Tire Pressure

alienator said:

Ah, I see: one of those. Well, then, there's no point in going further then, since it's very unlikely that you would even understand a scientific explanation. BTW, you're over-inflating.

Yep, I'm one of those..that prefer to hear it from a legitimate source than from a so-called "know it all". Funny, you have no idea of my education yet you say that I wouldn't understand a scientific explanation..that's just ignorant. BTW, I'm not overinflating because there are times that you want to inflate to max cold pressure marked on the tires placard..and other times you want to lower it..all based on load, temperature, etc. The only time you are "overinflating" is when you exceed the recommended max cold pressure number. Yep, I agree..no sense going further with you on this. BTW, you know my profession what is yours?

mullerrj said:

I get more "bounce" from an underinflated tire than I do an overinflated tire.

Also, I said nothing about overinflating or underinflating tires. I said I prefer inflating to (or up to) the recommended max pressure printed on the sidewall of the tire. And, until someone gives me a legitimate scientific explanation of why I shouldn't..I'll continue to do so. BTW, your explanation was far from a "scientific" explanation..sorry.

In your list of things that affect handling and ride, I'm surprised you left off spring rates and shock damping rates. I've had just enough experience with road motorcycle suspensions to know how excessive rebound damping can mess things up.

I also recall learning that too much pressure in the front tire of a motorcycle is the easiest way to ruin roadholding and grip. Same is true for bike tires....rock-hard tires can make a descent on rough roads a real thrill.....while adding nothing to downhill speed when the road smooths out.

I've never met anyone who inflated their car tires to the max allowable pressure, but I guess I come here to learn. You actually run your car tires at 44 psi? BTW, I run my tires at or just above the pressures recommended by the manufacturer and generally get excellent life from my tires. They have engineers too you know and are keenly motivated to post good fuel economy numbers. I've found the key to long tire life is rotation and rebalancing every 6-8K miles, not over-inflation.

I'll leave the scientific explanations to alienator. But what might seem obvious when you're thinking about a tire on a smooth steel roller in a lab just doesn't carry through to a tire running on most real-world roads.

mullerrj said:

I get more "bounce" from an underinflated tire than I do an overinflated tire.

Also, I said nothing about overinflating or underinflating tires. I said I prefer inflating to (or up to) the recommended max pressure printed on the sidewall of the tire. And, until someone gives me a legitimate scientific explanation of why I shouldn't..I'll continue to do so. BTW, your explanation was far from a "scientific" explanation..sorry.

110-120 psi is probably the proper/optimum range of you weight... but you say "recommended max pressure" but recommended pressure and max pressure are two different things... which is it? max or recommended. you seem to be doing exactly what most of the people you are arguing with are saying... using optimal pressure, not max pressure (seem to be in violent agreement with them) i gave the example of continental... who rate the continental spinters "rec. inflation" = 115psi", "max. inflation" = 170psi

conti-online.comsprinter en.htmlOpen ↗

again 110-120psi for your weight with 23-25mm tires sounds just about right to me... put a conti and 170psi on there or a vredstein tubular rated at max 200psi and see how your fillings fall out and you feel like you've been through 12 round with Tyson (when he could actually fight)... see how good you can corner with your tires pumped up to 170-200psi

dhk2 said:

In your list of things that affect handling and ride, I'm surprised you left off spring rates and shock damping rates. I've had just enough experience with road motorcycle suspensions to know how excessive rebound damping can mess things up.

I also recall learning that too much pressure in the front tire of a motorcycle is the easiest way to ruin roadholding and grip. Same is true for bike tires....rock-hard tires can make a descent on rough roads a real thrill.....while adding nothing to downhill speed when the road smooths out.

I've never met anyone who inflated their car tires to the max allowable pressure, but I guess I come here to learn. You actually run your car tires at 44 psi? BTW, I run my tires at or just above the pressures recommended by the manufacturer and generally get excellent life from my tires. They have engineers too you know and are keenly motivated to post good fuel economy numbers. I've found the key to long tire life is rotation and rebalancing every 6-8K miles, not over-inflation.

