Cooper ST - Compound Change

Submitted: Wednesday, Apr 16, 2003 at 00:36
ThreadID: 4421 Views:1778 Replies:5 FollowUps:4
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Hi all,

Info for anyone considering purchase of Cooper ST tyres.

I am thinking of fitting STs to my GU Patrol. Last week went through the archives and found a thread (19Feb) where Slunnie refers to side lug failure on STs fitted to a DiscoII. I followed this up with Coopers Oz distributor, who provided reply below. I was really pleased with the reply and they also phoned me to discuss - great service. I have had ATs before and will likely fit STs (though will wait for the new STC, due mid year). I think the bottom line here is selecting the correct tread pattern for intended application - such a subjective topic but one needing objectivity.


We have just had a visit from the technical people from Cooper USA so I am up to date with all the information about changes in Cooper product etc. As you may be aware Hugh our company has been the Australian importer of Cooper Tires for 13 years and we work with distributors in each state as well as having a retail store in Brisbane that specializes in 4x4 tyres. So we have seen a lot of tyres over the years and all the brands which has given us the ability as a wholesaler to see first hand the effects of the Aussie conditions on tyres, in fact we have had input into the design on some of the Cooper patterns in recent years.

The comments you have read on Explore OZ website on Cooper ST's chipping and tearing of lugs. Yes we are aware of it, and yes it has happened more than we first expected, however most of the people who experience this and feel that it excessive, have been comparing to other mud pattern tyres. You see Hugh the Cooper ST is a unique pattern and is designed to fit between a mud pattern and an All Terrain pattern and for people looking for more traction than other All Terrain tyres. The only trade off is that it is still an All Terrain pattern and does have limitations. What I mean by that is the ST has Sipes or tiny cuts in the tread blocks. These sipes are designed to squeeze water out form under the tyre on the black top, however on sharp dirt roads the tyre chips away as it does with all siped all terrain patterns. It is just that people think that it should not chip, however whenever we have seen a direct comparison between a Cooper ST and other brands of AT patterns the ST does better miles in the long run and does chip less in the same conditions. Remember that the mud patterns do not have sipes (even the Cooper Mud pattern) and that's why Mud pattens do not chip and do better in sharp or gravelling conditions. Also remember that many people that should be using mud pattens for these reasons and have switched to Cooper ST's to reduce tyre noise and improve on road performance have been the ones to notice the difference (many of these people that come through our retail outlet we have changed back to Cooper STT's and they have now realised that their application does require the Muddy's).

Tearing lugs is for similar reasons. The Cooper ST has a small but sharp
shoulder lug with a fine split or sipe in the middle of it and if you compare with the Cooper Mud pattern in the same size the Mud pattern lug is at least 3 times the size. It is obvious to us now why the ST lugs tear. Put simply, they are doing the job. What I mean is they are getting traction, to much traction, and because of the small lug they can tear. Now when given the same condition with a Muddy they don't tear and get the same grip, whereas if the same tyre had of been an All Terrain pattern it may have not torn, however it also would not have gripped like the ST (they probably would of got stuck). The people that
buy the ST for more traction than the average AT have been happy, it has only been the Mud tyre buyer that has bought ST's or people that use them for the same sort of work that have concerns.

Now the good news as some people have heard is Cooper are improving the ST compound. In late may we are expecting our first shipments of the new compound (the pattern name with be STC standing for Chip Resistant). Now all tests show a huge improvement with a 90% improvement in tear resistance and 40% improvement in chip resistance. Remember Hugh that although it will be improved it will still chip as the sipes are still in the design as well as the small shoulder lugs, so it will be far better that any other All Terrain but still not as resistant as a Mud pattern given the same conditions.
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Reply By: Michelle from ExplorOz - Wednesday, Apr 16, 2003 at 11:43

Wednesday, Apr 16, 2003 at 11:43
Hugh (and to all reading this...)

Never post the personal details of anyone (company or otherwise) in this forum without their express permission for its publication in this medium. As you will see we have had to delete the references you included in your post.ExplorOz
AnswerID: 17755

Follow Up By: Hugh - Wednesday, Apr 16, 2003 at 22:39

Wednesday, Apr 16, 2003 at 22:39
A big oops from me.......... thanks for the reminder Michelle
FollowupID: 11164

Reply By: Kev. - Wednesday, Apr 16, 2003 at 17:14

Wednesday, Apr 16, 2003 at 17:14
Apparently its against the law to do so.

