Tire Height/Rim Width

I want different wheels for my disc Roubaix. The nipples on the Axis 4.0 OE wheels have a habit of shearing off in the middle of a ride (e.g. yesterday), and although they're easy to repair, I don't feel like re-lacing the whole wheel. Plus, I want to switch to a standard non-SCS wheel (I have the required derailleur hanger and standard QR frame). Anyway . . . rim widths. Internal widths on many of the new "gravel" wheels are 19mm plus, and the manufacturers are suggesting tires no smaller than 28mm. A tire that size would present a problem with fenders on the Roubaix, but I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm. There is probably some calculation for this, but I don't know what it is.

-- Jay Beattie.

On Sun, 19 Feb 2017 08:03:02 -0800 (PST), jbeattie
wrote:

I want different wheels for my disc Roubaix. The nipples on the Axis 4.0 OE wheels have a habit of shearing off in the middle of a ride (e.g. yesterday), and although they're easy to repair, I don't feel like re-lacing the whole wheel. Plus, I want to switch to a standard non-SCS wheel (I have the required derailleur hanger and standard QR frame). Anyway . . . rim widths. Internal widths on many of the new "gravel" wheels are 19mm plus, and the manufacturers are suggesting tires no smaller than 28mm. A tire that size would present a problem with fenders on the Roubaix, but I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm. There is probably some calculation for this, but I don't know what it is.

-- Jay Beattie.

http://www.sheldonbrown.com/tire-sizing.html
might help here.

As for a tire being "lower" on a wider rim. The theory sounds
plausible but I'm not sure whether it works in practice.
Example: My "25mm" tires actually measure 24.4mm in width (80psi
pressure) and the outside width of the rim is 21.6mm. I'm not sure
that installing the same tire on a wider rim would result in a
noticeably smaller diameter wheel-tire combination unless, of course,
one went to a radically wider rim and than I'm not sure how "rideable"
it would be.
--
Cheers,

John B.

On Mon, 20 Feb 2017 08:04:45 +0700, John B.
wrote:

On Sun, 19 Feb 2017 08:03:02 -0800 (PST), jbeattie
wrote:

I want different wheels for my disc Roubaix. The nipples on the Axis 4.0 OE wheels have a habit of shearing off in the middle of a ride (e.g. yesterday), and although they're easy to repair, I don't feel like re-lacing the whole wheel. Plus, I want to switch to a standard non-SCS wheel (I have the required derailleur hanger and standard QR frame). Anyway . . . rim widths. Internal widths on many of the new "gravel" wheels are 19mm plus, and the manufacturers are suggesting tires no smaller than 28mm. A tire that size would present a problem with fenders on the Roubaix, but I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm. There is probably some calculation for this, but I don't know what it is.

-- Jay Beattie.

http://www.sheldonbrown.com/tire-sizing.html
might help here.

As for a tire being "lower" on a wider rim. The theory sounds
plausible but I'm not sure whether it works in practice.
Example: My "25mm" tires actually measure 24.4mm in width (80psi
pressure) and the outside width of the rim is 21.6mm. I'm not sure
that installing the same tire on a wider rim would result in a
noticeably smaller diameter wheel-tire combination unless, of course,
one went to a radically wider rim and than I'm not sure how "rideable"
it would be.

More to the above. See
https://janheine.wordpress.com/2013/...ire-can-i-run/
--
Cheers,

John B.

On 2/19/2017 11:03 AM, jbeattie wrote:
I want different wheels for my disc Roubaix. The nipples on the Axis 4.0 OE wheels have a habit of shearing off in the middle of a ride (e.g. yesterday), and although they're easy to repair, I don't feel like re-lacing the whole wheel. Plus, I want to switch to a standard non-SCS wheel (I have the required derailleur hanger and standard QR frame). Anyway . . . rim widths. Internal widths on many of the new "gravel" wheels are 19mm plus, and the manufacturers are suggesting tires no smaller than 28mm. A tire that size would present a problem with fenders on the Roubaix, but I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm. There is probably some calculation for this, but I don't know what it is.


If I were to try to calculate it theoretically, here's how I'd do it:

I think it's reasonable to assume the cross section of the inflated tire
is a partial circle, running from bead to bead. The perimeter of that
partial circle will be the same, no matter the width of the rim,
measured bead to bead.

So either by calculating based from your inside rim width and your tires
effective outside diameter - or much easier, just by spreading the
uninflated tire and measuring - I'd figure out the perimeter of that
partial circle. Then using a proposed new rim width (bead to bead) I'd
use that same perimeter to calculate the new maximum height of the
partial circle and thus the new effective outside diameter of the wheel
and tire.

But as a retired guy, I no longer have to do those sorts of
calculations. And I don't think this one would be fun. So I'll just
say, I doubt very much you could find a rim size that would both be
rideable and make the tire diameter significantly smaller.


