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I can't remember where I read this (maybe on this forum?), but it said that if tire pressure increases more than 10% from a cold reading to a hot reading (i.e., after riding), it is a sign the tire is under-inflated and 1 to 2 more psi should be added. Has anyone else ever heard that rule of thumb?

A related question for anyone who has checked tire pressures when cold and then again when hot...what kind of increases are you seeing from cold tire to hot? I realize there are a lot of variables. Just curious what kind of range you see, and is the amount of increase different for front versus rear tire.
 

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2018, with rear set to 41 cold, routinely runs at 46 hot.

What surprised me was how quickly it gets up to 46. (5 to 10 miles/minutes with rider and gear only, no passenger or extra luggage, so somewhere around 240 total)

46/41 = 1.12

I don't intend to change cold pressure from recommended.

Similar increase occurs on the front, from recommended 36. Like 40 or 41 hot, so similar ratio.
Yes, 1833 has same recommended as 1832.


Pressures rise quick enough that if ridden 10 minutes to a location with an air compressor - then the tires would need to be set higher to end up with the correct 'cold' pressure.

We regularly check with regular tire gauge at home, when cold, and top up if necessary.
 

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I have never heard of that rule of thumb, but then I may have just missed it.

From what I remember from my science, the relationship between pressure, temperature and volume is P1V1/T1 = P2V2/T2 where P is pressure and T is temperature and V is volume, Since the volume of the tire remains constant the pressure should change in direct proportion to the change in tire air temperature. Increase in T means P will increase. P1/T1 = P2/T2

However, as I think about it some, there is another variable. Theoretically, it would seem that as tire pressure is changed (lets say the pressure is lowered), there might well be more tire contact with the road. This increase in tire to road friction will cause the temperature of the tire to be higher than for a "normal" tire pressure.

So, it might well be that if a tire is under inflated there will be increased friction with the roadway (surface area contacting the roadway increases) resulting in an increase in the temperature of the air in the tire which will result in a increased change in the tire air pressure. But it would seem, again theoretically, that you would have to have a significantly lower tire pressure from the norm to see any impact with the tire gauge readout.

Since, I never check my tire pressure when warm (unless the TPMS lights comes on) I would not have a clue about what the pressure is at normal operating tire temperatures.

Then again I could be all wrong on this.
 

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Yes, have read that rule of thumb and follow it. I run 41/43 front and rear in Avon Cobras. I think they typically gain about 2-3 psi when hot.
 

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What I read just recently was 1 lb. of change per 10% F. What I was looking for was any reference to what temp is considered the cold tire temp.
Here is my question. If on Monday it is 60% F when you set the cold tire pressure to 41 and 36 and now on Tuesday it is 100 % F when

you check the cold tire pressure do you adjust the tires back to 41 and 36 or just leave then alone ?
 

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I can't remember where I read this (maybe on this forum?), but it said that if tire pressure increases more than 10% from a cold reading to a hot reading (i.e., after riding), it is a sign the tire is under-inflated and 1 to 2 more psi should be added. Has anyone else ever heard that rule of thumb?

A related question for anyone who has checked tire pressures when cold and then again when hot...what kind of increases are you seeing from cold tire to hot? I realize there are a lot of variables. Just curious what kind of range you see, and is the amount of increase different for front versus rear tire.
I was told the exact same thing by a tech at Cooper, (the company that makes Avon Tires) back when I had my Valk Interstate. A 10 percent increase in PSI from cold to hot is too much and I should increase the cold PSI.


According to my Steelmate TPMS on my 78 Wing and my F6B I would see an average increase of 4 to 5 psi after 10 or so miles.
 

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I was told, many years ago, that up to 10% is ok and I still follow the advice. I have a gain of about 3 psi on my tires.
 

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Thanks for all the great feedback. Wife and I are riding from PA to UT next month, so I want to keep an eye on tire pressures a little more closely since we'll have a lot of gear and pulling a trailer. Too late for this trip, but wish I had thought to get a FOBO TPMS. Maybe next trip...
 

