From: jobst.brandt@stanfordalumni.org
Subject: Re: Unusual chainrings and cranks wear
Newsgroups: rec.bicycles.tech
Message-ID: <duVPd.6693$m31.81607@typhoon.sonic.net>
Date: Mon, 14 Feb 2005 04:07:37 GMT

Prado bladteth Rzeznicki writes:

> My old road bike is over 15 years old. All aluminium alloy parts
> (except brake levers) are just polished, not anodized and there is
> not a single sign of corrosion on them. How can anodizing make it
> harder for salty air if the layer is, as you have written above,
> porous and less dense than metal itself?

An anodized surface is porous but the pores are not contiguous and do
not give a channel for corrosive agents to the base metal... unless
the anodizing is extremely thin as it is on some decoratively colored
items.

That these cranks are nickel plated seems odd to me because
electro-plating is not as good a corrosion protector.  It can be
progressively lifted by an advancing corrosion front of the base
metal.  Chrome plated steel without a sufficient protective copper
base layer is a classic, where the chrome blisters away rapidly.  I
guess Shimano decided that salt air is an environment they could
ignore.

I'm also not convinced that nickel plating improves the wear
resistance of sprocket teeth, nickel being so much harder than
aluminum that it must flake off on the chain contact faces as the
aluminum deforms and even yields.  Can you determine whether the load
bearing faces of the sprocket teeth have any plating left on them?
With the relatively low mileage they should still be plated if the
stuff works as advertised.

Jobst Brandt
jobst.brandt@stanfordalumni.org

From: jobst.brandt@stanfordalumni.org
Subject: Re: Unusual chainrings and cranks wear
Newsgroups: rec.bicycles.tech
Message-ID: <4p6Qd.6778$m31.82361@typhoon.sonic.net>
Date: Mon, 14 Feb 2005 18:49:36 GMT

Rado bladteth Rzeznicki writes:

>> An anodized surface is porous but the pores are not contiguous and
>> do not give a channel for corrosive agents to the base
>> metal... unless the anodizing is extremely thin as it is on some
>> decoratively colored items.

> I don't know how to check the thickness of the layer, but it's very
> easily removed.  Simple nylon scourer can leave scratches after few
> strokes.

>> That these cranks are nickel plated seems odd to me because
>> electro-plating is not as good a corrosion protector.

> No, they are anodized.  Chainrings are nickel plated.

>> I'm also not convinced that nickel plating improves the wear
>> resistance of sprocket teeth, nickel being so much harder than
>> aluminum that it must flake off on the chain contact faces as the
>> aluminum deforms and even yields.  Can you determine whether the load
>> bearing faces of the sprocket teeth have any plating left on them?
>> With the relatively low mileage they should still be plated if the
>> stuff works as advertised.

> I was told that these chainrings made about 20 000 km.  Plating is
> gone from the sides of the teeth and load bearing surfaces, but it's
> still present on tips and roots of the teeth.  My other crankset,
> TruVativ Stylo '99 has nickel plated 44T chainring and the teeth
> look almost exactly the same after about 4 thousands km.

If the contact wear areas are bare of plating, then this is another
one of those cosmetic costs passed on to customers with specious
explanations.  It's like the welded, anodized, machined rims that cost
4x what prior rims cost.  My un-plated principally used 50t chainring
has more than 100,000 miles on it and I can't complain that it hasn't
performed well.  The picture of its remaining tooth form appeared here
recently.

Jobst Brandt
jobst.brandt@stanfordalumni.org