Tyre tread depth, pressure

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Humberto

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  1. At what stage should tyres be replaced? To my knowledge the requirement in law is that tyres must have at least 1 mm of tread, but I suspect that tyres should be replaced before reaching this point.
  2. Is it advisable to slightly overinflate tyres? A knowledgeable person told me it's better to slightly overinflate tyres; ride comfort is not as great but longevity is improved. He advised me to inflate my tyres to 230 kPa rather than the manufacturer's recommended 220 kPa. Is this good advice?
  3. I estimate my tyres have about 3 mm of tread left. Do you think I should wait until the rainy highveld summer season before replacing them, and squeeze a last few thousand kilometers out of them? They've done 75,000 km so far.
 
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That's pretty decent mileage. What tyres are they?
Yes I think the legal limit is 1mm but your tyre also has a built in tread wear indicator, which I think will take precedence.

That small change in pressure shouldn't make a major difference imo

How old are your tyres? I would change them.
 
Dont overinflate your tyres... Sure, you might get vaguely better fuel consumption due to less of the trye being in contact with the road (less rolling resistance), but do you really think you (or your friend) knows better than a team of engineers who's job it is to figure out what pressure the tyres should be at for your specific vehicle? As for longevity, nope, you are in fact creating uneven wear on your tyres through overinflation. And you're making less contact with the road, so worse braking. And you're at a bigger risk of a blowout. Good times.
 
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The tyres are the Kumo Solus tyres that came with the car. They are three and a half years old.

To my knowledge and understanding:
  1. A slightly overinflated tyre (230kPa instead of 220kPa) will have slightly less grip.
  2. Tyre blowouts occur from underinflated tyres rather than overinflated tyres.

My tyres do seem to have worn evenly. It doesn't look like they've worn more at the center.

My knowledgeable friend told me car manufacturers recommend the slightly lower pressures to give a softer ride.

I don't know if all of this is correct.
 
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Underinflated tyres will give a softer ride but due to flexing of the sidewall (which causes heat) can have a premature failure and is not recommended on road cars.

Correctly inflated tires will give the best balance of comfort, grip and fuel efficiency.

Overinflated tyres will give a harder ride, be more fuel efficient but provide less grip (so requires more vigilant driving like longer following distance and such).

Tyres need to be inflated above average if carrying a heavyish load or towing.
 
I'm not 100% sure at what tread depth I change tyres. I usually play it by sight but I do change before I get to 1mm, that's for sure (at about 1.5mm - 2mm if I have to guess).
What I am sure of is that if you get 75,000km on a set of tyres, I wouldn't do anything different. Get the exact same tyres, same pressure as always, same rotation schedule etc. You are definitely doing something right because that is very good mileage.
 
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My rear tyres have not been changed in the last two and a half years and they have done just over 100k - also think it's time to change them when money permits.

With regards to tyre pressure, I always follow the manufactures advice, and no higher than recommend. Under load, I push them up more, obviously.
 
Tander said:
My rear tyres have not been changed in the last two and a half years and they have done just over 100k
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I've had bad luck with tyres. Twice I've had to change tyres after just 15,000km. Bridgestones both times. Don't recall the exact name, but these weren't performance tyres or soft compounds. Didn't abuse them or over/under inflated it either. Switched to Continentals and after 15,000km they still looked like new.
 
Bridgestones are meant to be very good. 15,000km for a set of tyres is stupidly low.
 
/me wonders how you managed to pass your driving tests without knowing these basics...?
 
Tander said:
Bridgestones are meant to be very good. 15,000km for a set of tyres is stupidly low.
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Agree, that's why I bought it twice. The only explanation is that there must have been something wrong with the specific tyres. The chances of this happening twice are very small, I know, but I can't think of another explanation.
 
The grip on a tyre is not related to the pressure at all. Inflating a tyre slightly higher than recommended will have three basic effects:-

It will make the ride harsher (also meaning that the car will handle slightly better)
It will shift the wear pattern on the tyre more towards the centre of the tread (which is only useful if your tyres are wearing unevenly)
It will cause the tyre to flex less per rotation meaning that the tyre will run cooler

A reference can be found here
 
If you look at the big gaps between your sections of tread, you will see little bridges of rubber joining the two sections. If these bridges are touching the road, then you have generally reached the Manufacturer's recommended replacement interval.

I have just reached that point on my fronts, but it won't rain here for months now, so I will keep them a little longer. They still meet the legal requirement of 1mm tread over 100% of the tyre.

If that makes sense :confused:
 
bromster said:
If you look at the big gaps between your sections of tread, you will see little bridges of rubber joining the two sections. If these bridges are touching the road, then you have generally reached the Manufacturer's recommended replacement interval.

I have just reached that point on my fronts, but it won't rain here for months now, so I will keep them a little longer. They still meet the legal requirement of 1mm tread over 100% of the tyre.

If that makes sense :confused:
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see my post above
saw it on the arrive alive show, not sure how true it is though
 
The Kumo Solus tyres that go on my car cost R 990 per tyre. Ouch.

I don't know if I should replace the current lot with Kumo Solus' again, or if I should move to an economy tyre of another manufacturer such as Michelen.
 
Colin62 said:
The grip on a tyre is not related to the pressure at all. Inflating a tyre slightly higher than recommended will have three basic effects:-

It will make the ride harsher (also meaning that the car will handle slightly better)
It will shift the wear pattern on the tyre more towards the centre of the tread (which is only useful if your tyres are wearing unevenly)
It will cause the tyre to flex less per rotation meaning that the tyre will run cooler

A reference can be found here
Click to expand...

+1


I've always run my front tyres 10kPa over specified values (FWD car) and my observations are:

- Never had uneven tyre wear
- Better tactile feedback
- Less tyre flex
- Slightly harsher ride but not in a bad way

For me it just provides a better ride.
 
Humberto said:
The Kumo Solus tyres that go on my car cost R 990 per tyre. Ouch.
Click to expand...

That's not a bad price for tyres, trust me you could be paying a LOT more. If you are happy with your previous tyres then get the same ones.
 
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