The Disc Brake Naughty Corner Thread

[Brucey]

if you want something that looks like a BB7, but isn't, Clarks CMD-15 brake is as cheap as chips.

No idea if they are any good whatsoever though!

BTW I'd worry that 140mm discs would run a bit hot on a tandem.

cheers

[reohn2]

BTW I'd worry that 140mm discs would run a bit hot on a tandem.

cheers

They're 160's now and will stay as such .
BTW the Ashima centerlock to six bolt converter is streets ahead of the Shimano design .

[RickH]

I think it is worth mentioning that (in terms of braking effort) 160mm discs on 20" wheels are better than 203mm discs on 700C sized wheels. The new tandem's brakes ought to be pretty stupendous.

cheers

I'd not thought of that
Perhaps I should've gone for 140's

I've never found the brakes on ours (160mm rotors, Shimano callipers) to be too powerful. But I've never found the braking power to be lacking either - even coming down some of Flintshire's best steep little lanes, which give a good test for any brakes.

I have at times wondered about fitting bigger rotors - not for more power but to improve the cooling (bigger proportion of disc cooling compared to the bit being heated) if we ever go touring in mountainous terrain.

Rick.

[reohn2]

I've never found the brakes on ours (160mm rotors, Shimano callipers) to be too powerful. But I've never found the braking power to be lacking either - even coming down some of Flintshire's best steep little lanes, which give a good test for any brakes.

That's good to know,I know some of those lanes and they can be steeeep,and mucky,and narrow,and,and...

I have at times wondered about fitting bigger rotors - not for more power but to improve the cooling (bigger proportion of disc cooling compared to the bit being heated) if we ever go touring in mountainous terrain.

Rick.

That sounds sensible,until Brucey mentioned it I hadn't given rotor size a second thought but that's mainly because I know we won't be going anywhere near Flintshire

[jb]

I noticed an alarming thing the other day whilst braking hard down a long steep decent. I looked down at the front disc and it was all pretzeled to an alarming degree, infact it looked more like a rubber disc than a steel one, I stopped braking on the front and used the rear brake - the front making a rubbing noise on the calliper, then as the cold wind blew over the disc, it just straightened up true again.
When I got to the bottom I was then left wondering if I'd imagined it.

Any body else out there in disc brake land experienced this as a matter of interest?

[reohn2]

Never noticed anything like that.
I know it sounds a bit odd,but could it have been the heat haze off the disc causing a mirage effect?

I've ridden a couple of steep descents on our C/dale that heated the rear up to straw colour with a blueish tinge,and was surprised that it cooled to touching temp in about 30 seconds .

[andrewjoseph]

my wife drags the brakes a lot, and it can warp a bit on a ride, but then they can straighten themselves out fairly well too.

[Tiberius]

my wife drags the brakes a lot, and it can warp a bit on a ride, but then they can straighten themselves out fairly well too.

.....sounds nasty......You're wife needs attention.......

[Cyril Haearn]

Really, can disks warp and then go back to being flat? Stoopid question?

[PT1029]

Can discs warp?
If the disc gets hot, it expands. Expanding a flat disc can only be done by it warping (if old enough, have you ever left a vinyl record in the sun?).
You can avoid a disc warping when hot by having the disc braking surface fixed to the spider arms by rivits that allow expansion radially, known as floating discs ; -
https://www.hopetech.com/products/brake ... sc-rotors/ (your computer might mutter about the website as being unsafe - certificates and all that)

Scrolling down the page gives ;
"Floating design deals with changes in temperature"
You can see the gap between the black spider and the silver braking surface, so its is just a ring that expands outwards.

Not that common on bicycles (I have Hope ones on the tandem), but are a lot more common on motor bikes.

[Brucey]

in most bicycle discs the expansion of the brake track appears to be accommodated by flexing of the 'spokes' in the disc. In most disc designs the spokes are configured so as to allow this expansion fairly easily.

cheers

[Manc33]

BB7 do the job adequately enough but I'm not that impressed with them, for all the raving I seem to see about them. The 7800 rim brakes I had a few years ago were far better. With the 7800 rim brakes it totally changed the way I rode, being able to safely brake considerably later than normal, they were damn powerful.

[Brucey]

worth mentioning that there are two variants of BB7; 'road ' and 'MTN'. 'Road' BB7 were designed back in the far mists of time so work well with older (slightly higher MA) brake levers. They are a bit underwhelming when paired with recent (NSSLR cable pull) shimano STIs. MTB BB7 work a bit more consistently because the cable tension is lower and the levers are more likely to be matched to the brakes better.

In truth there are now three main cable pulls that are used on bicycle brakes currently; (in order of increasing cable pull/decreasing MA)

1) Campag/SRAM/'old' shimano (most models of lever for DP calipers ~1993-2008),
2) 'new' shimano NSSLR (most new STI models 2008 onwards) and
3) V-brake

In view of this, some brakes (e.g. Paul's Klampers) are made in three variants, not just two; shimano NSSLR users were not well served by either variant until they introduced one with a middling MA value. I have not tried MTN calipers with NSSLR levers but I expect them to be very powerful with small (too small) running clearance.

IMHO the virtues of BB7s are that they are relatively better (including maintenance requirements) than most other cable discs. They are most powerful in MTN variant with matched levers.

cheers

[reohn2]

My experience with BB7's is as follows:-
Road with Shimano 9sp pre 2008 STI's and Tektro RL340's both levers give excellent braking even on tandems from the drops. I've never needed more than my index finger to brake even in an ES situation.
MTN with Shimano M610 flatbar levers and Tektro RL530,same story as the Road version but with slightly more power from the flat bar levers than any of drop levers which IMO is more due to ergonomics of flatbar leve grip.

I can lock up either wheel on solos with either drop or flat bar levers with 160mm rotors on 700C wheels with 40mm,50mm and 65mm tyres.
Tandems with 406mm wheels,50mm tyres and 160mm rotors,and 700C wheels 32mm tyres and 203mm rotors are the best braking I've ever experienced on tandems.
In all cases BB7's give superb modulation
Just to add,I don't find much difference between V's DP's(with either Koolstop salmon or BBB Techstop or Tristop pads)and BB7's in dry weather,but in wet or mucky conditions it's night and day in favour of BB7's either MTN or Road.
I use sintered pads whenever possible as they last much longer,though I'm working my way through a couple of pairs of Clarks organic pads presently,which I found at the back of a cupboard in the workshop and which I can't remember buying

[Cyril Haearn]

in most bicycle discs the expansion of the brake track appears to be accommodated by flexing of the 'spokes' in the disc. In most disc designs the spokes are configured so as to allow this expansion fairly easily.

cheers

Does a disc revert to the original shape perfectly on cooling? What metal are they made of, how is it treated?