roadcrankr

The low-tire-pressure minions never like to miss an opportunity to push their agenda.
I may not inflate my road tires to 140psi like SMD4, but no way will I bring mine down to 60-80psi.
Seen more than a few fellow group ride cyclists suffer punctures or, worse, destroy a rim.
Some of my roads get slightly rough, but I estimate that happens less than 3% of an entire 40-miler.
Thank you, but my 25 or 28 tire widths and 105psi suit me just fine.

Kontact 

So far I haven't seen anyone recommend "low" pressures. 118psi for 19c tires is not low. 60psi in a 28c tire isn't low if you weigh 100lbs either.

I just don't understand why you want to make your 28c tires ride worse than your 25s. Wouldn't you want them to be close to the same?

smd4

I ride at exactly the speed I enjoy. Thanks.

smd4

”Ride worse?” What does that even mean? My tires provide me a wonderful ride.

rumrunn6

haha they would never get started on their ride

mitchmellow62

Thank you.

smd4

Boy, you weren't kidding! It took me 10 minutes to roll out of the 25-foot driveway today, and that's down hill and with a tail wind! The bike rode so slow that I lapped myself!

40??!! On tires with a 100 psi MINIMUM, that would feel like crap, and likely lead to instant pinch flats front and rear. We'll put that suggestion in the round file.

mitchmellow62

I like this explanation as well: https://www.velonews.com/gear/techni...-verification/

Thanks for the lead.

roadcrankr

No need to get defensive, Kon. 105 on either size works fine for me. My Michelin Power or Pro's render a nice ride.

Kontact 

Pardon me, but the dismissive comment I quoted by you was insulting. My comment merely addressed its validity.

Riding 25s and 28s at the same pressure is like riding 25s at 105 and 120psi on two different bikes. That's all I was getting at.

roadcrankr

Sorry to hurt your feelings.

sweeks

I appreciate sarcasm when it's done well!

I've experimented with tire sizes and tire pressures over the last 20 years. I started out (on the AIrborne) with 700-23 tires at 115 psi. These were OK on a titanium frame with a steel fork. I went to 32s after a few years and ran these at 100 (rear) and 90 (front) at first. Over the last few years I've been persuaded to the "lower-pressure" side, and now find that 80 (rear) and 70 (front) works well* for me. I weigh about 215, am pushing 73 and usually average 13-15 MPH. I have a standard 35-mile loop I've been riding for years. The lower tire pressure doesn't seem to slow me down, and I do notice a more supple ride.
It seems to me that tire pressure is a personal choice unless one is a professional racer with serious competitive goals. Live and let live!
(* According to the Silca tire pressure calculator, these are still a bit too high!)

Russ Roth

Go read on low pressure some more. He's discussed 18c-23c tires at 140psi, run those at 40psi and you'll be walking, especially the 18c. When I ran 18c tires I kept them at 130psi and at 225lbs was pinch flatting those, its why I stopped running them and went to 20c at the time. But, unless you're running a wide internal width rim, like 19-20mm I wouldn't run a 23c tire below 60psi, really I still wouldn't run it below 90psi, but with the wider rim you won't pinch flat as much. 40psi is looking to pinch flat and break something. Even my kids at 100lbs run 80psi in their 23c tires.

Bill Kapaun

I've got a couple years on you.
I think when one gets into their 70's, you "turn the wick down" a bit so you're not so "stressed" at the end of the ride.
Since we are no longer trying to complete the circuit in the least time, we also soften the tires a bit and maybe give up another minute or 2 for the comfort aspect.
Less racy and more smell the roses.

elcruxio

Tire pressure testing these days is something that's probably as accurate as it gets in terms of cycling data as it's not selling anything. Except perhaps pressure gauges. Aerodynamics testing done by Zipp etc. is always a bit suspect as the companies claiming aero gains are usually selling the aero wheels / components. However Silca has no horse in the race and their testing corresponds with other individual tests done with tire pressures.

All that out of the way, as was stated in the link I posted earlier (here it is again https://silca.cc/blogs/silca/part-4b...-and-impedance ) it all boils down to the break point. A tire will get faster with increasing pressure up until the tire gets too hard to conform to the surface and starts bouncing instead. That moment the tire starts bouncing is called the break point and after that point the tire will start get slower rapidly because all that bouncing is the transmitted through the bike to the rider. All that bouncing is then transmitted to the tissues of the rider which is dissipated as heat and is thus wasted energy.

If you can't get around the word bouncing, call it vibration instead.

If we look at the most important chart of the earlier mentioned article



We notice that with a 25mm Continental GP4000S the break point for smooth asphalt is at 110psi after which the tire will start getting slower rapidly. At 140psi on new asphalt the rolling resistance is as high as it would be when the tire was inflated to under 60psi.

On coarse asphalt the break point is at 100psi and at 140psi the tire will be slower than if you ran the tire under 50psi.

On machine roughened concrete there's just no point in going above 90 psi and you'd just be better off riding something a lot wider. That red graph is actually really interesting, because it does kinda show that a 25mm tire can never get fast on rough surfaces.

