Tyres and I TV - a long shot

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ajtg1952
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Tyres and I TV - a long shot

Postby ajtg1952 » Sat May 14, 2016 5:47 pm

I have a 300 series Discovery due to go through it's ITV. It's never failed yet. At 16 years old, I only use it as a work horse and mainly on tracks. I've just noticed the front tyres are at the minimum wear mark.  They are 245/70-16. I had a 200 series which I scrapped but had just put 2 new tyres on it before bringing it to Spain which I've kept.  Unfortunately they are 235/70-16.

Do you think they would be noticed? 

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Re: Tyres and I TV - a long shot

Postby gerryh » Sat May 14, 2016 6:04 pm

I suppose it depends on the tester when you take it in.
They should check that the tyre sizes are the same as specified on the "log book"
Where I take mine for ITV they usually only look at the front RH tyre. :think:
I have had a car ITV'd where there have been different makes on the same axle, they should be the same make, the tester should have failed them, he just pointed out to me that they where different makes.

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Re: Tyres and I TV - a long shot

Postby ajtg1952 » Sat May 14, 2016 6:45 pm

One of my other concerns is putting a 235 on a 245 rim.

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Re: Tyres and I TV - a long shot

Postby Trooperman » Sat May 14, 2016 6:50 pm

I agree with Gerryh. The first action of the tester in Ronda is to crouch down, with paper and pen and write down the front RH tyre dimensions and then check it against the paperwork.
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Re: Tyres and I TV - a long shot

Postby Enrique » Sat May 14, 2016 7:24 pm

Hi ajtj1952,
" I've just noticed the front tyres are at the minimum wear mark." .......if it's definitely not under, Tester will give it an advisory , at least it will be as per spec.

As for putting 235 in place of 245 shouldn't be a problem.............slight speedo inaccuracy
in the example below 8,5 is rim size in ins
225 is minimum 235 or 245 ideal , 255 is maximum.

8,5 225 235 or 245 255

Ref: http://www.tyres-pneus-online.co.uk/tyr ... dvice.html

You don't say what the Load Rating of the tyres.................should be same or higher on 235 ones.
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Re: Tyres and I TV - a long shot

Postby costakid » Sat May 14, 2016 11:32 pm

Fitting the wrong tyres on a 4x4 could result in you winding up the diff. All tyres should be the same size. Very expensive mistake if it goes wrong. 225 , 235 ,255 is not a problem but all 4 should be the same.

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Re: Tyres and I TV - a long shot

Postby Torrox_campo » Mon May 16, 2016 5:23 pm

+1 with costakid. Fitting same tyres at each axle but front and back aren't the same will result in costly diff.repair. It is advisory to replace all 4 tyres at the same time or at least 2 tyres on same axle with the same model and make of the old tyres. I replaced all 4 tyres on my Freelander2 when my 2 fronts have less than 3mm and the back more than 3mm.

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Re: Tyres and I TV - a long shot

Postby spanish_lad » Tue May 17, 2016 3:32 pm

ajtg1952 the tyres that you can legally use, even if your paperwork only says one size are:

205/80, 215/75, 215/80, 225/75, 225/80, 235/70, 235/75, 255/65, 265/65, 275/60 or 275/65

these are all legally allowed to be fitted as the overall size of the tyre is less than 3% difference.
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Re: Tyres and I TV - a long shot

Postby ajtg1952 » Fri May 27, 2016 1:09 pm

Just to conclude, I decided to take the car for it's ITV without changing the tyres, in fact, doing absolutely nothing to it. I now have a shiny new "17" sticker on my windshield. The tester didn't even look at the tyres.

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Re: Tyres and I TV - a long shot

Postby country boy » Fri May 27, 2016 2:03 pm

My Range Rover handbook explicitly points out that all four tyres should be changed at the same time, presumably because of wind up as per CostaKid above. Fixed 4 wheel drive vehicles presumably are all the same?

