This is a curly one, and depends on your budget and/or willingness to engineer your own solutions.
29″ is the standard outer diameter for P38 tyres, regardless of whether you are running 16″ or 18″ rims. If you are running bigger rims on a P38, you are probably breaking some local law or you are a drug dealer 🙂 I am looking at this from an off-roading viewpoint, so I will focus on 16″ rims only, as they give more rubber on the sidewall for bagging and grip.
The P38 in standard form with stock tyre size (usually 255/65R16), standard Boge shocks and stock Land Rover/Dunlop air springs is a formidable on-road and off-road vehicle. For most people, the standard setup is more than adequate to do some weekend off-roading, beach work and recover the occasional lesser 4wd.
Then there are those of us who like to push the “best 4x4xFar” a bit further…
I am big fan of Arnott Gen III Air Springs as they give more travel on the suspension and are bound top and bottom, meaning they are less likely to pop the bag/bladder off when articulating or when airborne. The downside of the binding rings is that if/when they do go, you have no choice other than to send the bag back to Arnotts for fixing or replacement. The design of the Gen III’s gives a firmer ride at EAS Highway Mode and a softer ride at EAS High Mode. I like this firmer handling at speed (i.e. Highway Mode) and more give when navigating obstacles off-road.
Regardless of the amount of suspension lift or body lift you install in your P38, the lowest point on the car will always be the diff centres. Short of swapping out the diffs from a Unimog, you can only raise the diff centres by increasing tyre size.
31″ tyres will give a 1″ increase in diff height while 33″ tyres will give a 2″ lift above standard.
31″ tyres will fit a P38 with minimal modifications. You may need to trim the mud flaps on the front wheels as you may get scrubbing on Access and Highway modes. If you go wider than 255 (maybe 265) you might also scrub the wheel arches when articulating. Then there is the problem of the spare tyre… it probably won’t fit in the boot well any more.
33″ tyres will need a 2″ lift kit installed first. No way will you be able to steer or move without damaging the tyres or wheel arches unless you lift the car.
With Gen III Air Springs, you may get an extra 2″ of travel but this doesn’t mean you should automatically raise EAS settings. By raising the EAS height of the vehicle with standard shocks, you are reducing the amount of travel left in the shocks to absorb on and off-road drops etc.
Longer shocks are ok as long as they don’t over-extend the air springs, causing them to strain and potentially pop-off. If you go for longer extended shock length, also consider what it does to the compressed shock length. It is no good having an extra 1-2″ of shock length if it means that the compressed state causes them to bottom out and destroy themselves. Yeah, you could extend the bump stops to limit the shock compression, but then you are also limiting the articulation ability of the vehicle on each side.
So, a 2″ suspension lift will solve a lot of articulation and clearance problems and let you run 33″ tyres on your P38. Here’s the bad news:
- you need to get shocks to suit the lift (you can move existing fronts to the rear)
- you need to extend the EAS height sensors
- you need to get extended brake lines or fabricate brackets to lower the existing lines
- you will need extended bump stops (or other means to compensate)
- with 33″ tyres, speedo and diff ratios are no longer correct. You will be travelling faster than the speedo indicates (around 15%), fuel consumption calculations on the Message Centre will be out… and most importantly for off-road use, you will travel much faster downhill in Low-1 than is comfortable. Consider swapping the diff gears out a for 4.1:1 ratio.
- due to the permanent 2″ suspension lift, there will be a greater angle on the front and rear drive shafts. This may lead to some whining noises and extra wear on the UJ’s. A double cardan joint on the rear shaft should fix this.
I will put more stuff in here as it comes to mind.