What size tyres do I need?

[jpquinn91]

I have a Nissan Micra K11-U 1L. I recently had to put my spare on and found out that I have various size tyres on.

2 fronts were 155/70 R13 75T
2 backs were 165/70 R13 79T

One of the fronts is flat so I have the spare on which is 155/65 R14 75T

The manual says they should be 165/60 R14 75H but I took them to a tyre place today and he said the 155/70 R13 75T are the right size. Very confused. Which is correct and does it matter?

I understand that as long as the front two are the same and the back two are the same, there isn't a safety issue so if these are fine I'd like to just fix/replace the flat and have them as they were before.

 

[iamwiz82]

The first number is the width in mm, the second number is the percentage the side wall is of the width, so 155/70 would be 155mm wide and 108mm side wall. The R## is the size of the inner diameter, where the wheel will mount. If your old tire was R13 then you new one will have to be 13 as well if you want mount it to that wheel.

comparing the 155/70R13 and 165/70R13 tires, the 165 is 10mm wider and 12mm taller (because you have two sidewalls, plus the diameter of the wheel itself).

http://www.miata.net/garage/tirecalc.html

 

[jpquinn91]

Thanks, but what I wanted to know is does it matter or do I need to get new tyres?

Also, I changed the wheel, not the tyre. God knows why it was a different size.

 

[Ketchup]

Well, you have to have a tire size that matches your wheel, so if that is the question, you'll need to replace the 13 on your wheel with a 13.

 

[jpquinn91]

Yes, I'm going to least change the spare so that they are all 13s with the two at the front the same and the two at the back the same. What I want to know is whether this is OK, with the front and back slightly different sizes, or should I have 4 the same?

 

[Ketchup]

Yes, I'm going to least change the spare so that they are all 13s with the two at the front the same and the two at the back the same. What I want to know is whether this is OK, with the front and back slightly different sizes, or should I have 4 the same?

Different in what way? Going with a wider tire is usually ok, but the middle number would need to be lower so as not to make the whole car lean front to back or vice versa. Take it to a tire shop and they will tell you if you have options there.

To answer your question, you vehicle will perform best if all tires are the same size.

 

[iamwiz82]

Yes, I'm going to least change the spare so that they are all 13s with the two at the front the same and the two at the back the same. What I want to know is whether this is OK, with the front and back slightly different sizes, or should I have 4 the same?

If doesn't matter so much on a 2WD vehicle. You should always keep each axle (L and R of front or back) matching however.

 

[DominionSeraph]

Yes, I'm going to least change the spare so that they are all 13s with the two at the front the same and the two at the back the same.

Why?

 

[phucheneh]

If the car has ABS, different front/rear diameters can drive it slightly mad.

If not, and the tires fit without rubbing...meh, you'll be okay.

 

[Throckmorton]

First of all, don't worry about the spare. It will come off when you get your new tire, and stay in your trunk for when you need it again. It doesn't have to match.

Second, it's most important that the front tires match because that reduces wear on the differential. So don't mix old and new tires on the front axle because the worn down one will have slightly less radius. Mixing brands is a bad idea too because they're not always the same size. Basically, make sure the front 2 tires are as close in diameter as possible.

The rear tires should match each other too but it's not as crucial. Front and rear should be the same size ideally because different sizes could confuse ABS and traction control... not sure though.