I'll leave the scientific explanations to alienator. But what might seem obvious when you're thinking about a tire on a smooth steel roller in a lab just doesn't carry through to a tire running on most real-world roads.

I think I did finish my list of things with "etc." I agree with you..everything you mentioned will affect handling and ride.

I guess I'm the first guy you met that inflates up to the max cold pressure then. BTW, I didn't say at the max..I said, "up to" the max. Know why I'm probably the first? Because I'll bet you that 98% of the people that drive cars have no idea what the pressure is in their tires from day to day. I'm probaly the first guy you met that also carries around a very expensive/accurate tire pressure gauge and measures the pressure in his cars tires (BMW 540i) at least once a week.

BTW, I'm asking not quizzing..what are the tire manufacturer's recommended pressures? How do they differ than what is printed on the tires placard? And, where are they (recommended pressures) located..on the tire somewhere? Or on some literature? I know OEM data is printed on the inside of the door jam..but what if you don't have the OEM tires? Does it still apply to other tire manufacturers?

Yes, I'm on here to learn too..not listen to some perpetual student like Alienator who is obviously trying to impress me with how much he doesn't know. He still hasn't offered any useful information. I'm not going to respond to any of his posts anymore..I've seen guys like him on other message boards..the know it alls..that never offer any useful information..just their opinion..which aint worth a thing.

mullerrj said:

I think I.....

I don't like automotive analogies being used for bikes, but I'll try a bad one just for you 🙂

To get your car more like a bike, concerning weight and suspension relative to pressure, what if your car had no suspension (only some carbon struts), the tyres were 30mm deep and pumped up to 250 psi? Would you bounce around the road then, evena t moderate speeds? 🙂

Anyway, 120/110 ain't that high for you, but would you start using 140psi if you bought some high-end Vittorias or Vredesteins?

I ain't not no scientifician, but I rode 20mm Continentals with ~160psi in them for about 10 years, thinking I had the fasting thing going (I even bought 18mm Contis when I could get them), but I finally saw the light, and I now use 23s at about 110/120. I'm 85/86kg

[img]musicianforums.comthumb.gifOpen ↗[/img]

Oh, man: this guy's funny. It's amazing....before I grant the vaunted status that you as an engineer apparently deserve....I should remind you that there are many engineers following the direction of grad students. Look around cupcake.

You would think an engineer would know how to search for info. about how to inflate his bike tires......

1. The pressure listed on the side of a bike tire is generally the max inflation pressure. It has nothing to do with recommended inflation pressure. See, if it doesn't say "recommended" then it isn't the recommended value.
   
2. Certain tire manufacturers recommend unusually high inflation pressures, knowing that there are customers that don't know better that will think that high pressure equals fast. The fact is that the spring rate of the air in the tire more than dominates carcass differences for a given size tire.
   
3. Bike tires have small contact patches. Higher pressure means smaller contact patch. That means less traction. Have at it, cupcake, but I rather like traction mid-corner.
   
4. What do I do? I do science all day long, baby. I work with engineers, and explain to them the things they don't understand.
   
5. Tire bouncing is only the extreme example. The tire doesn't have to bounce. All that has to happen is the tire's load vector change direction or go down in magnitude. That leaves a whole lot of room between planted and bouncing. Work done to change that vector is energy wasted.
   
6. Rolling resistance. There is a lot of misunderstanding about rolling resistance. Yes, rolling resistance does vary inversely with pressure; however, that "bouncing" has a large enough effect to more than offset the increase in pressure and reduction in rolling resistance. The only place that knowledgeable cyclists will inflate their tires to or near the max is in a velodrome, where the track surface is butter smooth.
   
7. Over inflation of the tire will lead to increased wear for the following reasons:
   1. An overinflated tire will puncture and cut more easily since it will deflect less of the offending road detritus.
      
   2. Overinflated tires don't heat up properly, and as a result they are susceptible to "cold tearing." At colder temps (relative to optimum operating carcass temperature), the carcass is less pliable, less elastic, and thus more likely to tear. Look at any car or motorcycle race tire that has cold tearing if you don't believe.
   
