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Sidewall height...I didn't realise that....

Alloy wheels and tyre discussion
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Angelus666
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Sidewall height...I didn't realise that....

Post by Angelus666 » Sat Feb 24, 2018 11:43 am

So, I didn't realise the 35 in the 255/35/19 means the side wall is 35% of the 255mm width. I just presumed it was a MM measurement to a certain point of the wall.

Learn something new most days....

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Gaffa22
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Sidewall height...I didn't realise that....

Post by Gaffa22 » Sat Feb 24, 2018 1:29 pm

Yes that why the staggered wheels on the e89 take 255/30 rear and 225/35 front
If it was mm they would both be the same
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buzyg
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Sidewall height...I didn't realise that....

Post by buzyg » Sat Feb 24, 2018 1:57 pm

I didn't know that either. Learn something every day. :thumbsup:
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Ewazix
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Sidewall height...I didn't realise that....

Post by Ewazix » Sat Feb 24, 2018 2:24 pm

Something I picked up from here was how to check the age of a tyre, the series of letters and numbers after 'DOT' will have a four digit sequence relating to the week number and year of manufacture. I had a bit of a shock when I checked a tyre on my Forester runabout last year, it must have been the spare originally and was a 2004 !! :o
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patriot66
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Sidewall height...I didn't realise that....

Post by patriot66 » Sun Feb 25, 2018 8:58 pm

Angelus666 wrote: Sat Feb 24, 2018 11:43 am So, I didn't realise the 35 in the 255/35/19 means the side wall is 35% of the 255mm width. I just presumed it was a MM measurement to a certain point of the wall.

Learn something new most days....
This ratio between the tread width and sidewall height is called the Aspect Ratio. I still think it's weird that in this age of standardisation etc we have a descriptive series of numbers that contains millimetres, percentage and inches ! :cry:
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Mr Tidy
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Sidewall height...I didn't realise that....

Post by Mr Tidy » Sun Feb 25, 2018 10:25 pm

patriot66 wrote: Sun Feb 25, 2018 8:58 pm
This ratio between the tread width and sidewall height is called the Aspect Ratio. I still think it's weird that in this age of standardisation etc we have a descriptive series of numbers that contains millimetres, percentage and inches ! :cry:
I suppose it is a bit of a mish-mash when you think about it!

But when my Dad had cross-ply tyres in the 60s the width was also in inches! :)

Maybe because Michelin (IIRC) were the first to make radial tyres, all of a sudden width changed to millimetres and has stayed that way ever since.

But diameter has always been in inches - maybe because by then every car on the road already had wheels in inch sizes.

A couple of times in the 80s a couple of manufacturers did try metric wheel sizes (MK 2 Granada 2.8is, and Metro 1.3s) but thankfully this didn't take off - only Michelin made tyres for them, they were hard to find and seriously expensive!

But at least percentages fit with either Imperial or Metric.
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