Tribologists – brake material for hurtling down big hill on a vintage bike.
I’m trying to improve a set of rod brakes that will be operating on stainless steel rims.
I know they are crap brakes, but I have a very pressing reason for wanting them to be better. If I can improve them to adequate, I’ll be happy. 🙂
There’s limitations to how much force can be applied to the brake pad because of the design, so I’m looking at what materials I can use to improve the friction available.
A bike disk brake works on a revolving stainless steel disk and can stop a bike on a sixpence.
The clamping force is much higher I assume, but nonetheless it is a similar braking surface and so is it likely the material used would work on a rim?*
(I have some experiments in mind, but it would be handy to shortcut the process).
Also I have all the other brake components sorted, they’re all brand new shiny old stock, so there’s nothing there I can improve – as far as I can see – except the braking material.
*EDIT: obviously such a material it will not be available as a pad for for a 80+ year old bike, so I expect to have to carve the material into shape.Posted 2 months ago
I don’t think disc brake pad material is designed for maximum friction, more to handle the pressure, heat and abrasion of disc brake use. That’s why rim brake pads are made of rubber. So I’d be looking at a modern rim brake pad compound.
Thanks. Pretty much what I’m thinking too, but STW has some experts in esoteric fields, so you never know what they may come up with.
I will be trying modern rim brake pads.
(I need to keep the bike period and original in appearance and so I can’t use anything but rod brakes.)Posted 2 months ago
…Maybe an ‘auxiliary brake’ involving a thick, rubber-soled shoe jammed behind the fork crown is the answer?
I have experience of that going wrong when I was a lad. 🙂
Come to think of it, I’m sure I posted it on STW a few years back.
Edit: found it
Do a find on “Actually come to think of it I invented downhill mountainbiking around 1955.”
to be found down the page on https://singletrackworld.com/forum/topic/the-sport-is-now-40-years-old/page/3/
I can still feel the pain. :}Posted 2 months agoescrsMember
Years ago we used to put tar on steel bmx rims to make the brake work better
Tub of tar and a brush, place brush on rim and spin the wheel for an even coat, allow to dry and the brake worked much better
It will wear away with time but can be re applied or removed with tar removerPosted 2 months ago
can you use or mod any of these trials material pads? They are very stoppy.
Thanks for that link. Just had a good look at it. I hadn’t thought about looking at trials stuff.
I’m going to get a set because they’ll more than likely be far better than what I’m using. I may even be able to modify the pad holder and get a bit of heat sinking too. If it works, the rod-brake community will no doubt erect a monument to your name. 🙂
The hill* I’m going to need them for is long, reasonably steep and the last time I went down it with rim brakes it felt like the pads were losing performance because they were very hot – and that was with V-brakes.
This time however, I’ll not be trying to see how fast the bike will go, just trying to get down in one piece.
*Bealach na bahPosted 2 months agoGreybeardSubscriber
Compared to a disc brake, the rim won’t heat up as much as a disc, as the rim has much more surface area – but the block will still be relatively small so could get hot. Maybe softening a rubber block is good, until it wears away, so a crucial element of the design will be how long you’re going to be braking on it. What’s optimal for 1 minute won’t stand up to 10 minutes.Posted 2 months agocrogthomasMember
Firstly, are you sure they are stainless steel rims? Most steel rims are made from a more normal mild steel that is then chrome plated for corrosion resistance. Back in my days of cheap 10 speed racers, the brake pad material of choice for chrome steel rims was a rubber pad with a leather insert. I think the main advantage was for wet weather, i’ve no idea if the leather also made them better in the dry. A quick internet search suggests that they are still available.
Second; I once met a man on the side of a volcano in Kenya who was carting charcoal down from the summit to market on a Raleigh All Steel style bicycle. He had made him self a foot brake that was hinged near the bottom bracket and pulled two hand carved wooden brake blocks into the rim at the chainstay. It was probably completely useless, but a mighty impressive piece of engineering all the same.Just an idea.
