Flat spots on front tyres

[richwill]

I have noticed that the front tyres have flat spots on them. I had a problem with budget tyres I had fitted a couple of years ago and had these replaced with Continental Vanco tyres after spending time on the forum researching what others were running on their Bongos.These were recommended and I thought I had seen the last of the problem with flat spots. However after a while I noticed a regular bumping as I drove along which I initially put down to poor road surfaces but today while working on tidying up the Bongo before the worst of the winter sets in I checked the tyres and found both sides had flat spots. This is what is causing the bumping.
I have a 2.5 diesel aft and it is used regularly so I dont believe the flat spots are from being stood for long spells and the tyre pressures are correct.
Does anyone have any idea what the cause is.
Cheers Rich

[Northern Bongolow]

is it a 4wdrive?

[richwill]

yes it is 4 wd

[Northern Bongolow]

check that all the tyres have the same rolling circumference, or within 1% of each other.
thats not tyre size, but the circumference measurment.
you will prob find that your rears are either new, or newer than the fronts.
this means that the fronts are revolving faster or trying to than the rears, and skipping.
look at the plate on the door aperature for what should be fitted.
or do what most 4 wdrive peeps do---fit all 4 with the same size and aspect ratio, and rotate frequently to even out wear.

whats it like when you pull out of a t junction on to the main road, does it fight you and feel odd, but then ok when you straighten up ??

[richwill]

The tyres are the correct aspect as stated on the plate and it seems to behave normally at junctions.

[maxheadroom]

I had "van" tyres once on the front and they castellated changed for "car" tyres and no problem since (3 years later) but do check shocks etc

[tim & angie]

Might be worth checking wheel and diff bearings

[Northern Bongolow]

check the gearbox oil and the condition of the oil in the transfer box and both diffs.
if the transmition is fighting itself it should show up as smelly maybe even burnt smelling oil, this may lead you to the cause of the castling.
just remove each filler bung and check the level and remove a small amount and check its colour/smell.

[Simon Jones]

By 'flat spots', do you mean the type of thing you would expect if the vehicle had been parked in the same position for quite some time such that the side walls have bulged out at the bottom? If so, then I would not have thought it would have anything to do with the transmission side of things. What load rating are the tyres? I think you should be looking for something around about 96 or 98. I've used Vanco Contact 2's before and not had any issues other than they didn't wear as well as other tyres I've used.

If the problem is the castellated edges, then it's more likely to be transmission or tracking related as the problem is causes by the tyre 'scrubbing' while rotating. I think 4wd are always going to be more prone to these type of problems than 2wd.

[richwill]

I will be having the fluids changed tomorrow and will also have bearings and general transmission checked over to try and pinpoint any problems.
Will then need to replace the front tyres as well. I have some RX8 wheels I was waiting to refurbish which i will probably fit for now.

[skater]

By 'flat spots', do you mean the type of thing you would expect if the vehicle had been parked in the same position for quite some time such that the side walls have bulged out at the bottom?

If so, turn the wheels so flat bit is at the top.


Someone had to say it.

[richwill]

Had the fluids changed and checked out all the suspension, transmission and bearings and failed to find any obvious cause. I have now replaced the front tyres with new ones and will continue to keep an eye on them.
It is a complete mystery as to what caused the flat spots.

[Muzorewa]

Ours does the same, it's 4WD and the viscous coupling is probably well beyond its best which I take to be the cause, the tyres partly haveing to do what the vc should be doing.

I've noticed varying results depending on the tyres. I'm running standard sizes, 195/70R15 front and 215/65R15 rear and with Continental Vanco Contact 2 I found the grip excellent, especially in snow, but the odd wear & droning transmission noise came all too soon after renewing them. I'm now using Barum Cargo on the front which seem to wear much better. I was getting about 25,000km from a pair of fronts, that's now up to 38,000km.

[richwill]

Muz
I will be monitoring it closely over the coming year. It is at least a problem which has been experienced by yourself so I am not alone although its no comfort having to replace tyres which apart from the flat spots still had plenty of miles left in them.
I have had to spend a bit out lately on the Bongo including having a rear arch rebuilt due to rust and a partial respray to revive the paintwork. It looks great now and I am looking forward to a winter project of removing the rear conversion and fitting Rock and roll bed and side conversion.

[richwill]

Have been reading up on the viscous coupling and will try and test it. Now I am thinking of disconnecting the drive shaft to the front diff to run 2WD. Is this worthwhile or will it create other problems.
I assume all I need to do is unbolt it and remove. Will I need to seal the transfer box opening where the shaft is removed?