700 x 25 vs. 700 x 23

If I switch to the smaller (x 23) tire, about how much difference should
I expect to feel?


Kind of a loaded question, I know, but I'm just trying to get a rough
idea.


TIA,

-Bob

Hell and High Water wrote:

If I switch to the smaller (x 23) tire, about how much difference
should I expect to feel?

Exactly as much as you expect to feel. (Average = a skosh.)

HTH, BS

Hell and High Water wrote:
If I switch to the smaller (x 23) tire, about how much difference should
I expect to feel?


Kind of a loaded question, I know, but I'm just trying to get a rough
idea.


TIA,

-Bob

Not much. In fact one manufacturer's 25 may be virtually identical to
another's 23. Now, you will feel some difference from 25 to 20.

In article , says...
Hell and High Water wrote:
If I switch to the smaller (x 23) tire, about how much difference should
I expect to feel?


Kind of a loaded question, I know, but I'm just trying to get a rough
idea.


TIA,

-Bob

Not much. In fact one manufacturer's 25 may be virtually identical to
another's 23. Now, you will feel some difference from 25 to 20.



Thanks!

I may change tires for a different reason, but at the same time I may go
from 25 to 23...

-Bob

"Hell and High Water" wrote in message
...
If I switch to the smaller (x 23) tire, about how much difference should
I expect to feel?


Kind of a loaded question, I know, but I'm just trying to get a rough
idea.


TIA,

-Bob


I changed from Mich Pro 23 size to the same tire in 25 and found that the ride
is much smoother and there is no difference in rolling resistance. I think the
smoother ride has actually increased my average MPH.

Neal

I did the same thing and found that I am *faster* with my Avocet
Fasgrip 700x25. Rolling resistance is minimal, weight - my Avocet have
a listed weight of 230g, not too heavy; but the key is I can run my
Avocet 25s at 100-110psi, so I ALOT more comfortable. I will never go
smaller!

I found that at my weight (varies 190-220 lbs), 700x23 is asking for
pinch flats. Therefore I think that if you change from 700x25 to
700x23 you will feel the burden of pumping tires more often and
changing more flat tires, no matter how much kevlar is in your tire.

- Don Gillies
San Diego, CA

On Tue, 30 Aug 2005 09:48:52 -0500, Hell and High Water
wrote:

If I switch to the smaller (x 23) tire, about how much difference should
I expect to feel?


Kind of a loaded question, I know, but I'm just trying to get a rough
idea.


TIA,

-Bob

Dear Bob,

If they really are otherwise identical 23 and 25 mm tires,
there are at least five changes, most of which are too small
for the rider to notice. The last one, however, turns out to
be impressive.

1. Weight. Technically, the wider tire will weigh a few
grams more, so more force will be required to spin it up to
the same speed.

If you're curious, you can actually time the difference with
the bike upside-down by attaching a speedometer to the rear
wheel, cranking it up to over 30 mph, and timing the
spin-down time from 30 to 10 mph.

Removing a small weight will decrease the spin-down time,
but you can achieve the same effect by brushing your finger
against the tire for a moment, which tells you how tiny the
effect is--the extra few grams don't provide much actual
inertia. And the minuscule effect occurs only when you're
accelerating, not when you're cruising.

2. Wind drag. At what bicyclists consider high speeds, the
extra 2mm tire width slows you down a bit. Racers get
excited about this, but it's not really much to ordinary
riders.

A 700c tire is about 680 mm tall. With the front and back on
two of these tires, you're adding four roughly 2 x 680 mm
strips. That's around 5,440 mm^2, or about 8.43 inches^2.

It's very roughly equivalent to sticking a 3-inch square out
to one side, as if you'd grown an extra hand and stuck it
into the wind as a clenched fist.

Holding your head half an inch higher will increase your
frontal area just as much or more.

3. Cornering and braking. A slightly wider tire might turn
and stop slightly better.

The effect would depend on the inflation and the actual road
surface.

Despite our fantasies, it's unlikely that an ordinary rider
would ever test the limits of a tire's cornering or braking.

