Why toe-in brake pads?

General cycling advice ( NOT technical ! )
busb
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Why toe-in brake pads?

Postby busb » 6 Apr 2018, 2:40pm

Although I no longer have bikes with rim brakes, I have memories of setting toe-in on the pads. If I didn't - the pads would squeal like a pig. The thing is that they would wear parallel to the rims anyhow leaving plenty of pad thickness on their rear so end up wedge-shaped. Has anyone not toed-in their pads & just put up with the squealing for a while?

Roadster
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Re: Why toe-in brake pads?

Postby Roadster » 6 Apr 2018, 3:43pm

Up with squealing I have not, do not and will not put.

recumbentpanda
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Re: Why toe-in brake pads?

Postby recumbentpanda » 6 Apr 2018, 3:53pm

Some calliper brakes tend to be rather flexible. Both the pivot and the calliper arms themselves could contribute to this.

If you set up the pads parallel to the rim the friction pushes them forwards a little and the ‘toes’ outward.

At a certain point they spring back and repeat, hence the squeal sometimes experienced. If ‘toed in’ they tend to end up flat to the rim under braking. Of course, if your calipers happen to be stiff, toeing in your pads will just result in uneven wear at the front.

Flexibility tends to be much less of an issue with cantilever brakes as the pads are closer to the pivots, and the pivots themselves beefier with less ‘play’.

Anyway, that’s what I think :D

mercalia
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Re: Why toe-in brake pads?

Postby mercalia » 6 Apr 2018, 5:04pm

never found a bit of difference. Now preparing the rim with some burnt off brake pad detritus another matter

iandriver
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Re: Why toe-in brake pads?

Postby iandriver » 6 Apr 2018, 7:38pm

A quick Google for cantilever fork shudder will bring up countless results, many from this forum. Level blocks being toed out by application of the brake can cause horrendous vibrations. My old Surly Crosscheck used to do it with Tektro 720s. Re toeing in the blocks was a regular maintenance activity. Used to use a one pence piece at the rear of the block. Apply brake and tighten up the block.
Supporter of the A10 corridor cycling campaign serving Royston to Cambridge http://a10corridorcycle.com. Never knew gardening secateurs were an essential part of the on bike tool kit until I took up campaigning.....

Stradageek
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Re: Why toe-in brake pads?

Postby Stradageek » 7 Apr 2018, 8:31am

Just to stoke a little controversy, I've found the following:

Squealing brakes are a very useful pedestrian warning device, more likely than a bell to penetrate an ear-phoned pedestrian

Squealing brakes are much more powerful when braking from high speed than quiet brakes, providing you are aware that as the speed drops there is a risk of them snatching

I cured the squeal on my Bacchetta and found the vastly reduced high speed braking quite scary. The reason is possibly less overheating if brakes are being rapidly pulsed or is it just a very effective ABS analogue?

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Audax67
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Re: Why toe-in brake pads?

Postby Audax67 » 7 Apr 2018, 8:39am

Always did, but LBS (excellent) where I bought my Trek said "never bother" and the Trek's 105s do not squeal. Duh.
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pwa
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Re: Why toe-in brake pads?

Postby pwa » 7 Apr 2018, 10:03am

When setting blocks on my cantis I try to find someone else to lend a hand for a moment. I want them to apply the brake hard when I have the blocks exactly where I want them, with the bits of card inserted for toe-ing in. Then I put a strap around the brake lever to keep the brakes on while I tighten the bolts, holding them to resist the dreaded twisting. I can do it by myself but it just makes it swifter with the extra hand.

The toe-in does disappear as the pads touch the rim. I've observed that. Mainly due to play in the brake parts. So wear is fairly uniform.

Brucey
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Re: Why toe-in brake pads?

Postby Brucey » 7 Apr 2018, 10:25am

BITD there were three reasons for toeing in

1) brake arms are twisty
2) brake pivots get worn
3) brakes might squeal without.

of these only 2) applies to many modern brakes, and then only when the brake is worn.

If brake blocks wear evenly and don't squeal, it is job done more or less, no matter how they are set up, exactly.

Note that with some very flexy brakes, if they are not toed in, not only do the brake blocks wear unevenly, but the brake power is reduced. In extreme cases the brake blocks need to be angled so as to allow for the flex in the vertical plane, eg the brake blocks in the front brake can go into the tyre unless they are angled downwards slightly. The reduction in brake power without toe occurs because (I think) the area of the brake block that is in contact with the rim is reduced, and the part that is in contact simply overheats more easily.

cheers
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Marcus Aurelius
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Re: Why toe-in brake pads?

Postby Marcus Aurelius » 8 Apr 2018, 10:03pm

Stops ‘em squealing, stops uneven rim wear.

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Mick F
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Re: Why toe-in brake pads?

Postby Mick F » 9 Apr 2018, 8:49am

I've only had squealing brakes on a bike with a bendy plated rear bridge, or when there's oily marks on the rims.

I sold the bike, so that was cured!
I clean the rims, so that's cured too.

Never ever ever had squealing brakes other than those two issues, and never ever ever toed in the brakes.
Mick F. Cornwall