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What's the problem with tire pressure?

Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
 
There is a lot more to tire technology that just radial vs bias technology. You also have belted vs non belted in both bias and radial types. There was nylon cord, then polyester cord, then kevlar and steel. And if anybody thinks the rubber compounding and optimal operating temperature for a K112/RB2 combination is the same as for bias ply ME880s, .....

You can still buy tires that are almost identical to what you could buy in 1975. But most riders don't because there are significantly better tires available today. They are better because they are different, and don't necessarily need the same pressure as the tires of 1975. Some might wish it weren't so, but it is.

I remember Reg Pridmore telling me in 1986 (RATS, Laguna Seca at the MOA Rally) that the stock tires on his K75 fleet were better track tires than the ones he had on his superbike R90S when he won the championship. I'm confident that was true back then, and moreso now.
 
chewbacca said:
Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure?
Click to expand...

Of course not because there's no such thing as bone stock motorcycle or car racing and these teams aren't using highway tires. Silly question, proves nothing.
 
Cool! finally, we have another thread, in addition to the infamous "Oil Thread" that needs to be elaborated upon.:dance
 
chewbacca said:
Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
Click to expand...

Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.
 
Gonzo49 said:
Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.
Click to expand...

WRONG!!!!!!!

PV=nRT or simpler Gay-Lussac's Law P1/T1 = P2/T2
 
Gonzo49 said:
Changes in tire pressure are directly related to the amount of water in the "air" in the tire. Just a small amount of water,(and it can be from the lubrication used to mount the tire) will greatly affect the tire pressure in a m/c tire due to the small volume. I think you should rethink that old timers rule. Nitrogen will help to mitigate the change in tire pressure.
Click to expand...

I have 78% nitrogen in my tires. Seems to work fine.
 
Yes, moisture in a tire can theoretically add to pressure fluctuations. If the interior tire temperatures reach the point that water droplets are vaporized - something in excess of 212F - the steam can increase pressures more than simple heating of air. At the extreme, triple digit ambient temperatures and sustained Interstate speeds my rear tire gets to somewhere between 150 and 160F. No steam.

If concerned, put a drier on your compressor.
 
chewbacca said:
Just something to think about, do motorcycle racing teams or car racing teams call the vehicle manufacturer for a recommended tire pressure? Racing guys, even when a tire rep is supporting the team adjust pressure to meet conditions. When you look up most bike tires they usually have a statement to the effect of what the bike manufacturer recommends. Avon used to have specific recommendations. I don't recall Michelin, Metzler or Dunlop having them but that changed from time to time. As previously stated that sidewall pressure is a max loaded pressure. There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
Click to expand...
Not that I'm taking potshots at the "theory" above but obviously much is missing with the process as "go take a ride" for a rider in the desert, in the summer would far different than the result for "go take a ride" in the winter on say, the US/CA border.:)
As for Osbornk & his N source, I just googled the subject & the geologist whatever website says while N hasn't changed appreciably, oxygen levels have changed. Now , do we have a "tire pressure expert" to step forward & debate the effects of more or less oxygen in a MC tire?
 
lkchris said:
It's always interesting to see reference to "newer, higher pressure tires."

Correct me if I'm wrong, but in most cases this is the difference between radial and bias-ply tires.

In most cases, the tire specified for your bike is one or the other but never both. If that's the case, there simply aren't "newer, higher pressure tires" applicable to your bike.

(One exception may be Conti's new radials directed towards Airheads and maybe old Ks, but haven't studied that. They have just been introduced this summer.)

And, the numbers on the sidewall are completely meaningless except that they indicate the maximum pressure safe to use in this tire. This has NOTHING to do with BMW's or the tire manufacturer's recommended pressure for your particular bike and load conditions.

Except for the following, that is ... A recent presentation at our dealer by a Metzeler tire rep featured the notion that if your goal is to maximize tire mileage, i.e. tread life, then you should indeed run your tires at the maximum pressure indicated on the sidewall. It's printed a little less strongly in Metzeler brochures, too. This of course, is NEVER the basis for BMW's pressure recommendations for your bike and most obviously may involve some handling and/or comfort and/or performance compromises. I'm not doing it, as my goal is fun associated with riding and for sure not carefully saving every penny and diminishing the fun. I mean, if it's about only tread life, just never ride.

If you've a current model BMW, recommended tires by brand are listed at BMW's website. These charts don't go very far back as regards discontinued models IIRC. There is, not completely coincidentally, sometimes not sizes for older bikes in the latest/greatest tire models, and the older bike guys then use the older models anyway. The notion that perhaps tires (brands) not on the recommended list somehow require completely different pressures is a bit of stretch in logic, too, I think. Look for that brand to publish something instead.

