Help with Set-up Shimano BR-AT50 brakes….

[Brucey]

My front brake was set up like the above with a high straddle (and substantially less than 90 degrees between the two wires below the yoke. However because the Blackburn rack attaches only to the inside of the stays the yoke was set low to avoid the wires fouling the rack, with resulting angle a little greater than 90 degrees. So one of the brakes presumably has greater mechanical advantage......If the shimano instruction is right it'd be the front.

So are the Shimano instruction right for the strongest braking ?........

.

if the arms are horizontal (i.e. cable attachments level with the bosses) the straddle height makes no difference. With boss spacings as you describe, I'd expect the arms to be close to horizontal.

With the same brakes on wide-spaced bosses, the arms can be set more like a mid-arm canti, and here low straddles make for higher brake MA.

If using PTFE tape I recommend applying it to dry bosses, with a smear of grease inside the arm bushing.

cheers

[hoogerbooger]

(Blimey....didn't expect straddle cable angle/yoke height to make no difference)

Double check:

That would be horizontal on the lower arm of the brakes ? Whereas the shimano set up diagram is close to horizontal on the upper side.

( just googled park tools video that said brake pad bolt should be directly above the brake bosses and if lower arm were horizontal they wouldn't be..... .so I think I'm misunderstanding something)

[printedland]

if the arms are horizontal (i.e. cable attachments level with the bosses) the straddle height makes no difference. With boss spacings as you describe, I'd expect the arms to be close to horizontal.

With the same brakes on wide-spaced bosses, the arms can be set more like a mid-arm canti, and here low straddles make for higher brake MA.

I'm also getting to grips with the niceties of a pair of these BR-AT50s. In this case, the anti bosses are very narrow (55mm front, 65mm rear)

If I slip the brakes onto the bosses, they rest just below the horizontal if I use the bottom of the three spring holes:

Using the top of the 3 spring holes, they are ridiculously below the horizontal:

So, is the order of play:
1. mount brakes on bosses (lowest holes as per above)
2. install straddle wire so that, when taking up the slack in the brake springs, I get a wire angle at the straddle of just over 90deg.
3. Connect brake cable so that the brakes rest with this 90deg+ straddle angle
4. Set brake blocks so that there is around 2mm of clearance when the whole system is at rest

Or am I doing things arse-about-face as they say round here?

[Brucey]

my guess is that you should be able to get the brakes set so that the arms are at about the same angles as they are in the upper photo when the brake is on. The spring will need to be set in the middle (or upper) holes depending on how strongly you want/need the brakes to pull back at the cable when the brake is released.

In this setup the brake arms are very close to horizontal (when the brake is on) such that there is only a small effect from straddle height. However if you can get the arms a bit higher (when the brake is 'on') than that, it is worth worrying about the straddle height and this may well be the best setup for the front brake. Whether or not you can get far like this depends on the exact boss spacing, rim width and brake block type. FWIW those look like the original brake blocks in the picture which are fine but there are lower profile post-type brake blocks than that, such as 'XTR' type ones, and these may allow the arms to be set a touch higher.

Clarks CP522 'XTR' type

are a good substitute for the original brake blocks (for which inserts cannot any longer be obtained I think). The clarks brake shoes come with inserts which are in a compound which is kind to rims (if they are kept clean) but a bit hard so far as maximum power is concerned. However there are other inserts which are softer and provide more power if you want/need this.

cheers

[gaz]

An alternative to the Clarks are Koolstop Cross Pads, be sure to select the unthreaded version for use with BR-AT50.

The brake shoes on the Clarks extend back past the fork blades. I've one bike that doesn't have clearance between the fork blades for the Clarks shoes with a Sputnik rim.

[Brucey]

good point, OP's fork does look a bit narrow

cheers

[PH]

(Blimey....didn't expect straddle cable angle/yoke height to make no difference)

Took me a while to understand that, good explanation here helped...
viewtopic.php?p=481693#p481693

[slowster]

Even if the OP's rim is narrow enough for the Clarks shoes to fit between the rim and fork blades, unless it's a narrow tyre it's likely that there will still not be enough clearance to remove the front tyre without deflating it.

