Over Inflated Tyres And Hot Weather

[RunningInPleasePass]

Just a reminder for those who run with there tyres over inflated for economy.

During the recent hot spell the tyre pressure will increase, and if your tyre pressure is already on the high side it may become too high.

Perhaps it's a good idea to keep a close eye on your tyre pressure, and think about lowering it back down to manufactures recommendations, at least until the weather returns to normal British summer temperatures.

[Joseph D]

Just a reminder for those who run with their tyres over inflated for economy.

During the recent hot spell the tyre pressure will increase, and if your tyre pressure is already on the high side it may become too high.

Perhaps it's a good idea to keep a close eye on your tyre pressure, and think about lowering it back down to manufactures recommendations, at least until the weather returns to normal British summer temperatures.

Or at least check them and lower them to what you believe they should be.

[Chris Dance]

Checked tyre pressures this morning. They are all 1 PSI above recommended which is what I usually have them. The hot weather is giving a good MPG even on just local runs.

[timberwolf]

1 PSI for every 5 degree C. Is that really a dangerous increase in tyre pressure? Worst case Winter to Summer would be 6 PSI and it is likely to be less than that as our Winter was pretty mild.

[PeteB]

I have had an after-market Tyre Pressure Monitoring System for just over a year and it's been a real eye opener.

This one: http://www.tyrepal.co.uk/products/tb99-4-or-5-wheel-tpms

As well as giving me pressures, at a press of a button it displays temperatures as well. Now as the sensors are dust caps, I'm not sure how reliable they are when parked, but whilst moving I believe the temperature of air in the tyre is transmitted through the metal core of the valve.

When driving a short time after being parked in the shade (so the car's displayed temperature is likely to be more accurate) the monitors all closely match the car's temperature. In time, the spare gets hotter, I suspect from the exhaust system warming up the lower boot area.

What really surprised me was the side in strong sunlight can reach 5-10 C above the side in the shade, and the hotter tyres and display a pressure of 3-5 psi above those on the shaded side, which themselves may have risen by 1-2 PSI.

When I top up my pressures I always put 1 extra psi in, so the highest pressure they reach isn't a major concern to me.

FWIIW I've been very impressed with this system which needs no modification to the car. You can set upper and lower limits for temperature and pressure by axle, and it will flash a warning light and bleep if those limits are passed, or if a tyre is losing pressure.

If I had a car like the new Aygo which has the now mandatory TMPS, it is just a warning light that tells you one of your tyres is going down but not which one. I would keep this system too for the extra information if provides. The pressures always seem to concur with my digital gauge and the gauge at my dealer.

I've only had to plug it into the lighter socket to recharge about 5 times in the year I've had the system. It powers down after about 10 minutes of no movement, and shutting a car door normally restarts it. A backlight comes on automatically when it's dark.

[Sagitar]

It's data like these that make me say from time to time that setting tyre pressures on domestic vehicles is not an exact science and manufacturers recommendations are their best attempt to find a good compromise.

Rolling tyre failures are most often the result of under-inflation giving rise to excessive carcass flexing and consequent increased carcass temperatures taking the elastomers beyond their working limits.

Strangely enough, setting pressures a little higher may have the result of actually reducing carcass temperature because of reduced flexing.

The golden rule is to ensure that tyres are not under-inflated.

I'm with G.C. on this. We have said it all before, but the misconceptions persist.

[RunningInPleasePass]

I agree about under inflated tyres are more likely to cause tyre damage and you should check tyres regularly.

I think the only problem with greatly over inflated tyres is your cars handling is worse, one or two psi over is fine, but if you inflate them to the maximum recommended presser, then we have a hot day and the pressure increases by another 4 or 5 psi your handling will be compromised.

After saying all that, a bit of good weather is a very welcome change.

[Cyker]

@PeteB - Nifty system :) How do you stop people nicking them tho'???

A friend of mine had these neat tyre pressure monitors that were basically just a sprung pressure gauge with green, yellow and red bands, but they were 'secured' from theft with hex-headed grub screws. Unfortunately someone did try to nick them, and in doing so really mangled the valve's screw thread.

[johalareewi]

During the recent hot spell the tyre pressure will increase, and if your tyre pressure is already on the high side it may become too high.

