Over-inflate by a few psi?



alienator

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Jun 10, 2004
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Mojo Johnson said:
Okay - tying it all together:

The max and min psi figures are posted on the sidewall. The ideal psi is dependent upon anatomy but should be somewhere between the posted max and min to allow for optimal performance and safety. My ideal is approximately 107 psi and I adjusted as such yesterday per the suggestions in this thread.

Trial run of 20 miles yeilded no reduction in speed but no discernable improvement in comfort (I was never uncomfortable at 120 psi though). I will continue to run at this pressure for my next long ride to see if it makes a difference over the long haul.

Thanks for all your comments and help. Keep it friendly, eh? :)

You can also reduce your pressure a bit more. The Michelin chart is a guideline and a good starting point, but it isn't cast in stone.
 

Funseeker

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Jul 6, 2010
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Actually when I bought my tires, same brand, the manufacturer clearly stated the reason for the maximum and minimum pressures had mostly to do with tire durability. Below the minimum and the risk of flats increased and tire durability decreased. Over inflating wasn't considered quite the same level of sin. Comfort never entered into the presentation. Now Michelin tires may be different and my comments are restricted to Armadillos.

This has been an interesting thread. In my over 50 years in technical fields I've never before encountered anyone who misunderstood the terms. But, I'm a cycling newbie so I guess its' different here. I'll remember that.
 

alienator

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Funseeker said:
Actually when I bought my tires, same brand, the manufacturer clearly stated the reason for the maximum and minimum pressures had mostly to do with tire durability. Below the minimum and the risk of flats increased and tire durability decreased. Over inflating wasn't considered quite the same level of sin. Comfort never entered into the presentation. Now Michelin tires may be different and my comments are restricted to Armadillos.

This has been an interesting thread. In my over 50 years in technical fields I've never before encountered anyone who misunderstood the terms. But, I'm a cycling newbie so I guess its' different here. I'll remember that.

This is what Sheldon Brown's site has to say about tire pressure:
Most tyres have a "maximum" pressure, or a recommended pressure range marked on the side of the tyre. These pressure ratings are established by the tyre manufacturers after consultation with the legal and marketing departments.
The legal department wants the number kept conservatively low, in case the tyre gets mounted on a defective or otherwise loose fitting rim. They commonly shoot for half of the real blow-off pressure. The marketing department wants the number high, because many tyre purchasers make the (unreliable) assumption that the higher the pressure rating, the better the quality of the tyre.

Newbies often take these arbitrary ratings as if they had some scientific basis. While you'll rarely get in trouble with this approach, you will usually not be getting the best possible performance with this rote approach. Savvy cyclists experiment with different pressures, and often even vary the pressure for different surface conditions. Optimal pressure for any given tyre will depend on the load it is being asked to support. Thus, a heavier rider needs a higher pressure than a lighter rider, for identical tyres. Since most bicycles have substantially more weight on the rear wheel than on the front, the rear tyre should almost always be inflated to a higher pressure than the front, typically by about 10%.

That's about the sum of it.
 

Funseeker

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So, unlike airplanes, cars, trucks, etc the pressure markings on bicycle tires are not derived from performance engineering and have very little meaning?
 

alienator

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Funseeker said:
So, unlike airplanes, cars, trucks, etc the pressure markings on bicycle tires are not derived from performance engineering and have very little meaning?

What's the performance metric: contact patch size, rolling resistance, wear, flat resistance? The important metrics vary depending on the situation. And no, the pressures listed on bike tire sidewalls are not from extensive testing, save for blow off testing, as mentioned by Sheldon Brown.
 

frenchyge

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Mojo Johnson said:
Trial run of 20 miles yeilded no reduction in speed but no discernable improvement in comfort (I was never uncomfortable at 120 psi though). I will continue to run at this pressure for my next long ride to see if it makes a difference over the long haul.

A careful review of what's posted on the Michelin site shows that what a tire manufacturer considers tire "performance" is actually a blend of not only rolling efficiency and comfort, but also grip and durability. While you might not have noticed an improvement in comfort by running the lower pressure, it's likely that grip and durability will be better, without a sacrifice in rolling efficiency. Overall, that's better "performance."

Edit: additional comments deleted.
 

frenchyge

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alienator said:
And no, the pressures listed on bike tire sidewalls are not from extensive testing, save for blow off testing, as mentioned by Sheldon Brown.

That seems unlikely from the info on the Michelin and Zipp sites. Half the blow off pressure might set the posted maximum pressure (too allow room for rim/tire heating during riding and braking), but that wouldn't explain how the recommended sub-maximal pressures by rider weight and tire width were derived.

