Spare wheels

[taff33]

Can any one tell me why spare wheels on cars are smaller than the other wheels,I have a Chevrolet Sonic ,16 inch wheels but the spare is 15 inch the Cruze has 17 inch wheels the spare is 16 inch I was also told Toyota are the same.

[giddyup]

Should be all the same.

[cumgranosalum]

Spare wheels are often smaller as they take up less space. THey are intended these days as a "get-u-home" only device.

The other thing is that they sometimes have the standard or basic wheel/tyre combo and on models fitted with accessories such as alloy rims the original "cheap" spare is kept to keep the cost down

[giddyup]

Spare wheels are often smaller as they take up less space. THey are intended these days as a "get-u-home" only device.

The other thing is that they sometimes have the standard or basic wheel/tyre combo and on models fitted with accessories such as alloy rims the original "cheap" spare is kept to keep the cost down

Smaller as in thinner, but the diameter should still be the same.

[taff33]

The wheels on the sonic are 205/55/r16,the spare is 195/65/r15.

[richard_smith237]

A lot of Cars have a 'space saver' spare... which are thinner (but the same circumference) which are designed to get you home or to the nearest garage at a limited speed (i.e. 80 kmh)

Some cars (mine) have 'run-flats' which when a puncture is encountered the side wall is strong enough to take the weight of the car which can still be driven at limited speed for a limited distance.

Other cars (yours) have a 'cheaper' spare.... these are unlikely to be the same as the 4 main wheels (alloys) on your car. Alloys are more expensive, this is simply a cost saving measure.

[taff33]

A lot of Cars have a 'space saver' spare... which are thinner (but the same circumference) which are designed to get you home or to the nearest garage at a limited speed (i.e. 80 kmh)

Some cars (mine) have 'run-flats' which when a puncture is encountered the side wall is strong enough to take the weight of the car which can still be driven at limited speed for a limited distance.

Other cars (yours) have a 'cheaper' spare.... these are unlikely to be the same as the 4 main wheels (alloys) on your car. Alloys are more expensive, this is simply a cost saving measure.

i under stand what you say about the spare not being an alloy but why a smaller diameter though?

[Sviss Geez]

The smaller (but same circumference) wheels/tyres save weight, save space (they're narrower) and are cheaper, saving the manufacturer a lot of money. They're usually described as temporary spares.

[kartman]

Because the similar overall outer diameter spare costs less, times that in Baht/Pound /Euro/Dollar by the number of vehicles built in that model and the profit margin for manufacturers lots better.

[richard_smith237]

A lot of Cars have a 'space saver' spare... which are thinner (but the same circumference) which are designed to get you home or to the nearest garage at a limited speed (i.e. 80 kmh)

Some cars (mine) have 'run-flats' which when a puncture is encountered the side wall is strong enough to take the weight of the car which can still be driven at limited speed for a limited distance.

Other cars (yours) have a 'cheaper' spare.... these are unlikely to be the same as the 4 main wheels (alloys) on your car. Alloys are more expensive, this is simply a cost saving measure.

i under stand what you say about the spare not being an alloy but why a smaller diameter though?

Is the Circumference (and Diameter) of the outside of the tyre the same?

i.e. a Smaller Diameter tyre - but a thicker sidewall?

You've mentioned that the sizes are:

Wheels: 205 / 55 / r16 [Diameter: 631.9mm / Circumference 1985.2mm]

Spare: 195 / 55 / r16 [Diameter: 634.5mm / Circumference 1993.3mm]

Your spare would give you an equivalent speedo error of -0.41% (on that wheel)

i.e. if you had the Spare wheel size on all wheels 60mph your speedo would think you are driving at 59.75 mph

Or in other words, at 60 mph there is a difference of 0.25mph - a negligible difference.

This is your manufacture cutting down costs using a cheaper spare wheel / tyre combination.

[taff33]

No 195/65/r15 that is the spare.

[richard_smith237]

No 195/65/r15 that is the spare.

My Apologies for the typo: Figures are for 195 / 65 / r15 (Spare)

Wheels: 205 / 55 / r16 [Diameter: 631.9mm / Circumference 1985.2mm]

Spare: 195 / 65 / r16 [Diameter: 634.5mm / Circumference 1993.3mm]

[cumgranosalum]

A lot of Cars have a 'space saver' spare... which are thinner (but the same circumference) which are designed to get you home or to the nearest garage at a limited speed (i.e. 80 kmh)

Some cars (mine) have 'run-flats' which when a puncture is encountered the side wall is strong enough to take the weight of the car which can still be driven at limited speed for a limited distance.

Other cars (yours) have a 'cheaper' spare.... these are unlikely to be the same as the 4 main wheels (alloys) on your car. Alloys are more expensive, this is simply a cost saving measure.

i under stand what you say about the spare not being an alloy but why a smaller diameter though?

I think that has been said now.... The difference is negligible on a get-u-home basis. Some cars though have considerably smaller spares to save space... It looks like yours just has the "original" standard model.

On my pickup the alloy wheel won't even fit onto the spare holder... It has to be a steel wheel..... As I have o/s tyres fitted there is a much bigger difference... But I still carry 2 small spares..... Better than none!

[Don Mega]

The wheels on the sonic are 205/55/r16,the spare is 195/65/r15.

The difference in rolling diameter is what matters and in this case the difference is nothing to be concerned with.

Note that the smaller (if it is infact a space saver) tyre is most likely speed limited.

[IMHO]

1. Cost cutting

2. Design considerations (space - many cars don't have a spare wheel at all for this reason)

3. Theft deterrent (e.g. pickups and PPV's where it's exposed)

[arthurwait]

The difference is only 2.6mmm in diameter basically the same.

1.3mm difference in radius and as that is a thinner tyre it will lose more radius due to load (loaded rolling radius) than the original. They are the same. It's just to get you home.

[paulchiangmai]

The size of the wheel has nothing to do with it, what counts is the rolling circumference of the assembled wheel and tyre. You will find in your case the rolling circumference of the standard wheels and the spare are the same.

[taff33]

Thanks to all for the explanations.