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Old 04-28-07, 07:44 PM   #1
Motorad
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How Wide a Tire that Allows Simple Removal of Wheel from Dura Ace Gruppo'd Bike?

I pretty much keep my Trek 730 in the trunk of my car when not riding, by removing the front wheel. But to get the front tire (32-38mm widths) past the brake pads, I have to disconnect the brake cable from the brake, to increase the gap between the pads. It's a hassle, and would rather not have to mess with the brake cable ... or deflate the front tire ... with my new bike if I want to carry it in my trunk.

My new bike will have Shimano 7801-SL wheels, and Shimano BR-7800 dual-pivot caliper brakes. The wheels are 20.8mm wide and 24mm in height. A lot of technical tests of the 7801-SL were done using 23mm wide tires, so I'm led to believe that Shimano had the 23mm tires in mind when they designed the 7801-SL.

But I'm thinking about using tires wider than 23mm, so here is my question: When removing the 7801-SL wheel from the frame ... and through the Shimano BR-7800 "Dual Pivot Caliper Brake" ... does anybody know the maximum tire widths that I could have on the 7801-SL wheels ... where I would not have to deflate the tire or disconnnect the brake cable to remove the front wheel? The Shimano website does not provide that information.
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Old 04-28-07, 07:53 PM   #2
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OK, what am I missing. As with pretty much all calipers the BR-7800 has a release lever specifically to allow the brake to set wider for tire installation and removal. Are you saying that you expect to use tires so wide that they won't clear even with the caliper released? If so the only thing I could suggest is that you set the adjustment barrel up fairly high and turn it a few turns when you need to for extra clearance.
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Old 04-28-07, 08:03 PM   #3
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I would just get 25 mm tires which is on the wide side for that wheel and be done with it. The reason the technical tests were done with 23mm tires is because that is the size most riders use on that wheel.There is no reason to do tests with a size nobody is going to use. Right? Some even go narrower to 20mm. Is there some kind of special problem or situation you are not telling us where you would need tires wider than 25 mm with a bike and wheel set up that way??
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Old 04-28-07, 08:09 PM   #4
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Quit whining and just use the knob on the brake lever. If that is too much of a hassle, I'd hate to see the trouble you'll have putting on a helmet. Get Campy with their neat little button on the brake lever. Better, go fixed and forgo brakes altogether.
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Old 04-28-07, 08:41 PM   #5
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Tire size is usually limited by the frame or fork, not the brakes. You haven't said what frame the "new bike" has. I'm pretty sure the new Shimano wheels will have the standard 700c road rim which will accept from a 20mm up to 28mm tire, don't know about the frame or fork. 25mm is a good compromise size for paved roads.

Al
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Old 04-28-07, 09:06 PM   #6
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Quote:
Originally Posted by Al1943
Tire size is usually limited by the frame or fork, not the brakes. You haven't said what frame the "new bike" has. I'm pretty sure the new Shimano wheels will have the standard 700c road rim which will accept from a 20mm up to 28mm tire, don't know about the frame or fork. 25mm is a good compromise size for paved roads.Al
Al, the forks will be Serotta's F3-6.5 with a 52mm rake.

Actually, the issue is not width of tire when riding. Rather, the issue is removing the wheel with tires perhaps wider than was designed for the wheel. I look forward to using Shimano's 7801-SL wheels, but I'm guessing with the 16/20 radial spokes ... the ride might be pretty harsh on some roads. I was thinking on the possibility of 25mm or even 28mm tubed clincher tire widths that can be run at reduced PSI to take the edge off the wheel-harshness. The tubeless concept is to ride at lower PSI, and that is what got me thinking about 25mm-28mm tubed clinchers ... as prelude to riding tubeless clinchers at lower PSI.

I've seen comments from colleagues that indicate even with 25mm tires ... and the lever fully open ... that the tire still needs to be deflated to get the tire/wheel through the brake pads when removing the wheel. It's not that I'm whining, but when transporting my bike in my car's trunk, it becomes a PITA to have to remove front tire/wheel before and after every bicycle ride ... when I have to putz with the brake and/or deflate the air out of the tire. Yes, I would rather use my trunk than a bike rack.

So, that is the reason why I asked the question: With Shimano's 7801-SL wheels and BR-7800 brakes ... how wide can the tire be without having to over-adjust the brake pads and deflate the tire ... twice ... on every day that I ride my new bike (to remove the front wheel for transporting bike in trunk)?
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Old 04-29-07, 05:14 AM   #7
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A friend of mine rides an older Diamondback (made by Centurion) with 105 stuff on it. He has to release tension on the front brake cable to get 700x28 Armadillos in and out, just the quick release lever is not enough. He could also slide it in deflated, then inflate it. The rear fits, but it is very (read Bump it to get in) tight.
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Old 04-29-07, 06:08 PM   #8
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Ok, I'm just going to pretend there aren't 20 reasons why you should be fine with 25 or even 28mm tires - and try and answer your question.

Ritchey logic makes a special little cable gizmo for their breakaway frames that you can screw and unscrew to completely release the brake cable - this might help you get a bit more clearance from your brakes, if the barrel adjuster and release mechanism doesn't already give you enough. See their website for the info.
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Old 04-29-07, 06:31 PM   #9
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What will you do about lawyer tabs?
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Old 04-29-07, 07:36 PM   #10
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There's WAY more than enough width to fit the largest tyres possible through those brakes. I've used tyres so big that they ended up rubbing the tyre under the caliper. What you want to do is install the cable with maximum slack in it:

1. unclamp cable from caliper.
2. Unscrew the barrel adjuster ALL THE WAY except for 1-2 threads.
3. Open the QR on the caliper arm.
4. Then install the cable, pull it tight and clamp it down.
5. Install the wheel
6. Close the QR and inspect the lever-throw and make sure the lever doesn't bottom out against the handlebars. This may result in a little more lever-throw than you're used to, but you can still lock up the front wheel before bottoming out the lever.

Now, to remove the front-wheel:

1. open QR on caliper
2. screw IN the barrel adjuster all the way
3. remove wheel.
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