Mavic x221 Tire size help

[Tom]

Hello all,

I had a wheel built for me with a Mavic x221 rim at my lbs. I had
specified that it was to run a 559 x 1.9 tire but now I've got it home and
had a good look at it, I can't believe that a 17mm rim would be able to keep
a 1.9" (48mm) tire on properly.

Would someone please reassure me that everything will be fine as I can't
get back to the shop until next Saturday and I hate to be bikeless.

Thanks

Tom

[Peter B]

Post by Tom
I had a wheel built for me with a Mavic x221 rim at my lbs. I had
specified that it was to run a 559 x 1.9 tire but now I've got it home and
had a good look at it, I can't believe that a 17mm rim would be able to keep
a 1.9" (48mm) tire on properly.
Would someone please reassure me that everything will be fine as I can't
get back to the shop until next Saturday and I hate to be bikeless.

Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1"
knobblies on 221's.

Pete

[davek]

Post by Peter B
Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1"
knobblies on 221's.

Perhaps you'll know the answer to this: why do so many mountain bikes
have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run a
fat tyre on a narrow rim, but surely a fatter rim would be more appropriate?

d.

[Peter B]

Post by davek

Post by davek
Perhaps you'll know the answer to this: why do so many mountain bikes

have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run a
fat tyre on a narrow rim, but surely a fatter rim would be more appropriate?

In a nutshell: weight!
The narrowish 32 hole rims I have nearly always used for many moons (about
144 IIRC) have proved up to the job bouncing down boulders, steps,
gawd-knows-what etc whilst carrying my 80kg (more with a loaded 3litre
Camelbak), what problem would making the rim wider solve?

Rgds,
Pete

[davek]

Post by Peter B
In a nutshell: weight!

Should have guessed!

Post by Peter B
what problem would making the rim wider solve?

I guess I assumed that wider rims would be stronger (assuming comparable
quality of build/materials) which might be an issue for mountain bikes.
And like the OP I also assumed that a tyre could be too wide for a rim
and be at risk of coming off.

I don't object to having my illusions on this subject shattered.

d.

[Simon Brooke]

Post by davek

Post by davek

Post by davek
Perhaps you'll know the answer to this: why do so many mountain bikes

have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run
a fat tyre on a narrow rim, but surely a fatter rim would be more

appropriate?
In a nutshell: weight!
The narrowish 32 hole rims I have nearly always used for many moons (about
144 IIRC) have proved up to the job bouncing down boulders, steps,
gawd-knows-what etc whilst carrying my 80kg (more with a loaded 3litre
Camelbak), what problem would making the rim wider solve?

FWIW my Cannondale came with rims which look remarkably narrow to me,
but they've caused no problems. If Cannondale choose to put narrow rims
on a fairly high-end mountain bike I'm prepared to believe they have a
reason, and that there won't be problems (although I didn't think much
of their choice of ultra-lightweight, ultra-puncturable tyres).

[Mark South]

Post by davek

Post by davek

Post by davek
Perhaps you'll know the answer to this: why do so many mountain bikes

have these ultra-narrow rims with hugely fat tyres? OK, you /can/ run a
fat tyre on a narrow rim, but surely a fatter rim would be more

appropriate?
In a nutshell: weight!
The narrowish 32 hole rims I have nearly always used for many moons (about
144 IIRC) have proved up to the job bouncing down boulders, steps,
gawd-knows-what etc whilst carrying my 80kg (more with a loaded 3litre
Camelbak), what problem would making the rim wider solve?

It would create problems. A wider rim would have less protection accorded it by
excess tyre width, and would suffer more sidewall damage offroad.

Of course, the weight thing is a big factor in ATBing.

[Pete Biggs]

Post by Peter B
what problem would making the rim wider solve?

I'm not sure I agree with it but here is Sheldon Brown's view:

"If you use a very wide tire on a narrow rim, you risk sidewall or rim
failure. This combination causes very sloppy handling at low speeds.
Unfortunately, current mountain-bike fashion pushes the edge of this. In
the interest of weight saving, most current mountain bikes have
excessively narrow rims. Such narrow rims work very poorly with wide
tires, unless the tires are overinflated...but that defeats the purpose of
wide tires, and puts undue stress on the rim sidewalls."
- www.sheldonbrown.com/tire-sizing.html

and from rec.bicycles.tech:
--------------------------------------
Imagine two similar tires,
one of which is 2 inches wide from bead to bead, the other 4 inches.
We'll suppose them to be inflated to the same pressure, lets say 100
psi, though this wouldn't be appropriate in practice.

