Tire PSI Cold vs. Hot

[EricV]

Michelin does agree with you Sierra1. They have a blurb about not running tires at max pressure on the street. Oddly, they don't list the specs of their tires on their web site. When I asked for some specs, their reply was to check with retailers. They further stated that their web site was primarily to help riders choose a tire to meet their application and needs. Gee, the specs might help me with that...

Most car tires have max pressure ratings of 50 psi or more. And it is clearly stated so on the sidewall. Literally saying "Max Pressure"

Again, what you think you know is incorrect. Go read your tires. No where does it say "Max Pressure". What it says is "Max Load at XXX Kgs (XXX Lbs) at XXX KPo (XX PSI) COLD. Note that the Max Load corresponds exactly to the Load Index value also marked on the tire. 69 = 716 lbs. V = max speed of 149 mph. If you look up the Speed Index table, you'll see a * after that 149 mph. That indicates the following note: " * At speeds above 130 mph, the maximum permissible load is reduced. Consult tire manufacturer for details. " It says the same thing for W and (W) rated tires, (168 mph & 168+ mph), except for speeds above 149 mph. LINK

Bridgestone Battle Wing BW-502: LR B : Max load 325 Kg (716 Lbs) AT 290 Kpa (42 Psi) Cold.


Michelin Anakee 3 - Load range B Max Load 355 Kg (783 Lbs) at 290 kPa (42 psi) cold.


MotoZ Tractionator GPS (50/50 bias ply tire) - Load range B Max Load 250 Kg (551 Lbs) at 230 kPa (33 psi) Cold.


These are the max loads for those tires at the cold psi pressure stated. Not the max pressures for those tires. This simply states the terms of the testing. I can't tell you what the max pressure ratings of these tires are, it's not listed on the tires or on the manufacturers web sites.

Car tires will say "Max Load XXX Kg (XXXX Lbs) Max Pressure XXX kPa (XX psi)"


You are incorrectly assuming that the listed pressure on motorcycle tires is the max pressure of the tire. It may be, but we don't know that. We have no way of knowing, since that info isn't given. And this is the problem and misconception of many riders. Call MotoZ and they will tell you that 33 psi is not the max pressure of that tire. It's the pressure the test was conducted at for the load the test was conducted at. Not the same thing as max pressure and why motorcycle tires don't actually say "Max Pressure". And yes, I've had that conversation personally. This is not second hand.

I suggest to you that most motorcycle tires have a realistic max pressure rating of around 50 psi, just like auto tires. All of these examples are tubeless tires. This is nuts, but nearly everything you read about max pressure for a motorcycle tire is wrong. Everyone is assuming that the pressure on the sidewall is the max pressure instead of actually reading the sidewall and seeing what it says. Again, it does NOT say max pressure anywhere. You are assuming it means that, based upon what car tires are marked with.

And trying to get a strait answer out of a motorcycle tire manufacturer about his is next to impossible for liability reasons. I've had this talk in person with one of the Michelin motorcycle tire guys at "The Glass Palace" , Michelin's US headquarters in Greenville, SC. He was very careful what he said, and didn't say and would never actually tell me what the real max pressure for any of their motorcycle tires was. What they consistently tell you is to refer to your motorcycle manufacturers literature. It's just passing the buck, no one wants to be held to a number and there are not DOT requirements for them to list the max pressure, unlike auto tires, which clearly have max pressure listed on the side wall and those values are easy to find online for any tire.

So in real world terms of what works for you, here is a quote from a motorcycle tire engineer who didn't want me to use his name. "There is no simple rule. Go and experiment."

 

[Sierra1]

Ok....I concede that I ass-summed that the pressure for max load was max pressure also. But, if the speed rating is at max pressure, and max pressure is not listed, do we just trust the tire to not shred at stupid high speeds? Granted, it will likely take a while, for an "under inflated" tire to fail at those high speeds.

….Most of the 50/50 tires I have seen have much lower speed ratings.

And, I guess this is where I was kind of going with the speed ratings....the Tenere is capable of sport bike speeds....but many are riding on dirt bike tires....loaded. We've read on here about guys riding for hours at 85+mph. (which is hard to do even in west Texas) I'm wondering what impact, if any, it has on the tire. I do understand it all come down to heat; heat is a killer of tires. I had an almost brand new Bridgestone on the ST1300, and was able to spend some time at a track. Afterwards, the tire appeared the same....but you could see it had been ridden hard. The very next week, I had to have the tire replace because it was worn out. The bike was/is heavy, and so am I, so I know the heat build up didn't help. But, apparently the heat changed something in the rubber, causing the accelerated wear.

