lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning Home lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning lambretta scooter lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning lambretta uk lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning lambretta parts lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning lambretta spares lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning lambretta tuning lambretta scooter, lambretta uk, lambretta parts, lambretta spares, lambretta tuning Search engineering ISP,hosting,design,online shopping local national standard rate phone numbers, 0845, 0870, 0906 vepsa and lambretta motorcycles


You are here: Home > Lambretta > Lambretta tuning > Gearing information
    

Gearing information

GEARING RECOMMENDATIONS FOR TUNED LAMBRETTAS

Gearing is very simple but very misunderstood.
Getting the gearing right on a tuned Lambretta is very important.
Over gearing would mean the scooter doesn't pull in 4th and sometimes in 3rd.
Under gearing would mean the engine is being thrashed all the time.
Lambretta engines are very lucky in the fact that there are so many possibilities available given standard Lambretta gearboxes, special close ratio gearboxes, different drive / crownwheel sprockets and rear tyre sizes.

THERE ARE NOW 720 GEARING VARIATIONS AVAILABLE.

We don't need to go into any theories about gearing we need to look at what is possible, what works, what is worth doing and what is not worth doing.

125 ENGINES

There are four engines with three different gearboxes.

MODEL GEAR CLUSTER TEETH GEAR TEETH DRIVE SPROCKET CROWNWHEEL OVERALL RATIO
Li125
Series 1 and 2
Early Series 3
1
2
3
4
9
12
16
19
51
42
39
35
15
46
17.41
10.75
7.49
5.65
Li125
Late Series 3
1
2
3
4
11
13
17
19
50
41
39
35
15
46
13.97
9.67
7.03
5.64
Li125 Special
GP 125
1
2
3
4
10
12
15
18
50
42
39
36
15
46
15.35
10.75
7.98
6.14

Li 125 Series 1 and 2, Early Series 3

This gearbox has a very high revving 1st and 2nd gear with a big jump between 2nd to 3rd.
It tends to over rev in top gear which would limit its top speed.
If the scooter is a wide style then standard gearing could possibly be fine as a high revving gearbox would suit the weight and size of the machine.
Increasing the front sprocket to a 16 tooth would raise the gearing to have an overall top ratio of 5.30:1 which possibly its best set up, this would however make the jump between 2nd and 3rd even more noticeable!
Swapping the gearbox to a LI 150 Italian would improve the all round performance.

Li 125 Late Series 3

This gearbox tends to over rev which would limit its top speed.
Increasing the front sprocket to a 16 tooth would raise the gearing to have an overall top ratio of 5.30:1 which possibly its best set up.
Swapping the gearbox to a LI 150 Italian would improve the all round performance.

Li 125 Special and GP 125

This gear box certainly over revs, which definitely limits the top speed.
Increasing the front sprocket to a 16 tooth would only raise the gearing to 5.76:1 in top gear, which in most circumstances is still too high revving.
Swapping the gearbox to a LI 150 Italian would be the easiest solution or swap the drive sprocket, crownwheel, chain and bottom chain guide to GP200 (18 x 47, 82 link) this then gives the same top gear ratio as the LI150 ideal for the 150 Ė 175 conversions.

150 ENGINES

There are 6 engines with 4 different gearboxes.

MODEL GEAR CLUSTER TEETH GEAR TEETH DRIVE SPROCKET CROWNWHEEL OVERALL RATIO
Li150
Special
Pacemaker
1
2
3
4
11
13
17
19
50
41
39
35
15
46
13.97
9.67
7.03
5.64
SX150
GP150
Li150
Special
1
2
3
4
10
12
15
19
50
42
39
35
15
46
15.36
10.75
7.98
5.65
Li150
Series 1/2/3
Italian
1
2
3
4
11
14
17
20
50
41
37
34
15
46
13.97
9.01
6.69
5.22
Li150
Series 3
Spanish
1
2
3
4
11
13
17
20
50
41
39
34
15
46
13.97
9.67
7.03
5.22

Li 150 Special Pacemaker

This gearbox tends to over rev which would limit its top speed.
Increasing the front sprocket to a 16 tooth would raise the gearing to have an overall top ratio of 5.30:1 which possibly its best set up.
There is a post mod and pre mod version of this gearbox, both should be fine in 175 conversions, but the pre-mod versions tend to break used in 200 motors.
Swapping the gearbox to a LI 150 Italian would improve the all round performance.

