Better braking needed

mathematics

I really want to improve braking force my soras downhill at the weekend did not instill confidence!!

I'm going to replace the pads firstly, but should I go whole hog and get 105 calipers while I'm at it? Will the 105 calipers be an improvement on the sora even if still using sora shifters??

taon24

Brake pads first, see if they do enough to feel confident. I do like the 105/tiagra brakes over the tektro brakes I have on my giant and boardman bikes, but am unsure they made a big difference compared with the pads.

gozzy

Swisstop or koolstop pads is the standard response. Unless you simply have to spend money on new brakes, I'd see how you get on with better pads first.

mathematics

Thanks guys.

Will these blocks and carriers fit the soras?

http://www.probikekit.co.uk/bicycle-bra ... 87974.html

Jon_1976

As mentioned, try new pads first. Swissstop or Koolstop. I've been running Swissstop blues for a while and find them pretty good. I've found they have to be toed in a tad, otherwise they squeal like mad.Also check how far your pads are away from the rim. The further away they are, will result in more lever travel. I try to set them about 2mm from the rim as this gives a good initial bite.

Monty Dog

Also make sure you have decent quality cables - cheapy outers flex and bulge. If they're unmarked, try changing to some branded ones like Shimano or Jagwire.

smidsy

mathematics wrote:

I really want to improve braking force my soras downhill at the weekend did not instill confidence!!

Compared to what?

I only ask as from your low post count it may be that you are relatively inexperienced (or just have a life and do not need to frequent forums every day :oops: ).

Brakes on a cycle are never going to be amazing - you have less than 10mm wide contact patch on most brake tracks.

sectongguo

yes,will result in more lever travel. I try to set them about 2mm from the rim as this gives a good initial bite.

mathematics

smidsy wrote:

mathematics wrote:

I really want to improve braking force my soras downhill at the weekend did not instill confidence!!

Compared to what?

I only ask as from your low post count it may be that you are relatively inexperienced (or just have a life and do not need to frequent forums every day :oops: ).

Brakes on a cycle are never going to be amazing - you have less than 10mm wide contact patch on most brake tracks.

Compared to disc brakes on MTB - I understand they will never be as good as hydraulic disc brakes, but I wasn't expecting to overshoot turns and struggle to slow on the down hills!!

They just dont feel like theyre biting they hit the rim fine but making an awful scratching sound - IO had this years ago with a cheap cable disc brake on an MTB, so thought it may be down to a quality issue.

mathematics

sectongguo wrote:

yes,will result in more lever travel. I try to set them about 2mm from the rim as this gives a good initial bite.

Thanks for response - what was yes in relation to?

smidsy

New brake pads and new brake track by any chance?

Scratching sounds like contamination on the pad amd/or rim (not unlikely in this weather) or the joint on the brake track surface which will wear in with use.

When braking in wet weather for optimum performance you need to pre-brake to remove the crud, let go and then apply for actual braking.

Down hill you need to brake early and get the speed right into the corner. Harder braking for shorter duration is better than dragging them for longer.

kajjal

mathematics wrote:

smidsy wrote:

mathematics wrote:

I really want to improve braking force my soras downhill at the weekend did not instill confidence!!

Compared to what?

I only ask as from your low post count it may be that you are relatively inexperienced (or just have a life and do not need to frequent forums every day :oops: ).

Brakes on a cycle are never going to be amazing - you have less than 10mm wide contact patch on most brake tracks.

Compared to disc brakes on MTB - I understand they will never be as good as hydraulic disc brakes, but I wasn't expecting to overshoot turns and struggle to slow on the down hills!!

They just dont feel like theyre biting they hit the rim fine but making an awful scratching sound - IO had this years ago with a cheap cable disc brake on an MTB, so thought it may be down to a quality issue.

Rim brakes at their best do not compare to MTB disc brakes. There is alot less power and modulation but they are safe enough if you allow for this. The problem comes in the wet and if you are fairly heavy compared to most cyclists. At this point a wide gulf opens up between discs and rim brakes. I use Swisstop greens on my road bike and they stop OK in the wet. My 105 pads were good in the dry but next to useless in the wet.

rolf_f

Actually, there isn't much difference between good rim brakes with good pads and hydraulic disc brakes - in the dry. The limiting factor in stopping a road bike is that if you brake any harder, you can go over the bars; increasing braking power will just make it easier for that to happen. I did some comparative testing - the differences were remarkably small.

kajjal

Rolf F wrote:

Actually, there isn't much difference between good rim brakes with good pads and hydraulic disc brakes - in the dry. The limiting factor in stopping a road bike is that if you brake any harder, you can go over the bars; increasing braking power will just make it easier for that to happen. I did some comparative testing - the differences were remarkably small.

