Better braking needed

cycleclinic

That was a reference to spelling and grammers errors that crop up in anything I write. They are sometimes embarassing when read omething back. There a number of words in that post that I have no clue how to spell.

giant_man

at least you're honest, Malcolm! interesting thread ...

rjkflyer

The braking FORCE is independent of the area over which it is applied, and force plus friction coeff determines THEORETICAL stopping capability.

Yes, larger areas can assist heat dissipation and lower rate of consumption of friction material which starts to affect REAL stopping capability.

The cartridge types of pads generally have more rigid holder AND better pad materials so tend to perform better (i.e. a worthwhile upgrade from e.g Tiagra - my chum did this on his Spec Roubaix).

Certainly +1 for SwissStop Blue (BXP) on ali rims.

wishitwasallflat

thecycleclinic wrote:

That was a reference to spelling and grammers errors that crop up in anything I write. They are sometimes embarassing when read omething back. There a number of words in that post that I have no clue how to spell.

Never embarrassing always informative and super helpful keep up the good work it's much apprecaited.


Milk and custard though .... Now that is embarrasing

mathematics

wow! All I wanted to know was how I could make my brakes better

Thats takes me back to A level physics all this co-efficient of friction talk - I remember thinking it was bonkers too.

Im quite proud my humble thread has turned into an intellectual debate - good work

wishitwasallflat

mathematics wrote:

wow! All I wanted to know was how I could make my brakes better

Well the answer seems pretty clear to me first do a PhD in Physics then buy some Koolstop salmon cartridge pads!

cycleclinic

Milk was to make the custdard not the two together there are laws against that.

rolf_f

ArgonDon wrote:

Dear Rolf F , i did say the rims had wear, they were actually slightly dished , so please take my word for it, they were better, the point of my post was to add another thought process to what may have been an issue for "mathmatics" , surely that is the point of a forum, to help people think outside of the box, it worked for me, it might help someone else, so why be so quick to be a pedant and shoot it down so quickly? This is why I stay away from forums unless i really need help, which you will see from some other posts i greatfully rec'd from two knoweledgable individuals, people love to turn this into some kind of p***ing competition, I find it unhelpful and unendearing. :evil:

You made a misleading post - you said that the rims were worn smooth. This might lead people to believe that once the milled surface on the rims is worn away (which doesn't take long if you ride in poor conditions) then their braking would no longer be as effective. This might lead them to think that they can solve their problems by spending money on new wheels (which would be a complete waste or money) when they can make genuine improvements by looking at the pads they are using.

The dishing (which you didn't mention) should also not affect the braking - it doesn't take long for a rim to become dished because the middle of the track is worn more rapidly than the edges (though you do need to be careful to identify the point at which the rim edge starts to widen just before the rim fails - but that is something else). The brake pads conform to the shape of the rims so it is hard to see how that would make a difference - maybe the cycleclinic has an idea on that one. Probably your "improved braking" was a combination of clean rims and wishful thinking. It certainly wasn't because they were worn.

FWIW, I commonly run a hardly used pair of wheels and another heavily worn pair that have over 12000 miles on them. There is no difference in braking performance between them. That is because the metal is the same and the pads are the same. The only time this isn't the case is when the old rims are dirty.

TBH, I can't really see why you had such a hissy fit over my post - I explained why your post was mistaken in simple, non aggressive terms - yet you are quick to call me a pedant (not sure where that comes from anyway!) and accuse me of starting a pissing competition. Just as well that I am thicker skinned than you eh or I'd have been terribly upset!

PS - but if you must get upset by my post, please don't let it put you of BR. It's a really useful place and you can always put me on ignore or whatever it is called (I've never used it) so you can't see my posts if it helps.

wishitwasallflat

Rolf F wrote:

... it doesn't take long for a rim to become dished because the middle of the track is worn more rapidly than the edges (though you do need to be careful to identify the point at which the rim edge starts to widen just before the rim fails - but that is something else).

