Can I under inflate bike tires to reach a 15 percent drop? The recommended tire pressure is when the tire's height drops by 15% when it's loaded because it makes the ride comfortable without increasing the tire's rolling resistance too much. Less bumpy rides mean the tires may even roll faster. Unfortunately, the recommended pressure may exceed the tire's minimum rating. Should we still follow the chart to get a 15% drop? Would handling be poor?

I use the 700c x 38c Schwalbe Marathon Greenguard tire which is rated at 50 to 85 PSI. Even though I keep its pressure between 50 and 60 PSI, the ride is still bumpy on neighbourhood streets, the edges of potholes, and expansion joints.

My weight is 140 lbs which means the front wheel's load should be less than 40 kg including the weight of my bike. Based on the chart, I should inflate my front wheel to less than 40 PSI.



Chart from article in Bicycle Quarterly (pdf)
You can try to lower the pressure further, but 2.8bar (40PSI) is already quite low for a 38mm trekking tire. Expect snakebites (pinch flats), increased rolling resistance and cracked sidewalls. There is no hard limit and if your rims are wide enough, handling shouldn’t suffer too much.

You could upgrade to wider tires if your rims, brakes and frame allow for it.

More flexible tires (e.g. cyclocross tires) would be a bit more comfortable and better at handling low pressure. However, they are generally less puncture resistant.

On a sidenote: A more relaxed and active riding style helps a lot. Try to avoid potholes or at least get out of the saddle!