Alluminum Vs. Steel for Axle design

[VtwinSpeed]

Hello Everyone,

First post on this forum. Didn't see a rules for posting questions so I apologize if its not in the format needed...

I want to make a lighter axle for my Motorcycle and also a friend. Had one machined from Titanium (Grade 5) for the friend. I haven't received feedback if he likes it yet. Now I am wondering If I could use 7075 instead and still get stiffness and strength needed to do the job but also be much lighter than O.E.? O.E. is steel of some kind- a magnet sticks to it. Aluminum (Even 7075 and C4) is still much less expensive than Ti.

What do you guys think? I don't think heat build up will be an issue as it does not spin, the bearings do. It has to resist twisting forces from braking and cornering but that doesn't seem like it should be that bad. You want a stiff material to improve handling which is why I don't think Ti is used commonly (besides $$$).

Thanks for your help.

 

[MintJulep]

If you are working within the physical size constraints of the OEM axle then it will be impossible to have anywhere near the same stiffness or strength as steel.

Fatigue.

Cost vs benefit seems absurdly biased towards cost. Only possible benefit is weight. Axles are small and don't weigh all that much to start with. As a percent of the total weight of the bike the axles are what, maybe 0.05%? Even cutting the axle weight in half reduces the bike's weight by about nothing.

 

[BrianPetersen]

Well, it is unsprung weight, but it's still a small part of the big picture.

Aluminum is not suitable. Titanium is. Whether it's worth the cost, only you can decide.

 

[VtwinSpeed]

Thanks for the input. I know cost is ridiculous compared to steel but when it is a "toy" Logic goes out the window. Drool Factor becomes a thing. Just trying to find a way to make a better part than the factory regardless of price.

 

[dgallup]

Titanium and aluminum are both bad ideas for axles. Stiffness is far too low. Not to mention fatigue failures with aluminum.

https://www.cycleworld.com/2014/04/18/ask-kevin-what-do-you-think-of-aluminum-axles

https://www.cycleworld.com/this-is-why-motorcycles-blend-art-and-engineering

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[BrianPetersen]

^ In fairness, the bikes discussed in the first article are old. They would have used relatively small diameter (12mm - 16mm or thereabouts) solid axles - basically, the axle is simply a long bolt. Many smaller/cheaper new bikes still use axles like this, but a good many high performance models use tubular axles of much greater outside diameter and obviously hollow. The larger diameter tubular section contributes a lot of stiffness, and the hollow center allows the opportunity to tailor that stiffness. The original poster hasn't stated what they are working with.

I still wouldn't use aluminum, but I'd consider titanium for the hollow-axle design. If the axle is a solid bolt, stay with steel.

 

[GregLocock]

For the solar car we used Titanium, but that was a unique design. The camber stiffness of the stub axle is significant for cars, but for bikes I find it hard to imagine it is vital.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[VtwinSpeed]

I am working on a Harley Dyna. Before everyone starts laughing. Many people spend enormous amounts of $$$ to try and make these bikes perform like a sport bike.

You can spend a lot of money to upgrade the suspension with exotic stuff and they still come with steel axles and it sounds like that is about the only material that "checks all of the boxes" for that task.

Thanks guys.

 

[BrianPetersen]

Geometry is wrong, weight distribution is wrong, weight is wrong, engine is wrong, gearbox is wrong, brakes are wrong, riding position is wrong, tires are wrong, the axle is the least of your worries LOL

 

[BUGGAR]

What do you want? Drag Specialties has a drag race axle that only weighs 1.75 pounds and can take wheelstanding. Maybe just skip that extra taco for lunch before the race.