discool
Well-Known Member
325
Most of us would see that as a 'typo' for 235.
300bhp/ton
Well-Known Member
Do you mean a 225/75R16 and a 325/70R16?
I think there is a lack of basic tyre size understanding. The profile is a percentage of the width in mm.
e.g. a 225 is 225mm wide. The sidewall is 75% of 225 = 168.75mm
70% of 325mm = 227.5mm
So in this example, the '70' profile tyre has a substantially bigger side wall and is a much taller tyre.
Rim size will vary with width, generally wider tyres need wider rims. But profile can also have a bearing on this, as can construction, as they will alter how the side wall of the tyre will look, bulging, stretch, square.
Sorry its me just being a bit dim and a Typo error.
I was looking at a 225/75/16 on a 6.5 rim with a diam of 744 mm
Vrs a 235/70/16 diam of 736mm . According to the tyre/rim fitment chart I looked at the 235/70/16 diam 736mm should go on a 7" rim BUT a 235/75/16 diam 733mm would fit on a 6.5 rim?
the side wall flex must allow a tyre to fit a narrower rim
I was looking at a 225/75/16 on a 6.5 rim with a diam of 744 mm
Vrs a 235/70/16 diam of 736mm . According to the tyre/rim fitment chart I looked at the 235/70/16 diam 736mm should go on a 7" rim BUT a 235/75/16 diam 733mm would fit on a 6.5 rim?
the side wall flex must allow a tyre to fit a narrower rim
The minimum tyre width according to my info for a 6.5" rim is 185mm. Maximum tyre width 215mm. For a 7" rim it is 195mm and 225mm respectively. 235 tyres should not be fitted to less than a 7.5" rim.
http://www.kouki.co.uk/utilities/visual-tyre-size-calculator
brian47
Well-Known Member
From what I can see from a tyre selection calculator on t'interweb is that both the sizes quoted in the first message by the OP fall into the range of wheel sizes from 6.00" x 16" to 7.50" x 16", there will also be a recommended size. The "J" is somewhat of a misunderstood indicator. Many people take it to mean something about the width of the rim, but the actual meaning for "J" is that it "Indicates the shape of the wheel on the place where the tyre bead sits on the wheel".
The size of tyre depends on more than just the rim width and diameter, the profile of the tyre must be considered too.
Wheel sizes for a given tyre size:
After checking even further, the web site I've used would indicate that the "width" figure for any given tyre is not the width of the rim, but the width of the tyre tread face on the outside of the tyre where it meets the road. 225 mm is 8.86 inches, 235 mm is 9.25 inches.
Website: http://www.tyresizecalculator.com/tyre-wheel-calculators/wheel-rim-size-calculator
The size of tyre depends on more than just the rim width and diameter, the profile of the tyre must be considered too.
Wheel sizes for a given tyre size:
- 225/75/16
6.00" x 16" to 7.50" x 16". Recommendation 6.00" x 16" - 225/70/16
6.00" x 16" to 7.50" x 16". Recommendation 6.50" x 16"
- 235/70/16
6.00" x 16" to 8.00" x 16". Recommendation 7.00" x 16" - 235/75/16
6.00" x 16" to 8.00" x 16". Recommendation 6.50" x 16"
After checking even further, the web site I've used would indicate that the "width" figure for any given tyre is not the width of the rim, but the width of the tyre tread face on the outside of the tyre where it meets the road. 225 mm is 8.86 inches, 235 mm is 9.25 inches.
Website: http://www.tyresizecalculator.com/tyre-wheel-calculators/wheel-rim-size-calculator
neilly
Well-Known Member
300bhp/ton
Well-Known Member
I think you are adding confusion, the op isn't asking about old English tyre size alternatives compared to modern sizes. They are asking about rim sizes for a give tyre size.
Also I do not believe there is any single standard on where a tyre "width" is measured from, i.e. bead to bead, side wall to side wall, outer tread to outer tread or something else.
Hence why you can get such a huge array of different tyre dimensions for the same "size" tyre.
neilly
Well-Known Member
I do think you will also find that for a given tyre size from a manufacturer then it will quite possibly recommend a range of wheel rim sizes that may be different when compared to the same tyre size from a different manufacturer when the extreme rim ranges are compared, or even between the same manufacturer and tyre size when the tyre type and application are taken into account regarding side wall strength and distortion allowed.
The only true answer to this question is contact the tyre supplier confirming your exact tyre size and the tyre model / type / load limit. Then ask them what they recommend as a range of rim sizes.
Cheers
The only true answer to this question is contact the tyre supplier confirming your exact tyre size and the tyre model / type / load limit. Then ask them what they recommend as a range of rim sizes.
Cheers
300bhp/ton
Well-Known Member
225/75 = 168.75mm sidewall
235/70 = 164.5mm sidewall
235/75 = 176.25mm sidewall
Now imagine you could lay the tyre out flat, i.e. SIDEWALL - TREAD - SIDEWALL
168.75 + 225 + 168.75 = 562.5mm bead to bead for the 225/75
164.5 + 235 + 164.5 = 564mm bead to bead for the 235/70
So the '70' profile tyre in the example is about the same amount of rubber bead to bead. But the ratio of sidewall to tread is different. And the tyre maker deems the angle of the sidewall on a narrower rim would be out of spec.
Bottom of tyre as a cross section: |__| vs \__/
Different tyre makers and car makers will have different specs and standards. It may also vary for the tread/type of tyre or load rating too. Or even were it was originally type approved and when.
brian47
Well-Known Member
I was making no reference at all to "old English" tyre sizes. I'm well aware that the OP was asking about wheel sizes. I was merely quoting minimum and maximum wheel RIM width and diameter sizes in inches, since he first mentioned 6 and 7.5 rims.
With regard to the "width" of a tyre, my way of thinking would indicate that the only valid measurement would be one that remains unchanged irrespective of inflation pressure or load placed upon it. The sidewall to sidewall is liable to change the most due to flexing, so that cannot be realistically quoted. The bead to bead measurement will depend upon exactly on the rim size on which the tyre is fitted, so that cannot be quoted as the tyre width. The only dimension which doesn't change dramatically, other than changes due to age and wear is the tread width where the tyre presents a flat surface on the road and thereby disregarding any apparent tread pattern such as side grooves etc. which by design run onto the sidewall.
300bhp/ton
Well-Known Member
As I said, I know of no standard on how tyre width is measured. The tread width that is flat surface on the road is not really valid, as not all tyres are flat, they are often domed. And tread patterns vary far too wildly. Also the tread width is actually the only part of the tyre that doesn't have any bearing on the rim, all other parts of the tyre will affect how a tyre fits on a rim. And it is width that plays a major role in rim suitability.
To give some examples:
Three of these tyres are the same size, but look how they vary in real size.
The tread on these clearly extends well beyond the width of the side wall or bead but is tread that makes contact on the ground.
Not all tyres are as flat as you think, so the distance from edge to edge will vary depending if you follow the curve or the tyre or not.
Or they go to the other extreme
To give some examples:
Three of these tyres are the same size, but look how they vary in real size.
The tread on these clearly extends well beyond the width of the side wall or bead but is tread that makes contact on the ground.
Not all tyres are as flat as you think, so the distance from edge to edge will vary depending if you follow the curve or the tyre or not.
Or they go to the other extreme