   
8. For future reference, just tossing out the word "engineer" gains you nothing. There's no implied credibility. There are more than one or two engineers that suck, so as far as anyone here is concerned, you are just as likely to be one of the engineers that suck as you are to be one that is passable or one that excels. Titles mean [censored].

My favorite forum on this site ? I always get the informative, worthwhile stuff by clicking on Alienator's name and going to his last post...😄

[quote="alienator"]

1. Over inflation of the tire will lead to increased wear for the following reasons:
   1. An overinflated tire will puncture and cut more easily since it will deflect less of the offending road detritus.
      
   [/QUOTE]
   

well as far as your cars go the best tire presure is the one on your door sticker. best wear best MPG best performance for the street have a nice day

alienator said:

How do you know you don't get any bounce? The amount of force applied in directions not parallel and of the same sign as the vector defining the direction of travel doesn't have to be so much as to make you feel a "bounce." It can be much more subtle than that.

I can also guarantee that both underinflation and overinflation cause increased wear, worse traction, and thus worse handling. I've seen it first hand and up close on tires that have come off superbikes that I raced.

Being an engineer you'd think you would have thought this through more.

Sorry to say, but Alienator is completely correct (once again). No one who knows anything about tires and cars would inflate their tires to the tire manufacturer's max rather than the auto manufacturer's recommendation!

mullerrj said:

I think I did finish my list of things with "etc." I agree with you..everything you mentioned will affect handling and ride.

I guess I'm the first guy you met that inflates up to the max cold pressure then. BTW, I didn't say at the max..I said, "up to" the max. Know why I'm probably the first? Because I'll bet you that 98% of the people that drive cars have no idea what the pressure is in their tires from day to day. I'm probaly the first guy you met that also carries around a very expensive/accurate tire pressure gauge and measures the pressure in his cars tires (BMW 540i) at least once a week.

BTW, I'm asking not quizzing..what are the tire manufacturer's recommended pressures? How do they differ than what is printed on the tires placard? And, where are they (recommended pressures) located..on the tire somewhere? Or on some literature? I know OEM data is printed on the inside of the door jam..but what if you don't have the OEM tires? Does it still apply to other tire manufacturers?

Yes, I'm on here to learn too..not listen to some perpetual student like Alienator who is obviously trying to impress me with how much he doesn't know. He still hasn't offered any useful information. I'm not going to respond to any of his posts anymore..I've seen guys like him on other message boards..the know it alls..that never offer any useful information..just their opinion..which aint worth a thing.

Yes, I carry two gauges also in the car....a digital and a regular pencil gauge. Only check them about once a month though, and usually let them leak down a good 2 psi before refilling. Agree many drivers don't check them often enough.

I'm confused now. Do you run your car tires at 44 psi cold, or whatever is stamped into the sidewall as a max load pressure rating, or do you use the car's placard recommended pressures which are quite a bit lower? BMW charges a lot for that german engineering; I'd trust their specs on tire pressures without hesitation.

For replacement tires, my guess is the car maker's recommendations would still be valid providing the new tires are the same size and speed ratings.

dhk2 said:

Yes, I carry two gauges also in the car....a digital and a regular pencil gauge. Only check them about once a month though, and usually let them leak down a good 2 psi before refilling. Agree many drivers don't check them often enough.

I'm confused now. Do you run your car tires at 44 psi cold, or whatever is stamped into the sidewall as a max load pressure rating, or do you use the car's placard recommended pressures which are quite a bit lower? BMW charges a lot for that german engineering; I'd trust their specs on tire pressures without hesitation.

For replacement tires, my guess is the car maker's recommendations would still be valid providing the new tires are the same size and speed ratings.

On my Chevy Tahoe, my tires (265/70R16) have a 44psi cold max rating stamped on them. Since I tow a boat, or have a heavy load in the truck most of the time, I keep the tires inflated btwn 40-44 psi. i.e. 44 when I tow and bled down to 40 when I'm not towing or carrying a heavy load. No placard on the doorjam..not the front or rear. Must've been removed after the door was replaced in a recent accident..guy backed in to me. I'll have to check and see what it is from another Tahoe owner I know or the dealer.

