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Old 04-28-07, 04:48 PM   #1
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Tire Width Limitations for Shimano BR-7800 Brakes?

Please read comment that Will gave us in an earlier message:
Originally Posted by will dehne
I have recently used 700 x 28, x 25, x 23. They all got me there ... The downside is that they are harder to install because of the brakes. I have to deflate them and inflate after the wheels are installed. I take the wheels off to get the bike stored in a trunk.
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.

Everybody's comments about using tires wider than 23mm width makes sense. Because the 7801-SL radial wheels can be harsh, it would not be a bad idea to consider 25mm as a minimum width to begin with.

QUESTION 1: 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 where I "Will" (pun intended Mr. Dehne) not have to deflate the tire or disconnnect the brake cable to remove the front wheel? The Shimano website does not provide that information, so I guess that only someone who has brakes similar to Shimano's BR-7800 brakes would have an idea.

QUESTION 2: It had been mentioned that the 7801-SL wheels can accommodate tire widths up to 28mm. Is there a maximum tire width where the Shimano BR-7800 brake's efficiency becomes compromised from the tire rubbing the braking mechanism?
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Old 04-28-07, 06:36 PM   #2
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You are more detail oriented than I will ever be. This is in reference to the numbers you are using for the brakes. My brakes are all Shimano and have this "thing" which allows to open the brakes up some for installing/removing tires and wheels.
Despite this feature, my Cannondale R2000 will make 28 tires hard to get in or out without deflating. I can put the bike upside down and give it a good push or pull and it is done. Someone smarter than me suggested the deflating idea. Since I need to pump the tires anyhow, why not deflate a bit?

Same story with my Treck Madone except it does not like 28 tires at all. 25 tire will go in with a hard push as described above.
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Old 04-28-07, 08:02 PM   #3
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Shimano dual pivot calipers will handle a 28mm tire (with the quick release open) without rubbing the inflated tire. The trick is to back off the cable tension a little bit but not so much that the brake lever bottoms against the handlebar. I know this for sure because one of my personal bikes is set up that way.
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Old 04-29-07, 06:23 AM   #4
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In addition to releasing the lever, how about screwing in the adjuster 2 turns or so and the screwing it back out when done.
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Old 04-30-07, 12:01 PM   #5
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Just a ditto about what others have written. My Cannondale R2000 w/ ultegra brakes will handle a 28 tire with the quick release open without deflating. It's a very tight fit, but with a little practice it works fine.

I have my brakes adjusted pretty close, I really don't think they could be adjusted much tighter. When I put the wheel on and off, the tire does rub against the brake pads when I push it through, but it isn't a problem. Loosening the brakes a little would help if one's tire can't make it through. The barrel adjuster on these brakes is so convenient and easy to use that it really wouldn't be a problem to turn it a couple turns putting the wheel on and off. I would definitely try this before deflating and inflating the tire.

I've found that it is important to make sure the axle and dropouts are lined up so the axle slips right into the dropouts when the tire goes through the brake pads. It's hard for me to describe it any better, but if it doesn't pretty much go right into the dropouts when the tire slides through the brake pads, you won't get it. This is only slightly tricky and mastered after one or two tries.

My friend was helping me put on my wheel the other day (I was late and unloading a bike for another guy, and my friend was a little impatient and wanted to help me get going). I was happy for the help, but I noticed he was struggling to get that fat tire on - I had to show him the trick of making sure the axle and dropouts were aligned.

My main source of concern with my particular frame (CAAD7, 54 cm) is that the rear 28 tire is very close to the back surface of the seat tube, and front derailleur bracket on that tube. I think that if I pick up mud or other road debris like mud or sticky fresh asphault sand granules (that really sticks to the tires for a 1/2 mile or so), I'll have to make sure it doesn't cause a problem. If it is, I think I'll switch back to 25's or 23's, but I do like the ride of the 28's.
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