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[wedge]

hi all

about 4 weeks ago, i put my car in to a local garage, that prepared and took it to get MOT'd, they told me that it needed brakes and a new tyre.

all round i have 235 45R17 97W's, but just noticed tonight that their replacement, on the back axle, is 235 40R17 90, which from my freshly learnt tyre markings search, means a 20.8mm diameter difference!

A) Are my calculations right?
B) isn't this illegal?
C) Therefore should the car have passed the MOT?
D) Most importantly, having just driven to Liverpool and back, 350mile trip, cruising in the motorway fast lane, also country roads in the dark and the wet, how safe was i, and anyone near me?

i'm hoping that it's an apprentice screw up, not that a garage would knowingly do it just to get rid of old stock

any insight would be most welcome   

[Kevin Wood]

Tyres must be identical spec across each axle, so, if they passed it with that tyre on..

Might be worth asking them to replace it with the correct spec. You can always threaten to report them to VOSA if they don't rectify their mistake, assuming they didn't take it elsewhere to get the MOT?

[Nick W]

I haven't done the calculations, but a 20mm diameter change from a 5% decrease in aspect ratio seems a lot.

It's academic, as different tyre sizes across an axle is illegal. Whether it was a mistake or deliberate, the garage is responsible for putting it right.

[Diamond Black Geezer]

You've not risked life and limb... but on the other hand certainly play up the fact that you have risked life and limb. As above it is illegal and it should not have passed an MoT test like that. At best an honest mistake, at worst, someone who literally couldn't be bothered to do their job right, and knew what they were doing.

[robson]

If it is illegal why is our spare a smaller wheel and how about those thin emergency wheels. perhaps its ok in an emergency? Anyway chase up that garage.

[Diamond Black Geezer]

It is an MoT fail. 

However, I quite agree - why is it 'no good' for normal driving, but apparently 'fine' for emergencies, the fact that any of us could be driving on a space-saver for all of half an hour, encounter adverse weather, and cause to swerve. You then only just hit the kiddy/old lady etc. better rubber would have meant you only just missed them. Sounds dangerous to me, but it comes down to a lovely simple word - cost.

That's why anything is done. 

[steve6367]

It is an MoT fail. 

However, I quite agree - why is it 'no good' for normal driving, but apparently 'fine' for emergencies, the fact that any of us could be driving on a space-saver for all of half an hour, encounter adverse weather, and cause to swerve. You then only just hit the kiddy/old lady etc. better rubber would have meant you only just missed them. Sounds dangerous to me, but it comes down to a lovely simple word - cost.

That's why anything is done. 

The space saver does come with the drive slowly, move directly to a garage for replacement with passing go etc warnings.

[Doctor Gollum]

If it is illegal why is our spare a smaller wheel and how about those thin emergency wheels. perhaps its ok in an emergency? Anyway chase up that garage.

You're limited to 50 mph (and a max of 50miles in most cases), facelift Omega included

[wedge]

thanks to all for the replies 

they did take it to another garage for the MOT.

on the tyre, the 40 & 45 is the tyre wall size as a percentage of the width, so 235x40%=94mm width and 235x45%=105.75 width meaning 11.75extra per wall, so 23.5mm overall difference on the back axle - i got my original calc wrong, it's even more than i first thought.

it wasn't on as a temp, this was for my next year of driving. i read last night that the difference can at least really screw up the differential - i want to keep my miggy trundling as long as i can, not speed it's journey over the oil can bridge 

Thanks for the support, i'll go back, get them to dig out the bill breakdown, see how that reads, and exactly what i've been charged for, i'll let you all know what the outcome is 

[wedge]

P.S. as i have lpg, there is no spare wheel, it's not from vauxhall, this is one they have chosen from their shelves to replace my worn one - which does make it quite hard to see how it was an accident 

[Nick W]

P.S. as i have lpg, there is no spare wheel, it's not from vauxhall, this is one they have chosen from their shelves to replace my worn one - which does make it quite hard to see how it was an accident 

It's wrong. It's their problem. They must deal with it.


Any more questions?

[TheBoy]

The load rating - 90 - is insufficient for an Omega, and does not meet manufacturer specifications.  Thus, your insurance cover is a grey area, and you potentially could be in catastrophic tyre failure territory.

[robson]

Hello Nick you didn't comment on the fact that the Omega spare is smaller than the road wheels I believe this is because the wheel well is too small for a normal size. Does this only apply to certain models?

[Nick W]

Hello Nick you didn't comment on the fact that the Omega spare is smaller than the road wheels I believe this is because the wheel well is too small for a normal size. Does this only apply to certain models?

That's a legacy from the early models that were fitted with those 15" wheels as standard. I believe that a saloon wheel-well cannot accommodate a larger wheel, but I've never owned one to confirm that. I've had a stock FL 17" wheel as a spare for my estate for about 4 years now; the only downside appears to be that the boot floor doesn't latch reliably. Gravity is reliable, so I don't worry about it.


Spacesaver(non-standard size) spares are legal only as a temporary fix and are limited to 50mph. Everyone I've fitted has a big yellow sticker stating that. I'm not a fan of them, but they are a much better solution to a puncture than a can of 'repair foam' and a compressor. Although the compressors are a useful addition to your cars toolkit.

[annihilator]

a 16" alloy with a 225 tyre will fit a saloon spare well but the cover carpet wont fit over it.
John.