Not sure why anyone got upset about your posts but that aside - this issue is concerning me greatly at the moment. My Open Pro Rims are dished (concave) I can feel it and see if I put a straight edge against then. When I measure them with Iwanson Guage ( http://www.ebay.co.uk/itm/DENTAL-METAL- ... 0562571634 ) they are still just above 1mm thick maybe 1.1 - BUT - its very limited where I can measure. You can only measure wall thickness between the bead ridge and down to where the bottom of the rim is (i.e where the wall merges with the floor/well of the rim). I feel the peak of wear is below that level so your post above seems on the mark.

How can you id where the rim edge starts to widen?
How do you spot signs of immenant failure?

Essentialy would you please expand on the

something else

?

rolf_f

wishitwasallflat wrote:

How can you id where the rim edge starts to widen?
How do you spot signs of immenant failure?

Essentialy would you please expand on the

something else

?

That is a question I am currently mulling over! There are lots of dire warnings on here about concave rims but they have to get concave long before they fail by definition so concavity itself doesn't mean anything (unless I've been living life on the ragged edge for the last 6000 miles plus! )

See pic below - the top image is the rim and brake pad in black - badly drawn and deliberately exaggerated! You can see that the pad spends much more time in contact with the middle of the rim (the beige showing the how only a small part of the pad is ever in contact with the edge of the rim with a much larger part in contact with the middle.

On that basis, your rim goes from the section below left to middle left as part of normal wear and tear. If you have Campag or Fulcrum, somewhere in the instructions it will tell you that the distance between the shoulders should not exceed 15.5mm (which is the dimension the rim is manufactured to - ie any change and it's dustbin time).

So, the rim wears but the 15.5mm stays the same and everyone is happy. Eventually though, the metal becomes worn too much. Now it can't support the outward pressure of the tyre bead on it and it starts to bow out. The rim shoulders are now more than 15.5mm apart but look pretty much the same as before.

The solutions are 1) take the tyre off and measure the distance between the shoulders or 2) get some calipers (apparently dental calipers do the job well and are cheap on Ebay) and measure the outside of the shoulder when you know the rim is not worn. The outside of the shoulder shouldn't wear much so if this measurement widens you know that the rim is dead.

I think that the key point is is that it doesn't matter if the distance between the outside faces of the braking track is getting smaller - it is that the rim edge is getting wider. The bit I don't know is how long it takes to get from the concave but straight to the concave and distorted and concave and broken!

ArgonDon

RolfF, well done for responding to my personal vent in such a courteous manner, you get points and recognition for that! However, (and maybe I missed this out .....) the braking improvement was more noticeable in the wet than in the dry, huge improvement, and I guess this Is what bugged me, I've been riding long enough to know whether the difference was real or perceived, I ride road and tt bikes, and get used to noticing their individual characteristics, kind of important if you don't want to fall off!
I get all the technical stuff, but don't get why you'd be so dismissive of my opinion, I get you were trying to give good advice and not throw money at a lost cause, but that detracted from my honest opinion, and that's why we have a forum isn't it? :?
FYI, the new rims were mavic cxp22. The old ones Mavic ksyrium sl wheels, worn slightly, dished at centre of braking surface but not showing wear indicator holes in the rim, so there we have it

rolf_f

ArgonDon wrote:

I get all the technical stuff, but don't get why you'd be so dismissive of my opinion, I get you were trying to give good advice and not throw money at a lost cause, but that detracted from my honest opinion, and that's why we have a forum isn't it? :?
FYI, the new rims were mavic cxp22. The old ones Mavic ksyrium sl wheels, worn slightly, dished at centre of braking surface but not showing wear indicator holes in the rim, so there we have it

I'm sorry for sounding dismissive!

Are you sure the old rims were clean? Look at it this way. You have rims and pads. If we assume the alloy is pretty much the same material from wheel to wheel and the pads were the same pads, what do we have left?

1) The shape of the braking surface
2) The cleanliness of the rims (and pads if you changed those at the same time).

Now with the best will in the world, I can't see that a very slightly concave braking surface is going to make any serious change to the braking performance assuming that the pad has bedded into it. There has to be a physical explanation for a change in performance. And if 1) is unlikely, then 2) is quite likely. Now if, when you got your new wheels, you did as I would do and fitted new pads and adjusted the caliper arms then I might find actual braking and braking feel had improved significantly - but I wouldn't blame it on the rim until I had cleaned the rim to within an inch of its life and tested it with the new pads.