It has a higher... modulous or something or other some engineer could bore you about, but basically steel bikes are usually springier than aluminum bikes because that's the nature of steel. I haven't ridden very many aluminum bikes but the ones I have they were all much stiffer than my steel bikes. Mountainbike-wise I had a full rigid aluminum rockhopper and compared to my full rigid steel miyata mtb it was night and day. The rockhopper had no give and hurt my back it was so stiff, the miyata has give and doesn't hurt me.
Aluminum can flex, surely, but springs is made of steel and not AL for a reason. This is not to say I think aluminum bikes suck if someone gets all offended and wants to bore me with a list of the properties of AL.
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fun facts:
Psychopaths have trouble understanding abstract concepts.
"Incompetent individuals, compared with their more competent peers, will dramatically overestimate their ability and performance relative to objective criteria."