A usable "formula" for determining correct tire psi - maybe?
Not a lot. It leaks through rubber a little slower than ordinary air, and it tends to have much lower moisture content than ordinary compressed air.
If you have condensed water in your tire, the pressure will rise dramatically as the temperature rises. That's the only reason why nitrogen is considered more stable with temperature variations. Aside from moisture content, it obeys the same gas laws as any other gas, or combination of gases.
If you have condensed water in your tire, the pressure will rise dramatically as the temperature rises. That's the only reason why nitrogen is considered more stable with temperature variations. Aside from moisture content, it obeys the same gas laws as any other gas, or combination of gases.
Again, this is way too much thinking for simple tire pressure.
Club Member
Joined: May 2007
Posts: 145,895
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From: 40 miles Northeast of Indy..
because of their Liabilities some company's won't recommend what psi to use for different bikes and if someone has a wreck due to their Specs and is injured by their recommended PSI per say some would go right to court.
Last edited by oct1949; Apr 22, 2015 at 04:20 PM.
Road Master
Joined: Sep 2013
Posts: 1,091
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From: Southern Maine / Seacoast NH
I believe you are WAY over thinking this. I rode cross country a few years ago, and in some cases saw morning temps in the 40's in the mountains, and 100+ in the desert in the afternoon. 7500 miles and 21 days on the road. Checked my tire pressure 2 maybe 3 times the whole trip. No way was I stopping to adjust the pressure every hour as the temp rose 5 degrees.
Also, there is no way that tire pressure could possibly be that complicated. The general public (99% of drivers/riders) are not going to check their pressures more than once a month at best, let alone every 5* temp change. I might check mine twice a month, or if they look low. If proper tire safety was truly dependent on that precise of a range, then it would be more than just Firestone who needed a good lawyer.
I run somewhere around 38 rear, 38 front....or thereabouts.
Also, there is no way that tire pressure could possibly be that complicated. The general public (99% of drivers/riders) are not going to check their pressures more than once a month at best, let alone every 5* temp change. I might check mine twice a month, or if they look low. If proper tire safety was truly dependent on that precise of a range, then it would be more than just Firestone who needed a good lawyer.
I run somewhere around 38 rear, 38 front....or thereabouts.
As I understand it, the OP isn't worried about adjusting running pressure for changing air temps - he's just accounting for the changing temps during his testing. I think he's on to something. The earlier poster who mentioned using the tire pressures in the manual is correct, but ONLY for OEM tires. Once you put different tires on the bike, you're off the reservation as far as correct cold inflation PSI.
Sounds like the OP has done his homework - his approach makes sense to me. Unless Michelin has a recommended pressure for Commander IIs on an '08 Deluxe, I'll be using this plan to find optimum pressure when I swap out the Dunlops I have on there now.
Cruiser
Joined: Apr 2010
Posts: 153
Likes: 0
From: Texas
We'll, I don't understand all your saying, but it's interesting information.
All I know is that I keep my tires on my 2013 Heritage at 36 and 40 psi per service manual, and I didn't get but 5k on the rear tire.
I'm a easy rider and don't weigh but 180, and ride solo.
There's something wrong with that. I might lower my rear tire to 38 psi after reading your post to see what happens.
There was plenty of tread left on each side of the rear tire, and it wore evenly, but the center was wore down to very little tread.
So in my situation I think there's something to your formula.
All I know is that I keep my tires on my 2013 Heritage at 36 and 40 psi per service manual, and I didn't get but 5k on the rear tire.
I'm a easy rider and don't weigh but 180, and ride solo.
There's something wrong with that. I might lower my rear tire to 38 psi after reading your post to see what happens.
There was plenty of tread left on each side of the rear tire, and it wore evenly, but the center was wore down to very little tread.
So in my situation I think there's something to your formula.
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Stellar HDF Member
Joined: Feb 2014
Posts: 2,710
Likes: 529
From: Lethbridge, Alberta Canada
I believe you are WAY over thinking this. I rode cross country a few years ago, and in some cases saw morning temps in the 40's in the mountains, and 100+ in the desert in the afternoon. 7500 miles and 21 days on the road. Checked my tire pressure 2 maybe 3 times the whole trip. No way was I stopping to adjust the pressure every hour as the temp rose 5 degrees.
Also, there is no way that tire pressure could possibly be that complicated. The general public (99% of drivers/riders) are not going to check their pressures more than once a month at best, let alone every 5* temp change. I might check mine twice a month, or if they look low. If proper tire safety was truly dependent on that precise of a range, then it would be more than just Firestone who needed a good lawyer.
I run somewhere around 38 rear, 38 front....or thereabouts.
Also, there is no way that tire pressure could possibly be that complicated. The general public (99% of drivers/riders) are not going to check their pressures more than once a month at best, let alone every 5* temp change. I might check mine twice a month, or if they look low. If proper tire safety was truly dependent on that precise of a range, then it would be more than just Firestone who needed a good lawyer.
I run somewhere around 38 rear, 38 front....or thereabouts.
So, I went looking for guidance on the Net. It took me a surprisingly long time to find any useful information, and then finally these formulas. I just figured I'd save everyone else the grief of repeating my lengthy research. I figured I;d be helping others by doing so. if that offends you, I'm sorry.
Based on the results of my research and testing, I intend to run 38 psi in my rear tire and check it every 2 weeks or whenever my wife wishes to join me for a ride, whichever comes sooner. I have a good air compressor at home, so I can do this without too much trouble.
That's my plan.
Jim G
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Stellar HDF Member
Joined: Feb 2014
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From: Lethbridge, Alberta Canada
Jim G
Seasoned HDF Member
Joined: Nov 2009
Posts: 15,705
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From: Farmington ,MS
One thing you need to take in account is all this information you are reading is for "normal" sized tires, and when you run a wide tire it all goes out the window. A 240 tire has many more square inches across the tread than say a 150 tire, so it will become "over-inflated" and wear out the center of the tread at a much lower PSI. I run a 250 and have to run it at 35 to keep the tire wear even.
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Stellar HDF Member
Joined: Feb 2014
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From: Lethbridge, Alberta Canada
One thing you need to take in account is all this information you are reading is for "normal" sized tires, and when you run a wide tire it all goes out the window. A 240 tire has many more square inches across the tread than say a 150 tire, so it will become "over-inflated" and wear out the center of the tread at a much lower PSI. I run a 250 and have to run it at 35 to keep the tire wear even.
If you are willing:
- Find out what the ambient temperature is just before starting the ride
- Measure the cold psi just before the actual ride (since it DOES vary from what you set it to, with significant changes in outdoor temperature)
- After say 25 miles, measure the HOT psi
- Send me the data.
Not demanding, just asking.
Pleading actually.
Jim G
