Tire Pressures?

[ItalianStig]

hey guys, just wondering what the tyre front and rear tires pressures should be for my 2001 yaris vvti?

cheers

[Cyker]

It's in the manual, or on the edge of the door IIRC

It was something like 35/32 IIRC (I run 40/35 for fuel efficiency tho' :))

[Hartside]

(I run 40/35 for fuel efficiency tho'

That might give you better fuel efficiency, but it will lead to premature tyre wear in the centre and also reduce your braking effiency as you are reducing the contact patch presented to the road by over inflating. It could be quite dangerous in the wet. What's wrong with the manufacturers recommended pressures?

[Cyker]

They say overpressure will lead to premature wear in the centre but I haven't found that at all.

The theory for premature centre wear is that the tyre bulges out in the middle when you over inflate it, but I reckon you'd have to go over the recommended spec by considerably more than 5psi for that to happen.

I've been running that setup for a while now, and if anything the tyre wear has been a lot more even; At the recommended pressures I was getting noticeably more wear on the outer edges of the tyre compared to now.

Hasn't affected braking or acceleration negatively that I've noticed (If anything they've been sharper!) and you can 'feel' the car better at motorway speeds.

The only nasty detriment of the higher pressures that I've found is that the car is noticeably more understeery in the wet, especially on loose surfaces, but that might be partly down to the fact that they need changing (Nearing 3mm; I generally replace them round there rather than waiting until they drop to the legal minimum!).

(When I say it's more understeery, this is when I'm thrashing it down some open country road BTW; Under normal driving conditions I'd never get near the tyre's grip limit no matter what pressure it's at! )

But it is worth mentioning these things; Over inflating changes the behaviour of the car and tyre, and it's a lot like a 1st generation low rolling resistance tyre.

And deffo go back to stock pressures in the snow!

I'm going to be getting some ContiEcoContact 3's soon... still debating whether to go high-pressure with those or not!

[Korny_Yaris]

just go here mate, bang in ur license plate number, job done.

http://www.kwik-fit.com/tyre-pressure-search.asp

[GS John]

It was something like 35/32 IIRC (I run 40/35 for fuel efficiency tho' :))

Have you read the Highway Coode recently, or Law CUR reg 27?

Also here if you haven't: http://www.direct.gov.uk/en/TravelAndTransport/Highwaycode/DG_069871

[carlowlad]

They say overpressure will lead to premature wear in the centre but I haven't found that at all.....................................................................

And deffo go back to stock pressures in the snow!

I'm going to be getting some ContiEcoContact 3's soon... still debating whether to go high-pressure with those or not!

+1

Mind you, if overinflated from new they will wear in the centre. Leave them at the recommended pressure for say 1000miles then bump up the pressure. I've done this and all was ok. Apparently when the wire beds in it will stay that way. so from new it will bed in in a bulge if overinflated. But leave the pressure down and it will bed in evenly. Then overinflate as much as you dare... High pressures from new had my tyres wearing more in the middle, despite lowering the pressure to even it out. That uneven-ness stayed there.

Re; the regs on tyre presure. Thats interesting alright. However, there is NO evidence ANYWHERE that i can find that shows how grip decreases at higher tyre pressures. Believe me, i've looked. By all means show me though.

Let me know how the conti eco contact tyres go for you. I was thinking along these lines:http://www.tyrereviews.co.uk/Tyre/Toyo/350.htm

http://www.ctyres.co.uk/tyres/Toyo/350.html

Thoughts?

[Cyker]

Thanks for the tip :)

I guess I'll run them at stock to see how they feel and then experiment with the higher pressures later :)

I think that as the tyre compound is harder, it might not deform as much under load vs normal tyres and thus not benefit so much from the higher pressures.

The other thing is as it naturally has less grip than a normal tyre, it might actually be much worse so I guess it'll be a case of experimentation :)

[markweatherill]

That old warning about overinflated tyres wearing out the centre of the tread is from the olden days of cross-ply tyres, by the way.

