, but here goes.

I've been running an Imola 185 kitted bike for about eight years. After the initial set-up which took months It was going along O/K on 17/46 through an SX150 box. The only problem i had was the well known 3rd to 4th jump. This could cause a lot of gearchanging on inclines.
It got to the point of needing a new clutch, so i decided to change the gearbox too. I replaced it with a Li125s/GP200 and retained the 17/46.
If you look at the two gearboxes, they are identical except for 4th gear which is fractionally lower in the Lis125/GP200 version.
The difference has been astounding. It has all but eliminated the gear changing on inclines.
Just for info. Running through a Clubman exhaust.

P.S. you certainly aren't being thick. Gearing is a complex issue as i've found out.

[stoneislandv8]

Cheers Daggs, that does make sense and help. From what I've been reading I reckon the drop from 3rd to 4th would be almost the same between what I'm running and the GP200 as its still gonna hit the decreasing torque curve.
Have got a problem jumping out of 4th at high revs so might swap if I have to rip it apart to inspect!!

[rosscla]

If it's jumping out of gear then you need to solve that first which will mean a strip out of the gear box, probably a new selector and spring but you ought to check for wear on the loose gears as well. Fitting an uprated spring might help.

You need to work out what your final ratio is at present.

18/47 will give you primary ratio reduction of 2.61

17/46 gives you 2.7

16/46 gives you 2.875

You then take that and multiply by the ratio of the loose 4th gear to the cluster

Both indian and italian GP200 4ths (18/36 = 2) will give you a final ratio of 5.22 with 18/47 primary but the jump from 3rd to 4th is bigger on the italian box compared to the indian, where as the indian has a bigger jump from 2nd to 3rd

Your spanish li125 should be giving 19/35 = 1.84 and with your current sprocket set up should be giving you 5.29

With that box and 17 / 46 you'd be getting 4.96

I'd say that the GP box will make it a little less likely to pull 4h but this will very much depend on your exhaust and where the kit is producing the peak power and torque.

[stoneislandv8]

If it's jumping out of gear then you need to solve that first which will mean a strip out of the gear box, probably a new selector and spring but you ought to check for wear on the loose gears as well. Fitting an uprated spring might help.

When the engine was rebuilt it had uprated springs,gears were checked for wear and new selector was used. Cables will be starting point then strip down if that doesn't work.

You need to work out what your final ratio is at present.

18/47 will give you primary ratio reduction of 2.61

17/46 gives you 2.7

16/46 gives you 2.875

You then take that and multiply by the ratio of the loose 4th gear to the cluster

Both indian and italian GP200 4ths (18/36 = 2) will give you a final ratio of 5.22 with 18/47 primary but the jump from 3rd to 4th is bigger on the italian box compared to the indian, where as the indian has a bigger jump from 2nd to 3rd

Your spanish li125 should be giving 19/35 = 1.84 and with your current sprocket set up should be giving you 5.29

With that box and 17 / 46 you'd be getting 4.96

Yup, I've had all the gearbox ratio stuff out inc the gearbox visualiser and have got all the ratios but I was trying to suss out in the real world what the effect will be.

I'd say that the GP box will make it a little less likely to pull 4h but this will very much depend on your exhaust and where the kit is producing the peak power and torque.

Thats probably about it having looked at the recent dyno graph and the gearbox visualiser.

Thanks for the info.

[Monty]

Good luck with your gearing on the Casa, I ran an early one on my LI till it was pinched, it ran an Italian LI125 box on a 46-19, jetex and an ancilotti The Casa was a very torque engine but it stonewalls rev wise. Mine would pull like a train so I opted for 4th acting like an over dive, it ran a good 65 and after a tweak to the exhaust port by raising it 3mm it pulled 70. Yes I had to change down to 3rd for a hill, but it went up them like a train when others were going down into 2nd. I tried all combinations of sprockets and it does the same revs on any, the final speed was determined by the sprocket and you could gain or loose 5mph. My imola-JL3 is a different breed and needs to be kept buzzing