SX, GP and Li 150 Special

This gearbox tends to over rev which would limit its top speed.
Increasing the front sprocket to a 16 tooth would raise the gearing to have an overall top ratio of 5.30:1 which possibly its best set up.
This gearbox has a massive jump between 3rd and 4th gear raising the front sprocket makes the gap more noticeable!
The best conversion would be to swap the gearbox to Li150 Italian.

Li150 Series 1/2/3

This gearbox is a very good all round gearbox suiting all tunes.
Fitting a 16 tooth sprocket raises the gearing too 4.90:1 which is ideal for the more powerful engines.

Li150 Spanish

This gearbox has a massive gap between 3rd and 4th and I don't recommend it, change the box to Li150 Italian.
Definitely don't fit a 16 tooth sprocket!

175 ENGINES

There is only one gearbox for the 175 engines.

MODEL GEAR CLUSTER TEETH GEAR TEETH DRIVE SPROCKET CROWNWHEEL OVERALL RATIO
TV175
Series 1,2 and 3
1
2
3
4
12
14
18
21
49
40
37
33
15
46
12.53
8.78
6.32
4.84

TV 175

This engine has a very high ratio gearbox only suited to very torquey engines.
If your engine is intended for two up driving then consider fitting the Li 150 gearbox.
Fitting a 16-tooth sprocket usually makes the engine slower in 4th.
Changing the rear crownwheel sprocket helps the gearing and gives a top ratio of 4.91:1 this ratio would be more suited to this engine.

200 ENGINES

There are 3 engines and gearboxes

MODEL GEAR CLUSTER TEETH GEAR TEETH DRIVE SPROCKET CROWNWHEEL OVERALL RATIO
SX200
Jet 200
(Same as TV175)
1
2
3
4
12
14
18
21
49
40
37
33
15
46
12.53
8.78
6.32
4.84
GP 200
Italian
Indian (16/38) 3rd
1
2
3
4
10
12
15
18
50
42
39
36
18
47
13.05
9.14
6.79
5.22
TV/GT 200
1
2
3
4
13
15
19
22
47
39
36
32
15
46
11.11
7.98
5.81
4.45

SX 200 Engines

The SX 200 gearbox is a good all round gearbox, but the engine needs some pulling power to pull 4th especially two up!
Changing the crownwheel to a 47 tooth improves the top gear ratio too 4.91:1.
Consider changing the gearbox to Li 150 to improve engines that don't pull 4th.

GP 200 Engines

There are 2 types of gearboxes, Italian and Indian.
These gearboxes rev quite high in 4th gear, changing the front sprocket to a 19 tooth is the first conversion most people do, and will give a ratio of 4.94.
It is possible with some engines to use 19 x 46 which gives a ratio of 4.84.
The Italian gearbox has a larger jump between 3rd to 4th.
The Indian gearbox has a larger jump between 2nd to 3rd.
The GP 200 engine altered the drive sprocket arrangement to larger sprockets, this means the actual gearbox spins so much faster!
Increasing the front sprocket increases the speed of the gearbox, which in turn over the years chips away at each loose gear.
The gear selector chips also and usually the cluster bearing surface wears away too.
For this reason I tend not to recommend this gear set up unless all parts are perfect!
It is not uncommon for gear teeth to chip off also.

TV 200 Engines

This gearbox in most circumstances has too high gearing!
Fitting a 47 tooth rear sprocket helps and gives a top ratio of 4.54:1 but is still usually too high.

ODD BALL GEARBOXES

There have over the years been a number of odd ball gearboxes to come and go.
If you read the various booklets around some are mentioned, some are common some are not.
The most famous was probably the 5 speed item, this is still available to day, beware! even the remade one is not up to any power.
The Rally master of the early sixties had a special cluster made up. These are so rare I haven't seen one.