I haven't heard of brand new (radial) tyres developing a bulge if overinflated, and I've not experienced that. (If they're on the car, the tread would be flattening against the road surface all round the tyre circumference, all the time the wheels were going round anyway which would counteract any tendency to bulge, even if the tyre construction allowed it to happen)

This thread reminds me to check my tyre pressures tomorrow. Thanks!

[Hartside]

Wow, I can't believe what I'm reading - you guys are worrying me!

http://www.theaa.com/motoring_advice/safety/tyre-pressures.html

http://www.michelin.co.uk/tyres/learn-share/care-guide/three-main-causes-of-tyre-problems

http://www.kwik-fit.com/tyre-pressure.asp

http://www.safermotoring.co.uk/CheckingTyrePressure.html

All the above make reference to over inflation as well as under inflation.

[Cyker]

Wow, I can't believe what I'm reading - you guys are worrying me!

http://www.theaa.com/motoring_advice/safety/tyre-pressures.html

http://www.michelin.co.uk/tyres/learn-share/care-guide/three-main-causes-of-tyre-problems

http://www.kwik-fit.com/tyre-pressure.asp

http://www.safermotoring.co.uk/CheckingTyrePressure.html

All the above make reference to over inflation as well as under inflation.

UNDER-inflating is the really dangerous one; At low speeds it's okay, and can actually be beneficial in e.g. snow, but as you drive faster you get increased tyre wear because the tyre is constantly flexing and at high speeds there is an increasing risk that the tyre will shred itself because it's flexing so much.

With over inflating, the tyre is much harder and won't flex about so much; It's actually safer at high speed for this reason. (I had some guy telling me that at speed the tyre would heat up even more and make the tyre explode, but this is a myth; Tyres can be inflated to over twice their rated pressure before they will explode! It's the extreme heating and wear caused by flexing at low pressures that causes tyre failure at speed.)

Assuming the tyre isn't over-inflated to ridiculous levels (I'm only going 3-5-psi over the rated for instance), the main undesirable effect with over-inflating is reduced cornering grip, but I think it's about on par with hard compound 'eco' tyres. (I'll be able to compare when I get the EcoContact3's :D). On my current tyres (stock Firestone Multihawks) it isn't generally noticeable except in the wet and on loose surfaces. (But that might also be because my tyres are nearing the end of their life )

[t-spiritpete]

Hello, anyone know the correct tyre pressure for a 2009 (2008 model) 1.3 Sr with 195/50/16 Dunlop SP Sport tyres, this size is not listed in the handbook, on the door pillars or any website like Kwikfit, I have done them at 34 front and 32 rear.

Thanks ..... Pete.

[carlowlad]

Wow, I can't believe what I'm reading - you guys are worrying me!

http://www.theaa.com/motoring_advice/safety/tyre-pressures.html

http://www.michelin.co.uk/tyres/learn-share/care-guide/three-main-causes-of-tyre-problems

http://www.kwik-fit.com/tyre-pressure.asp

http://www.safermotoring.co.uk/CheckingTyrePressure.html

All the above make reference to over inflation as well as under inflation.

I've seen stuff like that for a long time. They never go into specifics on overinflation, just general statements that look ok but when read properly, like reading a legal document, there is not much substance in them.

As i've said before, there is almost no information on how the level of grip changes with tyre pressure.

Actually, the NHTSA in America did a study on that but only up to 35psi iirc. They didn't go any higher. They should have because most of the graphs they showed had the trend going upwards all the way to the 35psi cutoff. A more scientific study would have kept rising the pressures till the graph started going downwards. That would show where the best grip was at, in terms of psi. Of course, cars are different, tyres are different but thats no excuse to do even one or two.

http://www.nhtsa.gov/cars/rules/rulings/TirePresFinal/FEA/TPMS3.html

hope this table shows ok:

Table III-7

Braking Distance (in feet) provided by Goodyear

Wet Stopping Distance (0.050� water depth)

Surface Speed 17 psi 25 psi 29 psi 35 psi

Macadam 25 mph 32.4 30.8 29 27.4

Macadam 45 mph 107.6 101 100.8 98.6

Concrete 25 mph 47.4 48.2 48.2 48

Concrete 45 mph 182.6 167.2 167.4 163.6

[carlowlad]

Hello, anyone know the correct tyre pressure for a 2009 (2008 model) 1.3 Sr with 195/50/16 Dunlop SP Sport tyres, this size is not listed in the handbook, on the door pillars or any website like Kwikfit, I have done them at 34 front and 32 rear.

