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Cooper ST - running off unevenly
Posted: Wed Jul 07, 2010 3:29 pm
by macjohnw
What causes tires to run off unevenly? The blocks on the tire next to eachother are running off scew and unevenly - what is the story?
The tires only have 23,000km on.
Re: Cooper ST - running off unevenly
Posted: Wed Jul 07, 2010 3:38 pm
by 4ePajero
- alignment (toe-in / camber / caster)
- worn shocks
- worn ball joints / tie rod ends / Pitman Arm / idler arm
Re: Cooper ST - running off unevenly
Posted: Wed Jul 07, 2010 3:45 pm
by macjohnw
4ePajero wrote:- alignment (toe-in / camber / caster)
- worn shocks
- worn ball joints / tie rod ends / Pitman Arm / idler arm
I am having the alignment and shocks looked at tomorrow - I reckon it might be shocks when I come to think of it, it is not so stable around bends/curves.
Re: Cooper ST - running off unevenly
Posted: Wed Jul 07, 2010 3:54 pm
by 4ePajero
Keep us informed.
I would put my money on all the other items (except shocks).
4x4's steering components wear out very quickly, especially if large tyres are fitted.
Re: Cooper ST - running off unevenly
Posted: Wed Jul 07, 2010 9:22 pm
by Scubadude
macjohnw wrote:What causes tires to run off unevenly? The blocks on the tire next to eachother are running off scew and unevenly - what is the story?
Hard to tell from the pics, but I have a suspicion it is "feathering" from extended high speed driving ...
Re: Cooper ST - running off unevenly
Posted: Fri Jul 09, 2010 1:01 pm
by Gerrit Loubser
That looks like heal-and-toe wear. Although poor wheel alignment can aggravate this, it is something that is unavoidable on tyres of a more aggressive design with "knobbly" type tread blocks (such as the STs).
The root cause is that the tread block is bent over as tractive effort is applied in the contact patch, which increases the vertical load on the rear of the block and reduces it on the front. This leads to accelerated wear at the rear of each block, as in the picture.
The only cure is to cross rotate the tyres (at intervals of around 10000 km or less), which alternates the direction of rotation and equalises the heal-and-toe wear.
Re: Cooper ST - running off unevenly
Posted: Fri Jul 09, 2010 1:18 pm
by macjohnw
Gerrit Loubser wrote:That looks like heal-and-toe wear. Although poor wheel alignment can aggravate this, it is something that is unavoidable on tyres of a more aggressive design with "knobbly" type tread blocks (such as the STs).
The root cause is that the tread block is bent over as tractive effort is applied in the contact patch, which increases the vertical load on the rear of the block and reduces it on the front. This leads to accelerated wear at the rear of each block, as in the picture.
The only cure is to cross rotate the tyres (at intervals of around 10000 km or less), which alternates the direction of rotation and equalises the heal-and-toe wear.
Gerrit, if I understand correctly this "tractive effort" occurs when you use 4wd? The reason being that this is on the front tyres only, the back ones are 100% ok.
Re: Cooper ST - running off unevenly
Posted: Fri Jul 09, 2010 1:28 pm
by 4ePajero
The problem with this type of wear is that it is "self-perpetuating".
Once it starts, it gets progressively worse (the problem makes the problem worse, if you know what I mean
)
To rotate the tyre's direction of travel has two effexts:
- it starts a new cycle (the same pattern of wear, but in 'reverse'
- it increases the total rate of wear. Since less of the tread is in contact with the road (the high spots), they wear away faster than the rest of the tyre. (Catch-22)
I personally think the only solution (assuming there are no other issues such as shocks / steering components), is very frequent directional rotation, at say 1000-2000 km intervals. This will be a major "schlepp", but will minimize the problem.
When I was in the Army, we had this problem on the "knobbly" tyres fitted to eg Jeeps and Bedford troop carriers.
When it starts, it can ruin a tyre in one long trip on asphalt.
These wear patterns make the tyres very noisy as well (low frequency drone).
It seldom happens when the vehicle is used exclusively on loose surfaces, eg gravel.
Re: Cooper ST - running off unevenly
Posted: Fri Jul 09, 2010 1:31 pm
by Gerrit Loubser
The deformation of tread blocks happens on non-driven wheels as well, but it is more significant on driven wheels. Have the tyres with the heel-and-toe wear always been at the front or might they have been rotated from the rear to the front?
Re: Cooper ST - running off unevenly
Posted: Fri Jul 09, 2010 1:42 pm
by macjohnw
4ePajero wrote:These wear patterns make the tyres very noisy as well (low frequency drone).
It seldom happens when the vehicle is used exclusively on loose surfaces, eg gravel.
Yes it is exactly what happens - on rough rough asphalt it is quite as a mouse, but on smooth asphalt it really hums/drones. It feels like the nose is a bit boat'ish around corners, so I hope it is the shocks. Funny that the wear only occurs on the front wheels and not the back ones.