Recommended tire pressures by rider weight:
Rider WeightFront psi (bar)Rear psi (bar)<125 lbs
(<57 kg)107 (7.38)110 (7.58)125-150 lbs
(57-68 kg)112 (7.72)116 (8.00)150-175 lbs
(68-79.5 kg)115 (7.93)119 (8.20)175-200 lbs
(79.5-91 kg)118 (8.14)122 (8.41)>200 lbs
(>91 kg)122 (8.41)125 (8.62)Triathlon/TTUse Rear Press.SameRain or rough RoadsMinus 2-4 psiMinus 3-5 psiIndoor Track125 (8.6)125 (8.6)Outdoor TrackPlus 2-5 psi*Plus 3-5 psi*
*Not to exceed 125 psi/8.6 bar
The above tire inflation pressures are recommended for optimal rolling resistance and grip. These pressures are for room temperature tires and rims. Tire pressures may increase as much as 25psi due to high rim temperatures caused by prolonged braking or as much as 5psi from high ambient or road surface temperatures.

Zipp - Speed Weaponry | Accessories | Tires | Tangente Clincher Tires
 

alienator

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frenchyge said:
That seems unlikely from the info on the Michelin and Zipp sites. Half the blow off pressure might set the posted maximum pressure (too allow room for rim/tire heating during riding and braking), but that wouldn't explain how the recommended sub-maximal pressures by rider weight and tire width were derived.

Their suggestions are perfectly linear, save for the <125 lb category, so I don't see anything surprising there. They could be standard suggestions from Vittoria, since they are the makers of the Tangente tire. Maybe they did tests. They don't say, and Zipp does love to tout it's testing.
 

Funseeker

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So, at this point this thread seems to be following a non-logical path in that it is trying to somehow match empirical with subjective. Air pressure, or nitrogen pressure if you follow the latest fads, with Comfort. And is doing so without some common definitions.

I'm left with some wondering: Just how transferrable is information from one manufacturer to the tires of another? If one person makes assertions regarding what pressures at which one can operate tires if outside the manufacturers recommendations upon what objective testing do they base those assertions? Just what safety standards are there for bicycle tires?
 

roadhouse

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cutegirl said:
I wouldn't worry about. 4 psi sounds like way too much anyway. Almost all the air you hear escaping is the pressurized air in the pump hose.


hehe, Alienator got cutegirl spammed.
 

alienator

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Funseeker said:
So, at this point this thread seems to be following a non-logical path in that it is trying to somehow match empirical with subjective. Air pressure, or nitrogen pressure if you follow the latest fads, with Comfort. And is doing so without some common definitions.

I'm left with some wondering: Just how transferrable is information from one manufacturer to the tires of another? If one person makes assertions regarding what pressures at which one can operate tires if outside the manufacturers recommendations upon what objective testing do they base those assertions? Just what safety standards are there for bicycle tires?

Nitrogen? When did that become a fad?

What non-logical path? What common definitions?
 

Funseeker

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alienator said:
Nitrogen? When did that become a fad?

What non-logical path? What common definitions?

As far as this thread goes it feels like I dropped through the looking glass. Headed back to Kansas....
 

tafi

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Jul 31, 2003
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maanderx said:
When I did a bike maintenance course a couple of years ago, the guy in charge
said that tyres can easily go to almost twice the max psi they are rated for. The
conservative figure stated on the side of the tyre is something to do with fear of
some sort of litigation (by the manufacturers) if it exploded at the higher rate.

I've been running Michelin Krylion Carbon at 120 psi with no problems on
Mavic Open Pros and Shimano Dura Ace 7850 CL. I'll continue to do so.

This is quite true of the casing. Almost every casing can easily withstand very high pressures. But, for a clincher tyre, there are two other factors which come into play a lot ealier than casing strength and the tyre manufacturer has little-to-no control over these.

Both relate to the rim. The flanges of the rim are pushed apart by the force due to tyre pressure (and larger tyres will exert more force at the same pressure). If this is high enough the rim will split apart. If brake track wear is high, this is made worse. Mavic (for example) have often provided recommended maximum tyre inflation pressures for use with their rims.

The other consideration is the tyre bead/rim hook interface. Tyre pressure also pulls the tyre outwards aginst this joint. One half is designed by the tyre maker, the other by the rim maker. While it might be "standardised" there is a huge variability in the strength of this joint depending on tyre and rim combination.

Over-infaltiion is common but all should remember that this is done at the riders own risk.
 

frenchyge

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Funseeker said:
So, at this point this thread seems to be following a non-logical path in that it is trying to somehow match empirical with subjective.

Forum threads don't really follow paths and typically don't have a logical structure to them. It's more accurate to think of them as many people talking at the same time about a related topic, but not necessarily the same thing at the same time. Each subsequent post hopefully adds something to the overall picture, but not necessarily in a logical path. Coupled with the fact that this topic has both subjective and objective aspects to it, I think your expectations of what you'll get from a free internet thread might be a tad high. This is a free and open discussion about tire pressures, not a paid lecture series.

Funseeker said:
I'm left with some wondering: Just how transferrable is information from one manufacturer to the tires of another? If one person makes assertions regarding what pressures at which one can operate tires if outside the manufacturers recommendations upon what objective testing do they base those assertions? Just what safety standards are there for bicycle tires?

For best results, take each individual post with a grain of salt but expect that the overall discussion will contain a good amount of useful information and advice. I think this thread has provided enough good information that someone wanting to know more has been shown a couple good directions to research further. If you have specific questions regarding an assertion in an individual post, then quote the statement in your reply and ask your related questions.

