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Tire pressure, two-up


Rex R

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the M.O.M. (motorcycle owner's manual) for my 16 RTW recommends 2.5/2.9 bar (36/42 psi) front and back. But (unlike previous bikes) it does not specify different pressure for the rear tire when riding two-up.

 

Did I miss something? Do I have to re-read it? Or does BMW not recommend adjusting the pressure when adding a passenger and luggage?

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realshelby

That is the only pressure recommendation they offer. Most rear tires have a maximum cold inflation pressure of 42 or 44 psi so there is no way to add for a passenger.

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Checked twice in owners manual and in the OEM service manual (dvd). Yup one pressure setting regardless of load. I used to run solo+ gear pressure as the minimum pressure on my '99RT (Metzler) when I first had the bike, because the sidewalls felt too squirmy, but in last several generations of tires from Metzler and now Michelin PR4-GT on my '15 RT that didn't seem to be a problem. I even tried 34 front and 38 rear on my '15 RT and it seemed fine for lack squirminess but did not seem to offer any better grip either wet or dry, so I went back to OEM settings.

 

The good news is that they have relieved one more of my geeked out delays before a ride to reset tire pressure when my wife out of the blue says let's go for a ride.

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Adjust the rear shock?

I think there is a range that the bike is prepared to handle, in theory.

I used to adjust my Wilbers for one up or two up.

Took 15 seconds or less...

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Checked twice in owners manual and in the OEM service manual (dvd). Yup one pressure setting regardless of load. I used to run solo+ gear pressure as the minimum pressure on my '99RT (Metzler) when I first had the bike, because the sidewalls felt too squirmy, but in last several generations of tires from Metzler and now Michelin PR4-GT on my '15 RT that didn't seem to be a problem. I even tried 34 front and 38 rear on my '15 RT and it seemed fine for lack squirminess but did not seem to offer any better grip either wet or dry, so I went back to OEM settings.

 

The good news is that they have relieved one more of my geeked out delays before a ride to reset tire pressure when my wife out of the blue says let's go for a ride.

 

On the wet heads, mine at least, you can adjust the spring preload for rider-only, rider-plus-luggage, or rider-plus-pillion with a button on the right handgrip.

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old_farmer

I kind of had the same reaction about the lack of variance on the pressure recommendation. I used to run about 42 on the rear of my 1100, but after the Z8 hit cords in the center way too soon, I dropped the pressure down closer to BMW recommendations.

 

I'm running my new wethead at the recommended 36 front, 42 rear per the manual, even though I run solo and am a little guy. Guess I'll see how that works out.

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My dealer said 45 and 40 to prevent cupping. 45 was too hard for me so I now run 43 in the rear and 40 in the front. It handles really well at those pressures and the ride is still good with suspension set to normal-road. I ride single all the time too.

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My dealer said 45 and 40 to prevent cupping. 45 was too hard for me so I now run 43 in the rear and 40 in the front. It handles really well at those pressures and the ride is still good with suspension set to normal-road. I ride single all the time too.

 

Can't see why a dealer would recommend a tire pressure 9 PSI higher than what the manufacturer recommends. When you say dealer, was it a tech, service advisor, service manager who suggested this?

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Tire Pressure is a mysterious thing on My Wethead '14.

 

I can set the TP before a ride (using a professional compressor and gauge to 42/38. Of course the T.P. indicator on the dash shows it as 38/36 or so... I always thought that was because the tires were cold- but no... they do not seem to change the displayed pressures even after being fully warmed.

 

There have been articles about the transmitters inside the new tire stems requiring being calibrated but still. I don't really care to have dashboard indicators I cannot trust.

 

So there.

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Tire Pressure is a mysterious thing on My Wethead '14.

 

I can set the TP before a ride (using a professional compressor and gauge to 42/38. Of course the T.P. indicator on the dash shows it as 38/36 or so... I always thought that was because the tires were cold- but no... they do not seem to change the displayed pressures even after being fully warmed.

 

There have been articles about the transmitters inside the new tire stems requiring being calibrated but still. I don't really care to have dashboard indicators I cannot trust.

