njkayaker

I think it was a basically a reprint with a note by Berto that said nothing had changed in the interim that would change the conclusions of the original article. That is, it is not (it seems) based on recent (circa 2006) research.

This is basically the Berto article. It's not (it seems) based on recent tests.

cooleric1234

https://en.wikipedia.org/wiki/Ad_hominem

https://en.wikipedia.org/wiki/Argument_from_authority

MKahrl

Correct.


This article is based on the 2006 tests. It is written by Jan Heine, the editor of Bicycle Quarterly. It mentions that tire construction was the biggest determinate in rolling resistence. A relatively fast tire, the Michelin Pro Race 2, in widths of 21mm, 23.5mm and 25.5mm but with the same construction, had nearly the same speed. (the 25.5mm was 2% faster than the 21mm). The differences between tires of different construction were much greater.

The reason Frank Berto's older graph keeps showing up is that it agrees with more recent testing done by others AND it's a handy starting point for anyone trying to figure out what size tires and pressure to use for their application. This is especially important for anyone doing self supported touring where the loads may vary 40 or more pounds depending on what their doing.

I think tire manufacturers have known all along the importance of tire construction and have started to offer premium construction tires in widths 28mm and larger.

The market's move towards narrow tires starting in the 1980's had more to do with everyone's fascination with light weight than measured performance gains. Consumers would look over catalogues and order the tire with the lowest gram count. Manufacturers would market a low-gram 23mm tire by relabeling a 21mm tire 23mm. There was no correlation between marked size and actual width. This has slowly been corrected in the 2000's.

The one good thing to come of narrow clincher tires was that since they HAD to be higher pressure they HAD to be better built. Today we are are enjoying better built tires in a range of sizes.

Runner 1

Is this like an internet special? I see it everywhere. "I'd like to order two Latin phrases from Wikipedia. Why, it does make me look smarter than you!"

pacificcyclist

Different riding positions dictate the different pressure contact points on the front and on the rear. You still have contact on the saddle and on the handlebar, but the varying degrees of those points vary with pedal effort. Weighting the front and back on the scale while you are on it is a good start. But remember that you can not move the bike without spinning the crank. After that, it is all about perception of ride comfort with a reasonable pedaling effort.

A lot of riders here use a varying degree of tire pressure ranging from the high a 130psi to a low of 40psi or maybe lower. The principle of the Bicycle Quarterly article addresses the common mistake most riders make and that is, they believe that over-inflation helps them ride faster when in fact, over-inflation does not after a certain point.

Lastly, I am advocating the article because it applies to a majority of riders out there who do over-inflate and should not be. But, I like to point out that article is not bible or be all end all as you notice there are other people who ride with much higher tire pressure. This is a reflection of the quality of tires used and the skill level they are at. Newer race quality tires and most tires in general are better built, have exceptionally lower rolling resistance that setting up tire pressures now is just a matter of personal preference rather than following the bible.



Cheers,

chas58

+1 Now that is a good summary, Pacific.

And, it gets people thinking - do I really need the max PSI for the type of riding I do? In a few cases, the answer is yes, in many cases the anwer is no. It is worth it to experiment for your type of riding - lowering the pressure a bit isn't going to kill your performance. A little less in the front tire (which typically takes less weight) can really improve your ride.

It is a good discussion. Read the pro's and Con's, experiment, and make your own conclusion.

Minion1

Thanks Bob, your comments and insight have provided plenty of food for thought.

njkayaker

This matches my understanding. My point that there wasn't new research was to make sure that was clear (not as a criticism). It appeared that some people may have thought that Jan Heine's 2009 was based on new data.

njkayaker

Huh? There is no practical way of determening the fore/aft load while riding! So, while what you are saying is (obviously) true, it's not clear how one would use what you are saying to pick a tire pressure.

Since you can't vary the tire pressure while riding (to accommodate different riding positions or terrain), you are forced to pick one pressure for a given ride. It's possible that the properties of a particular ride (eg, rough road conditions) can be used to choose a tire pressure.

People are free to do what they want and use whatever method they like to get there. But, that doesn't mean it make any sense. These kinds of observations are notoriously unreliable.

I don't recall people talking about "40 psi or lower" (for 23 mm tires?). Yes, a lot of riders use different pressure. We don't really know on what (if anything) they base the pressure they. We don't even know their weights!

If people are treating one part of the article as a "bible", they are missing the point. Berto and others make it quite clear that, if your situation is significantly different from the "average" situation their numbers apply to, you should use different numbers.

The higher pressure is not reflection of anything because we have no idea why people choose to higher pressure. Indeed, the rational for it is much more mysterious than the rational in the Berto (and related) articles!

People are free to to follow their "personal preference" but that doesn't mean it makes any sort of sense. And no one is (or should be) suggesting following a "bible".

