V Brake arm length

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PH
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V Brake arm length

Postby PH » 2 Aug 2020, 11:19am

Does anyone know the length of the commonly available V brake arm lengths?
I have a XT on the front of a bike which also has a crown mounted dynamo light. Clearance is tight and although it doesn't touch, I'd feel more comfortable with a little more space there. These measure 107mm from the centre of the bolt to the cable attachment, which is on the top of the arm on these.
I have some Shimano mini V's which are intended for their flat bar road levers, 90mm arms, I could fit these with the appropriate levers, though from memory these were not as effective as full v's.
So ideally, looking for something between the two.

tatanab
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Re: V Brake arm length

Postby tatanab » 2 Aug 2020, 11:30am

Full length V is 100 sometimes plus a bit. As well as 90, Mini Vs also come in 84 https://trpcycling.com/product/cx-8-4/ and 80 https://www.tektro.com/products.php?p=187 I use, or have used all of 80, 84 and 90 with normal road levers (not V brake specific) including a couple of generations of Campag Ergo, all of which work very well.

Edit - I also use fork crown mounted bracket for a dynamo light with no clearance problems at all.
Last edited by tatanab on 2 Aug 2020, 11:32am, edited 3 times in total.

reohn2
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Re: V Brake arm length

Postby reohn2 » 2 Aug 2020, 11:31am

Can the light fitting bracket arm not be adjusted(bent)a little to give more clearance?
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PH
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Re: V Brake arm length

Postby PH » 2 Aug 2020, 11:43am

tatanab wrote:Full length V is 100 sometimes plus a bit.

So far, research has shown manufacturers quoting from 102 to 120 so if they're all measuring the same, that plus a bit is vairiable enough to make a difference.
Edit - I also use fork crown mounted bracket for a dynamo light with no clearance problems at all

Indeed, it isn't as tight on my other forks either.
I use, or have used all of 80, 84 and 90 with normal road levers (not V brake specific) including a couple of generations of Campag Ergo, all of which work very well.

Thanks, maybe my memory is wrong. As I have that kit I'll probably try it first, with everything else the same it'll be a fair comparison.
Last edited by PH on 2 Aug 2020, 11:52am, edited 1 time in total.

PH
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Re: V Brake arm length

Postby PH » 2 Aug 2020, 11:49am

reohn2 wrote:Can the light fitting bracket arm not be adjusted(bent)a little to give more clearance?

No, it isn't a bendable bracket.
it isn't helped by the crown having less height than some others, or that the headset protrudes further than some. I don't want to fall down the rabbit hole of mismatching components, I've already fond a brake that is apparently 5mm shorter, which will probably do.

slowster
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Joined: 7 Jul 2017, 10:37am

Re: V Brake arm length

Postby slowster » 2 Aug 2020, 12:14pm

PH wrote:Clearance is tight and although it doesn't touch, I'd feel more comfortable with a little more space there.

If it's not touching, then I wouldn't be concerned (but maybe I'm missing something?). The standard bent wire Son bracket has a good few millimetres of up/down adjustability, which I found enough.

My solution to the bracket fouling on the headset was to use a full thread bolt and use a standard depth nut as a stand off spacer. So in order of what went on the bolt:
- penny washer
- Son bracket
- penny washer
- nut (tightened to clamp the bracket firmly in place)
- washer (then insert into the fork crown).

B&M make brackets intended for use with cantilever brakes, and the bracket goes under the straddle cable - would one of those work?

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PH
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Re: V Brake arm length

Postby PH » 2 Aug 2020, 2:28pm

slowster wrote:
PH wrote:Clearance is tight and although it doesn't touch, I'd feel more comfortable with a little more space there.

If it's not touching, then I wouldn't be concerned (but maybe I'm missing something?).

I doubt you've missed anything and are probably right.
It could just be my cautious nature - If something looks like it's almost touching, there's probably a scenario where it will...
I am aware there are other components I could change that might increase the clearance - bracket, headset, fork! For now I'm just interested in the brake.