Thread: 235/85R16 vs. 265/75R16 vs. 255/85R16

Originally posted by uninformed
basicly brand to brand they will vary slightly but for a 235/85 r16 it is:
235 = 235 mm wide
85 = aspect ratio in height, 85% 0f 235 = 199.75
r = radial
16 = inch rim, 16 x 25.4 = 406.4

therefore 199.75 x 2 (tyre above rim and tyre below rim) + 406.4 = 805.9mm or 31.72834646 inches tall
this will also vary due to rim width and air pressure.
now IMO a narrowISH tyre is better because it has less rolling resistance. think of it this way look across the width of the tyre and imagine this pushing through soft sand or mud its actullay creating friction so the wider the more friction or resistance. Now grond pressure is different, this is where a tall tyre is good because its long foot print supports the vehicle and stops it digging straight down
serg

Tall/narrow has same contact patch as wide/short. Contact patch is dependent on pressure in the tyre and weight of vehicle.

Originally posted by VladTepes
that's great serg but where does the 25.4 come from ?

25.4mm to the inch.

In bfg mud terrains

235/85-r16 is 32inch O/D

255/85-r16 is 34inch O/D

Doh :!: ops:

RMP QUOTE

Tall/narrow has same contact patch as wide/short. Contact patch is dependent on pressure in the tyre and weight of vehicle.[/quote]

yes but a narrow tyre dosn't have the same resistance, think of 4 cyclists riding in single profile and then side by side, they have the same surface contact but less resistance, in there case wind/drag. in our case mud/sand- plus wider tyres/rims with more offset put more pressure on wheel bearings etc.
serg

I went from 235 stock general grabbers to 265s Coopers SST. That way I could keep my ratios, speedo, insurance and add a bit of beef to the tyres. They work well off and on road, a bit noisy but its a defender right...?

265s arent that fat anyway.....

Originally Posted by uninformed

RMP QUOTE

Tall/narrow has same contact patch as wide/short. Contact patch is dependent on pressure in the tyre and weight of vehicle.

yes but a narrow tyre dosn't have the same resistance, think of 4 cyclists riding in single profile and then side by side, they have the same surface contact but less resistance, in there case wind/drag. in our case mud/sand- plus wider tyres/rims with more offset put more pressure on wheel bearings etc.
serg[/quote]

I agree, and I didn't contradict that part of the post when you stated that. You have a good analogy there, I'll borrow it for some time in the next two weeks when this topic comes up again!

There are disadvantages to narrow tyres, but they do have advantages even if they aren't the current trend.

There is a mindset that sees people desperately trying to fit the tallest and fattest tyres they possibly can on their 4WD without really thinking about whether they need to do so, the pros and cons, and the other ramifications of such mods. Some cars are very well engineering and much more capable as a result, others are reliabilty problems waiting to happen.

Ok then - what disadvanatges are there to narrow tyres ?