Just after a bit of knowledge from an adult. I downloaded the 4 link calculator for excel from Pirate 4x4 and stuck in the figures for the Disco trayback (with standard LR setup) having got underneath with a tape measure. What I get is

Anti Squat - 145%
Roll centre height - 22"
Roll centre angle - 10 degrees (roll oversteer)

Does that sound about right for standard?

I then modified the figures for the Nissan rear axle I am currently fitting which basically means the upper axle mount is about 4" higher than the LR setup and this changes the figures as follows


Anti Squat - 174%
Roll centre height - 24"
Roll centre angle - 7 degrees (roll oversteer)

I can get the figure back to something approaching the LR ones by either raising the chassis mounts for the A-frame or by using longer trailing arms (like Gigglepin). So what I want to know is whether the figures for the Nissan set-up fall within acceptable levels (assuming 99% offroad usage) or is it going to be horrible to drive/problematic on climbs, etc?

Cheers for any informed input

Mark

Stop p*****g around and weld the brackets on the axle will you. The axle casing will have rusted away and you will have suffered a breakdown from worrying about it before you get to use your truck! If its not ready for the SWMC you will be sulking coz were all having fun and you cant go like last year.

I thought this was going to be a thread about stopping people moving into your house whilst we're in Portugal !

Mo

Don't be silly Mo - it's in Wales!

Mark, the antisquat looks pretty high to me, more than 100% is imo not desirable. The rollcentre higher up will help stability, for sure. Could you maybe get some options for the antisquat and try them on the car? It is a personal preference really, but you might find the rear suspension goes solid if you apply a lot of power.

Daan

Thank you Daan for a voice of reason in a world of funny buggers

I Have done a bit of reading and you are right it would appear to be a bit on the high side.

Interestingly if I dial in the standard Land rover settings with 235/70 tyres instead of 35" ones and standard spings instead of 2" lift ones then the figures are as follows

Anti Squat - 108%
Roll centre height - 15"
Roll centre angle - 5 degrees (roll oversteer)

Seems LR were pretty close to 100%

Now I don't know if this is related but at the moment the Disco only has RWD since the front diff is bust (again) and while out fencing yesterday I struggled to drive on the slightest incline on wet grass. it was as iff there was no weight on the rear wheels. Perhaps there really is something in all this geometry stuff!

Are you sure with your centre of gravity( height)? There also some unwritten rules in therms of length difference between lower and upper arms and angles. You should have the arms at a minimum of 40% (lower or upper, or combined). But this is just my opinion. Do let you pull off doing the job right. It will pay off...and make those brackets ADJUSTABLE!!! m

Would you have a link to the Pirate4x4 4 link calculator please?

Thank you.

Correct me if I am wrong but anti squat is a measure of how much the back end squats under power, much the same as anti dive measures how much the front end dives under braking.
How much power would you need to make a differnce? I would have thought the run of the mill lr engine would struggle to make anything squat.

Yes, at 100%, there is no movement. Below 100%, it squats, above it rises.

In low range, there is a lot of force available.....

It is more a question of how the tire behave dynamically when climbing. With a very high AS, the tires will push down, with very low, they will lift up. These forces will cycle with power application. When you are a long way from 100%, you can get the wheels hoping and makes climbing difficult. Some people like some AS (>100%) as theoretically under power the wheel push down adding to traction. Others like to get close to 100% to prevent the load cycling.

Night-train

here is the link to the 4 link calculator I used and a 3 link one too

http://mysite.verizon.net/triaged/files/4BarLinkV3.0.zip

http://mysite.verizon.net/triaged/files/3LinkV1.0bBETA.zip

Stick em in the address bar of your browser and they should automatically start to download.

Yep, Suspension geometry is very important

But how usefull are these figures in the real world. You take measurement off the vehicle in its static possition which is very much different to how it will react when driven. There are so many external factors, Spring rate, CofG, Weight transfer, reactive tourque through axle and many many more. Throughout the movement of the suspension, As the angle and length of the arms in relation to each other vary so do the figures. so you know how the suspension works when its parked but only have a rough idea when its moving. (actually, yours spend most its time parked so I take it back )

I have a small amount of experience with Motorsport engineering and have a good friend who spent years working in suspension development for some of the biggest teams (also called Mark funilly enough) who always says they wasted years building the perfect setup on paper and didn't make any real progress untill they decided to relly more heavily on "track based testing and development" (trial and error to you or I) And didn't pay too much attention to how it should be.

Knowing what mark is doing and having seen the proposed setup. During the main of driving, powering up hill etc etc, where the anti squat is most important, the links will be at a point in their arc where the link length variation will be minimal. Therefore the difference in height of A frame joint will have very little effect and be not too much different from std. Bearing in mind the std LR setup is a pretty good comprimise (yes, I know its far from perfect but it works as well as most things) I think it will be fine. The main difference will come at the extreams of articulation, Droop and bump, at these positions Anti squat etc is pretty irelevent.

Orgasmic Farmer, thanks for that. I remember the good old days of trying to work it out long hand and then reverting to miniature models and then full scale trials. I shall have a play when I have a bit of time.

Steve is right, suspension geometry is very important, but it is much easier to control on a racing car where suspension travel of 2 or 3 inches will be used. You can then plan everything to the nth degree and work out the best compromise (and it will allways be a compromise, unless you're doing something very specific such as drag racing).

In the world of challenge trucks where articulation and travel are king I found the best possible geometry is massively compromised by where you can fit the links. It would be different for a scratch built tube buggy, but when looking at my front 3 link set-up every option I could fit in gave a high roll centre, roll over steer and loads of anti dive. In the end I positioned the links for ease of mounting and focused more on keeping the diff pinion angle correct than anything.

In practice the anti-dive is very noticeable with next to no dive under breaking, but the roll over-steering is not really any worse than a lifted land rover.

I would say play with the computer, find the best compromise, and then go and see how easily you can fit that to the truck. Then re-think!

must be a market in the UK now for a Bolt/Weld on 4 link kit

There is also working it the other way.
Find the best positions on the vehicle and then see what the computer says about it.
Find the next best positions on the vehicle and recheck on the computer.

No point having a great geometry that doesn't fit.

There are 4-link kits floating on eflay. But the heims are probably poor quality. I guess, there is too much welding/cuting involved to make a kit ready to fit, IMO. Biggest job on my 4-link was to notch crossmember to make space for upper arms at full bump.

If you really want some sleepless nights try this