255 60 R18 tyres looking for chunky tyres

[Mortimer Firewood]

55 is just a slightly lower profile, basically 55% of the width rather than 60%...

 

here is a useful bit of 'rithmetic for you...

 

255 - width of tyre in mm = 255mm

55 - aspect ratio, or height of sidewall as percentage of width, 55% of 255 = 140.25mm

18 - Wheel diameter in inches, or in mm it's times 25.4 = 457.2

 

Add that lot together, 457.2mm + 140.25mm [x2 for top and bottom of tyre] gives you a diameter of 737.7 diameter [doesn't allow for variations in tread depth & projection, all tyres are different]

A 255/60R18 has a sidewall height of 153mm, so 13mm taller than a 55 profile near as makes no difference... That's not a lot but bear in mind you're losing that space beneath your diffs...

 

So what could it do to the diffs.

[niftysteve]

it would mean the ground clearamce would be slightly less

[felixthelogchopper]

it would mean the ground clearamce would be slightly less

 

And your speedo would read wrong as well

[Mortimer Firewood]

ok thanks for the help so far how much would it throw my speedo out and would it read slower or quicker?

[felixthelogchopper]

ok thanks for the help so far how much would it throw my speedo out and would it read slower or quicker?

 

Not sure on how much but you could always check it against a GPS unit. As far as I understand it, if you have smaller wheels then you will cover less ground per revolution so you will be travelling slower than the speedo says. Don't take that as gospel though

[Pedroski]

The difference in distance covered per revolution, expressed as a percentage, is:

100 x (d1-d2)/d1 where d1 is the total diameter or wheel and tyre you're changing to and d2 is the other total diameter of wheel and tyre. We don't need to calculate the circumference as "Pi" is common to both and cancels out (i.e. circumference = d x Pi).

 

So, difference in distance covered between 738mm diameter combination and 738mm + 26mm (i.e. 738 + 2 lots of 13) is 100 x (764 - 738)/764 = 3.4%. The bigger wheel combination will travel 3.4% further per rev, so speed will be 3.4% higher than previous.

[mixedangased]

http://www.tyres-pneus-online.co.uk/:thumbup:got my bfgs off them mts 130 a corner delivered

[D.M.Taylor Firewood Supp]

Thanks everybody for your inputs never knew tyres sizes were so complicated!!!Im still looking waiting for a few responses from tyre dealers.More input welcomed all the same:thumbup:

[niftysteve]

Tyre Selector

 

 

these look quite good ive seen some where they go upto 20 inch

[Pedroski]