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Date Registered: 05-2012
Location: Sunshine Coast
TOTAL POSTS: 481
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I damaged one Dunlop in newish set - what I learned from the experience:


What I discovered after damaging one tyre in a newish set of four Dunlop Grandtrek ST 20 225/60R17's at 12,000 Km seemed to cross several threads so it seemed better to start a new thread with a data dump of everything I learned and hope that it is of some use to others.

Firstly, I ran over a piece of metal on the road ( my fault for doing so ) and damaged the sidewall of the rear left Dunlop which led to gradual deflation on the way home .

Oddly, I felt nothing unusual until the tyre pressure was low enough to allow the striations in the sidewalls to contact the bitumen and cause a grinding noise.

I pulled over within 50m and replaced the tyre with the "spare" which is sized at 215/65R16 and continued the journey home then started looking for a used Dunlop of the right size and wear to complete the now deficient set.

It was a huge learning process and I discovered the following:

1. The Spare:- Speed limited to 80 Kph for good reason.
As it is a different size, according to the online calculators it runs with a 2.3% smaller circumference so its revolution rate is not the same as the rest of the tyres on the vehicle.

Also, it has a much higher rolling resistance, so with a combination of those factors,at 80 Kph with the Spare, the car was showing 2000 RPM when usually it shows 1600 RPM at that speed.

Fuel usage increased in the 100 odd Km it was on, from 8.6 to 9.0 L/100Km.

2. Replacement Dunlop ST20: don't bother looking for second hand ones, there are none. (Edit: At least not when I was looking for one, probably more common than Herpes now that I don't need it {or the Herpes})
 
Plenty of 215/60R17's but again, the rolling radius is different, so not worth the exercise.

3. New Dunlop ST20: RRP of $450 but readily available at $330-350. Best deal was from my local Nissan Dealer at $295 as he'd bought a stack when they were cheaper.

Strangely they sell in USA from between 144 and 190 $ U.S.A .

4. Treadwear: The Dunlops have a treadwear rating of 300 which is not much in the scheme of things as the Pirelli Scorpion Zero asymmetric in 235/60R17 at $269 from Bob J have a treadwear rating of 420.

I ran the digital calipers over all the tyres and found 80% remaining on everything except the blown tyre which showed 70%.

The other three were manufactured in the 50th week of 2011, but that one was manufactured in the 48th week of 2011.

So that one had worn 30% but all the others only 20%... curious - but probably not significant.

Edit: I was expecting the usual Run Board downtime to wipe the above so I sent it in haste.

Continued: At that rate of wear, the remaining Dunlops (after 12,000 Km of use) look as if they could possibly reach 50,000 Km. before replacement is necessary in this instance.

There is a lot of previous for an expected 30,000 Km lifespan for that tyre, which would be in line with its low tread wear rating of only 300 .

Some A/T tyres seem to have a 560 wear rating...I would expect 450 to be a useful compromise between too hard and too soft.

However, when they do wear out sooner or later - hopefully later rather than sooner - I will not replace them with the same thing as it seems that there are better priced tyres with a higher wear rating which also have a 'road hazard' warranty (eg Yokohama) which would have saved me this expense.

Also, the next size up is more readily available, so it is only reasonable to go up a size and both increase the variety on offer and lower the cost of the available tyres - as well as improve the vehicle clearance.






Last edited by DogTrail, 1/Nov/2012, 8:33 pm


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2011/12 Australia:- 2.5 litre petrol 4WD, Series IV ST, CVT with Nissan bonnet & headlight protectors, mats + after-market HD towbar with added step for old dogs. ;) Garmin GPS, K&N air filter, DashMate, Black Pearl Tint , Dirt. X-2429(c).
1/Nov/2012, 7:12 pm Link to this post Send Email PM   Send Private Message
 
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Date Registered: 06-2008
Location: Blue Mountains, NSW
TOTAL POSTS: 5966
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Re:


You should be OK to drive with the tyre being the rear cause it's not the main drive line, even if it is nearly 2 sizes smaller.
I don't understand how there could be a difference of 400 rpm just by changing a tyre, the smaller tyre would simply rotate a lot more than it's R/H side equivalent.
Unless you had it in Auto or Lock which I doubt.

Should have gone with the Yoki's.

---
Tony X-891c

HERE is my D22 Navara
HERE is my old 2008 T31, ST Series1

2/Nov/2012, 4:44 am Link to this post Send Private Message
 
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Date Registered: 05-2012
Location: Sunshine Coast
TOTAL POSTS: 481
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Re: Re:


"I don't understand how there could be a difference of 400 rpm just by changing a tyre, the smaller tyre would simply rotate a lot more than it's R/H side equivalent.
Unless you had it in Auto or Lock which I doubt."


Maybe with the CVT box there is room for variation as it compensates for resistance.

Certainly does not compute for any other gearbox.

I put it down to increased rolling resistance from the spare and my heightened awareness that the system could be out of balance.

Unfortunately, when I crunch the numbers, it all seems to indicate that I have been a victim of my heightened perception as when I did a fuel economy check on refilling the tank after 100 Km of limited speed by the Spare and another 100km with a real tyre, the total fuel economy over that distance was better than anything else I have ever done.

Probably /maybe as I was driving exceptionally softly ?

More variables in working out fuel economy than one could shake a stick at.

Figures are available on Spritmonitor at Jalal's site.

As an aside:-

Certainly figures are available for re-crunching, but at the moment on Spritmonitor it appears that I am driving the most economical 2.5L T31...-...

.... In The World !

( apologies to Jeremy's style on TopGear)

Last edited by DogTrail, 3/Nov/2012, 11:32 pm


---
2011/12 Australia:- 2.5 litre petrol 4WD, Series IV ST, CVT with Nissan bonnet & headlight protectors, mats + after-market HD towbar with added step for old dogs. ;) Garmin GPS, K&N air filter, DashMate, Black Pearl Tint , Dirt. X-2429(c).
3/Nov/2012, 10:53 pm Link to this post Send Email PM   Send Private Message
 


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