air pressure in tyres

Toon--soldier

hi i have a 16 inch diameter tyre with a 45mm sidewall and its 205mm wide just wondring what the best tyre pressure would be?

Senna

i use 28psi front and 30psi back. 28-32 is the standard pressures. my car feels better with a slight lower psi at the front. Experiment yourself till it feels 'right'.

daedalus2097

I take it they're not the standard wheels for your car then? As Senna said, you're probably safe around the 30psi mark, but maybe find out what's recommended for those tyres on your car from the tyre fitters.

batman2000

I would always do a 30psi front and 28psi back (17'' 225/45). More psi in the front due to the loadings (engine)

Rovi

Toon--soldier wrote: »

hi i have a 16 inch diameter tyre with a 45mm sidewall and its 205mm wide just wondring what the best tyre pressure would be?

45mm sidewall x 205mm treadwidth = approx. 22% aspect ratio.

That's a pretty low profile tyre, so I'd expect the correct pressure to be relatively high; somewhere in the mid 30s to 40 psi or thereabouts wouldn't be unexpected.

This will all be very dependant on the weight of the vehicle and it's intended use.
On the sidewall of the tyre you should find a block of figures entitled "Maximum Load" (or something similar).
It'll be expressed as ****lbs at **psi and/or ***kg at ***kPa, or something along those lines.
Unless you know your vehicle to be particularly heavy, start at 60-70% of these maximum pressures, and experiment up or down from there.

Anan1

Toon--soldier wrote: »

hi i have a 16 inch diameter tyre with a 45mm sidewall and its 205mm wide just wondring what the best tyre pressure would be?

If it's a 205/45 16 then the sidewall is 45% of 205mm, not 45mm. Does everyone else already know what car these tyres are on?

vectra

Rovi wrote: »

45mm sidewall x 205mm treadwidth = approx. 22% aspect ratio.

I honestly do not know where people came up with this conclusion to the tyre profile

205 = width in MM
45 = 45% of the width

batman2000

Sorry for the hijack.: So if my tyres are 225/45/ R17, what pressures should they be for 1.6 Octavia for normal load.?

Rovi

vectra wrote: »

Rovi wrote: »

45mm sidewall x 205mm treadwidth = approx. 22% aspect ratio.

I honestly do not know where people came up with this conclusion to the tyre profile

The hint is in the OP's first post:

Toon--soldier wrote: »

hi i have a 16 inch diameter tyre with a 45mm sidewall and its 205mm wide just wondring what the best tyre pressure would be?

batman2000

I am going to bring this thread back up.. got a puncture repaired to day and my tyres ar 225/45/R17. The guy inflated them to 45psi. The recommended psi is 32psi (on the petrol cap). They argued they were right and I was wrong...I think I am right sticking by the manufactures recommendations.....Any comments or opinions on what the PSI should be, is the manufacturer wrong ???

HJL

45psi seems very high, i think they are over-inflated at that pressure.

antodeco

Batman, are they the original tyres and wheels? MInes are 215/45/17s and im running 34 - 36 psi all round. Being honest, they do kinda look a little "flat". Saying that, the handling seems good.

vibe666

batman, I would have asked them to explain why they think it's the correct pressure for those tyres on that vehicle. if they can't do that then I wouldn't be respecting their opinion on the correct pressure.

if they can't tell you how they came to that conclusion then their opinion on the matter isn't woth spit IMHO.

batman2000

antodeco wrote: »

Batman, are they the original tyres and wheels? MInes are 215/45/17s and im running 34 - 36 psi all round. Being honest, they do kinda look a little "flat". Saying that, the handling seems good.

Yep there are the tyres and wheels shipped with the car...

When I asked the guy why was the tyre 15 psi above what the manufactures state, he said "how do you know the gauge you used is correct"....

I didn't feel like arguing, he is the arrogant bas*ard in Blakes Cross tyre centre...All the other tyres were correct (2.1bar) so I checked the rest myself and drove off.

Seth Brundle

What pressure is mentioned in your user manual?

.Longshanks.

....isn't the correct tyre pressure marked on the inside the fuel cap on all cars? It has been on the last 3 difference cars i had to look for it

Seth Brundle

Its inside the door on mine but these badges/stickers may have been removed by previous owners, etc.

Anan1

batman2000 wrote: »

Yep there are the tyres and wheels shipped with the car...

Without meaning to be rude, are you quite sure? It's just that 225/45 17" strikes me as rather an odd size to be factory fitted to a 1.6 Octavia.:)

batman2000

Yup...defo for sure.....my mate ordered it, I now own it so I know they are as shipped.

The pressures are on a label on the inside petrol cap (which is what I was going by)

Anan1

batman2000 wrote: »

Yup...defo for sure.....my mate ordered it, I now own it so I know they are as shipped.

The pressures are on a label on the inside petrol cap (which is what I was going by)

In that case, like you, i'd sooner trust the label than some guy in a tyre place.

blackbox

The main danger with tyres is under-inflation which can lead to overheating and blow-out. For high speed or heavy loads you should use the upper limit as stated by the car manufacturer (they usually give a range).

Handling will be better at higher pressures due to less flexing of the sidewalls.

Lower pressure will give more comfort.

Radial tyres do not distort with over-inflation in the same way that old cross-plys used to.

It is difficult to assess the correct pressure for non-standard sized tyres, but it is safer to err on the high side (without going mad!). Personally I would be thinking in the range 35-40 psi.

Fey!

The owners manuals or the plate on the car (on the drivers B pillar on mine) usually give a range of pressures for a range of tyre sizes, including pressures for a fully occupied or empty car.