4. Rolling resistance. At the same pressure, a wider tire
has less rolling resistance, but . . .

"If you are comparing two tyres of similar construction,
with the same load, and the same pressure, either the wider
tyre is overinflated, or the narrower tyre is
underinflated!"

http://www.sheldonbrown.com/tyres.html

In a blind test, no rider can "feel" the rolling resistance
difference between two similar 23 and 25 mm tires at the
same pressure--the difference is ridiculously small.

How small? Lower the tire pressure from 120 psi to 80 psi on
this calculator and click on "run model":

http://www.analyticcycling.com/ForcesTires_Page.html

A premium clicher that's lost one-third of its tire pressure
is predicted to slow down only 70 seconds in a 40 km ride at
8 meters per second. That's 5,000 seconds versus 5,070, a
1.4% difference, 17.90 mph versus 18.15 mph--you need a
stopwatch or a very accurate speedometer to measure such
differences.

5. Comfort. Aha! This is what people probably feel. The
wider tire is a bigger piece of squashy suspension.

How much bigger? Cut and unroll a 700c tire, and we have a
cylinder about 2124 mm long. The volume of cylinders of the
same length increases with the square of the diameter, so
the ratio is 23^2 to 25^2, or 529 to 625--the 25 mm tire has
about 18% more volume.

Here are the volumes for idealized tires:

If the diameter is 23 mm, the volume is (23/2)^2 * pi * 2124
= 882,470 mm^3

If the diameter is 25 mm, the volume is (25/2)^2 * pi * 2124
= 1,042,616 mm^3

Again, that's about 18% more air volume. This is why you see
so many posts on this newsgroup suggesting wider tires for a
more comfortable ride--this kind of increase really is
noticeable. (Go from a 23 to a 28 mm tire, and the volume
rises about 50%.)

And this cushier ride acts as suspension to improve rolling
resistance and traction. A higher-volume tire can run lower
pressures and is less likely to bounce completely off the
ground. The smoother ride wastes less effort because the
rider is not bouncing up and down as much, and it keeps the
tires in better contact with the ground, so traction is
improved.

Two minor points are suitable for speculation.

First, what effect would the wider tire have on flats?

Ordinary punctures are probably going to increase because
the wider tire sweeps a wider path and therefore rolls over
more debris. The 25 mm tire is about 8.7% wider, so it
should impale itself on about 8.7% more thorns and glass.

Most riders, however, get flats so rarely that they wouldn't
notice such an increase--who would notice 13 flats versus 12
flats? And the wider tire is likely to reduce pinch flats,
so even that difference could be lost.

Second, once you have a flat tire, the wider tire will take
about 18% more pumping to get back on the road. This builds
character.

Carl Fogel

In article ,
says...


Dear Bob,

If they really are otherwise identical 23 and 25 mm tires,
there are at least five changes, most of which are too small
for the rider to notice. The last one, however, turns out to
be impressive.


Awesome answer! Thanks so much!


Here's the deal:

I had two flats the other day on a thirty mile ride. Pretty
frustrating, so I swapped tubes, and I'm now riding on Specialized
'Airlock' tubes.

Slightly more weight, I've been told, but as you can guess, I feel no
difference what-so-ever.

If I DO continue to get flats, (new paved trail I found) I plan to
possibly try the Specialized Armadillo tires.

LBS guys said I might want to switch from 25 (my current Vittorio's) to
23 to 'somewhat make up for the added weight.'


I really don't think I'm going to be able to tell much of a difference
here, except that my Vittorio tires can only be inflated to 100 lbs.

I'm not sure, but I think the Armadillos might be able to handle more
pressure....


Anyway, I appreciate your response!

Thanks so much!


-Bianchi Bob

In article
.com,
"bfd" wrote:

I did the same thing and found that I am *faster* with my Avocet
Fasgrip 700x25. Rolling resistance is minimal, weight - my Avocet have
a listed weight of 230g, not too heavy; but the key is I can run my
Avocet 25s at 100-110psi, so I ALOT more comfortable. I will never go
smaller!

I recently installed those Avocet Fasgrip 700x25 myself.
The 127 tpi sidewalls and totally smooth contact surface
gives me a more comfortable ride and much better grip.

I heard a rumor that Avocet may be going out of business???

--
Michael Press