Tyre Size Question

[astam]

The tyres on my Lux are 31X10.5XR15.

As explained to me by the HIQ 'expert'
31 refers to their width
10.5 refers to the sidewall height (as a % of the width?)
and R15 is the rim size.

My understanding is:
31 refers to the overall height
10.5 refers to the width
R15 is the rim size

Now I'm confused. Or is it the 'expert' who is confused?

[ThysdJ]

The tyres on my Lux are 31X10.5XR15.

If I am not mistaken (please correct me if I am)
31 refers to their width
10.5 refers to the sidewall height (as a % of the width?)
and R15 is the rim size.

My questions then are:

What difference would it make to performance,handling, consumption,etc, etc if I put on 31X9.5XR15 ?

What is the purpose or what are the pros/cons of having a bigger/smaller sidewall?

The dimension work as follows:
31 refers to their height
10.5 refers to width
and R15 is the rim size.

The 9.5 would be narrower than the 10.5. :D :D :D

[CasKru]

I would say it all depends on what you want to do. According to me on road use you want lower profile and off road you want higher profile. The advantages of higher profile us that the tyres absorbs more of the "noise" from the road in other words it gives you a smoother ride but the drawback is that you have more sidewards roll / movement which makes it more unstable when carrying load or towing. The lower profile is beter in sidewards roll / movement but does not absorb the "noise" from the road as much.

When off roading you want a high profile because if you deflate the tyres, they form a bigger footprint than low profiles at the same pressure.

31x10.5x15 will have a greater circumference than a 31x9.5x15 but will be the same width as far as I know m2cw

[astam]

Thanks gents. Did a small edit to the original question after thinking this through for 10 mins. You are too quick! But from the above replies I'm still confused. Is 10.5 wider or higher than 9.5 ?

[ThysdJ]

Is 10.5 wider or higher than 9.5 ?

It is wider... :D

[astam]

Caskru wat se jy? Benhur? Dadstoy? I'll have to wait for more answers before I decide who to believe.

[ThysdJ]

Caskru wat se jy? Benhur? Dadstoy? I'll have to wait for more answers before I decide who to believe.

poor you

[ToyX4]

As explained to me by the HIQ 'expert'
31 refers to their width
10.5 refers to the sidewall height (as a % of the width?)
and R15 is the rim size.

My understanding is:
31 refers to the overall height
10.5 refers to the width
R15 is the rim size

If tyre size is 245/75R16, then you can use your explaination - ie, 245 refers to their width
75 refers to the sidewall height (as a % of the width?)
and R16 is the rim size.

One is imperial, the other metric, I think. Dunno which is which though

[ThysdJ]

One is imperial, the other metric, I think. Dunno which is which though

The 31 is inches... (imperial size)
The 245 is mm (metric)

[ToyX4]

If tyre size is set out as 245/75R16 or 225/45R15 or so, it is metric.
31x10.5R15 or 33/12.5R15 is inches, or imperial.

Oops, thanks Thys

[JohanM]

The 10.5 is the width of the tyre but it will also have an effect on the sidewall ratio of the tyre. However I do not how much it will effect the vehicle, all i can add is that the wider the tyre, the higer the sidewall ratio is. Thus the longer gears you will have and that will cause again your vehicle to feel sluggish, due to higher profiles and more rolling resistance.......

[CasKru]

I need to correct my previous statement...

245/ 75 R15 =

• 245mm (tyre width)
  75% of the width of the tyre (245 * 0.75)
  R15 tyre fits 15 inch diameter wheels

31/10.5 R15 =

• Tyre is 31" in diameter
  Tyres width is 10.5"
  R15 tyre fits 15 inch diameter wheels

[astam]

Right. Sorted! Thank you! :)