Lambretta Gearbox Calculator

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Lambretta Gearbox Calculator

Calculate gear ratios, top speed per gear, and RPM for all Lambretta models. Enter your sprocket teeth, engine RPM, and tyre size — get instant split-by-gear results.

⚙️ All 4 gears calculated
🛵 All Lambretta models covered
🏁 Top speed per gear
🔧 Custom sprocket support
4
Gears calculated
Individual speeds & RPMs
6+
Lambretta models
Series 1 to GP & beyond
km/h
& mph output
Both units displayed
100%
Free to use
No sign-up needed
Free Tool

Calculate your Lambretta gear ratios & top speed

Select your model to auto-fill standard gearbox specs, then customise sprocket teeth, engine RPM, and tyre size to calculate speed and ratio for each gear.

Your Lambretta details

Select a model or enter your own gearbox specs below

Model preset
Engine & drive
RPM

Typical range: 5,500–7,000 RPM stock. Tuned engines may reach 8,000–10,000+.

drive
driven

Standard: 18/68 (LI/SX), 17/65 (GP). Drive sprocket / driven gear teeth.

engine
wheel

Engine (drive) sprocket teeth / rear wheel (driven) sprocket teeth.

Internal gearbox ratios

Enter the tooth count for each gear pair (driving / driven). Standard values are auto-filled when you select a model above.

1st Gear
2nd Gear
3rd Gear
4th Gear
Tyre & wheel

Your Gearbox Results

Ratios, speeds & RPM per gear

⚙️

Select a Lambretta model or enter your own gearbox specs, then click Calculate to see gear ratios, top speed per gear, and RPM breakdown.

Model Guide

Lambretta models explained

From the original Series 1 to the iconic GP, here’s a guide to the key Lambretta models and their standard gearbox specifications.

🛵

LI 125 / LI 150 Series

The backbone of Lambretta’s lineup. Produced from 1958, the LI (Lusso Internazionale) established the classic Lambretta format. The 150cc version became the most popular.

Production1958–1971
Gears4-speed
Primary drive18/68
Final drive16/47
🏁

TV 175 / TV 200

The touring (Turismo Veloce) range — sportier versions with larger engines and uprated gearing. The TV 200 was the fastest production Lambretta of its era.

Production1957–1965
Gears4-speed
Primary drive18/68
Final drive17/47
✨

SX 200

The SX (Super Extra) range launched in 1966 brought a sportier look. The SX 200 was the performance flagship — fitted with the uprated engine from the TV 200.

Production1966–1969
Gears4-speed
Primary drive18/68
Final drive17/47
🔥

GP 200 (DL 200)

The final Lambretta produced in Italy — and arguably the most refined. Known in some markets as the DL 200. Still considered the peak of Lambretta development by many enthusiasts.

Production1969–1975
Gears4-speed
Primary drive17/65
Final drive17/47
🔧

Indian / Serveta variants

Licensed production continued in India (SIL) and Spain (Serveta) after Italian factory closure. Some models featured slightly different gearing to standard Italian specs.

Production1975–1997 (India)
Gears4-speed
Primary drive17/65 (GP-based)
Final drive17/47
⚡

Custom & Tuned Builds

Many Lambrettas run non-standard gearing — close-ratio gearsets, alternative sprocket combos, or uprated primary drives. Use the Custom option to enter any sprocket combination.

Close ratio kitsAvailable
Primary options15–21 tooth
Final driveAny combination
RPM rangeUp to 10,000+
Reference

Standard Lambretta gearbox specifications

Factory gearbox tooth counts and drive ratios for the main Lambretta models. Use these as a baseline for your own calculations.

Model Primary ratio Final drive 1st gear 2nd gear 3rd gear 4th gear
LI 125 S318/6816/4713/3517/3221/2826/26
LI 150 S318/6816/4713/3517/3221/2826/26
TV 175 S318/6817/4713/3517/3222/2827/26
SX 20018/6817/4713/3517/3222/2827/26
GP 20017/6517/4713/3517/3222/2827/26
Tuning Guide

How to optimise your gearing

Changing sprocket sizes is one of the most effective and affordable ways to tune your Lambretta for your riding style.

🔼

Taller gearing (more top speed)

Increase the engine sprocket teeth OR decrease the rear wheel sprocket teeth. A 17-tooth engine sprocket vs 16-tooth gives approximately 6% more top speed but reduces acceleration.