Third (of two); Disk brake material will be useless as mentioned above. It has a very low coefficient of friction compared with rubber. It benefits from a much higher contact pressure in it’s application. You can buy rod brake pads in modern rubber compounds, so I think you’ll just have to try them. Making sure the rod system is adjusted properly and lubricated at the pivots of course.Posted 2 months ago
What’s optimal for 1 minute won’t stand up to 10 minutes.
According to Google Maps, a car takes 16 minutes for the descent.
I’ll be trying to be slower than that, so easily 20 minutes of almost continuous brake application to keep the speed within the handling capabilities of the bike.
Firstly, are you sure they are stainless steel rims?
Yes, definitely stainless. Took me ages to find them in the 28″ size. 🙂
Went round part of the Puffer the other day on a rod-brake bike, so I know modern rod brake pads aren’t up to the job – and those weren’t descents anywhere near as long as the Bealach.
But Puffer Bill approved my bike choice (also with stainless rims). 🙂Posted 2 months ago
The trials pads are usually used in conjunction with grinding the braking surface to create a very aggressive surface. Trials pads are therefore very hard compound.
If you want good performance with normal pads and don’t wish to grind your rims use Rosin. Used on the bow of stringed instruments to make them grabby. works a treat on non ground rimsPosted 2 months ago
Just adding the last post:
Rosin comes in a small block. Spin the wheel and rub the block against the rim. Its clear and works amazingly well as long as conditions are dry. Even wet will work better than a non treated rim but with it one finger lockups should be easy.Posted 2 months ago
…If you want good performance with normal pads and don’t wish to grind your rims use Rosin…
Thanks. I can steal some from my daughter. That’s something I can try without doing any modifications. Is it easy enough to remove if it doesn’t work?
Do you reckon it would work for extended braking like I mentioned or is it a short term thing? I don’t want to find out the hard way. 🙂
(I won’t be able to grind that style of rim)Posted 2 months ago
There’s some good leads there, but I suppose I should be framing the question more technically.
Does anyone know the cold dynamic friction coefficient and hot friction coefficient of the various materials used in brake blocks (or material suitable for cutting into brake blocks)?Posted 2 months ago
I have used it on the offsprings trials bike. He had a little kids one that i did not want to grind the rims on. (resale). One applications every few months was enough to keep the brakes pin sharp. Caveat being trials brakes are usually on or off but he used to drag his brakes a bit and that is why i was not keen on grinding the rims. He would have gone through a set of pads in an afternoon.
I think it is just refined pine resin so will come off with solvent if you dont like it.Posted 2 months ago
…I think it is just refined pine resin so will come off with solvent if you dont like it.
That’s handy, thanks.
In the meantime i’ve found this from 2005 (http://forums.roadbikereview.com/components-wrenching/best-brake-pads-68341.html#post716035)
FSA did a test in February of 2005 of their new brakes (SL-K) using different brake pads. They used aluminum Mavic rims. I do not know what the speed was, but I do have the stopping distances in meters for each set of pads used.
DRY CONDITIONS ON ASPHALT
Fibrax-13.14 (being the best)
Shimano Dura Ace-15.18
Clark’s-18.84 (being the worst)
WET CONDITIONS ON ASPHALT
Tektro-16.75 (being the best)
Shimano Dura Ace-40 (being the worst)
ProMax (being the most unsafe for continualy locking up at around 15.49 meters)
On an average for dry and wet conditions, the Koolstop Dual (2nd and 5th) and the SwissStop GHP (7th and 3rd) proved to be the best pads for combined weather conditions.
Useful info, but it’s for an aluminium rim.Posted 2 months agoGreybeardSubscriber
If making a Google search for coefficients of friction, beware as there are some odd figures out there, and it looks as if most of the tables on the web have copied from the same source, ie, sliding friction of aluminium on aluminium is given as 1.4, which is very high.
From a different angle, does the bike actually have remain authentic, or just look authentic, and do you need to ride it up the hill as well as down? For example, can you introduce other non-visible forms of braking like heavy grease in the hubs, or overtightening the cones slightly?Posted 2 months ago
…does the bike actually have remain authentic, or just look authentic, and do you need to ride it up the hill as well as down? For example, can you introduce other non-visible forms of braking like heavy grease in the hubs, or overtightening the cones slightly?
