# About this tire pressure thing...



## Cadent (May 16, 2010)

Thanks, folks for the warm welcome...

Now, for the newbie questions.

My other bike is a moutain hybrid, but essentially a mountain bike with smaller tires. The air pressure range is VERY flexible... it maxes out at 55 PSI, IIRC, but essentially you inflate as much or as little as you want, as long as you are off the rims.

The Cadent has a max TP of 75 PSI, which seems massive to me. But this is what the LBS mgr. said the tire should be set at.

Now, I live in a rural county, and to get to paved roads, I go over gravel for a quarter mile, then chip 'n seal for 3/4ths mile, then over potholes for the rest of my ride. Actually, I try to avoid the potholes, but the gravel is hard to dodge around.

I end up beating myself to death going over the gravel sections. The Univega is far more forgiving in that area.

I figure that if I lower the TP a bit it will help absorb some of the gravel bumps. The claimed flex action of the carbon fork is - well, overemphasized.

But what is a good compromise pressure that provides good low-rolling resistance on a semi-decent roadway, but doesn't batter my teeth on gravel? 60PSI? More? Less?

Any thoughts appreciated.

Thx!

Don


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## Hank Stamper (Sep 9, 2009)

Just do some trial & error.

Or provide the tire size and your body weight.


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## JCavilia (Sep 12, 2005)

Hank Stamper said:


> Just do some trial & error.
> 
> Or provide the tire size and your body weight.


Right. Tire size and weight of rider/bike is crucial information. You want enough pressure in the tire so you don't get pinch flats when you hit the edges of those potholes and those chunks of gravel. That's the minimum, but it depends crucially on load and tire size.


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## Camilo (Jun 23, 2007)

There are pressure guides that relate total weight (rider + bike) to tire size and recommend pressure. Look on the website of your tire manufacturer to see if they have one. There is a difference between front and rear - front is usually significantly less because more weight is on rear (rule of thumb: 60/40).

Here's some generic info: http://www.sheldonbrown.com/tires.html#pressure. (look for section on width and pressure)

Again, remember, wheel load is different front and rear.

Without that info (weight, tire size), nobody has any idea what pressure you should be riding.


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## Cadent (May 16, 2010)

Ahh..thx! Goo point regarding tire and weight.

Me: 210 lbs.
Tires: 700x32c (although this numeric descriptor makes no sense to me... maybe someone could explain?)

Sidewall max pressure as stated: 75 PSI

Having a motorcycle, I am of course familiar with different pressures for front and rear, but never thought the same applied to bicycles. <duh>

Given mixed road surface then, any suggestions appreciated! I understand ballparking and experimenting. I am assuming that low pressures - 35-50, would be pushing that too far, and the handling of the bike would be degraded. -- The thing handles like a cat in the corners... FAR different than my Univega hybrid. THINK turn and you turn!

Don


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## Hank Stamper (Sep 9, 2009)

Cadent said:


> Tires: 700x32c (although this numeric descriptor makes no sense to me... maybe someone could explain?)


700 is the diameter. The vast majority of road bikeish tires are 700 (because the wheels are).

32 is the width. (for perspecitve, those skinny tires the spandex guys who don't go off the tar use are generally 23 or 25)

From what I can gather from what you're said, 32 sound like a good size for your riding.


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## PJ352 (Dec 5, 2007)

Cadent said:


> Ahh..thx! Goo point regarding tire and weight.
> 
> Me: 210 lbs.
> Tires: 700x32c (although this numeric descriptor makes no sense to me... maybe someone could explain?)
> ...


Generally speaking, at a rider weight above 180 lbs. max pressure (listed on the sidewall) is recommended.
More info here:
http://www.michelinbicycletire.com/michelinbicycle/index.cfm?event=airpressure.view

Regarding your tires size question, Sheldon says it best:
http://www.sheldonbrown.com/tire-sizing.html


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## QuiQuaeQuod (Jan 24, 2003)

Cadent said:


> Given mixed road surface then, any suggestions appreciated! I understand ballparking and experimenting.


That's the best way to work it out, actually try it out.

