Thread: Any Suggestion on Off Road Modification for Disco 4

Originally Posted by ozscott

The autobiography was a celebration special.

Interestingly the autobiography has far higher torque per tonn than the D4 3.0TT. The stock 2.2 has about the same torque per tonn as the D4 (very slightly less for the deefer) - Deefer has significantly lower gearing so idling around in first or second low expect more actual torque through the wheels from the gearing advantage.

Cheers

A D90 has 198 Nm / T - an SDV6 has 234.

Found the Autobiography - the Limited Release Series (coincidentally I sat in a Def Adventure Limited Edition today - very nice!). No, it is not "far higher torque per tonn than the D4 3.0TT". It's 202 Nm /T for a 110.

Cheers,

Gordon

Mate - I got the number crunching wrong - yes there isnt much in it. The autobiography per tonn is as high as that in the 90 I think.


I was vascilating between throwing in a nice 4.6 into the D2 and getting one of the last defenders...ended up doing the former given all the other gear I have added, but the special deefers are a nice set up.

Cheers

Originally Posted by gghaggis

Tombie, I think your power to weight ratios are a tad optimistic - by a few orders of magnitude!

I think Tombie just transposed the units in his calc so it was kg/kW and therefore a smaller number is better.

Anyway, it shows that the D4 and Defender are similar (depending on which models are compared) for power/weight and torque/weight ratios.

But I've been wondering about factoring in tyre contact patch for sand driving? For example, how much bigger is the area of a contact patch for 16" wheel versus 18" wheel when both are aired down to typical sand driving pressure?

A bigger contact area means less pressure on the ground, reducing the tendency to sink into the sand. Does a smaller wheel with more tyre have a bigger contact patch? Perhaps not easily comparable because you would air down to different pressures to compensate anyway.

Scott

Yes mate - high profile equals longer footprint - when both tyres are aired down the higher profile one will always go further fore and aft - say when compaing a 19 inch 31 inch overall with a 16 inch 31 inch overall. Its not all about torque when not towing either - weights is important. Picture a Moris Minor strapped on top of the Defender and you are getting close to the weight of a D4

LT's take a fair bit more to air down properly than a passenger rated tyre. 18 PSI in my LT's (16 inch rims) hardly look different to 40 psi such is the carcass rigity from strength). I have to get to 14 before it starts to look ok.

Cheers

Theoretically, it's the same size footprint...

Why Wide Tyres Don't Help In Sand | outbackjoe

The radius of curvature is greater for a larger rim, so for the same profile, a larger rim will give a greater footprint. As most larger rims are fitted with lower profiles, you start to trade that off, but the difference is nowhere near what most people think. The real issue is how much more vulnerable the larger rim + tyre is when you air down a low profile tyre.

With respect to power and torque to weight, the D4 SDV6 has a 50% (power to weight) and 20% (torque to weight) advantage over a standard D90, which is considerable.

Cheers,

Gordon

Interesting. The conclusion of that article is ........

"So for tyres and sand driving, tyre pressure dominates all other factors to the extent that other factors mostly don't matter. There may be some other factors at play but they are dwarfed by the effect of pressure. Reduce pressure until you float on top. Any tyre will work."

<EDIT: supports Gordon's point above, except ignores consideration of vulnerability.>

Thus you can counteract the extra weight of the D4 with lower tyre pressure and then take full advantage of the extra torque and traction control.

Scott

On tyre footprints, have a play with this calculator.

BND TechSource - Tire Data Calculator

Milimetre for Milimetre there is not actually very much in it, say between 19s/20s and 18s.....although the LT 18 tyre has other advantages and characteristics, as noted above.