When you are doing 70 down the motorway, how hot do you think the tyres get?

You are more likely to be under inflated when the weather is hot.

If the air temperature is 25C and you inflate to the recommended PSI then get on the road, your tyre pressures under normal operation are going to be lower than if you inflated your tyres when the air temperature is 5C. Just sayin.

Just to compound the issue, under inflated tyres run hotter than over inflated tyres.

http://en.wikipedia.org/wiki/Tire

[PeteB]

@PeteB - Nifty system :) How do you stop people nicking them tho'???

They do come with a special nut, but as you say if someone tried to force them it could ruin the valve. I chose not to fit them and took the chance. Been lucky so far, but then they're not very obvious, they just look like slightly larger dust caps.

I always remind the service manager at my dealer when I go for service or new tyres not to throw them away and put them back on the right wheels. My dealer has always impressed me; if I had to go to a place I didn't know so well, I'd take them off before handing the car over.

[PeteB]

During the recent hot spell the tyre pressure will increase, and if your tyre pressure is already on the high side it may become too high.

When you are doing 70 down the motorway, how hot do you think the tyres get? ...

From memory, only about 2-3 C hotter then when doing 30. The sun seems to have less effect at higher speeds, possibly due to faster airflow having a cooling effect.

It would be interesting if I ever get to take this car to Scotland and going down steep 5-6 miles hills with the friction brakes on after the HV Battery tops out to see if they get very hot then.

[timberwolf]

Peteb, sounds like a nice system, but we aren't getting a choice, the manufacturer will stick their dumbed down and less helpful systems into their cars. I can imagine that each tpms system will be unique to a particular manufacturer and possibly even incompatible between models, and therefore just another excuse to over-inflate the cost to the owner. I wouldn't be surprised if the manufacturers were not behind some of the lobbying.

If the vast majority of owners are not interested now, it will just be another warning system to ignore and then grumble about when it goes wrong and cost serious wonga to fix. The annual mot only applies to cars three years old, and it only happens once a year, so there is a whole year minus 1 day that the owner can ignore the damn thing. It isn't going to improve safety any more than the mot currently prevents people driving on bald tyres.

[PeteB]

Peteb, sounds like a nice system, but we aren't getting a choice, the manufacturer will stick their dumbed down and less helpful systems into their cars. ...

Fair point, but as I said above, this system is so neat I'd transfer it if I bought another car that had an inferior system built in (like the new Aygo, for example).

It's better than nothing, though, whilst some people would ignore a warning light, many would investigate and maybe save themselves buying a new tyre when a repair is possible, or at least avoid turning into a tree!

From the manual, the system that's fitted to the Gen 3 Prius in some markets and used the centre Multi-Function Display is quite comprehensive.

The worst thing would be if they become prone to false alarms.

[timberwolf]

Depends if it is measurably better and worth the expense i.e. there are less accidents or less severe accidents that would have been caused by under-inflated tyres.

[RunningInPleasePass]

When you are doing 70 down the motorway, how hot do you think the tyres get?

I don't know, what temperature?

You are more likely to be under inflated when the weather is hot.

I'm sorry I don't get that?

​The Wikipedia thing was interesting though!

[Dizzo]

Pete B - Interested in the Tyrepal monitors - are they accurate, in other words have you checked what they tell you against a good pressure gauge? £135 not cheap but if they're good they're worth it!

I've got 2 tyres now with punctures fixed (sort of!) by the Holts aerosol re-flators. They hold the pressure for a 2/3 weeks before dropping a bit so I tend to over-inflate to allow for it - 38psi on front and 35psi on rears (Gen 2). One over a year ago, the other earlier this year. Might not get the thumbs up from everyone but saved me a lot of dosh in recent years as I pick up nails/screws and stuff regularly - last year I had 3 punctured at the same time!

[PeteB]

Pete B - Interested in the Tyrepal monitors - are they accurate...

They seem to be as far as I can tell: when my dealer fitted new tyres (2 last November and 2 more in July) I asked them to put 37 psi in the front and 36 in the rears (1 psi above light load recommended pressure).

Now I've used this dealer for 12 years and found them very reliable when carrying out out my instructions and the TyrePal read exactly what I asked for both times (when cold - goes up when driving or sun on tyres).