 

So there.

 

Interesting. My '15 RT TP display shows spot on for the rear and -1 psi for the front VS my known to be accurate hand gauge. Could be the sending units have a bit of variance and it is luck of the draw on how close to actual pressure. I guess it does not matter once you know the variance from true and besides I use the display psi to watch for a slow leaks during a ride and not to set my tire pressure.

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Tire Pressure is a mysterious thing on My Wethead '14.

 

I can set the TP before a ride (using a professional compressor and gauge to 42/38. Of course the T.P. indicator on the dash shows it as 38/36 or so... I always thought that was because the tires were cold- but no... they do not seem to change the displayed pressures even after being fully warmed.

 

There have been articles about the transmitters inside the new tire stems requiring being calibrated but still. I don't really care to have dashboard indicators I cannot trust.

 

So there.

 

Morning Hopz

 

Just keep I'm mind that the tire pressures shown are temperature compensated (within reason but not perfect) to about 68°f. Once ridden if you use a tire pressure gauge you should find the actual tire pressures considerably higher than shown on the dash due to the temperature compensation offset.

 

Look in your riders manual around page 119 or so (look for RDC) as that should sort of explain the temperature compensation reading.

 

This chart should give you some idea of what you see vs what you actually have__

 

Tire pressure vs temp chart

 

Edited by dirtrider
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Tallman & Green RT

 

Think we're only talking tire pressure here....

Don't get me started on suspension settings with all the adjustments for spring rate, sag, & damping settings as I get geek squared on that stuff :smile:

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I'm with you on trusting the TP monitor. However, if you take a look at the owners manual it explains how to "figure" the tire pressure based on temperature , etc. Not something I want to do when riding. Don't think there's anything wrong wth the sensors. I remember getting my bike in November and riding throughout the winter the TP sensors showed very high pressures but when I checked the actual tire pressure it was about where I wanted. I think when the outside temp hits 60 or above it reads pretty true....

 

John

 

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realshelby

While the factory may have meant well by using temperature compensated tire pressure monitoring, I wish they had just left them to show the "actual" pressure. I know the pressures go up when the tire is at operating temperature. I know the tire pressure may be higher when it is 95 outside and I measured pressure at 75 in my garage. Even at my age I can understand and compute the changes and tell if that is OK. But with this temperature compensated version, I don't really feel like it is telling me what I want to know. If I feel something a bit off I can check pressure to tell me that it is not a tire going down with this system. But to tell me I need to add 1 lb of pressure it does not do so well.

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While the factory may have meant well by using temperature compensated tire pressure monitoring, I wish they had just left them to show the "actual" pressure. I know the pressures go up when the tire is at operating temperature. I know the tire pressure may be higher when it is 95 outside and I measured pressure at 75 in my garage. Even at my age I can understand and compute the changes and tell if that is OK. But with this temperature compensated version, I don't really feel like it is telling me what I want to know. If I feel something a bit off I can check pressure to tell me that it is not a tire going down with this system. But to tell me I need to add 1 lb of pressure it does not do so well.

 

Afternoon Terry

 

But you aren't most riders. Most riders don't know tire temperatures vs pressures, or even how hot their tires operate.

 

Uncompensated, just having a bike sit out in the sun at 68° could show the tire pressure at 4 or 5 pounds high so the rider could let some air out thinking they are set too high.

 

As for the 1 pound thing-- most TPS systems are not that accurate as the driver or rider just doesn't know the tire temperature unless the vehicle is in the shade at 68°f & hasn't been ridden for a while.

 

At least the compensated systems s-h-o-u-l-d always read correctly no matter the tire temperature so assuming the compensation is accurate, if you put in 42 psi @ 68°f, then the at any time see 41 psi on the dash the tire would be 1 psi low. (unfortunately most are not 1 psi accurate)

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That section of the owner's manual confused me. Maybe Dirtrider or another member can clarify it for me.

