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tire pressures too high when hot ???

5K views 44 replies 27 participants last post by  Sparky57 
#1 ·
I recently installed a FOBO air monitoring system on my 2006 gl1800 and am running a new e3 rear tire, I put in exactly 41psi as the cold temp psi in the am as stated on the sidewall (I am 250lbs and do carry a lot in the saddlebags) but as I was riding in the high 80temps and riding aggressively, the FOBO kept alarming that the psi was too high. it kept climbing up to 51 psi my question is, is this normal for the pressure to raise that much, or do I need to lower the cold psi a little? also if that is normal to raise that high I will just raise the high psi warning range, but how high is still safe. I always had my psi set at the cold psi as stated on the tires but since installing the FOBO and now the alarms going off I am wondering if I'm just worrying for no reason as when I didn't have the monitor it probably always rose that high and never had a problem just didn't know what the pressures were before. but would really like to know how high can the pressure raise while hot and riding for long distances (and still be in safe range) as I am getting ready for a long distance ride.
 
#2 · (Edited)
That thing is going to drive you crazy.

Check your tires "cold" and be done with it.

For the past 10+ years we have run 42 PSI front and 44 PSI rear (cold) from 15 degrees to 100+ degrees. A front goes approx 18K and we get 12K from a rear tire.

The manufacturer has a recommended "cold" tire pressure, based on all of the expected operating conditions.

Ride more, worry less.
 
#3 ·
This doesn'tsound correct, as "rule of thumb", 10 ° F there is only 1 PSI change. You stated you indicated approximatelya PSI increase of 10 PSI (51). That would mean your tire/air raised 100°F. From your figures your tires/reached 180°F. That would be very hot for them. I would suggest youcheck the calibration setting of your FOBO units or at very least double checkit with a good manual tire gage. Something just doesn’t seem right


If you had Honda TPM, a pressureof 51 PSI and above is I believe where the units rest themselves.
 
#4 ·
By the way, you should know that the heat generated that raises the internal pressure as you're riding comes from the sidewalls flexing as the tire rolls. Lowering the pressure would result in more flexing, thus more heat generated. Try raising the tires a couple of psi and see where the hot pressure goes.
 
#5 ·
You most definitely don't want to lower the cold pressure. That would make the tire run even hotter. Lower pressure = more heat as the tire runs. Higher pressure = less heat as the tire runs. Justa Poster states that he runs 44psi which would probably be a good pressure for the weight you carry as well. The pressure on the sidewall can be varied within reason according to the load on the tire.
 
#6 ·
........or put 100% nitrogen in your tires, rather than the 78% nitrogen mix you are now running, and see where the hot running pressure ends up. I have heard that the hot/cold tire pressure swing is less when running 100% nitrogen, but I still run the 78% mixture in all my tires due to it's far greater accessability.
 
#7 ·
Tire manufacturers have taken in all standard air temps, tire construction, etc. in their recommended max cold tire pressure. If they suggest 41, then use that and don't worry about the high end; the tire was made to withstand those conditions.

DO NOT OVERINFLATE A TIRE! THERE IS A MAXIMUM COLD PRESSURE FOR A REASON.

Most tires overheat because of low inflation which increases sidewall flex particularly on a radial tire. The outside air temperature is only a small part of the equation contributing to internal tire pressure.
 
#8 ·
This has been a concern of mine for quite a while:

Recently, I took off in a 52deg. place to end up in a high 90s later that day.

Considering there is a variance of appx 45 deg Temp, it does not make sense that the original 41PSI i put in the tire in the am when the temp was 52 would be a correct setting when now, the tire is hotter from rolling at 80mph, and the temp is 96deg...

I once checked the temp on a GT while crossing the desert and the gauge showed 56PSI...Mercy!...it scared me sheetless and lowered the pressure before I continue.

I have never been able to get a manufacturer or a scientific document that would resolve this dilemma.

A lot of folk have stated their anecdotal experience; and I follow the suggestions of the 'more-experienced'...however, I have never seen good empirical data analysis on these temp/psi dynamics on a motto tire.
 
