I would like to get opinions on the air pressure. From what I can glean in this and other forums, there seems to be some confusion or different opinions in regards to pressure in comparison with butyl tubes: - higher: you can run latex tubes at a higher pressure since the comfort is better. +100psi. - the same: it all depends on your weight and preferences.
Yes, in an ideal world.
In the real world, depending on the roughness of the road surface, you may need to ride at a lower tire pressure to decrease rolling resistance. Sometimes a smoother ride has lower rolling resistance than a rougher ride.
There is a relationship between rolling resistance and smooth ride. Just like for tires, the more supple the tire (flexible) the more rolling resistance is reduced and ride harshness decreases.
Latex tubes provide less rolling resistance and therefore a smoother ride at a given tire pressure.
This means that a rider who is comfortable riding at a specific tire pressure on butyle tubes (say 90 psi) could switch to latex and increase tire pressure (to say 95 psi) gaining a reduction in rolling resistance and possibly maintain perceived ride smoothness (or roughness depending on how you look at it).
Note that in the data below illustrates that there is diminishing returns on increased tire pressure.
Update based on comments:
The wildcard in the rolling resistance formula is the road surface.
Generally, the rougher the road the less high tire pressure reduces rolling resistance.
On a smooth road rolling resistance is roughly the same as measured in the lab.
Rolling resistance will increase on a rough road using high tire pressure due to "impedance rolling resistance".
We can know that latex tubes have lower rolling resistance than other tube materials at a given tire pressure.
bicyclerollingresistance.com did a nice write up comparing different types of bicycle tubes including latex, butyle, light butyle and Tubolito tubes.
Here's the chart:
Here are the numbers:
Latex has the lowest rolling resistance at a given pressure because latex is more flexible than either butyle or Tubolito.
This flexibility translates into a smoother ride.
It's almost always about trading off one thing for another.
- Leaks air faster
- Has worse puncture resistance
There is more than just rolling resistance and comfort in the list of things people sometimes care about in a tube (assuming you have tubes at all).
Here's what we might be concerned about in a tube - no particular order:
- Rolling resistance
- How long the tube holds air
- Puncture resistance
- Other stuff
Another way to reduce rolling resistance and gain comfort might be to use a fatter tire.
But then you gain weight
EDIT: There is some great information in the comments that should be included in the answer.
The tests above were done in a lab and don't measure real world rolling resistance - unless you are riding on a very smooth road.
Using roller data from Al Morrison and on-road data from Tom Anhalt, you can see a clear breakpoint in the graph where rolling resistance appears to increase sharply (around 115psi – and note that this was a relatively smooth road). Rougher roads result in a breakpoint at significantly lower pressures.
Silca calls these losses beyond the tires’ ability “impedance losses”. While it shows up on the Crr graph as more resistance (i.e. requiring more power from the rider to maintain speed) – the cause is not the tires themselves – but the energy that is lost as your bike and body get tossed and shaken around.
From slowtwitch.com, Tire Pressure and Rolling Resistance
This means that real life tire rolling resistance would graph in the shape (very roughly) of the letter "U".
At zero pressure rolling resistance would be very high.
As tire pressure is increased rolling resistance would decrease.
As tire pressure is increased further at some point rolling resistance would increase again.
The point at which increased tire pressure begins to increase rolling resistance depends on how rough the road is.
According to the article above, on a smooth road that point is around 115 PSI for a 25c tire.
This roughly agrees with the lab tests at the top of the article.
From the blog Silca, Rolling Resistance and Impedance
Based on this chart here are some observations:
- These tests were done with a 25c tire
- The blue dotted line (lab results) approximates the chart above.
- The red line (machine roughened concrete) indicates that on this surface rolling resistance begins to increase at 60 psi and greatly increase at 70 psi.
Depending on rider weight, riding a 25c tire on a rough road at 70 psi is likely to damage tires, tubes and rims.
Lower pressures are safer with wider tires.
Rolling resistance is dependent upon:
- Tire construction
- Tube type
- Tire pressure
- Road surface
- Tire width
Sometimes a smoother ride offers less rolling resistance.