Since we're discussing 23mm tires you can use higher pressures than with 25mm tires on smooth roads. However the narrower tires are going to perform still worse on rough surfaces. Your casing losses never get a chance to get low when you already reach the break point and impendance losses set in.

The data seems to show that the only reasons one should use narrow tires in terms of speed is because of aerodynamics and weight.
However to fullfill the 105 % rule with aerodynamic rims one can get rims that are in the region of 32mm wide, allowing the use of 28mm tires.

If it's lower weight one is after, well that only helps on the uphills where rolling resistance is less important anyway.

In order to reduce the risk of pinch flats one should, according to the data, use wider tires. If the bike in question can't take wider tires, well that's a bummer.

smd4

BS. Quite simply. What does that mean..."slower?" If I'm riding at a certain speed, what am I slower than?

What does this even mean? "Get fast?" When I'm riding, my cadence is at a certain level, I'm in certain gear combinations, and I'm going the speed I like. So you're telling me that it's just an illusionthat I'm rolling along at a certain speed? I'm just imagining the breeze in my face? But really I'm barely above walking speed? It's a wonder I can even keep the bike upright! Unless you're racing, this is just a whole lot of hogwash and word salad.

A bummer? Um...no. If I want wider tires, I'll buy a hybrid.

Kontact 

I don't see anywhere in this data where it comments on tire width, just pressure.

A narrow tire is going to have the same breakpoint and performance curve because it is doing the same thing as the larger tire. So for standard roads there isn't necessarily a loss - the best 23c tires have the lowest rolling resistance. But you may get to impedance sooner on large chipseal with a narrow tire.

Koyote

Agreed. I just don't know why anyone would choose a super-high psi that turns a bike ride into an ass-pounding.

mpetry912 

it's because the popular wisdom on this topic has changed, so the Cycling industrial Complex can sell you more guages, pumps and wider tires

if less is good, even less must be better, right ? I've been riding 20 PSI, now I want to get down to 5 PSI so I can be cool like the big boys

/markp

smd4

High psi doesn't turn a bike ride into an "ass pounding." It's just that some of us prefer the ride of a Ferrari to that of a Lincoln Town Car.

elcruxio

Hey I know this one!

You are provided with articles and charts which explain hysteresis and impendance and which even a ten year old could easily understand. However you act stupid and fall back on semantics and make a big stink about a single word you choose to use the incorrect meaning for. Classic SMD4

Anyways, what the charts and articles clearly state is that the coefficient of rolling resistance is higher for a 25mm tire that's pumped to 140psi than it would be for the same tire that's pumped to 60psi.

That means that you need to use more energy to achieve the same speed with the 140psi tire than with the 60psi tire. Mind you, both have terribly high coefficients of rolling resistance but the 140psi tire has it higher, ie. is slower.

ThermionicScott 

I'm really glad this thread has moved on to more productive territory than its head-scratching premise.

smd4

It's simple, really: I don't give a rat's ass what the articles and charts say. I really don't. I love the ride I get with my skinny high PSI tires. Now show me an article that disproves this.

cyccommute 

You aren’t interpreting the data properly. The bike doesn’t “get slower”, the rolling resistance goes up. That translates into more power needed to maintain a given speed. Yes, that means that for a given power output, the bicycle would slow down but the magnitude isn’t what could be called “rapid”. The data in the chart is also for one mass data point…190 lb or 86 kg. Changes in mass in either direction is going to have an impact on the “break point” since that is a measure of where the tires stop conforming to the surface and start to lift the bicycle in a vertical direction. Without more data points with more mass, it would be difficult to tell where that break point would be for a heavier or lighter rider.

Only just and the difference isn’t all that large. But, as with all of these “studies”, I see no indication of what the error in the measurement is. Without knowing what the error in the measurement is, we can’t draw many conclusions about how large the difference is. It’s an interesting result but without that error measurement, that’s all it is…interesting. It’s not necessarily conclusive.

Neither of these tires are good choices for anything other than smooth pavement. But that has been well known for decades. However, you are missing another reason for using narrow tires. That is one of constraint and design. Some bikes simply cannot use anything wider as they aren’t designed for them. Many road bikes…particularly older ones…will not accommodate anything wider than 25mm and that may be a stretch.

No, that is the wrong conclusion. To avoid pinch flats use the proper pressure. That’s going to depend on the weight of the rider/bicycle and the road surface. It’s not practical to go around constantly changing pressure on a single ride for varying road surfaces. If there is a section of pavement that has been rotomilled, it’s not practical to reduce the pressure from that used on smooth pavement just so that you have a smoother ride on the rotomilled surface. Use your legs…the Real® suspension on the bike.

Finally, pinch flats are a symptom, not a problem. If your bike can accommodate wide tires…and even it if can’t…a pinch flat tells you that you have too little air in the tire for the conditions. A pinch flat should tell a rider that they are about to incur an expensive repair because their rim is bottoming out and is at risk of being bent. A pinch flat is a low cost repair and a warning. A bent rim is an expensive repair caused by an ignored warning.
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smd4

^^What he said!