--
- Frank Krygowski

On Sunday, February 19, 2017 at 4:03:04 PM UTC, jbeattie wrote:
I want different wheels for my disc Roubaix. The nipples on the Axis 4.0 OE wheels have a habit of shearing off in the middle of a ride (e.g. yesterday), and although they're easy to repair, I don't feel like re-lacing the whole wheel. Plus, I want to switch to a standard non-SCS wheel (I have the required derailleur hanger and standard QR frame). Anyway . . . rim widths. Internal widths on many of the new "gravel" wheels are 19mm plus, and the manufacturers are suggesting tires no smaller than 28mm. A tire that size would present a problem with fenders on the Roubaix, but I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm. There is probably some calculation for this, but I don't know what it is.

-- Jay Beattie.

The first assumption is that the tyre profile which is it's height beyond the bead is the same as its width across the bead retainers. This is near enough for government work, though in real life the tyre is generally a fraction wider than it is high. Thus the diameter of a tyre is the bead diameter, in this case say 622mm plus twice the tyre width, say 25mm times two or 50mm, for a total diameter of 672mm. Firms like Schwalbe publish the measured rolling circumference and/or the diameter of the mounted tyre, so that you can look it up and discover that it differs, though only marginally, from the calculated diameter.

You should be aware that these measurements are usually taken with some load on the tyre (it may be half of 75kg -- this is their assumption of the mass of a "normal rider") and you should further note that any distortion is at the contact patch, not uniformly spread around the tyre, so that it won't help you solve this mudguard problem at the top of the tyre.

In any event, it looks like you're hoping to win back something like 3mm by going to a wider rim, and I'm afraid that doesn't strike me as likely. Any kind of a banded tyre has a pretty stiff contact surface, with most of the give in the tyre in the sidewalls. According to folklore, which is where Jan Heine got his number from, a cyclist is supposed to inflate his tyres so that they deform 15% of height of the visible tyre at the contact patch. On a 25mm tyre, to make the match easy, that would be 3.75mm, at first glance enough, but in fact what happens is not that the tyre spreads in width and becomes "smaller" but that the stiff banding causes it to stay more or less round, and the "drop" at the contact patch is caused by the sidewall deforming at the bottom and stretching and flattening a little at the top to move the band in it's entirety, still more or less round. Thus, while the stretching of the sidewall may narrow down the tyre a fraction at the top, it will also make it taller, rather than lower. So, whatever you may think you gain on the wider rim will be lost again in the natural operation of the tyre once you load it.

Sorry. I know exactly how you feel. My Utopia Kranich is specified and built to clearances of 1mm, which is pain to adjust though adjustment is only needed every several years; Utopia designed it that way because generally the adjustments are made by trained dealer mechanics, not customers.

Andre Jute
Screwed by hysteresis. Sounds almost like a political disease.

On 2/19/2017 8:03 AM, jbeattie wrote:
... I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm.

No.

On Monday, February 20, 2017 at 3:12:24 PM UTC-5, sms wrote:
On 2/19/2017 8:03 AM, jbeattie wrote:
... I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm.

No.


Read here
http://www.sheldonbrown.com/rim-sizing.html
Boeger chart suggest what the tire rim can do if there’s good reason to wander of center …
Scroll down
http://www.sheldonbrown.com/tire-sizing.html
But tire carcasses are molded to one specific form..otherwise chaos or more chaos.
The primary design factor is road holding/response in the sidewall. Contact patches follow that n goatheads left behind as an advertising factor.
Thus, IMHO, the sidewall hinges …measure that hinge n work out the height drop
Report back, we’re lazy

On Monday, February 20, 2017 at 3:57:08 PM UTC-5, DATAKOLL MARINE RESEARCH wrote:
On Monday, February 20, 2017 at 3:12:24 PM UTC-5, sms wrote:
On 2/19/2017 8:03 AM, jbeattie wrote:
... I was wondering if the rim width would spread the tire out enough that it would be no higher than a 25mm.

No.


Read here
http://www.sheldonbrown.com/rim-sizing.html
Boeger chart suggest what the tire rim can do if there’s good reason to wander of center …
Scroll down
http://www.sheldonbrown.com/tire-sizing.html
But tire carcasses are molded to one specific form..otherwise chaos or more chaos.
The primary design factor is road holding/response in the sidewall. Contact patches follow that n goatheads left behind as an advertising factor.
Thus, IMHO, the sidewall hinges …measure that hinge n work out the height drop
Report back, we’re lazy

following a short walk...

the measurements are possible with 1x1" pine, finishing nails squooze into rim width holes ...with 3-one to measure, 2 sets outboard nails defining an unstressed area for measurement

one top measure 1x1" over center spreader

the 3 blocks plus 1x1" resting on tuba4 chair to chair or whatever. there are 2 different heights so locate the paperback carton

Wider beads move toward concave contact surfaces...poss a plus in Potland

Cutting a circumferential sipe groove is prob difficult needing a jig