When I've topped up myself and checked with my digital pressure gauge, they too have all agreed.

So either it's fairly accurate or all three are adrift by the same amount.

WARNING: however, if you use this version of TyrePal, you MUST NOT USE any of the gunge type inflators, as this will clog up the sensors and render them useless (£35 each to replace!) (same problem with many systems fitted by law to new cars - and those sensors can be £150+! - EACH!).

However, what really appeals is there no modifications to the car - I can simply take it all off and put it on another one (even a hire car on holiday, for example).

It's already potentially saved me one problem when a tyre had a slow puncture - was straight into the dealer for a free repair.

So far I think it's worth every penny.

[Sooty]

How do the car manufacturers and the law reckon buyers will be happy when no spare wheel of any kind is fitted to the car and they only supply this horrible gunk/inflator setup?

Seems to me that this is another stealth tax on the drivers.

Either use the gunk and then have to pay for a new tyre plus the sensor at approx. £150 a pop, or sit on the side of the road waiting for recovery or motoring association to bring a new wheel and tyre as I am sure they won't fit a new tyre on the roadside.

Unless I am wrong, once you have used the gunk then the tyre cannot be repaired.

[PeteB]

Tyres can often be repaired after the gunk has been used provided the side walls haven't been damaged and the puncture was in a part of the tyre that could have been repaired anyway.

Some tyre shops with refuse to repair them though, or charge extra for cleaning them and the rim.

Many of the sensor types used with built in TPMS will be knackered though, although some systems use the wheel rotation sensors in the ABS and calculate that a tyre must be under inflated if it's out of step with the others, and this obviously would be unaffected.

[Sooty]

Tyres can often be repaired after the gunk has been used provided the side walls haven't been damaged and the puncture was in a part of the tyre that could have been repaired anyway.

Some tyre shops with refuse to repair them though, or charge extra for cleaning them and the rim.

Many of the sensor types used with built in TPMS will be knackered though, although some systems use the wheel rotation sensors in the ABS and calculate that a tyre must be under inflated if it's out of step with the others, and this obviously would be unaffected.

I didn't know about this type of TPMS. Sounds like an interesting set up. I wonder how many manufacturers will use this one.

[Cyker]

Most tyre places won't even touch a tyre as soon as they hear the word gunk!

I remember when I had the puncture safe put in a while back: The installer buggered it up and the valve jammed and we had to take it to a nearby garage. They point blank refused to look at it and got borderline rude until I managed to explain we didn't want them to repair a puncture, just replace the jammed valve, and even then they wouldn't touch it until we flushed out the tyre.

I suspect he'd had some bad experiences with the normal latex-based tyre welds as he was quite surprised and impressed the puncture safe washed out so easy with just water! (He was also impressed that the tyre didn't smell of 'cats *****' as he put it, another side-effect of the latex based tyre welds!)

[PeteB]

To be more accurate, this type is a TPWS (warning system rather than monitoring system) and simply gives a warning light (and probably audible warning too) but leaves the driver to find out which tyre is going down.

The new Aygo just has a warning light, but I've no idea which system is behind it.

However, in the large manual for the Touch & Go Plus (2012 Prius onwards) is a section for the TPMS fitted in some countries (like USA where it's been mandatory in many states for several years) that shows the central MFD displaying a map with individual tyre pressures so this suggests sensors in the tyres.

[MEP's Yaris GS]

Does anyone know if Toyota dealers will repair tyres that have had gunk used under their free puncture repair service?

[PeteB]

Well, if it's a Toyota and that's all you've been given it would be pretty mean not to...

[Dizzo]

I suppose if you use the gunk to re-flate a punctured tyre you could leave off the Tyrepal valve cap until you get the tyre replaced. I've only once gone to my dealer with a puncture and they only offered to replace the tyre (screw was in tread) which is why I use the gunk aerosols.

I took my spare wheel/tyre and the associated boot compartment out to give me loads more space in the boot, and I'm sure my MPG has improved since as well! I acknowledge it's a bit risky - if you get a bad puncture that the gunk can't fix then you'd have to call out the recovery guys and presumably borrow one of their spare wheel/tyres. I assume they would do that - hope Green Flag do cos that's the one I'm with!