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  Latest update: 5/2/2024


Tire Pressure

The speed (as well as comfort) of a ride are affected by tire inflation pressure. For many years it was thought the rolling resistance of narrower (23 mm for example) tires was minimized by maximizing tire inflation pressures. But bench testing of modern, more supple side wall tires has proved that to be wrong.

This article summarizes current data on bicycle tire dynamics, refuting the previous presumption that higher tire pressures decrease a tire's rolling resistance. (Additional background here.)

The "effective" rolling resistance of a tire reflects the combined energy loss from:

On a smooth surface the two effects tend to cancel each other and various tire pressures have minimal impact on the effective rolling resistance. But on a rough surface, energy losses from vibration increases with higher pressures, soon outweighing any benefit from less deformation. This graph of energy loss versus tire pressure on smooth versus rough (orange line) surfaces shows 60 psi to be optimal on a very rough surface and 100 psi ideal on smooth asphalt.

In 2022, a world class team was willing to spend five thousand dollars on a system allowing lower tire pressures on a rough surface. They estimated a gain of "up to 30 watts....combined with improved comfort and safety in rough and wet conditions" with lower pressures.

This webpage again identifies two ideal pressures for supple tires:

For personalized optimal pressures based on your weight, tire size, and road surface: Even the pros are adopting wider tires and lower pressures. Rene Herse Cycles - 4/2024:

1) The pros are riding wider tires:

"With no speed advantage for wider tires, we thought that their heavier weight (more rubber) would discourage pros from going wider than 25 mm. After all, wider tires will spin up (marginally) slower in a sprint. But now the pros have adopted 28 mm tires, and many are experimenting with 30s. It seems that superior cornering grip and lower rolling resistance on rough surfaces are worth the slightly heavier weight of the wide tires, even for the pros."

"These days, 28 mm tires are considered 'normal' for road bikes."

2) And at lower pressures:

"Less noticed has been the rapid decrease in tire pressure in the pro peloton. Cyclist magazine reported that Tadej Pogacar is running just 55-58 psi (3.8-4.0 bar) in his 28 mm tires. That's less than half of what pros ran used to run!"

"..."we now know that running lower pressures has many advantages: more speed, more grip, more comfort, fewer flats. You've probably already noticed: Pogačar's pressure is exactly the 'soft' pressure that the Rene Herse tire pressure calculator recommends for him. I'm sure Pogacar and his team have experimented a lot with tire pressure, and they've probably tried all the popular tire pressure calculators. It's nice to see that they've arrived at the same pressure as the Rene Herse tire pressure calculator."

Tire Size and construction.

Tire sidewall construction impacts energy losses. Supple tires are faster than rigid tires. But supple casings don't do well with high pressures. Thus a traditional high pressure tire is by design less efficient as far as energy losses.

And if you are wondering how much better? "At moderately high speeds of 18-20 mph, a supple tire can make you 8-10% faster than a stiffer, but otherwise similar tire. That is far more than the difference a set of aero wheels makes (1-2%)."

For those of you interested, here is a link to Compass Bicycles, the company championing supple, low pressure tires. And whose blog got me thinking about the topic.

This blog post summarizes the factors that make a more supple tire - the higher the thread count, the more supple the casing. That's because the threads are thinner in high thread-count tires, making the casing thinner, lighter, and more flexible. Also, when the tire encounters an object, thinner, lower-mass threads will be able to move and absorb the object into the casing more quickly than will thicker threads.

And further data on the efficiency of supple tires with a comparison of 3 different tires -extremely supple, but less resistant to punctures and wear at one end, to a tough, able to ride over glass (puncture proof) tire at the other. Smooth or rough surface, the findings were the same. You would need 13.5% more power to keep up with a rider on the fastest (most supple) tire, or if you prefer to translate this into a pure speed improvement, a 5 % gain assuming no change in your power output (wattage). (Wind resistance goes up exponentially with speed, so you need 13.5% more power to increase your speed by 5% to stay with a rider on the most supple of the three tires).

This direct quote addresses what is more important to many of us - "What if you don't care about speed? Supple tires also are much more comfortable. And they just feel different, making cycling much more fun. To me, that is the most important difference, and why I ride them on all my bikes."

Wider tires, run at lower pressures, have a better cornering grip with more rubber on the road and less bouncing that can break traction.

As an additional bonus wider tires roll faster than narrow ones as there is less hysteresis with a wider foot print.

Pulling it together.