Correct me if im wrong but i think this law started a few years back when a guy passed on personal emails his girlfriend was sending him and decided to sue him (and won) therefore adding this problem to the privacy act.

On the other hand if the info is positive it could ad to extra sales !
AnswerID: 17787

Reply By: Member - Jeff - Wednesday, Apr 16, 2003 at 20:22

Wednesday, Apr 16, 2003 at 20:22
Gee I did not want to hear that info as I have only just fitted ST's. Well I'll keep an eye on them - anyway when I was in Cape York all the tour operators were swearing by Coopers, saying thay were the best.Cheers, Beddo
Surf KZN185
<- Nifold Plain, Cape York
AnswerID: 17799

Follow Up By: Hugh - Wednesday, Apr 16, 2003 at 23:53

Wednesday, Apr 16, 2003 at 23:53

Out of interest, how do you find the road noise from the STs? I have a GU Patrol currently fitted with factory Bridgestone road tyres, so am expecting some noise increase but unsure how much. I previously had ATs on a Pajero and they were very quiet.
FollowupID: 11171

Reply By: Member - Jeff - Thursday, Apr 17, 2003 at 21:27

Thursday, Apr 17, 2003 at 21:27
Road noise - slight hum compared to standard road going tyres but it does not annoy me - some tyres are really noisey on the HWY but these are not - they also have good wet weather grip - I am very pleased with them so far - hope this helps Cheers BeddoCheers, Beddo
Surf KZN185
<- Nifold Plain, Cape York
AnswerID: 17863

Reply By: Slunnie - Saturday, Apr 19, 2003 at 12:13

Saturday, Apr 19, 2003 at 12:13
Hi Hugh,

IMHO, this verifys a design flaw and something which Cooper have just stated themselves, that the side blocks tear with the traction generated. Its interesting that the OE Michelins which are sipped to the hills have absolutely no tears in them at all - absolutely none.
When I spoke to Coopers my comparision was not to mud terrains at all, it was to OE tyres on other vehicles I have owned of which none have sustained this type of damage. My concerns related to safety and roadworthyness of the tyres and consequences of the tyre failure and insurance implications of tyre lugs breaking off. This is also a problem especially when Cooper state "Yes we are aware of it, and yes it has happened more than we first expected." It reminds me of the Ford Pinto scenario where it was cheaper not to fix the problem. It would be interesting to ask the users of BFG AT's if they have lugs crack off - I've never used these so cant answer that.
Until Cooper rectify the side lug design I wouldn't use the ST or the STC, though everybody will have their own opinions on that. BTW the reason why I have switched to the STT pattern is because it is the toughest tyre that Cooper have, and they would not allow me to switch away from the Cooper brand under their warranty. When the STT's are no longer servicable (or I decide to get new ones) I will be looking elsewhere.

You have to wonder, why is a 4WD tyre manufacturer producing a 4WD tyre that isn't strong enough to be used in 4WDing conditions, which is exactly what the vehicle is designed for. Patterns are a compromise, but strength isn't.

AnswerID: 17921

Follow Up By: nugget - Sunday, Apr 27, 2003 at 23:48

Sunday, Apr 27, 2003 at 23:48
I have BFG A/T KO tyres and yes I have lugs that have cracked off them. They are wearing at an alarming rate aswell. I reckon about 40000 km will be all I'll get out of them. I was considering getting ST's next but you've got me thinking twice now.
FollowupID: 11587

Follow Up By: Slunnie - Monday, Apr 28, 2003 at 00:01

Monday, Apr 28, 2003 at 00:01
Hi Nugget,
It will be interesting to see how the new compounds go with the Cooper tyre, though I still think the problem lies more in the tread block design than the compound with the ST. The muddies seem to be more resiliant.
The dilema is, that you need to go to a less agressive or more agressive tyre to fix the problem. I'm not sure if there is anything else along the AT-MT lines of the ST. Perhaps the Goodyear MTR which is supposed to be quite good.

FollowupID: 11588

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