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10% rule makes sense as long as outside temp remains consistent. Measuring the tire pressure in the garage at 70 degrees and then riding while in the 90's has to be figured into the picture.
Wayne, I can't say I've noticed a trend downward in pressures that corresponds with the upward trend in size.
Michelin has a little tool on their website but the oldest Guzzi on the list looks like late 80's. For the Pilot Activ and my EV they recommend 2.2 bar front and 2.4 bar rear (32/35psi). Play with it and maybe you can find something close to your Eldo.http://motorcycle.michelinman.com/tire-selector#s=0
I've been running it at 38 and always felt is a little hard. Maybe I'll test it at 36 just to see.
The Ariel minimum recommendations are 20F and 26R for 3.25x19 tires and I run up to 10psi more with the modern tires. BTW Ariel recommended a minimum was 16 psi for 4.00x19s!
I prefer to add helium to reduce sprung weight and increase freedom of motion while excerbating rotational stability. Notable difference over air.Whatever you do, never use ambient air with politicians in proximity as the fecal matter will destroy the rim band inside tire, corrode aluminum, and reduce luster of the rubber.I know thi# is all true as I read it on the internet, and after switching to helium, I waxed a geezer in the Walmart parking lot on a electric cart. The old eldorado really handles those speed bumps, although you get a lot of air on those awesome jumps with helium.Honest. Really.
Everything about tire pressure is a rule of thumb. In general tires should be run close to their rated pressure to protect core and plys and other structural elements, but having said that I would suggest using what is printed on the tire as a starting point and experiment to find what works best for you.As a fallback you can always write the manufacturer, tell them exactly what tire you have, the width of the rim it is mounted on, and the loaded weight on the axle (a bathroom scale will tell you that) and the speeds you ride at. The manufacturer should respond with the correct pressure to use. Having said *that* their reply will probably come through their legal office and tell you to use the values printed on the side of the tire.