When a big tyre is too big?

That's what we were talking about sitting around the camp fire.
The theory behind is that by increasing the footprint you decrease the specific weight of the footprint. Also by deflating the tyres you want to increase your footprint front to back (becomes like a track of a bulldozer) and not so much from side to side.
So 235/85 would give better grip than 285/75? Where? Anywhere or just in sand or just on rocks?
Extremely confused now!

235/85 is about a 32", 285/75 is like a 33.5"

the 235 will have way less rolling resistance in the sand, although IMO the 285 will still get a bigger footprint.

I have 265/75 BFG ATKO went up the beach when I first put them on didn't even air down (so ~34 PSI) they went very well in the sand above the high tide line, just wish my D22 had more power since fitting them it just feels so slow, its that bad I am looking at getting a hilux with 4.0 V6.

That's right the 285 have a bigger footprint but then you spread the load on a bigger surface reducing the grip. I also do believe that with just a size above the standard and with accessories on you should still put enough load on the footprint.
Still confused but thanks a lot for the input.
Anyone else that can put more input to this thread?

120 viewers?

BUMP

Either way a larger diameter is better, but there is a trade off in gearing.

Think about would you rather climb stairs with 35s or skate board wheels.

Then the width, what you gain in sand you lose in rocks.

In sand you want flotation, not traction on rock climbs you want bite and traction. Serious rock climbers don't want wide tyres, skinny and tall, sticky doesn't hurt either.

Unfortunately height comes with an element of width.

285/75x16 is a wider tyre than a 235/85x16, but from memory it is slightly smaller in diameter.

Maybe think of it this way. The 235 tyre will be better in mud as the thinner tyre will cut through the mud, hopefully getting to a more firm purchase, whereas the wider tyre will float on top. In sand the thin tyre will cut through the sand and sink the vehicle.

Rock crawlers like wider tyres so they get more footprint squished over the rock surfaces, narrower tyres will slip more easily.

Regarding lack of traction due to the weight being shared over a larger footprint, think of it this way, instead of your traction footprint being spread over a 8"x6" spot, it's spread over a 10"x8" spot more contact with the ground gives you more traction.

Good thoughts Siringo

siringo said:

285/75x16 is a wider tyre than a 235/85x16, but from memory it is slightly smaller in diameter.

Maybe think of it this way. The 235 tyre will be better in mud as the thinner tyre will cut through the mud, hopefully getting to a more firm purchase, whereas the wider tyre will float on top. In sand the thin tyre will cut through the sand and sink the vehicle.

Rock crawlers like wider tyres so they get more footprint squished over the rock surfaces, narrower tyres will slip more easily.

Regarding lack of traction due to the weight being shared over a larger footprint, think of it this way, instead of your traction footprint being spread over a 8"x6" spot, it's spread over a 10"x8" spot more contact with the ground gives you more traction.

Click to expand...

To a degree, the increased footprint also reduces the contact pressure, hence reduces the friction area.

It's a balancing act.

That was the original question, when a big tyre is too big? What size is a good balance? Is 285/75 r16 to wide?
Cheers and thanks for the your thoughts

mgermasi said:

That was the original question, when a big tyre is too big? What size is a good balance? Is 285/75 r16 to wide?
Cheers and thanks for the your thoughts

Click to expand...

Too many elements, what weight, load, speed, did you have eggs for breakfast . .

I'll take a tall skinny any day.

I'm leaning away from putting 265/75/16 on my Nav cause I tow a considerable load every day.
Just worried that it's going to bog down more on take off.
Looks like I'll have to stick to the 265/70/16.

hi Busiboy
so what do you think of BFG Mud tyres 255/85r16?
Worth it?

I run the BFG 255/85R16 which is a 33.4inch, so many people talking bout 265/75/16
there are better tyres sizes out there, the extra clearence is a huge advantage, well for me anyway, NEVER had any issues in mud or sand
Check out my Avatar pic

Milkman said:

I run the BFG 255/85R16 which is a 33.4inch, so many people talking bout 265/75/16
there are better tyres sizes out there, the extra clearence is a huge advantage, well for me anyway, NEVER had any issues in mud or sand
Check out my Avatar pic

Click to expand...

This will be my next size.

Yes, tyre size depends on many things, weight of your vehicle, type of terrain you're going to drive on, and so on. It's too hard to nail down exactly.

Busiboy said:

To a degree, the increased footprint also reduces the contact pressure, hence reduces the friction area.

It's a balancing act.

Click to expand...

When you are working out friction forces you don't take contact area into consideration, a 285/75 r16 will have a higher coefficient of friction then a 235/75 r15 for instance but the vehicle weight will remain the same (which you can use both to work out friction) so the larger tyre (depending on a few other things) should have the higher frictional force, obviously tread compound plays a huge factor in this.

tony d22 said:

I'm leaning away from putting 265/75/16 on my Nav cause I tow a considerable load every day.
Just worried that it's going to bog down more on take off.
Looks like I'll have to stick to the 265/70/16.

Click to expand...

When I owned a D22 with the 2.5L (have 3.0L now) I had 265/75 BFG ATKO's on it and never noticed it slow down when I put them on, noticed my 3.0L take a pretty big performance hit from doing the same mod though.

Hi Milkman
what suspension setup do you have?
Would 255/85 R16 fit under a 2 inch lift without scrubbing?
I do like them a lot and I'm planning to install them.
Any other brand that make such size?
Thank a lot

Hi Mgermasi.

About a month ago i upgraded from Mickey T 265/75/16s to a 255/85/16 Maxxis Bighorn. The Bighorn 33's are the same width but alot higher comparing the two next to each other. I have 2inch toughdog susp lift and yes i had problems with scrubbing. If u want to go this way you will need to remove front mud flaps and get out the grinder to grind about an inch of the guard at the front and same at the rear. Rear mudflaps can stay though! Hope this helps.

You will also need to go away from the factory 16x7 inch rims to a 16x8inch rim to hold them

Only 3 brand make that size tyre:

BFG KM2
Maxxis Bighorn
Cooper

Hi Navman 17
thanks a lot for your info. I had a look at your garage, congratulations you have a nice rig and it looks like you are taking to nice places too.
did you find that going through all the troubles to fit the 33's was worth it?
Cheers

For those considering a radically larger tyre size from standard, you also need to consider the forces involved.

A larger tyre represents a longer lever that the engine has to turn. The forces required to turn that lever are greater and those forces travel through the components designed for the shorter lever (smaller tyre).

This means that there are additional strains placed on the axles, differentials, CV joints (these are the primary failure points). If you intend to take the vehicle off-road with much larger tyres, you would do well to install at least a front locker, or both front and rear (front first, it's a smaller diff). This will at least prevent you from lifting a wheel and spinning it - as it gains grip, it will transfer its own momentum (which being a larger wheel is of course larger than standard) into the axles/CVs/diff with the inevitably destructive results we've seen before.

I fitted 285/75/16 Dick Cepec AT's on my D40 on the stock 16x7 STX wheels with no probs. That's with 70mm rear and 60mm front lift. CV's are still perfect after a wheel alignment. No real loss in power or fuel economy either.