Berto came up with 15% drop as a recommendation for optimum performance, as opposed to using maximum pressure. As I recall, he collected data points used rollers with some roughness to plot efficiency curves, which gave him target pressure, then measured drop to empirically draw the pressure chart that many still use today. Bicycling saw no value in research, so they fired him. Thus it was 25 years before anyone picked up where he left off.

His chart does not cover very wide tires or higher loads, so I made my own calculator using the section of a torus mathematical model. It matches his chart almost exactly, in spite of how crappy some of the tires he was testing were. With very wide tires, 15% is unnecessarily hard because distance provides protection from pinch flats. I use a figure of 20% for 38mm or larger tires, which is not too squishy.

The roller method favors hard rubber and stiff casings, so not very useful as a test method.

So....three pages in on tires. I am wondering why something as banal as bicycle tires brings out such a passionate responses?

So are 20-23mm tires considered retro already?

Also, would I make a huge mistake putting 25mm tire on an early 90s bike?

If bicycle tires were banal, we wouldn't have so many manufacturers applying so much science and tech to improve them.

Ride some really high-quality tires (tubulars, or high-tpi lightweight clinchers) back to back with some really low-quality tires and let us know if the difference is banal.

I don't think the difference is ( I ride Compass EL tires, FWIW) but many others do. Also the topic illicits many strong opinions (see your post) and I am curious as to why people get so emotionally attached to tires?

If they are, I'm happy to be retro. As for 25s, do what makes you happy!

My '87 Mercian Pro has crit geometry and 23s make it sing. I'm big - 6'3 just under 200 so I run them hard, about 110 rear and 90 - 100 front. My Raleigh Sports on the other hand runs with Panaracer Col de la Vies at 50 - 55 tops for super smooth and pothole-resistant city riding.

Isn't it kind of an Internet maxim that the least-consequential topics lead to the most heated debates? See also: chain lube.

Right. For some reason, I thought it was the roller tests done by Avocet and others that led people to think that higher pressure always reduced rolling resistance -- I could be misremembering it.

Sounds right to me! Do you have a shareable calculator or chart that figures out 20% drop?

So true...thanks for reminding me.

Me too. No, make that me three!

[MENTION=152773]noglider[/MENTION] mentioned air seeping out. Lately I've been doing a lot of commuting on my Veloflex tubulars. The latex tubes can drop 40psi in a day. That means maybe 15psi difference between the ride to work and the ride home. If I started the day with 110 they'd be below 100 for the ride home. Even if I'm out for just 3 or 4 hours on a day ride they'd sink between start and end.

I can feel the difference. On the ride home they feel smoother, perhaps I should say softer, but less precise. But even when pumped they feel smoother than my clinchers so extra smoothness isn't a win. I actually prefer the higher road feel anyway. My commute roads are in good shape so maybe if I rode worse roads I'd feel differently.

When commuting to my previous job I had one pinch-flat event. I was riding 25mm Gatorskins which I always pumped to their rated 120psi. One morning only 1/4 mile from the office I hit some dip, maybe a sunken gas line access cap or something. I never could be sure what I'd hit because nothing in that stretch seemed especially serious. The rear tire went flat with snakebite holes and I finished the commute on foot. Later I realized that for the last few weeks I hadn't been meticulously topping off the tires like I usually did.

Lessons learned. 1. Check the tires. 2. The lower pressure you start with the sooner it will drop to unacceptably low.

There it is.

I just want to make sure I have this right: You're saying that I should inflate my tires to between 70 and 110psi?

I wouldn't consider tires choices to be inconsequential or trivial. In fact, tires probably have more effect on ride quality, comfort trouble-free riding than many other more "weighty" items, such as frame material, drive-train, shifters, etc. If tires flat easily or wear out quickly, they can make your rides miserable if not downright dangerous. Bike tires are relatively expensive compared to car tires, which are made with much more materials, but they wear out much quicker.

Choosing a tire is a balancing act between ride comfort, durability, performance and cost. Many of the tires that are highly touted by users are very expensive and less durable. On the other hand, many tires valued for their durability and flat-resistance have poor riding characteristics and weigh a lot. So, many cyclists are forever on the search for the Holy Grail tire that provides a plush ride, high performance, low rolling resistance, good flat resistance, durability and reasonable cost.

