Tyre Pressures?

[dwilson]

Sorry if this is already on here but what pressures do people use in their tyres. For my generation 2, Toyota say 35 psi front and 33 psi rear.

My car did 14000 miles before I bought it and the tyres are worn on the edges more than the centre suggesting underinflation by the previous owner. I am pondering a sensible pressure to compensate.

I have read the suggestion that 42 and 40 psi would improve mpg. Anyone like to confess their pressures?

[Jan&tone]

My gen 2 had done 14000 when I traded it in at the weekend, tyres were 6mm all over and I kept mine at 35 front and 33 rear as per the book

Gen3 is slightly less 34/32 I think.

[Grumpy Cabbie]

Pumping up tyres helps with economy but also reduced grip - esp in the wet. Also, have an accident and plod finds the tyres significantly higher than they should be and you'll find yourself in a lot of bother.

You might get away with 1 or 2 psi over the recommended levels, but anymore is a risk you have got to consider worth taking.

[timberwolf]

If you look on the door you'll see that 35/33 is the lowest with the highest suggested psi being 38/36.

I aim to have my tyres set at 38/36 although they got a little over that at F 39/R 37 during the summer.

I haven't checked in the last few weeks, so I've no idea what psi they are set to at the moment, oops!

[timberwolf]

Pumping up tyres helps with economy but also reduced grip - esp in the wet. Also, have an accident and plod finds the tyres significantly higher than they should be and you'll find yourself in a lot of bother.

You might get away with 1 or 2 psi over the recommended levels, but anymore is a risk you have got to consider worth taking.

I suspect you are more likely to prosecuted for under-inflation than over-inflation. Can anyone find an example of a successful prosecution for over-inflation of tyres?

VOSA Fixed Penalty Fines

[dwilson]

My gen 2 had done 14000 when I traded it in at the weekend, tyres were 6mm all over and I kept mine at 35 front and 33 rear as per the book

Gen3 is slightly less 34/32 I think.

Interesting 6 mm would be great but mine are down to about 4 mm on the edges on the front tyres.

[Grumpy Cabbie]

You're right about under inflated tyres but people have been prosecuted for over inflation - many unscrupulous taxi drivers trying to get a few more mpgs for one! (not me though - I'm safe).

[dwilson]

Thanks for all the replies so far. Sounds like 42F 40R is too high. Think I will try 39F 37R as indicated by my gauge which I believe to be be out anyway so will be more like 37F 35R "true" value. Hopefully that will even the wear out and still be safe.

[timberwolf]

Is it only taxi drivers who get done for over-inflated tyres?

How over-inflated does it have to be? And what sort of fines or punishments did the drivers and/or companies get?

[Grumpy Cabbie]

Is it only taxi drivers who get done for over-inflated tyres?

How over-inflated does it have to be? And what sort of fines or punishments did the drivers and/or companies get?

No its not, but we are probably likely to get caught as there are many inspections at airports and other popular places cabs hang out. Also, I guess some cabbies try to cut costs and save money and fuel - at the expense of safety.

Fines depend on the circumstances. If it's just a spot check then just correcting the pressure may be all thats needed, though if there are other issues with the car then the book can and will often be thrown at said driver. If there is an accident and the over inflated tyres are the cause, then you're in deep do do.

[timberwolf]

Thanks.

It's interesting to consider that you can't buy a gauge and be certain that it is accurate or that it remains within the spec. One wonders how the average motorist is supposed to keep their tyres at the correct pressure, what with inaccurate gauges, changes in temperature and atmospheric pressure, and the difficulty of knowing how many passengers or the load you'll be taking in your car.

[Cyker]

I run my Yaris at 40/35.

The good things are that the car feels like it has less drag and will roll/coast (in gear!) for longer, which is where I've made the most fuel saving.

It also feels better on the motorway and I dare say the accelerator response is slightly better at those speeds. Straight-line braking is also slightly sharper, and there is slightly better road-feel.

The dire warnings about the middle wearing out faster have so far been unfounded, but I suspect you'd have to inflate it a lot higher to get that problem. That and I sometimes carry heavy loads which would otherwise need me to inflate the tyres more anyway!

The bad things are the ride is noticeably harder (I officially hate speed bumps, pot holes, uneven roads, cattle grids and expansion gaps!!), grip from a standing start is not as good and the car's already poor understeering characteristics in the wet are made that bit worse. (It has made me a lot more cautious and respectful in the wet tho' 4x gap! )

I also think it may have had some part in the bump I had last winter (5mph, lost grip in a straight line braking for a mini roundabout , ABS useless, slowest collision ever, Ka bumpers apparently made out of cheese.)

It's basically the same trade-offs you'd have with a low friction tyre, except it's a lot cheaper

I must admit I don't know how much of the understeer is just down to the Yaris tho'; In my old crappy underpowered Fiesta, I could do the crooked mile 55-60mph all the way and it would feel stuck to the road, but I don't feel anywhere near as confident with the Yaris, even in the dry with the tyres at 32/30 as the manual recommends!

[acetip]

Is it only taxi drivers who get done for over-inflated tyres?

How over-inflated does it have to be? And what sort of fines or punishments did the drivers and/or companies get?

No its not, but we are probably likely to get caught as there are many inspections at airports and other popular places cabs hang out. Also, I guess some cabbies try to cut costs and save money and fuel - at the expense of safety.

Fines depend on the circumstances. If it's just a spot check then just correcting the pressure may be all thats needed, though if there are other issues with the car then the book can and will often be thrown at said driver. If there is an accident and the over inflated tyres are the cause, then you're in deep do do.

hi crabby

tyre press must be a headache for taxi work,as the number of passengers vary from one pickup to the next so it will be impossible to have press correct for every loading.

you cant be expected to get the footpump out of the boot and and increase/decrease each time.

[Cyker]

I think they'd be okay if they just inflated to the 'loaded' pressures and left it at that.

The inspector would have to be a total smeghead to call someone out about that!

It'd be much better than running at 'unloaded' pressures with a full car too; That'd just wear the tyres out faster as they flatten and flex under load.

Hmm... I wonder what happened to those air-less rubber matrix tyres they had on tomorrows world? Or that airjack for that matter. I still want one of those!

[johalareewi]

Tyre pressure also increases with temperature so as you set off and your tyres warm up, so do your tyre pressures. Or if you set your tyres to the recommended PSI after a nice warming up session, they will be well below recommended when the tyres cool down. At what point does a tyre become over inflated? The tyre has a max sidewall pressure so going over this is not a good idea.

[timberwolf]

I wasn't sure if your question was rhetorical? Tyre pressures are measured from cold, therefore over-inflation would also have to be measured from cold - the cold pressure value is the only one that the manufacturers have given us. I guess from school physics that we know that warm air expands and that the pressure increases in the tyre, but the tyre manufacturers will have designed the tyres to cope with the increase in pressure (and probably over-engineered because the tyres don't just have to put up with a short trip down to the shops).