Thanks ..... Pete.

They say that the placard pressure is for the tyres that came with the car. Different sized wheels and tyres means you cant go by the placard pressure. But i've never figured out what pressure you go by then! Sorry!

[t-spiritpete]

Hello, anyone know the correct tyre pressure for a 2009 (2008 model) 1.3 Sr with 195/50/16 Dunlop SP Sport tyres, this size is not listed in the handbook, on the door pillars or any website like Kwikfit, I have done them at 34 front and 32 rear.

Thanks ..... Pete.

They say that the placard pressure is for the tyres that came with the car. Different sized wheels and tyres means you cant go by the placard pressure. But i've never figured out what pressure you go by then! Sorry!

Thanks for the reply but the alloy wheels and tyres 195/50/16 were fitted to this car from new. I'm just suprised that the handbook doesn't have an amendment or a sticker on the door pillar, I don't think I'm to far off with 34 front and 32 rear so I will stick with that until I get in touch with Mr T. .

[mrpj]

Are they on a sticker inside the lower passenger glovebox lid? Mine are.

[ItalianStig]

ok guys i have no manual and my door doesnt say anything with a sticked basically we are two pages in this thread and there still is no definitive answer to my question:

My yaris is 2001,petrol, 998cc engine does anyone know the presures? cheers

sorry for the urgency but need to get them sorted

[t-spiritpete]

Are they on a sticker inside the lower passenger glovebox lid? Mine are.

Thanks mate I will check tomorrow when it's daylight .

Pete.

[t-spiritpete]

Are they on a sticker inside the lower passenger glovebox lid? Mine are.

Thanks mate I will check tomorrow when it's daylight .

Pete.

Checked in the glove box and yes it's in there but ..... it's for the size 185/60/15 and mine are 195/50/16 .

Pete.

[alfiejts]

Got this officially from Toyota Customer Services after we bought our SR in 2008.

As you say, the pressures for the 16" wheels aren't covered in the manual or on the stickers in the car.....

35psi front, 32psi rear.

Extract from official letter:

For models fitted with 195/50/16 tyres, the correct tyre pressure for normal driving (under 100mph):

Tyre Size Wheel size Front Rear

195/50/16 16 X 7J 240 (2.4, 35) 230 (2.2, 32) Kpa (kgf/cm² or Bar, psi)

I trust this is of assistance and thank you for taking the time to contact us.

Yours sincerely

Samantha Betts

Customer Relations Executive

[t-spiritpete]

Got this officially from Toyota Customer Services after we bought our SR in 2008.

As you say, the pressures for the 16" wheels aren't covered in the manual or on the stickers in the car.....

35psi front, 32psi rear.

Extract from official letter:

For models fitted with 195/50/16 tyres, the correct tyre pressure for normal driving (under 100mph):

Tyre Size Wheel size Front Rear

195/50/16 16 X 7J 240 (2.4, 35) 230 (2.2, 32) Kpa (kgf/cm² or Bar, psi)

I trust this is of assistance and thank you for taking the time to contact us.

Yours sincerely

Samantha Betts

Customer Relations Executive

Thanks mate for that ..... well I was only 1 psi out at the front ;).

Cheers Pete.

[mrpj]

Of course you must ignore Toyota and the tyre manufacturer's recommendation for the "correct" pressure and just over inflate them anyway.

[alfiejts]

Just had a thought....

The spare wheels run at 60psi - so you could fit four of those and get a great economy improvement!!!

[Bos]

Just had a thought....

The spare wheels run at 60psi - so you could fit four of those and get a great economy improvement!!!

Yes good economy but your top speed would be only 50mph, even better economy !!

[Cyker]

4 wheel drift!!!