110 Handling post tyre change MT KM2

[Somethingwitty]

Gents,

Until recently I had a 300 Tdi 110 that handled surprisingly well - you could really throw it about with confidence around bends, roundabouts etc at quite some speed. It was however getting a little hairy in the grip department (fun) and in the safety side (curious bits of wire found poking out of a much abused carcass) and since the tyres (BFG Mud Terrain KMs - 255/85R16) were pushing six years old and 60,000 miles I did the obvious and ordered more.

Sadly I missed the last of the KMs and so have 255/85R16 MT KM2 all round - simple swop I thought! Since fitting the new rubber the handling has varied from turbo dangerous to just about okish. Re-shiming the swivels (guestimated and too tight before) improved matters but it had a tendancey to wander, excessive roll, tuck under when swerving at speed and also a tendancy to tank slap on recovery from a swerve (again at speed).

Suspecting the Shocks (Pro Comp Explorers, really good when fitted many years ago) I replaced these. One rear shock had several inches of near unrestricted movement, the rest seemed fine! New shocks (Pro Comps again, from Paddocks... they can't possibly infect branded stuff can they?!) reduced the wander and perhaps a degree of the tuck under, however....

- Swerving at speed (motorway lane changes for instance) remains exciting and it still tank slaps in recovery

- there is still significant body roll

- it still can tuck under at the front

- Fast B-road where I used to have no problems the thing wants to leap to its (and my!) death

I've tried various things, the fronts are now at 36 psi! (anything over 28 on the old MT used to lead to understeer) Rears at 45psi (where I had the old ones to promote a degree of oversteer)

The wheel end of the drag link has a small amount of play in the ball joint but I don't think this is significant.

The overriding sense is that on turning the steering wheel there is an initial delay as the thing rolls and steers and then almost a sudden pull from the front wheels, quickening the rate of turn suddenly... its difficult to describe but somewhat analogous to a loose panhard rod bush/bolt - ie the axle steers then slack taken up and the body follows... except thats a hard drag of the chassis and body with no initial response - here there is a turn by axle AND body that occurs in almost two stages with a smooth, jolt free transition between the two.

Does that make sense? I hope so!

On rocking the body whilst stationary with new shocks fitted it continues to rock for a couple of cycles after - I had always thought it should cease motion almost immediatley?

What are people's thoughts please? I am sure the fact that the new tyres stick like sh*t to a blanket affects things (old ones slid even in dry :-) and it's worth mentioning that the springs are old, possibly as old as the veh (25yrs... but were fine with old tyres)

Ta very much,

A very confused Jim.

Edited to add: I did prime all shocks prior to fitting... and there was something else that I've now forgotten!

[Mo Murphy]

Sounds to me like soft sidewalls, like when a tyre is under inflated

Mo

[Somethingwitty]

Mo,

Thanks, I didn't want to put words into anyone's mouth but you've just said what I've been thinking, indeed what all others I've spoken to have said.

I've been trying to find an explaination other than the tyres... I remain suspiscious of the new shocks (I'm sure it should damp out quicker on rocking) but I can't escape the fact that it first started when these new pattern MT were fitted. The only other tyre related explaination I have is that since the grip bloody well that is now causing more roll. If (for sake of argument) the springs have grown very tired over the last 5 yrs or so then it would have been masked as the old tyres became more slide-happy... ie new tyres have shown up worn suspension.

Nonetheless, it does feel like something of an elastic nature is deforming then releasing the energy and sidewalls are certainly under suspicion. The questions then are:

- Why are they still 'Q' rated (100Mph I think it is) as they don't handle well enough to be safe IMHO at 90 let alone 100!

- What has changed? I know BFG have modified the old MT to the new KM2 to improve rock traction but have they in so doing changed construction to adversely affect the handling? I've noticed the tread width is much reduced, size for size.

- Have other BFG MT KM2 owners had similar issues?

- If they have not, are these incorrectly manufactured?

It's a shame BFG saw fit to meddle with the old MT - it was bloody brilliant... mind you, so was the Trac Edge and they pulled that too!

I think I might take the tiddle and stick in 50 psi on the fronts and 65 rear and see if it changes things - that would surely eliminate any sidewall issues?

[western]

I run my front KM2 MT's at 30psi don't have any handling issues, still got Original type KM MT's on the rear at 40psi on a heavy 110CSW, maybe it's because the tyres need to settle/bed in & the new tread blocks are much thicker than the old worn tyres.

