A few months back, I borrowed one of my friend’s cars, and the rear tire burst on the way. I checked the trunk for the spare and found that the spare tire was smaller than the other four tires. So I wondered if it’s safe to drive with a smaller spare tire.
I did some research right away and have prepared this resource for everyone who might face the same situation. So, can you drive with a smaller spare tire?
You can drive with a smaller spare tire but not more than 50 miles. Smaller spare tires are not meant to travel for a distance more than 50 miles and speed exceeding 50 mph as they have a much smaller size and little to no tread compared to normal tires for better traction handling and ABS control.
In this article, I have covered what happens when you drive on a smaller spare tire and why it can be bad for you to travel a longer distance on smaller spare tires.
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Can Your Spare Tire Be Smaller?
As discussed above, your spare tire can be smaller, and in fact, most car manufacturers now install smaller spare tires rather than full-sized spare tires. These tires are also known as Donuts or Safe-saver.
They are meant to get you to safety in case of an emergency. But these tires should never be thought of as a permanent solution. You should not drive on a donut for more than 50 miles and 50 mph.
You are supposed to replace your tires as soon as you can. However, if you tend to use it longer than usual, it might damage your spare due to excess wear and tear and might affect the car’s axle and ABS. Let’s see how.
What Happens When You Drive On A Smaller Spare Tire?
When you drive with a smaller spare tire, the spare tire rotates much faster than the other three tires due to its smaller circumference. The standard tires cover a greater distance in one rotation than the spare one due to smaller circumference.
So, to compensate, the spare tire needs to cover the same distance as other tires cover in one rotation, but it has to do so in the same period making the spare rotate much faster and revolving more than one complete rotation.
So, the spare’s RPM(Rotation per minute) is more than that of the other three tires. Thus, this increased distance and speed creates excess heat, increasing wear and tear. Imagine what happens if you keep doing so for a more extensive span, it will damage the tires and may cause a burst leaving you with no other options.
It’s just not limited to wear and tear, and there is more to it which we will cover in the next section.
Is It Bad To Drive With A Smaller Tire?
Along with the wear and tear due to smaller circumference, the difference in size also affects the vehicle’s alignment, traction handling, and ABS(Anti-Lock Braking System).
Smaller Spare Tire’s Effect on Vehicle’s Alignment:
As these spare tires are narrower, they have smaller contact patches, reducing their traction, which may lead to unpredictable handling. As a result, the drive may sometimes find it challenging to keep the vehicle straight. This is how it affects the vehicle’s alignment.
Smaller Spare Tire’s Effect On ABS:
It also affects ABS control. ABS is a safety mechanism that prevents your wheels from locking up in case of emergency or panic braking.
Thus, when ABS is not working correctly, there is a possibility to lose traction in case of panic braking, which may result in skidding of the vehicle, which is quite dangerous, that is why it is advised to not drive at more than 50 mph with the smaller spare tire.
Smaller Spare Tire’s Effect On The Differential:
The differential’s job is to transmit power from Transmission(Engine) to wheels. It also allows the wheel to rotate at a different speed which is very important while turning as inner wheels cover a smaller distance than outer wheels during a turn. So the outer tire has to rotate at a higher speed.
It’s pretty similar to what happens while driving on a spare wheel. The smaller spare must cover the same distance as other tires at a greater speed. Thus, the differential has to transfer to a lot more power than other tires. It’s like the vehicle is constantly in turn.
So, the differential has to work much harder than in a typical scenario. And doing so for a longer time would damage the differential.
You must be wondering if there are these many issues with smaller size spare tires, then why not go with the full-sized tires, right? Well, that’s what we have covered in the next section.
Why Is A Spare Tire Smaller Than Normal Tires?
For years, spare tires used to be the same size as the other four tires. However, in many older cars, you can find full-size spare tires.
However, this has changed. Nowadays, the spare tires are much smaller and often called “Donuts” or “Space-Saver” due to their compact size.
There are many reasons manufacturers now prefer to build cars with a donut instead of full-sized tires. Let’s have a look at some of them:
- They are not used as frequently as other tires and hence are made to last till you reach a safe distance.
- They are designed to take less space in your trunk to provide you with more storage capacity
- They are made lightweight. The weight savings leads to better fuel economy which is a huge focus based on both consumer demand and regulatory requirements.
- They are cheaper for both the manufacturers and the consumers.
- They are easier to lift and can be installed more easily than full-sized tires.
These tires are intended for short-term use and in case of an emergency rather than using them regularly. You should not use it for a longer distance, and you should replace your tires as soon as you reach your home or tire change shop.
At this point, you must be clear with all the questions you had about if you can drive with a smaller tire or not.
As a general rule, you should not drive more than 50 miles and not faster than 50 mph with the smaller spare tire. Going for more than that, the grease lubricating the differential will break down, causing unnecessary wear between the gears and the clutch plates.
The reason for the wear in the differential has been already discussed above. However, it is essential to understand that you should not use your donut for an extended period. Otherwise, it may cause problems in other parts of your car.
Please feel free to roam around the blog if you have other questions about your tires. You can find a lot of helpful resources related to your tire queries.