tire pressure

I have an '04 VStar 1100 Custom, just bought a new rear tire. It's an Avon Venom X and I've been running the psi at factory specs - 36psi cuz I ride with a passenger most of the time. While browsing thru a JP Cycles catalog recently I was looking in the tire section and in the Avon tire section I saw a pressure chart for Avon Venom tires that recommended rear tires be run anywhere from 44 to 50 psi, depending on the load I'm sure. Does anyone have any thoughts, comments, etc. about this?  

Just like car manufacturers, motorcycle manufacturers tell you what the minimum safe psi is, to avoid handling problems. Running that minimum pressure will give you the softest ride, but will also wear your tires out faster. This specification does not take into account the differences between brands and models of tires.

The tire manufacturer tells you what that particular model of tire is designed to handle. The chart should include a variety of factors, including speed, which your owners manual completely ignores. The chart should be designed to tell you what pressure to use to achieve the maximum traction, which will be a balancing act between temperature, load & speed.

The Tire manufacturer is also required to put a maximum safe load and pressure specification on the tire sidewall, for people who don't bother looking at the charts. If you run at that psi, but with less load weight, the tires will run cooler than the chart calls for, giving you less traction and lasting longer. This requirement does not include tires provided to the bike manufacturer, for installation on the bike in the factory (OEM tires), which are exempt from several other regulations which apply to all other tires sold by retailers.

The PSI that you choose to run in your tires for ordinary street riding, should be somewhere between the PSI figures in your owners manual and the PSI rating on the sidewall. Where in that range is something you will have to decide as you compromise between traction, longevity and ride comfort.

regards,
Joe  

I am currently running Metzlers on my RoadStar that call for 50 PSI max pressure , but I find they seem cause my bike to hunt a line when running at max.
So I backed down to running 46 to 48 PSi which feels better , more sure-footed to me when riding solo.

Terry  

I've had Venom X on my bike. I had them at 28psi... Kawi recommended pressure for the Bridgestones. They scared the @#$% out of me first time I hit scarified pavement. It seems the sidewalls are a little thinner than stock, so, they darted side to side. I got them under control by increasing to about 34 psi.
I replaced the rear shock with a progressive suspension unit, and the twitchies subsided. Replaced the front springs, and they went away completely, even at the Kawi 28psi.
The suspension condition is just as important as the tire pressure.  

The manual for the Kawi VN900LT calls for tire pressures of 28/28!!!  No way Jose'.  I ride solo and ran them at 40/38.  Now on a set of Pirellis and after 4K miles they look almost brand new.  I'll stick to the 40/38, thank you.  

As you bump up the pressure, you get less flexing, and thus a cooler running tire. On the flip side, at 28psi, it takes a contact area of 28 square inches to support 800lbs of bike plus rider. At 40psi, your contact area is reduced to 20 square inches. That leaves you with less braking force available.  

While that is true for car tires, motorcycle tires have a much more rigid structure than car tires do. Changes in psi have much less affect on contact patch size, for motorcycle tires, as part of the bike's weight is supported by the tires even when not inflated at all. With careful selection of tires on a bike that weighs less than 800 pounds, it's possible to just keep riding until you get to where you can get a deflated tire fixed and reinflated.

regards,
Joe  

Joe,
Think about it. xx psi pushes in all directions, including down. While you do invoke sidewall saving, the bottom(literally) line is the downward pressure is determined by the tire pressure. Only thing the sidewall stiffness does is to prevent a splat.
You still have to support the bike, and rider... the pressure from the tire is what does that.
If you want to say even 50% of the bike+rider is supported by the sidewall stiffness, please feel free to divide both my numbers by 2, and then tell me how it's different.  

frbock,
Because of the reduced flexibility of the motorcycle tire structure, the relationship between contact patch size, load weight and psi is non-linear.  

3 out of 4 tires on motorcycles are old tech bias ply, and probably half of that runs tubes. I don't see anything in the design that would imply non-linear nature. Non-symmetrical perhaps.

Radial tires, since the cords basically wrap perpendicular to the rotation, you may have a point that fiberglass and nylon when encapsulated in rubber, have some compressive strength.