Swerving at speed (motorway lane changes for instance) remains exciting and it still tank slaps in recovery

why are you swerving during lane changing, smooth changes at motoway speed is much better, your not on a race track.

[mickeyw]

It's a shame BFG saw fit to meddle with the old MT - it was bloody brilliant...

Alas we cannot blame BFG for this screwup! The world's beaurocrats can take the blame - apparently it's all in the name of fuel efficiency and noise emission that these tyres have been redesigned.

Given the above, it may be that the sidewalls are of a different construction, i.e. softer

[Somethingwitty]

I run my front KM2 MT's at 30psi don't have any handling issues, still got Original type KM MT's on the rear at 40psi on a heavy 110CSW, maybe it's because the tyres need to settle/bed in & the new tread blocks are much thicker than the old worn tyres.

why are you swerving during lane changing, smooth changes at motoway speed is much better, your not on a race track.

Western, good to hear you are not having snags with your front KM2s, thanks. I accept (and hope) that bedding in will help, nonetheless it handles like it has never before (in a bad way!). WRT swerving I was using lane changes as an example - because it's the kind of manoeuver that sets it off if done harshly. I can and do change lanes smoothly but on the old setup I could do so in an agressive manner and have no concerns - now it's a little bit of a lottery! Its not that I want to change lanes agressivly every day but sods law says that one day I will need to (HGV carcass, some random driving from the car ahead etc) in anger and its then that you get caught out; it remains difficult on fast A / B road too and here it used to be predictable and fun. I've been told its not a sports car but a LR - well aware, just trying to restore its handling to what it was before!

The old KMs were really great on and off road, I'm just hoping there is something else wrong on the veh that I can track down, if not then I would have to conclude that KM2 are a backwards step in handling - I know its a mud tyre but based on it's predecessor's abilities and its Q rating I hoped none of that was lost.

[Somethingwitty]

Alas we cannot blame BFG for this screwup! The world's beaurocrats can take the blame - apparently it's all in the name of fuel efficiency and noise emission that these tyres have been redesigned.

Given the above, it may be that the sidewalls are of a different construction, i.e. softer

Hmmm, if anything I'd say KM2 are louder (may quieten with block corners rounded a bit) and I would have thought stiffer sidewalls would improve MPG since you are not compressing / flexing them so much so disapating as much heat. Intrigued though and happy to blame beaurocrats!!

On a different note, I wish to appologise to the Ladies in the audience, regrettably I've been doing a lot of emailing to people at work all of whom are male hence was thumb up posterior on writing the initial post - please accept my apologies, you are very welcome to assist me!

[Off Road Toad]

I Doubt it is your tyres causing you the problems. It is a known fact that tyres do need bedding in before they give peak performance on the road. I suspect your springs and dampers are at fault here, maybe the newer tyres are behaving as they should and have allowed you to feel whats actually going on under your car. Have you checked all your bushes and track rod ends etc? if there is a small amount of play in your drag link then that is not acceptable - there should be none. tired springs won't be helping and as for pro-comps? !!! Take them off and throw them as far away from your car as you can get them. Standard LR Dampers are MUCH better for road use.

Just my two cents worth

Steve

[Somethingwitty]

I Doubt it is your tyres causing you the problems. It is a known fact that tyres do need bedding in before they give peak performance on the road. I suspect your springs and dampers are at fault here, maybe the newer tyres are behaving as they should and have allowed you to feel whats actually going on under your car. Have you checked all your bushes and track rod ends etc? if there is a small amount of play in your drag link then that is not acceptable - there should be none. tired springs won't be helping and as for pro-comps? !!! Take them off and throw them as far away from your car as you can get them. Standard LR Dampers are MUCH better for road use.

Just my two cents worth

Steve

Steve,

Thanks, I am hoping this is the case. Bushes are all relatively new (in the last year) and all genuine LR (got sick of the pattern rubbish) and look ok - however I will re-check. I had standard LR dampers before my first PCs and the change on fitting PC was enormous - much better (of course probably due to the old LR ones being shagged out!) What is it about Pro Comp ones (accept they are pretty cheap!) that makes them worse than standard LR dampers? Was hoping to leave the springs until the enevitable re-chassis in a couple of years but think I may well replace them. Its worth pointing out that there is no anti roll bar fitted, however thats always been the case.

Drag link is awaiting part and time and to be done in the next week or so but play is small... much less than what a mate of mine found on a customer's discovery that was 'a little vague' - he LIFTED the rod free of the ball... Scary!

[M&S]

Have to agree with Steve, doesn't really sound like the tyres to me.

