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Old 04-19-06, 06:32 AM   #1
duane041
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Tire to brake bridge clearance-How close is too close?

I recently installed a pair of Conti UltraGatorskins on my commuter, and I am a little concerned. The bike is a circa 1984 or 85 Raleigh Super Course, and it originally had 700x25's on it. I thought going a little larger would put an extra dose of comfort in the ridce, but I noticed that the tires are REALLY close to the brake bridge at the back, and the top of the fork at the front. How close is too close? They don't touch anything, no rubbing sounds, but I would guess the clearance at 1/16 to 1/8th of an inch, MAX. Am I going to have problems?

If a pic would help, I can probably get one on here tonight.

Thanks in advance.
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Old 04-19-06, 06:56 AM   #2
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If they don't rub you should be OK.
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Old 04-19-06, 07:45 AM   #3
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Quote:
Originally Posted by duane041
I would guess the clearance at 1/16 to 1/8th of an inch, MAX. Am I going to have problems?
Thanks in advance.
If you pick up any dirt on the road, it's going to touch the brake bridge with only a 1/16 of an inch clearance. I wouldn't put that tire on.
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Old 04-19-06, 08:36 AM   #4
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I wouldn't worry about it. You might be wiping a little more dirt off of your brake bridge/fork than most people, but any dirt that is soft enough to stick to the tire will be soft enough get knocked right off of there. Running those tires it sounds like this is a commuter anyway, unless you go through a lot of mud you'll never have a problem at all. Lots of cool kids are running track bikes on the street with impressively close to zero clearance and never having a problem. Just think of it as a radial truing indicator
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Old 04-19-06, 11:23 AM   #5
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I can't do 28c tires on my Raleigh road bike. No touching unless my tire picks up dirt, which happens every so often. then it rubs the brakes, brake bridge and seat tube. (Stupid tight-clearance racing bikes, proving purity of the rider by their inability to be adapted for other things.)

Short answer was, in my case, it was really annoying to have rubbing on the underside of the calipers every time the tires picked up any dirt. I'm back to 25c tires now.
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Old 04-19-06, 12:23 PM   #6
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Originally Posted by Landgolier
Lots of cool kids are running track bikes on the street with impressively close to zero clearance and never having a problem.
Yay! Someone called me cool! 700x23 ridden practically every day on the street. No problems with brake clearance either
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Old 04-19-06, 02:36 PM   #7
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Ride alot; eventually the tire will polish away wherever it's touching...

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Old 04-19-06, 09:18 PM   #8
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Yay! Someone called me cool! 700x23 ridden practically every day on the street. No problems with brake clearance either
YIKES!!!!! Doesn't that give you the willies???? That's even less clearance than mine, so I guess I'm good to go. Thanks for the help.
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Old 04-20-06, 04:39 AM   #9
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Why the heck do they design road forks like that??? It doesn't make them faster. All it does is to limit your options.
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Old 04-20-06, 05:14 AM   #10
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Originally Posted by jur
Why the heck do they design road forks like that??? It doesn't make them faster. All it does is to limit your options.
They design road forks like that so the bikes will handle properly at speed. Bikes with short wheelbases and steep frame angles work best with forks with short rake, which necessitates tight clearance under the fork crown. The best-handling bike I've ever owned was my Bianchi Eco Pista; 75 degree head tube angle, almost invisible fork rake, fork crown clearance so tight that they had to file the underside of the crown at the factory. That bike was incredibly stable in a straight line, and yet turns were instantaneous.

