Stiff Alu, Springy steel?

pilsburypie

Being a relative novice on frame feel, can someone explain the above. My frame is Aluminium and I'm told this is stiff compared to the more springy feel of steel. Without riding a steel frame I just can't comprehend...... can words paint me this picture?!

Sarnian

I have always ridden Aluminium up to about 18 months ago when I brought a on-one inbred. I have to say It Is the best hardtail I have ridden, the one down side Is trying to build It light, It started as a rigid ss but I like It so much It Is now my main ride so It has front suspension and gears.

I hate to say this but steel Is real

supersonic

Fact: steel is stiffer than aluminium. Steel is THREE times stiffer than aluminium!

How a frame feels depends how it is built. You can get soft feeling alu frames, stiff steel frames. Generally, for XC and trail riding, steel frames tend to have a bit of spring, while alu can be quite stiff. Look at the tube dimensions. Keeping the wall thickness the same, but doubling the tube diameter increases its stiffness by a factor of 8. Aluminiums density is a third that of steel, so it lends itself well to bigger tubes, stiffer frames and still come out lighter. The heavier steel tubes usually means skinnier diameters.

One reason why alu frames are built stiff is because it has no fatigue limit: repeated flex will weaken it, no matter how small (obviously the bigger the flex, the quicker this happens) while steel can be flexed many times upto a limit without weakening. Spring can be built into steel frames because of this, but alu can still last a long time and still have a bit of give.

Remember also that tyres, forks, saddles and seatposts all have give and flex which adds to the ride character.

TheKrikkitWars

So how do Titanium and Carbon Fiber compare? I've never had the opportunity to find out.

supersonic

Have a read here:

http://sheldonbrown.com/frame-materials.html

and here

http://spokesmanbicycles.com/page.cfm?PageID=328

pilsburypie

wow - good in depth answer supersonic - cheers!

supersonic

So basically, if someone says steel is comfier than aluminium, or aluminium is stiffer than steel, its rubbish!

dave_hill

That said, I've never yet ridden an aluminium hardtail which is as comfortable as a steel one.

The steel hardtails which I've owned have been -

Muddy Fox Courier
Giant Super Sierra
MS Racing CR1
Bontrager Race Lite RS

The aluminium hardtails which I've owned have been -

Scott Super Evolution
Scott Pro Race
Orange SubZero

Of all those bikes, the Bontrager was the best of the lot, without a shadow of a doubt. It weighed less than 23 lbs (the frame alone was under 4 pounds!) and it was like riding on air.

But look at the aluminium ones - the Super Evolution was a complete abortion. Too short by half (15,5" elevated chainstays) and no main tube less than 40mm diameter meant that it spent more time going sideways than forwards.

The Pro Race was just that - a race bike. It climbed hills like a scalded cat and every turn of the pedals was transformed into forward motion. But show it a rocky descent and it was time to get off and walk.

The SubZero is a freeride bike, pure and simple, so it has to be capable of big hits and stable at speed. It's long, low and slack and built like a brick outhouse. It isn't all-day comfortable by any stretch but it's one of the best bikes I've ridden.

It's all down to construction and use - for an all-day (hardtail) bike I'd choose steel every time. For a race bike (discounting carbon fibre) it would have to be aluminium. For everything else, it's kind of immaterial (no pun intended).

One thing that should also be borne in mind with aluminium is that it work hardens - that is to say repeated stressing and relieving (for example, beating with a hammer, bending and flexing or repeated trail shocks) causes the crystalline structure to change and the material becomes more friable (brittle). After a while it can become subject to sudden catastrophic failure. This is why aircraft are meticulously inspected for fatigue failures for every 24 hours flying time.

I've never experienced a frame failure personally, but those that I have witnessed through normal use (including motorcycle frames) have nearly all been aluminium...

Surf-Matt

Steel work hardens too - the first few deformations caused by various treatments such as hammering weaken the metal, but because of the crystalline structure of metal its strength increases with continued deformations. Crystals slip against each other; but, because of the complexity of the crystal structure, the more such slips are multiplied, the more they tend to place obstacles in the way of further slippage, as the various dislocation lines crisscross each other.

supersonic

"It's all down to construction and use - for an all-day (hardtail) bike I'd choose steel every time. For a race bike (discounting carbon fibre) it would have to be aluminium. For everything else, it's kind of immaterial (no pun intended)."

Surely you would test the bikes first just to see how comfy they were? I have found over the years that steel gives a huge variation in ride feel depending on construction. The harshest bikes I have ever ridden have all been steel.