Modern Rubber-Tire Pressure

[Eldrick]

Should I stick to the 400f Tire Pressure as stated on the bike or add more pressure to the tire (manufacturer recommendation) based on maybe they know the shape the tire wants to be?

[Johnwebley]

On my 500 I used to run Avons at
28f
33R

Now running Bridgestone

At the same pressure



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[Ken4004]

I would have thought the tyre pressure would depend on the bike and the weight of the rider if you want to be accurate and not what the tyre spec says, the pressure on the tyre is normally a maximum because the same tyre could be fitted to many different models and manufacturers and so the recommended running pressure will be different.
The amount of deformation and therefore shape of the tyre when loaded will depend on bike weight plus rider weight.

Just my opinion and not based hard facts but this sounds logical to me .

[Mikep328]

I've found that the TP as stated on my '76 CB400F's sticker - 26psi F/28psi R. works fine with current tires of the OEM size.  Higher pressure just makes it a harsh ride.  OTOH, a couple of pounds lower improves the ride AND cornering grip but at the expense of increased wear.  So it seems to me that the OEM pressures are the best for normal riding.  I weigh about 77Kg with riding gear.

[K2-K6]

Ordinarily there's load information on tyre sidewall to calculate the starting pressure.

Usually max load @ Xpsi which can be divided to give load carried by each psi unit.

From this you can take the overall vehicle weight (possible split 45% front 55% rear) plus rider, to then determine a start point psi that will safely carry the load asked of it.

The carcass load capacity dictates the pressure setting to prevent too much heat build from flexing, and sufficient flexibility to fully utilise the tyre's latent characteristics in providing grip and handling response.

[Mikep328]

Can you give an example?  I'm not understanding the calculation.  If the max pressure on the tire sidewall is say, 800 lbs max load at 44PSI, the moto weighs 450 lbs and the rider 175, what would you calculate a starting tire pressure to be?

[K2-K6]

Example as given above.

800/44 = 18.2lb potential from each psi.

625/2 = 312.5 lb per tyre (@ 50/50 weight distribution)

312.5/ 18.2 = 17.7 psi

Are those example figures given, or estimated  ? You'll need data from both tyres as they maybe different.

[Bryanj]

Unless you are hooning it on racing slicks pressures for old tyres should be same as new tyres

[Otis]

Unless you are hooning it on racing slicks pressures for old tyres should be same as new tyres

I concur. That is the correct advice.

[SeanFD]

Example as given above.

800/44 = 18.2lb potential from each psi.

625/2 = 312.5 lb per tyre (@ 50/50 weight distribution)

312.5/ 18.2 = 17.7 psi

Are those example figures given, or estimated  ? You'll need data from both tyres as they maybe different.

At 17.7 psi the bike will be unmanageable! Something not right there.
On my 750, I used Honda pressures and this resulted in more wear at the edges, leaving a ridge in the centre. Then I read, on the US site I think, that with modern rubber, pressures need to be much higher. Now I run 38/40 F & 40/44 R with more even wear.

[K2-K6]

Firstly you'd need genuine information included on the sidewall to give a calculation.

I used the stated information provided in above post, but also asked if it was correct 

At 800lb, I'd be surprised to see a bike tyre with that capability, it would probably support the bike without inflation at that figure.

Generally, they agree within reason of manufacturer bike data as that's realistically the calculations they would make in specifying a tyre during design.

If someone has accurate sidewall data, it could be looked at to provide insight. Effectively it will show the minimum pressure, in that  tyre, needed to carry the load without compromise to its own structure, and hence avoid failure through use.