Sport demon PSI

[Rob S.]

I just checked my (relatively) new (1900 miles) Pirelli Sport Demons cold. Front showed 36 PSI, rear 30.5.

Manual says, "normal riding solo" 25 front, 28 rear.

Rear seems close enough for me. The manual lists a max of 32 for the front, and that's for, "continuous high speed dual."

I don't know why my mechanic would have done this, but I'm thinking about lowering the front to 27 or 28.

Comments, suggestions?

 

[Rob S.]

Just lowered the front to approx. 27.5 PSI.

 

[bccap]

I use the 10 to 20% rule for tire pressures..........

"A technique for those wanting to get the most out of their tires on the street is to use the 10/20% rule.

First check the tire pressure when the tire is cold. Then take a ride on your favorite twisty piece of road. Then, measure the tire pressure immediately after stopping. If the pressure has risen less than 10% on the
front or 20% on the rear, the rider should remove air from the tire. So for example, starting at a front tire pressure of 32.5 psi should bring you up to 36 psi hot. Once you obtain this pressure increase for a given rider, bike, tire, road and road temperature combination, check the tire pressure again while cold and record it for future reference.

Each manufacturer is different. Each tire model is different. A tire design that runs cooler needs to run a lower pressure (2-3 psi front) to get up to optimum temperature. The rear tire runs hotter than the front tire, road and track. So the rear tire cold-to-hot increase is greater. Dropping air pressure has the additional side effect of scrubbing more rubber area."

 

[Steve]

Best suggestion is to follow the 10% rule. :-k

For easiest calculation, start with an easy number. Inflate both tires to 30 psi, go for a ride. The longer, the better, with a minimum of about 50 miles. Check your warm pressure. You are looking for a 10% rise in pressure. If the pressure is over 10% higher (33 psi), the tire flexed too much, which warmed it up too much, so raise the pressure about 2 or 3 psi (when cold) and go for another ride. If the pressure did NOT go up 10%, lower the (cold) pressure by 2 or 3 and repeat the process.

Keep in mind that tires have changed drastically since the bike was new and that sticker was printed. The max pressure on most tires was about 32, and they were rated to handle a certain amount of weight at that pressure. With today's tires, some of them can handle more weight and require higher pressures to do so. In other words, because of different tire construction, today's tire might need 30 psi to handle what the original tires could handle at 25 psi, so you can't really rely on the sticker.

If you ever change brand or model of tires, you will likely have to repeat this process, and basically for the same reason. The Shinko tire might handle xxx amount of weight at 36 psi, but an Avon might require 40 psi to do the same thing. That means that at a lower-than-maximum weight, you might need 30 psi in the Shinko, but 34 psi in the Avon. (These numbers are ficticious examples, not real-life pressures.)

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[bwringer]

What Steve said.

Use the 10% rule.

Forget the pressures listed in the manual -- they're usually way too low for modern tires. On the other hand, the pressures listed on the tires are MAXIMUM pressures, not recommended pressures -- read the fine print.

Get a GOOD gauge and experiment. It's an excuse to go for a nice long fast ride...