Question for the cycling geeks out there…

It’s been a busy spring, so my bike has been sitting in the garage since winter. I finally dug it out last night and was filling the tires when a question popped up in my mind that I don’t know the answer to. I’ve got an old Schwinn Searcher that I picked up from the good folks at the Sibley Bike Depot a few years back, and the tires on it (700 x 38c) are rated at between 50 and 85 psi. I punted and filled them up to about 65-68, since I wasn’t sure what the effects of low-end or high-end pressure would be. I’m assuming that lower pressure equals a squishier, possibly slower ride whereas higher pressure means the opposite. I’m a larger fellow ( 6’2″/250) so I’m guessing that higher pressure would be a better choice for me.

Any opinons?  Enquiring minds want to know…


7 Responses to Question for the cycling geeks out there…

  1. doc says:

    Ooh, I’m a bike geek! You’re on the right track. At 250#, 38s are perfect for you. You should also inflate them to the higher of the range in order to avoid pinch flats. Wider “puffier” tires aren’t necessarily slower. They are far more effective at absorbing the bumps in the pavement, which can actually move you along faster than a pair of 23s that would shake you to the bone.

  2. Jim says:

    Heavier riders tend to need more pressure to ward off a phenomenon called pinch flats. Pinch flats happen when you hit a rock, crb, or the sharp edge of a pothole and the tire bottoms out on the rim, pinching the tube and puncuring it at the two pinch points.

    Higher inflation reduces rolling resistance on smooth streets, but a slightly softer tire can help you roll more smoothly, more comfortably, and possibly faster over bumpier roads.

    In general, you should probably inflate your tires to around 70-80 psi, but it’s not a big deal if you occasionally stray a little outside that range.

  3. phaedrus says:

    Well, Jim knows more about this than I so I’ll just share my own experiences.

    As a lighter rider with a heavier bike and sometimes significant loads, the only time I drop down below near-max PSI on my tires is in adverse road conditions and even then, I prefer to switch to tires with better tread and keep high-ish PSI.

    I’d bet the difference between max and min PSI on my fairly fat tires results in around a 25% difference in both speed and effort for me (I push harder and go slower.

  4. d.a. says:

    I see the question has already been answered! 😀 My husband is a big guy, and also inflates his tires a bit higher.

  5. Bart says:

    Thanks everyone for the replies… I’ll pump the tires up to at least 70 prior to taking it out for a spin.

    Funny people mention pinch flats, since I had one shortly after I got the bike and had no idea why at the time. The tires were barely inflated to 50-55 as I recall. 🙂

  6. Dan says:

    Someone correct me if I’m wrong, but I heard they figure out the max PSI for inner tubes by figuring out the PSI it takes to explode the tube and then multiplying it by something like 75% or 50% to get the maximum. If that’s correct, you should be able to go outside the range a little and not worry.

    I’m a similar sized dude as you and usually pump my tires to the max PSI.

  7. Jim says:

    Dan, what you say is true for tires, not tubes – tubes have little capacity for restraining pressure. I have had a 50 PSI tire up to 160 PSI with a lubricated bead (don’t ask), and it didn’t appear to be in danger of coming off the rim.

    Tire pressure ratings are a balance between marketing and liability. Most customers believe a higher pressure rating is indicative of a better quality tire. Therefore, tire manufacturers have an incentive to recommend a higher pressure (knowing that the real max pressure is actually much, much higher anyway). On the other hand, even the best tire mounted on a shoddy rim will be trouble at higher pressures. Since tire manufacturers have little control over what type of rim you use, they tend to err on the side of caution. When tires blow off rims, which does happen, the quality of the tire is often called into question when, as often as not, the rim is at fault (actually, most of the time it’s user error, but that’s another topic).

    Bicycle tires are a topic of an amazing amount of controversy, hype, misinformation, and outright dishonesty. One periodical recently did a tire rolling resistance test, which caused all manner of irrational hysteria. It would have been funny to watch if I wasn’t in the business of selling tires. Of course, a better tire can improve a bicycle’s performance and enjoyability much more than an upgrade in most other parts of the bike.

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