Tyre Pressures

[Ancient Nerd]

Thanks, a nice long explanation about tyre pressure, but it doesn't answer why a dealer would set all four tyres to the same low 30 psi. The door sticker indicates that there should be a 2 psi difference between front and rear tyres for a Gen 2.

Incompetence. It's probably the same dealer that thinks all cars use the same oil. Go somewhere else.

[acetip]

Thanks, a nice long explanation about tyre pressure, but it doesn't answer why a dealer would set all four tyres to the same low 30 psi. The door sticker indicates that there should be a 2 psi difference between front and rear tyres for a Gen 2.

what happens at a lot of dealerships,and not only toyota ones is that they use apprentises/trainies to to do the to do the services as part of their trainig and the qualified staff do the repairs and and more complecated work.

this as happened for years in the motor trade.but their work should be supervised.

as my old passat was still under warrany i had it serviced at vw againt,this car had the old type rotary fuel pump

the boy they they put on decided he would adjust the slow running,instead of adjusting the throttle stop crew he adjusted what is called the volume screw,this had the effect of of increasing slow running,caused a huge turbo lag,that i discovered when driving home. i called them and and complained,but they said the fuel pump nt been touched as it was not part of the service. there are 4 adjustment screws on that fuel pump and they are

given a blob of yellow paint on the adjustment screw and lock nut after final adjustments.this yellow paint i could see had been disturbed.i was not going to argue with them.i managed to get photostated copy of the vw workshop manuel covering the adjustment of this volume screw and fixeditand turbo problem was solved.

had that car 15 years without problems.a garage is only as good a its worst mechanic.

i used to be in the motor trade many years ago,and worked alongside those whos motto was near enough is good enough when sevicing/repairing customers cars.i could be posting horror stories all day about what ive seen going on.but yoo cannot Paint all garages with the same brush for that would not only untrue but unfair.

.

[johalareewi]

... those whos motto was near enough is good enough ...

Seems to be the order of the day in many fields. These days getting it right is deemed to be inefficient. :(

[rodi]

Prius gen 2 ... 40psi front and 38 psi rear tyre presure for better economy

[acetip]

The manufacturer specifics the pressure when the tyres are cold, so you've got to be pretty close to the garage, so that in driving there you don't heat the air up in the tyres. I can't recall the distance but it was very low maybe only a mile or two?

Yes I understand that but I just want to compare my pressure gauge reading with an accurate reading - my problem is knowing where that accurate reading can be found. I think a dealer that has just had their gauge calibrated would be good.

The reading of my rear tyres should be a useful pressure to compare gauges whether hot or cold (as long as the same temperature for both readings).

hi dwilson

phoned ( at least tried )weights & measures today, but got a company that handles all calls to them, explained to a young lady what i is was calling about, she put me on hold that seemed forever,with a very distorted tune blasting in my ear.she then informed me that some one would phone me back before 1700 hrs on friday.

should i not receive a call i should call again quoting a reference number she gave me.

as SHARON TATES grandma would say WHAT A LOAD OF S**T.

agree best check tyre press at home when tyres are cold.

hi all

have had call that i was promised from weights and measures at county hall in norwich,a very nice man indeed.

some years ago a rule was brought in that forecourt tyre press gauge should be accurate with in a certain tolerance.and people were responsible for keeping their tyres to correct press,and police were running around carrying inaccurate pocket gauges hoping for a cheap pinch of poor motorist.

but the system was almost impossible keep up.

the weights and measures are still responsible for checking these forecourt gauges.

but as they have to check fuel pumps are accurate in their dispensing,and arrive un announced, spot check if you like no set peroid,just arrive in an area mob handed and check all pumps in that area at at the garages.

when they have finished checking the pumps, the check tyre press equipment.

i asked if they checked the same gauges at tyre fitting depots.

he said they do not,but thought it should done and would bring it up their next meeting.

they do not check gauges at car dealerships or repaires, and doing that would swamp the system. he said

hope this is of some interest to you all.

they gauges they use are tested against a master gauge they have at county hall.

if they have a complaint from a member of the public about a gauge they will check it as soon as possible.

[dwilson]

The manufacturer specifics the pressure when the tyres are cold, so you've got to be pretty close to the garage, so that in driving there you don't heat the air up in the tyres. I can't recall the distance but it was very low maybe only a mile or two?

Yes I understand that but I just want to compare my pressure gauge reading with an accurate reading - my problem is knowing where that accurate reading can be found. I think a dealer that has just had their gauge calibrated would be good.