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Altitude change

Thanks for all the great feedback. Wife and I are riding from PA to UT next month, so I want to keep an eye on tire pressures a little more closely since we'll have a lot of gear and pulling a trailer. Too late for this trip, but wish I had thought to get a FOBO TPMS. Maybe next trip...
Since your headed for Utah and your concerned about tire pressure, note that as you go up in altitude you will see your tire pressure increase. If memory serves me correctly when I rode from Wis to Dillion, Co (9000 ft), I started at 41 PSI and a cold check at Dillion was 50 PSI.
 

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Gcube gave good advice. Altitude and temp changes will cause your pressures to go up and down and need to be checked and adjusted daily when going up and down in altitude. I do a pre-ride check every day to ensure all is well and it gives me confidence knowing I've done all I can to prevent problems. I rotate both tires 360 degrees to look and run my hand over the width of the tread for nails, punctures, cuts and tread condition. Check oil, coolant, lights, turn signals, brake lights, horn, visual on brake fluids. Takes 5 minutes, gets your hands filthy, gives me complete peace of mind. Mind you these are 400+ miles days of pushing it very hard on demanding mountain roads, so equipment condition is critical. But, I still do it even when going on a short 100 mile ride locally. It's that important. Sermon over, thank you for tolerating.
 

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Discussion Starter #13
Thanks Gcube for the reminder about how altitude affects tire pressure. I would not have remembered that important fact.

And Sladep, I appreciate the sermon. Those tips are a great reminder to do what I can to avoid problems.
 

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I can't remember where I read this (maybe on this forum?), but it said that if tire pressure increases more than 10% from a cold reading to a hot reading (i.e., after riding), it is a sign the tire is under-inflated and 1 to 2 more psi should be added. Has anyone else ever heard that rule of thumb?
I've never heard of that but can believe it to be true. Most heat in a tire is cause from its own internal friction. For example ... belts rubbing against cord, tread segments rubbing against tread segments. The less air a tire has in relation to the weight the tire carries the more internal friction, and friction create heat, which expands air, which increasing air pressure.
 

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I have never heard of that rule of thumb, but then I may have just missed it.

From what I remember from my science, the relationship between pressure, temperature and volume is P1V1/T1 = P2V2/T2 where P is pressure and T is temperature and V is volume, Since the volume of the tire remains constant the pressure should change in direct proportion to the change in tire air temperature. Increase in T means P will increase. P1/T1 = P2/T2

However, as I think about it some, there is another variable. Theoretically, it would seem that as tire pressure is changed (lets say the pressure is lowered), there might well be more tire contact with the road. This increase in tire to road friction will cause the temperature of the tire to be higher than for a "normal" tire pressure.

So, it might well be that if a tire is under inflated there will be increased friction with the roadway (surface area contacting the roadway increases) resulting in an increase in the temperature of the air in the tire which will result in a increased change in the tire air pressure. But it would seem, again theoretically, that you would have to have a significantly lower tire pressure from the norm to see any impact with the tire gauge readout.

Since, I never check my tire pressure when warm (unless the TPMS lights comes on) I would not have a clue about what the pressure is at normal operating tire temperatures.

Then again I could be all wrong on this.
Being under-inflated was my biggest concern due to the heat that is generated when under-inflated. Although there may be some small amount of heat from increased friction, my understanding is the real heat is generated as the tire flexes during rotation, which occurs when any given cross section changes shape as it rotates through contact with the ground. A tire that is under-inflated apparently flexes more than a properly inflated tire.

And then I was reminded that altitude affects tire pressure by increasing it, so I'll definitely be checking tire pressures daily on this trip.
 

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Of course the colder to hot will increase it. On a normal cool morning to riding in the hot afternoon mine will rise about 6 psi front and back.
 

