Road Noise problem

[Crazy Diamond]

O.K. Here goes. I'm new to forums so if this goes wrong, well.................


I used to have a 1990 2.8TD swb Trooper which I successfully lifted 2" on 31-10.50 R15 BFG MT's. Road noise was acceptable. Ride was superb on tarmac, Off Road ability was way better than stock, and the car was still in the making, but along came two children, and suddenly I needed a 5 door car.

I'm now running a 1998 3.0TD lwb which I promised the wife would remain stock. Anyway, I've had it 12 months and I've lifted it 1.25" ( so far ) using OME springs & shocks, running 265 / 75 r16 BFG MT's ( The new ones ).
The difference is unbelievable. Between 20 - 35mph the road noise is deafening to the point that I've replaced front wheel bearings beleiving that to be the problem. I'm running manual hubs, so I know the noise isn't drivetrain. Does anyone know whether these new BFGs are noisier than the old ones, or is this likely to be a camber issue ?

I know the suspension is slightly different on post 98 models, but is there really that much of a difference that such a small lift would make MT's so noisy ?

It's also not too easy to detect uneven wear on these new BFGs coz they're too new and the shoulder lugs are so wide the old ' run the hand over the shoulder ' trick doesn't work.

Does anybody have any advice on tyre pressures ?

I'm planning a ball joint flip in the not too distant future, with a view to going higher. However I need to get this problem solved first, AND it depends on whether I can actually get any coil spacers in this country !


Any input would be much appreciated

[Eric]

There's nothing that stands out in my mind as to why a '98 would be noisier than a '90.

If anything, it should be much quieter, since it's a heavier build and more plush.

Dunno. Could be that the diesel makes for more vibrations, or something. With no diesels here in the states with which to compare road noise with my '98 gasser, I have no frame of reference.

Of course, it's not all that likely that it's the engine at all.

What does the noise sound like? Is it proportionately louder as you accellerate? Does the noise change at different speeds?

Is the noise not that bad up to a certain speed, then really loud, and then get quieter as you pass a given speed?

More info is required, at least by me, to form an opinion.

We'll get to the bottom of it!

[Crazy Diamond]

Sorry about the delay in replying, just got back off holiday 3 days ago, having covered over 700 miles in the Trooper, half expecting to be coming home on the back of a recovery truck !

The noise has been there throughout, definitely tyre noise.

Since then I've done a bit of back to basics thinking, and I think I've solved the problem, but its left me a bit perplexed .

I think It's to do with the change in Castor angle induced by the torsion bar crank and subsequent settling of the front end.

Now, having visited several small Australian and N.Z. websites ( because no-one in the U.K. takes the Trooper seriously as an off roader ) I have learnt that the Diesel Trooper is a lot heavier at the front than the V6, and actually uses different length Torsion bars. Therefore it takes more turns of the bolt to acheive the same lift.

When I did the initial lift I took pre-lift measurements, and simply wound the torsion bars up to match the rear coils( 10 full turns of the bolt ), and then remeasured. +40mm rear, +45mm front.

A week later I remeasured, expecting some settling, and found the rear had settled 5mm, and the front about 10mm.
This left me with a 35 mm ( 1.25"approx ) lift.

Because the diesel torsion bars are longer, and require more turns to gain the same lift, and the engine is heavier, the front end will also settle further, and take its time doing so.

What I have done now is to ignore all my pre lift measurements and simply taken measurements from the sill ( rocker panel ) to the ground.

I found the sill to be 15mm lower at the front than the rear.

I have now put another 4 full turns on the torsion bar bolts, bringing the sill parallel to the ground, and hey presto, the noise has almost gone. All I can hear now is what I would call acceptable noise for MT tyres on tarmac.

This means the front has had 13 full turns on the bolt to acheive the equivalent of 35mm lift at the rear.

I think the previous owner may have even lowered the front end !, because according to my calculations I have now lifted the front some 65mm !

Quite why a change in castor would make so much difference to road noise I don't know. I can only suppose that it alters the damping characteristics of the shockers.

Anyway, that problem seems to be solved, so what am I going to lie in bed worrying about now ?

I'm going to have to take it out at the weekend and break something