 

I always understood recommended tire pressure this way:

The manufacturer recommends checking and adjusting the pressure when "cold". Cold is defined as not heated due to the friction created when driving/riding. Cold is also defined as the ambient air temperature at which the tire will be used.

 

General knowledge of physics also tells us that in a closed container (like a sealed tire), with a constant external pressure (at sea level or any constant elevation), a give volume of air (or any gas) will contract and create lower pressure as temps drop and expand and increase pressure as temp rises.

 

Therefore, if you set the pressure at 5am before a trip, when the bike has been sitting in your driveway overnight, and air temp rises 15 degrees by 9am and 30 degrees by noon, assuming no leaks in your tire/valve/etc. and no other confounding variables, you are probably riding over-inflated. Checking your tires at a fuel/bathroom/meal stop is futile because friction from riding precludes an accurate reading at that time.

 

Conversely, if you set the pressure in your heated garage before a winter ride when ambient temperature is 20 degrees lower than your garage, you are most likely under-inflated.

 

So if the BMW engineers use a formula to adjust actual tire pressure to what it WOULD be IF ambient temperature were 68 deg fahrenheit, does that REALLY tell me if I am properly inflated for my riding conditions?

 

 

 

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realshelby

DR, you are probably right.

 

I guess it does what it is designed to do, meaning it will alert you to a tire going down or one where pressure has creeped down below safe levels from not being properly monitored. I check my tires often with a decent tire gauge so that is not a concern for me.

 

Sort of like the oil level check built into the RT. I had it read "CHECK" twice on this last trip. Pulled over both times and it was just fine. Sometimes you get no reading, others "OK". Meaning it is pretty much worthless.......

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That section of the owner's manual confused me. Maybe Dirtrider or another member can clarify it for me.

 

I always understood recommended tire pressure this way:

The manufacturer recommends checking and adjusting the pressure when "cold". Cold is defined as not heated due to the friction created when driving/riding. Cold is also defined as the ambient air temperature at which the tire will be used.

 

General knowledge of physics also tells us that in a closed container (like a sealed tire), with a constant external pressure (at sea level or any constant elevation), a give volume of air (or any gas) will contract and create lower pressure as temps drop and expand and increase pressure as temp rises.

 

Therefore, if you set the pressure at 5am before a trip, when the bike has been sitting in your driveway overnight, and air temp rises 15 degrees by 9am and 30 degrees by noon, assuming no leaks in your tire/valve/etc. and no other confounding variables, you are probably riding over-inflated. Checking your tires at a fuel/bathroom/meal stop is futile because friction from riding precludes an accurate reading at that time.

 

Conversely, if you set the pressure in your heated garage before a winter ride when ambient temperature is 20 degrees lower than your garage, you are most likely under-inflated.

 

So if the BMW engineers use a formula to adjust actual tire pressure to what it WOULD be IF ambient temperature were 68 deg fahrenheit, does that REALLY tell me if I am properly inflated for my riding conditions?

 

 

 

That's how I interpret the TPMS on my GSA. Essentially the manual says to compare the TPMS pressure on the display to the recommended tire pressure in the manual. My manual recommends 42 PSI for the rear tire on my bike. If I see that TPMS says I'm at 40 PSI, I know that I should add 2 PSI (assuming I choose to add air). To my mind, that's a lot easier than trying to figure out what my tire pressure should read -- using a gauge -- at an ambient temperature that's not 20C/68F.

 

Just last week, at the UnRally, I also experienced another benefit of TPMS. I had just left a rest stop, and after about ¼ mile, my Nav VI displayed a yellow warning triangle (something I'd never seen), and when I looked at the dash, the tires pressures were flashing on the bike's display. My rear tire showed 30 PSI (and I had just added air the night before to bring it up to 42 PSI). Yup, I had a puncture, and was warned about it very soon after hitting the road. I plugged the tire, with the help of Bernie, and Bob (actually, all I did was operate the air pump. :grin:).