One gearbox rears its ugly head now and then and most dealers haven't seen one either. This gearbox was fitted to a batch of Indian scooters in the 1980ís. Again I wouldn't worry about this gearbox, as it is quite rare!
There have been a number of scooter racers that have made their own close ratio clusters and used loose gears.
Probably the most well known was MSC, who modified Pacemaker and Spanish clusters to make close ratio gearboxes.
AF Rayspeed had a complete close ratio gearbox made based on to MSC item. These were made in India and is still available today, beware! power full engines break gear teeth regularly.
Taffspeed also made a total one off gearbox but this didn't work and disappeared.

MB Developments have also made a number of close ratio gearboxes for different applications, mainly racing and sprinting.
Our most common gearbox uses an exchange Li or SX gear cluster.
Gearbox 1, uses 4 loose Li gears with a modified cluster to make the jumps between 2nd, 3rd and 4th very close.
Gearbox 2, uses 1st and 2nd gears from a SX 200, then uses 3rd and 4th Li gears to make another close ratio box but with a higher 1st and 2nd gears.
Both gearboxes were ideally suited to road race spec TS1 engines and used 18 x 47 sprockets as standard, which gives a very good all-round gear ratio especially when riding two up!

MODEL GEAR CLUSTER TEETH GEAR TEETH DRIVE SPROCKET CROWNWHEEL OVERALL RATIO
MRB (UK)
Li150 gears
Special cluster
1
2
3
4
11
14
16
18
50
41
37
34
18
47
11.88
7.65
6.03
4.93
MRB (UK)
SX200 1st and 2nd
Li150 3rd and 4th
Special cluster
1
2
3
4
12
14
16
18
49
40
37
34
18
47
10.65
7.46
6.03
4.93

GEARBOXES THAT WORK

There are hundreds of gearing combinations available for Lambretta engines.
What is best for each engine presuming the gearbox is original to the engine has already been covered.
MB Developments recommend for most engine applications the LI 150 Italian and SX 200 gear box.
The reason is; both have reasonably good gear ratios and jumps between each gear, which suits nearly all road going Lambrettas.
The gear parts are strong, they don't usually break or wear out.
You can fine-tune the gearbox by changing usually only one sprocket in either direction.
Slight differences in tyre sizes can also fine-tune the gearboxes further.

GEARING ALTERATIONS THAT WORK

You could play around with Lambretta gearboxes forever!

What makes one Lambretta pull a certain gear set up and another Lambretta not pull the same set up can depend on a number of factors.
What works comes down to experience with a particular engine type and size, height of exhaust port and exhaust used.

Gearing should be set up to suit the factors given and your type of riding.
You need to look at 3 areas that could suit you.

  1. Do you only ride two up?
    You would require a gearbox that lets the engine pull off from a stand still with out stalling or having to use to much clutch slip and a combination of pulling 4th gear at the speeds you want to travel.
  2. Do you ride occasionally one up and occasionally two up?
    You would require a combination to suit both styles of riding. Over gearing would make life hard work two up but OK on your own. Under gearing would lower the scooters top speed when on your own.
  3. Do you only drive one up?
    If you ride on your own then set the gearing to suit the type of riding and speed you do. If you cruise at 60mph then high gearing is not required just average standard gearing. If you what to do excessive speeds then very high gearing would be required.
Then you need to consider some facts:-

Then you need to consider some more facts:-

All these factors will effect the perfect engine. An engine set up correctly works better and becomes more reliable.

GEAR RATIOS EXPLAINED

Some confusion can take place when mentioning high and low gearing, or lowering or raising the gearing. A GP 125 gearbox has a high revving gearbox with a top gear ratio of 6.12:1 and is considered to have a low gear ratio. A GT 200 gearbox has a low revving gearbox with a top gear ratio of 4.44:1 and is considered to have a high gear ratio. The gear ratio means for the GP 125, the engine has to turn 6.12 times to make the rear wheel turn once. Raising the gearing usually means increasing the front sprocket making the gear ratio higher! This all doesn't seem correct thinking about it practically but thatís how it goes, its not too important anyway.

PRACTICAL GEAR ALTERATIONS

What ever gear box you use you will have to choose a correct sprocket arrangement.

All gearboxes use 15 x 46 as standard this uses an 80 link chain, new or slightly worn.
To raise your gearing (i.e. increase the gear ratio) you can do this by fitting a 16 tooth front sprocket, this requires a worn 80 link chain for the sprocket to fit.
To lower your gearing you could use a 47-tooth rear sprocket this requires a well-worn 80-link chain.

