Reynolds 92.2 rim --- contact patch/tire profile questions

Discuss light weight issues concerning road bikes & parts.
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kwazi
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by kwazi

from CN http://www.velonews.com/article/98568/i ... -the-catch

I understand the seating method, but my question has to do with the tire's contact profile. I'm trying to figure out if the wider rim will make the contact patch/inflated tire's profile similar to that of the HED C2 rims. I know the rim itself is wider, but if the tire is seated deeper into rim or if the beads seat any closer together, does that mean the tire profile will actually end up being closer to the current norm? Does any of this make sense to anyone else or have I finally lost it?

obviously it would be different for different tire widths, but I'm wondering specifically about a 23mm

Thanks guys for your input!
Roll out.

musket
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by musket

The tyre bed is the same width - the rim flares below it (and the brake track).

It's a very similar idea to the Stan's mtb rims, so far as the "bead" goes.
Don't be alarmed.

by Weenie


kwazi
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by kwazi

got it. thanks for the reply
Roll out.

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djconnel
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by djconnel

It took me a few minutes of head-scratching to figure out how the tire is held in place. I'm obviously not a very 3-dimensional thinker. I forgot that tires are round.

I wonder how the rolling resistance compares to a conventional clincher. More sliding of the bead against the rim surface? Or less energy-sapping deformation of tire sidewalls, perhaps?

gitsome
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by gitsome

would a smarter mind than mine please explain this to me?? how does the tire stay in place if not for a bead-rim-lip to catch the tire bead and hook it? how does the tire stay in place if theres no lip? the pic looks like a standard rim bead/lip but with a wider wheel rim at the bottom. what am i missing?
My wallet is the lightest thing on my bike.

unit
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by unit

gitsome wrote:would a smarter mind than mine please explain this to me?? how does the tire stay in place if not for a bead-rim-lip to catch the tire bead and hook it? how does the tire stay in place if theres no lip? the pic looks like a standard rim bead/lip but with a wider wheel rim at the bottom. what am i missing?



OK I will try.

Have you ever looked at a car wheel? There is a "drop center" which makes mounting the tire possible, and it has no "hook".

Lets say you have a tire than measured 20 inches diameter from the inner most portion of the beads. The wheel that this tire mounts on will have a drop center of perhaps 18 inches to allow mounting. The the bench that the bead sits on will have a diameter that matches the tire (20 inches). The rim of the wheel will be greater than 20 inches (perhaps 21 inches) this prevents the tire from coming off.

Because the wheel rim is greater diameter than the tire bead, and because the bead is the same diameter as the bench, the tire can not come off unless the bead breaks, or stretches. It can only be dismounted by pushing the tire bead off the bench (inboard) into the drop center.

Here is a link with pictures. http://www.procarcare.com/icarumba/reso ... wheels.asp

Here is the photo to consider. Notice how there are no hooks. Once the beads are forced outwards onto the bench, it can not come off the wheel.
Image

gitsome
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by gitsome

Thanks, so the tire bead is essentially pushing sideways/outwards on the wheel/rim/wall but can't be pushed out because the rim is greater diameter?

I always thought car tires had a lip too... I guess I need to see it to understand fully.
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unit
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by unit

gitsome wrote:I always thought car tires had a lip too... I guess I need to see it to understand fully.



If you head to your local car tire shop and have a look at whatever wheels they have on display you probably will fully understand, but baring that...you are right, once you see them (bike rims like the 92.2) and install a set of tires on them, you will fully understand.

It is a very simple concept really, and I am not sure why they mention aircraft wheels as an example, they would have a better chance of people understanding the concept by using a more common example. I imagine that part of the decision process involved intentionally making it harder to understand. It is not nearly as exciting to simply state that their design very closely resembles what has been available for years in the MTB market, and decades in the car, motorcycle, and truck market.

czvekslak
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by czvekslak

Stan's No tube ZTR rims use a regular hook, there is just very little side wall or they are super shallow. Nothing like the Reynolds rim.

by Weenie


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djconnel
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by djconnel

They key questions to me are:
  • Rolling resistance compared to a conventional clincher?
  • Wind resistance?
The issue on wind resistance would be the additional lip where the rim extends beyond the cross-section of the tire bead. The issue on rolling resistance is whether the hook affords the bead more room to move slide the rim.

In any case, I don't think the pros will be switching from their sew-ups just yet.

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