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Setting Tire Pressure in Cold Weather

88bmwjeff

88bmwjeff

SF Bay Area
I took my bike in for service yesterday, and went out to the garage to make sure the tire pressure was good. It was about 35 F (2 C) and set my tire pressure to spec (36 front and 42 rear). While riding I checked tire pressure and the bike (2018 R1200 GS) indicated 40 front and 45 rear. I get that air expands when heated, but I thought that a rather large bump. Typically, the bike is within one psi of my gauge. My guess is that the increase is due to the air in the tires warming up. What do people normally do here? Is it best to be 1-2 psi low when checking when cold or just not worry about the increase?
 
BMW and most tire makers specify "cold" air pressure as at 20 degrees centrigrade. This is 68 degrees F. And, air pressure in a confined container changes by approximately one (1) p.s.i. per 10 degrees F. change.

So a "cold" tire at 36 p.s.i. at 70 F would be expected to be 37 p.s.i. at 80F. And conversely, pressure will decline as the tire is colder. So a tire with 36 p.s.i. at 70F would be at approximately 32 p.s.i. at 30F. All of these examples would be within spec.
 
Last I was aware, the "cold" tire pressure setting is when the vehicle hasn't been driven or at least sat for 3-4 hours.

I have never adjusted for a "speculated temperature", only what it was before the vehicle was driven.

OM
 
I’m not sure from your post the method you used to check cold pressure and warm pressure. Were both done using the same gauge, or both by the dash indicator, or a mix? If both by gauge, that’s a greater than normal pressure delta and I’d question the gauge. As for the dash indication—via TFT on my ‘18GS—I find it quite inaccurate even on 68 degree days when checked cold and again after some riding, so my only attention to that indicator is if it shows a significant drop in pressure on a ride. It’s strictly a deflation alerter to me.

Bottom line is to buy a quality gauge (they don’t have to be expensive) and use it consistently to set cold pressure.

Best,
DeVern
 
I understand some people nix this idea, but

Knowing it's 36/42 at 68F, and knowing it's 1# higher or lower per 10 degrees F as stated above-------- if it's 90F in the garage, I load to the tires to 38/44. If it's 50F in the garage, I set them to 34/40.

This is, of course, for cold tires [ not warmed up by riding ] that have sat for at least 3-4 hours.

Some mornings here it can be 70 in the morning and climb to 115F throughout the day. A difference of 4.5#'s pushing the tire pressures up to 40/46 if checked with a gauge.
 
Omega Man said:
Last I was aware, the "cold" tire pressure setting is when the vehicle hasn't been driven or at least sat for 3-4 hours.

OM
Click to expand...

So if the spec is 36 psi cold - does that mean that an unridden bike outside in Minneapolis at 35 degrees F and an unridden bike in Phoenix at 105 should both be at 36 psi? I don't think so.
 
PGlaves said:
So if the spec is 36 psi cold - does that mean that an unridden bike outside in Minneapolis at 35 degrees F and an unridden bike in Phoenix at 105 should both be at 36 psi? I don't think so.
Click to expand...

Pressure is adjusted to where the "tire" is geographically/environmentally located. If it was different, there would be a warning to readjust tire pressure before, during and after tire use.

19.5 tires on the motorhome will gain as much as 15psi from morning to mid afternoon (hot) temperatures. -90psi to 105psi for reference.

I think I have around 48 or so tires in the fleet. Never even thought of running any pressures different that "cold" or on something special, a variation of "cold".

Whatever works is good.

OM
 
The bike TPMS sensors adjust for temp. The bike display only comes close to gauge if you checked them at 68F with gauge. Covered on many forums and I think some manuals tell you to adjust tire pressure based on ambient temp when checked.
 
brownie0486 said:
I understand some people nix this idea, but

Knowing it's 36/42 at 68F, and knowing it's 1# higher or lower per 10 degrees F as stated above-------- if it's 90F in the garage, I load to the tires to 38/44. If it's 50F in the garage, I set them to 34/40.

This is, of course, for cold tires [ not warmed up by riding ] that have sat for at least 3-4 hours.

Some mornings here it can be 70 in the morning and climb to 115F throughout the day. A difference of 4.5#'s pushing the tire pressures up to 40/46 if checked with a gauge.
Click to expand...

Like you, I follow what the manual says. My 2011, 2016 and 2022 manuals state the tire pressure is compensated to 68 degrees.
When you compensate to 68 F my tire gauge matches what my dash readout shows.
If it's 40 F in my garage and my tire gauge shows 33 and 39 PSI it will show 36 and 42 on my dash.
Some people will tell you to follow the manual for oil specs but then they say the manual is wrong on how to check tire pressure on a BMW bike.
 
88bmwjeff said:
I took my bike in for service yesterday, and went out to the garage to make sure the tire pressure was good. It was about 35 F (2 C) and set my tire pressure to spec (36 front and 42 rear). While riding I checked tire pressure and the bike (2018 R1200 GS) indicated 40 front and 45 rear. I get that air expands when heated, but I thought that a rather large bump. Typically, the bike is within one psi of my gauge. My guess is that the increase is due to the air in the tires warming up. What do people normally do here? Is it best to be 1-2 psi low when checking when cold or just not worry about the increase?
Click to expand...

