Are my tyres under inflated?

the182guy

Here we go again sorry!

The car is a 2002 (51 plate) Renault Clio II 1.2 16v. The tyre sizes that are on now are all 185/55/R15 which contradicts the car manual. The manual says the tyres should be 14" not 15", so I don't think the pressure chart is correct.

The chart says for the 1.2 16v model the pressure should be

• Motorway: Front 2.0 BAR (29 PSI), Back 1.9 BAR (27 PSI)
• Normal use: Front 1.9 BAR (27 PSI), Back 1.8 BAR (26 PSI)

The same chart says the tyre size should be 175/65/R14T. Given that my tyres are bigger than the ones in the chart, that means I shoudn't be using those pressures, right?

The chart says my current tyres should be on the 1.6 16v model. It gives the pressures for those which are:

• Motorway: Front 2.3 BAR, Back 2.1 BAR
• Normal use: Front 2.2 BAR, Back 2.0 BAR

Recently I had the two front tyres replaced and the garage had them inflated to above 30 PSI. When I went to check the pressures, I inputted what the manual said (29 PSI), and the machine ended up deflated my tyres to that.

I have a 10 hour round trip this weekend so really want to make sure the tyre pressures are correct. So should I be using the pressures for the 1.6 16v model which has my tyres? The only trouble with doing that is the 1.6 model will be heavier than my 1.2 model so the pressures can't be accurate...

Any thoughts?

TiTheRev

30psi will do for most vehicles unless a fully laden Estate. 1 or 2 psi will make little or no difference to tyre wear, fuel consumption or anything else. Cars from the factory come with 60-70psi in their tyres and drive fine

gilbert_and_sullivan

I'd split the difference unless someone happens to have the recommended readings for your particular engine/tyre size, so say approx 30F 28R, and increase 2 or 3 lbs all round for high speed full load running.
In all cases Renault recommend a slightly lower rear pressure so makes sense to do that.

thescouselander

TiTheRev wrote: »

30psi will do for most vehicles unless a fully laden Estate. 1 or 2 psi will make little or no difference to tyre wear, fuel consumption or anything else. Cars from the factory come with 60-70psi in their tyres and drive fine

Bad advice - many cars require higher pressures than 30 PSI and underinflation could result in a blow out and a crash (although 1 or 2 PSI isn't really a worry). Its always best to check the manufacturers specs.

I usually find that lower profile tyres tend to require higher pressures - perhaps the OP should go with the higher pressures for the 1.6 model.

mikey72

1.6 won't be that much heavier, and covers a range of conditions and loads anyway.
Use the 1.6 figures for the tyres you have fitted.

molerat

My handbook gives the pressures for the size of wheel / tyre and ignores the model / engine spec.

rev_henry

Yup I'd just go for the 1.6 pressures as well.

the182guy

Cheers all, will stick to the 1.6 pressures and see what the mpg is like this weekend.

ailuro2

I'd have a look in the petrol cap cover, or inside the driver's door, that's normally where different sizes and pressures are listed.

Plus or minus 5% of pressure can make all the difference to fuel economy and tyre performance, why not phone up the people who fitted your tyres and ask them what to inflate them to?;)

the182guy

ailuro2 wrote: »

I'd have a look in the petrol cap cover, or inside the driver's door, that's normally where different sizes and pressures are listed.

Plus or minus 5% of pressure can make all the difference to fuel economy and tyre performance, why not phone up the people who fitted your tyres and ask them what to inflate them to?;)

Might do that but they tried to sell me tracking which I said I'd bring it back sometime for.

anewman

I've read a suggestion that a certain amount under the "max psi" figure marked on the sidewall is a good idea. I guess this doesn't match up with the manufacturer's recommended figures though. See http://www.carbibles.com/tyre_bible_pg3.html