Thread: Big Tyres: Pros and cons

Why are the narrow tyre nazis even in 'The Modified Zone'?

Jeff

Originally Posted by Jeff

Why are the narrow tyre nazis even in 'The Modified Zone'?

Jeff

Because you can have narrow tyres with large rolling diameter

Larger rolling diameter plays a reasonable part in capability regardless of width...

Originally Posted by MrLandy

Its simple. A wider tyre has a wider contact patch. Therefore more frontal resistance.

Can you reference any studies on how much impact this really has?

The best explanation I ever saw regards wheels in soft terrain likened what's happening to there being a small virtual "ramp" constantly in front of tyres. The length and angle of the ramp being a function of how deep the tyres sink into the ground, the rolling radius of the tyre.

Not the same calculations in every case - as the calculations that would be needed in a model that assumes the tyre is "pushing through" the medium. (Though this works for media like water, really sloppy mud)

Obviously tyre width has little impact on the tyre climbing a ramp.

I cannot find a reference to the "virtual ramp" model for tyres on soft ground (as opposed to models that imagine tyres in soft ground are like bulldozers... Where pushing a wider blade (tyre) means harder work- so narrower tyres are better). But it was something like 20yrs ago I read it. Sorry.


I did find this though...
[ame]http://ethesis.helsinki.fi/julkaisut/maa/mvaro/publications/31/appendix7.pdf[/ame]

On about page 7 of the thesis found here, you find the diagram in the pic attached below. The diagram illustrates what I was describing. The deeper the depression obviously the more work to overcome.

Mr. Land Rover would postulate that for any fixed depth the "frontal resistance" is greater with a wider tyre. That's likely right and applicable if both the wide and narrow tyre sink to the same degree on the same ground.

They don't. Of course. In reality. (Unless we are talking watery slop)

Narrow tyre pundits (avoiding the "nazi" term someone else used! for those who maintain that narrow is (nearly) always better) are always quick to point out that the narrow tyre does in fact "dig down" better to find traction if there is a solid bottom to the trail.
- Of course this is only useful if there is a solid bottom
- and they argue the wide tyre doesn't manage to dig that deep and find the solid bottom. (If it did - no point in making this "narrow digs down better" point and narrow is no better than wide if both find that nice solid bottom)

So at least we agree that wides do NOT sink in as deep as narrows. And that's the point: while wide tyres have a wider frontage - those ditch digging narrows go deeper.

What is harder to roll out of? A wide shallow hole or a narrow deep one? Which has the higher "frontal resistance"?

I am sure I don't know. But I have seen and driven both narrow and wide on soft stuff and don't see a lot of difference. (As said before in words and pictures in this thread)

I guess I could go out on a limb and state that in conditions sloppy enough that both wide and narrow tyres did find a bottom at the same depth (water or really sloppy mud - else the wide tyre won't sink as deep as the narrow) - then the wide tyre's greater frontage would certainly make for harder going... So good luck all you wide tyre ******* getting through a few feet of water(or equivalent!).

Originally Posted by PAUL200

Hi all,

I see a lot of 4WDs in Australia with large tires and lift kits etc...

Does installing big tires and lifting the suspension have much impact on the fuel economy? I know it must have some but has anyone ever measured it?

Another thing I have observed is that the military don't install all this stuff on their vehicles which makes me wonder whether it actually increases off road capability much? Are all these lifted 4WDs with big tyres just poser cars?

I'm hesitant to wade into this ****uation, but what the heck.

To the OP, put a modest (2 inch) lift and slightly larger than standard (255/85) tyres on my Defender and experienced a noticeable improvement in offroad performance, particularly on more challenging tracks. Improved performance included a (perceived) increase in traction, reduced diff dragging and better body clearance to the trail.

The cost to on road performance has been minimal and a worthwhile trade off for my intended use - YMMV.

Hope this helps.

PS in the interests of keeping the pot stirred I'll leave the room on this note, why does a comp rig have better offroad performance than a stock 4wd?

Originally Posted by n plus one

PS in the interests of keeping the pot stirred I'll leave the room on this note, why does a comp rig have better offroad performance than a stock 4wd?

Because of all the stickers on it! Duh!

Seriously, I think the narrow vs wide tyre argument has been done to death. If you search Google there are pages upon pages of forums from all over the world that have all had the same discussions as us going back years. I stumbled upon this article which is well written and makes a lot of sense yet doesn't cover all situations as it's mainly about sand driving. Although this will probably spark up the debate again lol..

http://outbackjoe.com/macho-divertis...-help-in-sand/

Originally Posted by Rick122

Seriously, I think the narrow vs wide tyre argument has been done to death. If you search Google there are pages upon pages of forums from all over the world that have all had the same discussions as us going back years. I stumbled upon this article which is well written and makes a lot of sense yet doesn't cover all situations as it's mainly about sand driving. Although this will probably spark up the debate again lol..

Why Wide Tyres Don't Help In Sand | outbackjoe

This picture below immediately falsifies the article in that link.

Originally Posted by Slunnie

An example:

Beadell Tours - Tyre Footprints by Mick Hutton

• Goodyear Wrangler RT/S ? 265/75R16LT ? 10 Ply (original fitment on F250s)
• MRF M77 ? 7.50-16 ? 14 Ply

And so the wide/skinny debate wheel goes around again!