#9 ·
thanks everyone and yes I will keep the cold psi at 41 as printed on sidewall and worry less the fobo supposedly also records the temp and I believe it went up to approx. 104 degrees and psi went to 51 doing an average of 80mph for about 70 miles it was just when the fobo began alarming when it hit 51psi that I got really worried but I'm sure that's no where near max hot psi that it can handle
 
#12 ·
You need to account for the increase in ambient air temp. If the temps from the AM when you checked the tires to the afternoon is a 20-30F increase, then that is 2-3 lbs of pressure just from the air temp increase and not necessarily from you riding. I try and set my tire pressures with that in mind and certainly when calculating appropriate pressure increase during the day. Wait until you start the day at 8500 feet at 32F in the morning and head for 4000 feet and 90F in the afternoon. :surprise:
 
#13 ·
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#14 ·
Would also be good to note when setting the cold tire pressure it is with an ambient air temperature of approximately 65 degrees. If setting tire pressure when air temp is 25 degrees or 105 degrees would need to set pressure about 4 lb lower or 4 lb higher depending on air temp.
 
#17 ·
I love these threads. First thing is, I learn a lot. Second thing is, I learn how much misinformation there is floating around. Third thing is, I am reminded that we have TMI.....which causes us to react as though it means more today then it did 20 yrs ago when most of us didn't have it......just because we have it does not mean we need to do anything with it.
Now I'm going back to enjoy a good oil thread or the oil filter thread or maybe a squabble over belly pans.
 
#18 ·
At first I had high pressure alarms going off all the time with the FOBO as well. I believe their base percentage for a high pressure warning is set rather on the conservative side. I raised the settings for high pressure alarms and quit worrying about it. I do run DS though. >:)

E3's has the highest load rating for a MC tire for this bike. Set your cold tire pressure at/for 70 degrees and enjoy your ride.
 
#19 ·
I was a ds too (will be again soon) but needed a new tire and was given a brand new e3 for the ride home and reset the fobo for that tire but the high alarm kept going off on the ride home figured fobo had high setting set to low for that tire/bike/load lol
 
#21 ·
My rear will run 51-52 psi when hot. I would consider it normal. 1 psi per 10 degrees don't hold water.

If anyone cares my front only runs about 46-48.

Both front and rear 41psi.

Nothing to worry about in my opinion. That is all!


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#23 ·
If your tire pressure sensor isn't INSIDE the tire and you also read temperature, the temperature reading isn't even correct. Mine are inside the tire... the 10 degree increase 1 lb increase is incredibly close. As close as the accuracy of the sensors. It isn't uncommon for the rear tire on my RF Alpin to increase 6-8 lbs. have never had it increase 10 lbs though. If your pressure increases 10 lbs, you can be pretty certain the temperature inside the tire has increased about 100 degrees
 
#25 · (Edited)
Well my sensor temp is dead on ambient temp when sitting in the garage and the pressure agrees with other gauges as well. If it's right sitting in the garage, it's right running down the road.

The measured increase is about 40 degrees on the rear and 20 on the front...

The low 50's number is a good number for the rear. Other bikes with internal sensors [Indian Chieftan] report the same numbers...

Curious what you see for rear temps? Mine will hit the 50psi mark at about 110 degrees. The hottest I've seen is about 120 on 85+ degree days. The 120 can't be anything but the inside temp.

********
After all that, I see that you are talking about a car tire. We are comparing apples to oranges at this point. My truck tire pressures don't increase near as much as the MC tires. And probably fit the 1psi per 10 degree formula better.
**********


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#24 · (Edited)
Your post has had me wondering. I have a number of years experience selling / training groups on car and truck tires. Normally on car / truck tires the air pressure will rise 2-4 psi from cold temp to a warmed up tire. I've never checked to see what the variance is with MC tires. Guess I always figured it had the same adjustment. If that holds true....What makes me wonder, is if you have the cold air pressure correct for the weight load being put on the tire . Do you have the correct load rated tire on the bike? An under inflated tire or a tire being pushed beyond its load limits will increase the amount the tire heats up which will cause the warm air pressure to rise substantially more compared to PSI when the tire is cold. Something doesn't sound right and concerns me for you safety. Just my .02 cents worth. I would do some additional research before riding on that tire. Hopefully you find that you have an over sensitive TPMS set up .