Imagine a 1 inch length of tire/rim. The section of tire fabric in this
length is 2 square inches for the narrow tire, 4 square inches for the
wide one. Thus, at 100 psi, the narrow tire is withstanding 200 pounds
of force, while the wider tire will be withstanding 400 pounds. This
represents the difference in "hoop stress" between them.

As a practical matter, tire width varies more than rim width, so narrow
tires tend to assume more of a "U" profile, while wider tires tend to
assume a profile like a capital omega. The narrow tire pulls up nearly
straight outward from the bead, since the rim is nearly as wide as the
tire.

The wider tire, on a similar rim, will bulge out, so, where it contacts
the edge of the rim, there's a strong sideways component to the force.
This places a high stress on the cords that are in contact with the rim
edge (also a high spreading stress on the rim.) Normal working of the
tire as you ride can cause the cords to rub against the rim and be
abraded by it. This is a common failure mode of wide tires. Using
thicker cords helps resist this sort of damage.

Sheldon "Does That Help Clarify?" Brown
--------------------------------------

~PB

[Peter B]

Post by Peter B
what problem would making the rim wider solve?

<snipped>

Well I'm a great admirer of Sheldon but......
In practice I've never heard of, let alone witnessed an mtb rim bursting for
any reason other than the sidewalls being worn away by rim brakes, based on
Sheldons argument a wider rim may delay this failure mode whearas disc
brakes will prevent it. And as it happens without much warning I'd sooner
prevent it.
Regarding the narrower rim altering the tyre footprint due to the "U"ness of
the tyre: this is something that struck when I first started using narrower
rims in the days when Panaracer Smokes were state-of-the-art. Because the
Smokes were superior to the tyres I previously used the benefit of them
would have masked any detriment caused by the narrower rim. I'd also
assume, perhaps incorrectly, that high performance tyres are designed to be
used with high performance rims which by default are narrow.
Regarding sidewall wear and tear and bead abrasion again IME performance mtb
tyres are scrapped because the tread is worn, the sidewall damaged by trail
debris or simply because the rider is a fashion victim. Mtbers paying circa
25 quid for a tyre that lasts perhaps a year are no more bothered by this
overhead than roadies whose tyres manage 2000 miles (and I fall into both
camps).

Regards,
Pete

[James Thomson]

Post by Peter B
In practice I've never heard of, let alone witnessed an mtb rim
bursting for any reason other than the sidewalls being worn
away by rim brakes, based on Sheldons argument a wider
rim may delay this failure mode whearas disc brakes will
prevent it. And as it happens without much warning I'd sooner
prevent it.

Rim failure isn't always instant: the rim walls may begin to crack or splay
long before any separation takes place. Disk brakes certainly solve the
problem of rim wear, but to disk-equip a diskless bike might cost several
hundred pounds.

Post by Peter B
I'd also assume, perhaps incorrectly, that high performance tyres are
designed to be used with high performance rims which by default are
narrow.

There are a lot of broad, high-performance rims on the market, assuming
you're not limiting your definition of performance to XC racing. The Sun
Rhyno Lite is one example, and the trend is toward both broader rims and
broader tyres. A Nokian Gazzaloddi tyre and a Snowcat rim are both
high-performance (if extreme) products in their fields.

That many people use fairly broad tyres on narrow XC rims shows that this
isn't a big problem, but broader tyres handle much better at lower
pressures on broader rims.

James Thomson

[Peter B]

Post by James Thomson
There are a lot of broad, high-performance rims on the market, assuming
you're not limiting your definition of performance to XC racing.

I must admit I was for two reasons:
1) I based my comments on my own experience of long trail rides, often quite
rugged (Peaks, Lakes, Welsh purpose built trails, enduros etc) and to a
lesser extent XC racing which to me is a refinement of the former.
2) Outside of the above I have little knowledge but assume weight isn't a
factor for downhilling and certain types of playbikes designed for getting
air-time etc.so yes, I can't see a detriment with wider rims and those bikes
generally have even wider tyres than XC racing and trail bikes.

Pete

[Tom]

Post by Peter B
Rest assured, I've used everything from 1.25" Pasela road tyres to 2.1"
knobblies on 221's.

Thanks Pete,

I've fitted the tyre and had a little test ride and everything seems to
be ok. Still looks weird though.

Tom