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I've never heard of that but can believe it to be true. Most heat in a tire is cause from its own internal friction. For example ... belts rubbing against cord, tread segments rubbing against tread segments. The less air a tire has in relation to the weight the tire carries the more internal friction, and friction create heat, which expands air, which increasing air pressure.
Greg where do you get all the pictures of all my sisters LOL
 

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I have been watching TP now for the last 3 wings I've owned & they have all acted about the same. Of course the pressure in the morning is the result of the temp. While I don't worry about a couple of lbs difference, I do change the pressure if there is more change than that. I was advised several years ago by a person that tested tires on Gold Wings for the best ware that the best ware was at 41 lbs in both tires. However, by dropping the front by 2 lbs there was very little difference in ware & there was a difference in ride quality. So he advised that he found 39 & 41 was the best all around combination. I believed him then & I believe him now, as that is what I always run.

I do not agree with the cold to warm differences listed here all the time. Mine certainly changes quickly like is mentioned. However, the differences are dependent on the warm temps of the day. On a day where cold temp is 60 degrees & warms up to 80 degrees the rear will increase by about 6 lbs. However, on a day where the morning is 60 & the hot part of the day is 100 degrees the rear will increase 10 degrees. So I see my rear tire pressure at 50 or 51 lbs quite often & do not think a thing of it, since I believe that is normal. The front pressure changes about half that. :serious: :smile2: :surprise:
 

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Set tire pressure at the recommended pressure in the morning before riding and do not ever adjust it back to recommended while riding. You could end up with an underinflated tire that overheats and is dangerous. The recommended pressure is specified at approx. 65-68 degrees F. That is why it is recommended to set pressure in the morning before riding...it is assumed that the ambient temperature will be within a few degrees of 65.
Pressure will increase or decrease by about 1 psi for every 10 degrees F. So, if it is 80 degrees in the morning when you set it and you have not ridden it yet and it is not in the sun, pressure should be set to about 1.5 psi above recommended. Likewise, if it is 40 degrees in the morning when you check your pressure the set point should be about 2.5 psi below recommended.


The temperature of the tire will typically rise from:
  • internal rolling friction
  • exposure to the road surface
  • exposure to the sun.
The pressure will rise as the tire temperature rises at the aforementioned approx. ratio of 1 psi per 10 deg F. This could all add up to 10 psi or more from the recommended, especially with a loaded bike on hot pavement in summer. The tire is designed for that pressure rise.
Once you have ridden the bike, the only way to properly adjust the pressure would be to measure the temperature of the tire itself. That is why it is always recommended to set pressure before riding.


I don't remember the ratio for pressure adjustment for altitude but I don't think it is significant. Pressure does increase slightly at higher altitudes. At really high altitudes that would matter, it is cool in the morning anytime of year so when you check your pressure first thing, the temperature probably has the biggest influence on pressure.


My best example of all this is leaving Lake Tahoe at around 6,800 feet altitude in July. At 6am, it is 31 deg F, so my pressure, based on temperature alone, should be (65-31=34. 34/10 = 3.4 psi below my recommended. So my rear tire pressure should read 41-3.4 = 37.6 (say ~38 psi). I understand that altitude adds maybe 1 psi so if it reads 39, OK. If not, I adjust it to 38-39. (A psi high is better than a psi low.)
Later that same day I'm passing through Ridgecrest where it is 104 deg F and maybe 2,000 feet elevation. The air is hot, the road surface is hot and my bike is loaded with me, the wife and our gear. If I checked the air pressure, I would expect it to be 104-31 = 73, 6-7 psi higher than it was in the morning (38+7 = 45psi) based on ambient air temp alone, not even considering road surface temp, sun, and sidewall friction. So, even if it read 50 psi, I would not do any adjustment and would not be concerned (because I know I set it properly that morning). I would also not go over 100 mph. And, I'll add here that I do not ride on worn out tires.


When I get home and check my pressure the next morning in my garage, in cool Huntington Beach, at sea level, it ought to be really close to my recommended set point of 41 psi.


https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=147
 
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