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235/85R16 vs. 225/75R16 tyres, which is best?

Discovery & Defender

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#1 Boydie

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Posted 26 April 2012 - 10:47 PM

It's that time of the year again and I'm looking at replacing the round rubber things that keep the chassis of my Disco from dragging on the dirt :(

The last set of 6 were Coopers ATT 225?75R16 and while the grip was gopod the tyres were shockers and I didnt get 8000 kilometers out of the set.

When I returned from our odessy into the Simpson & the Stoney Deserts last Christmas the fronts were down to around 25% of the tread depth,( partly due to a slightly bent drag link and therefore poor steerring geometry) while the rears were down to around 50% of the original tread depth.
Of the 7500 kilometers we traveled on these tyres from brand new only 2000 was on black-top the rest was on sand hills and desert tracks, hard packed dirt roads, muddy tracks and gravel river beds.

I will never buy a set of Coopers again and would never ever recomend them to anyone else, I took them back to the supplier and the local Cooper sales manager claimed that the wear was quite normal and that they didnt guarantee any milage for their tyres. Forr a light truck tyre that is supposed to be good for 60,000 kilometers or more they were woeful and the attitude of Coopers even worse and in my humble opinion far too soft a compound for Australian outback conditions with ambient temperatures up above 50 degrees celcius :rtfm: .

So, to my question, has anyone on the forum run their Disco with 85% profile tyres and if so what were their experiences? Incidentally I'm looking at a set of six Bridgestone D694, while they are4'nt as aggressive as the D673 they have a better all round capability.

By my calculations the 235/85R16 should be around 2 1/2" increase in overall diameter (6.35cm) over the "normal" tyre used the 225/75R16 so teh 85 profile tyre should fill out the wheel arch well, with an increase in ride height, without scrubbing on anything on the front steer wheels and the rears should still have maximum vertical travel without coming into contact with any body parts.
The speedometer should be okay as this is electronic on my Disco and driven frm the final gear in the ZF4HP22 gearbox.
Iain Boyd,
Engineer, raconteur, Rally Driver, Hunter, Adventurer, National Cricket Umpire and Bespoke Epicurean.

#2 landroversforever

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Posted 26 April 2012 - 10:56 PM

Coopers have a mileage guarantee in the states IIRC.
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#3 Boydie

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Posted 27 April 2012 - 12:16 AM

Yes Ross, thats what I believed as well when I purchased them but their warranty does not extend beyond the USA :angry2: Metro tyres who supplied and fitted them on my behalf were so disgusted at the attitude of Coopers that they will no longer deal with Coopers. Even allowing for the poor wheel alignment of the front tyres (I bent the drag link on a submerged rock and straightened it out at Innamainka after driving some 300 kilometers with it bent and the steering pulling to the left) they had no excuses for the shocking wear on the rears
Iain Boyd,
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#4 BogMonster

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Posted 27 April 2012 - 12:39 AM

Speedo will be out by whatever the change in diameter is, if you increase the tyre size it can't detect that electronic or not!

Don't write off Cooper, it depends on where you are and what sort of roads you are on. I have worn out BFG ATs in 20,000 miles here, the thought of 100,000 that some folk claim is a joke! I wore out three sets of Grabber AT2s in 50,000km on my old Ford Ranger, and I don't expect to get any more than 20000 km out of a set on my current vehicle. It just depends on what the road conditions are like and loose gravel can be murder. I know somebody who wore out a set of Michelin XPCs in less than 8000 by driving fast on gravel.

"Light truck" is a bit like "mud and snow rated" its some bowlux they put on the sidewall to make it sound better.
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#5 Boydie

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Posted 27 April 2012 - 02:44 AM

Understood all that, BTW the electronic speedo is adjustable by swapping the sender on the side of the box, several aftermarket units are available - the Volvo Series 70 Station wagon for example will suit as they have 32" diameter tyres. ZF make the senders, LR and other vehicle manufacturers supply their own speedo to suit the ZF output.

As for excessive speed our maximum speed we achieved on the dirt was 80kph and never more than 90kph (2000 rpm) on the black-top. My old set of Maxims (225/75R16) that I've put back on have done in excess of 40,000 k's and still have 40% of their original tread depth left. I think the Cooper ATT will be fine in the Snow and cooler climates but simply are too soft to cope with the high temps we experience.
One day on the Oonandatta track the road I measured the road temperature which was in excess of 85 degrees, on the same section of road in December 1998 an Austrian girl, Caroline Gross-Munchen died due to heat stroke when she and her boyfriend got bogged in their Toyota Land Cruiser and she tried to walk the 60 kilometers to the main road. She perished with 6 litres of water in her rucksack.
Iain Boyd,
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#6 Niamh

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Posted 27 April 2012 - 07:54 AM

By my calculations the 235/85R16 should be around 2 1/2" increase in overall diameter (6.35cm) over the "normal" tyre used the 225/75R16 so teh 85 profile tyre should fill out the wheel arch well, with an increase in ride height, without scrubbing on anything on the front steer wheels and the rears should still have maximum vertical travel without coming into contact with any body parts.


We've got 235/85R16 tyres on ours which has a 2" lift. You'll probably need to adjust the lock stops, and we found that we needed a camel cut at the rear.

The speedometer should be okay as this is electronic on my Disco and driven frm the final gear in the ZF4HP22 gearbox.


235/85R16 tyres nicely adjusted the speedo reading to spot on for us :)

Niamh

#7 Boydie

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Posted 29 April 2012 - 04:51 AM

Thanks for that Niamh, that saves me buying the Volvo sender, how did you find the increase in diameter of the tyres? for example did you notice any increase in sidewall flex ?
Iain Boyd,
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#8 Niamh

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Posted 29 April 2012 - 07:47 AM

I suspect that sidewall flex is likely to vary more between tyre manufacturers than anything else.

Niamh

#9 Boydie

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Posted 30 April 2012 - 04:04 AM

I guess you would be right about that, sidewall flex - or lack of it - was the only good thing I can say about Coopers, there was almost zero. The tyres I've settled on are Brigestone D694 235/85R16 - just ordered 6 of them :wacko: I chose them against the more aggresive D673 which has a softer compound and less land than the 694's.
Iain Boyd,
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#10 Boydie

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Posted 02 May 2012 - 10:57 PM

To close this I ended up with a set (6 off) of Bridgestone 225/75R16 in their D694 profile.

I tried a set of the 235/85R16's borrowed from my tyre dealer and the ZF4HP22 simply wouldnt go up into 4th overdrive gear, the bigger diameter tyres were simply causing the gearing to be too high. I guess Niamh has a R380 manual in his Disco. I've considered several times swapping over from the auto to the R380 but for the style of driving that I do and the places I go, - sandy deserts, long gravel roads (over 600k's) the auto box is by far the better option so I'm stuck with the lower profile unless I can come up with a lower set of gears for the ZF which would be highly unlikely.

anyway thanks to you all for your input.
Iain Boyd,
Engineer, raconteur, Rally Driver, Hunter, Adventurer, National Cricket Umpire and Bespoke Epicurean.

#11 Niamh

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Posted 03 May 2012 - 05:56 AM

I guess Niamh has a R380 manual in his Disco


She does, but I have friends with autos who use the same tyres.





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