Nowadays....I ride because I enjoy it. I should never have to worry about tire failure; my trips to hyper speed are very infrequent, and I have good tires with proper pressure. But, sometimes is see things and start wondering....

 

[EricV]

I certainly can't answer all of your questions Sierra!. What I can say is that I rode my Super Tenere during the Iron Butt Rally in July of 2013 running Heidenau K60 Scouts. I chose that 50/50 tire over other tires because I had run many sets on the S10 and knew I could consistently get 10-12k under a wide variety of conditions. I put about 5k on that tire during the first two legs, (virtually all pavement riding), then removed it and installed a second K60 for the third leg. The first tire still had plenty of tread left, but the unknown nature of the rally meant I did not know where I would be going or how many miles I would be riding for the third leg. I later put that same tire back on and put another 6k plus on it before it was at the wear bars. Much of this was pavement riding in very hot weather. A significant amount of miles were done on fast roads, but speeds no more than 85 and often more like 70-75 or less. The tire showed zero signs of damage or failure. No cracking around lugs.

I have run an Anakee 3 rear at elevated speeds in Northern NV in summer temps over 100F for 1600 miles continuously and it never showed any signs of problems. That tire was removed at 8200 miles for a fresh tire not because it was worn out, but because I was at the start of the IBR and needed to start with fresh tires.

Both rear tires were run at 42 psi. One radial, one bias ply. Similar conditions and time of year. I have had both of these tires up to S10 max speed for brief periods. No handling issues. I have run other tires at much higher speeds for extended periods, 20 hours a day for 5 and 10 day periods with no issues. All run at 36F/42R and heavily loaded.

I would suggest that tires rarely just fail. You get warning signs and if you're looking at your tires before rides, you're going to notice something before you see a catastrophic failure. I have seen a 50/50 tire with cracking at the lugs ridden on for thousands of miles w/o having any actual tread separation or de-laminating occurring. That tire was never spun on or off pavement. That tire manufacturer, after looking at pictures of the tire, felt that the OEM size was wider than optimal for that rim size and suggested a narrower tire. They felt the carcass was being stressed more with a wider tire on a narrower rim. The narrower replacement tire has shown zero cracking so far, (3k).

Track use is extreme. You are under acceleration or hard braking all the time. Lean angles are generally more severe than on the street. You're constantly stressing the tire at higher levels and higher heat is being generated. Track tires are designed for this extreme more than sport touring tires. I've read where some riders feel a sport touring tire is fine for a track day/school event, but to expect significant wear compared to street use. that makes sense to me. And full on track tires are not expected to last long. In some cases they are only run for one event, then removed.

I've known some racers that sold their take off tires to street riders for cheap. The racers felt that after a race, that tire was shot and would not perform the same again, despite having useful rubber left on it. The street riders they sold them to were probably never going to push the tires as hard as the racer did, and in a weird twist, the high heat cycled track tire was likely going to last a bit longer on the street than a fresh track tire likely would.

 

[ballisticexchris]

32/36 cold is a good all around pressure on any street bike (or car/ truck). Been going with that pressure for years. I don’t worry much at how high pressure is while hot. The beauty with my tires is Michelin does not recommend airing down for off road. This is the only radial knobby I know of.

Any pressure higher feels too harsh for my taste and traction loss is a real concern. Of course you will maybe get a little more mileage out of the tires. I like my tires to grab.

 

[Grumpy]

At the start of the day it's cool in the garage and I have the bikes recommended 33/42 in the Adventures for a two up ride. On a warm 25c+ day the rear will increase to 48psi, the front is a little less dramatic, about another 3 psi to 36. That is the reading on my TPMS.

 

[squarebore]

I dont worry too much about tyre pressure. I don't race or ride to the extent of the tyres. I thought k60s were the worst tyre for comfort I had ever ridden so I didn some tests and rode them at about 25/28 everywhere and still got 15k kms. The temps never went up much.


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[EricV]

It would add useful information to the thread if when you give the tire pressures you run, that you also tell us how the bike is loaded and what types of rides you typically do.

As an example, I run 36F/42R (psi) and typically am fully loaded for traveling with full hard panniers, extra fuel and a gallon of water. I weigh 260 lbs w/o gear at the moment. My riding is 90% pavement these days with some easy gravel and two track making up the remaining 10%. Speeds are typically 50-75 mph.

