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Brake assembly and tire clearance

Old 05-13-17, 10:12 AM
  #1  
kevlar_heart 
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Brake assembly and tire clearance

Hi folks. Hope I can get some guidance here

Finishing a rebuild on a 1989 Specialized Allex with Suntour GPX components. I am having an issue with tire clearance for the rear brake assembly (Fig 1)
DSC_0881.jpg

Logic would say that pulling the wheel deeper into the drops should create better clearance...but NO grasshopper...in fact the only way I can get clearance is to have the wheel mounted precariously shallow in the drops (Fig 2 and 3)
DSC_0882.jpgDSC_0883.jpg

With the wheel mounted as above I get about 3-5 mm clearanceDSC_0884.jpg

Wheels are 700C Wolber GTX (standard for the Allez) with 700 x 25c tires. Tried 700 x 23c tires with same results.

Tips tricks (magic or otherwise) appreciated
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Old 05-13-17, 11:11 AM
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Probably designed with 21mm tires in mind, with super tight clearances, which was fassionable in that era. 3mm clearance should be enough. As far as the 23 vs 25mm, sounds like normal variation in tires, but with same make and model, in theory should give 2mm additional.

How about a 650b conversion?
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Old 05-13-17, 11:25 AM
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Originally Posted by catgita View Post
Probably designed with 21mm tires in mind, with super tight clearances, which was fassionable in that era. 3mm clearance should be enough. As far as the 23 vs 25mm, sounds like normal variation in tires, but with same make and model, in theory should give 2mm additional.

How about a 650b conversion?
I hadn't thought of a conversion. I was trying to get the bike back to spec as a project. Won't be ridden too often

I am stumped because the wheels are original (trued and sturdy), and I replaced the older tires with exact size/brand/model. Maybe I didn't so such a good job re-installing the brake assembly. I'll check again

I'm going to see how the bike rides underload with the wheel in the position that allows clearance...just a bit scared the wheel will not have enough support.
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Old 05-13-17, 11:26 AM
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kevlar heart, Quick and ugly is to move the rear brake to the front of the brake stay.

What size tire are you trying to use? Tire brand can also play a factor as sizing from one brand to another varies.

Brad
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Old 05-13-17, 11:48 AM
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Originally Posted by bradtx View Post
kevlar heart, Quick and ugly is to move the rear brake to the front of the brake stay.

What size tire are you trying to use? Tire brand can also play a factor as sizing from one brand to another varies.

Brad
Hi Brad: Michelin Pro4 700 x 25c. Literally the SAME tire I took off.

Moving the brake...that I need to get my mind around. It's raining here so let's see how that looks/works
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Old 05-13-17, 01:17 PM
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ok, people... time to find this nice man some lower profile tires that will fit better....... the Continental Gatorskins on my Trek 2000 measure exactly 25 x 25mm at 85 lbs.... my Fuji has Vittoria Rubinos that measure 23.2 wide, and only 21.5 tall, at 100 lbs. pressure... Rubinos are a LOWER PROFILE tire! I measured height from rim lip, to outer tread height...

any other ACTUAL measurements, folks?

to Kevlar Heart.... is there ANY indication that the brake mount crossmember has been twisted, by chance? get out the magnifing glass, and look at the crossmember/seat stay junctions...
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Old 05-13-17, 04:43 PM
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Originally Posted by maddog34 View Post
<snipped>
to Kevlar Heart.... is there ANY indication that the brake mount crossmember has been twisted, by chance? get out the magnifying glass, and look at the crossmember/seat stay junctions...
None whatsoever. Looked the bike over for that type of damage before I began rebuilding it. This was my first "true" road bike, so it's a labor of love...not necessity
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Old 05-13-17, 04:48 PM
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Assuming the wheel and tire are installed correctly (which seems like a safe assumption), this is a stupid frame design.
But as @catgita said, super-narrow tires were fashionable at one point.

If you want to stick with this frame, I too would recommend a 650b conversion if you want to use this frame and run 35-38mm tires.
However, you'd probably need actual long-reach brakes, as the rim will be about 19mm further away from the brake pads.

This conversion would require new rims, spokes, and brakes. Since you can use fatter tires, the outer wheel diameter won't change much compared to 700c x 21mm tires, but fatter tires effectively cause a bike's steering to be a bit slower, similar to increasing the trail.

Your call as to whether this is worth the effort.
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Old 05-13-17, 06:29 PM
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Try installing a spacer between the caliper and brake mount. This may angle the caliper up enough to clear the tire. If you don't have a proper spacer handy just stack some washers until you can determine the proper thickness needed and then get a real spacer. Not sure I'd want to go more than 10mm thick but that's just a safe guess.
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Old 05-13-17, 07:24 PM
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What clearance do you have to the brake crossmount?

If it were me, I'd make, or have made an adapter that mounts to the brake crossmember and then has a brake mounting hole just above the crossmember. May need a machine shop to get the right radius, or just rake your time and make one if you are so inclined. Probably need to be made out of steel for strength.

John
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Old 05-13-17, 08:58 PM
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Originally Posted by kevlar_heart View Post
Hi Brad: Michelin Pro4 700 x 25c. Literally the SAME tire I took off.

Moving the brake...that I need to get my mind around. It's raining here so let's see how that looks/works
In some way either the tires are different or there was an error installing the caliper, that's obvious. Moving the brake to the front of the brake bridge is fugly and the very last resort. Make sure that you didn't leave out a spacer between the brake and the brake stay, or possibly even mounted a spacer meant for the rear accidentally on the front brake. Look for a thick washer that's concave on one side and flat on the other and or just a thick washer/spacer.

Brad
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Old 05-13-17, 10:54 PM
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Originally Posted by Crankycrank View Post
Try installing a spacer between the caliper and brake mount. This may angle the caliper up enough to clear the tire. If you don't have a proper spacer handy just stack some washers until you can determine the proper thickness needed and then get a real spacer. Not sure I'd want to go more than 10mm thick but that's just a safe guess.
This is probably the best answer.

Short of dumping the 25 and going back to a 23.
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Old 05-14-17, 10:49 AM
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Workable solution

Hi all:

Many thanks for the suggestions. All stock spacers and fitments had been installed. I put a 2 mm thick lock washer between the brake assembly and the frame brake bracket (Fig 1...kinda hard to see)
DSC_0885.jpg

The resulting clearance (Figure 2) is with the wheel mounted securely in the drops...I took it for a spin under load (and I AM a load), no rubbing between brake assembly and tire. Brake pads hit square on brake surface. I should think I could go up to 5 mm with a spacer before there would be an issue.
DSC_0886.jpg


Glad this forum is here to assist. Again, my thanks for all the suggestions.
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Old 05-15-17, 02:20 PM
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Shakeout ride went OK. Still hinky on gears staying indexed, but the bike rode well for a mile or so around the neighborhood. Next step is to level the brake levers and wrap the bars
DSC_0890.jpg
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