Eight point V bar. From the moment I bought my first set of high quality road clinchers, I’ve ridden at that pressure. I started with that number because that’s the pressure the sidewall told me to pump them up to; I didn’t yet understand much about balancing the benefits of high and low pressures to optimize comfort and friction; I just pumped them up as instructed and off I went merrily down the road.
I’m not as thin as I’d like to be, which is the same thing as saying I’m fatter than I should be, though I certainly hope I climb well for my weight, especially as my third (and hopefully charmed) ascent up Haleakala is looming large in Vajanuary. The point is, I’m not a whippet and even if I starved myself for the next five months and subsist exclusively on IPAs (I draw the line at cutting beer out of my theoretical diet; I might get desperate, but I’m no savage) I’d still be an Eros Poli at best. Being a big guy, the only factor that mattered to me when it came to tire pressure was avoiding the pinch flats that plagued me during my time riding cheaper tires and that meant maximum pressure, no questions asked.
We always dialed our pressure in for Mountain biking and would pull a few pounds out of our road tires when riding in the rain, but by and large, tire pressure was tire pressure, and as far as I was concerned, more was better. I even had a set of 20mm tires on a makeshift TT bike I had that I blew up to a whopping 10 bar. In the last few years, however, the Cycling world has become obsessed with doing the limbo and seeing how low they can go on tire pressure. It all began with an article in Bicycle Quarterly which conducted an extensive and flawed study on the effects of tire pressure and tire width, and concluded that lower pressure and wider tires are faster and more comfortable than high pressure, narrow tires; the idea is that lower pressure allows small bumps to be absorbed by the tire rather than bouncing the bicycle (and rider) in the air, and that wide tires flex more efficiently than narrow tires resulting in lower rolling resistance. Its important to remember that this gain in comfort and efficiency also comes with an increased risk of pinch flats.
This is all well and good, of course, though we always have to be careful to remember the basic principles of such a compromise; lower pressure and wider tires also mean an enlarged surface area which necessarily means more friction; a perfectly hard, narrow tire on a perfectly smooth surface would have almost zero friction, to the point that you’d be unable to gain enough traction to actually move the bicycle at all. What we’re after, in a practical sense, is a balance between the two extremes which optimizes comfort and tire efficiency against reduced surface area and the risk of pinch flats.
I became infected with Tire Pressure Fever myself as the Cycling world became increasingly obsessed with tire pressure. Down went the pressure in my tires and immediately I felt sluggish and lethargic on the bike. Climbing out of the saddle, I could feel the tires flex as I unleashed the Awesome Devastation of the Toothpicks of Navarone. Cornering was like steering in molasses; turn the bars, weight the pedals and then wait a few moments while the bike got round to responding.
These observations first had me reaching for the pump and then got me theorizing about what is really going on with tire pressure and what pressure is right for a given rider. I say “theorizing”, but most other people would use something closer to “guessing assertively”. But that doesn’t mean I’m wrong.
Basically, it comes down to finding the highest pressure and narrowest tire you can that gives a rider of your weight the right amount of tire flex such that your bike isn’t bouncing as it rolls over the tarmac and allows it to roll efficiently, all while minimizing surface area, risk of punctures, and sidewall deformation when accelerating (cornering and climbing are basically the same as accelerating; the acceleration vector is just in some other direction than forward.) This means that each rider at each weight with different preferences on the sliding scale between the above compromises will find a different optimal pressure. Impressed by Tom Boonen’s tire pressure at Roubaix? Tread carefully; that pressure was dialed in based on very specific criteria and unless you’re eating the same cobbles and weigh the same as he does, you’ll need a different pressure to find the same balance. Bicycle Quarterly has a chart that shows what they believe to be the ideal pressure by rider weight, though I don’t believe a word of it; I do however entertain the possibility that I could be missing something based on the fact that I didn’t actually read the article.
Me? I’m still happily riding at 8 point V. I’m comfortable, I’m not flatting, and I’ve got good control. Besides, it just has a nice ring to it.
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@Monty
This is sage advice; in fact in CX the most important thing is to feel the trail and ride so you bottom out rarely - if you don't bottom out, drop some air and try again. Based on that, you might check your pressure, but the key advice is always to use the same gauge - it doesn't really matter what the pressure is, just make sure you're using the same tool to measure it so you're consistent.
So dump one of your pumps and settle on a number, preferably one that ends in a V because that means you're tougher.
@zalamanda
Funny you mention this, I was going to scold people for announcing their pressure without their size, but it appears I'm just as guilty as the rest. Glad I didn't get round to that.
So, I'm about 82kg and about 1.9 meters.
@Adrian
Yikes. That's Boonen Roubaixish pressure. Rough roads?
@Chris
Apologies to @E 100 distribution of rider weight on one wheel doesn't necessarily require a unicycle...
There's not much squish going on there
@VeloVita Im not sure that my own insensitive arse can distinguish between 95 and 100psi but you make a good point. I read an interview with a local (to me) and well-known wheel builder - Pete Matthews - who suggests that the frame material isn't such a major factor in determining ride quality but that tyre pressure, wheel-stiffness and frame geometry is what it's all about.
http://www.spincyclemag.com/
Page 17 of issue 1. You can download the PDF from their "about" page. I have no affiliations to these guys but free cycle mags deserve to be shared! Hope it's okay for me to post.
Pump gauges measure the pressure in the pump hose, not in your tire. This can be slightly different.
A dedicated tire pressure meter is the way to go for accuracy. I hope to buy one after my tubular wheels are built.
@heinous Thanks for the link - I'll definitely check it out!
@Chris that's taken here in the city I love in. Tucson gets a few pro teams every winter.
@scaler911
@Barracuda
One more try after consulting the Oracle (not @Oracle):
@HeinrichHauslersHairstyle
amen.
@Chris Rollers-- I'm with you on the need for 8 bar there. Hate it when I get that bouncy feeling.
@frank
You are going about this wrong. Unless you have a serious medical condition, farts are lighter than air, so retaining them makes it easier to get up the hill. It's like pumping your tires up with helium.
@frank
Boonen runs much lower than that for Roubaix:
Omega Pharma-Quick Step
Wheels: Zipp 303 Firecrest
Tire: FMB cotton casing
Size: 27mm
Measured size: 28.2mm
Pressure front: 59.5 psi Boonen, 58 psi Chavanel (58 psi or less in the rain)
Pressure rear: 62.4 psi Boonen, 59.5 psi Chavanel
Sealant: no
@G'rilla
Good point, I got one recently and found that I was running 5-10 less psi than indicated by the pump gauge.