Something to consider with ride quality. Most people have been confused by OEMs to think that tires are about ride quality. They are not. You don't adjust tire pressure to change ride quality, (firm/soft). You manage ride quality with suspension design and components. For an OEM, it's hugely cheaper to put crappy suspension on a vehicle and then run lower tire pressure. Mileage suffers, but tires are wear items and most people will accept shorter tire wear for perceived or real benefits in ride comfort or other factors.

 

[ballisticexchris]

. You don't adjust tire pressure to change ride quality, (firm/soft). You manage ride quality with suspension design and components. For an OEM, it's hugely cheaper to put crappy suspension on a vehicle and then run lower tire pressure. Mileage suffers, but tires are wear items and most people will accept shorter tire wear for perceived or real benefits in ride comfort or other factors.

For me tire pressure are an important factor in ride quality and comfort. Suspension settings and tire pressures both work together for a quality ride and how the bike handles. It's even more important on dirt bikes where pressures are a lot more critical for handling depending on speed and terrain.

For an example when I knew I would be doing mixed super steep rock crawling/dual sporting, I ran 0psi in the back and 6psi in the front. That is with my Dunlop RC81/908RR combo. I have a Tubliss system that allows me to run zero pressure in the rear. I can still peel off sub 50mph pavement blasts in relative safety. The rear tire is only good for a few hundred miles before the sidewalls start to breakdown.

It is interesting all our different perspectives and what pressures we run. One thing for sure is you can't go wrong using the manufacturers recommended pressures on the OEM tires. On the Super Tenere those pressures are just too high for me. I did the 33/42 when I first got the bike from the dealer. It was way too harsh for me. As time goes on my pressures might change depending on the tire I'm running.

Here is my last street bike loaded down to the gills for travel. 32/36 loaded or not:



For this riding 0psi/6psi is perfect. Just have to be careful in the transfer sections. This is very steep and technical. Sometimes I have to get off the bike and bulldog it through. This is my buddy who dropped his bike and he is a way more advanced rider than me:

 

[EricV]

All tires have traction. They only spin if you twist the throttle too much, too quickly.

The 650R weighs something like 120 lbs less than the Super Ten. And your loaded down for travel is equal to about one pannier for me.

On the dirt section. 0-6 pis with bib mouss, uphill, sure. Now, about down hill. How much does it cost to replace a rim? I'm guessing you know that number from personal experience.

 

[Sierra1]

Funny you should mention tire pressure effecting ride comfort. My father in law used to run his tires at about 21psi....on an F-150....because the ride was better. The thing wallowed all over the place when it was loaded. Low pressure is fine off road, often recommended. I don't like my tires low on pavement. I assume the manufacturer(s) specify pressure(s) for their tires for a reason; I follow there recommendations. Eric is right, again, about the ride quality; it's all in the suspension. Like the ES or not, the adjustability it has allows you to find your desired ride quality; within reason. Even though, or maybe because, I'm 300lbs even minor changes in the rebound/dampening make a noticeable difference in ride quality.

 

[ballisticexchris]

All tires have traction. They only spin if you twist the throttle too much, too quickly.

The 650R weighs something like 120 lbs less than the Super Ten. And your loaded down for travel is equal to about one pannier for me.

On the dirt section. 0-6 pis with bib mouss, uphill, sure. Now, about down hill. How much does it cost to replace a rim? I'm guessing you know that number from personal experience.

Tubliss System protects the rim from damage somewhat. So far have not had to replace a rim while using the system.

 

[Grumpy]

Back in the 1980's I had the XT600Z, the owners hand book tyre pressures where 20/22psi. When the OE tyres wore out, I changed them (Metzela?) I carried on useing the same pressures, this caused overheating of the tyres and resulted in a tiny thread of the cross-ply pokeing through the inner wall of the rear tyre and puncturing the tube. If I remember rightly, after 2 or 3 tube repairs I went to my local bike shop, I found out from a tyre fitter that I should have had 29/36psi. A new rear tyre and a lesson learned.

 

[Checkswrecks]

I made this cross section of three tires to show why tires fail as part of an investigation and as a teaching aid. (For the newbies, I'm a long time engineer and accident investigator.)