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Re: Tyres and I TV - a long shot

Postby spanish_lad » Fri May 27, 2016 2:55 pm

While it does feel good to have a new sticker.. tyres at the minimum wear mark are lethal. I´d consider a new set anyways. even if you buy pre-used tyres from a scrapyard or tyre place, they will be better than what you currently have. Imagine it gets to winter and you take it down hill...
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Re: Tyres and I TV - a long shot

Postby ajtg1952 » Fri May 27, 2016 2:59 pm

This car will now spend 90% of it's next year on tracks. I may treat it to a set of part worn tyres and a new set of windscreen wipers; that was embarrassing when I was asked to put on the washers as there is only base rubber left on them and it doesn't clear the water so I couldn't see the tester for a couple of minutes. It seems to be are the washers working but not the efficiency of the wipers. I had the back seats lying flat so the rear belts couldn't be checked, so she asked me if the worked.
I think the strength of the ITV is dynamic testing of the suspension, brakes and especially emissions, all else is a bonus if it works.

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Re: Tyres and I TV - a long shot

Postby Trooperman » Fri May 27, 2016 3:51 pm

Fixed 4 wheel drive vehicles presumably are all the same?


Permanent 4WD should have a diff (in the transfer box) between front & rear to cope with the difference. My Discovery 2 is a permanent 4WD system and axle wind-up is never going to be a problem. Before that, my Isuzu Trooper (from which I derived my forum name! :thumbup: ) was 2WD until you moved a lever to make it 4WD and there were warnings only to do that on loose surfaces so that the wind-up was dissipated by the road surface.

There's a very good explanation here from a car site:

When a 4WD is travelling in a straight line all four wheels rotate at the same speed, but during cornering each wheel travels at a different speed due to the radius of the turn. All vehicles have a differential on the front and rear axles to allow the wheels on the same axle to rotate at a different speed. Constant 4WD’s have a central differential fitted to allow for different speeds between front and back wheels, but most part-time four wheel drives do not.

When a part-time 4WD (without a centre differential) is in 4WD an attempts to corner on bitumen, all wheels need to rotate at different speeds, but without a centre differential they cannot. This creates the phenomena called "axle windup" or "transmission windup". High strain is placed on the drive shafts and transmission, eventually causing one of two things to happen. Either one of the wheels slips or spins to overcome the stress or the drive-shaft/transmission breaks. This is why part time 4WD’s should never select 4WD on bitumen.

Constant 4WD’s have a central differential within the transmission to overcome this problem. However once in the dirt a constant four wheel drive can be bogged with only one wheel spinning. This is why they have a central differential lock that stops the action of the centre diff and makes it like a part-time four wheel drive in 4WD mode. The centre diff lock should never be used on bitumen or non-slip surfaces for the reasons mentioned above.

In reality, a 4WD is only a two wheel drive with one front and one back wheel driving when traction is lost. One wheel on each axle spins while the other receives no drive at all due to the action of the differential. The exception to this is where a limited slip or locking differential is fitted. A limited slip diff allows a limited amount of drive to be applied to the stationary wheel before the other wheel on the same axle spins. A locking diff allows no slip at all and both wheels on the same axle turn at the same speed, regardless of the amount of traction.
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Re: Tyres and I TV - a long shot

Postby Trooperman » Fri May 27, 2016 4:28 pm

Further to my post above, the Disco 300 that was the OP's concern also has permanent 4WD and has a centre diff-lock (differential locking lever) that does just what it says: i.e. locks the differential between front and rear for really slippery surfaces.

Country Boy: your RR will have the same system, and depending on its age, will either have a centre diff-lock lever or have an automatic locking system provided electronically like my Disco 2 has.
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Re: Tyres and I TV - a long shot

Postby country boy » Sun May 29, 2016 2:36 pm

So Trooperman, does that mean I can replace just one tyre at a time without mechanical implications?