Last edited by Trakhak; 04-20-06 at 06:26 AM.
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Old 04-20-06, 08:10 PM   #11
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Quote:
Originally Posted by duane041
YIKES!!!!! Doesn't that give you the willies???? That's even less clearance than mine, so I guess I'm good to go. Thanks for the help.
What gives me the willies is the apparent lack of a front brake.
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Old 04-21-06, 12:45 AM   #12
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Quote:
Originally Posted by Trakhak
They design road forks like that so the bikes will handle properly at speed. Bikes with short wheelbases and steep frame angles work best with forks with short rake, which necessitates tight clearance under the fork crown. The best-handling bike I've ever owned was my Bianchi Eco Pista; 75 degree head tube angle, almost invisible fork rake, fork crown clearance so tight that they had to file the underside of the crown at the factory. That bike was incredibly stable in a straight line, and yet turns were instantaneous.
OK I'm dense. Head tube angle, rake and trail are all independent of fork length. Sure, for a steep angled head tube, you need less rake to maintain trail. And sure, if the fork length on a given frame is changed, so will the head tube angle; but if you are designing a frame from scratch, you don't have these constraints, so could design in a bigger clearance. Or am I missing something? Surely 5mm extra is not going to render the bike less useful?
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Old 04-21-06, 08:45 AM   #13
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Originally Posted by jur
OK I'm dense. Head tube angle, rake and trail are all independent of fork length. Sure, for a steep angled head tube, you need less rake to maintain trail. And sure, if the fork length on a given frame is changed, so will the head tube angle; but if you are designing a frame from scratch, you don't have these constraints, so could design in a bigger clearance. Or am I missing something? Surely 5mm extra is not going to render the bike less useful?
My guess is that the fork was designed uber-short b/c it's a track bike (75deg HT) and shortening the fork helps to put the handlebars down as low as possible. You could achieve the same handling on a slightly taller fork by adjusting the rake and achieving the same trail figure.
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Old 04-21-06, 08:46 AM   #14
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What gives me the willies is the apparent lack of a front brake.
mmmm.....fixies don't need no brake. They're so kore.
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Old 04-21-06, 09:57 AM   #15
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The way to be sure is to lower your tire pressure a little and with the frame suspended in a work-stand spin your wheel. At speed your tire will expand slightly. If there is no rubbing then you are good to go.

The closer the gap is the more conscious you must be about dusting your tires with your gloved hand as you pass over debris or small gravel. You don’t want to risk trapping a sharp object that your tire picks up.
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Old 04-21-06, 03:06 PM   #16
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Originally Posted by AfterThisNap
Yay! Someone called me cool! 700x23 ridden practically every day on the street. No problems with brake clearance either
Let me tell you a story: I once had a DH mountain bike that I converted to mixed road/off-road use by mounting a 80mm low-end fork I had lying around. I was riding the thing with my usual 2.5" knobbies front and rear. With the crappy fork, the front tire was running very VERY close to the fork crown. Almost as close as your tire. One day, I rolled onto an empty soda can: the can wrapped around the tire, went around the wheel and *bang* - instant endo.

Since that day, I always leave as much clearance as possible at the front. If the rear locks up, I don't care, but the front, well... I don't want to go flying like that ever again.
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Old 04-21-06, 03:55 PM   #17
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The likelihood of sucking an entire soda can into my 700c wheel, relative to 2.5" knobbies, is very low, and even if it were possible even the greatest clearances found on most road bikes wouldn't be big enough to pass a can through the crown.
And in the event I did catch a can with this setup, it would probably just slide as opposed to a knobbie that will catch and hold the object.
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Old 04-21-06, 06:24 PM   #18
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Quote:
Originally Posted by Francis Buxton
My guess is that the fork was designed uber-short b/c it's a track bike (75deg HT) and shortening the fork helps to put the handlebars down as low as possible. You could achieve the same handling on a slightly taller fork by adjusting the rake and achieving the same trail figure.
the blades are short for the same reason most modern road bikes have short chainstays and fork blades--to make the bike as stiff as possible and theoretically improve performace. plenty of track bikes in the past had slacker angles and more clearance. and were drilled for brakes and had eyelets for that matter.
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Old 04-23-06, 05:42 PM   #19
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I vote for some tire clearance.The tire markings are more accurate than the old days,,but please.Narrow tires will give a sportier ride.I got something caught in my Centurion rearwheel last month,,2 leaves,skidded half a block.I just put new rubber on it.I got a bungee cord caught in the cogs once,,real scare.I helped 2 girls with the fatal bungee a few years ago,they'd look stupid if they had to push it home.
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