Tyre size · Fuel cost · MPG · Towing
What does 205/55R16 mean?
205 mm wide, a sidewall 55% of the width, radial, for a 16-inch wheel. Every number on your tyre sidewall means something — and changing it changes your speedometer, your fuel bill and how your car handles. TyreCalc decodes any tyre size, compares sizes side by side, checks speedometer error and works out trip costs, free and with no sign-up.
Search all 326 common tyre sizes, or browse the full chart. Tyre Size Chart →
Every calculator, grouped
Tyre tools
Tyre sizes, pressures, tread, load index and speed rating — everything about the four patches of rubber that hold your car to the road.
Tyre Size Calculator
Decode any tyre size
Tyre Size Comparison
Compare two tyre sizes
Speedometer Error Calculator
Actual speed after a tyre change
Plus Sizing Calculator
Plus-one and plus-two fitments
Tyre Pressure Calculator
Pressure by load — estimate
Tyre Age Checker
DOT date code to tyre age
Tyre Tread Depth Calculator
Remaining tread vs the legal limit
Tyre Load Index Calculator
Load index to kg and back
Tyre Speed Rating Calculator
Speed rating to max speed
Tyre Size Converter
Metric to flotation sizes
Fuel & running-cost tools
MPG, fuel cost, trip cost, EV comparisons and CO₂ — what your car costs to run, per mile and per year.
MPG Calculator
Miles per gallon
Fuel Cost Calculator
Cost of a tank or a trip
Trip Cost Calculator
Fuel plus tolls for a trip
EV vs Petrol Calculator
Electric vs petrol running cost
Fuel Economy Converter
MPG to L/100km and back
CO2 Emissions Calculator
CO2 from your driving
Diesel vs Petrol Calculator
Which fuel costs less per year
Fuel Tank Range Calculator
How far on a full tank
Cost Per Mile Calculator
All-in running cost per mile
Annual Fuel Cost Calculator
Yearly fuel bill
Performance tools
Gear ratios, rpm, towing, braking distance and quarter-mile estimates — the numbers behind how a car moves.
Gear Ratio Calculator
Ring and pinion ratio
RPM Speed Calculator
Engine rpm at road speed
Towing Capacity Calculator
Can you tow that trailer?
Tyre Cost Per Mile Calculator
Tyre wear cost per mile
Wheel Offset Calculator
Offset, ET and backspacing
Bolt Pattern Calculator
PCD from lug count
Tyre Diameter Calculator
Overall diameter from width and aspect
Revs Per Mile Calculator
Tyre revolutions per mile
Braking Distance Calculator
Stopping distance, dry and wet
Horsepower Torque Calculator
HP to torque and back
Quarter Mile Calculator
Rough ET and trap speed
Payload Calculator
GVWR minus curb weight
Guides by topic
Tyre Sizes Explained
Every number and letter on a tyre sidewall means something — width, aspect ratio, rim diameter, load index and speed rating. These guides decode any tyre size, explain what each marking means, and show how to read the size stamped on your own tyres.
Tyre Size Comparisons
Thinking of fitting a different tyre size? These comparisons put two sizes side by side — overall diameter, sidewall height, circumference, speedometer error and clearance — so you can see exactly what changes before you buy.
Tyres by Vehicle
The right tyre size depends on the vehicle. These guides list factory tyre sizes and common alternatives by make and model, with the speedometer and clearance effects of each change.
Fuel Cost Guides
Fuel is one of the biggest running costs of any car. These guides show how to work out the cost of a trip, a commute or a full year of driving from your car's consumption and the pump price — and where the money actually goes.
MPG Guides
Miles per gallon is the headline efficiency number, but it hides a lot. These guides explain how MPG is measured, how to convert between MPG, litres per 100 km and km per litre, and what your real-world MPG should be.
EV vs Petrol Cost Guides
Electric or petrol — which costs less to run? These guides compare charging costs against pump prices, mile for mile, including home charging, public charging and the petrol car you already own.
Towing Guides
Towing changes everything about how a car behaves — and how much fuel it uses. These guides cover towing capacity, nose weight, trailer weight ratios and the fuel cost of towing a caravan or trailer.
Gear Ratio Guides
Gear ratios decide how fast your engine spins at a given road speed. These guides explain final drive ratios, how a tyre size change alters your effective gearing, and how to work out RPM at motorway speed.
Speedometer Accuracy Guides
Your speedometer is allowed to read fast, but never slow — and changing tyre size moves the error. These guides explain speedometer error, the legal tolerance, and how much a new tyre size throws your speed reading off.
Tyre Cost per Mile Guides
A cheap tyre that wears out in 15,000 miles can cost more per mile than a premium tyre that lasts 30,000. These guides show how to work out the true cost per mile of any tyre from its price and tread life.
