Why is alloy better for braking than steel?

[brokenbetty]

With steel wheels and rod brakes, braking is on my mind right now...

I was wondering why alloy rims stop better than steel. Is it just because they are lighter (less momentum to fight) or does the material itself make a difference?

 

[tyred]

I would guess it's because chrome plated rims tend to be highly polished.

Alloy also dissipates heat better which has a big effect on the efficiency of the bicycle brakes according to Jobst Brandt.

The other thing to consider is that rod operated stirrup brakes have every little mechanical advantage. Cable operated brakes on chrome rims are usually effective enough in the dry if the pad compound is right and the calipers are of decent quality but rod brakes are just about adequate in the dry and totally shite in the rain.

 

[byegad]

I rode the same bike, a 1980s Raleigh 10 speed, with both steel and alloy wheels. Apart from swapping the wheels I also swapped the brake blocks. In the wet the steel rims really didn't slow you much, the alloys were reasonable. The bike had horrible side pull brakes.

When I bought my next bike, in 2000, it had V-brakes and alloy rims and the way they performed in the wet compared to my old bike on alloy rims was as different again.

Memories of riding steel rims in the 1960s are full of heart stopping hauls on the brakes while approaching danger and desperate past minute swerves to void impact. Bikes, and brakes in particular, are just so much better now.

 

[bobg]

Steel rims do wonders for your antipation though. See a hazard 100 yards away and start breaking ... now! Maybe thats why the Raleigh Roadsters weigh 40lbs, you travel that slowly that you can always jump off

The old leather impregnated brake blocks ( Fibrax used to do them ) seem to work best with chrome rims. Odd that up until the late 50's steel rims were the rim of choice although aluminium was available .. at a cost

 

[bobg]

BTW Betty, if your rod brakes judder when you apply them its because the wheels may be slightly oval, its a common problem with roller lever (rod) brakes

 

[Davidc]

It's something to do with the fine surface structure of the metal. Steel and chrome are smoother (or so I was told by a metallurgy lecturer in 1972 after I hit a policeman in the wet on a zebra crossing - big trouble).

That incident wasn't the worst, I was going down Cheddar Gorge the next year, with 3 mates, when the skies opened in a monster thunder storm. Doing an estimated 40 mph down there with no brakes was probably the most terrifying 5 minutes or so I've ever had on a bike. I said I'd never go down there on a bike again. I did earlier this year, but steel was out and ali alloy was in, Weinman 999 centre pull brakes with standard hard rubber blocks were out too and replaced with cantilevers with kool stop blocks, not perfect but at least they work!

 

[ColinJ]

When I was 12 or 13, I cycled home from school for lunch one day and was a bit late heading back. I was bombing down the road when it started to pour with rain. My bike's wheels had stainless steel er, chrome-plated rims!

I was whizzing down a hill (Barkers Butts Lane, Coventry) towards the traffic lights at the bottom and they had changed to green so I engaged warp drive to try and get through before they changed back.

Too late - they went back to red a few seconds before I got to them!

I pulled the brake levers so hard that they were touching the handlebars, but I was hardly slowing. The traffic started moving across in front of me and I shot through a small gap between two cars and barely missed getting hit by someone going the other way!

It was the closest I've ever come to getting killed or seriously injured. Stainless steel Chrome-plated rims should be banned!

 

[tyred]

I actually think stainless rims brake better than chrome plated ones!

I gave myself a major scare on my rod braked Rudge shortly after I got it back on the road as I was intending to turn right at a crossroads half way down a steep hill and it had just started drizzling rain. I felt I was going slowly in anticipation of my lack of braking power. Wrong! Car coming up the the hill indicating to turn across me, me with a white knuckle grip and both brake levers clamped to the underside of the handlebars and apparently still picking up speed. I just glared at the driver through the windscreen and mentally dared him to turn across me because if he did, I knew I was going to flying over the roof of the car. Thankfully he waited until I got past, and I had to forget about my right turn and carry on down the hill and take an alternative route home.

I now have another rod braked bike, a 1939 Elswick-Hopper which seems to stop better than the Rudge for reasons I can't figure out. I like riding old roadsters but if it's wet, they stay in the garage for my own safety.

 

[Zoiders]

With steel wheels and rod brakes, braking is on my mind right now...

I was wondering why alloy rims stop better than steel. Is it just because they are lighter (less momentum to fight) or does the material itself make a difference?

Between stainless steel and aluminium which one is easier to cut?

The one that abrades more easily will offer a better braking surface.

 

[ColinJ]

I actually think stainless rims brake better than chrome plated ones!

Actually, I think my dodgy ones were probably chrome-plated!

Yes, they were because I remember them going a bit rusty when I left my bike outside for a few days in the rain.

Ban chrome-plated rims!

 

[Zoiders]

http://en.wikipedia.org/wiki/Rockwell_scale

 

[ColinJ]

Between stainless steel and aluminium which one is easier to cut?

The one that abrades more easily will offer a better braking surface.

That doesn't make much sense - a rim made of polystyrene would abrade really easily but I wouldn't rate it highly for braking! (Breaking, yes! )

 

[Zoiders]

That doesn't make much sense - a rim made of polystyrene would abrade really easily but I wouldn't rate it highly for braking! (Breaking, yes! )

Yes it does.

I offered a choice between two materials that are suitable for rim construction, not any material that is not suitable.

 

[ColinJ]

Okay, let's do it your way ...

Between stainless steel and aluminium which one is easier to cut?

The one that abrades more easily will offer a better braking surface.

Why?

(The article about the Rockwell Scale was interesting but I still don't understand why an extremely hard material with a high coefficient of friction wouldn't provide a good braking surface.)

 

[Night Train]

It is the coefficient of friction that will be the important bit I think.

So long as teh rim is 'grippy' and not 'slippy' then the brakes will be better.

I changed the steel rims on my folder for aluminium BMX rims last week, one plain and one black painted. The chrome steel had little 'friction dots' on the surface and I could feel and hear them rubbing on the blocks. All in all the dots were proabably only 10% of the surface so 90% was still slippery.

The BMX rims were a lot better, especially when I used a power sander on the surface to take the grime off one and the black paint off the other.
The black paint was more slippery then the chrome steel.