Tire Pressure

[ny biker]

I'd think you'd need a power meter and laboratory conditions to really know the difference. Most everyone I know says they can feel the difference in rolling resistance - myself included - but of course that's subjective, even for individuals using a power meter outside.

But it's well known that higher tire pressure always increases fuel efficiency in cars. There's just a tradeoff in traction on imperfect roads, that becomes more apparent the worse the road gets.

I would think that the theory is no different for general road riding than it is for racing or mountain bike riding - the smoother the road surface and the better the traction, the higher the pressure should be for best efficiency. There's never any "one size fits all" for tire pressure. It's just that paved roads are more uniform than unpaved trails.

Yes I thought the same thing but my friend is a persistent statistician. And really, I've actually tried it and am riding the same speed without working harder.

[redrhodie]

So, I ran lower pressure today, 108 instead of 118, and I felt like my brake was rubbing. I actually stopped and checked to see if my brake was rubbing, then I remembered it was the tires.

Hard to say if I was any slower. I don't use a computer, and although my time was a little off, I did get a few more red lights than usual. Maybe that was because I was slower. Eh, I'm going back to 118. I didn't like how it felt.

[Crankin]

I'm with Red. I keep my tires at 120 and I have had 2 flats in 10 years. Generally, the roads here are OK; no chip seal. I do feel the bumps, but, to me, it's part of riding. I also ride Contis, and I've never seen anything about 120 being "dangerous." My DH has different Contis that are actually rated up to 135, which is what he uses.

[Thorn]

While I stand amazed at the depth of TE knowledge and the number of women with strong technical degrees, unless one of you must-run-high-pressure people fess up to not being lawyers, but, instead are physicists or mechanical engineers....well, one last time for the masses (like the 100 pound woman I met who has been struggling to get her tires up to 135 pounds when she needs only 90)

Here's Michelin's guide:
http://www.michelinbicycletire.com/m...rpressure.view

And, the latest Jim Langely blog where he tells a reader named Pam (ok, fess up which one of you sent the question ) that at 220 pounds she'll need more than he and then references the Bicycle Quarterly article:
http://jimlangley.blogspot.com/2010/...nder-best.html

[OakLeaf]

I'd note that the Michelin page says it's a "reasonable guide of where to start experimenting," not a hard and fast rule.

On a hardtail bicycle, your tire pressure IS your suspension, so the optimum will vary according to road conditions, just as you'd adjust your ride height, preload and damping if you had full suspension. (And even with full suspension, optimum tire pressure varies according to conditions. That's why at a motor race, the tire people will post their recommended pressures.)

I'd also note that "recommended" tire pressures for automobiles have much more to do with comfort than efficiency. A lot of people (for unknown reasons ) don't like getting beat to death by the roads. The Michelin page also mentions comfort as one of the factors that went into their chart. You know how when you test drive a car at the dealer, if you buy the car, the first thing you do is check the tires and they'll be 5# low? Same idea.

There's a continuum between a plush ride and an efficient one, and every driver/rider has to make a decision as to where they like to be on that continuum. I like efficient. Other people might prefer plush.

Riding style has a lot to do with it, too. On my motos, for general street riding, I prefer fork springs that are very stiff for my weight. If I take the manufacturers' charts, add 30# to my weight and plug in that I'm an expert racer (which I most definitely am NOT ), I'll come up with the spring rate that is most comfortable for me and gives me the best handling. But in the rear, I'm fine with a pretty soft shock spring, as long as I've got a ton of rebound damping dialed in. All of which points to I just load the front end pretty heavily. Other people might ride differently, with or without a motor.

I'll 'fess up to being a (retired) lawyer, but I think most of the others who've commented are not. AFAIK, none of us here is a suspension engineer, so we're all just going from general knowledge and personal experience. And I'm still waiting for those articles about the laboratory tests...



And finally... who among us has had her tire pressure gauge professionally calibrated? Anyone who hasn't, which includes myself, is just going by a vague notion of what tire pressures she's actually running, which could be plus or minus 15# from indicated...

[HipGnosis6]

Just for the sake of saying something about running on lower pressures being okay... I run 700x25C at about 110 psi. I'm big, too - 5'11", 275 pounds. I haven't had a pinch flat since I hit a raised metal drain edge at 20 MPH, but I had a whole bunch of them shortly before I came to understand that the higher the pressure the faster the air bleeds out. For me that means checking the tires every time I want to ride.

[indysteel]

While I stand amazed at the depth of TE knowledge and the number of women with strong technical degrees, unless one of you must-run-high-pressure people fess up to not being lawyers, but, instead are physicists or mechanical engineers....well, one last time for the masses (like the 100 pound woman I met who has been struggling to get her tires up to 135 pounds when she needs only 90)

Here's Michelin's guide:
http://www.michelinbicycletire.com/m...rpressure.view

And, the latest Jim Langely blog where he tells a reader named Pam (ok, fess up which one of you sent the question ) that at 220 pounds she'll need more than he and then references the Bicycle Quarterly article:
http://jimlangley.blogspot.com/2010/...nder-best.html

LOL. I'm a lawyer and my husband is an engineer. We both run under the indicated max for our tires.

[Norse]

Ok, I am a lawyer, my road tires are Conti GPs and, until about 1 year ago, I used to ride them at just under 120. I now ride at around 105-110 and did it just for the comfort factor - I do seem about 1/2 mph slower but I don't race and the older I get, the more comfort I want! Also, if it's raining, I will lower the psi to 90-100.

Interesting on the front/back difference. I sometimes go slightly lower on the rear for the comfort of my body. Sounds like I am doing that wrong.