Builders - brake bridge alignment questions

[yarg]

I thinks I know the answers except for last but confirmation is always good.

I went to put brakes on a frame with a wheel to check tire clearances, and brake pads had to be at the very top of brake caliper slots to hit rim center. Looking for reason, and it took me awhile to figure this out, the rear brake is not tangental to wheel and as result underside of brake furthest away from bridge has little/zero clearance of normal tire.

1)The brake bridge bolt hole/cylinder should always be tangent to the wheel, correct?

2)If it is not and there is no sign of damage, the bridge was initially welded incorrectly?

3)The frame in question is titanium, can the bridge be cut inside of the existing welds to the seat stays and be rewelded at the correct orientation without strength/fatigue concerns? Looks not to much of a concern.

my own answers - yes, yes, please yes

[Louis]

1)The brake bridge bolt hole/cylinder should always be tangent to the wheel, correct?

Instead of performing minor surgery on the bike why not just get some brake calipers with a shorter reach?

Also, wouldn't you be able to rotate the the brake shoe angle before tightening it down to accommodate the angle of the hole relative to the wheel? As long as the cylinder defined by the bolt hole is at the correct yaw angle the pitch angle shouldn't really matter. (Airplane talk: Yaw = side to side, Pitch = up and down).

Louis

[yarg]

Yes the angle of the bolt hole does matter for tire clearance, and whether the frame was constructed correctly, these are the issues. Modern brakes have about as short of a reach as anyone could possibly want already and like I said work here but barely for a normal tire. Maybe tonight after work I will take a picture to post and show this problem.

[sspielman]

Is this a Colnago?

[yarg]

Is this a Colnago?

Nope - an older litespeed. pictures later.

[bostondrunk]

Is this a Colnago?

You stole my thunder!!!!!!!!!!!! :butt:

Yarg-
In case you missed the colnago thread, most of the experts agree that a misaligned part of a frame is not a defect, it is a sign of handbuilt craftsmanship.... :)

[sspielman]

You stole my thunder!!!!!!!!!!!! :butt:

In case you missed the colnago thread, most of the experts agree that a misaligned part of a frame is not a defect, it is a sign of handbuilt craftsmanship.... :)
Whew...That's a relief. I have been checking in periodically. It's always alot of fun watching somebody defend the indefensible....

[cpg]

You stole my thunder!!!!!!!!!!!! :butt:

Yarg-
In case you missed the colnago thread, most of the experts agree that a misaligned part of a frame is not a defect, it is a sign of handbuilt craftsmanship.... :)


That wasn't/isn't my opinion just in case there's any confusion.

Yarg-
That's a screw up. I can't believe someone lived with that mess. Did you get it cheap? It can be fixed relatively easily. Good luck.

Curt

[bostondrunk]

That wasn't/isn't my opinion just in case there's any confusion.

Yarg-
That's a screw up. I can't believe someone lived with that mess. Did you get it cheap? It can be fixed relatively easily. Good luck.

Curt

Curt,
I wasn't referring to you. You actually provided very clear feedback in the nago thread, thanks!

[yarg]

here is what I am talking about, I hope.

[Louis]

Will calipers fit on the other side of the bridge / stays?

[yarg]

one more pic.

[Louis]

one more pic.

I guess this one answers my question. That would be an option.

[yarg]

So the $64,000 question is can the brake bridge be cut inside the existing seat stay welds and be rewelded at the correct angle?

Got one vote from Curt says an easy yes.

Anybody else?

[csm]

do you really need a back brake? they are kinda overrated!

[mosca]

Will it not have sufficient clearance once the cable is connected and the brake adjusted?

[thwart]

Are those 25's or 23's (tires)? May save you some repair trouble by running smaller circumference tires...

Michelin P2R's run big---even the 23's.

[yarg]

Louis - Will calipers fit on the other side of the bridge / stays?

You have got be kidding.

csm - do you really need a back brake? they are kinda overrated!

This is sarcasm I recognize.

mosca - Will it not have sufficient clearance once the cable is connected and the brake adjusted?

No

thwart - Are those 25's or 23's (tires)? May save you some repair trouble by running smaller circumference tires...

Michelin P2R's run big---even the 23's.

Look - 25s are my standard and are not a problem on any bike I own even my legend, usually if 25s are tight it is at the fork not the rear brake.


The funny thing is this frame and fork has a lot of room for bigger tires everywhere else, so I want to fix it if possible.

[Louis]

Louis - Will calipers fit on the other side of the bridge / stays?

You have got be kidding.

It's been done before.

Just brainstorming and looking for the best / simplest solution. Sometimes it pays to have an open mind.

Louis

[csm]

not sure it was sarcasm so much as just being a smarta$$.

[soulspinner]

You stole my thunder!!!!!!!!!!!! :butt:

Yarg-
In case you missed the colnago thread, most of the experts agree that a misaligned part of a frame is not a defect, it is a sign of handbuilt craftsmanship.... :)

:p

[Peter P.]

The suggestion to mount the brake on the other side of the rear triangle is NOT far fetched.

Harry Havnoonian builds his frames this way with the following logic:
As you apply the rear brake, the forces from the spinning rear wheel will cause the brake bolt to flex and the brake to rotate away from the wheel. Tire pressure causes the rim to flare out at its perimeter. Therefore, as the brake is applied, braking force will inherently INCREASE as the pads rotate up towards the wider section of the rim.

I'm sure it's a minute improvement. I did it once, on an older bike with a nutted brake axle. If you have a recessed allen bolt attachment, it might not work.

My other suggestion is, since you've got the photos, to contact Litespeed via e-mail and ask whether it's a feasible repair. If you're lucky they'll even cover it under warranty.

Otherwise, I'd sell it. You could advertise it as having "authentic Colnago defects" and it will probably sell for big bucks. ;-)

[Tom Matchak]

Looking at your photos, it's apparent that the real problem is brake bridge location, not bridge rotation (or pitch). Yes, as you note, the side-view photo reveals that the brake's center axis is not tangential to the rim as it passes through the seatstays. That's not necessary. With the brake's center axis perpendicular to the stays (as yours is, and most are), the builder just needs to position the bridge at a height which accounts for the sweep of the rim out there where it passes the brake shoe slot. From the bridge's point of view, this sweep path can vary up/down by a mm or two, depending on where the rear axle is relative to the centerline of the seatstay. Thoughtful design and careful execution is all that's required.

This particular construction is not art, it's a flaw. atmo.

And, with 10mm of brake-adjusting height to work with, I fail to see the logic for positioning the bridge such that you start out shoved up against the minimum-clearance end of that range. But that's another thread, I guess.

Cheers,
Tom

http://tommatchakcycles.blogspot.com/