tyre differences

whats the difference between a 255 85 and a 265 75 tyre?

Reply to
Mark Solesbury
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Both the same rim size I assume - 15" or 16" or ....?

Reply to
Dougal

yeah sorry

16inch

Ive got 255 85 16 at the moment, but have the offer of some 265 75 16s

Just wonder what the difference was.

Reply to
Mark Solesbury

Probably easiest to point you where you can read for yourself:

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The 255/85 is a taller tire - fewer revs per mile and more comfort as a result of the higher aspect ratio.

Reply to
Dougal

10mm each way!
Reply to
Nige

Width % Profile Rim Size Tyre Diameter Tyre Circumference 255 85 16 33.067 103.883

Width % Profile Rim Size Tyre Diameter Tyre Circumference 265 75 16 31.650 99.430

Reply to
Brian Tonks

That did not look very clear

255/85 R16 Width = 255 % Profile = 85% Rim Size = 16" Tyre Diameter = 33.067 inches Tyre Circumference = 103.883 inches

265/75 R16 Width = 265 % Profile = 75% Rim Size = 16" Tyre Diameter = 31.650 inches Tyre Circumference = 99.430 inches

This would make a considerable difference in gearing making your vehicle quicker at accelleration.

Regards

Brian Tonks

Tonks4x4

27-29 Main Street Huthwaite Sutton-In-Ashfield Nottinghamshire NG17 2LD Tel: 01623 452885 Web:
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Reply to
Brian Tonks

Looking at those figures it makes for a very tall side wall, 216 mm.

I have 255 *65* R16 that "look right" at 165mm sidewall (just nipped out an measured it as well as calculated, so I don't think I have the maths backwards, do I?). Another 50ish mmm (2") on the sidewall would look very odd and I suspect be like driving on jelly...

Reply to
Dave Liquorice

It's 4.4% larger diameter -which means same margin of error on your speedo. 265x75 is a standard LR size - 0.25% different to 235 x 85 so depending on your LR model your speedo would be accurate.

Your 255x85s are reading slow which is illegal. (I think if I've got all these numbers the right way round - my brain hurts)

I got the comparative diameters from

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Reply to
hugh

On or around Wed, 10 Oct 2007 19:48:56 +0100 (BST), "Dave Liquorice" enlightened us thusly:

I don't recall seeing 255/85 around. 235/85 is a common size, as you say so is 255/65, which is IIRC standard on the disco II.

Reply to
Austin Shackles

With regards to speedo accuracy, what you have to consider is not what the difference is between existing and new tyres are but what the difference between standard fit and new tyres would be. As an example; Discovery 1 standard fit tyres were 205/80R16 or 235/70R16 which are (almost) exactly the same diameter (28.9"). 255/85R16 are 33.3" tall and give a speedo error (compared to standard) of 15%. 265/75R16 are 31.7" tall and give a speedo error of 10%.

UIM changing tyres for larger diameter without changing the speedo is an offence - not because the speedo is incorrect (you could easily use a GPS to recalibrate the readings) but because the mileage recorded on the odometer will also be incorrect. Falsifying the mileage is, IIRC, an offence - and BIB want to confirm or decry that?

Reply to
SteveG

I have 235/85/16 on my disco2, which under reads on the odo and speedo by a small amount. I figure it makes no odds because the engine has done the same number of revolutions as if the tyres were normal size. My understanding is that 235/85 and 265/75 are the same diameter, but the 265's are wider. CMIIW but I think the profile is given as a percentage of the width, so the profile of the 235/85/16 would be 85% of 235, probably in mm

Reply to
madhatchetman

doh. must read all the thread first. ignore me

Reply to
madhatchetman

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