OT: MOT advisory: tyres cracking.

[mike]

Took the car in for service and MOT last year. The garage who do the service (and who I have no reason to distrust) take it elsewhere for the MOT.

It passed but with the advisory "Both rear tyres cracking".

Garage chap and me went out to look for these cracks and eventually spotted what I'd call microscopic surface crazing to some parts of the sidewall. The garage chap didn't think it was a problem. I've taken some photos to upload but you just can't see the "cracks".

I dutifully check the tread and the pressure every month and have been watching the "cracks" which look exactly the same now as they did then.

MOT is due Friday, and I'm planning to take it to the same garage. Can this be reason to fail MOT? The car does average mileage and I'd expect the tyres will be changed in the next 12-18 months due to tread depth.

[Lobster]

If in doubt, do what I did at my local garage last week. A few days before they were due to do the MOT test, when I was equally unsure whether my tyres were up to scratch or not, I popped in and explained the situation, and asked them to take a quick look.

They were happy to do so - in my case the answer was "no" :( but at least I got the chance to get new ones fitted by the nice man from etyres, at about £50 less :)

[fred]

In article , mike writes

Re MOT fail, absolutely, the cracks/crazing indicate a breakdown in the rubber of the tyre leaving it in a potentially unsafe condition. Old tyres (and I'm assuming they are getting on) can just break down and need changed if they are in poor condition, irrespective of tread depth.

Also be aware that, depending on the severity of the condition, a tyre kicking plod could view the tyres as unsafe and hit you with a ticket for using a vehicle in an unsafe condition, fine and 3 points per affected tyre!

After this if you still feel they condition is superficial then put it through the MOT and change them if it fails, the re-test will cost you nothing.

[Chris J Dixon]

Which reminds me that I have one about due for replacement.

I inherited a mixed bag of tyres when I bought my Mk 4 Mondeo about 12 months ago.

The tyre size is 235/45R 17 97W

What I have, with tread depth, is:

Front Pirelli Pzero Rosso 3 mm Maxis MA-V1 6 mm

Rear 2 x Goodyear Excellence 4.5 mm

The spare is a space saver.

What are the thoughts about mixing different types? I know it is perfectly legal (Does anybody use cross ply these days?) but is it a good idea on the same axle?

Do I just replace the Pirelli, as is, or get a pair, putting the Maxis on the back, throwing away one of the Goodyears still with some life in it? Am I wrong to put the newer tyres on the front?

These days I do less than 8k miles per year, comprising a little local mileage and occasional long runs, some with caravan.

Chris

[Davey]

Back when radials were coming onto the market, and it was recommended that radials and cross-plies were not put on the same car, and certainly not with the radials on the front, we automotive students did just that to see what would happen.

DON'T DO IT. IT'S BAD.

--=20 Davey.

[NT]

Cracking has to be a certain depth for there to be a fail due to loss of structural strength. Superficial crazing is not big deal.

You can mix different radials on one axle, it is possible to encounter slightly different grip limits cornering each way, but not enough to make it a danger. Putting crossplies into the mix is another thing entirely, and shouldn't be done, but those arent found on any normal car these days.

NT

[Dave Liquorice]

wouldn't, see above. New tyres on the front, 1/2 or maybe a bit more worn on the back, road cold, wet, slippy. Back end lost grip, I controlled at least three wild side to side swings before giving up hitting the wall and being flipped. Combination of front glued to road, back less grip, slippy road and driver error. Driver error that I'd lifted off for a gentle corner, I suspect if I'd flooored it the back end would have been pulled back into line and eventually regained grip.

[Tim]

Plenty of films on YouTube illustrating the dangers of new tyres on the front with part worn tyres on the back if you're not convinced.

Tim

[Clive George]

Lift off oversteer - yup, you should have floored it to get some weight on the back wheels. Or of course not gone in as fast in the first place :-)

(had a reasonably fun session on a skid pan doing this last year).

[Dave Plowman (News)]

Has this with mine too, but front tyres. I'd describe mine as more of a surface crazing - you can't 'hook' into it with a finger nail. So to my mind purely cosmetic. I'd expect a crack to have a real depth - is there any guidance in the MOT 'bible'?

[Dave Plowman (News)]

It depends on the handling characteristics of the car. But in general, ultimate understeer is safer than oversteer.

[Lobster]

But why would the situation have been any better if your front tyres had been as worn as the back ones rather than being new?

David

[Dave Baker]

Cracking in the sidewalls is not an MOT issue unless the tyre carcass is visible through the crack in which case it's a fail.

[Kevin]

MoT Testers' Manual lists Reasons for Rejection as:

1. a. A tyre has a cut the length of which is in excess of 25 mm or 10% of section width, whichever is greater, deep enough to reach the ply or cords b. a tyre has: ? a lump, bulge or tear caused by separation or partial failure of its structure. This includes any lifting of the tread rubber ? any of its ply or cord exposed c. a recut tyre fitted to a vehicle not permitted to be so equipped d. a tyre incorrectly seated on the wheel rim e. a seriously damaged or misaligned valve stem which could cause sudden deflation of the tyre f. a tyre not fitted in compliance with the manufacturers sidewall instruction, e.g. ? a tyre marked ?NHS?, ?Not for Highway use? or similar ? an asymmetric with a sidewall marked ?outer? fitted with the marking to the inner side of the wheel.

plus other sections on tread depth, construction, and so on.

So crazing is OK.

I always check the date code on tyres since the oft-quoted fatality of an MGB driver with old but apparently sound tyres. It's in a panel, usually after the DOT codes, and is of the form wwyy. If it's only got three characters, or three and a triangle, it's at least 12 years old, and time for growing potatoes in.

Current advice seems to be always to put new tyres on the back, regardless of which is the driven end. I believe Costco refuse to do anything else.

In Chris's case, I'd fit the Goodyears on the fron and buy a pair of new tyres for the back. The Maxxis can go in the loft ready to fitted if very hard up when the next puncture happens. No, let's be exact: I'd put the lot, tyres and wheels, on ebay and fit tyres of a sensible aspect ratio on suitable wheels. Rubber bands are for postmen.

[The Natural Philosopher]

There is, but its subject to interpretation. You should NOT be able to see the cording basically. What 'seeing the cording 'means' is where the interpretation comes in. I.e. if you stick a knife in the carck and open it up and there's a glint of steel ..or is it rather that the tyre is so damaged that the cords are exposed to teh naked eye at a casual glance?

[Davey]

This was an A-H Sprite, the later one. The front with radials tracked tight to the corner, the rear with cross-plies didn't, and eventually the whole car spun round. And this was at a fairly low speed.

[The Natural Philosopher]

I'd probably challenge that statement as an absolute.

[The Natural Philosopher]

because the natural thing to do in a skid is lift off..and lifting off transfers weight and hence grip to the FRONT.

If its the front that has lost grip, thats a GOOD thing. If its the back it makes things worse.

[Caecilius]

Remember that public information film about it?

[Dave Plowman (News)]

Interesting. That's more or less what I'd assumed.