Anyway, we aren't really talking about icecream flavors: ideally, people should understand what the trade-offs of higher/lower pressure and choose an appropriate pressure for them that makes sense.

njkayaker

In the Berto graph, 70 psi is shown for 23 mm tires with a ~140 lb total load (rider+bike).

Very, very few riders (if any) are doing that!

Bob Dopolina 

I hope you're not hiding behind wiki links as you call me a liar.

That would just make me so sad.

So very, very sad.

mooska

If I weigh 198lbs and I pump my 25cm tires up to 130psi, should my weight make it flatten at all or should it be able to completely hold it's shape where it meets the pavement?

cooleric1234

Yes, I can see you're torn up. I'm not calling you a liar or trying to hurt anyone. Obviously this is a topic of heated debate. I'm just saying it would be beneficial to everyone to stick to the facts that we know.

I'm not trying to say I'm smarter than anyone. Don't blame me, I didn't name them

revchuck 

The only way it's going to not deflect whatsoever is if it's made of a non-malleable material. I don't know why you'd want that (if in fact that's what you want), but it's a free country.

FWIW, we weigh about the same, and I run 90 psi in the front and 100 psi in the rear in my 700x25s.

Minion1

Also depends on the type and condition of the tire. Gatorskins? A little bit. Veloflex? A bit more. Silk track tires? Heaps. There is no magic weight to sag measurement, just a pressure where you're comfortable, the tire grips properly and you don't flat every 4 metres.

Reynolds 

I remember when I had a rod brake Raleigh with original 28 x 1 1/2 Dunlop tires. On the sidewall it read "INFLATE HARD"!

Bob Dopolina 

Ok.

Fact. I worked with/for Continental AG. The people who designed and produced the tires I've mentioned gave me first hand information.

I also saw several test conducted germane to the topic at hand therefore I feel I can be pretty confident in what I know.

I think I've been pretty open to conflicting information as long as the information stands up to scrutany. I honestly have little tolerance for non-sense (admittedly a character flaw) and can be dismissive of those proposing such but I don't hink I've launched any ad hominem attacks.

What is interesting in the section of my post that you quoted is that the author of the article I was commenting on specifically said he stopped working with the magazine for the reasons I mentiond. At least I agree with him on that.

njkayaker

Fact: Berto is a well-respected and well-known bicycle tech expert. While that doesn't preclude reading what he said critically, just being dismissive about what he says isn't a strong critique. Your authority doesn't match his.

cooleric1234 criticism of you is really trying to point out the weakness of your argument (which is pretty weak).

He also manages to provide much more detail about the basis of what he is talking about (which seems correct to me) while you have provided no details at all.

The only thing that really seems odd in Berto's advice is the low pressure for narrow tires (eg 70 psi for 23mm times with a 140lb total load).

z90

I'd just like to point out that, assuming a 20 pound bike, that means a 120lb rider. That might actually be not "too fat for this sport"!

Bob Dopolina 

The information I have is first hand experience gained while working for a major tire manufacturer. Seems pretty credible to me. This is iincluded in the 25 years I have in the industry.

Any hard data I have access to is not mine to publish in an open forum.

Next we'll all be asked to swallow Zinn.

I've said all I have to say in this thread so I'll just leave it at that.

z90

Which basically leaves us with no published, reviewable hard data at all to refute Berto's advice.

Bob Dopolina 

Seriously?

This whole thread has been about 1 article that has questionable protocols.

First page on google.

z90

Here's all the information your link gives about the protocol they used:
Protocol: The Coefficient of Rolling Resistance (Crr), was aquired by testing all tires on a 120 cm (47.244") drum at 30 km/h (18.64 mph). Loading was similated with a 44/56% balance of front and rear tire. Total bike including rider weight was 85 kg (187.39 lbs).

The picture seems to show some kind of testing rig with the tire contacting a smooth metal surface (favors higher pressures). The data table on clinchers only used one pressure. No tires used were greater than 24mm width. One speed, one rider weight, poor simulation of road surface, only one pressure for clinchers. Two pressures for tubulars show very small differences in rolling resistance, and differences on the order of 1-2 watts in power. Meh.

njkayaker

The only particular advice you've provided is to use 110 psi! And you really don't say why.

I don't think you are wrong but you are being vague and your supporting argument is mostly "trust me"!

Is that a good or bad study? You don't say.

That link showing results for tests at 101 psi in 23+- mm tires with a 187.39 lb total load.

And it doesn't refute Berto's article at all. It appears to be showing the differences in rolling distance at one particular pressure and load.

It isn't attempting to provided guidance for what pressure to use to balance load-capacity, rolling resistance, cornering, and comfort.

motobecane69

the only thing i've gotten out of this is that apparently people that weigh 240lbs like me can't ride road bikes at all because no 23mm clincher tire is rated for 160psi