Spacesaver wheel size - critical??

Space savers are rarely, if ever, the same diameter as a standard wheel so that shouldn’t be a problem with regards to legality.

A more immediate concern is the nut spacing (PDC) which has to be right otherwise it simply won’t fit!

Tim

Tim+ snipped-for-privacy@yahoo.co.youkay> wrote in news: snipped-for-privacy@news.individ ual.net:

Perhaps not the same wheel size but I would say that having the same rolling radius is very important. At the very least any rotation counting tyre inflation monitors would go nuts.

To o/p, take data from both running and spare tyres and calculate the spec'd diameter eg:

I'd be wary of using anything that wasn't within very few mm of same.

You’d think so but they are often smaller in overall diameter.

Tim

And limited in speed and distance, possible because of that?

Isn't 20 years old a bit risky for a tyre? It wouldn't be allowed on most vehicles other than cars?

nib

Good point! I mean, if it’s been in the dark the whole time it would probably be fine but it’s well over the “10 year limit” for tires.

A bit of googling suggests that space savers have to be within 3% of the original tyres diameter. Certainly the one on my jag looked smaller but maybe that was an illusion.

Tim

A space saving wheel is not intended as a permanent replacement and they usually have a limitation of max 50mph and 50 miles of travel. If this results in the car flagging up a problem with the wheel then its a good reminder that you are running with a temporary wheel.

There is a good chance that when the Tyre Pressure Monitoring System is a sensor internal to the tyre the car will detect the punctured flat tyre in the boot rather than the space saver (which may not have been fitted with a sensor)

Possibly yes, it may have just been thinner. Both space savers that I had had, supplied with the car, have been inflated to approx 60 psi whereas the normal road tyres half this value.

I am not sure whether a 20 year old tyre in the boot would be checked in an MOT, but someone I know got an MOT fail because he had a couple of tyres in use on his car that were over 10 years old.

Jim

Well yes, 80psi isn't unknown for spacesavers. The tyre is much narrower than the original, and the contact patch much smaller - so it needs a much higher pressure to support the weight of the car.

Do _any_ spacesaver tyres have tyre pressure sensors on them?

The difference is radius is probably one of the reasons why they have low max speed and distance limits imposed.

Unless things have changed quite recently, the age of tyres is not an item checked on a (non-commercial) car's MOT. If they were showing signs of age-related deterioration, then yes they ought to cause a fail.

I wonder how many cars there are out there which are running on a spacesaver tyre - at least until they fail their next MOT?

They are considerably narrower so need higher pressures. The don't have TPMS fitted, and the tread depth isn't much over the legal limit.

On one car I specified a full size spare, same price, but it was a different profile on a smaller wheel, so was still limited to 55mph.

A Halfords tyre fitter told me that tyres over 10 years old are illegal on the front and inadvisable on the back.

I bought a 2003 C5 two years ago and one of the rear tyres was 18 years old.

Only on HGVs and buses/coaches.

They may be inadvisable, but tyre age alone is not an issue on vehicles with fewer than 8 passengers, e.g. MOT guidance

Or for the full legal gobbledygook

I don't notice that many, and the rims typically have alternating yellow/black markings to *make* them noticeable ...

Sam Plusnet snipped-for-privacy@home.com wrote in news:6lHxQ.7700$ snipped-for-privacy@fx17.ams:

That's why I said the tyre rotation counting method of flat detection. In this method a flattening tyre is detected by it rotating faster than the other wheels (via ABS sensors). Slight differences in rotational speed (different tyre wear levels) accommodated by relative speed calibration via the nav/media/user settings interface.

Incidentally when I needed to use my spare the flat detection system didn't see enough of a difference to trigger a flat notification.

I'd say that the speed/distance limits for space savers come from their higher per unit area loading due to their smaller contact patch.

As another has posted the requirement appears to be for space savers to be within 3% of the original.

Typically, I need to use my space-saver after the ABS/TPMS system has detected a problem, in which case I deliberately don't reset the warning light until after I've taken the space-saver back off.