How do you pull this all together? To quote: "On smooth roads, 25s are about as fast you get - our research indicates that 28s and 32s aren't slower, but neither are they any faster (that includes air resistance at speeds of about 18 mph)....if your bike can handle wider tires, you can get more comfort and better cornering with wider tires, without losing any speed.

On the average back road, wider tires make your cycling much more enjoyable: the significant additional air volume they allow makes for a more comfortable ride, and they better handle the bumps and related vibrations, in effect smoothing out the ride. Additional good news is that when they are made right, these wider tires aren't any slower than narrower ones."

If you need more proof before you make the change, this series of quotes from Quentin Kurc-Boucau who placed 14th in the Cozumel Ironman in Mexico emphasizes the benefits more than just the pure numbers.

"Regarding my tire choice, I've tested many different tires, and I found that I'm fastest on supple 28 mm tires at relatively low pressure - less than 6 bar (85 psi). The difference is quite remarkable.

Most people now ride 25 mm tires. It used to be 23, but with Enve and Zipp optimizing the aerodynamics of their rims for wider tires, people have switched. They still inflate them to 8 or 10 bars (115/145 psi), though, and they ride really stiff tires, like Continental or Hutchinson. It makes the bike so stiff and doesn't do any good. All the vibrations are just lost energy.

On my road bike, I ride Rene Herse 32 mm Extralights. I inflate them to 4 bar (58 psi) on the front, 4.2 bar (61 psi) on the rear. I've measured the power and speed, and they are as fast as narrower tires, but more comfortable. My race bike only fits a maximum of 28 mm tires, so I run those. I'd go wider if I could.

The wider, more supple tires at lower pressures have really changed my life."

Tubes versus tubeless

A nice discussion of the pros and cons of tubes.

The issues are rolling resistance (it appears that tubeless - with sealant - have a higher rolling resistance) and pinch flats (wider tires are less prone to them). Plus any benefit of fewer flats with a tubeless tire may be outweighed by weight and maintenance issues. My conclusion is that a tubed wider tire (28 to 30) at a lower pressure is faster and more comfortable, and the risk of a pinch flat is within acceptable limits. But if you are riding on gravel or in the desert, then a tubeless is a reasonable option to consider.

This is reinforced in these FAQs. The author concluded: "On most rides, I run my tires with tubes, mostly because I don’t like to worry whether the sealant has dried up. However, when I head into truly rough terrain, I run my tires tubeless to avoid pinch flats. Setting up tires tubeless isn’t difficult. I’ve found that both work equally well, and I can’t say that I feel a difference in speed or comfort."

Changing a Flat

As you put the tire around the rim, squeeze it so the beads (the open edges) go into the rim's center, which is the deepest part. With the beads in this depression, the effective diameter of the rim is reduced. Then when you get to the last several inches of unmounted tire, you can pull it up and slip it into place.

It helps to have a thin rim strip and a skinny tube that takes up minimal space inside the tire. And make sure that no part of the tube gets trapped between the beads and the rim. (This would increase the effective rim diameter and makes it even more difficult to mount the tire by hand.) Inflating the tube just enough to remove wrinkles prevents it from getting floppy and finding its way beneath the beads. But remember to deflate it before rolling the last tough section of tire onto the rim. Dusting the tube and inside of the tire with talcum powder may make a difference. The theory is that it helps the last bit of bead slide easily over the rim. (an added benefit - talc may reduce flats by preventing abrasion between the tube and tire.)

Here's a step by step:

Patching a tube

Glueless patches? They work well. The hard part is peeling the backing away, especially with cold hands. Either use sandpaper provided or wipe the punctured area with a clean rag to remove any tire talc. Remember to clean an area bigger than the patch.

Traditional patches are a bit messier because of the glue. For these, use the sandpaper to gently rough up an area slightly bigger than the patch. Put on glue sparingly in an area slightly bigger than the patch. Wait for the glue to dry. Peel off the foil and apply the patch. Removing the cellophane is optional although the directions say you should.

How many patches? That is a personal choice, more patches mean more chance there will be a slow leak. Is the next flat a leaky patch, a new hole, or all of the above? The best approach is to avoid patching a flat during a ride. To do this, carry a couple of new tubes in your seat bag and if you puncture, find the culprit in the tire, remove it and put in a fresh tube. Then you can patch the bad one when you get home (don't forget) and put it in your bag as a spare.

All questions and suggestions are appreciated and will be answered.

Cycling Performance Tips
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