Tyre & Fuel Guides
The general guides: how to check tyre pressure, read tread wear, choose between summer, winter and all-season tyres, and keep your tyres — and your fuel bill — in good shape.
Why tyre size matters
A tyre is not just a rubber ring — it is the gearing, the speedometer and the suspension working together. Change the overall diameter by 3% and your speedometer reads 3% wrong, your gearing gets taller or shorter, and your ground clearance moves. Change the width and you change grip, aquaplaning resistance and fuel consumption. That is why the size on your door-jamb placard is not a suggestion: it is the size your car was designed, tested and type-approved with.
The same honesty applies to the money side. Fuel is usually the biggest running cost after depreciation, and small differences compound: 5 MPG is worth hundreds of pounds a year at 12,000 miles. A cheap tyre that lasts 15,000 miles can cost more per mile than a premium tyre that lasts 30,000. TyreCalc works all of it out from the numbers you already have — your tyre size, your MPG, your pump price — and labels every result an estimate, because real cars vary with driving style, load and conditions.
One warning that belongs on every page of this site: a calculation is never a safety approval. If a tool says a size “fits” within ±3%, that is a diameter check, not a guarantee that the tyre clears your arches, matches your load index or is legal on your car. Check the placard, match or exceed the load index and speed rating, and ask a tyre professional before you buy. Read how we work in our Editorial Policy, and see the full tyre size chart for all 326 common sizes.
From the guides
145/80R13 vs 155/70R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect
145/80r13 vs 155/70r14 tyre size comparison: diameter differs by +10.4 mm (+1.8%), with the side-by-side dimensions, speedometer error at 30, 50 and 70 mph,.
145/80R13 vs 165/70R13: Tyre Size Comparison, Diameter Difference & Speedometer Effect
145/80r13 vs 165/70r13: diameter differs by -1.0 mm (-0.2%), with the side-by-side dimensions, speedometer error at 30, 50 and 70 mph, and clearance checks.
155/65R13 Tyre Size: Dimensions, Alternatives & Speedometer Effect
What is 155/65R13? Diameter 531.7 mm, sidewall 100.8 mm, circumference 1670.4 mm, 963.5 revs per mile and the closest alternatives explained. — full guide.
155/65R13 vs 165/60R13: Tyre Size Comparison, Diameter Difference & Speedometer Effect
155/65r13 vs 165/60r13: diameter differs by -3.5 mm (-0.7%), with the side-by-side dimensions, speedometer error at 30, 50 and 70 mph, and clearance checks.
155/65R14 Tire Size: Dimensions, Alternatives & Speedometer Effect
What is 155/65R14? Diameter 557.1 mm, sidewall 100.8 mm, circumference 1750.2 mm, 919.5 revs per mile and the closest alternatives explained. — full guide.
155/65R14 vs 165/60R14: Tyre Size Comparison, Diameter Difference & Speedometer Effect
155/65r14 vs 165/60r14: diameter differs by -3.5 mm (-0.6%), with the side-by-side dimensions, speedometer error at 30, 50 and 70 mph, and clearance checks.
Frequently asked questions
What does 205/55R16 mean on a tyre?
205 is the width in millimetres, 55 is the aspect ratio — the sidewall height is 55% of the width — R means radial construction, and 16 is the rim diameter in inches. So 205/55R16 is a 205 mm wide radial tyre for a 16-inch wheel. The letters and numbers after it are the load index and speed rating.
Can I fit a different tyre size to my car?
Sometimes, but only within limits. The overall diameter should stay within about ±3% of the original size, and the load index and speed rating must match or exceed the original. Even then, clearance, braking and handling can change. Always check your door-jamb placard and owner's manual, and ask a tyre professional before fitting a different size — a calculation is not a safety approval.
How much does changing tyre size affect my speedometer?
Your speedometer reads from wheel revolutions, so a larger tyre makes it read slow and a smaller tyre makes it read fast. A 3% larger diameter means at a true 70 mph your speedometer reads about 68 mph. Use the speedometer error calculator to check any size change before you buy.
How do I work out fuel cost for a trip?
Divide the trip distance by your car's MPG to get gallons used, then multiply by the price per gallon. For a 200-mile trip at 40 MPG and £1.45 per litre, that is 5 gallons — about 22.7 litres — costing roughly £33. The fuel cost calculator does the maths for any distance, MPG and pump price.
Are the results on TyreCalc exact?
No — every result is an estimate for planning. Tyre dimensions vary slightly by manufacturer, fuel consumption varies with driving style and conditions, and pump prices change daily. Fitment results are calculations, not safety approvals: check your door-jamb placard, load index and speed rating, and consult a tyre professional before changing tyre size.