Discussions about tires often get contentious because cyclists have different needs, road conditions, weights and incomes. I ride a lot of miles (600-800 month year round), many of those commuting, so I can't afford to ride expensive tires that might get destroyed by a shard of glass while I'm riding to work. However, I value nice riding tires with low rolling resistance and weight because the roads are hilly around here and I rack up a lot of mileage. So, I am forever on the search of a tire that balances that needs at a decent price.

[MENTION=46029]fender1[/MENTION], you call it banal after telling us what a marvelous difference good tires and proper inflation makes. So uh you're joking, right? It's actually one of the consequential equipment choices among many choices that are far less consequential such as headsets and derailleurs and whatever else. In fact, in my view, tires matter more than frames except that frames are expensive and much harder to replace than tires which brings frames back up the scale of consequentiality, if that's a word.

[MENTION=391744]catgita[/MENTION], could you please share your chart with us? It sounds very useful.

I don't agree if these new articles impart nothing new. It's the first time I've seen rider-to-bike friction mentioned as part of the equation, though maybe it was implied earlier.

Wouldn't rider-to-bike friction be more a matter of the saddle than the tires?

It was Heine that brought friction loss within the rider into the discussion, which he prefers to call 'suspension losses' to allow for all the variables that he has not directly measured, though it is intuitively implied in any discussion about tires and suspension.

I would love to share my pressure calculator, it even draws a diagram of the contact patch accounting for wheel size, tire width, pressure and weight (which challenges many common assumptions about contact patch shape). But it is Excel/Numbers; not very web friendly. With the huge range of tire sizes available now, a chart would be huge.

Maybe your intuition, but it helped me to have it mentioned verbally.

Please email it to me, and I'll see about making a handful of charts from it. I'm not that adept at this stuff, but I might be able to manage this.

Tom. True. What can I say I am complicated..... Kidding aside, after thinking about it maybe a clarification is order. What I find uninteresting are the discussions where people try to convince each other that their view is the right one. I like what I like because I like it. I don't have to have everyone agree with me to validate what I like. When it comes to tires people require different things and as such, different tires.

The science (or maybe experimentation is a better description) part is interesting to me because long standing conventions are challenged and information that is new (to me) is shared. I feel the wider, nicer tires improved my riding experience but that is just my experience. Tire choices don't make people right or wrong and I guess that part of the discussion is what I find banal.

[MENTION=46029]fender1[/MENTION], that is so clear and wise, and I hope others consider what you're saying. Acrimony for the sake of chest thumping is worse than useless, but findings are useful even if you need to reject them.

I took a two-day tour this week, with 35 pounds of luggage on my old Raleigh Super Course. It felt like such a perfectly balanced bike. It had a 28mm front and a 32mm rear, but who is to say those are right for everyone? They are in my range of favorite size tires. Perhaps my body weight and weight balance play a part of this. Maybe there is a resonance and an impedance interplay, which explains why different people like different kinds of bikes, even in the same kinds of riding.

Having waded through this discussion I will now summarize:

Ride what works for you.

You just ruined the whole thread.

Decades of riding on all manner of surfaces, at all ranges of tire pressures, all types of tires, various hazards, etc has lead to this solution. It really works (for me). This recipe has worked for decades on every tire brand I've ridden. I have not had a flat in a long time. Tires handle/maneuver very well.

Front tire - 700C X 25 mm clincher (Challenge), ~100 psi, butyl tube

Rear tire - 700C X 28 clincher (Challenge Parigi-Roubaix), ~120 psi, butyl tube

I weigh about 225 lb.

Lower pressures in the rear or a smaller rear tire generally resulted in punctures or occasional pinch flat from potholes.

Flat-free riding is paramount with me. Everything else comes next. So, I want excellent feel that is flat free. The Challenge tires are the best feel since I gave up on tubulars. If they punctured, I would move on.

who's giving me friction?

What it always seems to come down to in the end......

Yes of course, but some information from recent research can open your mind to what works for you that you didn't expect to work for you. That's why discussing stuff can be fruitful.