Tyre Pressures

[Soeley]

Having just swapped my standard wheels with175/60/16 tyres for a set of 17" rims with 205/45/17 tyres on them. I was wondering about what is the best pressure to run them on. Ithink the originals were run at 32psi front and 30psi rear (I will have double check later). I asked the place that fitted my new wheels and they have inflated my new ones to 30psi all round and said that should be OK for my car.

Just after a second opinion really.

[tarquin]

Not a good opinion i suspect Mark but i am running 18x215x35. And mine are 32psi set at that by elite tyres where i bought them. There are some good tyre specialists on here

David

[s44gtw]

Others may have other views,

I personally would run the tyre pressures at the hand book pressures.

You dont need to change them according to the size of the tyres, the 'bar' will be the same.

Just pay attention to the Ambient temp when doing tyres, and be aware the pressure may require to be higher in winter/cold weather, not as believed, reduce pressures for 'snow driving'.

As to Tyre fitting centres pressures as you leave the centre, always be ready to check and set yourself.

Many just bung up the pressure to seat the tyres and then lets them down again.

Too many times i find tyres sitting with 40 odd lb in them.

& always check the wheel nuts yourself, to be sure they are safe, but also to be sure you can get them loose yourself without the need of 2 foot of scaffolding pole as an extention to improve your leverage..

george

[DFish]

George, he's going from a tall/skinny tyre to a much shorter fat tyre, so the pressures will be different. From memory the book has them at around 35psi (need to check when I get home), which my guess and experience would say that running book pressures on 17's will wear the middle out too quickly. I would go with 30-32psi myself.

Fish

[craggle]

Tyre pressures are strange things.

Take my Dax Cobra Kit car. Rear tyres are 255/45 R17 and the fronts are 235/45 R17. The car weighs about 1200Kg all up with full tank and a driver.

I played for ages trying to find a usable pressure for them and finally settled on 20psi front and 22psi on the rear. That seems really low but any higher and the car becomes really slippery on the road. Any softer and it feels a bit spongy on the corners.

I'm not alone either, 99% of Cobra owners running 17" or 18" tyres run about the same figures.

Not suggesting you drop them that low but do experiment a bit but in small stages, Dangerous to drop them too much!

Just for reference the BMW Mini with the same 205/45 R17 tyres recommend 32psi all around. The Mini weighs 1100Kg though and the iQ only weighs 860Kg.

I think you'll be safe somewhere around the 30psi mark.

Craig.

[s44gtw]

I set my tyres by 'bar' not psi.

http://www.centauro....les/psibar.html

http://www.tvr-webma...vr_info_psi.asp

I have had on winter tyres @ 205/45/16, now 205/40/17 & next week to do the quarter mile with lower tyre pressures i will use 205/45/17's

That is on a car with a Kerb weight of 1270 KG about the same as the Gross Vehicle weight of an iQ

i set at 2.5 bar front & 2.4 bar rear, and drop by a few points as required.

i run 185 winter tyres & 205 summer tyres on my Kia & they require the same pressure.

The quoted tyre pressures for your car will normally be quoted at 20 degree celcius.

There is around a 0.1 BAR drop per 10 degree celcius.

+20 celcius = 68f, cold tyre pressure is 2.1 bar = 30.4psi

+10 celcius = 50f, now the pressure is 1.98 bar = 28.66 psi

0 celcius = 32f, now the pressure is 1.93 bar =26.86 psi

- 10c = 14f, now the pressure is 1.73 bar = 25.06 psi

That is why i say be aware of ambient temperatures.

I set & check my tyres and reset my TPMS to suit the weather.

Once you know what the suitable pressures are for your tyres,

i would look at setting & reading up on pressures.

A good acurate pressure gauge is well worth buying IMO.

All a little anal all these pressures, but then thats me.

this is handy for standard size tyre pressures.

http://www.tyre-shop...repressure.aspx

george

[Soeley]

George, those links don't appear to be working (not for me any way).

Just checked the owners manual. Pressure for standard is 33 psi (2.3 bar) front & 32 (2.2 bar) psi rear. Those figures are quoted for both 15" and 16", that to me reinforces that those pressures would be suitable for my 17".

Hmm, more to it than you think :o

[s44gtw]

Sorry,

i think the links work once it has gone to the page for the second click.

I am on a mobile dongle and keep loosing any signal.

Plenty of conversion tables online.

I usually drop the pressure by a point till the feel is right as long as thats not going too low.

george

[Cyker]

My Yarisususesis' 14"'s are at 38/35psi atm.

[tarquin]

When i get in my iQ in these cold mornings my tyres show 7-8 deg c and a pressure of 30psi ,, when i am up and running and breaking they creep up to 25deg on the front @ 33 psi and 13 deg on the rear @ 30 psi hope that helps with peoples calculation.

David

[MarkyPancake]

I've got stock wheels and tyres (iQ3) and have been running them at the owner manual pressures. Today I had my second service and they said both front tyres are wearing more on their outer edges and suggested I put a little more air in them.

[s44gtw]

When setting your tyres in or for cold weather it is important to understand the differences.

http://www.michelin....ld-weather-tips

Set your tyres to the car manufactures pressures, or you may need to set to the tyre manufacturers.

Cold weathe/snow tyres, but remember the cars weight.

Re big tyres, or bigger wheels smaller tyres. pressure is pressure regardless of the space it is going in.

Maybe with sporty tyres for sporty driving you remember tyres will be heating when used hard, check pressures before going on a track type thing and understand the pressure rise when having hot tyres.

For winter do not run cold weather tyres at Low pressures, they may heat far too much.

Commonly people think that 4x4's might let tyres down to aid traction and get out of a sticky situation.,

but they get re-inflated for the road. or should be..

george

[MarkyPancake]

iQ3 owners with the stock wheels (16" alloys) and tyres: Do you run your front tyres at 33 psi or 35 psi around town?

[craggle]

I use the lower figures that are on the sticker inside the driver door shut. I don't travel over 160km/h very often so they seem about right.

32psi rear and 33psi front.

Craig.

[tarquin]

Mine have a 4psi difference between hot and cold

David