Business jet on top.
Worn-out motorcycle in the middle. Note the shoulder of the tread is easiest to see on the right.
Car on bottom.
The dime is shown for scale. fwiw - Zoom in and you can see the steel belts in the treads of the car and m/c tires.

The more rubber flexes, the more it heats and softens the rubber. In the mid to high 300-400F range, rubber molecules rubbing together develop a blue tint as they revert to goo, let the fabric plies slip, and the plies are the strength of a tire. You call it a blow-out, the tire industry prefers to say sudden air loss. (fwiw - The blue is one way that investigators can tell a tire was under-inflated.)

It's not that the whole tire heats, the part of the heat build-up being discussed is how localized the flexing is in the sidewall. This is sort of like how localized flexing of metal can cause a fatigue fracture, while a metal part will last longer if the flex is spread over a larger area. In the case of a tire, it's not really a fracture of the fabric that first becomes the problem, the issue is localized heating of the rubber to release the plies. (Thread fatigue is another discussion) As you can see, the short sidewall sections for the jet and motorcycle mean that if under-inflated the flexing/heating will be more focused in short portions of the sidewalls.

To not have this problem, higher pressure results in less flex, creating less heat build up, and the big trade-off is less friction with the road. (Obviously, till over-inflation causes structural issues.)

The second part of the heat equation is how easily heat can leave the rubber and two things reduce how well heat can get out. First is the material, because rubber is a great insulator. Just like a kitchen pot-holder, the rubber in a tire does not let heat get from the center of the plies to the surfaces so the heat is retained with the plies. The tires are about the same in this, so there's not much we can do.

But the second aspect of heat escape from the plies is how many square inches of area (aspect ratio) there are for the heat to get out. The large areas of thin sidewall in the car tire mean lots of opportunity for heat to be conducted to the air, both inside and outside the tire. This is what you want. The 210 psi jet tire is the worst in being able to shed heat form inside the construction. It is so thick and with such short sidewalls that it can only roll under load for short distances and these tires always fail where the white mark is on the left. (iirc 7 miles at max load)

The m/c tire is closer to the jet in terms of aspect ratio so you have two choices. Limit how far it rolls or limit the sidewall flex. The flex is the result of the tire designer targeting how much load the tire can carry at a given pressure.

And that is why proper inflation is so damned important.

 

[Jlq1969]

I made this cross section of three tires to show why tires fail as part of an investigation and as a teaching aid. (For the newbies, I'm a long time engineer and accident investigator.)

Business jet on top.
Worn-out motorcycle in the middle. Note the shoulder of the tread is easiest to see on the right.
Car on bottom.
The dime is shown for scale. fwiw - Zoom in and you can see the steel belts in the treads of the car and m/c tires.

The more rubber flexes, the more it heats and softens the rubber. In the mid to high 300-400F range, rubber molecules rubbing together develop a blue tint as they revert to goo, let the fabric plies slip, and the plies are the strength of a tire. You call it a blow-out, the tire industry prefers to say sudden air loss. (fwiw - The blue is one way that investigators can tell a tire was under-inflated.)

It's not that the whole tire heats, the part of the heat build-up being discussed is how localized the flexing is in the sidewall. This is sort of like how localized flexing of metal can cause a fatigue fracture, while a metal part will last longer if the flex is spread over a larger area. In the case of a tire, it's not really a fracture of the fabric that first becomes the problem, the issue is localized heating of the rubber to release the plies. (Thread fatigue is another discussion) As you can see, the short sidewall sections for the jet and motorcycle mean that if under-inflated the flexing/heating will be more focused in short portions of the sidewalls.

To not have this problem, higher pressure results in less flex, creating less heat build up, and the big trade-off is less friction with the road. (Obviously, till over-inflation causes structural issues.)

The second part of the heat equation is how easily heat can leave the rubber and two things reduce how well heat can get out. First is the material, because rubber is a great insulator. Just like a kitchen pot-holder, the rubber in a tire does not let heat get from the center of the plies to the surfaces so the heat is retained with the plies. The tires are about the same in this, so there's not much we can do.

But the second aspect of heat escape from the plies is how many square inches of area (aspect ratio) there are for the heat to get out. The large areas of thin sidewall in the car tire mean lots of opportunity for heat to be conducted to the air, both inside and outside the tire. This is what you want. The 210 psi jet tire is the worst in being able to shed heat form inside the construction. It is so thick and with such short sidewalls that it can only roll under load for short distances and these tires always fail where the white mark is on the left. (iirc 7 miles at max load)

The m/c tire is closer to the jet in terms of aspect ratio so you have two choices. Limit how far it rolls or limit the sidewall flex. The flex is the result of the tire designer targeting how much load the tire can carry at a given pressure.