The Clarks pads are a lot cheaper than the Koolstop Cross Pads (£21 vs £4.99, albeit the latter is out of stock at the moment at SJS), and to keep the costs down the OP could fit the Clarks pads at the rear and the Kools Stop Pads at the front.

[tatanab]

Even if the OP's rim is narrow enough for the Clarks shoes to fit between the rim and fork blades, unless it's a narrow tyre it's likely that there will still not be enough clearance to remove the front tyre without deflating it.

Cut the shoes and blocks down to a suitable length if they foul the forks - or use shorter ones without the large rearwards extension. Removing the wheel should not be a problem, just unhook the straddle wire, which is even easier if your hanger has a quick release.

[printedland]

Even if the OP's rim is narrow enough for the Clarks shoes to fit between the rim and fork blades, unless it's a narrow tyre it's likely that there will still not be enough clearance to remove the front tyre without deflating it.

The Clarks pads are a lot cheaper than the Koolstop Cross Pads (£21 vs £4.99, albeit the latter is out of stock at the moment at SJS), and to keep the costs down the OP could fit the Clarks pads at the rear and the Kools Stop Pads at the front.

In a fit of enthusiasm, I ordered 2 pairs of the Clarks last night. Ho-hum. Thanks for the advice on the fit. Am I to assume that whatever goes on the front should be the shorter and stubbier version of anti brake pads? For example, these: https://www.spacycles.co.uk/m7b0s104p81 ... le-2-Canti

They are a non-removable pads version, but you get my drift....

[slowster]

In a fit of enthusiasm, I ordered 2 pairs of the Clarks last night. Ho-hum.

If, unlike gaz, your rim is not so wide that the pad simply will not fit, it's not that big a deal if you have to deflate the front tyre to remove it. I bought two pairs of the Clarks pads, but I admit I found the need to deflate the front tyre to remove the wheel irritating enough to buy a pair of the Kool Stops for the front.

Am I to assume that whatever goes on the front should be the shorter and stubbier version of anti brake pads? For example, these: https://www.spacycles.co.uk/m7b0s104p81 ... le-2-Canti

They are a non-removable pads version, but you get my drift....

Those Eagle 2 pads look like they might extend back between the rim and forkblade. You can buy similar brake blocks with a post to fit your cantilevers which are shorter, e.g. like those in the photograph below. However, the reason why I and others recommend the Clarks and Kool Stop pads is that they are cartridge holders. When the pad in a cartridge holder wears out, you just slide a new pad in, so fitting the cartridge and toe-ing in is something you only need to do once. You also have the choice of better and/or cheaper pads, i.e. the Kool Stop Cross Pad cartridges use the standard Shimano caliper pad shape and the Clarks take a standard V brake pad, so when the supplied pads are worn you can fit your preferred choice of aftermarket pad and compound, e.g. I like the Kool Stop pads in their salmon pink compound here and here.

[printedland]

In a fit of enthusiasm, I ordered 2 pairs of the Clarks last night. Ho-hum.

If, unlike gaz, your rim is not so wide that the pad simply will not fit, it's not that big a deal if you have to deflate the front tyre to remove it. I bought two pairs of the Clarks pads, but I admit I found the need to deflate the front tyre to remove the wheel irritating enough to buy a pair of the Kool Stops for the front.

Am I to assume that whatever goes on the front should be the shorter and stubbier version of anti brake pads? For example, these: https://www.spacycles.co.uk/m7b0s104p81 ... le-2-Canti

They are a non-removable pads version, but you get my drift....

Those Eagle 2 pads look like they might extend back between the rim and forkblade. You can buy similar brake blocks with a post to fit your cantilevers which are shorter, e.g. like those in the photograph below. However, the reason why I and others recommend the Clarks and Kool Stop pads is that they are cartridge holders. When the pad in a cartridge holder wears out, you just slide a new pad in, so fitting the cartridge and toe-ing in is something you only need to do once. You also have the choice of better and/or cheaper pads, i.e. the Kool Stop Cross Pad cartridges use the standard Shimano caliper pad shape and the Clarks take a standard V brake pad, so when the supplied pads are worn you can fit your preferred choice of aftermarket pad and compound, e.g. I like the Kool Stop pads in their salmon pink compound here and here.