The exception to the above is the GP 200 which uses 18 x 47 as standard this uses an 82 link chain, new or slightly worn.
To raise your gearing (i.e. increase the gear ratio) you can do this by fitting a 19 tooth front sprocket, this requires a worn 82 link chain for the sprocket to fit. To raise the gearing further you could use 19 x 46 this requires a new 82 link chain but still looks worn.

These are the easy conversions as used by MB Developments, chosen for their simplicity and gear ratios that work for an all round performance.

If you decide to use a combination of 14, 17, 20, 21 or 22 front sprockets or 45 and 48 crownwheels then half links or one and a half links would have to be added to a chain. This is a big mess around and practically is not really needed for road engines!
If your engine is a track scooter then you may well choose to go down this route!

A common example of this is a TS1 using a LI 150 with 17 x 46/47 it requires an 81-link chain, gearing may be perfect but there were no good off the shelf chains available making this set up not very good.

We now stock the IWIS type chain with a riveted in half-link. Although it is early days we have not heard of any problems with these type of 81 link chains.

GEARING FOR TS1 ENGINES

Until the TS1 cylinder was introduced Scooterists used to have stage 4 or 5 type 200 tunes as quick engines.
These engines in their day had relatively small exhaust ports that gave good pulling power through out the rev range.
OK, the horsepower was down compared to the TS1 but they pulled nearly any gearing going.
It wasn't uncommon for engines to use GT 200, SX200 with 16 tooth sprockets, GP 125 with 46/47 x 19/20/21 or 22 teeth!
Giving top gear ratios of up to 4.38:1, indeed very high gearing by todays standard, cylinder heads used higher compression ratios, the fuel had higher octane and engines pulled the high gearing.

The TS1 cylinder has larger transfer and exhaust port heights with larger port timings putting the power higher up in the rev range, with less amount of low down power or a lack of power until you hit the power band!
When the TS1 cylinder appeared SX 200 46 x 15 and GP 200 46 x 19 gearing was suggested.
This gives a top gear ratio of 4.84:1 to 4.80:1. based around what had always been used.
Factors already mentioned dictates what gearing can be used. In reality the suggested gearing was far too high for every day use.

Depending on how the exhausts power comes in MB Developments suggests slightly higher revving gear ratios, from 5.20:1 to 4.90:1.
OK, you may loose some top end speed but life is much easier at normal cruising speeds.

At the end of the day a TS1 cylinder is a race cylinder.
The original TS1 set up would use a 34-36mm carb, race expansion etc set up for top end speed coupled with the suggested gearing.
This would be fine to drive one up with most of the time driving with your head down and yes if the exhaust allowed it, engines could maybe top the ton!
Put two people on the same scooter and suddenly the old cast cylinders left you standing!

EXHAUSTS AND HOW THEY EFFECT GEARING

A lot of exhaust development has gone ahead since the introduction of the TS1 cylinder and it could be said some engine designers have come on leaps and bounds.
The exhaust system tells the engine how it is going to work.

Most of this work has gone ahead on Dynoís they are an excellent way to show power but are not the be all and end all!

If you read a print out of that engines power output graph, the graph starts at zero horsepower and zero revs or in some cases zero speed.
The graph will then rise and reaches a peak giving maximum horsepower, the graph then drops on a downward scale but keeps revving on.
Every read out in a magazine I have seen follows the horse power to the end of the graph stating its maximum top end revs or speed. This is fine on a dyno with no rolling drag or wind and with a ľ of a ton of roller still in full motion, in reality this doesn't work.

Reality is a full body Lambretta with a normal weighted person, with normal gearing and a correctly set up engine in normal road going conditions. As soon as the graph drops and for approximately another 500 rpm this will be the engines true top end speed! Believe it or not you may think you are doing 90mph but in fact it may only be doing 75mph!

For an example a MB Developments stage 2 road race tune worked well with most common exhausts and gave 19 - 22 horsepower, our Devtour gave 23 - 24HP, one of our race exhausts gave 28 HP! A standard tail pipe Clubman gave 15HP! That is the difference that exhausts can make to your engine.