A pretty good article on MC Tires


https://www.mic.org/downloads/MIC_Tire_Guide_2012V1.pdf

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#26 ·
You hit the nail on the head. Yours and mine should bothe read "ambient" temp when just sitting in the garage. But get it hot running down the road, and yours doesn't read hot enough. Your are only measuring the temp at the end of the valve stem.... more ambient efffect. I can see 154F in the rear tire. And I am running a car tire. Both the front and rear increase almost exactly 1 lb for ever 10 degrees of internal tire temperature. The screw on sensors can measure pressure great, but temperature on the inside air in the tire.... not so great.

One example:
Both sensors cold temp was 64.4F
Front tire pressure 36 psi
Rear pressure. 25 psi

Heated up from a bit of road time
Front tire 42 psi @ 120F. 6 lb increase and 5.6F increase (10 deg per lb)
Rear tire 34 psi @ 154F. 9 lb increase and 90F increase (10 deg per lb)

Lots of data that shows this is a very close value to use. Certainly it isn't exactly precise in all cases... but if your pressure goes up 10lbs, you can just about bet the internal temp has increased about ~100 F!
If you have. An infrared gun, shoot the tire for temp....you will be surprised how hot that tire is. The rear tire gets real hot with less air hitting it to "cool it down" and running up in between the exhausts.
 
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#29 ·
You hit the nail on the head. Yours and mine should bothe read "ambient" temp when just sitting in the garage. But get it hot running down the road, and yours doesn't read hot enough. Your are only measuring the temp at the end of the valve stem.... more ambient efffect. I can see 154F in the rear tire. And I am running a car tire. Both the front and rear increase almost exactly 1 lb for ever 10 degrees of internal tire temperature. The screw on sensors can measure pressure great, but temperature on the inside air in the tire.... not so great.



One example:

Both sensors cold temp was 64.4F

Front tire pressure 36 psi

Rear pressure. 25 psi



Heated up from a bit of road time

Front tire 42 psi @ 120F. 6 lb increase and 5.6F increase (10 deg per lb)

Rear tire 34 psi @ 154F. 9 lb increase and 90F increase (10 deg per lb)



Lots of data that shows this is a very close value to use. Certainly it isn't exactly precise in all cases... but if your pressure goes up 10lbs, you can just about bet the internal temp has increased about ~100 F!

If you have. An infrared gun, shoot the tire for temp....you will be surprised how hot that tire is. The rear tire gets real hot with less air hitting it to "cool it down" and running up in between the exhausts.


What is internal tire temperature? The air or the tire itself. I suspect based of actual tire temp the 1 to 10 rule is probably good.

Have you ran both types in parallel to prove that the measured air temp is wrong?

Being at the valve stem is analogous to screwing an oil temp sensor to the side of the pan and claiming it's not accurate because it's not fully immersed in the oil.








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#27 ·
Yep... It's gonna drive you crazy.
 
#28 ·
How much air expands when heated increases drastically with the humidity content of the air. This is why nitrogen doesn't expand much when heated, because it is very dry.

One thing you can do to decrease the amount of fluctuation, is use a desiccant drier on your air hose when you fill your tires. I use a desicant snake hose on my compressor when I fill tires, and I've seen a significant decrease from cold to hot pressures as a result. I also have a tire pressure monitor that reads out the real pressure, and prior using the desiccant snake, I've seen a rear tire go nearly to 60psi under the right circumstances (hot ambient temps and extended high speeds under heavy load).
 
#30 ·
I will not attempt to change your thinking. I suggest you research the various sensor types and read what others say. At least the pressure should be as good as the accuracy of the sensing device. A temperature sensor on the OUTSIDE of the tire is influenced by the air temperature outside the tire as well. A sensor on the INSIDE is only influenced by the temperatures inside the tire. If the outside air temp is cooler, it is extremely likely that your sensor is being influenced by that and reading cooler then reality. Believe as you choose.... I'm fine with that. Trust you have a good weekend.


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#31 ·
Are there links with real testing of the difference? Google doesn't seem to find them.


While this has become a tangent. I think it is fair to say 51lbs with a screw on tpms on the rear tire is nothing to worry about.


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#32 ·
The OEM Honda sensors provide both temp and pressure, but the system does not display temp. I have a Tire Watch receiver that can read out both temp and pressure from the OEM sensors and I've seen internal rear tire temps of 170 degrees before. Dunlop E3 tires seem to run hotter than other brands. I've seen rear tire pressures quite a bit above 50psi.
 
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