A program to calculate optimized bicycle tire pressure based on research that found a small sag or droop in the profile of the tire, led to better performance and comfort.
Imagine that you could ride one gear faster or feel less fatigued at the end of your ride and it cost you nothing. Tuning your bike tire pressure to your own unique situation may do just that. There are now 2 independent studies that support lower pressures are significantly better than pumping up your tires until they are rock hard. It all depends on wider bike tires with flexible sidewalls. Riding one gear higher, depending on your gearing, is a 5 - 8% increase.
The first step is evaluating whether your tires have flexible sidewalls which will respond readily to tire pressure changes. Tires marketed as racing tires, marketed as having a casing from a tubular tire, used by professional racers, or are a folding tire are good candidates. On the other hand, puncture resistant tires, snow tires, and thick touring tires are supported by their sidewalls and do not respond to pressure changes very well.
The simplest way to calculate your tire pressure is to use the companion web app, which uses this package.
To calculate your tire pressures, execute this code sequence:
my_bike <- bike_tire_pressures() # Supply your values for the parameters plot_bike_inflation(bike = my_bike)
If a test ride indicates that the tire pressure is really too low, it's likely your pressure gauge is reading too high. Try increasing your pressure by 10psi. Remember this is not an exact science nor setting so some experimentation may be needed.
Extra light casings need an extra 10-15% pressure to prevent the casing threads from breaking.
Suppose your trials indicate a performance improvement and you'd like to explore other tire options, or it's simply time for new tires. A wider tire is a great option to consider. The following code compares 2 setups and builds upon the first example.
new_tires <- bike_tire_pressures() # Supply new tires for the parameters plot_2_bike_inflation(bike_a = my_bike, bike_b = new_tires)
Bikes are for transporting gear around, but where your gear is attached will impact bike handling. Increasing load weight decreases handling stability. While your bike weight remains constant, your cargo weight could vary from 0 to 20lbs and that will change tire pressure quite a bit.
Calculating how your load is distributed between both wheels depends on factors unique to each bike that it is best to measure them. We can generalize about standard configurations and the following example will highlight the limitations.
Example coming soon!
If the rider is carrying a bike lock or backpack, their weight should be added to the rider weight, not the load weight.
It's unwise to assume a front/rear weight distribution when there are loads
on both the front and rear racks. My recommendation is to measure the
distribution on a level surface. Place a bathroom scale under one wheel
and a spacer block, the same height as the scale, under the other
wheel. Load up the bike, hop on, and have a helper steady you and read the
numbers. Flip the bike around and measure the other wheel. Divide the front
weight by the rear weight and use that for the front_distribution
parameter.
The original research was conducted when internal widths for road rims were around 19mm. Today's rims are available in wider sizes, 23 - 25mm, increasing the volume up to 33%. For these rims, measure the tire width with a digital or analog caliper and use that value for the tire width parameters.
Built-in pump gauges are inaccurate. Between a wide tolerance range of the pressure-sensing mechanism and imprecise reading of the gauge needle due to parallex, the indicated pressure should be considered an approximation.
A simple experiment can help determine how your pump is reading. Inflate your tires to the calculated pressure plus another 15psi. If a test ride seems harsher or your bike bounces around more, the pressure is too high. Repeat, but this time inflate to 15psi less than the calculated pressure. If your wheels bottom out or the handling is squirmy, the pressure is too low. Adjust in increments of 5psi and repeat until satisfied.
For road tubeless setups, exceeding 60psi seems to increase the likelihood of a tire blowoff as nicely summarized in this post.
Under development...
If using an inner tube, inflate it so it barely holds its shape and lightly coat with talc (talcum power). Then sprinkle some talc on the inside of the tire casing to coat the entire surface. Flip the tire inside out if you find it's easier to apply that way. This proceedure is mandatory for latex and light weight butyl tubes.
Then follow Sven Cycles marvelous instructions.
Under development...
At the end of the day, these two are effectively the same. That said, Weight is used for the individual components that go into the calculations. Load is used to describe the forces the tires are subject to.
Compass Bon Jon Pass 700C x 35 in Top 5 Fastest Tires in the World
Part one, Tire Size, Pressure, Aero, Comfort, Rolling Resistance and More. Part 1: How We Got to Now, of a five part series.
The original Bicycle Quarterly article
Source for data and pratical application to Jan Heine and Frank Berto published in Bicycle Quarterly.
The empirical curve fitting formula from the BikeTinker.
Biking riding is an inherently risky activity. Remember the bike racer's motto: Falling is a matter of 'when', not 'if'. You are solely responsible for not exceeding any limits including, but not exclusive of your abilities, maximum tire inflation pressure, rim inflation pressure, mininum tire clearance, and compatibility of tubeless tire and rim combinations. Use of this app is at your risk and you assume all liabilities.
I ride and recommend Compass Bicycle tires and subscribe to Bicycle Quarterly. I received no compensation for this program.