Handelbars.

[Gibson]

Problem is fatigue resistance of steel and its stiffness makes it a different animal. Aluminum alloys typically do not perform nearly as well when pushed close to elastic limits. Shot peening the surface makes it harder and improves fatigue resistance but the affected material is very thin.

[Kurt in S.A.]

Problem is fatigue resistance of steel and its stiffness makes it a different animal. Aluminum alloys typically do not perform nearly as well when pushed close to elastic limits. Shot peening the surface makes it harder and improves fatigue resistance but the affected material is very thin.

Define "nearly as well". Plus there are some steels which are horrible for fatigue. The aircraft industry finally began to understand fatigue for aluminum and have stopped using alloys that don't offer great fatigue properties. Stress corrosion cracking was a problem because cracks would form just because of time or local corrosion. They've gone to materials that have as good strength but eliminated the stress corrosion. If a crack doesn't start, the part will last a long time. Not to mention the improve material processes that are used today that result in better formed grains near stress risers. In the old days, the grains were huge which resulted in voids, etc., which were natural crack starters. Not so today.

Shot peening might add to "fatigue resistance" in that it puts a compressive stress into the material and any loads must create stresses to move the local compressive stress into a tensile stress, thus lowering the peak tensile stress. Holes are treated with a process called cold working which creates a compressive field around the hole. Cracks start in the circumference of the hole due to the mentioned stress riser affect. But with a compressive stress field, a crack is less likely, or will take longer, to form. The downside side is that just outside the compressive zone, there is a tension zone. So, if a crack makes it through the compressive zone, it can grow faster because of the added tensile stresses.

Then there's crack growth retardation. In limited fashion, large loads can actually slow crack growth down. They create a plastic zone of compressive stresses ahead of the crack. Once the crack grows through the plastic zone, crack growth picks back up. A bad situation is where there are mid level loads over and over without the overloads (and no plastic zone). Mid level loads usually happen more frequently and the crack grows along rapidly. So, an occasional overload is actually a good thing...provided it's below the elastic limit.

Aluminum aircraft are flying that were built in the 40s and 50s...e.g., B-52 and T-38. They are still flying and slated for more years. The key to long lives is an aggressive inspection program to find the cracks before they become too big. The earlier a crack is found, the more options available there are to fix. Once it's too big, the part has to be condemned.

Kurt in S.A.

[Beemerboff]

Sometimes all you need to know is that it is best to follow the instructions, and every set of Aluminum alloy bars I have seen have quite explicit fixing instruction regarding holes , scratches, whatever , which you ignore at your peril..
You dont really have to know why!

[Wobbly]

Sometimes all you need to know is that it is best to follow the instructions, and every set of Aluminum alloy bars I have seen have quite explicit fixing instruction regarding holes, scratches, whatever, which you ignore at your peril...

The question is not 'what could happen', but 'what can you realistically expect'. Your Viagra could kick in and you MIGHT break a set of steel bars while puttering around the block to the neighborhood bar ! But I highly doubt it.

On the other hand, I've been hanging around motorcycle race shops since the mid-1960's and I don't ever recall seeing a broken set of handlebars, where the guy crashed becasue the bars broke first. That's not the same as bars bent or broken during a crash.

You don't really have to know why!

Compliance is always a good thing. Agreed. But maybe understanding why is even better.

[Beemerboff]

Race shop mechanics probably know enough to follow the instructions.
Unlike internet know it alls.
I also understand the complexities of working with complex aluminum alloys - it was explained to me by my father who worked for Rolls Royce when they were at the vanguard in developing them, and he subsequently opened his own specialist welding shop.
But my knowledge is a theoretical, not practical,these days and I am quite happy to accept that I know less about aluminum bars than Renthal -= something some others seem to have a little difficulty in accepting!

[Wobbly]

I apologize if I've upset you. That was not my intent.

All I wanted to do was point out that everything we do in life involves a Risk Assessment. Even dropping the soap in the shower calls for a decision of whether to stoop there and run the risk of busting your head, or getting out and standing on the non-slip floor mat ! Or better yet, simply grabbing a new bar of soap !

The more I learn, the more I laugh. Try it.

[Beemerboff]

The more I read your posts the more I laugh.
Pity, as some are provably meant to be serious.
But we all owe each other a moral and legal duty of care - if we are going to give advice on anything which has potentially dangerous consequences we should be certain of our facts.
And that same obligation applies to other members of the forum to correct dangerous posts.
FWIW this is a simple legal fact - the widow of a small state based Honda forum successfully sued the members of the forum after hes husband was killed because of advice he was given on the forum, in a multi million dollar lawsuit.

[Gibson]

I agree with following the manufacturers instructions. I have posted accordingly. Attempting to gain understanding and exchanging information is why forums are good. Calling anyone an internet "know it all" is not really appropriate in my opinion. Sorry.

[Wobbly]

Race shop mechanics probably know enough to follow the instructions.

Just to put your mind at rest, I am a race shop mechanic ! In fact, I'm the only employee in the shop besides the owner. My boss has a stable of some 20+ AHRMA race bikes which he road races, TT's, dirt tracks, motocrosses, and does trials on. He's been an AMA amateur expert for well over 25 years, and is currently rated national #1 in several AHRMA classes. He attends every outing from Daytona to Barber on an annual basis riding bikes I help prepare.

I started my professional mechanic career in 1966 and have attended Triumph and Honda factory schools while working at dealerships in the 70's. I do all his frame, wheel, fork work... everything but build the engine bottom ends, and that's only becasue he likes to do the "fun" part himself.

Here's my boss racing at the Isle of Man...


Here's a photo of the 30,000 sq ft bike shop I work in, with 2 of the Manx Nortons I maintain...


Typical work day in the shop. I do all sorts of specialty work to "special" bikes...




So I feel fairly confident to make the statements I make. If you'd like to laugh, then please be my guest. But, I know what I know, and know enough to only answer the questions I have direct experience with.

All the best.

[Gibson]

Hey Wobbly, cool pics! Thanks for all the help you have generously taken the time to share. I has been appreciated.