Tyre pressure

[roy_2819]

Hi all

 

Got some 175/70/R13 tyres on minilites on my Spitfire 1500 - any ideas on the best pressure to use please

[Clive]

As a start I would be trying the same as std factory pressures, 21 front 26 rear. however, I have generally run mine around 24-26 all round. So try and see what works best for you. 

[roy_2819]

^{As theres more rubber on the road  would I need more pressure to keep it there? Are modern tyre walls stiffer or more forgiving than 40 years ago?}

^{Old tyres had more pressure at the rear but weight at the front - seems counter intuitive}

^{As you can see I don't know much about tyres......}

 

^{Will try the 24 - 25 tonight}

^{Thanks for your help}

 

^Roy

[Clive]

The factory specs 21F/26R would be for a 155 section tyre. But the factory should have got those right. Hopefully.

More rubber would mean less pressure required.....but the difference is negligible. 

Wall stiffness varies hugely from make to make. try a few pressures and experiment. Best not go too wild (spitfires are truly horrible if you try 35psi!)

[roy_2819]

Thank you Clive - appreciate your advice.

[KevinR]

The size of the contact patch is constant irrespective of tyre size when the tyre pressure is the same.

The only thing that changes is the shape of the contact patch.

Wide tyres have a wide short contact patch.

Narrow tyres have a narrow long contact patch.

That is why wide tyres are not very good in the wet, snow or ice.

[Pete Lewis]

thats one reason you never see a builder with a wide tyre wheel  barrow, they wont cut through the mud

 

back to the old forumla            pressure = load x area

 

unless you change one of the three ...nowt changes 

 

Pete