Recommended tire pressure

[Hoople]

they aren't invented in a vacuum.

Sometimes I wonder about that.

Lets just say you were Harley and you did the calculated math for a 650 pound bike with 1 rider, with this size tire, and you came up needing 38 PSI for that tire to operate properly without generating excess heat.
So now you want 38 PSI (target pressure) in that tire once at operating temp. Would you state you want the tire pressure to be 38 cold knowing that when at operating road temp the pressure will be 43 psi? Or would you subtract 5 PSI from your target for a cold reading.

If all of this is not that critical, why do they want different tire pressures (by 5 PSI) for 2 up?
When you think about it, 5 PSI is a lot of extra pressure for just 1 extra rider. That screams to me a few pounds of tire pressure means a lot.

 

[NEWHD74FAN]

Well that makes sense to me. "absolute Max Cold Tire pressure".

But now I ask this:

This has been a long time puzzle for me since I use nitrogen...
I do know the user manual states the tire pressures when cold, in my case are: 30 front/ 36 rear (1 up). And 30 Front 40 Rear (2 up)
I do know a 30 front /36 rear when cold will yield 34 Front & 41 rear when Hot.
Does that mean Harley really wants the tires to run at 34 & 41 when hot? If so, would I then add extra PSI into the tires if using nitrogen because nitrogen has a lower coefficient of expansion?

Since I use nitrogen, I have no clue what my tire pressures should be.
Any ideas?

The majority of "atmospheric" air is mostly nitrogen to start...the use of nitrogen only just means there is little to no oxygen or moisture components to degrade (Oxidize) or rust metallic rim or dissimilar metals. Just read the proper tire pressure 30 & 36psi Solo, 40psi 2-up to start off your HD frame decal or HD owners manual and you will be fine.

Yes, since tires heat with use, as you surmised, and the expected normal operating temperature of the tire is probably in the mid 80's or so quite likely as 4-5 lbs correction factor warm is probably accurate. The real tale of the tape is how well the tire performs at temperature, and how even the wear is on both tires to be equal tread depth across that face of the tires.

 

[larryjmiller]

Nitrogen is a joke.

Sorry if you have been bamboozled into thinking it is the panacea for tires. As NEWHD74FAN says, the air we breath is ~ 80% nitrogen and 20% O2 (oxygen). If you have a compressor as most of us do, you will not be able to fill your tires before a ride. Heck, you can sit at the tire place and twiddle your thumbs waiting for them to open so you can ride. I hope you can catch up with us...This is just like the guy that can't handle a few drops of 87 gas in his tank when he fills up after someone else. Give it up and just ride...

We are so conditioned by these marketing whackos that we are driving ourselves crazy and they are sitting back and taking a few days extra of vacation on our dime. remember "pet rocks", Cabbage Patch Kids, Tickle me Elmo...on and on.

What's next? Snake oil...Oh yeah, that's already run it's course!

 

[Hoople]

Nitrogen is a joke.

Sorry if you have been bamboozled into thinking it is the panacea for tires.

I was not talked into trying nitrogen.
Check that tire pressure - Page 2 - Harley Davidson Community

I am not big on heresy so I wanted to conduct my own controlled test just to see if there was any truth to the belief. I agree it would be way too much trouble to maintain my tires with nitrogen unless I had my own tank/regulator to start with. But the fact the inside of the tire is now "dry" is a big plus in my eyes. Also the "Cold" to "Hot" tire pressures are so much closer in readings. (The swing is 2 PSI vs. 6 psi with air.) But don't know if that means anything positive. Still testing to see if pressure is lost over time.

Wasn't bamboozled. I just enjoy seeing for myself and base my conclusions on old fashion testing.

 

[glider]

I think the "dry" or "wet" effect is the result of a poor or missing moisture trap on the air line used to fill the tires.
I have never seen any problems caused by "moist" air or any moisture in a tire when breaking it down,but then again I only use my own compressor which has a moisture trap on it which I think is the difference.

 

[NEWHD74FAN]

Minimum oxygen means less possibility of "oxidation" and Glider as usual is correct that oft times than not most air compressors have no moisture trap to contain excess moisture and most service stations & dare I say home users probably do not "purge" excess water settling in their air tanks, much less any regular maintenance. It really is another of those "accessories" that are seldom purchased at the time that shiny new air compressor is first installed...:small3d031:

 

[Porter]

I think there was a previous post on this point, but I haven't found it yet:
The whole "solo tire pressures" vs. "two-up tire pressures".

I am about 250lbs with all my leathers and helmet on. Add to that the rain gear and tool kit I always carry and based on weight, I always ride at the "two-up/rider and passenger" recommended pressures of 36 front and 40 rear for my 07UC. Mass matters regardless if it is luggage or a body.

I found a crack in my rear tire once, between the treads. The tire manufacturer listed that type of failure as likely due to riding "under recommended pressure" for the weight load. At that time, I was riding at the "solo rider" pressures listed because that is what the maintenace manual said. Not anymore...

 

[walleye]

I think there was a previous post on this point, but I haven't found it yet:
The whole "solo tire pressures" vs. "two-up tire pressures".

Look at post number three on this thread for the link you mentioned.

 

[WildThang]

Given your 09 has the 407 tire..it is best to run it at the max...in fact, a few extra pounds will even be better. I have alway ran 2-4lbs over the recommended 36 psi and at 6K miles, I haven't had any cupping issues with a tire known to cup...

 

[glider]

Given your 09 has the 407 tire..it is best to run it at the max...in fact, a few extra pounds will even be better. I have alway ran 2-4lbs over the recommended 36 psi and at 6K miles, I haven't had any cupping issues with a tire known to cup...

Does it make any sense that the tire has a MAX pressure on it for a reason and running the pressure over that could be hazardous? The recommended running pressures are specified in the owners manual for a given tire and shouldn't be exceeded by more than a couple of pounds.