Tyre Pressures

Pug307

Pug307

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Fellow Frogger
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Mar 8, 2002
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Location
Australia
My 307's factory sticker says that with a small load the front & rears need to be at 2.5 bar (253kpa, 37psi). With a full load, 2.5 at the front & 3 at the rear. That sounds pretty high at the rear (that's 44PSI, 304kPa).

The local sticker they add at the wharves here says 240 kPa or 35psi for front & rear. What do I trust :)

Cheers,

Justin

BTW: If you're interested, the exact conversion factors for pressure are as follows

1 bar = 101.325 kPa
1 kPa = 0.145037725 PSI
 
Hmm they do sound a tad high.

My old Honda used to be rated at 200kpa (or 220kph for 'consistent high speed travel' :p )... the 306 says somewhere around the 230-240kpa mark. But they've put a tyre pressure placard for a 306 XR, on my GTi6 :confused: tongue

BTW if my head is screwed on right this evening, a higher tyre pressure will result in better fuel economy, but less grip; and might promote uneven tread wear (more wear in the middle than the edges.)

And tyre pressures increase when they're being driven on (due to the buildup of heat in the tyre.) I'm pretty sure all the door placard ratings are for a cold tyre.

There is a thread or two on setting up tyre pressures and the result on handling characteristics floating somewhere about ..
 
Ahh I've got 38 alround in my parents 306 sedan and even then that is too much side wall flex (runs 185/60 R14 michelin taxi tyres, damn things need more GRIP GRRRRR) so I would run it as high as you can stand or close to the rated pressure on the tyre if it has one. As long as you can handle the harder ride you should run the pressures high but keep an eye out for too much wear in the centre cause then your pressures are too high.

Ohh and all rated tyre pressure are cold values. It would be for a set value too but I can't remember it.
ohh and the higher your pressure the less sidewall flex, hence the less heat build up. so you are better running the pressure high.
 
I run 36 on the front and 34 on the rear. Tyres are 195/50/15. Seems to be a good balance and the F/R difference gives very neutral handleing.
 
For a RWD car like my 505, would it be better to have more pressure in the rear or front, or even balance?

Its the first RWD car I've had (well, its my first car, but my parents cars are FWD tongue )
 
nJm:
For a RWD car like my 505, would it be better to have more pressure in the rear or front, or even balance?

Its the first RWD car I've had (well, its my first car, but my parents cars are FWD tongue )
Click to expand...
Nick,

I've found that any more than 30psi on the rear tyres of a 504/505 wears the centres of the tyre too quickly, but I think that any less than 28psi is too low.

On the front I stay between 30psi and 34psi. Any less than this and the tyre wears too much on the outsides. Any more than this and the car wanders all over the road (although if you have more castor, camber, kingpin inclination or tow in, you might be able to get away with higher pressures on the front).

You'll find that 30psi all around works well on a 504/505, although I've been finding that best tyre wear is with about 34psi front, 28psi rear.
This goes against the tyre placard (26 front, 29rear), but I don't take much notice of them.

Dave
 
Wow! Those 307 pressures are high! Just goes to show that a handling biased mfr doesn't follow the general trend of mfrs that quote far too low tyre pressures for liability's sake (my opinion). I reckon the placard figures are only to maintain the safest possible handling for Mrs Cantdrive and her kids - ie. understeer and early progressive breakaway. Following on from that, higher pressures generally give more grip and less progressive breakaway. Of course, this is within reason - if the tyre's so hard that the tread isn't flat, it'll start to lose grip.

Just one thing - some tyres have a maximum pressure of less than 44psi eek!

I run 31 rear/33 front in my car whereas Renault recommend 27/23. And the tyres wear DEAD flat, until they're bald. I just fiddle round with pressures until I like the handling balance.

Hope that's of some use.

Cheers

Stuey
 
I thought they sounded crazy. The Contis say they'll handle up to 350kPa/51PSI.

They're at 36psi/250kpa now.

Cheers,

Justin
 
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