The reading of my rear tyres should be a useful pressure to compare gauges whether hot or cold (as long as the same temperature for both readings).

hi dwilson

phoned ( at least tried )weights & measures today, but got a company that handles all calls to them, explained to a young lady what i is was calling about, she put me on hold that seemed forever,with a very distorted tune blasting in my ear.she then informed me that some one would phone me back before 1700 hrs on friday.

should i not receive a call i should call again quoting a reference number she gave me.

as SHARON TATES grandma would say WHAT A LOAD OF S**T.

agree best check tyre press at home when tyres are cold.

hi all

have had call that i was promised from weights and measures at county hall in norwich,a very nice man indeed.

some years ago a rule was brought in that forecourt tyre press gauge should be accurate with in a certain tolerance.and people were responsible for keeping their tyres to correct press,and police were running around carrying inaccurate pocket gauges hoping for a cheap pinch of poor motorist.

but the system was almost impossible keep up.

the weights and measures are still responsible for checking these forecourt gauges.

but as they have to check fuel pumps are accurate in their dispensing,and arrive un announced, spot check if you like no set peroid,just arrive in an area mob handed and check all pumps in that area at at the garages.

when they have finished checking the pumps, the check tyre press equipment.

i asked if they checked the same gauges at tyre fitting depots.

he said they do not,but thought it should done and would bring it up their next meeting.

they do not check gauges at car dealerships or repaires, and doing that would swamp the system. he said

hope this is of some interest to you all.

they gauges they use are tested against a master gauge they have at county hall.

if they have a complaint from a member of the public about a gauge they will check it as soon as possible.

Hi "acetip", thanks for getting back with all this information

[martswain]

I am amazed that so many people who own the Prius totally disregard the recommended pressures and over-inflate their tyres.

Toyota and the tyre manufacturers must spend millions on Yen getting the right balance between handling, noise, wear and safety and then the idiot drivers decide that THEY know better.

On the Prius UK Yahoo group there is exactly the same attitude, pump up your tyres to save little petrol but no regard to the crap handling, braking and tyre wear issues.

I wonder what the insurance companies would think of Prius drivers that are so anal about fractions of MPG that they compromise safety in this way.

[Sagitar]

Toyota and the tyre manufacturers must spend millions on Yen getting the right balance between handling, noise, wear and safety and then the idiot drivers decide that THEY know better.

You wouldn't agree with Douglas Bader's view of "rules" then? . . . . . .

[martswain]

You wouldn't agree with Douglas Bader's view of "rules" then?

No.

Look what got him into his situation in the first place, NOT following rules and complete stupidity.

From Wikipedia

In 1928, Bader joined the RAF, but, on 14 December 1931 at Woodley airfield near Reading, lost both his legs in an aircraft crash attempting a slow roll at very low level following jibes about his not wanting to perform aerobatics that day.

So, shall we all pump up our tyres well above normal pressures, book some track time and see if we can get round without having an accident.

[acetip]

Toyota and the tyre manufacturers must spend millions on Yen getting the right balance between handling, noise, wear and safety and then the idiot drivers decide that THEY know better.

You wouldn't agree with Douglas Bader's view of "rules" then? . . . . . .

hi

RULES ARE FOR FOOLS

WISER MEN HAVE GUIDE LINES

[Jan&tone]

Toyota and the tyre manufacturers must spend millions on Yen getting the right balance between handling, noise, wear and safety and then the idiot drivers decide that THEY know better.

You wouldn't agree with Douglas Bader's view of "rules" then? . . . . . .

hi

RULES ARE FOR FOOLS

WISER MEN HAVE GUIDE LINES

Sorry Acetip, I must disagree with you. As far as driving is concerned the rules are there to be obeyed.

Generally they have been formed from others experience over the last 100 years or so, and pretty much demand obedience. For example, who in their right mind would jump a red light, and we all saw this week what happens if you ignore the rules at level crossings!

Safety is paramount and anything that is done deliberately to compromise it is crass stupidity.

[acetip]

Toyota and the tyre manufacturers must spend millions on Yen getting the right balance between handling, noise, wear and safety and then the idiot drivers decide that THEY know better.

You wouldn't agree with Douglas Bader's view of "rules" then? . . . . . .

hi

RULES ARE FOR FOOLS

WISER MEN HAVE GUIDE LINES

Sorry Acetip, I must disagree with you. As far as driving is concerned the rules are there to be obeyed.

