Puncture on one side, replace the other side too?

[Mysterae]

I've always been told that if you have to replace a tyre on one side due to a puncture, you should also replace the other tyre of the same axle at the same time.

This would obviously be silly if both tyres were brand new, but at what remaining depth of the good one do you make the call to replace it in the above situation? 6mm, 5mm, etc?

[SnailTrail]

How much tread does the remaining one have and how old is it?

Edit: or is this just a general query and I've missed the point?

[Mysterae]

SnailTrail said:

How much tread does the remaining one have and how old is it?

Edit: or is this just a general query and I've missed the point?

Yep, that's the query!

[sherman]

Less than 3mm and its orobably worthwhile.

[CraigyMc]

Mysterae said:

SnailTrail said:

How much tread does the remaining one have and how old is it?

Edit: or is this just a general query and I've missed the point?

Yep, that's the query!

And the answer to the tread and age question is...?

[Mysterae]

Okay, I'll be a bit more specific. I had a puncture on one of my rears, 20" run flats with just less than 4mm left on both rears, tyres no more than 3 years old. I decided to replace them as a pair. Was this wise considering it's a rear wheel drive car (F13 640d)?

[sherman]

In your case. I would of done the same thing. Especially as its the driven wheels.

[amstrange1]

Replace 'em both, but keep the non-punctured one - either as a spare or to punt on eBay.

[Bungleaio]

I would change if they are more than 50% worn, I don't really like to go below 3mm anyway.

[swisstoni]

I'd probably have done the same if feeling flush as it saves messing about in the near future. But I don't think it was necessary.

[Mysterae]

Much of what I thought, thanks guys.

I did wonder though at what depth would I have thought differently. At 5mm I would have replaced it but kept the tyre as an emergency spare. I looked on ebay and there are lots of used tyres for not much money, but who wants to post one and it's usually too far to pick it up, if you even could.

[Mysterae]

Bungleaio said:

I would change if they are more than 50% worn, I don't really like to go below 3mm anyway.

Here's some man maths - 0 to 8mm isn't technically 100% as you'd replace them at 2mm, minimum. So 8-2=6 = the new 100%. So if the tyre was worn by 4mm, it's actually 67% worn .

I was more concerned that it's rear wheel drive, may upset the handling of the car, and that I'd have the same situation when the other one needed replacing.

[007 VXR]

I would have changed both.

[Claudia Skies]

Mysterae said:

I've always been told that if you have to replace a tyre on one side due to a puncture, you should also replace the other tyre of the same axle at the same time.

Depends on the car.

Some cars (especially 4WD) are hyper-sensitive to any difference in rolling radius between wheels and a worn tyre is inevitably smaller than a brand new one. The issue is that the differentials in the driveline can be constantly "working" if they are asked to drive different sized wheels. In a limited slip differential this can mean constant wear on the slip mechanism and/or excessive heat.

[Claudia Skies]

Maths:

• Assume a wheel/tyre has a "new" diameter of 650 mm
• Assume the new tyre has 8mm of tread and a worn tyre has 2mm
• The "worn" wheel/tyre therefore has a diameter of 638mm

• Rolling circumference of the new tyre is pi x diameter = 2,041
• Rolling circumference of the worn tyre is pi x diameter = 2,003
• The difference is 38mm which is about 2%

This means that for every 100 revolutions of the new tyre the worn tyre has to rotate 102 times. So the differential mechanism is constantly rotating at that rate when the car is driving in a straight line. With a wheel circumference of about 2 metres the differential has to make up one rotation for every 100 metres you drive.

A mile is about 1,600 metres so at 60 mph the diff would be constantly working at 16 rpm.