tire pressure question
Stellar HDF Member
Joined: Feb 2010
Posts: 2,674
Likes: 84
From: New Jersey
Higher pressures than recommended for a given weight are dangerous since the intended contact patch of the tire is not correct with too much pressure for a given weight.
Cruiser
Joined: Feb 2021
Posts: 186
Likes: 38
From: bendigo
Tyre pressure
Always inflate the tyre to the correct pressure. Be sure to check cold inflation pressure frequently, i.e. once a week. Although most motorcyclists love to work on their bikes, many seldom remember to check their bikes tyre pressures. Correct pressures are critical for safe handling. Over inflation or extreme tyre pressure will impair your riding comfort and decrease the size of the contact patch of the tyre with the road. Under inflation or too little air pressure will result in poor handling and the bike will be inclined to “wander”. Improper and insufficient tyre pressure will also cause rapid tyre wear, an increase in fuel consumption, lower top speed, and provide less control. Remember to check the inflation pressure of your tyres weekly. You will find the correct pressure in the operating manual of the motorcycle. Use Metzeler’s information only as reference. Attention: when the recommended pressure has been changed for use off the public highway (race track, off-road), it must be reset to the correct value before riding on the street.From metzlers web site. Go by harleys pressures. Metzlers is just a guide.
Stellar HDF Member
Joined: Mar 2011
Posts: 3,481
Likes: 630
From: NorCal Rocklin
This guy knows. Sounds like a Haiku or poem
I adjust my pressures for my riding. If I'm carrying a big load, I use the settings on the frame. If Im riding solo, Im dropping the pressures to 33/38 F/R
Grand HDF Member
Joined: Jan 2012
Posts: 4,445
Likes: 2,816
From: Oklahoma
How accurate is your gauge? What if it shows 3 PSI MORE than what is actually in your tire? You are always 3 PSI UNDER inflated. What if your gauge shows 3 PSI LESS than what is in your tires? Now you are always 3 PSI OVER inflated. Just how complicated do you want your life to be? Is there a reasonable short cut or compromise? You reject the idea of using the max on the sidewall but that is the ONE figure that will safely handle all of the variations in load you are likely to encounter. Personally, that is the short cut I use. I just installed my second set of Michelin Commander IIs and I got over 22,000 trouble free miles out of the first set. As is always the case, your bike, your choice.
How does Harley decide on the recommended pressures? Did they assume a 150 pound rider, a 200 pound rider, or perhaps a 250 pound rider? How much "stuff" in the saddle bags? I don't remember them even specifying sole or two up. So, what is the "base line" and what is the adjustment factor for above and below that base line? Based on these questions, just how trustworthy is that "set in stone" book figure? Is this a case where logic and good judgement won't be tolerated?
Last edited by btsom; May 3, 2022 at 08:21 PM.
Grand HDF Member
Joined: Jan 2012
Posts: 4,445
Likes: 2,816
From: Oklahoma
And tire failure from overheating. Counter intuitively, under inflation is a very common cause of blow outs and tire disintegration due to high heat buildup.
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HDF Community Team
Joined: Nov 2012
Posts: 6,186
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From: USA
No need to go to the lengths and drama you rolled out. A tire gauge and a little notebook will do.
First off, if you want to take Harleys recommendations and stop there, thats fine. Itll work well enough almost all the time.
But, if youre running different tires, or ride in very different ways, or just feel like twiddling, its not very complex.
Start stock, ride, make notes. Handling, ride quality, palm on tire for heat, tread wear appearance, etc. itll help if you keep working over a similar track as you do this.
Now bump it by 2psi or so. Repeat the ride and make the notes. Keep tweaking up and down. Youll hit a limit in both directions that will be clearly degraded. Fine tuning is in between.
This can be pretty important to do when really changing tire types. Like going from bias ply to radials, or going up or down in size, or different load ratings. As well if grossly overloaded, or running on a race track.
You can quickly get in the ballpark this way, which is helpful when youre doing something really odd. My 1952 MG running on modern radial tires for example. At 30 psi it skitters so badly as to be almost undriveable. Only took a few minutes to figure that out. 28 psi was better. 26 psi was better still. 24 psi felt similar. 22 psi and it started washing out. So after an hour or two of driving, I knew 24-26 psi was roughly right, with those particular tires.
First off, if you want to take Harleys recommendations and stop there, thats fine. Itll work well enough almost all the time.
But, if youre running different tires, or ride in very different ways, or just feel like twiddling, its not very complex.
Start stock, ride, make notes. Handling, ride quality, palm on tire for heat, tread wear appearance, etc. itll help if you keep working over a similar track as you do this.
Now bump it by 2psi or so. Repeat the ride and make the notes. Keep tweaking up and down. Youll hit a limit in both directions that will be clearly degraded. Fine tuning is in between.
This can be pretty important to do when really changing tire types. Like going from bias ply to radials, or going up or down in size, or different load ratings. As well if grossly overloaded, or running on a race track.
You can quickly get in the ballpark this way, which is helpful when youre doing something really odd. My 1952 MG running on modern radial tires for example. At 30 psi it skitters so badly as to be almost undriveable. Only took a few minutes to figure that out. 28 psi was better. 26 psi was better still. 24 psi felt similar. 22 psi and it started washing out. So after an hour or two of driving, I knew 24-26 psi was roughly right, with those particular tires.
Grand HDF Member
Joined: Jan 2012
Posts: 4,445
Likes: 2,816
From: Oklahoma
Quote: "Start stock, ride, make notes. Handling, ride quality, palm on tire for heat, tread wear appearance,"
How much of a "ride" is needed to see variations in tread wear appearance etc. and for what does one look? What are the visual signs that 38 is too little for two up and 42 is too much for solo? This is your technique so you are the expert to teach the rest of us. In your example, handling was surprisingly sensitive to small variations in tire pressure, what else would you look for if handling had been about the same over a 20 psi range?
How much of a "ride" is needed to see variations in tread wear appearance etc. and for what does one look? What are the visual signs that 38 is too little for two up and 42 is too much for solo? This is your technique so you are the expert to teach the rest of us. In your example, handling was surprisingly sensitive to small variations in tire pressure, what else would you look for if handling had been about the same over a 20 psi range?