Generally they have been formed from others experience over the last 100 years or so, and pretty much demand obedience. For example, who in their right mind would jump a red light, and we all saw this week what happens if you ignore the rules at level crossings!

Safety is paramount and anything that is done deliberately to compromise it is crass stupidity.

hi sorry but i was not being serious just quoting old adage.

i am in agreement with you.if we did not have rules for motoring what a mess we would be in.

[Jan&tone]

No probs, and where safety - mine and others - is not concerned I may well agree with you.. But I heard it as:-

Rules are for the obedience of fools and the guidance of wise men....

[Sagitar]

The first and in my view most important, rule is not to disengage your brain.

First, my handbook does not lay down any "rule" for tyre pressure, but it does make a "recommendation" for the wheels and tyres that I have fitted, of 33 p.s.i. front and 32 p.s.i. rear. The additional information on the door pillar indicates that this pressure is appropriate with five people in the car and since I never drive with a full car, the recommendation is immediately brought into question. To repeat what I said earlier, the recommendation is a compromise that attempts to cover a wide range of driving conditions.

The tyre pressure recommendation is usually related to a "cold" tyre, but cold is not usually defined. Today it is around 20C; in the winter it might be below zero. What difference do you imagine that might make?

The purpose in setting a cold pressure is to try to arrive at an ideal working pressure and carcass temperature when the vehicle is in motion. The working pressure will be affected by the axle load, the speed of travel, by braking and acceleration, by the amount of steering that you do, by the road surface temperature, by the ambient temperature, by the nature of the road surface i.e. rough or smooth and by whether the road surface is wet or dry. So, if you are going to drive for several hours at high speed on dry motorway, you ought to set a different initial pressure than if you are going to potter slowly along some wet country lanes.

In terms of grip, the co-efficient of friction of the tyre material against the road surface is. within a wide range of pressures, independent of the pressure in the tyre. The compliance of the tyre will however be affected in that it is influenced by the stiffness of the side wall and that is affected by pressure.

I hope I have said enough by now to support my earlier statement that setting tyre pressures for domestic motoring is not an exact science. The manufacturer's recommendation is really no more that a good starting point from which a skilled and experienced driver will move to pressures that are ideal for him, on the basis of other acquired objective data, such as the pattern of tread wear.

Of course, if you haven't got the skill, experience and education necessary to make judgements about these things, then by all means stick to the manufacturer's very sensible recommendations. You wont necessarily get the absolute best out of your tyres, but you wont go far wrong.

Whatever you do, check pressures regularly and avoid prolonged under-inflation.

[acetip]

No probs, and where safety - mine and others - is not concerned I may well agree with you.. But I heard it as:-

Rules are for the obedience of fools and the guidance of wise men....

hi you are no doubt correct.

you could substitute fools for jobsworth,we all met them.

where common sense does not prevail.

[kevin h]

Had my first service two weeks ago and have noticed that the MPG has dropped by about 5 mpg.

So, thought I'd check the tyre pressure (should have done it straight away), and hey presto, the dealer had reduced fronts from 42 to 35 PSI and rears from 40 to 33 psi.

Now that I've put them back to "My normal" I'll see how the MPG changes.

Must rmember to tell them to leave things alone next time.

[Jan&tone]

No probs, and where safety - mine and others - is not concerned I may well agree with you.. But I heard it as:-

Rules are for the obedience of fools and the guidance of wise men....

hi you are no doubt correct.

you could substitute fools for jobsworth,we all met them.

where common sense does not prevail.

Common sense??? What's that? Is that where people have flexibility in their actions?? :)

[acetip]

No probs, and where safety - mine and others - is not concerned I may well agree with you.. But I heard it as:-

Rules are for the obedience of fools and the guidance of wise men....

hi you are no doubt correct.

you could substitute fools for jobsworth,we all met them.

where common sense does not prevail.

Common sense??? What's that? Is that where people have flexibility in their actions?? :)

yes.

[johalareewi]

Common sense??? What's that? Is that where people have flexibility in their actions?? :)

Common sense isn't encouraged anymore. Can't have people thinking for themselves you know.

[timberwolf]

I used to think it is was mad to run with higher psi than recommended, but I'm not so concerned now.

How many accidents have you heard of where the tyre pressure was higher than the manufacturer's recommendation and a contributory factor to the accident?

Prius forums and other hyper-miler forums account for a tiny percentage of the overall Prius ownership. My guess would be that most Prius owners (like other make/model onwers) check their tyres very infrequently. So you are much more likely to see another Prius where the tyre pressures are probably only checked by the garage, and are more likely to be under-inflated than over-inflated.

