Why are spare wheels smaller than normal wheels?

Question

I want to purchase a VW Ameo Highline. It comes with stock tyres (185/60 R15), and alloy rims. The spare wheel, however, is a standard steel rim (non-alloy) with 175/70 R14 tyres. The dealer explained this to me as an international norm, that a spare wheel is to be sparingly used.

It made sense to me but I had never heard this before. Do all cars that come factory fitted with alloys follow this rule?

Answer 1

Do all cars that come factory fitted with alloys follow this rule?

No, there are three basic options that I see all the time.

1. An Emergency wheel - Will get you to the next tire shop or gas station. Has a speed limit of 55/mph and is smaller than normal. Also has a limited range. Usually 50 miles or so. There will be a label on the tire. Used to cut costs, and to reduce required storage space. Popular on small cars.

2. A full size spare - A normal sized wheel without the fancy rim. Just like the normal wheel but looks different. Common on work trucks, vans, SUVs where the size is needed for the weight or load, but there is plenty of space to spare. Optionally, these "full size spares" can some times be bought with matching rims.

3. A set of 5 tires and wheels. This is mostly seen from the factory on newer Jeeps, but is very common for other 4x4 trucks and vehicles to have a matching set of 5 wheels and tires that can be rotated in a 5 tire pattern. This is common for off road vehicles when tires can be easily popped, but traction is extremely important. However, many newer Jeeps just have it because it looks nice.

4. Fix-a-flat or the like. No spare, but a free can of fix a flat. This is more and more common. Especially on cars with self sealing tires, or electronic sensors that warn you for problems before a blow out. Really good in town, not so great outside of town where you have to travel a long distance.

Answer 2

Because you rarely use it, reducing its size and weight is an effective method for cutting down costs. It also saves space and makes packaging easier for the engineers. The cost aspect is also the reason for the spare being being a steel one instead of the more expensive alloy.

Answer 3

This is very common in smaller vehicles, and anywhere economy is the driving factor. These compact temporary spares have nowhere near the performance characteristics of a full size tire. Indeed, you will likely see some type of warning on it to limit speed to below 50 mph. In America, and in places where service centers may be few and far between, full size spares are common. Most work trucks, jeeps, large passenger vans, and luxury automobiles come with full size spares. There are two different ways to run a full size spare. You can get a steel one, or get and alloy one that matches the rims on your other wheels. The latter option allows you to work your spare into your tire rotation pattern, which is the way I prefer to operate my vehicles. That way I know that my spare is ready to roll if I need it. When I purchased my Toyota Sequoia, it came with a full size alloy spare. As with any emergency equipment, you will need to periodically check your spare to make sure it is in operational condition. I have come across a few stranded motorists, in my time, with a flat spare tire.

Answer 4

An Automotive developer here... and this is a PITA.

Not sure how/why companies are following this. The smaller tyre results in different tyre RPM while running and this messes up the internal algorithms of ECUs. Companies don't realize that people tend to drive with spare and forget about it; or grab two spares and use them; or put in what ever combination. and this results in lot of visits to Garage due to calibration problems.

suggestion: if you have a smaller spare, better get a same sized spare or drive to the Garage first thing. don't be surprised if you get a service light in your dashboard if you drive a lot with the spare on.

Answer 5

There are three reasons for that.

1. Money: Smaller spare is cheaper. also the tyre is usually low-spec.
2. Boot size: Smaller spare means more room for the boot. This results in more money in your pocket due to advantage over the rest of the market.
3. Fancy comparison charts: Lower weight means lower fuel consumption. If you look close how it is measured - what cheats are actually acceptable to get as low number as possible - you will understand. This results in more money in your pocket.

Ok, there is only one reason, actually.

I don't think there is some ISO, DIN, JS or whatever standard of using spare wheels. There are different approaches to solve the puncture and there are different people welcoming them.

1. Full spec spare wheel(s). Exactly the same rim and tyre as the wheels used. Most expensive and usually space wasting. Option for off-roaders, rally racers and drivers who want to be affected by puncture as least as possible.
2. Full size emergency wheel. Same tyre diameter as the wheels used, (smaller and/or slightly narrower) steel rim, lower spec. tyre. Cheaper version of #1.
3. Emergency wheel. Narrow steel rim and tyre with simillar diameter as regular wheels. Really cheap and space saving. Option for people looking for boot size.
4. Flat tyre repair kit. The second most space-saving solution. Small punctures are solved as it was #1. More serious damages - destroyed tyre, damaged rim, etc. cannot be solved. Option for people looking for biggest boot and wanting lowest comfort affection or people with LPG rebuild.
5. Run-flats. Tyres with thicker walls. Option for people looking for ultimate boot or no need to care regardless the driving expirience and comfort.
6. Tyre pressure control. Unit that inflates/deflates the tyres according to actual needs. Used in offroad racing vehicles, military trucks and vehicles or heavy duty vehicles.
7. Tweel. There is no compressed air, so hole in the tyre is not fault. It can be a feature.
8. Something round-shaped. Just for fun.