Conference noted::bicycle

This is the subject of many a battle on rec.bicycles.racing.  Higher pressure
does give less rolling resistance, but also decreases traction, particularly in
corners.  120PSI tires are the "standard" because they offer about the best
compromise.  150PSI-170PSI tires are useful for time trials, where rolling
resistance is more important then cornering.  120PSI tubulars are a very good
all-around tire choice, and one a lot of racers use.

Tim

    I notice (or think I do) a slight difference with BRAND new tires...
    new tires tend to sit nicely up on that "peak" of tread, but after
    a few hundred miles they've developed a slight flat spot and more
    rolling resistance kicks in.  It would be interesting to see what
    the "effective psi difference" in rolling resistance is between old
    and new tires at the same actual psi. K 

    I agree with Tim. I run Avocet K20s for training and racing. They're a
    standard 115-120psi tire.
    
    I run Conti Grand Prixs and run them about 165-170psi. They perform
    extremely well.
    
    One thing that requires some thought as well, you loose a great deal of
    comfort when you run high pressure tires at their maximum. Is the 
    reduced rolling resistance worth the discomfort? Probably not enough
    is gained on shorter "rides" and will certainly not be worth
    sacrificing comfort on long or very long rides.
    
    Chip

    In fact, at the same pressure, a larger tire will have lower rolling
    resistance (due to less sidewall flex), and slightly better comfort
    (more tire volumn).  However it will also have more aerodynamic drag.
    
    Those differences are all pretty small, however, and aerodynamic drag
    of the rider is the dominant factor ules you're moving slowly.
    
    Not being a racer I run 28mm tires at 105-110 psi.  If I wanted to go
    faster in the occasional time trial, I'd put on aerobars before I
    changed tires.
    
    Karl

    There are so many variables on the performance of tires including the
    tread pattern, materials, materials performance at certain temperature,
    and so on, and so on.
    
    As noted, the major drag comes from you (90% approx.). While there are
    vast differences in a racing tire compared to some touring or cross
    tires, racing tire performance (within comparable price ranges)
    probably can't be discerned by the average guy.
    
    Chip
    

    Sort of the same subject...  I'm curious as to what the difference is
    between the 20 x 700 is vs. the 23 x 700 (and don't say 3! ;)).
    
    I've always ridden 700 x 23,... but can I move to 700 x 20?
    
    Is there less rolling resistance?  The Conti's can be pumped up to
    150psi on the 20's but only 120 on the 23's.  
    
    Less comfort on the 20's vs. 23's?
    
    Less stability? (if pumped up high)
    
    More chance of rim damage?
    
    Thanks
    
    John
    

    I personally think it is a market push for smaller/lighter is "better".
    
    20's would definitely be more harsh riding, this could negatively
    impact your overall speed.
    
    20's would probably a bit less rolling resistance.
    
    I would think life of the 23's would be longer. 
    
    Note that tubulars are usually 22 to 23 mm width.
    
    Note that different manufactures real width is different.  I am running
    Victoria techno's 700x25 on our tandem, they are much wider than the
    former continental 25's that they replaced. 
    
    Steve

    I cant quantify the difference in performance gain unfortunately but
    its probably not much and IMHO (and personal experience) is not worth
    the added flat risk of the 20c.  Maybe if your racing
    and feel you need the extra edge (real or imagined).
    -Larry                        

700x23 are *approximately* 23 mm wide.  It varies from maker to maker.  Some
have 700x22.

The wider tires hold more volume of air and if correctly inflated (as Larry
notes) reduce the risk of flats.

Wider tires have more contact with the road, which means: increased rolling
resistance, but better traction, especially when wet.  700x20C are for time
trialing.  If you are 200+ pounds, or ride really rough pavement, or don't pay
attention to potholes, you might want to go to 700x25 (or 28!) for increased
flat prevention.

Width also varies with tire pressure.

I started with 700x25.  I then tried 700x20 and flatted too much.  I've got 1500
miles on 700x23 tires this year without incident.  I will probably not use
anything else.  There is more variety in the 700x23C size then any other size.

Smaller tires *do* increase the chance of rim damage.

Tim

    In my opinion, a 23 to a 20 does not increase your chances of flatting.
    
    I think it has more to do with tire pressures, tire materials and just
    plain luck. I rode more than 10k miles (front tire) Avocet K20 never
    flatting. I had to dump the tire because it was starting to crack (died
    of old age, I guess).
    
    Rim damage? That would depend on which circumstances you're talking
    about (cause). There are significant variables in flat risks and 
    rim damage. There are variables involved in what is described as 
    rim damage as well, e.g. truing, dish, dents, chips, etc.
    
    I just don't see any appreciable protection from 3mm.
    
    My $.02
    
    Chip

Chip,

While I can't quote chapter and verse, there is something like 20% more air in a
700x23 at 120PSI then a 700x20.  Think about how many more pump strokes it takes
to fill the tire.  I think I went from about 18-20 to 23-25.  We're talking
pinch flats here, don't forget.  The rec.bicycles.racing crowd (including Jobst
Brandt, author of _The_Bicycle_Wheel_ claim that a 23C tire at 100-120PSI is the
best compromise of handling (cornering, braking), weight, and aerodynamics.

Tim

    When talking about flats, volume would have less to with avoidance
    than tire pressure. As for the other claims, I'll defer to your
    background article.
    
    Chip

I recently visited Vittoria's web page. They have lots of information about
these topics. For example they have a page on Tubulars vs. clinchers.

   www.vittoria.it

Karol