Peer Pressure
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.
@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.
@Nate, @Chris
Sounds like a problem with your stroke more than your pressure.
@frank
Nah there is just a point at which the tires get too mushy.
@frank
Possibly but I prefer to think of it as one of the few downsides to my stature. Being 7 or 8 kgs heavier but 15 cm shorter I’m obviously much more efficient at containing my molecules. The downside is that shorter levers allied to increased bulk will exacerbate any symmetrical spinning.
Maybe I should get some egg shaped rings.
@Nate
I find if you pump your tyre, then take the pump off (with the accompanying ‘pst’, that can only be air leaving the pump and tube), then put it back on again, you generally lose 5-10psi anyway. I have never put the pump back on after removing it, and have it up at the same pressure. Try it and let me know.
@Nate
62.4 – the spurious credibility of decimal point accuracy. I remember when we measured things in the police we always put two decimals in just make it look like we’d calibrated whatever we were measuring with and had actually measured what we were supposed to be measuring.
Next you’ll be telling me that the pros calibrate their tyres to take account of altitude or the prevailing barometric pressure.
Awright, you engineer weenies. Tell me a wireless pressure sensor inside a tyre wouldn’t be useful. Make it so it works with any tyre system, perhaps as a type of spoke nipple (yes, nipple lube required.) A very small receiver unit could be made for not only pre ride calibration, but to scream an alarm if pressures begin to drop rapidly – a blow out in progress.
One of you bright young engineers go make one, and I’ll buy. Might even donate to a kickstrarter project for it.
@eightzero You’d need a counterweight to keep the wheel balanced.
@eightzero, @Nate
Build it into the removable valve core.
Oh, and as for the siren to notify an impending blowout, that is handled by the pilot already, thank you very much.
@frank, @eightzero
Stepping back, typical solution in search of problem. Next thing you’ll tell me is I should have disc brakes on my road bike.
@frank
Yes to the counterweight in theory. Not sure anyone has actually balanced a bike wheel taking into account the valve stem, so most wheels may actually already be unbalanced. Put the sensor opposite the valve stem? And if building into a valve stem core, the difference in weight would theortically unbalance the wheel (fiurther?)
@frank I’m an engineer. I don’t tust the pilot. Gotta say most of the flats I’ve had are the slow type. A few “hey, that feels squishy” and I look down and sure ’nuff. But…isn’t there are bit of safety knowing your tyres are at spec before blasting down a descent? Yeah, a catastrophic failure isn’t going to be avoided, but that’s not a reason to try to avoid other types.
Like everything else on the Fucking Bike, it has it’s balance of form, function and price. The Fucking Bike is a system, and not all features are desirable for every application, ride, rider, or variable situation. But being a bike engineer is a different deal – people pay Big Money for shit they don’t need. Make one of these things for like $30 and I’d likely buy. Different than a $2000 power meter to yell at me “pedal harder.” Yeah. I need that. I’m a pilot. I don’t fucking trust engineers, especially when they try to sell me shitte.
I don’t need more bike shitte. I need more time to ride my Fucking Bike. As I look out at the rain, snow and darkness.
@Nate
Well played. Yeah, fuck, who’d want that?
88 kilos here, riding a 8.1 kg bike. Running 23mm tires on 22mm wide rims, 7.25 bar in the front and 7.6 bar in the rear. Seems good to me. Wider rims require less pressure since internal volume is larger, holding tires constant, no?
@Barracuda
I should also add more details per @frank regarding rider details to match the rolling stock.
79 kgs on average ( depending on whether ive been focused and eaten properly or whether its been a shit day and Ive just smashed a “Farmers Union Iced Coffee” – google it, you wont look back and you will forever thank me, those living in Oz anyway, and a block of dark chocolate ) and 178 cm tall ( previous bracketed comments apply to height also )..
@eightzero
As an engineer, I’d expect you recognize, then, that a blow out is just that – there is no reduction in pressure, just the explosion. Well, maybe there is one, but it doesn’t matter because its so quick. It would be like putting a sensor on the casing of a nuke that went off an instant before the bomb hit the ground to warn you that its about to go off.
Hence, the rider provides all the sirens we need in this case as once the tire blows, there will be a lot of wailing as they try to keep the operation upright.
