BIKEPGH MESSAGE BOARD ARCHIVE

How wide are your tires? And how much do you weigh?

120 to 140 is a lot, most people only run that on very narrow tires.

they are 700x25 and I weigh 169 and falling

Theoretically there's a risk of the tire failing over the recommended pressure, regardless of how much or how little you weigh. Also you're sacrificing traction. On the other hand, those recommendations are probably just for liability protection, and you're less likely to get pinch flats at pressures like that.

I would be scared of putting in that much pressure. I think I run around 80lbs on my hybrid and 90 on my road bike (with fairly wide tires)

Super high PSI could also contribute to less traction, which might cause more slips when cornering?

Yeah, I'd stay within the recommended range, or at least not exceed the top end. It's a common misconception that harder tires === faster tires, but in fact, if you're tires are pumped up too hard, you end losing momentum because every little bump in the road sucks energy. I believe both Bicycle Quarterly and VeloNews (among others) have done tests showing that lower pressure, higher volumes tires have generally low rolling resistance.

You can go lower than recommended PSI (sometimes conditions call for it), but with clinchers you run the risk of pinch flats.

I always believed higher psi = faster tires. Now that I see that's wrong should I use the recommended max or a little less. My lbs uses less I guess it's because they know I use the bike for commuting.

80 psi is probably a good starting point. Experiment, see what you like.

Find a rough Pittsburgh road and do a rollout test, I think you'll find that higher isn't necessarily better unless it's glass smooth.

I run 100 - 110 psi on 23mm tires, 10 - 20 psi less than their rated max. If you roll too soft, you'll easily snakebite on small potholes. I've done it twice over the last 6 months or so when psi dropped around 80... and now generally top up the tires 2x per week.

it's, as always, worth reading what sheldon has to say on the subject. if you scroll down a page or two, there's even a table with recommended pressures by size and load.

my philosophy is: within reason, higher pressure = lower rolling resistance, but stay with in reason. my road bike, with 23s, i generally pump up to about 120, then let it get down to like 80 before i refill. my hybrid, which has 32s, and which i've been riding an awful lot more often lately, i pump up to somewhere around 90, and then refill when i get worried about pinch flats (i'm not calibrated enough to know the exact psi yet).

so: yes, if you are filling your tires past the recommended range, you are surely overfilling them. for normal, every day riding, you probably don't want your tires filled past whatever won't get you pinch flats (of course, that presumes you will keep filling them all the damned time, and no thank you).

110-120 on 120psi max tires for commuting into town. I will run as low as 90 if I know the roads will be smooth (North Park), 25c tires. Under 100 when commuting is a no-go, 110 and up really is the most successful.

I can't speak to what you should do... through experimentation I've found that 90psi in front/100 in back on tires that are rated 80-110 works well for me as an all purpose setting.(These are 23s btw.]

What I *can* say is that having over-inflated tires fail is not a fun experience.

I don't know what it *really* sounded like... but I can say that to me it sounded like that mythbusters episode where they blew up the cement truck.

That was accompanied by a rush of air against my leg, that felt like a very large, very angry spider trying to get to my nethers(*)...And a swerving into the road as my instincts tried to get me away from whatever was going on.

Fortunately, I was 1) on an empty road and 2) only about a mile from my starting point.

The worst part (other than imaginary spiders) was this was less than 24 hours after I had a tire fail from being worn. I was teased mightily about it....

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* Yes, I am arachnophobic, why do you ask?

[double post... oops!]

140 is ridiculous unless you are riding on

the best pavement on earth. or a smooth

Velodrome

There is a trend of going toward

wider rims/tires with lower pressure.

You are getting bounced on a micro level

all over the road, and it is actually

slowing you down.

Do what I do, pump until your tubes explode. Then put in less the next time.

Here's a Bicycle Quarterly article about high-performance clinchers which references their own study of how tire widths and pressures affect performance.

My favorite commuter tires are my old knobby tires that have lost their knobs. 2.0" wide or greater. 35psi or less. I know, not the norm...I just like how they ride.

And here's a Bicycle Quarterly article on how to optimize your tire pressure: http://www.bikequarterly.com/images/BQTireDrop.pdf

The difference in rolling resistance between 80 psi and 160 psi is pretty small compared to the effect of wind, body position, helmet or clothing choice. Unless you're doing a time trial, to me the primary trade-off is between comfort and the chance of pinch-flatting.

FWIW, I usually run 25mm tires at ~100-110 psi, and weigh close to 80 kg.

Today I ran with about 100 psi in the rear and 80 psi in the front. I don't know if there was any difference in speed, but the ride was WAY more comfortable.

Mr. M- I have to ask about your frequent references to speed while riding. Do you time all of your commutes? Are you on a really tight schedule where a few seconds makes a difference? Or do you just like to go really fast?

Sometimes I ride fast, but sometimes I just ride. The effort I put in makes all the difference.

@ Helen s, when I ride I treat every ride like a time trial. For no real reason other than to work out during my commute. I push my rides a fast as I can just to work up a sweat. I do time my rides andi'm on a tight schedule

Ah! That makes sense then.

How do you reconcile traffic and hitting the green lights in your times?

I haven't worked that out yet.