Tyre size/width/profile calculations, spacers

BIG_GINGA_BEARD said:

Its been covered before!

I didnt want to disapoint.

The 265's will throw your speedo out. By how much i couldnt be sure but my 285/75/16's throw it out by about 4mph at 30, so i have to do 26mph on the clock to actually do 30mph on the gps.

your 265's will make it slightly less difference.

You will not need spacers with the 265/75/16's. 265 being the surface area side wall to side wall and 75 the height of each side wall, you know have a greater width tyre that will fill the arch on a standard defender.

There all terrain tyres there made for "all terrain" that includes the road. They will be fine for everyday driving and off road and will last a fair while. I doubt youd notice any increase in noise either.


On a side note, if you experience rubbing on full lock you may have to adjust your lock stops.

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shotgun0589 said:

Thanks BGB, top reply.

The Boost's offset is (I think) +33mm, the steels I have are +8mm, with the 265's fitted they come nicely to the edge of the wheel arch, so if I swapped the 265's to the Boost then surely they would be 25mm inside where they are now? Does that make sense?
I also can't understand (I must be thicker than I thought) why the width of the tyre would make any difference to the circumference, like Blue Beasty says - '265/75's and 235/85's are the same diameter' - how can this be?

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redhand said:

Nope you're not making any sense.

the sidewall height is a percentage of the tyre width I:E 265/75 =75% OF 265mm equals the side wall height.

the offset is the distance from the centre of the wheel rim to the back of the rim. + offset moves the rim outwards -offset moves the centre of the rim inwards.

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shotgun0589 said:

OK, thanks for explaining the tyre size thing, I never knew the percentage equation. You learn something every day.

I'm still sure of the wheel offsets though, the Boost are +33, the steels are +8, so it stands to reason that the difference is going to be 25mm? This'll move the outer edge of the wheel/tyre inwards by 25mm. Extreme offset wheels have a larger negative number. So the bigger the minus offset, the more it'll move the tyre/rim outwards and give it a wider track?

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• 
  Rim width Min tyre width Ideal width Max tyre width
  5 .0 inches 155 mm 165 to 175 mm 185 mm
  5.5 inches 165 mm 175 to 185 mm 195 mm
  6.0 inches 175 mm 185 to 195 mm 205 mm
  6.5 inches 185 mm 195 to 205 mm 215 mm
  7.0 inches 195 mm 205 to 215 mm 225 mm
  7.5 inches 205 mm 215 to 225 mm 235 mm
  8.0 inches 215 mm 225 to 235 mm 245 mm
  8.5 inches 225 mm 235 to 245 mm 255 mm
  9,0 inches 235 mm 245 to 255 mm 265 mm
  9.5 inches 245 mm 255 to 265 mm 275 mm
  10.0 inches 255 mm 265 or 275 mm 285 mm
  10.5 inches 265 mm 275 or 285 mm 295 mm
  11.0 inches 275 mm 285 or 295 mm 305 mm
  11.5 inches 285 mm 295 or 305 mm 315 mm
  12.0 inches 295 mm 305 or 315 mm 325 mm
  12.5 inches 305 mm 315 or 325 mm 335 mm

couga861900 said:

I have 265 75 16 Cooper STT tyres on alloy Boost rims and they fit nicely. I must say I have 33mm spacers and a 2" lift kit. They look wonderful. I am wondering if I will be over doing it when I change tyres to 285 75 16 Cooper STT tyres. When I change tyres sizes, I will also put extended wheel arches. What do you guys think?

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Dave90 said:

Most tyre companies don't recommend putting 285's on 7" wide rims
As far as the extended arches go, I would have thought you would have massive arches and tiny wheels that won't sit 'flush' with the arch, if it's what you want to do then go for it though
I think that 16x8 modulars with a -32mm offset and 285/75 R16 tyres will sit flush-ish to the edge of the 2" extended arches, but this is only going by what people I've asked have told me It's you're choice that counts

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