SOHC.co.uk Forums > CB350/400

Modern Rubber-Tire Pressure

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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:

--- Quote from: Bryanj on November 19, 2025, 12:24:31 PM ---Unless you are hooning it on racing slicks pressures for old tyres should be same as new tyres

--- End quote ---

I concur. That is the correct advice.

SeanFD:

--- Quote from: K2-K6 on November 19, 2025, 09:40:49 AM ---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.

--- End quote ---

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.

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