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Re: Tyres and I TV - a long shot

Postby ajtg1952 » Sun May 29, 2016 2:59 pm

Slightly off topic, but it has concluded anyway, by I also have a Discovery series 2 TD5 automatic. I love it, best car ever by far. All the locks are selectable but electronic. It has electronic traction control, downhill descent, you name it it's got it.

However when we had all that heavy rain few weeks ago, I hauled a trailer load of building material up from Velez Malaga. Just under 2 tonnes. It never missed a beat all the way up our mountain in the rain. The problem came in the last 500m which is my track. I have a 25% grade over about 40m. I stopped at the bottom and selected low range, locked all the diffs but left the traction control on. I got half way up the slope and it ground to a halt. Nothing would make it move. Reversed back down and tried again with traction control of. Even worse, everything just spinning. Reversed again and unhitched the trailer. Went home, 200m and got my old manual 300, bald tyres and all. Reversed it down the slope and hitched up. Locked the diff, engaged low range and it walked up the slope. It didn't even feel like it was pulling a load, in fact half way up I thought I couldn't have hitched properly. But the trailer was still there.

The TD5 hung it's headlights in shame when we got into the yard.

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Re: Tyres and I TV - a long shot

Postby gerryh » Sun May 29, 2016 3:03 pm

Following on from Trooperman's explanation it's logical that there should be a differential between the front and rear axles.
Think about it, when you have your car ITV'd for the brake test for the front brakes the front wheels are turning and the back wheels are stationary and viz versa for the back brakes.
Would be interesting to see the brake test done on a vehicle where the central differential is locked?
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Re: Tyres and I TV - a long shot

Postby Trooperman » Sun May 29, 2016 7:04 pm

it's logical that there should be a differential between the front and rear axles.


That's the whole point! cos if there ain't, you're gonna get a "wind-up" in the prop-shafts" and that's the difference between an "off-roader" and a "soft-roader". It's there on a Land Rover, but it does mean that you can get wheels spinning on a really slippery surface which is why a LR will have either a mechanical centre diff-lock (which over-rides the differential) or have an electronic means of doing it like my (and atg1952's) Td5 Disco 2s via the ABS sensors.
When you do the ITV brake test, it's the rolling road that turns the wheels and not the other way round. The tester always gets the gearbox in "N" so there's no connection with the non-tested axle.

does that mean I can replace just one tyre at a time without mechanical implications?


There are other ramifications. If you've got an electrical "diff-lock", the wheel sensors may behave erratically if there's different diameter tyres on the same axle - they're very sensitive pieces of kit. Just "google" "Los tres amigos" on a LR forum and you'll see what I mean! But you'll recall that it was always suggested that the wheels on the same axle for any car should have tyres replaced at the same time for stability purposes.

atg1952:
locked all the diffs but left the traction control on.
Have you got a centre diff lock? The early disco2s had the mechanism in place but without a lever and you had to add it as an aftermarket modification. If not, you had to rely on the electronic and automatic means via the ABS sensors. Maybe as this is all off topic, we can discuss the strange ways of Disco 2s by private emails! :lol:
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Re: Tyres and I TV - a long shot

Postby ajtg1952 » Fri Jun 02, 2017 1:22 pm

A year on and just back from the ITV station. Fail.

I took Spanish lads advice and changed all the tyres. On the front a put on the spare and one I got from a scrapyard. On the back two cheap tyres I got from a dealer in Malaga.

It failed on the front tyres not being the same. I know they look totally different and have different speed ratings. But at least they have tread and no wire sticking out the side which is what it had on when it passed last year.

Do tyres on the same axle have to be the same make or just the same speed rating?

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Re: Tyres and I TV - a long shot

Postby Enrique » Fri Jun 02, 2017 3:58 pm

Hi ajtg1952,
Tyres on the same axle have to be same make, tread pattern and as per the vehicle spec.
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