? Tire pressure??

[joeb]

When reading about what people use for tire pressures the statement is often made that they pretty much use the vehicle manufacturers recommendations.

Got me wondering, since the manufacturers have no idea what type of tire is on the wheel, wouldnt the tire manufacturers know best which pressures compliment the specific construction of their unique tire ??

Just wondering.  

[dirtrider]

2 hours ago, joeb said:

When reading about what people use for tire pressures the statement is often made that they pretty much use the vehicle manufacturers recommendations.

Got me wondering, since the manufacturers have no idea what type of tire is on the wheel, wouldnt the tire manufacturers know best which pressures compliment the specific construction of their unique tire ??

Just wondering.  

 

Afternoon Joeb

 

BMW does have an idea of what tire is on the rim (IF) the rider follows BMW recommendations on replacement tires as BMW only tests certain tires on each motorcycle so those are the only ones that they recommend. Both BMW & your BMW dealer should have this info available.

 

It is kind of a gray area as BMW tests certain tires on each motorcycle type  so those are a known as far as performance, handling, & safety goes (BMW also recommends the tire pressures for those tires based on THEIR testing).

 

On the other hand the tire manufactures do not test each of their offerings on each motorcycle that they will fit (most of their tire testing is done on stationary machines) so about all you get from the tire manufacture is a generic safe-to-run tire pressure for the suggested tire loading & tire position. Usually tire manufactures suggested tire pressures are on the high side as they have no idea of what bike they will used on so they default to a generic safe but high suggestion.

 

Vehicle tire pressure recommendations are a mix of lean to the safety side, lean to the possibility of inadvertent overloading, high enough  to include varied ambient temperatures  during operation (you almost never see a tire pressure sticker on a vehicle giving a different check/set pressure for higher altitude,  or a different check/set pressure based on ambient temperatures at checking/filling time). So the assumption is that some drivers/riders will fill tires at 80°f (cold tire) then drive/ride the next morning at 40°f (that's a 4 psi difference right there).

 

The BMW motorcycle TPMS system compensates the (dash readout)  tire pressure reading to somewhere between 68°-72°f so what a riders sees on the dash readout is not actual tire pressure but is what the pressure would be if the tire was at a nominal 68°-72°f.

 

The tire manufactures & motorcycle manufactures also need to figure in a slight safety fudge factor as the assumption is that NO ONE checks and/or sets their tire pressures before each & every usage (just doesn't happen). So if a suggested cold tire pressure of 32psi is recommended then that tire better be safe to run at 30 psi as that is where a lot will end up before the next pressure check.   

 

I don't know what the motorcycle tire safety load factor is  but most passenger automobiles are safe at  10% over tire's rated load (they are tested at least 10% over load rating) & most light trucks have a 25% over tire's rated load (they are tested at least 25% over rated load capacity).

 

 

[joeb]

Makes sense. Seems like a lot of thought goes into little placards.  While talking with some of the instructors at the Road America  track day the issue of suspension set up was discused. The consensus was, if in doubt dont vary too far from the manufacturers settings. I think i have a little more appreciation for the engineers  and builders of these machines.Thanks for the info.

[Selden]

Rule of thumb (good enough daily riding, if not the track) : With full riding gear,  30% rider sag to rear and 20 to 25% to the front (if adjustable). My RT has Öhlins shocks, so I turned the preload rings on the rear shock to get the desired sag with the remote hydraulic preload adjuster knob at zero turns. This is the base setting; add turns as needed for luggage, passenger, individual weight gain, etc. Ideally, you need three people to do this properly: rider, stabilizer, and measurer. This can be reduced to two people if you rig up a measuring stick and a felt tip marker to record rear suspension travel. 

 

Long version: http://blog.touratech-usa.com/2013/08/06/how-to-setting-suspension-sag/

 

 

[Lowndes]

NOT to detract from what has been stated above, just to add my observations on tire pressures:

 

After installing an aftermarket TPMS on my bike and watching the real-time pressures while riding in all kinds of conditions for a year or so, the pressures vary considerably (5 or more PSIG) all day.  This is due to ambient temp rise and fall, tire heating from riding, rain, even sunlight on the tire, so what we are talking about is an AVERAGE or ACCEPTABLE RANGE of pressures while riding.  I've not encountered anyone who adjusts their tire pressures during the day or on a ride, I don't but I'm a novice.

 

The "suspension gurus" (i.e, Dave Moss) explain "reading the tread", or closely inspecting the tread to find out (among other things) if the tire pressure is correct for the conditions to maximize tread life, traction, and handling.  This is usually for the track where conditions are much more controlled (elevation, road surface, speed, etc), but would have applications for street riding as well.

 

Bottom line for me is the TPMS is an easy morning pressure check and an item of interest while riding.  It has already saved my butt when I picked up a tiny nail in the front tire and it lost a lot of pressure while eating lunch two weeks ago in the mountains of N GA.  I'm just not anal about "EXACTLY 42 psi" because it will NOT be that pressure for long.

