Space saver wheel help...

[JoeJoe]

My wife replaced her car last week - a Hyundai i10, 2014.

It had 14" wheels, and came with no spare tyre, so she purchased a space saver one from the dealer when she bought the car. As it has never been used, I took it out of the car before she part exchanged it in the hope of eBaying it for £50 or so, put towards a similar spare for her new car that also came with none.

Just had a closer look at it before listing, and when I measured the rim, it is in fact a 16"... Would that have worked when replacing a

14" wheel?

Also, her new car, also an i10, has 16" wheels, but the tyres are low profile ones, at least an inch narrower than the space saver.

Will she be able to use this one as a spare? Are the lug holes standard? Both old and new car has/d 4, as does the space saver.

[alan_m]

Often different versions of same basic car come with different size wheels. Look up the specification for the base model, the model with extras as standard and perhaps the sporty version to see the range of wheel sizes.

Space savers are only intended for a get you home/garage type journey at limited speeds.

You will/may also find that the spare tyre of a different size is not fitted with the tyre pressure sensors and you will/may get a dash warning the TPMS has detected a fault whilst running with the spare.

[JoeJoe]

Thanks, you are correct. The current base model comes with 14" wheels. Hers is the top of the range one and the wheels are 16".

Her old car was also the top of the range at the time, but it had 14" wheels. Was just wondering why they gave her a 16" space saver wheel for it?

Yep, it says 50 mph max speed on it - just enouge to get you to the tyre place which is what she is after. It also says to inflate it to 60 PSI on it - around twice the pressure of the other tyres in her car.

[John Miller]

(Snip) Space saver tyres will be a different size to the tyres on the car and probably a lower profile so the larger size wheel is probably there to bring the space saver diameter up to the same approximate size as the car tyres

[Brian]

It isn?t unknown for space saver wheels to be a different diameter overall to the ?proper? wheels- usually they are smaller.

BUT, besides (obviously) fitting the studs / holes, they need to clear the brake assembly etc. Plus, some electric / hybrid cars are sensitive to overall wheel ( including tyre) diameter.

Our Smart Car had different tyres front and rear ( normal on most Smarts). We carried one space saver.

Some motorhome owners who up plate and change to 16? rims either don?t change their spare or keep one of the old 15? wheels etc as a spare. ( Not sure if this is wise / safe as the reason you change is to increase load rating of tyres. I changed all five.)

[JoeJoe]

Thanks! Interesting and worth taking into account. Just the input I was looking for as I am completely clueless as you have probably gathered...

[JoeJoe]

Thanks for that. Will hold it against one of the wheels and check to see if can be used as a replacement if needed.

[Robin]

Space savers can have a smaller rolling radius than the regular tyres. The law allows for it; and owners' manuals* sometimes warn about ground clearance being reduced when they're fitted.

*I know it goes against the grain to RTFM but...

[Tim Lamb]

In message [e-mail], Robin [e-mail] writes

Snip

Limited slip differentials should be considered..

>

[John Rumm]

You can have two different wheel sizes but still come out at the same overall wheel diameter when you include the tyre. Measuring it is obviously the way to go, but you could also do it by calculation.

Type sizing is "odd" since it uses a pigs breakfast of different measurements and units.

So say the original tyre was a 175/65 R14, would mean the tread is 175mm wide. The height of the side wall is 65% of the width, so 113.75mm or ~4.5", and it's designed for a rim diameter of 14". So that would give you a total diameter of 18.5"

Say the space saver is 16", but takes a tyre that is 105/60 R16, that would give a tyre side wall height of 63mm or ~2.5", add that back to the 16" rim diameter and you are back to 18.5" again.

Yup, which is what you would expect if they are going to come out at the same overall diameter.

Offer it up and see.

[Andrew]

Might confuse tyre pressure warning too and possibly seriously affect the ABS and Brake Assist (on newer cars, another reason to keep to 50).

Apparently because spacesavers are lower profile and run at a higher pressure the ride quality is dire from what I've heard. Another reason to keep your speed down.

[Dave Plowman (News]

It's the rolling radius of the wheel and tyre that matters. Not the wheel size. Plenty cars changed wheel sizes during their production run without altering the overall gearing.

Not only the stud pattern but the size of the locating hole in the centre. And just about every maker has their own combination.

[Brian]

No problem.

Break down services like the AA / RAC carry ( or used to) a few ?standard? space saver wheels for cars that don?t carry them. I remember a AA or RAC Van turning up with one to a car on a campsite we were on. He had a few in the back. No idea how the system works - ie if they take you wheel and have it repaired etc or you borrow the space saver and return it somehow.

I?m not a fan of space savers but I certainly don?t trust the gunge many cars come with.

[John Rumm]

Doh! Although one should allow for the maths cockup there :-)

(obviously the tyre wall height increases the *diameter* by twice as much as it increases the radius - but the logic stands)

[JoeJoe]

Noticed that too... Thanks a lot!

[JoeJoe]

Thanks for that - a few others suggested the same.

Great :-(

[alan_m]

Possibly not in the UK but it is common for people to change to winter tyres with a different profile or wheel size.

[Dave Plowman (News]

Changing all the wheel rolling radius likely OK. But if buying new winter wheels and tyres I'd still check with the maker these are suitable.

A different rolling radius on driven wheels might well result in the differential overheating. The bearings and gears in that not designed to rotate for long periods

[Roger Mills]

Yes, the rolling radius is a function of the rim radius plus the tyre standing height - which, in turn, is a function of the tyre width and aspect ratio.

My previous car (A Volvo V70) had 225 x 45 x 17" tyres as standard. I also had a set of winter tyres and rims which were 215 x 55 x 16" (I think). At any rate, these higher profile tyres on 16" rims had virtually the same rolling radius as the standard low profile tyres on

17" rims.

Coming back to the original subject, spacesaver wheels have very narrow tyres compared to the regular tyres, with a much smaller standing height

- which is why the rim diameter needs to be higher in order to maintain the correct rolling radius. They also run at a much higher pressure - typically 80 psi c.f. 35 psi and are only intended for emergency use at speeds of no more than 50 mph.

[The Natural Philosopher]

No, the rolling radius is a function of the tyre *circumference* divided by 2 Pi

It has almost nothing to do with the 'standing height'.