Bottom line, I think, is that BMW's recommendations are simply fine and are good for a long time. If a tire manufacturer will publish in writing or on its web page that they indeed have different recommendations for you, then pay attention. There's not a lot of data provided by various internet contributors to back up their claims when it comes to varying from BMW specifications, and they should direct you to data rather than their opinions and unscientific observations. I know for sure that I've never seen specifically published by a tire manufacturer that pressures recommended by BMW in, say, the 1990s or 80s or 70s have been superceded by "new technology." I'd love to be directed to it.

You can also rationalize that somehow BMW's specifications don't apply specifically to you because you must weigh something different than their average rider or something like that, but I'd instead conclude their figures can be recognized as covering normal variations. BMW's figures are quite fine and it's not really about demonstrating that you know more than they do, is it? When it comes to "voice of experience," nobody tops BMW.
Click to expand...

+1
 
chewbacca said:
There is an old timers rule of thumb and I'll probably screw it up. Set the pressure cold. Go ride for maybe half an hour. Check the pressure. If it goes up about 10% your good. More than 10%, add some air and try again. Less than that, let some air out.

IMO, to get good, consistent readings you have to measure cold. Also, don't use the TPS readings for anything else than to determine you have leak.
Click to expand...

no screw up, that 10% gain is the target. That translates to a ~ 3 to 4 psi increase.
 
More importantly

I've been running PR3's at 38 front and 42 in the rear on my R1200RT down here in lower alabama, ambient temperatures have been running in the low 90's and for the life of me I can't figure out what tire pressure is best for keeping the love bugs from hitting the bike....
 
The partial pressure of nitrogen in tire air is much greater than oxygen. See http://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text9/Tx96/tx96.html for details. A bit of water will have some vapor, but I don't think it will be significant. Some chemical engineer might comment.

Max sidewall pressure applies when the carcass and air inside are at 60F or 20C at sea level. Other temps or altitudes will require some adjustment.

Gotta be a nerd (me?) to do the math ... My RT will do temp calculations, but altitude, must be negligible or BMW would have done that too?
 
rangerreece said:
I've been running PR3's at 38 front and 42 in the rear on my R1200RT down here in lower alabama, ambient temperatures have been running in the low 90's and for the life of me I can't figure out what tire pressure is best for keeping the love bugs from hitting the bike....
Click to expand...

:laugh:laugh well played
 
kantuckid said:
Not that I'm taking potshots at the "theory" above but obviously much is missing with the process as "go take a ride" for a rider in the desert, in the summer would far different than the result for "go take a ride" in the winter on say, the US/CA border.:)
As for Osbornk & his N source, I just googled the subject & the geologist whatever website says while N hasn't changed appreciably, oxygen levels have changed. Now , do we have a "tire pressure expert" to step forward & debate the effects of more or less oxygen in a MC tire?
Click to expand...
Take your potshots, but also think a bit. Why it works has to do with operating temp of tire. Operating temp is what you are shooting for. In the desert of AZ you will get hot quicker and have to let air out. In the cold you will have to add air to get it up to operating temp. As the man said you already have 78% nitrogen in air, but that universal gas law really doesn't tell you a whole lot. It is under perfect conditions for a perfect gas.
 
PGlaves said:
Yes, moisture in a tire can theoretically add to pressure fluctuations. If the interior tire temperatures reach the point that water droplets are vaporized - something in excess of 212F - the steam can increase pressures more than simple heating of air. At the extreme, triple digit ambient temperatures and sustained Interstate speeds my rear tire gets to somewhere between 150 and 160F. No steam.

If concerned, put a drier on your compressor.
Click to expand...

This is from the nitrogen institute it is a direct quote

Fundamentally; air, oxygen and nitrogen will all behave exactly the same in terms of pressure change for each 10 degrees of temperature change. However temperature alone is not the whole story.

Ambient air contains moisture, nitrogen does not. If moisture is present it contributes to a greater change in pressure simply because at lower temperatures water condenses to become a liquid. The liquid form of water occupies very little volume and contributes only a negligible pressure to the tire. But at higher temperatures, such as those in a running tire, water evaporates inside the tire and becomes a gas which increases pressure in the tire.

Ambient air contains about 21% oxygen. Oxygen?s smaller molecular size allows it to permeate through the rubber of the tire. By inflating with nitrogen, which is much less permeable than oxygen, the pressure changes due to oxygen loss are greatly reduced.

The racing industry is correct; nitrogen is more predictable. Because nitrogen is dry it has no moisture to contribute extra pressure changes with temperature. Because nitrogen permeates out much slower than oxygen pressure changes due to that leakage are almost eliminated compared with ambient air.
 
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