The Clubman limited the engine revs to 7000 to 7500rpm.
Other exhausts limited the revs to 7000 to 7500rpm but gave more horsepower allowing higher gearing to be used!
Other exhausts lost bottom end power and gained power higher up in the rev range revving to 8000 to 8500rpm.
Some exhausts allowed the engine to rev to 10,000rpm.

The difference in speed between 7000rpm and 10,000rpm is 30 miles per hour! A massive difference!

As shown by our example exhausts do make a big difference.
The Clubman looks poor at 15HP but it gave the best spread of power and some people love their engines set up that way, as it will give 70mph all day!
Other exhausts can give the same top HP but power can be in a different part of their rev range. This can depend on a number of factors already mentioned.
It is impossible to make an exhaust to give perfect power across the rev range, I know I have dynoed different exhausts over 400 times to try to improve our Devtour exhaust which is now over 8 years old, and to date we havenít found a better exhaust for all round spread of power with speed!

TS1 EXHAUST EXAMPLES

I am not stating this to slag off any mentioned exhausts, itís a fact of how that exhaust works.

Taffspeed exhausts give excellent low down power but donít rev much beyond 6500 Ė 7500 rpm.
Making it good for two up riding but no good for racing.
If you used normal gearing like an SX200, which basically equates to one to one, gearing to speed then your true top road speed is actually around 65 - 75mph.
Because the Taffspeed exhaust has so much low down power higher gearing can be used to compensate for more top end speed.
We had one engine set up with a Taffspeed that used SX200 gears with 46 x 16 tooth sprockets giving a top gear ratio of 4.52:1, that engine pulled easy down to 30 mph in top making it very easy to drive and still revved out in top gear.
This engine was an exception and normal gearing recommendations would be 4.84:1 to 4.60:1 for a good engine using the Taffspeed exhaust.

On the other hand a NK exhaust or Kegra does the opposite and doesnít hit power until around 5000 - 6000 then the power kicks in.
This style of exhaust tends to be no good for touring or two up riding as there isnít enough power out of its power band.
Using normal gearing usually means the engine doesnít pull 4th gear unless riding conditions are in your favour.
But if ridden hard constantly it could be possible to get 10,000 in top gear giving you that 100mph!
You may chose to use a higher revving gearbox i.e. straight Li or GP, this would limit your top end speed but makes life easier at lower speeds as its is easier to stay in the engines power band at normal riding speeds.

The MB Developments Devtour was developed to work on either cast or TS1 type engines.
We looked at how the opposition's pipes worked and listened to customers requirements.
Basically people wanted a mixture of bottom end power and top end power.
As previously mentioned having all this is impossible!
This is probably why the automatic 2 strokes have taken off so well as they give an all round performance using variable gearing!
The Devtour has slightly less bottom end than a Taffspeed and slightly less top end to a NK, but has power between the both of them.
The Devtour has good usable pulling power from 5000 (50mph) to 8000rpm (80mph) with peak power at 7000rpm or 70mph with reasonably high horse power making it a perfect touring pipe! Higher gearing raises the speed if required.

SPEEDOS AND REV COUNTERS

Never trust a Lambrettas speedo itís a well-known fact that some work some donít.
Some look like windscreen wipers, some are slow and some are fast!
But then again you get the odd one that is perfect! I had a perfect one on my LC in the early 80ís, I know because I was doing 85mph with my head down to look at the side of me only to see a Police car clocking me!
The best way to read your speed is to fit a good rev counter and using a formula based on revs, gear ratio and rolling circumference of your tyre you can work out your speed in top gear.
I use my rev counter as my speedo as this method is very accurate.
When testing my sprinter once I worked out my revs to speed and confirmed it correct to 0.5 of a mph at 108.5mph by a police speed camera! Thatís good enough for me!
If you're worried about your speed then purchase a good rev counter.

CHAINS

Whatever chain and sprocket arrangement you use MB Developments only use these chains,

Any other makes beware they wear out and rollers fall off!

Available from MB Developments is a total gearing spec sheet showing every possible gear combination, with information about all aspects of Lambretta gearboxes, only £3 for all you could want to know about gearing.

Please E-mail us with any questions or comments.