I found a marked difference in power and modulation but I am over 6ft6 and weight about 100kg which makes a big difference compared to lighter riders. Disc brakes mean I can brake a lot later due to the increased power , modulation and consistency of braking. In the dry the difference is reduced but there for me is still a very noticeable gap.

I come from mountain biking for many years and am used to going down steep rocky drops which involve shifting your weight a lot as well as continually modulating both brakes to keep a good line, speed and balance. This may also be why I noticed the difference more.

buckles

I find Aztec black pads very good, and they're not expensive, £9 for two pairs

ArgonDon

Just to throw in an added dimension, my brakes were struggling in the wet, I had older mavic wheels and the rim had some wear, very smooth, I went to a new set of mavics, the difference was enormous, put the braking in a completely different league, so don't just fixate on calipers and pads !
Good luck Don

rolf_f

ArgonDon wrote:

Just to throw in an added dimension, my brakes were struggling in the wet, I had older mavic wheels and the rim had some wear, very smooth, I went to a new set of mavics, the difference was enormous, put the braking in a completely different league, so don't just fixate on calipers and pads !
Good luck Don

When you brake, you wear the braking surface - it's meant to be smooth. Eventually the rim becomes too thin and starts widening. At that point, the rim is toast. Not before. Unless it has a fancy (temporary) coating, it doesn't matter what rim you use - a clean alloy braking track is a clean alloy braking track and as long as it is clean, performance should be fine and pretty much the same from wheel to wheel. Getting new wheels isn't a solution to poor braking.

cycleclinic

Aztec road plus are excellent.

contact area is not a consideration for friction brakes. friction in physics is modelled by two terms, reaction force and the coefficient of friction which is dimensionless constant.

Brake performance is limited entirely by the limit of tyre adhesion. Once you have locked up your wheels better brakes will not help. Disc brakes come into there own in terms of modulation and wet braking performance.

Caliper and cantilever brakes as they operate on the same cable pull offer but they suffer from pad squish which is why you can pull the lever more and more. Disc pads do not squish so the extra lever effort you make is transfered directly to the disc as increased reaction force and by Friction = reaction x coeff friction that means more braking force. that is why discs are better.

Clean rim are agood as new rims so long as the braking surface is flat.

smidsy

thecycleclinic wrote:

contact area is not a consideration for friction brakes.

Interesting! So if you had 5 times the contact area you would not create any more friction?

thecycleclinic wrote:

Brake performance is limited entirely by the limit of tyre adhesion. Once you have locked up your wheels better brakes will not help.

Yes but if your brakes do not generate enough friction this can not happen.

cycleclinic

Friction theory certainly suggests that result. Friction it self is a strange thing it operate in a counter intuative way, reaction force depend no area dependent.

Pads with metal holders flex less so use these and that results in a higher reaction force and pads with a high coeff of friction like Kool stops, Aztec road plus et.c will increase friction force. Thinner pads should also help as they can squish less but I am not sure if they exsist.

wishitwasallflat

smidsy wrote:

thecycleclinic wrote:

contact area is not a consideration for friction brakes.

Interesting! So if you had 5 times the contact area you would not create any more friction?

I remember being taught this in Biomechanics by an engineer (who knew his stuff as far as I could see) and doing calculations involved friction equations and getting them marked correctly. Despite that I still cannot quite believe that the only thing that influences this is the co-eff of friction of the materials and area doesn't appear in the equations! Counter intuitive indeed but that's what we were taught.

rolf_f

thecycleclinic wrote:

Pads with metal holders flex less so use these and that results in a higher reaction force and pads with a high coeff of friction like Kool stops, Aztec road plus et.c will increase friction force. Thinner pads should also help as they can squish less but I am not sure if they exsist.

Surely if the pad area doesn't matter, then it also doesn't matter if the pad flexes because that's just effectively reducing the contact area (sort of).

I'd assume that the issue about pad area not mattering is that the more you increase pad area, the less pressure you are applying per unit area of the pad for a given finger pressure on the brakes. To make the bigger pad work more, you have to apply proportionately more force.

On that basis, the size of the pad is optimised for feel and modulation. Using a pad holder then assures that you are applying that pressure equally over the whole pad area rather than less firmly at the ends.

Warning - all of the above maybe cobblers....

smidsy

Right so size of contact area does not matter in friction terms..hhmmmm.

On that basis why do tyre manufacturers (generally not cycles) go to great lengths to develop cross sections that give a bigger 'footptrint' on the road???? And before you say it I am talking (dry tyres) slicks, so shifting water is not the answer.

keef66

I'm thinking since you get bigger discs and pads on performance cars, that the contact area does influence braking performance.

Ditto the metal cartridge holders vs the all-in-one moulded brake blocks; the lack of flex must improve braking, even if it's by just a tiny amount.

rolf_f

smidsy wrote:

Right so size of contact area does not matter in friction terms..hhmmmm.

