Tyre inflation

[MattJR]

I have a 1969 2-door saloon. Can anyone suggest the correct inflation rate for the tyres please? A while ago, someone told me 30 psi for each tyre. Any other views?

Thanks,
Matt

[bmcecosse]

Yes - at least 30/32 assuming you have radials. Maybe 34 if they are 155 section...

[graham1957]

i run 145 radial tyres on a 2 door saloon and have found 24 psi to give a small bulge at the bottom similar to the look of a radial tyre on a new car. With 30 psi the car felt a little skatey. I also run a 1000 van with 155 radials at same pressure. I have looked in the handbook and the workshop manual but has no referance to radial tyres. What do all you others do with radials for psi???

[mike.perry]

I find that 26psi all round on my 155/14s give a good feel of the road surface, over 28psi the car feels skitish especially on wet roads. Under 26psi and you can feel ths sidewalls flexing.
If you drive off the road through a hedge then you know that you have got the pressures wrong

[MattJR]

Ok,thanks all.
Matt

[drivewasher]

Here's a tyre pressure calculator

http://arumdevil.com/pressures/

[drivewasher]

My van will be 24 psi. I arrive at this using the calculator

First get data from your tyres, My tyres are: 165-70-14.
The side wall data says:
MAX LOAD 462Kg @ MAX PRESSURE 44 psi

My brake test results that weighed the van indicate a kerbside weight of 588 Kg with my fat but in the seat! So I added it's carrying capacity of 8cwt = 406Kg. So vehicle weight will be 994Kg.

So the calculator says:[frame][/frame]

[ManyMinors]

It also depends a bit on the tyre you use. Generally speaking I'd agree with Mike and find that my car is best at around 26psi all round. However I once fitted Toyo 155/14 radials and found them to require a bit more pressure as they seemed to have very soft sidewalls. 30psi suited them. I have Nangkang tyres of the same size now and prefer them to the Toyos. Our other Minor is fitted with the narrower 145/14 radials and the steering/handling is slightly better. I have found that about 26psi suits them best. The last couple of years of Minor production saw radial ply tyres offered as an option and the later handbook does give a recommended pressure for these of 24psi front and 26psi rear.

[bmcecosse]

My Trav wobbles about like a jelly on low pressures like that!!!

[drivewasher]

Its all a calculation depending on amongst other things, the tyre load index. The max load and pressure of my chosen tyre is 462Kg @ 44psi those tyres that wobble of flex on the sidewalls may well be a heavier or higher max pressure to start with. After all the car manufactures get the recommended tyre psi from somewhere, they don't just go for a ride and keep trying them until they get it right! Thats why tyre fitters should always fit the load rated tyre that comes on car when it's new.
BMC you may find if you do the calcs for your fitted tyres the running pressure could well be higher than 24 as you have them

I must admit I have been running my van at 28 psi all round as thats what felt right, but I will try 24 psi see how they look/handle

[SteveClem]

I don't think there's a definitive answer to this. Original recommendations are prob useless because our cars//tyres are not often to orig spec. I'm inclined to agree with Bmc on tyre pressures for the trav( highish) but our saloon is better on 28 front,26 rear. Don't know why, just trial and error.

[bmcecosse]

I do carry a few spares in the back... Modern cars run at higher pressures - usually AT LEAST 34 psi and up.

[drivewasher]

we find most moderns are around 32psi front and 30 psi rear. Some of the big Vauxhalls seem to be a bit higher at around 34/ish

My point being that there is a calculation to arrive at the optimal pressures try looking at your tyre data on the tyre walls and use the calculator. It takes into account the weight of vehicle and the stiffness (load index) of the tyres to be used.

If I get time tomorrow I'll get the data off my Galaxy tyrewalls, put that into the calculator and see if the result matches Fords reccomended tyre presssures. I bet it does!

[MikeNash]

I'm running my 1963 Trav at 25 psi all round and that gives dead even wear on the four radial CAMAC 145R14.
Did once accidentally put the pressure gauge to metric and pumped them up to 2.5 bar all round. Corr! It bounced all over the place!
Regards, MikeN.

[bmcecosse]

Problem is that the Calculator will assume the tyres are fitted to correct width wheels.... The standard wheels are only 3" wide - so even 145 tyres ( 5.71" wide tread) are pretty ridiculous , and 155 tyres (6.1" wide tread) are crazy. The overhang on the rims is well outside any recommended tyre fitting guide, and probably should be refused by the garage... The later van wheels at 4.5" are much better but probably still not ideal. Feel the sidewalls and treads of the tyres after a decent run on a dry day (obviously) - if they are hot, or even 'quite warm' the pressures are too low... This running will of course have increased the pressure somewhat.... but always work with the 'cold' pressures.

[ManyMinors]

145 section tyres on a Minor are not "pretty ridiculous", they are the size recommended by the car manufacturer and the pressure recommended for them is 24psi front and 26psi rear. Owners running at these pressures are not running them underinflated.

As for pressures on modern cars. Most small, light cars (which a Morris Minor is) have similar pressures. Many modern cars weigh greatly more than a Minor which is one reason for their higher recommended pressures.

[drivewasher]

Iv'e just taken tyre details of a Renault clio and put them in the calculator.
Results came back at 31.68 Psi. The tyre card on door pillar said 32 psi.

Increasing the vehicle weight gives a result of more psi as expected

[bmcecosse]

And it has nice fat rims and 165 tyres... Our Clio (with alloys and 185 tyres) wears the shoulders like mad unless run at 36 psi.

[SteveClem]

Is there not just a range of pressures that are safe and we can all experiment and choose our preferred choice within that range?

[drivewasher]

And it has nice fat rims and 165 tyres... Our Clio (with alloys and 185 tyres) wears the shoulders like mad unless run at 36 psi.

I think 36 psi for a small car that is more than likely lightly loaded is far to high and won't hold the road as it should. The manufacturer has specified 30/32 psi. Mind you the manufacturer didn't recommend the use of grease on copper head gaskets!

I'm just posting the results as I said I would. They do seem to tally with the manufacturers specs. The manufacturers do quote higher pressures for a mid or fully loaded vehicle. If any car is fitted with a higher load tyre than origonal then that would alter req psi upwards.
Customers think we are trying to blag them when we quote for tyres that SHOULD be fitted to the car and not just what we happen to have on the shelf.