If you inflated to 36/42 at 35 F, the bike's computer is designed to display a temperature compensated value to 68 F (approx +3 psi) which is why yours showed 40/45. The manual on my '22 RT would want me to inflate to 33/39 using a gauge at 35 F.
 
As Paul has noted, setting the pressure in the tire for a standard cold temperature of 20 C or 68 F is correct. If it's hotter or colder than those temperatures, the tire pressure will be higher or lower. The concern may be that at colder temperatures, the tire will be underinflated, but keep in mind, cold rubber is much harder and higher pressure is not needed for the tire to be firm enough to do its job. The tire will warm up in use and the pressure will increase as well. Over inflating the tire when colder than the standard temperature will mean the tire will be overinflated still as it heats up in use or as outside temperature increases and possibly dangerously so in hotter conditions. This is likely why the TPMS is designed to compensate for temperature, it gives a more accurate indication of correct inflation rather than actual pressure.
 
I checked the cold tire pressure with a good gauge before I left. While riding was observed from the bike's menu. While a slight difference would be expected between the two with all things being equal, the higher temp was after riding when the tire and air had warmed up. As such, the majority of the increase would be due to the air expanding after warming up. It seems as though the best solution would be to lower the cold pressure a bit to compensate for the air expansion when warm on very cold mornings.
 
88bmwjeff said:
I checked the cold tire pressure with a good gauge before I left. While riding was observed from the bike's menu. While a slight difference would be expected between the two with all things being equal, the higher temp was after riding when the tire and air had warmed up. As such, the majority of the increase would be due to the air expanding after warming up. It seems as though the best solution would be to lower the cold pressure a bit to compensate for the air expansion when warm on very cold mornings.
Click to expand...

No, better to be more precise than "a bit". Calculate the air pressure for the temperature you are in and inflate or deflate to that temperature. I have a chart designed for the GS that shows the appropriate air pressure reading at a wide range of temperatures. I'll take a picture and post it once I make my way over to the shop.
 
88bmwjeff said:
I checked the cold tire pressure with a good gauge before I left. While riding was observed from the bike's menu. While a slight difference would be expected between the two with all things being equal, the higher temp was after riding when the tire and air had warmed up. As such, the majority of the increase would be due to the air expanding after warming up. It seems as though the best solution would be to lower the cold pressure a bit to compensate for the air expansion when warm on very cold mornings.
Click to expand...

As mentioned the TPMS on the BMW bikes are temperature compensated. The displayed pressure will always be the pressure compensated to 68 degrees. If you set them when it is cold out your tire gauge is probably not temp compensated so you over inflated them according to BMW. 42 at 35 degrees is going to be 45 at 65 degrees. If you want the TPMS to be happy and rad correct for 35 degrees you tire pressure should be set to 39psi. That will result in a compensated pressure of 42.
 
I used wish BMW would display a true PSI reading but this post has made me realize that BMW's engineers know better than I do. I never stopped to think about how often I'd be doing calculations in my head rather than just taking a glance of the TPM readout and enjoying the scenery. :clap

Tire Pressure by Temp.JPG
 
But what about altitude? What if I start off in Death Valley on a 35F morning and climb a range of 10,000 ft. mountains where its 85F and come down again to 40F weather? It's so confusing!

Yes, I'm being facetious.
 
BC1100S said:
But what about altitude? What if I start off in Death Valley on a 35F morning and climb a range of 10,000 ft. mountains where its 85F and come down again to 40F weather? It's so confusing!

Yes, I'm being facetious.
Click to expand...

Not so facetious…

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167

I’ve seen altitude changes of >7k feet in a day of riding and watched the change on the TPMS display. Mostly what the above article points out is the value in checking your tire pressures every day on a ride.

Best,
DeVern
 
Gernerally speaking you want about a 10% rise in temp from cold to hot (about 10-15 miles of riding).

My dad preached this to us kids back in the 70's as he was an engineer with Uniroyal.
 
GTRider said:
Not so facetious…

https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167

I’ve seen altitude changes of >7k feet in a day of riding and watched the change on the TPMS display. Mostly what the above article points out is the value in checking your tire pressures every day on a ride.

Best,
DeVern
Click to expand...

I like climbing the higher elevations in Colorado in the summer. Mt. Evans is 14,200 feet as an example but there's a dozen peaks over 12K feet to get up as well out there.

We leave my brothers house at 9K feet, setting the tires based on current temp and using the formula mentioned [ 1 psi for every 10F in temp change ]. A difference of 5K feet. Once set in the morning, I don't pay any attention to tire pressures.

We were caught in a hail/sleet freezing rain last June on Independence pass. When we started the trek up over the pass it was 75F or so, I saw 35F near the top of the pass. A difference of 40F in less than an hours time. I never looked at the computers tire pressure reading, never do after I set the tires in the morning according to the formula discussed.
 
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