I'm Guessing Tyres Are Not Meant to do This

[Diesel_vert]

I was thinking that, between the two years when the vehicle was built and when you bought it, there may have been one or several external factors which caused this - assuming the tyres themselves are not faulty.

Hopefully, it just turns out to be superficial damage.

[Wolfgang]

Had a chat to the guys at the local Bob Jane today.

They seem to think the pressures have been a little low while the car has been driven hard allowing the sidewall to flex cuasing damage that has appeared as the tyres have started dyring out as they have gotten older.

Good thing is they are not dangerous... yet. As long as the cracks don't get any bigger they will be fine.

They recommended runnng a slightly higher pressure to reduce some stress on the sidewall under acceleration.

[brad]

how low & what pressures are they recommending?

[Wolfgang]

how low & what pressures are they recommending?

Sorry Brad, missed your post.

They didn't really say how low, but they have recommended to up the pressure to 40 psi. Sounds too high to me, the interior rattles enough already. Haha!

They said it wouldn't be worthwhile for the local Michelin Rep to have a look as the tyre would most likely need to be removed for a proper inspection which would probably make the cracks bigger.

[brad]

40psi won't hurt but it will be somewhat harsh & (as you said) will bring out the rattles & make the springs & dampers work harder. 36psi would be more pleasant.

I would ring Michelin Technical direct & send them the photos & have a friendly chat expressing your concerns. When i was at Goodyear (almost 30 years back), if a tyre came in like that it was in our interest for it not to let it fail (huge problems with SuperSteels at the time) and our tech guys wanted to examine the tyres. Depending on the customer (we had a lot of repeat purchasers / regulars in our workshop), we would either give them prorata discount (either off RRP or street price) on new tyres or even staff prices if they were struggling financially. We could do this as we were owned by Goodyear - the dealers didn't have the authority.

[Wolfgang]

Thanks for the advice Brad. Will give them a ring in the next few days.

I'm running the factory recommended 2.4 bar (35-6 psi), will up it to 38psi and see how the car rides.

[Diesel_vert]

Thanks for the advice Brad. Will give them a ring in the next few days.

I'm running the factory recommended 2.4 bar (35-6 psi), will up it to 38psi and see how the car rides.

The OEM spec pressures are almost always cold figures, i.e. before the tyres have warmed up.

Gases expand when heated, so you need to add 0.2 - 0.3 bar (3 - 4 psi) to the pressures listed in the fuel flap if you need to drive the car anywhere in order to add air.

I suspect the previous owner didn't really check the pressures often, or used the cold pressure figures whenever they added air at a service station - which means by the time the tyre has cooled down, it would be underinflated.

[brad]

It takes at least 15 minutes of "normal" suburban driving to get enough temperature into a tyre to make a noticeable difference in pressure unless the tyre is grossly (like <20psi) under-inflated.

Previous owner possibly never added air or checked the pressure. I have plenty of friends of both genders that never do anything to their car beyond adding fuel. They rely soley on the Service Centre to look after their cars. One of the dingbats is trying to get warranty on the paintwork of their 8yo Mazda because the clearcoat is peeling. Don't mind the fact that it has never been garaged, washed or had any body maintenance in the whole time she's owned it.

[Diesel_vert]

It takes at least 15 minutes of "normal" suburban driving to get enough temperature into a tyre to make a noticeable difference in pressure unless the tyre is grossly (like <20psi) under-inflated.

The relationship between air pressure and temperature, brought to you by Tire Rack:

Tire Tech Information - Air Pressure, Temperature Fluctuations

Tire Tech Information - Air Pressure: When and How to Set


The gist of it being...

... even a short drive to inflate your tires will result in tires that will probably be under-inflated by a few psi the following morning.

Some conversions (change in air pressure per difference in temperature)

Imperial: 1 psi per 10°F

Metric: 0.1 bar per 10°C

Hybrid: 1.5 psi per 10°C

Previous owner possibly never added air or checked the pressure. I have plenty of friends of both genders that never do anything to their car beyond adding fuel. They rely soley on the Service Centre to look after their cars.

One of the pitfalls of long service intervals.

A proactive attitude towards maintenance is needed in order to benefit from such a regime, otherwise it can end up costing the owner more money than would otherwise be saved.

[brad]

The change in pressure is fairly easy to check - simply record the pressure before leaving home & then when you get to the service station. I've done it several times & under the conditions I drive there is no significant change in the 3km between my house & the servo.

I think you'll find the heat cycling machine Tirerack uses puts a bit more stress on the tyre than a 5-10 minute drive up the road does. Also you'll note they didn't test on a more typical pressure (these days) of 35psi. I don't believe it would have experienced the same increase in temp/pressure.

I'm fairly anal about this stuff but based on experience, I'll even check my tyres after doing a 45minute trip from Campbelltown to Hurstville. I figure it's better to do the monthly check rather than let it go. I know how much I inflated it to the last time & I'm using the same guage, so i adjust how much air I put in based on the highest reading i get from all 4 tyres (eg: if I get 38psi from the first tyre I do I inflate them all to 38 & I'm happy that all the tyres are inflated within a pound or 2 of each other & above the vehicle manufacturers recomendation (Skoda says 31psi FFS). That's probably better than 70% of the cars on the road