Riding on Autumn’s Air
Posted by Kevin on Oct 16 2009
Tags: Bike Commuting, Tips
Have you checked the air pressure in your bicycle’s tires recently? If so, you may have noticed a markedly lower reading than what your gauge read in mid-summer.
Time and temperature both affect tire pressure. Expect to lose at least 1 psi of pressure with the passing of each month (hence the “flat” tires on bikes that have been stored for long periods). You’ll lose even more pressure when the temperatures fall. As we transition from summer to the crisp autumn air, expect to lose about 2% of your tire’s pressure for each 10 degree drop in temperature.
How does this all add up? Let’s say, for instance, the last time you checked your tire’s air pressure was on an 80 degree day in June. (Did we have any of those this year?) The combination of time (4 months) and temperature change (50 degrees) can mean that a tire that was inflated to 60 pounds of pressure in June may be reading less than 50 pounds today. If you haven’t checked your tire pressure since spring you may be riding on significantly under-inflated tires!
In addition to having increased rolling resistance, an under-inflated tire runs the risk of pinch flats (“snakebites”) when the tube is pinched between the rim and a hard, sharp object such as a pothole, curb, or rock. Worse yet, you may cause irreparable damage to your rim on impact.
Conversely, over-inflated tires will give a harsh ride and run the risk of damage due to their inability to flex when riding over sharp objects.
Determining the correct pressure for your tires
As a general rule, a narrow tire calls for higher pressure than a wider tire. A narrow road tire may run pressures in the 100 – 120 psi range while a wider mountain bike or cruiser tire may require pressures in the 35 – 45 psi range. Look at your tire’s sidewall and you will find either the maximum pressure or a recommended pressure range (typically in raised letters on the rubber). Heavier riders will want to inflate their tires to the higher end of the range and lighter riders should run pressures closer to the lower end. Additionally, since your rear tire supports more of the load, you should inflate your rear tire approximately 10% higher than the front. If you store your bike indoors, keep in mind that you should inflate your tires while at the outside temperature to avoid a reduction in pressure as you take the bike from the heated space to the cool autumn air.
Tire pressure is dynamic and should be checked regularly. Pay particular attention after idle months or when temperatures change with the season. From mid-May through late October, stop by Local Motion’s Trailside Center where our pumps and gauges are always available to keep you rolling smoothly.
1 Comment »
on 19 Oct 2009 at 5:57 pm 1.Joan Denizot said …
Great tips, thank you Kevin. A reminder to heavier riders, it's always a good idea to inflate your tires to the maximum (as per Kevin's indications), as you get more support and there will be less wear and tear on the rims.