Understanding the markings on the sidewalls of tyres will help you to choose the right tyres for your car. Here's a guide to those sidewall markings using a 175/80 R14 88H tyre as an example. (29.6.08)

175 - Tyre width across the tread measured in mm.

80 - Aspect ratio or profile height of the tyre calculated as the sidewall height expressed as a percentage of the tyre width. So a tyre with an aspect ratio of 80 is a tyre whose height is equal to 80% of its width. Modern tyres have lower aspect ratios - for example 60 - than the 80 originally fitted to the MGBGTV8.

R - Radial construction. This marking is almost redundant these days because very nearly all tyres for cars are radials but when the MGBGTV8 was launched in 1973 tyres with crossply construction were still available and fitted to some vehicles. Radial tyres were specified equipment for the MGBGTV8 from its launch.

14 - Wheel rim diameter. This is the diameter in inches of the rim of the wheel that the tyre has been designed to fit.

88 - Load index is a numerical code which gives the maximum load that the tyre can carry whilst it is travelling at up to the maximum speed set by the speed rating of the tyre.

H - Speed rating indicates the maximum permitted speed that the tyre can endure for a period of ten minutes without being in danger of sustaining damage.
This is a summary of a more detailed note which is available as a download. More

Important note
regarding load index and speed rating. It is essential you do not fit tyres to your vehicle with a lower speed rating or load index than recommended by the vehicle manufacturer. Fitting lower speed rated tyres or tyres with a lower load index may invalidate your insurance. Although the UK speed limit is just 70mph, most vehicles are more than capable of exceeding this speed. Therefore vehicle insurance companies will insist that the tyres of the correct speed rating are fitted to your vehicle.

Replacement tyres for the MGBGTV8 model
The original tyre specified in MGBGTV8 Driver's Handbook AKD 8423 was 175HR x 14 radial ply. The current replacement tyre to maintain the key original features of the model - the original appearance of the wheels in the wheel arches and drive train gearing - is a 175/80 R14 88H.

Replacement tyres for the MG RV8 model
The original tyre specified in MG RV8 Owner's Handbook AKM 7144ENG was 205/65 ZR 15. The current replacement tyre to maintain the key original features of the model - the original appearance of the wheels in the wheel arches and drive train gearing - would be a 205/65 R15 94V.

Tyre Size Change Calculator
Enthusiasts preferring what they feel might be uprated handling with other wheel size and/or tyre width and aspect ratio combinations will need to use the Tyre Size Change Calculator on the etyres website to check the net effect on drive train gearing, refer to the useful information in V8NOTE187 and seek advice from a reputable tyre specialist with experience of modern tyres for classic sportscars like the MGBGTV8 and MG RV8.
Tyre Size Change Calculator
This note has been prepared by Victor Smith with helpful contributions from Gordon Hesketh-Jones, Chris Hunt Cooke, Bob Owen, Ian Quarrington and Dave Wellings. (1.7.08)
V8 Register - MG Car Club - the leading group for MG V8 enthusiasts at www.v8register.net