[dirtrider]

24 minutes ago, Lowndes said:

NOT to detract from what has been stated above, just to add my observations on tire pressures:

 

After installing an aftermarket TPMS on my bike and watching the real-time pressures while riding in all kinds of conditions for a year or so, the pressures vary considerably (5 or more PSIG) all day.  This is due to ambient temp rise and fall, tire heating from riding, rain, even sunlight on the tire, so what we are talking about is an AVERAGE or ACCEPTABLE RANGE of pressures while riding.  I've not encountered anyone who adjusts their tire pressures during the day or on a ride, I don't but I'm a novice.

 

The "suspension gurus" (i.e, Dave Moss) explain "reading the tread", or closely inspecting the tread to find out (among other things) if the tire pressure is correct for the conditions to maximize tread life, traction, and handling.  This is usually for the track where conditions are much more controlled (elevation, road surface, speed, etc), but would have applications for street riding as well.

 

Bottom line for me is the TPMS is an easy morning pressure check and an item of interest while riding.  It has already saved my butt when I picked up a tiny nail in the front tire and it lost a lot of pressure while eating lunch two weeks ago in the mountains of N GA.  I'm just not anal about EXACTLY 42 psi because it will NOT be that pressure for long.

 

 

Morning  Lowndes

 

A rider is not supposed to adjust their tire pressure during operation.

 

BMW's suggested tire pressures are for a COLD tire (ie before riding on it). The cold nominal tire temperature that BMW uses is 20°c  (68°f) but that doesn't have to be exact as all BMW says is to check/set on cold tires.    

 

If you want to be closest to ideal (BMW ideal spec) then set the tire pressure cold but using 68°f as a nominal. Then using the general accepted offset of 1psi change per 10°f .

 

So if your motorcycle/ tire has sat unused overnight & the ambient temperature has been around 78°f for a while then set the tire pressure to +1 psi from the desired spec.  (if you want 42 psi & the ambient/tire temp is 78°f then set tire pressure to 43 psi).

[6speedTi]

Out of curiosity is the temperature compensation feature directly outputted from the sensor or from another source via onboard computers? Can this feature some how be manipulated or turned off so you can read actual tire pressures without temperature compensation? There is so much hype about how BMW's TPMS works and the biggest confusion is the temperature compensation input. So much for the KISS method of days ago.

[Michaelr11]

20 minutes ago, 6speedTi said:

Out of curiosity is the temperature compensation feature directly outputted from the sensor or from another source via onboard computers? Can this feature some how be manipulated or turned off so you can read actual tire pressures without temperature compensation?    .................

 

This depends on the particular TPMS system.  My aftermarket TPMS shows the actual pressure of the tires. I set the alarms for high and low pressure for the actual pressure in the tire, not temperature compensated.  The BMW TPMS system apparently adjusts the pressure displayed to adjust for temperatures. So if you set your tire at 40 PSI, the display should remain at 40 PSI throughout the ride unless something occurs to alter the tire pressure (leak). I have no problems adjusting (in my head) my display PSI for the conditions I ride. If I start out at 40, I expect the display to end up at 44-45 PSI during the ride.  If it's cold in the morning I'm okay if the tire starts out at 38 or 39.

[dirtrider]

1 hour ago, 6speedTi said:

Out of curiosity is the temperature compensation feature directly outputted from the sensor or from another source via onboard computers? Can this feature some how be manipulated or turned off so you can read actual tire pressures without temperature compensation? There is so much hype about how BMW's TPMS works and the biggest confusion is the temperature compensation input. So much for the KISS method of days ago.

 

 

Afternoon  6speedTi   

 

That's a good question, I don't know for sure but an educated guess on my part would be it is the actual wheel sensors doing the conversion before signal output  as THEY are the only part of the TPMS system that knows the tire's internal temperature.  

 

There shouldn't any hype on how the  BMW TPMS system works  as it is spelled out in the riders manual. Not in detail but in function)

 

A number of automobiles also have the temperature compensation feature on their factory TMPS systems. They basically market it as a consumer useful feature but in reality it is more for the law mandated low tire warning system operation.  

 

Without temperature compensation the low tire pressure warning system could/would indicate a low tire if a tire was filled in a warm area then the   vehicle is driven to a very cold area & parked.

Or just the opposite, a  tire could be  low on air pressure but it wouldn't trigger the dash  low pressure warning if the vehicle was driven with heated tires in a warm ambient area.    

[Paul De]

I played around with tire pressure but came back to the BMW 36 and 42 settings for the PR4GTs that came on my '15RT.    I do run higher tire pressures from the solo settings listed for my '99RT, running  36 & 39 psi (currently running Metzlers Z8s). I set tire pressure after sitting overnight before pulling the bike out of the garage.

 

I check/set my pressure with a known accurate pressure analog dial gauge kept in my garage (verified it VS a certified gauge from 30  to 60 PSI) about twice a month.  I have a small slime digital gauge I keep on the bike that I've cross referenced to the dial gauge.  Interestingly enough the $8 slime gauge is pretty near spot on reading only 0.5 to 1 psi low.  When ambient temp has been in the 68 to 72 F range and I set the pressure with my dial gauge, I find TPMS units on my '15RT read spot on for the rear and -1 psi low for the front.  I leave my dash monitor set to show tire pressure all the time, but am unconcerned with the specific PSI value and use it to monitor for slow leaks between setting pressures with my own gauges.  I never assume the pressure set by the dealer after service or tire change is correct (some of those shop gauges get bashed around pretty hard).  I never use a borrowed pencil gauge at the gas station.