How to Read Tire Markings
- 215/225: The tire width in millimeters from sidewall to sidewall.
- 70: The aspect ratio (sidewall height). This is the height of the tire expressed as a percentage of the width.
- 15: The wheel or rim diameter measured in inches
Tire width has increased from 215 to 225 mm i.e. 10mm (under 1/2 inch)
Tire height has increase from 70% of 215 mm to 70% of 225mm which is 7mm (under 1/3 inch).
The increase in tire height increases the diameter of the wheel & thus the circumference.
This means that one revolution of the wheel will take the MoHo further than the speedometer & the odometer think it has gone.
i.e. the speedometer & the odometer will give low readings.
I'm not going to show the calculation because for those who know it is trivial, and for those who don't it looks complex, but the under reading will be just over 1.3%.
i,e, when you are travelling at 50mph the speedo will show just over 49mph.
When you travel 1,000 files the odometer will show over 9988,
Instead of revving at 4,000 rpm at a given speed the engine will be at over 3,950 rpm
Management summary - the impact of upsizing the tyres of speedometer / odometer is not worth worrying about.
A word to the wise the - increase in tyre width may result in tyres contacting body work or chassis.
I used to be involved in 4x4 off road motor sport and saw a lot of over sized tyres damaged by steering stops.
Adjustment would have taken under 5 minutes but some people will not listen.