The bike has got to be ridden up the Bealach na Bah first, and seeing as it’s singlespeed, I want it as free running as possible. 🙂
I’m trying to find a way to improve rod-brakes, not just for myself, but for others in our riding group, Rod-brake Randonneurs*, ie folk who want to do decent distances on these old bikes rather than polish their restorations.
I could stick a coaster brake on the rear and use that in combination with the rod-brakes, or for that matter put period drum brakes on, but the bike is heavy enough as it is, and it is intended for long rides, which will mainly be in mountainous regions.
I can solve the problem for myself as I have period drums and coasters, but the others don’t, and seeing as I’m scouting out routes for the group I’d like to know it’s safe to do a descent with the rod brakes.
*I might put a post up about this group. There’s bound to be some madmen in STW who this idea appeals to. We have some great gravel and offroad mountain rides in the offing.Posted 2 months agomolgripsSubscriber
Back in my days of cheap 10 speed racers, the brake pad material of choice for chrome steel rims was a rubber pad with a leather insert
I had those on my first adult bike that I used to ride all over. We lived at the top of a long ish but pretty gentle hill. If it was raining on the way to college I had to apply my brakes full on at the top to have any chance of stopping at the T junction at the bottom. And hope no-one was coming up when I got to the narrow bit half way down.Posted 2 months ago
…We lived at the top of a long ish but pretty gentle hill. If it was raining on the way to college I had to apply my brakes full on at the top to have any chance of stopping at the T junction at the bottom…
You can relive those exciting days. 🙂
Old rod brake bikes are a dirt cheap hobby if you avoid the collectables, or you can buy an Indian one brand new and complete for £200.
I put new rubber brake blocks on the bike above a few years back and took it on a quick spin round Wester Ross from Dingwall.
My big worry was the hill at Braemore near Ullapool. Turned out it wasn’t too bad. I could slow the bike down on that hill to a speed I’d be happy jumping off at, but not stop. Good enough I thought.
So once I got to Ullapool I decided to complete the loop and continue to Ledmore Junction, Bonar Bridge, up the Struie, and home, about 120 miles. I knew there were a few stiff hills on the way, but Braemore had made me confident.
All was fine until I hit the hill just before Ardmair. It started raining heavily.
Heading down that hill I decided to start slowing once the bike hit 25mph because I knew the rain would affect the brakes, and there’s an S bend which you don’t want to take too fast on that sort of bike.
I had forgotten to what extent rain affects rod brakes…
When I pulled on the brakes it seemed the bike accelerated. A later scan of the GPS showed it did, right up to 33mph with the brakes full on. Then it seemed to have cleaned off the water because the bike gradually slowed down – I reckon it took about 20-30 metres at least before I felt any sign of slowing. I was able to go round the S bend over the bridge at a mere 20mph. An oncoming car was just far enough away to make it an oops moment not an ouch one.
I walked down most of the next steep hill. 🙂Posted 2 months agobigyinnMember
I can still recall the sheer terror of trying to brake a chromed rim’d bike with rubber and leather brake blocks in the wet. You would pull the brakes as hard as you could, as soon as you could and then, you waited…
Then just when all hope was lost and you were looking for an exit they’d bite, which was almost as dangerous because they had a habit of locking up the wheel if you weren’t ready for it!
One question I have is regarding the braking comparison table in the dry vs wet. How on earth can a pad have a SHORTER stopping distance in the wet than in the dry? Is that even possible?Posted 2 months ago
Bealach na bah? Is that the bad tempered version?
I’m getting slightly worried that epicyclo hasn’t been seen for two days…
Been busy digging out tree roots from the garden, plus built a shed over the last 2 days.
It’ll be a couple of weeks, I have visitors from USA over and requiring to go to every Outlander location in Scotland plus no doubt wanting to meet the clan chiefs they think they’re related to.
Fortunately my cousin (several times removed) Donald has not scheduled a visit.
But there is a 1930s Rudge Roadster frame on my workstand right now and some 28″ wheels to be built…Posted 2 months ago
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