OK lads, that's some really intelligent stuff to read there. 300bhp you really seem to know your stuff on this..
So I have a disco 2, with 18 inch wheels. And I got stuck on the axle twister at yarwell which raised questions in my mind. So am I right I thinking that if I change to 16 Inch wheels, 2 inch+ light or medium duty springs ( 2 passengers, 1 infant, pram and tool box haha) and the longest travel d2 shocks I've seen are terrafirma 3"+ ones. This should be a win for up and down travel plus a nice ride on the road?
Or am I just lost here..
The biggest issue you face is, improving off road ability, is normally at the detriment to on road ability, and vice versa. Land Rover did a pretty good job with their setup, to offer about the best mix of both.
So it really depends what your end goal is. No matter how many mods you put on the vehicle, there will always be obstacles that will stop you. And ultimately when you get stuck, you may find you are far more stuck and possibly in more damaging situations. If you compete in competition such as trials events, then making the vehicle more capable has obvious benefits. If it's just for Pay & Play or even laning, then the benefits are much smaller.
The main issues Discovery's face off road are:
-lack of clearance under the diffs
-approach and departure angles
-break over angles
There are many ways to address these issues.
Personally trimming the front bumper or fitting aftermarket bumpers front and rear is a good solution to the approach and departure angle issues.
Remember a suspension lift on its own won't increase the ground clearance for the diffs.
And fitting taller tyres will address the other two points. Now sadly the wheel arch limits the size of tyre you can fit, which is where you face the decision. When I had a D1 I opted to trim the arches to fit taller tyres. And left the suspension alone, this was actually cheaper, but the main reason was, there really was little wrong with the stock suspension. Off road you want to keep the centre of gravity as low as you can for stability reasons.
Now I can understand on a tidy D2 you may be less inclined to want to trim the arches and it is generally a non reversible mod. This means the only option for taller tyres is a suspension lift. But note, that a lift might allow clearance at normal ride height, but might still result in the tyres impacting the body under articulation, so even with a lift, you may still have to trim some body work.
A good size tyre for a Disco is a 235/85R16 or 7.50 x 16. These are 31-32" tall and narrow. Narrow will generally work better in the muddy conditions we get in the UK (although if I remember correctly, Yarwell is sandy, but tyre questions are probably best left to another post), it will also give you more steering lock and will mean less likelihood of the tyre impacting the body as much.
In terms of tyres and rims. A 16" rims vs an 18" rim has a much bigger side wall for the same diameter tyre. This is important off road, as the side wall will allow more deflation of the tyre and a wider foot print on the ground. For normal off road use on 16" rims 21-28psi works well. For really wet muddy conditions or rocks you'll want to air down to around 12-15psi. Although this is too low for road use, so make sure you have a way to re-inflate again. Any lower and you'll run real risk of the tyre coming off the rim.
18" rims will always be a heavy compromise off road, the side wall is small and you can't air down as much, as it'll just over deform the sidewall and run the risk of damaging the rim & tyre. Tyre choice is also limited for 18" rims.
As for axle twisters. Well there are probably several things going on here.
1. Land Rover's for the most part run open axle differentials. This means cross axling is just a thing that happens. Driving style will be key here, you either need to go a little faster, to let momentum carry the vehicle far enough through, so as the wheels being driven will have traction. You could change your line slightly. Sometimes left foot braking can help or even the angle you enter the cross axle. Ultimately you need to assess the situation at the time, and simply accept that it can happen. But it's mostly off road experience that will be at play here.
2. Disco 2's all have traction control. So in theory they should suffer less cross axling. However to make the traction control work properly, you need to drive the vehicle correctly. You need enough throttle input to make the system work and sadly it won't work until wheel slippage occurs. Once the TCS kicks in, you need to keep the throttle open, don't back off, the TCS needs throttle in order to work.
3. Most D2's do not have a centre diff lock. This means the TCS has to work over time in cross axle situations. Without the TCS and having 3 open diffs in the drivetrain will effectively give you 1 wheel drive. The TCS has to work hard to overcome this. Retro fitting a centre difflock to a D2 will make it much better off road. This is easy on some model years, but more costly on others, so you'll need to check. Difflock and TCS work very very well.
4. Tyres. If you are on 18's, then at best you are on mild AT's or road tyres. If it was a little wet or damp ground conditions, then simply tyres with more bite, might have been enough to prevent being stopped. A good set of MT's is well worth while if you off road. They don't need to be extreme, but an MT's will always be superior to an AT in muddy conditions. If you get an MT with sipes in, then they work very well on the road too, in all conditions. You'll find a wealth of sizes for 16" rims.
5. Suspension. It is true, if you had more travel, then it 'may' have prevent being cross axled. But it isn't a given. The standard suspension moves about pretty well, and I personally think you'd see more gains from good tyres and a diff lock.
Overall I'm not saying don't lift it. But there may be things you want to consider before doing that. A Disco2 with a centre diff lock and good MT's should work very well off road. The TCS will keep all 4 wheels spinning, even if one or two are lifted off the ground if you have the centre diff lock too. Which means most axle twisters are unlikely to stop it. Getting a taller tyre on, will be a benefit in every way however, but does require a fairly major mod in terms of wheel arch trimming or lifting.
Personally I think lifted trucks can look awesome, so in many ways this is reason enough to do it. But in pure off road performance terms, it isn't always the best choice. And it will have some effect on on-road ride and handling. If you want to go the lift route, then yes, a lighter or medium duty spring will be far better than a HD one. And longer shocks will give you more travel too. The downside is, on road it may lean more and be less sharp in the corners.
There are other options, not so popular in the UK, but common in the USA is to look at a body lift. This just lifts the body up from the chassis, so as to give more clearance for bigger tyres. It keeps the centre of gravity low, although doesn't directly improve breakover angles (but the bigger tyres will). Body lift kits are usually cheap too, but can be more difficult to fix, as things like the gear lever, linkages, and hoses might need extending too.
The Watts linkage on the D2, while a better solution on road than a Panhard rod, has been known not to flex as well as the older A frame setup on the D1. So while you can get gains over the stock suspension, there might still be more to consider for really big improvements. And don't forget, standard suspension works more than well enough as is.
And don't forget other mods. The TCS is good, brilliant with a centre difflock and if you added Limited slip axles diffs it's even better. Or there are axle diff lockers to consider, although these are more pricey and will negate the TCS.