@Nate
Oh, shit; I didn’t even realize you were taking this seriously. I thought we were taking the piss. In that case, yes. Fuck that.
@frank You thought I was being serious?
This is all you really need.
http://m.youtube.com/#/watch?v=_kZGTOLBvek&desktop_uri=%2Fwatch%3Fv%3D_kZGTOLBvek
@frank
Never had one of those kinds of failures – although Mrs/Dr eightzero has. I have no data or anecdotal evidence to support it, but it is possible that some failures occur with some warning. Even 5-10s would be desirable. And of course, a primary function of the sensor would be pre-ride inflation with some accuracy.
@eightzero
You could make it so that the tyre sensor signalled your wirelessly controlled gears to change down and your (hydraulic anti-skid disc) brakes to actuate (provided of course that your radar sensors showed that there was nothing around you) so that you come to a safe halt before you even realise you have a problem. Ideally you could have a big warning light and triangle deploy from your epms as you decelerate.
Once again I claim copyright on these ideas. Colon, hyphen, close brackets – irony.
@the Engine
Just wondering, is this the bike you’re riding?
And I can I please get a collective “Whole Lotta WHAT THE FUCK?”
On an unrelated note, had I not just given the +1 badge away, you’d have gotten it for that. Funny how I go weeks without awarding it and then it’s always a few in a row that are worthy. You basically just gave the comprehensive dissertation on Anti-V.
@the Engine well played. But honestly, I got the biggest laugh out of the claim copyright of these ideas. Masterful; truely masterful.
@frank
I have absolutely no desire to ride with, or meet this guy. Can you imagine the stable he could have if that money was spent on carbon?
@frank
WOW !! A good example of over thinking or maybe not enough? I mean where does he keep the beer?
@Russ M
I bet he has the chicks bring the beer.
@frank
This is why we should be thankful that America poured billions into the space race. If NASA hadn’t have needed miniaturise circuit boards to fit a house sized computer into the lunar lander, this is what your Garmin 500 would have looked like.
Either his guns deliver power on a Saturn V scale or his gearing is tiny.
@Chris
I suspect that’s not all that’s tiny.
However on another tack – what about a Lexicon entry for Saturn V’s for guns like Forstermann’s or Hoy’s? Yeah I know, the Saturn V is a rocket but there is a V in there and its nearly Christmas.
@Chris
Oh (and I shit you not) Scotland is launching its first satellite next year – http://www.bbc.co.uk/news/uk-scotland-glasgow-west-17439236
@frank
I’ve made several attempts but have not, as yet, been able to come up with an imaginary crazed and ludicrous technological development for a bike that hasn’t actually already been designed, patented, sold and (presumably) purchased by someone.
App to show you’re going uphill – check
App to control gear changes – check
A bike that’ll fly – check
Anti-skid – check
Rearview TV – check
I mean what’s a cynic to to do if all his material is stolen before he even writes it?
@the Engine I read the artilce and he’s got 105 fucking gears. Yes 105! 7.9 gear inches up to a much bigger number.
Don’t read it. It’ll make you feel odd.
@frank
You said it. Talking that guy down a few euros is like talking down a French tubular tyre artisan. Either that or my Québécois is getting in the way of the translation, hosti
@the Engine
All that is in Merckx’s grace! MY EYES. THE GOGGLES DO NOTHING!
@eightzero
HEY careful there. I am in the sell stuff to roadies that they don’t need but fulfills their desire to look fuckin’ cool business. But I ain’t no engineer.
oh, my stuff will make you faster. Way faster!
@the Engine
No doubt to monitor global peat depletion levels.
@frahnk
shit! have you been eating bowls air and drinking water? 82kg was my old race weight: I used to look like a skinned rabbit. another point what pressure do you run your FMB’s?
@eightzero
You asked, you receive (can’t link on ipad)
http://www.kickstarter.com/projects/670926116/btps-bike-tire-pressure-system-because-pressure-ma
One time I cycled into London, didn’t pump my tires up before and guess what, I got a puncture! (I relied on the other guy to bring a pump with him too…rookie error). Now I religiously pump the tires up to 120psi and take a pump/repair kit/inner tube for EVERY ride.
p.s. if anyone ever gets a mechanical/is stupid like me in Chiswick, the lads in Evans Cycles are super helpful.