The BMW is a little more complicated. And now I'm confused. I have 235/40ZR18 on the front with a 51psi cold max rating and 265/35ZR18's on the back with the same 51 psi cold max rating printed on the tires. The recommended max load pressure for the front (according to the placard in the door jam) is 41 psi and for loads up to max- 38 psi recommended. Since I usually drive the BMW alone, I was setting the pressure at 45 psi..which I just realize now is too high..7 psi too high for the front. For the rear tires, the recommended max load pressure is 48 psi, and 41 psi for loads up to max. So, for the rear I was 4 psi overinflated. I don't go far with the bimmer but I do drive FAST...but I never realized excessive tire wear or handling issues..and the ride is awesome. Anyway, what I'd like to know is why the tire has a cold max load pressure printed on it that differs from the door jam placard? For the front tires on the BMW, it differs by 10 psi.

So, it seems like I was fine with the tire pressure in the Tahoe, off with the Bimmer (which is more crucial since I generally drive a lot faster and more concerned with safety and tire wear- cause the tires cost a bundle) and on my bike with my Conti GP 4000's I was ok (btwn 110-120 based on my 80 kg weight).

Anyway, good learning experience and lesson on tires. See if you can help answer my question on the max pressures. i.e. that printed on the tire vs. that printed on the door jam placard differing by 10 psi on the BMW. Thanks for your help/advice.

mullerrj said:

On my Chevy Tahoe, my tires (265/70R16) have a 44psi cold max rating stamped on them. Since I tow a boat, or have a heavy load in the truck most of the time, I keep the tires inflated btwn 40-44 psi. i.e. 44 when I tow and bled down to 40 when I'm not towing or carrying a heavy load. No placard on the doorjam..not the front or rear. Must've been removed after the door was replaced in a recent accident..guy backed in to me. I'll have to check and see what it is from another Tahoe owner I know or the dealer.

The BMW is a little more complicated. And now I'm confused. I have 235/40ZR18 on the front with a 51psi cold max rating and 265/35ZR18's on the back with the same 51 psi cold max rating printed on the tires. The recommended max load pressure for the front (according to the placard in the door jam) is 41 psi and for loads up to max- 38 psi recommended. Since I usually drive the BMW alone, I was setting the pressure at 45 psi..which I just realize now is too high..7 psi too high for the front. For the rear tires, the recommended max load pressure is 48 psi, and 41 psi for loads up to max. So, for the rear I was 4 psi overinflated. I don't go far with the bimmer but I do drive FAST...but I never realized excessive tire wear or handling issues..and the ride is awesome. Anyway, what I'd like to know is why the tire has a cold max load pressure printed on it that differs from the door jam placard? For the front tires on the BMW, it differs by 10 psi.

So, it seems like I was fine with the tire pressure in the Tahoe, off with the Bimmer (which is more crucial since I generally drive a lot faster and more concerned with safety and tire wear- cause the tires cost a bundle) and on my bike with my Conti GP 4000's I was ok (btwn 110-120 based on my 80 kg weight).

Anyway, good learning experience and lesson on tires. See if you can help answer my question on the max pressures. i.e. that printed on the tire vs. that printed on the door jam placard differing by 10 psi on the BMW. Thanks for your help/advice.

The tire max pressure is the tire makers rated pressure to carry the max load rating on the tire, without regard for what vehicle it will be used on. You might check the max load rating on the tire and see how that compares to the estimated weight your BMW puts on each wheel; it should be below vehicle fully-loaded weights by a good margin, maybe 20% or more. In that case, you never need to go up to the 51 psi.

I'll bet you like the ride better on the BMW with the lower pressures, with no loss of fuel economy. After all, that big 5-series V8 is supposed to be a smooth GT machine, not a harsh street racer.

Back to bikes, today I cut my rear GP4000 on a sharp rock and had a blowout; first one in 3 years. With a Park stick-on boot patch on the inside of the tire all looks fine so should be able to continue to run the tire. As we all know, no tire is bulletproof.