Thanks very much for the tips. Are you aware of a short cartridge-style brake pad that'll fit the bill?

[Brucey]

...In a fit of enthusiasm, I ordered 2 pairs of the Clarks last night. Ho-hum.....

They are a non-removable pads version, but you get my drift....

Part of the reason for suggesting the XTR cartridge-style brake blocks (holders + inserts) was that they are generally as thin or thinner where they are between the fork blades, and that they are as thin or thinner where the post mounts too. This both allows them to fit in most forks (usually, with at the worst having to deflate the front tyre to remove the front wheel as slowster says -which I omitted to mention, sorry-) and this allows the canti-arms to be elevated as far as possible, which always gives you more choices if you want to fine-tune brake MA. Thirdly the brake insert compound can be selected to be different in later inserts, or different front to rear, thus fine-tuning brake performance.

For some reason post-mount holders which accept shorter 'road' style inserts are fiercely expensive. However I would point out that most 'road' style inserts are inherently less suitable for use in cantilever brakes, in that they are both

a) fairly thick and
b) don't have a big enough chamfer angle on the top edge.

These two things together mean that the contact between the brake block and the rim usually moves downwards as the inserts wear, which can turn into a significant issue especially if the rim has a shallow brake track. This is less of a problem with the XTR style inserts because they are designed for cantis/Vs, being thinner and usually having a steeper angle on the top edge, which means that the top edge of the brake block is closer to being at constant radius from the brake arm pivot. At worst this normally means that an insert might develop a small lip on the lower edge as it wears, but braking is not usually badly affected.

cheers

[printedland]

...In a fit of enthusiasm, I ordered 2 pairs of the Clarks last night. Ho-hum.....

They are a non-removable pads version, but you get my drift....

Part of the reason for suggesting the XTR cartridge-style brake blocks (holders + inserts) was that they are generally as thin or thinner where they are between the fork blades, and that they are as thin or thinner where the post mounts too. This both allows them to fit in most forks (usually, with at the worst having to deflate the front tyre to remove the front wheel as slowster says -which I omitted to mention, sorry-) and this allows the canti-arms to be elevated as far as possible, which always gives you more choices if you want to fine-tune brake MA. Thirdly the brake insert compound can be selected to be different in later inserts, or different front to rear, thus fine-tuning brake performance.

For some reason post-mount holders which accept shorter 'road' style inserts are fiercely expensive. However I would point out that most 'road' style inserts are inherently less suitable for use in cantilever brakes, in that they are both

a) fairly thick and
b) don't have a big enough chamfer angle on the top edge.

These two things together mean that the contact between the brake block and the rim usually moves downwards as the inserts wear, which can turn into a significant issue especially if the rim has a shallow brake track. This is less of a problem with the XTR style inserts because they are designed for cantis/Vs, being thinner and usually having a steeper angle on the top edge, which means that the top edge of the brake block is closer to being at constant radius from the brake arm pivot. At worst this normally means that an insert might develop a small lip on the lower edge as it wears, but braking is not usually badly affected.

cheers

That all makes sense! I'll persevere with the Clarks when they arrive, and only look for a front alternative if they really don't fit

FWIW, canti blocks seem to come in (commonly) 55, 60 and 70mm. The distance from the post arm to the widest part of my front fork is around 47mm. If we assume that roughly two-thirds of those long brake pads sits behind the post arm, then that would be precisely 47mm - in other words, 70mm ones may not poke into the space between the fork blade and the rim.

It does mean that I can't position the post arm behind the canti arm, on the fork side of the brake, as you have suggested elsewhere, but let's hope that with decent brake pads it won't be necessary.

Thanks once again

[Brucey]

It does mean that I can't position the post arm behind the canti arm, on the fork side of the brake, as you have suggested elsewhere, but let's hope that with decent brake pads it won't be necessary.

well if you read to the end of that thread, you will see that Colin531 thought that such a brake block position might encourage judder and other evils; it didn't do this at first, but eventually the rot set in, in exactly that way, so Colin was quite right. In the end I abandoned the experiment and reverted to a more forwards position for the post.

cheers