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Afternoon Rex R

 

I always understood recommended tire pressure this way:

The manufacturer recommends checking and adjusting the pressure when "cold". Cold is defined as not heated due to the friction created when driving/riding. Cold is also defined as the ambient air temperature at which the tire will be used. -- As far as most manufactures are concerned COLD is defined as 20°c (68°f)-- at least that is the nominal temp they use during development tire testing. BUT (big but here) they also don't assume that the average rider or driver will only set/or/check at 68°f so the recommended cold tire pressures have some wiggle room. But same can be said for recommended tire pressures. If the BMW recommended tire inflation pressure is 42 psi cold then the ideal (desired) cold tire pressure is probably around 40-41 psi as most manufactures don't expect a rider or driver to set tire pressures before every ride or drive so they assume a slightly low tire will be used at some time before the next check.

 

General knowledge of physics also tells us that in a closed container (like a sealed tire), with a constant external pressure (at sea level or any constant elevation), a give volume of air (or any gas) will contract and create lower pressure as temps drop and expand and increase pressure as temp rises. --yes, the universal gas law.

 

Therefore, if you set the pressure at 5am before a trip, when the bike has been sitting in your driveway overnight, and air temp rises 15 degrees by 9am and 30 degrees by noon, assuming no leaks in your tire/valve/etc. and no other confounding variables, you are probably riding over-inflated. Checking your tires at a fuel/bathroom/meal stop is futile because friction from riding precludes an accurate reading at that time.-- That is why the "set tire pressure cold" is the usual advise. Even if the ambient temps are the same just having the bike out in the sun can heat the black tires enough to change internal pressures (again that is why the 20°c is used as the nominal cold setting). If the tires are not at 20°c (68°f) then see my posted tire temp vs pressure cart in a couple of posts above.

 

Conversely, if you set the pressure in your heated garage before a winter ride when ambient temperature is 20 degrees lower than your garage, you are most likely under-inflated.--NO, that is unless the garage is heated to well above 20°c. If you set your tire pressures at 20°c (68°f) then they will ALWAYS be correct no matter the ambient temp or heated tire riding temps (this is also why the compensated dash reading is probably the best for MOST riders as it is based on the 20°c (68°f) starting point. If the compensated system was totally accurate it would be perfect (as long as you don't significantly change riding altitudes)--& even then with internal pressure transducers the compensated TPS system will probably be pretty close.

 

So if the BMW engineers use a formula to adjust actual tire pressure to what it WOULD be IF ambient temperature were 68 deg fahrenheit, does that REALLY tell me if I am properly inflated for my riding conditions? Yes, Well yes for the normal riding conditions anyhow. If it was like 40°f below zero then you might be starting your ride on a somewhat flat tire so if riding at 40° below you might want to start out with a little more air in your tires. (as usual, common sense trumps written directions)

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That's how I interpret the TPMS on my GSA. Essentially the manual says to compare the TPMS pressure on the display to the recommended tire pressure in the manual. My manual recommends 42 PSI for the rear tire on my bike. If I see that TPMS says I'm at 40 PSI, I know that I should add 2 PSI (assuming I choose to add air). To my mind, that's a lot easier than trying to figure out what my tire pressure should read -- using a gauge -- at an ambient temperature that's not 20C/68F.

 

Just last week, at the UnRally, I also experienced another benefit of TPMS. I had just left a rest stop, and after about ¼ mile, my Nav VI displayed a yellow warning triangle (something I'd never seen), and when I looked at the dash, the tires pressures were flashing on the bike's display. My rear tire showed 30 PSI (and I had just added air the night before to bring it up to 42 PSI). Yup, I had a puncture, and was warned about it very soon after hitting the road. I plugged the tire, with the help of Bernie, and Bob (actually, all I did was operate the air pump. :grin:).

 

 

ONE of the things that confuses me in the TPMS section of the owner's manual, it that it seems to be saying that instead of adjusting pressure to 36/42 at ambient air temperature (like I always believed to be the correct method) we should have always calculated the necessary increase or decrease so it WOULD be 36/42 at 68 deg fahr.

 

Did I phrase that well? Does that question make sense?

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Sort of like the oil level check built into the RT. I had it read "CHECK" twice on this last trip. Pulled over both times and it was just fine. Sometimes you get no reading, others "OK". Meaning it is pretty much worthless.......