On that basis why do tyre manufacturers (generally not cycles) go to great lengths to develop cross sections that give a bigger 'footptrint' on the road???? And before you say it I am talking (dry tyres) slicks, so shifting water is not the answer.

That's an interesting point. Of course, one difference is that a road surface isn't perfectly flat. Going back to iwishhehadashorterusernames intuition, I think that mine would be different with a mirror smooth road surface rather than a rough, uneven one.

You get bigger discs on downhill mtbs than cross country ones but I assume that is more about the distance that the disc is from the fulcrum and heat dissipation than a physically larger pad providing more power (and you don't afaik use larger pads with larger discs anyway - the caliper itself is the same).

wishitwasallflat

My memory being taught this stuff is that bigger surface area in contact means there is more force pressing the two surfaces together and friction is a function of the co-eff of friction and the force pressing the two surfaces together. Its a while ago now but I remember it crearly as it seemed so bonkers that more surface area in contact didn't increase the friction. What we need is an engineer (with a nice short user name ) to come along and explain why that is. mmm off to google to see if the answer is out there.

wishitwasallflat

Amontons' First Law: The force of friction is directly proportional to the applied load.
Amontons' Second Law: The force of friction is independent of the apparent area of contact.


•The equation
image4.png

•relates the magnitude of the force of friction to the magnitude of the normal force. The normal force is always directed perpendicular to the surface, and the friction force is always directed parallel to the surface. FF and FN are always perpendicular to each other.


•The force due to friction is generally independent of the contact area between the two surfaces. This means that even if you have two heavy objects of the same mass, where one is half as long and twice as high as the other one, they still experience the same frictional force when you drag them over the ground. This makes sense, because if the area of contact doubles, you may think that you should get twice as much friction. But when you double the length of an object, you halve the force on each square centimeter, because less weight is above it to push down. Note that this relationship breaks down when the surface area gets too small, since then the coefficient of friction increases because the object may begin to dig into the surface.

But - and this may support the argument that the stuff about tyres is not just marketing BS

, adhesive tape resists sliding even when there is no normal force, or a negative normal force). In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive in this way. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications.

ArgonDon

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:

cycleclinic

To go back to a post above, if the pad flexes that reduces the rection force on the pad hence friction drops as some of the force applied (work done too) to the pad has gone into bend the pad itself rather than pushing into the rim. The get 100% transfer of force the pad itself would have to be perfectly rigid, this is impossible of course but disc brake pads are lot closer to ideal than rim brake pads.

Larger disc on sports car and down hill MTB's is all to do with heat dissapation. A larger steel disc is a bigger heat sink and you get higher torque applied to the disc as well. Friction really is independent of contact area. I used to teach physics and this is on thing that is easily demonstrated by experiment.

Tyre grip is even more confusing as contact patch shape is very important but this rolling not sliding friction as in brake pads, the rule are a bit different. The basic maths of rolling friction is the same but the coeff of rolling friction is dependent on contact are shape. Long thin contact patches have low rolling resistance and short wide ones have more lateral grip.

Think for a minute why sports cars have low profile tyres and town cars don't. The lower profile tyre is stiffer and this lack of compliance is directly related to the maximum lateral grip. The amount of energy that can be stored in the sidewall while flexing is related to lateral grip limits. The stiffer the sidewall the more energy that can be stored and the higher the limits of grip but also when the tyre lets go it does so more suddenly with a snap releasing all that stored energy. This is why a modern car may feel more grippy in the bends but with the traction control and ESP off they can become a handful very suddenly when you pass the limits of the tyre. Older cars with high profile tyre have a tendency to let you know in advance that things are getting out of shape. There are exception of course TVR's and BMW E21's they had a habit due to the poor rear suspension design of loosing your contact patch therefore parking you backwards in hedge or in the case of the TVR you are getting on fine and suddenly it turns round and smacks you right in the face. This was all suspension design though not the tyres.

In fact for straight line drag racing higher profile are better. This is also behind the latest trend for rim that wide to stretch your 23mm tyres on - sidewalls that flex less so improved lateral grip slightly. For MTB's wide tyres work very well as lower pressure are needed (also the case for road tyres) and they deform to the same of the road better which chnanges the shape of the contact patch making it wider and shorter.

Bicycle Science edition 3 gives a very good treatment of this. I hope if have not summerised incorrectly as it is rather counterintuative.

I remind you all I used to teach Physics not English that what I told my students. I covered the board in maths not words.

cycleclinic

Sorry I rambled there a bit off to get some milk and eat some custard.

smidsy

thecycleclinic wrote:

I remind you all I used to teach Physics not English that what I told my students. I covered the board in maths not words.

Well you seem to have made up for it with that reply

Interesting topic and one that I am enjoying very much :oops: