Thorn Cycles Forum
Technical => Wheels, Tyres and Brakes => Topic started by: Matt2matt2002 on April 22, 2013, 08:32:12 AM
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Out for a short run last night that had me coming down a wee Scottish hill for 400m.
I usually descend quickly since I know the road and have a clear view ahead of me.
This time I took it very slowly, for no other reason than to enjoy the fine views.
As I came down I wonder if I was causing less wear on the pads.
Sounds an obvious question but I wonder if anyone has researched the causes of brake pad wear (apart from braking ;))
Matt - who likes to save the pennies even when it may only be a micron or 2 of brake pad.
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Hi Matt,
I have find that my Pads wear the most on wet days (and in the Mud too)
It comes down to which Pads you are running
Happy Braking
Pete
:o
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Hi Matt,
I have find that my Pads wear the most on wet days (and in the Mud too)
It comes down to which Pads you are running
Happy Braking
Pete
:o
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Thanks Pete. Guess the mud acts as a grinding paste?
I have the blue Swiss top pads and special shot blasted rims. Name escapes me at the mo.
I was thinking more about the effect of speed.
If I go down the hill slowly braking am I going to wear out the pads less than when I bomb down hanging onto the leavers for dear life
M
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I was thinking more about the effect of speed.
If I go down the hill slowly braking am I going to wear out the pads less than when I bomb down hanging onto the leavers for dear life
M
Yes I think so :-X But if you Brake Hard all the way down a long hill you will heat up your Rim's and this can blow a tube out :'( (Pain Full)
Yes about Mud! But the same for in the Rain on the road (road dirt and water)
Pete
8)
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Yes I think so :-X But if you Brake Hard all the way down a long hill you will heat up your Rim's and this can blow a tube out :'( (Pain Full)
Yes about Mud! But the same for in the Rain on the road (road dirt and water)
Pete
8)
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I never think about cleaning the rims and pads. But maybe I will start now. Even a wet cloth to remove any grit should be a good idea?
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No just wash your Bike from time to time.
For me that is???
Pete
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My head gets all twisted when I think about braking and long descents!
The total energy to be dissipated is pretty much fixed by the height of the hill and the weight of the bike etc. This energy will be dissipated by braking, by wind resistance, rolling resistance... that ought to be about it!
Wind resistance gets quite strong when you get going fast. It also increases if you sit more upright to increase cross section. Sometimes I'll unzip my jacket a bit so the jacket puffs out and acts a bit like a parachute. Loose clothing can really increase wind resistance!
Whatever energy is dissipated by the brakes will go into heating up the pads and rims. But the pads and rims will also dissipated that heat into the air. Using the brakes to go slowly down the hill will give the rims more time to dissipate the heat into the air, so the rims will be cooler at the bottom of the hill.
So it seems like the rims will stay cool if you brake a lot to go slowly down the hill, and they'll also stay cool if you can just keep off the brakes and let wind resistance limit your speed. Of course, if there are curves or traffic or whatever, wind resistance might not be enough to avoid energy dissipation through structural deformation, definitely the least desirable option!
Seems there must be some intermediate speed which maximizes the temperature of the rims at the bottom of the hill!
Hey, for nifty gadgets, how about little drag parachutes for bikes, a little packet on the back of the rack and maybe a ring to pull down by the seat post clamp?
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Seems there must be some intermediate speed which maximizes the temperature of the rims at the bottom of the hill!
That reminded me of a conversation I had with a pal years ago who was very into cars and engines. I am sure he told me that as far as tires and braking goes, the maximum or most efficient point of braking happens just before the wheel stops turning.
Not sure if this is what he said or even if it is true. But it rang my bell
Comments folks...
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the maximum or most efficient point of braking happens just before the wheel stops turning.
As long as the tire is not skidding, its rate of rotation is fixed by the speed of the vehicle. The rate of energy dissipation from braking is the braking torque times the wheel's rotational speed. So, as long as the rotational speed is fixed, the higher the braking torque the higher will be the rate of energy dissipation.
Of course, the vehicle's speed is liable to change because of braking, so then it starts to get complicated!
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The question is: If you have brakes that squeel is less energy going into heat up the rim so therefore squeeling brakes could be seen as a performance item?
Andy (quick move this to the muppets section)
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If we are going to start introducing squeels into this thread then it defo. belongs in the Muppet section
;)
All I wanted to know was if I go slow down a hill am I going to wear out the brake pads less than if I whiz down squeeling?
:D
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I am guessing that the rate of brake pad wear has a lot to do with the temperature, that hot brake pads wear more quickly. So going down slow would wear the pads less than going down pretty fast, but if you can mostly let off the brakes and sit up and let your jacket work like a parachute.... if you can use wind resistance to limit your speed to something manageable for most of the hill.... you can sometimes avoid the brakes altogether!
I would bet... descending at 15 mph is easier on the brakes than descending at 20 mph. Probably the wind resistance method kicks in best above 30 mph or so. Is 35 mph a safe speed on your hill?
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Adding fuel to the fire... ;)
http://mrbill.homeip.net/rimTempStudy.php
http://sheldonbrown.com/rim-brakes.html
http://jimlangley.blogspot.com/2008/10/q-brake-pads-and-rim-wear.html
Best,
Dan.
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I know this is a hypothetical question, but with swisstop blue and CCS rims you can forget about break block wear! I'm about 10,000 miles on the same set now.
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I know this is a hypothetical question, but with swisstop blue and CCS rims you can forget about break block wear! I'm about 10,000 miles on the same set now.
Thanks. Nice to know that I don't have to start saving for my next set. Infact I have a spare set already.
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Thanks. Nice to know that I don't have to start saving for my next set. Infact I have a spare set already.
I also have a spare set; what a waste of money they have been so far! I fully expect not to be able to find them when the time comes.