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Stupid Tyre Sizes ......

General Tech Talk

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V8Patrol
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Stupid Tyre Sizes ......

Post by V8Patrol »

So I perfer the old system of measurement .....
31x10.5r15 is a 31 inch tyre thats 10.5 inches wide and fits a 15" rim

SIMPLE !!!!

but WTF and HTF do you work out .....
255/85 /16

Could it be something like this .....

the "255" means the tyre width ....... yes ????, in which case our tyre would be 255mm wide.

the "85" means the tyre wall height ..... yes/no ??? in which case our tyre would have a wall height of 85mm but that seems too small ...

and the "16" is obviously the rim

so I add the wall height twice, and then the rim size ( converted to metric) and I get .....
85+85=170mm, + 405 mm ( for the rim ) and I get 575mm which = 22.5"

So thats oviously WRONG :bad-words:


so is it this way....

255mm + 405mm ( for the rim) which = 660mm which is 26"

nope fail again :bad-words: :bad-words:

or perhaps .....
255mm + 255mm + 405mm ( rim) = 915mm which = 36"

SO HOW THE PHUCK does it work out


the OLD system is so much EASIER

I think I'll just go n buy some "old" tyres with proper measurements on em

Kingy

p/s I know a 255/85/16 is a 33.5" tyre cause I measured d fawker :finger: , but ya cant do that when searching the web..... phuckin monitor is just not big enuff. :armsup:
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Post by 80lsy gq »

actually its pretty easy

285/75/16 285mm wide tyre. 75 is the profile in percentage eg 75% of 285 = 213.75 and 16 is rim size....

so to convert it to old terms then a 285/75/16 would be

213.75converted to inches is 8.55 or a total profile of 17.1 inches of tyre plus 16 inches of rim giving a total of 33.1inch tall tyre

the width would be 285 divided by 25 giving you 11.4


so the tyre is basically a 33/11.5/16 :cool:

just substitute any of your sizes in this equation :D
Last edited by 80lsy gq on Sat Oct 09, 2004 10:55 am, edited 1 time in total.
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Re: Stupid Tyre Sizes ......

Post by DaveS3 »

V8Patrol wrote:So I perfer the old system of measurement .....
31x10.5r15 is a 31 inch tyre thats 10.5 inches wide and fits a 15" rim

SIMPLE !!!!

but WTF and HTF do you work out .....
255/85 /16

Could it be something like this .....

the "255" means the tyre width ....... yes ????, in which case our tyre would be 255mm wide.

the "85" means the tyre wall height ..... yes/no ??? in which case our tyre would have a wall height of 85mm but that seems too small ...
and the "16" is obviously the rim



The '85' means that the tyre height is 85% of the width of the tyre.

Total height is -

(255 x 85 / 100) x 2 - this gives total sidewall height

+ the rim (16 x 25.4)

= 433.5 + 406.4

= 839.9 mm

= 33.06inches. (theoretical)

Correct?

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Post by DaveS3 »

80lsy gq wrote:actually its pretty easy

285/75/16 285mm wide tyre. 75 is the profile in percentage eg 75% of 285 = 213.75 and 16 is rim size....

so to convert it to old terms then a 285/75/16 would be

213.75converted to inches is 8.55 or a total profile of 17.1 inches of tyre plus 16 inches of rim giving a total of 33.1inch tall tyre

the width would be 285 divided by 25 giving you 11.4


so the tyre is basically a 33/11.5/16 :cool:


Arrgh You beat me!

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Post by 80lsy gq »

gotta be quick mate

cheers david :cool:
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Re: Stupid Tyre Sizes ......

Post by bogged »

V8Patrol wrote:So I perfer the old system of measurement .....
the OLD system is so much EASIER


i agree
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Post by Tasrocky »

80lsy gq wrote:actually its pretty easy

285/75/16 285mm wide tyre. 75 is the profile in percentage eg 75% of 285 = 213.75 and 16 is rim size....

so to convert it to old terms then a 285/75/16 would be

213.75converted to inches is 8.55 or a total profile of 17.1 inches of tyre plus 16 inches of rim giving a total of 33.1inch tall tyre

the width would be 285 divided by 25 giving you 11.4


so the tyre is basically a 33/11.5/16 :cool:

just substitute any of your sizes in this equation :D


Ok fine. But why bother with the maths when you can just look at it and tell straight away what size it is?
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Post by MARKx4 »

Its to much to work out. Stick to the old method and it would be eaiser on every one. The last thing i want to be doing when im buying tyres is getting out the calculator out and doing maths... :armsup: :armsup: :armsup:
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Post by STIKA »

i have been driving for 20 years the metric system was in back then so i dont see whats new
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Post by up2nogood »

It is odd though that 245 is mm, 80 is a percentage of mm and 16 is inches.

Why not leave it all in one type of measurement?
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Post by Big Red Toy »

up2nogood wrote:It is odd though that 245 is mm, 80 is a percentage of mm and 16 is inches.

Why not leave it all in one type of measurement?

Americans :roll:
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Post by bogged »

Big Red Toy wrote:Americans :roll:

yes those americans and their metric system... :armsup: :armsup:
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Post by Gwagensteve »

The french tried to metricate (?) rim diameters in the 80's.

A guy at my work used to have a renault Fuego, which had 380mm diameter rims (or something, don't quote me) owners of these rims now have three options to replace their tyres:

a)retreads, $120 each, but I believe you have to supply your old tyres
b)a pretty low rent Michelin, $260
c)New "inch" rims, (very difficult to find in the wacky PCD and offset used by renault inthe 80's.

PS I reckon that 255/85/16 is easy to deal with. How about a 35 12.5 that measures 33.5 tall, or what about a Q78 15- I reckon that the only reason Q78's aren't more popular is it doesn;t say how tall the tyre is on the side. (by the way, 35.5X11ish)

The ONLY way to REALLY find out how tall a tyre is is to mount and inflate one and measure it.
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Post by V8Patrol »

Thanks for clearing that up guys, the world is all sweet again



I'll just take me tape measure with me in future :armsup:

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Post by Beastmavster »

Bought 285/75/16 to get a real 33" tyre not like a 33" being 32.6 at best.

(285/75 is normally 33.1")

Sadly theyre a bit warn and measure like 32.6" :D lol but better than they would be if i had 33x12.5" in same wear.
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Post by DIRTY ROCK STAR »

Ahhh you can feel the lurv in here.

it would surely have been easier for them to just use the actual figures instead of the %.

my 2cents.
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Post by gurumon »

or you could just go here... (handy for speedo re-calibration as well)

http://www.miata.net/garage/tirecalc.html
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Post by Davidh »

Or you could buy Simex which have both the imperial and metric measurements on the sidewall, and are awesome tyres to boot!
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Post by Pesky Pete »

Davidh wrote:Or you could buy Simex which have both the imperial and metric measurements on the sidewall, and are awesome tyres to boot!


Or buy Q78's and have no measurements on the sidewall
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