🔽

Shorter gearing (more acceleration)

Decrease the engine sprocket teeth OR increase the rear wheel sprocket teeth. Useful for two-up riding, hills, or stop-start city riding. Reduces maximum speed by roughly the same percentage.

⚙️

Close-ratio gearsets

After-market close-ratio gearsets reduce the gap between gears — more common in tuned engines running on a narrower powerband. Less step between each gear change improves performance.

🔄

Primary drive ratio

The primary drive (from crank to clutch) is often overlooked. A larger drive sprocket increases primary ratio and engine braking but can affect clutch operation if not set up correctly.

🏎️

RPM & powerband matching

The ideal gearing puts your engine at peak power RPM at your target speed in 4th gear. Use this calculator to find the final drive ratio that achieves this for your specific engine tune.

🔵

Tyre size impact

A larger diameter tyre effectively tallens your gearing — it covers more ground per wheel revolution. A 110/90-10 vs a 3.00-10 can add several km/h to top speed without touching a sprocket.

About This Tool

Accurate ratios for every build

Our Lambretta gearbox calculator uses the proven overall gear ratio formula — combining primary drive, internal gearbox ratio, and final drive sprockets — to give precise speed and RPM results for each gear.

Standard presets are sourced from factory service manuals and verified against the Lambretta Club GB technical data. Custom mode lets you enter any sprocket combination for modified builds.

  • ✓Full 4-gear speed and ratio breakdown
  • ✓Primary drive, internal gears, and final drive all combined
  • ✓Standard presets from factory service manual data
  • ✓Custom sprocket entry for any build
  • ✓km/h and mph output with visual speed bars
  • ✓No data stored — runs entirely in your browser
Help & Info

Lambretta gearbox FAQs

How do I calculate Lambretta gear ratios?
The overall gear ratio for any gear combines three separate ratios: primary drive ratio (crankshaft sprocket ÷ clutch gear), internal gearbox ratio (driving gear teeth ÷ driven gear teeth for that gear), and final drive ratio (engine sprocket ÷ rear wheel sprocket). Multiply all three together to get the overall ratio. Divide engine RPM by this ratio, then multiply by wheel circumference to get speed in metres per minute, which converts to km/h or mph.
The GP 200 uses a primary drive of 17/65, a final drive of 17/47, and internal gearbox ratios of 13/35 (1st), 17/32 (2nd), 22/28 (3rd), and 27/26 (4th). These can be loaded instantly by clicking the GP 200 preset in the calculator above. With standard 3.50-10 tyres and 6,500 RPM, this typically gives a top speed of around 90–95 km/h in 4th gear.
To increase top speed without engine modifications, you can fit a larger engine sprocket (e.g. 17-tooth instead of 16-tooth) or a smaller rear wheel sprocket. Each tooth added to the engine sprocket adds roughly 5–7% more top speed. A 17/47 final drive is taller than 16/47 and will increase top speed. You can also fit slightly larger tyres. However, taller gearing reduces acceleration — use this calculator to model different combinations before buying parts.
The main differences are in the primary drive and the 3rd/4th gear ratios. The LI 150 uses an 18/68 primary drive, while the GP 200 uses a slightly lower 17/65 primary. The GP also has taller 3rd and 4th gears (22/28 and 27/26 vs 21/28 and 26/26 on the LI 150). Combined with the larger 200cc engine producing more torque, the GP can carry these taller ratios comfortably — making it faster overall but needing more revs to pull away from low speeds.
Yes — tyre overall diameter directly affects your effective gearing. A larger tyre travels further per wheel revolution, which effectively tallens your gearing. The standard Lambretta 3.50-10 tyre has an overall diameter of approximately 457mm. Switching to a 110/90-10 modern tyre (approx. 468mm diameter) adds roughly 2.5% to your effective top speed. Our calculator lets you select from common tyre sizes or enter a custom diameter.
Standard Lambretta engines typically produce peak power between 5,500 and 6,500 RPM, with a comfortable cruising range of 4,000–5,500 RPM. Tuned engines with ported cylinders, uprated carburettors, and expansion chambers can extend the power band to 7,000–9,000+ RPM. When setting up gearing, aim to have 4th gear top speed occur at or slightly below your engine’s peak RPM — this ensures you’re using the full power range without over-revving.
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