I don't normally carry four passengers and luggage, but I've been using 38/36 psi in my tyres for the last year, and apart from a harder ride - I haven't noticed any handling issues other than feeling the bumps more over man-hole covers.

If you believe the manufacturer always gets it right, why did the Gen 3 have a braking "feel" (using Toyota speak) recall (which wasn't a recall but just used the same process :!Removed!:)?

[timberwolf]

I used to think it is was mad to run with higher psi than recommended, but I'm not so concerned now.

How many accidents have you heard of where the tyre pressure was higher than the manufacturer's recommendation and a contributory factor to the accident?

Prius forums and other hyper-miler forums account for a tiny percentage of the overall Prius ownership. My guess would be that most Prius owners (like other make/model onwers) check their tyres very infrequently. So you are much more likely to see another Prius where the tyre pressures are probably only checked by the garage, and are more likely to be under-inflated than over-inflated.

I don't normally carry four passengers and luggage, but I've been using 38/36 psi in my tyres for the last year, and apart from a harder ride - I haven't noticed any handling issues other than feeling the bumps more over man-hole covers.

If you believe the manufacturer always gets it right, why did the Gen 3 have a braking "feel" (using Toyota speak) recall (which wasn't a recall but just used the same process :!Removed!:)?

[Ancient Nerd]

If the recommended tyre pressures are correct, they should result in even tyre contact over the full width of the tyre.

If you increase the pressure significantly, the centre radius of the tyre will increase, reducing tread contact mostly to the centre of the tyre. This will result in shorter tyre life and poorer grip.

My take is that the increased cost of replacing tyres will probably more than offset any savings from reduced fuel consumption. Add poorer road contact, and undoubtedly much worse wet weather grip, and for me it's a no-brainer to stick with the recommended pressures.

[Sagitar]

If the recommended tyre pressures are correct, they should result in even tyre contact over the full width of the tyre.

The important words in this sentence, are "if" and "should".

I have Michelin Pilot Primacy 215/45 R17 87W on both front and rear. The handbook recommendation is 33 p.s.i front and 32 p.s.i rear and those are the pressures with which I started. However, it quickly became clear from measuring tread depth that the tyres were not wearing evenly across the width. Both front and rear were wearing more quickly on the outside edges than in the centre. i.e. they appeared to be running under-inflated.

Over the period that I have owned the car I have gradually increased the inflation pressures until I now have 37 p.s.i. in the front tyres and 35 p.s.i. in the rear. Tread wear is now very even - only about 0.5 mm variation across the width of any tyre - but the wear is still slightly greater on the outside than in the centre. i.e. I am getting more even contact across the width of the tyre than I did with the recommended pressures and the indication is that I could still do with raising the pressure a little.

Your experience may of course be different, depending upon the way in which your car is driven.

If you increase the pressure significantly, the centre radius of the tyre will increase, reducing tread contact mostly to the centre of the tyre. This will result in shorter tyre life and poorer grip.

Not if you monitor tread wear carefully and adjust inflation pressures accordingly.

My take is that the increased cost of replacing tyres will probably more than offset any savings from reduced fuel consumption.

My adjustment of tyre pressures is concerned only with improving the performance of the tyre - if I get improved consumption also, that is an unsought bonus.

Add poorer road contact,

My even tyre wear indicates better road contact

and undoubtedly much worse wet weather grip,

I would be interested to see your evidence for this assertion

and for me it's a no-brainer to stick with the recommended pressures.

There I am afraid we will have to agree to disagree.

[Ancient Nerd]

Hi Sagitar,

No arguments, you are taking the sensible approach, more so than me. I was taking my argument somewhat to the extreme, because if you pump the pressure up enough, the tyre will become convex and behave as I said. And I think that there are some who really do take it to the extreme (but mostly in the US - see Priuschat).

My experience is with the same Michelin tyres as your own, on recomended pressures of 33/32, or more typically 34/33, as I prefer to overinflate slightly, so that pressure doesn't drop below recommended. The car has done around 28,500 miles with an even tread depth of 5mm all round, and across the tyre.

(Changing subject) I'm not sure what the original depth was, but it promises a considerably longer life than the Bridgestones on the GenII - and they managed 45,000 on the front and nearly 60,000 on the rear

[timberwolf]

How are you measuring tyre tread depth accurately? I'm think maybe there's a new little gadget I can get.