Soft Sand & Tires

John said:

I have a 1997 Cannondale hybrid I use for beach crusing ONLY and I want
to make it the most efficient for getting through soft wet and semi wet
sand

....

Quoted message said:

(I have 700c's, 38mm front and a 42mm rear now( not knobbies but
some tread). I'd like to get a pair of 47mm wide slicks. The problem
is the rear tire will fit between the chain stays(frame) but with only
a mm or 2 of space to spare.

The Michelin Transworld City 700x47 is a street tire with a very tall
casing for its width. That is, it has an oval cross section with the
short axis across the width of the tire. Since it's not even close to
an actual 47mm wide, it fits in frames that other tires of similar
outer diameter will not. OTOH, it will need more tire pressure to
resist rolling off the rim than a tire with a short profile would need.

You can probably get away with a tire that leaves just 2mm of clearance
on each side, but it might rub occasionally when you're really honking
on the bike. 3mm per side is a much safer bet.

Quoted message said:

COULD I FILE DOWN THE CHAIN STAYS A LITTLE? Are the chain
stays hollow or are they solid aluminum?

Do not, under any circumstances, file your frame. It's made of thin
aluminum and you will destroy it before you get any meaningful change
in tire clearance.

I have increased tire clearance on frames before by using a ball peen
hammer as a punch, but I wouldn't recommend it in your case. Just live
with the tire clearance you have, or get a mountain bike with lots of
room for fat tires.

Quoted message said:

Do you think thesee 47mm's are the best choice or should I just stay
with 42's?

Fatter is better, as long as it fits without problems.

Quoted message said:

Should I get a little tread for the front tire?

It won't make any difference in soft sand, in my experience.

Quoted message said:

And finally, what pressure should I fill them to to get the lowest
rolling resistance for wet sand?.

The lower the pressure, the easier it will be for you. Every little
bit helps a /lot/. Bring a frame pump and gauge with you and
experiment to see what you can get away with. On sand, you'll be able
to run pressures that would almost guarantee pinch flats if used on
pavement. How low you can go is directly related to your weight and
the tires' width. You should be able to use at least 20% lower
pressure in the front than in the rear, for the same size tire.

Quoted message said:

I have read Sheldon's site on tires and I'm not sure what he means
by "Narrow" back. How much narrower? This is from Sheldon's site.
Hope he doesn't mind me posting it here.

For sand, you really and truly just want to use the widest tires you
can. If you get a "twenty-niner" suspension-corrected fork (or a
suspension fork), you'll be able to use the colossal 700x60 Schwalbe
Big Apple in the front. That would be an excellent choice. 30 psi is
plenty for that tire on a soft surface, and you may be able to use much
less than that.

http://harriscyclery.net/site/page.cfm?PageID=49&SKU=FK0004
http://www.unicycle.com/shopping/shopexd.asp?id=674

Chalo Colina

Chalo wrote:
<snip>

Quoted message said:

For sand, you really and truly just want to use the widest tires you
can. If you get a "twenty-niner" suspension-corrected fork (or a
suspension fork), you'll be able to use the colossal 700x60 Schwalbe
Big Apple in the front. That would be an excellent choice. 30 psi is
plenty for that tire on a soft surface, and you may be able to use much
less than that.

http://harriscyclery.net/site/page.cfm?PageID=49&SKU=FK0004
http://www.unicycle.com/shopping/shopexd.asp?id=674

Chalo Colina

I'll ditto Chalo. Fatter floats better. If you want to give up on the
Cannondale, this is the fattest:
http://www.hanebrink.net/etb/index.html

Jeff

"Chalo" wrote: (clip) The lower the pressure, the easier it will be for
you. Every little bit helps a /lot/. (clip)
^^^^^^^^^^^^^^^^
By lowering the pressure, you are causing the tire to bulge to a width which
would not fit between the chainstays or fork, but, since the wide part stays
at the bottom, you can get away with it.

As Chalo says, on sand, pinch flats are not a problem. And also. since
traction is so poor, the side forces on the bead are not likely to pull the
tire off the rim. You will probably find that it is best to run the tires
almost flat. (Don't forget to add air if you leave the sand, though.)

Thanks for your imput

Chalo said:

The Michelin Transworld City 700x47 is a street tire with a very tall
casing for its width. That is, it has an oval cross section with the
short axis across the width of the tire. Since it's not even close to
an actual 47mm wide, it fits in frames that other tires of similar
outer diameter will not.

Interesting, it got me thinking if the tires I have on now are really
the width that they claim to be. I measured them and found out they are
not. The 38mm is really only 34mm and the 42mm is really only 38mm
wide. Both are different make tires. Is this common for tires to be a
shorter width then they're marked for?

John

John said:

Interesting, it got me thinking if the tires I have on now are really
the width that they claim to be. I measured them and found out they are
not. The 38mm is really only 34mm and the 42mm is really only 38mm
wide. Both are different make tires. Is this common for tires to be a
shorter width then they're marked for?

John

Measured width in bicycle tires is tricky. To some degree, the tire's
width depends on which rim the tire is mounted on. If the rim is on the
narrow side, the tire will measure narrower than its nominal width.

The marked width *should* be the width of the flattened-out casing,
measured bead-to-bead, divided by 2.5. I *think* this is the ISO/ETRTO
method of determining a given tire's width. I've never been able to
turn up a reference to this standard, though.

Of course, the manufacturer could simply be untruthful:
http://www.sheldonbrown.com/tire_sizing.html#dishonest

Jeff

John said:

Interesting, it got me thinking if the tires I have on now are really
the width that they claim to be. I measured them and found out they are
not. The 38mm is really only 34mm and the 42mm is really only 38mm
wide. Both are different make tires. Is this common for tires to be a
shorter width then they're marked for?

It's very common. So common, in fact, that the only way to know for
sure what size your tire will be is to mount one, inflate it, and
measure it.

It's a decent rule of thumb, in my observation, to assume that a given
tire is one size category smaller than claimed, e.g. "35mm" is actually
about 32mm, "38mm" is more like 35mm, etc. Probably three out of every
four tires I've tried come out that way.

Chalo Colina