Proper Tire Pressure

Tires are rated by their manufacturers with a recommended and maximum PSI [pounds per square inch] inflation rating.  For the purposes of this discussion, the focus is on maximum PSI inflation.

The maximum PSI rating of a tire does not suggest that inflating one additional PSI over the maximum will result in the tire blowing off the rim.  It does, however, indicate the strength of the bead, while concurrently maintaining a buffer for pump gauge variance and rider weight.

In recent years, cyclists have pushed for higher PSI tires, thinking that more tire pressure converts to a faster bike.  In a fashion they are correct.  The greater the PSI, the less the tire is in contact with the ground which translates to less rolling resistance.  However, less tread on the ground also means reduced cornering and braking performance as well as reduced comfort.  One could argue that being comfortable on the bike might be equal to, if not more important than, the SMALL reduction in rolling resistance gained by higher tire PSI.

Where the Rubber Hits the Road

For the average cyclist, PSI is determined by ride comfort.  A 170-pound rider on a 120-PSI rated tire can inflate tires to 80 or 90-PSI, or go up to 130-PSI.  The risk of a problem is minimal; however the risk is not zero.  As the 170-pound rider on a 120-PSI rated tire goes from 80 to 130-PSI there is a corresponding reduction in tire contact on the road, decreasing breaking and cornering performance while slightly increasing speed.

For a lighter weight 130-pound cyclist riding on tires at or above the maximum PSI, the ride can be noticeably uncomfortable.  The same tire that bulged a little under a 170-pound cyclist, will stand tall for a 130-pound cyclist, with no give to imperfections in the road.  Ride quality, as well as braking and cornering performance, is diminished.  Reducing the PSI to the point where the tire has a slight bulge when ridden, will increase comfort and performance.

Heavier 200-pound-plus cyclists have less tire PSI flexibility.  There are no hard and fast rules.  Going beyond the manufacturer’s rating becomes a personal experiment.  One could view the maximum PSI as the not-to-exceed limit.  The consequences of inflating and running on tires at 120% of the maximum PSI are not documented.  Tire size and rider weight are just two factors to gauge maximum PSI.  Some heavier riders need to run at, or slightly above, the maximum PSI to reduce pinch flats.  (See “Avoiding Flats” for more on pinch flats.)

Something to Consider

When inflating tires, the PSI on the pump gauge does not include the cyclist’s weight.  Stress on the bead increases with a rider seated on a stationary bike and spikes when riding.  Changes in that stress are caused by bumps, potholes, changes in altitude, heat and an occasional bunny-hop.  One of these factors in isolation is not likely to cause a problem, but when pushing limits on the bead, they all become factors of potential failure.  All are worth consideration when inflating tires over the maximum PSI.

We Keep You Cycling recommends running at or below the maximum PSI rating of the tire.