And that is why proper inflation is so damned important.

Congratulations, I would give the explanation, a 9.99 and applause. If anyone has something else to add? .... otherwise .... case closed

 

[bigbob]

Does the jet tire have metal spikes in it? Keeps it from total collapse?

 

[EricV]

Hopefully the lesson will be accepted as a learning moment. But despite explaining how things really are, some prefer to ignore evidence and experience and instead continue to do as they always have. Not being willing to accept that they have things to learn and we never stop learning.

 

[squarebore]

Hopefully the lesson will be accepted as a learning moment. But despite explaining how things really are, some prefer to ignore evidence and experience and instead continue to do as they always have. Not being willing to accept that they have things to learn and we never stop learning.

Hi Eric , I am emjoying our banter. There are few absolutes in life and many circumstances where what we are sure should happen does not. Checkswrecks has experience and knowledge however he also knows many tyres will go for a long time at lower than perfect pressures without fail. You BELIEVE things you know to be true and are very keen to tell people they are wrong and you are right. BUT maybe you are not always right but don't know it. I have been proven wrong on my absolute convictions many times. I thought Santa was real when I was young and devastated to be wrong. I thought Pluto was a planet. Some thought the earth was flat. The speed of sound was an absolute and could not be passed. My latest one was the worst. I was a Christian for 53 years. Now I can't understand how a rational human can believe in that god without evidence and use faith alone. Of course, I could still be wrong. I accept that.

I'm just asking for some tolerance for other's views. It doesnt have to be black and white. Occasionally we can also let someone be wrong and not tell them as no-one likes a smart ass.

Please, this is not a personal attack but a discussion. I've seen tyres fail at very low pressures but never with regular use at 20 to 30 % below recommended. I bet I could run my rear S10 at 30psi for 10k kms at normal highway speeds without incident. Maybe wear faster but that is all. I know this because I have done it. K60 12k kms at 27-30psi.

OTOH, I have run landcruiser tyres for more than 600,000kms at 34 psi and the recommended is 55-60psi. That would be like riding on solid rubber. Yes higher pressures may run cooler, but at what pressure is it so low it wall cause catastrophic failure? As many have said, the tyre manufacturers won't tell us.

Cheers fellas.

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[Jlq1969]

There is nothing distributed more equitably in the world than reason: “everyone is convinced of having enough. ” (DESCARTES)

 

[Pdrhound]

Well this thread definitely went off the rails but I was searching to find some middle ground. Sorry for the rehash
On my west coast trip last September I road 800 and 600 miles in 2 days to seattle. Bike was not too heavy cause I used almost everything I brought. But I'm a big guy and maybe with all my farkles and gear it's a total of 375 lbs. I was Running k60 nicely broke in with 300 miles. First day was 400 miles of hurricane and remains a blur of water. Day 2 I checked air in salmon Idaho filled to 41 psi as recommended in my manual. It was 40 degrees. I really noticed the tire had worn more then I was expecting. In have tpms and 75 miles into my I 90 section I looked down and noticed rear pressure at 54lbs at 85mph. It was about 70 degrees. I swung into next rest stop to double check and the gauge confirmed. Also I really noticed tire wearing. I dropped pressure to 42 hot and continued another 400miles.

I truly felt that I had less wear. The next AM my cold psi was 32. I road conservative until psi hit 36. (About 5 miles) then hit interstate and pressure hit 41 and ranged 38-41 for the next 4000 miles. Temps usually around 55-65 degrees. My wear slowed dramatically

I'm a bit of a tire geek and get everything that is supposed to be. I'm good now starting a little low and easing into my ride. I was looking to see if anyone else had similar results but I don't see any......

Maybe ill do some temps to add to those psi if it every quits freaking snowing!

 

[Cycledude]

If you start out with cold 42 psi on a hot 100 degrees Fahrenheit day in an hour or less at highway speed the heat will raise the pressure to 50 psi or more.
Max recommended cold pressure is the same 42 psi for the rear tire no matter what the load is , that’s clearly listed on a little chart under the drivers seat for your own safety, minimum cold pressure is 36.
The front tire is listed at 33 cold psi and its The same recommendation loaded or empty.

Personally I mostly try to run 33 front and 38-40 rear.