Cooper ST MAXX braking on wet tar

[Tony]

Just had an oil change done and the last oil sweat repaired at RGM, and on my way home I came to a traffic light that was in the pocess of changing on a slight downhill, and a wet surface, I decided to stop (speed was under 60km/h) the brake pedal vibrated - as in ABS kicking in, and I sailed over right the intersection!

Last year, having experienced the same thing on 3 occasions, I asked Graham to check everything out and all was good. Earlier this year I got a load sensor from David (through Tinus) and RGM fitted it and had the Patrol on their brake dyno to make sure that everything was ok - no problems there either.

So I am now thinking that these tyres are not at all great in the wet. Anyone out there with the same tyre that can compare??

[Stefan]

I had the same with Dueller 694s on my bakkie. Not the STTs though - they stick like proverbial 'k@k aan 'n wolkombers'

[AndriesS]

If your ABS kicks in then it pretty much means you have enough stopping power to stop the wheels from rotating, of you had serious racing rubber on and you can't lock it then you might argue that there is not enough. It takes a lot of experience and feel to modulate your brakes to the point of just not loosing traction. Last night on my BFG on a barely wet road also tested the ABS . key thing is just keep the pressure dont' release else you will increase the braking distance.

That said, keep in mind the roads will be very very slippery until most of the gunk is washed off the road, so no full throttle in corners untill the good rains have washed our roads.

[ricster]

Also bear in mind that ABS will NOT make your car stop in a shorter distance in the wet than if you just braked hard, without locking up the tyres. With the tyre braking and releasing in quick succession the stopping distance will increase, however you will get better traction between road and tyre to have better steering control. It's a fine line when braking hard with a 3ton weight around you to get the Patrol to stop without locking up the wheels.

Tyres I believe play a HUGE role in how quick you can stop. Tyre pressure too. My Patrol doesn't have ABS, and from experience on the 2 different brands of tyres I've had/have on my Patrol, I can say confidently that some tyres are not as good as others in certain conditions. For example I previously had 33" Kumho KL71 mud terrain tyres on, and currently have 33" Maxxi Bighorns - mud terrain tyres on. The Maxxi's are very good in all spheres. On dry they are quieter and feel very stable on the road at 2.5 bar all round. The grip is in my opinion not quite as good as the Kumho's but the Maxxi's do give me a slightly better fuel consumption (the Kumho's really stick to the road with VERY aggressive tread pattern). In the wet the Maxxis are also good, however again not as good as the Kumho's ( have done many hard braking exercises on both tyres ) in both wet and dry conditions.

The more aggressive the tread pattern, in my opinion the easier the water can flow through the tread grooves preventing the tyre "aquaplaning". However the more aggressive the tread pattern is the noisier the tyre will be, but the better you will stop. Yes there may be less mm2 of rubber making contract with the tar, but that rubber is at least making contact and not aquaplaning.

Also to get good mileage out of a tyre, generally it needs to be a harder compound, irrespective of tread pattern. My Patols doesn't have ABS and all the fancy stuff, so when I chose the Kumho's, I knew they would not give me huge mileage, but I could stop VERY quickly. By the way, I got 65 000 - 70 000 odd Km out of my Kumho's, with doing LOADS of challenging 4x4 trails with beach sand, normal sand/gravel, rocks and mud..... oh yes and snow too ....So for my safety I feel 65 000 km was a good run on them.

Double check your tyre pressure. I find 2.5 bar all round on my "heavier than most" Patrols works great for me.

[Tinus lotz]

We have had some pretty hot winter days so all the oil diesel smoke dust is sitting on top of the road ....I nearly made doughnuts at every stop street just pulling away the other day after a couple of drops of rain
Give it a decent wash and all will be good again .....
That was with my slow lux 2.7 with my km2 muddies ....they stick on the tar like you can't believe. ...when I got out the car and felt the tar ....it was like snot so slippery

[marakasmalan]

having experienced the same thing on 3 occasions

Hmm, habitual. In spite of the ABS working. And only in wet. You need to adjust the braking system - and by the sound of it there is only one component, look for three levers on the operator and increase:

Awareness of wet conditions.
Additional distance allowed for deccelaration in wet conditions.
Awareness of the >2 tons of dead weight / own weight of the vehicle.



The fact is that the compounds used on 4x4 tyres yields incredible milage, but does not perform so well in wet as it is inherently harder and provides less friction. A MT tyre has larger threads and consequently less tyre surface on the tarmac. This difference is amplified by a reduction of the friction coefficient in wet conditions. In the wet it is possible that you may find better braking with a moderate load, if centrally distributed, as it increases the friction force.

On a gravel road, the opposite may be true, provided there is enough gravel and ground to fill up the thread-voids on the footprint, and perhaps better braking is achieved. I know on gravel the non ABS has the ability to stop faster than ABS, unless the ABS vehicle is skillfully operated and no blunt dependence placed on the ABS syustem to do the work.

Get one of your patrol mates and go do some stopping tests on the skid pan, this comparison will quickly point out if there are problems.

[ricster]

Good advise there..... High mileage on tyres generally means a harder compound which means not so good handling in certain/most conditions. Softer compound will not last as long, but will stop you quicker. Tinus will probably disagree with me, saying he gets 150 000km out of a set of BF's, but I'm sure my Patrol would have stopped quicker with a softer compound tyre even without ABS on the same piece of road at the same time, same circumstances.

Safety for me is priority. So good distance judgement adjustments needed when wet will always help..... but sometimes that damn robot changes just too quick, and I drive a diesel ( waiting for IanT to chirp something.... )

[Tony]

Ok, thanks for all the info everyone, I have always stuck to the manual with tyre pressure ie. 2.0 bar front & 2.6 bar rear. I never noticed this problem in the first 3 years I had the 'Troll and drove on the Mitchelin 4x4 Synchrones (now discontinued) that came with the car. It has only ever happened when making that last minute decision to stop for a red light, but never at anything above 50 km/h, and only on a wet surface - on the previous occasions however it was well into the wet season so the roads should'nt have been that slippery anymore.
The skidpan sounds like a good idea - where can I go to that has this facility??

[Tinus lotz]

Tony we are looking at zwartkops will arrange early next year

[Grant]

Gents


This is one of the reasons I have moved to AT's. As we spend most of the time on tar when we travel to our destinations I opted for Cooper AT3's and i am very impressed.


This was confirmed in the latest SA 4X4. Most popular AT tyre's tested.

As for tyre life, it is not high on my priority list. First is braking, road holding , tracking, wet road holding . Tyre cost must be looked at in a cost per km format. This give a far truer reflection of the actual cost.