 

Afternoon Terry

 

The ---- no reading is pretty normal as it probably wasn't at idle sitting still, or wasn't hot enough yet, or not ridden far enough yet. (this I wouldn't worry about)

 

The CHECK reading is a bit troublesome, you might want to check with your BMW dealer to see if they have a bulletin on this. The early hexheads had the same erroneous CHECK reading so BMW came out with a revised & updated oil level sensor & float assembly.

 

You also need to be sure that the bike is standing level at time of reading-- I get an occasional CHECK on my GS if I am sitting on a side hill with the bike idling & the bike is leaning.

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ONE of the things that confuses me in the TPMS section of the owner's manual, it that it seems to be saying that instead of adjusting pressure to 36/42 at ambient air temperature (like I always believed to be the correct method) we should have always calculated the necessary increase or decrease so it WOULD be 36/42 at 68 deg fahr.

 

Did I phrase that well? Does that question make sense?

 

Afternoon Rex

 

The absolute correct way is always figure the cold setting pressure back to 68°f. But, as I said above the MoCo's also assume the most riders/drivers won't (or aren't capable of) really doing that so for most applications just overnight cold is close enough.

 

If a rider used the (current) ambient cold as a base setting point then there are conditions that could bite them. lets say your manual said to use 42 psi cold-- Its a hot night in Arazona so in the morning you set cold tire pressures to 42 psi (your carport where the cold bike is at is 100°f). Now you ride up into the mountains & the morning temps are 30°f (the tires are now around 9 pounds low for the cold conditions at next morning ride off) .

 

If you figure back to 68°f then the pressures would be closer to nominal for the entire ride. Plus your dash readout should then read correct for the trip.

 

The company that I work for resisted for many years using a different front & rear tire pressure on cars as the thought was that most car drivers wouldn't do it correctly. Then they started to use different front/rear tire pressures on the performance vehicles figuring that performance car derivers would be more capable. The part I never understood is that during that same time period some light trucks not only used different front/rear pressures but also different pressures depending on the load carried.

 

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Afternoon Rex

 

The absolute correct way is always figure the cold setting pressure back to 68°f. But, as I said above the MoCo's also assume the most riders/drivers won't (or aren't capable of) really doing that so for most applications just overnight cold is close enough.

 

If a rider used the (current) ambient cold as a base setting point then there are conditions that could bite them. lets say your manual said to use 42 psi cold-- Its a hot night in Arazona so in the morning you set cold tire pressures to 42 psi (your carport where the cold bike is at is 100°f). Now you ride up into the mountains & the morning temps are 30°f (the tires are now around 9 pounds low for the cold conditions at next morning ride off) .

 

If you figure back to 68°f then the pressures would be closer to nominal for the entire ride. Plus your dash readout should then read correct for the trip.

Guess I've been doing it wrong for decades! :old:

 

 

The company that I work for resisted for many years using a different front & rear tire pressure on cars as the thought was that most car drivers wouldn't do it correctly. Then they started to use different front/rear tire pressures on the performance vehicles figuring that performance car derivers would be more capable. The part I never understood is that during that same time period some light trucks not only used different front/rear pressures but also different pressures depending on the load carried.

Unfortunately, they were probably right. Most people can't check their own fluids, belts... or air pressure. Sad. It reminds me of a few stand-up bits:

 

I think this one was George Carlin: Think about how stupid the average person is, and then remember that 1/2 of the population is stupider than THAT!

The New York attitude in a nutshell says: Everyone is an asshole... But me!

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Tallman & Green RT

 

Think we're only talking tire pressure here....

Don't get me started on suspension settings with all the adjustments for spring rate, sag, & damping settings as I get geek squared on that stuff :smile:

 

Yes, but, he can do both.

We ran 40/42 solo and 2 up.

No issues, temperature/elevation/load/wear variation.

The remote Wilbers adjustment was simple, so tire pressue eliminated as they build the tires to

carry the "load", whatever it is, IMO.

 

 

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