emobo

Hi all,
I've read a lot of threads indicating that changing steel rims to aluminum rims is a guaranteed improvement. I recall one saying braking power could even increase by 4 times!
Mostly common consensus is that wet braking will go from none to reasonable?

I recently converted the front wheel of my 1974 Peugeot ue-08 (or some model like that) from the original chrome steel run with rim grooves, to a 27" x404 aluminum rim.

I was disappointed to discover the braking performance is pretty much the same as my steel rim.
In fact, the rear wheel, which is still steel, has better dry braking than the front...

I'm trying to figure out if this is just a reality of the mafac brakes I'm using? Or perhaps that I screwed something up....like that aluminum wheels are directional or something silly like that (in did try both directions with no improvements).

I tried cleaning the rim with a little vinager and water, but that had little effect.

It may be worth mentioning that I am using the original cable housings with new brake cables and standard horizontal brake levers (recycled from some old bike - I can't ride with dropped bars anymore - back issues: ( )
The pads are the same as the ones used on the steel rim. They are standard rubber pads, not cool stops or anything special like that.

Up next I am considering a little bit of sanding - the pads first, the rim next.

Any thoughts would be appreciated.

Cheers!

DannoXYZ 

1. You need to change to new brake-cable set with matched cable & housing. You probably have old rusty housing, doesn't matter if you have new cables inside, there will still be excessive friction. Teflon-lined housing with rolled cables (perfectly smooth outer surface) makes HUGE difference.

2. While you have the cable disconnected from the brake, squeeze the arms together by hand. Does it move smoothly with no binding? Do the arms spread back by themselves easily?

3. Also need new pads, Kool Stop salmon are good.


Ultimately, what will determine your stopping-power, as in deceleration-rate and distances, is not your brakes, cables, pads, or rims, it's the front tyre's traction on the ground. With sub-par equipment, you will just have to squeeze the levers harder to get to that same maximum deceleration-rate (about -0.85g). Have you squeezed the levers hard enough to send yourself over the bars? Or locked up the front tyre?

To get even better front traction, go with fatter tyres using lower-pressure. This will increase the contact area and spread out the load.

dabac

Probably not. There's HUGE change between stamped metal/plastic encased brakes as found on some low-end bikes and pretty much anything out of aluminum. But once you're into that range, differences shouldn't be that dramatic.

No, rims aren't directional. OTOH the anodised layer, if you have one, can be quite slick. Easiest seen on black rims with a a silver braking surface.

That's a novel concept ! Rubbing alcohol, brake/clutch cleaner, degreaser, Brillo pads are probably the the most common stuff used.

Housings, unless you can see them squirm & compress probably aren't the culprit. Brake levers, unless you've switched in V-brake levers, probably aren't the culprit.

I'd go for anodised rim and/or old pads as the prime suspects.

And I'd say 4x improvement is a bit much to hope for.

prathmann

My experience when switching from steel rims to aluminum back in the early '70s was that dry braking performance got slightly worse while wet performance increased dramatically. Since dry performance was still adequate (i.e. hard brake pressure could still skid a tire) that made a significant improvement in safety.

02Pilot

Using old pads that were bedded in on another rim is not ideal, as the contact surface may be a poor fit for the new rim. You could sand them smooth, but personally I'd just replace them with new. Also bear in mind that pads need to break in before optimal braking force will be available.

Kimmo

IMO you don't need rolled cables, but lined housing makes a huge difference. Also, ensure the brake caliper is functioning optimally, with as little play as possible without binding. Lubricating the point where the springs bear on the calipers helps too.

The Salmon pads are meant to be the duck's guts, but you should still be able to get good braking from random pads. There's almost certainly a glaze on your old pads; I just drag them over concrete a few times to sort that out. Don't sand your rim, it won't last as long.

Actually, is the rim anodised a dark grey, or even brownish? If so, it's likely the thicker hardox anodising, which isn't a whole lot better than chrome as a braking surface... I suspect the only reason such rims stop better than steel ones is their lighter weight. So anyway, if it's hardox you should prolly get some Salmon pads.

I'd say a fourfold improvement isn't implausible, but unlikely. Two or three times better is more like it.

Actually, I'd say there are three tiers of caliper quality - nasty, pressed steel ones, cheap, thin ally ones, and beefy proper ally ones. The beefy calipers didn't really exist until the 80s, although I had some '74 Dura-Ace sidepulls that were a fair bit thicker than usual. And then there's the design. The best design (the dual-pivot sidepull) didn't turn up until the late 80s. However, the older type of dual pivot caliper with the straddle cable (the name for em eludes me at the moment) can often be made to work surprisingly well.

HillRider

Center Pulls.

FrankHudson

I never heard of or noted anything like 4x improvement in dry braking back in the day either, but wet braking on the set of shiney chome rims went from just about none to good. The patterns on some steel rims were supposed to help, and maybe they do. My old Raliegh Sports had usuable, if reduced, braking in the wet with it's steel rims as I recall--but it's been nearly 30 years.

My main memory in making this swap back in the day on the same bike and brake arms (besides the much better wet braking) was how much quicker accelleration was with the lighter rims.

If you just reused the pads, I'm also thinking they're bedded to the shape of the old rims.

Kimmo

/forehead slap

...And I said 'sidepull' twice

FastJake

I'm guessing they are Mafac Racer centerpulls? Seems like every French bike ever made used those brakes.

I have an old rotten set on a bike. With Shimano SLR aero levers I would bottom the lever out on the bar before I could lift the rear wheel with the front brake, but since I've switched to bullhorns and a Tekro "cross" lever the mechanical advantage works out much better and now I can throw myself over the handlebars.

Kimmo

Yeah, they look pretty damn spindly for the amount of power they can have...

Oh yeah, I was gonna mention before when I was talking about caliper quality, how when it comes to V-brakes, it hardly matters a damn. Pressed steel crap can haul this puppy up a treat.

emobo

Thanks for the helpful and detailed response.

Your comments got me thinking...

1. Replaced brake-cable set
I did have the original housing (which had the spiral metal interior - and which I believe needed to be greased). I've replaced it more modern cable housing with plastic interior liners. Smooth indeed.

2. I fiddled with the brake levers and realized something key...after some some research I discovered I have linear pull (vbrake) levers on a centerpull cantilever braking system. If you've ever done this, it's mighty strange feeling. The brakes move when you squeeze the lever, but once they hit the rim that's it. Zero increase in power. Clearly the mechanical advantage ratios come into play here - thanks Sheldon

I quickly dropped by my local community bikes and picked up some simple metal cantilever brake levers and swapped those in. Naturally, the change was enormous - the old Peugeot stops like a beast now. It's not as good as V-Brakes (as I have on my hybrid) but it's pretty darn good.

3. I didn't change the pads, but kool stop salmon's (probably black because that's all MEC sells) is what I'll be getting next.

Thanks again for the advice and ideas. I'm a little embarrassed to say the cause was that I had the wrong levers (probably a capital no no) but hopefully this may help someone else one day.
I was told one way to identify linear pull brakes is to look for the little hinge in the lever. Canti's don't have these.

Here is a quick pic to share


Thanks!

emobo

Wow, I missed a bunch more awesome posts - some comments.

Yes - I am using mafac Racer center pulls.

With the new levers I still can't throw myself over the front, but they are much better now. I think I am experiencing similar behavior to what Fastjake mentioned.

Thanks again for everyone's reponses. I'm always checking out bikeforums.net, but I don't post much - probably because all the answers are always already here!

Cheers