Funseeker said:
As far as this thread goes it feels like I dropped through the looking glass. Headed back to Kansas....

Kansas is nice this time of year, and we're having a mild summer so far.

Welcome to the forums. I look forward to reading some of your contributions in the future. :)
 

pat5319

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Jan 9, 2002
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jojoma said:
A mechanic once told me that about 4 psi are lost when removing the pump head. Is this true? My Michelin Pro3 race have a max of 120psi. I usually go to about 118 and call it quits. To get to 120psi, should I go to 124psi??:confused:

why not under-inflate for a smoother ride? and smooth is faster
 

pat5319

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I generally unde-rinflate as ther ride and grip are better the numbers on the tire are generally for MAXiMUM ingflation. recent research confirms that under inflated tires are acutually faster as they absorb shock better etc thepros and "old timers" have kownn this for decades
 

tonyzackery

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Originally Posted by pat5319 .

I generally unde-rinflate as ther ride and grip are better the numbers on the tire are generally for MAXiMUM ingflation. recent research confirms that under inflated tires are acutually faster as they absorb shock better etc thepros and "old timers" have kownn this for decades
Disagree. Unless you're racing in Europe on cobbles or very poor pavement (in my racing locale we race on courses that more often than not involve very good pavement with an occasional less than smooth section), I'm going the higher pressure > lower rolling resistance > less wattage required for a given speed route. With myself being a heavier (195) than average roadie, higher pressures provide an even greater advantage...Bigger than average racers should run higher pressures, IMO, and if you don't race it doesn't really matter all that much...ymmv.

Not tryin' to start an argument, simply stating my opinion based on my experience and published tire test results on smooth surfaces - of which my races are predominantly conducted on...
 

Daddo

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Originally Posted by tonyzackery .

" . . . Not tryin' to start an argument, simply stating my opinion based on my experience and published tire test results on smooth surfaces - of which my races are predominantly conducted on...
Nothing wrong with your opinion/comment (which I agree with). Tire pressure selection should be an educated decision based upon expected road conditions, temperature, type of tires in use and most importantly rider weight - the weight of the bike and rider is supported on two, tire to road (or trail) contact patches. In VERY simple terms, if 2 square inches of contact need to support a load of 200lbs. Those tires will need to run 100PSI.

This is a seat-of-the-pants type of formula since lower pressures will generally result in a larger "contact patch" area. The "best" pressure can change radically on wet roads, or hard or soft packed dirt trails. It is really a "How does the bike feel kind of thing,"

Again, good comment.


Adiós, Daddo --- Daytona Beach, Florida - USA
"Wovon man nicht sprechen kann, darüber muß man schweigen." ("What we cannot speak of we must pass over in silence.")
 

tonyzackery

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Originally Posted by Daddo .




Nothing wrong with your opinion/comment (which I agree with). Tire pressure selection should be an educated decision based upon expected road conditions, temperature, type of tires in use and most importantly rider weight - the weight of the bike and rider is supported on two, tire to road (or trail) contact patches. In VERY simple terms, if 2 square inches of contact need to support a load of 200lbs. Those tires will need to run 100PSI.

This is a seat-of-the-pants type of formula since lower pressures will generally result in a larger "contact patch" area. The "best" pressure can change radically on wet roads, or hard or soft packed dirt trails. It is really a "How does the bike feel kind of thing,"

Again, good comment.


Adiós, Daddo --- Daytona Beach, Florida - USA
"Wovon man nicht sprechen kann, darüber muß man schweigen." ("What we cannot speak of we must pass over in silence.")
Appreciate you sharing your opinion. Not really a matter of who's right or wrong - people have their beliefs on this matter as there are published test reports on both sides of the contention. Personal experience and the race conditions are usually the deciding factors. Might I add, however, the only time I run pressures less than 100psi (for races 130-140) is on the stationary trainer as I don't race in the wet...again, ymmv.
 

Mak'em Lad

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Originally Posted by Funseeker .

So, unlike airplanes, cars, trucks, etc the pressure markings on bicycle tires are not derived from performance engineering and have very little meaning
My car tyres are marked at max. 44psi but the car manufacture recommends a lower pressure (around 30psi with front a couple of psi higher than the rear). If carrying a heavier than normal weight then it is normally advised to increase the tyre pressures slightly (don't have exact figures available but it's only 2-4psi) Are you suggesting I should ignore Nissan & inflate to 44psi?


I don't think so, that would go against all I was taught as a motor mechanic

Tyres also have a max. speed rating, should I drive at that max. speed all the time (but officer, it says on my tyres max 90mph so I HAD to drive that speed. Can't see me getting let off a speeding charge with that excuse).

As others say, max is the recommended MAXIMUM, not the idea running pressure (the tyres are manufactured to withstand higher pressure although it's not advised to run above the max. figure). The heavier the bike/rider combo the higher the pressure needs to be but should not exceed the max. (and in most cases would still be under the max. even with a rider at max. weight for the bike).