Also I'd be looking at the steering box, any play in that?

[ToyRoverlander]

I got the same size KM2's on my heavily modified Series. I run them at 2.5bar front and rear. The series sits spring over on parabolic springs, so the lift is quite generous, it's got a really wide track and very good shocks (bilstein 5125 offroad shocks).

And it handles very well. I can fly around the bends with ease and the only vague handling caracteristivs it's got is because of its suspension, not the tyres.

I reckon your suspension needs a bit of TLC....

[landmannnn]

Vague handling can be caused by a lot of things, but reading

here there is a turn by axle AND body that occurs in almost two stages with a smooth, jolt free transition between the two.

seems more like the rear axle steer caused by worn/cheap radius arm bushes than poor dampers.

[Somethingwitty]

Vague handling can be caused by a lot of things, but reading

seems more like the rear axle steer caused by worn/cheap radius arm bushes than poor dampers.

Hmmm... interesting! The (THE? ...one of the!) theory I am now working with is exactly that - I've put 50 psi in the fronts and 60 in the rears! That has barely changed the response and for me that's got to mean the sidewalls are not an issue. There was a bit of a clunk from the back end throwing it into a RH turn at a roundabout... although symptoms are really there without clunks and so bushes are more likely. A-frame might have issues(although again, ball joint is only a couple of years old, no obvious clunk on taking up drive and the bushes have very little room for play even if shagged) Anyway, I am going out to double check the back end.

[Somethingwitty]

Have to agree with Steve, doesn't really sound like the tyres to me.

Also I'd be looking at the steering box, any play in that?

None that I've found - and from past experience play means lost movement but when in a turn the castoring action keeps that backlash taken up as the wheels try to centre the steering against your input... although I did have a track issue many years ago, a little too much toe out (20 degrees I guess with a bannana track rod) masked by icy roads. In the afternoon after the ice melted it developed a deep love for hedges when steered off centre! In the current problem there is no feedback through the steering suggesting a change in steering angle from that demanded - but also going to re-check.

[Somethingwitty]

I got the same size KM2's on my heavily modified Series. I run them at 2.5bar front and rear. The series sits spring over on parabolic springs, so the lift is quite generous, it's got a really wide track and very good shocks (bilstein 5125 offroad shocks).

And it handles very well. I can fly around the bends with ease and the only vague handling caracteristivs it's got is because of its suspension, not the tyres.

I reckon your suspension needs a bit of TLC....

The consensus is with you - glad to hear your tyres are fine! 2.5 bar.. 37Psi? What width rims are you on?

[cackshifter]

Is there anyone you could swap a set of wheels with for half an hour? That would let you see if the problem moved with the tyres or remained...

Nigel

[Aragorn]

If you compress the suspension on one corner and then release, it should rise and then settle.

If it oscillates any more than that, the dampers arent doing their job.

[Sirocco]

Using the same size KM2's as you. No problems. Have not noticed much difference from the same size KM's (fairly worn)braking is better and noise has reduced significantly.

I like them.

G

[ToyRoverlander]

The consensus is with you - glad to hear your tyres are fine! 2.5 bar.. 37Psi? What width rims are you on?

7Jx16 black 8spoke

[Somethingwitty]

7Jx16 black 8spoke

Ah! I'm on Wolf rims (6.5 inch) so unable to go as high a px as would like as it balloons the tread a bit.

To all those that contributed their thoughts, thank you and I'm sorry its taken a while to get back to you... However, I believe I have found the snag (s):

Dampers - some improvement after changing

Drag link & drop arm B/J - further improvement but again, not the cure.

A-Frame ball joint - well worn so replaced today - significant improvement but still experienced some rear axle steer.

A-Frame - chassis bushes - Bolts loose and bush worn on one side, changed both and abused new bolts with the air gun - RESULT!!!! Still TBC as only short test drive but major improvement

So in summary - Initial symptoms only shown by tyre change; slow to turn in then tightening turn with your arrse suddenly accelerated sideways at same time, together with wandering and jumpiness all essentially cured by TLC of the A-frame.

Thanks again,

Jim

[western]

my 255 KM2's are on XD/Wolf rims too, no issues with tyres/wheels or handling.

poor rear bushes as you've found can cause a rear axle steering affect, are the trailing rod to axle bush in good condition ? if not or suspect change those too.

[ajh]

One thing that was not mentioned is to check and make sure the KM and KM2 were both of the same load rating.

[cackshifter]

Worth repeating Les's advice - 'orange streaks are a sure sign of a worn bush.' How true.

Nigel