Start by dropping 5 psi from the max and see how that works. If you still want to go lower, try another 5psi, then after that 2.5 psi at a time. Very small changes can make a world of difference in the feel of the ride.


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## Cadent (May 16, 2010)

Hmmm... thanks PJ.. I guess with all things, stay with the default settings until you know enough to screw things up knowledgeably...


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## PJ352 (Dec 5, 2007)

Cadent said:


> Hmmm... thanks PJ.. I guess with all things, stay with the default settings until you know enough to screw things up knowledgeably...


I would say _start _with the recommended settings amd screw things up from there. (JK) 

I agree with dr hoo. There's no rule saying you can't stray from recommendations by a small percentage - they're established with an 'all things considered' mentality. Just keep them in mind as you experiment.


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## JCavilia (Sep 12, 2005)

Hank Stamper said:


> 700 is the diameter. The vast majority of road bikeish tires are 700 (because the wheels are)


It doesn't matter, but it's actually more complicated than that, with some weird historical roots. Technically, the diameter of a standard road wheel should be designated" 700C", rather than just "700". It originally meant a rim diameter that would give you an outer wheel diameter of 700mm when you installed a "C" width tire. Nobody designates tire widths that way anymore (there were narrower A and B tires, too), and the actual diameter of a 700C rim (at the bead seat where the tire anchors) is 622mm, but they still use the hybrid nomenclature. It gets even weirder with some other sizes. There are rims designated 650A, 650B, and 650C, and there are at least four different (incompatible) wheel sizes that are usually designated "26 inch".

The actual outer diameter of a 700x32c wheel is somewhere around 686mm. Somewhere on the rim or tire the "622" designation also appears.

Here's way more than you would ever want to know on the subject:
http://www.sheldonbrown.com/tire-sizing.html
Some of us bike-history geeks find all this quite fascinating, but most people have more sense than that.


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## Hank Stamper (Sep 9, 2009)

JCavilia said:


> It doesn't matter, but..........................Some of us bike-history geeks find all this quite fascinating, but most people have more sense than that.



Interesting. Thanks for the info. I probably fall somewhere between fascinating and having sense.


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## JCavilia (Sep 12, 2005)

Hank Stamper said:


> Interesting. Thanks for the info. I probably fall somewhere between fascinating and having sense.


It is kind of goofy. That "C" really confuses a lot of people, who think it should mean something comprehensible. You'll hear people refer to a "700 cc" wheel, as if it were a volume. I once heard a bike shop guy call them "700 centimeter" wheels, which would be nearly 23 feet. Even the Devil hasn't gone that far.


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## Cadent (May 16, 2010)

JC: I can't tell...is that guy using clipon or clipless??

In my example, I pulled the wheel specs from the Raleigh site... so the sizes then indicate diameter/width in mms.

I am all for the metric system. I just wish the numbers weren't so large. <sigh>

Still, it makes my humble Raleigh appear to be very exotic.

And I have enjoyed the links to Sheldon Brown.... CLEARLY the guy has spend more time with bikes that is considered healthy....

Don


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## JCavilia (Sep 12, 2005)

Cadent said:


> And I have enjoyed the links to Sheldon Brown.... CLEARLY the guy has spend more time with bikes that is considered healthy....
> 
> Don


The guy was a remarkable bike mechanic and lots of other things, too. An all-around good guy and Renaissance man of many talents. Though he probably didn't believe in such stuff as an afterlife, many bike geeks think of him as a saint now. He died a little over two years ago, after suffering from MS for a couple of years. He wrote a bit about his last struggles in his online journals, with never a whiff of self-pity. In his last months the only riding he could do was on a recumbent trike at 6 or 7 mph on a bike path, but he still seemed to take joy from it.

There is a ton of stuff on that site worth reading. When you have a question about bikes, Sheldon's glossary of bike terms, with links to lots of other stuff, is as good a research starter as you can find. And don't pass up his humor writing. He would often post sometihing on April fool's day, like the Real Man Saddle, or the classic chain cleaning method.

http://www.sheldonbrown.com/harris/index.html#articles


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