Coincidence?

[Rob S.]

I've got two bikes, an '82 and a '16 (34 years apart for those who flunked math). One uses tubes, one does not. Neither has spokes, but I can barely imagine the improvements in mags over 34 years.

The only thing the wheels or tires have in common is the recommended pressure is identical for both - 36psi front, 42 rear.

I wonder if it's a coincidence. Certainly makes it easier for me to remember.

I didn't mention, should it matter, that both bikes have 'matched' sets of tires. The original Harley branded Michelins on the Sportster, and Pirelli "Sport Demons" on the Suzuki.

36 front, 42 rear - are these common numbers? (Both bikes weigh the same).

[Nessism]

Pirelli recommends 2.0/2.5 bar (29/36 psi) for the GS1100 w/tubes.

[Steve]

Are those “recommended” pressures or the “MAXIMUM” pressures on the sidewall?

Be aware that different bikes use different pressures (probably based on weight), but the tire manufacturer has no idea what bike is going to wear the tire.

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[Baatfam]

Did you do the 10% thing?

[Rob S.]

Did you do the 10% thing?

No.

Are those “recommended” pressures or the “MAXIMUM” pressures on the sidewall?

Be aware that different bikes use different pressures (probably based on weight), but the tire manufacturer has no idea what bike is going to wear the tire.

.

Probably maximum (for single rider with no passenger or luggage) from sidewall. I'll check when I go down to cover them up after Sportster cools down. I hate having them so far from my living quarters.

[Baatfam]

No.

You should.........................

[Steve]

Probably maximum (for single rider with no passenger or luggage) from sidewall.

What is printed on the sidewall has nothing to do with single or dual rider, luggage or no luggage, sidecar, trailer, or anything else. That number is the maximum weight that the tire is rated to carry, and the pressure that is required for that capacity.

Tire construction has changed over the years since the bike was made, so even the manufacturer's suggestions might be different. They might have recommended 24psi for a single rider at "normal" speeds, 26psi for rider and passenger, 28 for solo at higher speeds and 30 for passenger at higher speeds. These might have all been with tires that had a maximum pressure of 32 psi. Many of today's tires are rated to carry their maximum weight at 42psi. Since you are not likely at that maximum weight, you will not need the maximum pressure. Start with something like 30psi (cold), then go for a ride. About 50 miles or so will get the tire up to "normal" temperature. Check pressure again. You should see a 10% increase due to the tire warming up. If you see more than 10%, the tire was flexing too much, so add 2-3psi when the tire is cool, then go for another ride to repeat the test. Note that you need to do this for front and rear, which will likely need different pressures. If you ever carry a passenger, you will need to repeat the test for the additional load.

.

[Gorminrider]

Tire construction has changed over the years since the bike was made

...I wonder how this would radically change inflation pressures as many suggest.

Maybe I would agree if replacing the tubed tires of a 69 honda on a spoked wheel with modern street tires but since the 80's and tubeless rims, I especially haemydoots...They are still mostly bias-ply...and tires of the same dimensions are still going to want a certain amount of rubber on the road...a certain "profile".

Air hasn't changed either. In a density to suspend a load, it'll be the same. If modern sidewalls are thicker, or more "stable" wouldn't they do with less air? Or if 'expansion" is the question , expansion of air per heat, hasn't changed either.

"improvements" would seem to be mostly in the rubber -grip and wear. And, of course, the required escalation of "features" to sell the tires...

[Steve]

Whatever you want to look at to account for older tires rated to carry their maximum at 32 or 36 psi and newer tires at 46 psi. Different construction? Different maximum weight (in the same tire size)? I don’t know, either, but the bottom line is that you don’t simply inflate the tire to what’s on the sidewall, but you should also not blindly inflate to what the factory sticker says.

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[Nessism]

Like mentioned earlier, Pirelli recommends 32/36 psi. Why question further? The tires should not be set at the max allowable pressure unless there is specific reason to, such as carrying a heavy load.

[fbody_mike]

Where did the 10% figure come from? Is there a source for this?

[Steve]

Have seen that in some publications, but it's generally-accepted as common knowledge in most bike circles.

I first heard it from the Dunlop vendor at a rally in New Mexico in 1980.

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[fbody_mike]

https://www.mad-ducati.com/Articles/TirePressure.html

I found some other sites discussing the 10% method, but this one guy in particular stated it should be 10/20%. 10 percent for the front and 20 percent for the rear tire. I go by the factory specs for mine, so it will be interesting to see how the measurements work out.

[Steve]

I go by the factory specs for mine, so it will be interesting to see how the measurements work out.

Do you still use factory-supplied tires?

Or at least tires with the same specs?

THAT would be a valid comparison.

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[fbody_mike]

Correct sizes, but most are bias ply with radial looking tread patterns. Today's tread pattern is nothing like the OEM, and the material has changed too, probably for the better. So factory pressure specs are a good starting point but if there is a way to fine tune I'm all for it.

My bandit is the only bike I have with modern tires, I run 36 and 36 psi as specified on the swing arm sticker. I think it world be cool to compare the pressure measurements cold vs hot, as I commute the same route on each bike.