Liggero wrote:davidalone wrote:havana wrote:I fail to understand Shimano's crank strategy. No BB30, weird 4-arm design, assymetric blades, no 110mm 39T blades, etc, etc.
shimano does not do BB30 because they do not believe that BB30 is a superior standard. they have argued this before, and as a mechanical engineer, their argument does have merits. BB30 gives you a tiny and, to a human, imperceptible increase in stiffness for much much higher complexity in maintaining the system. you get smaller Q factor, yes, but that is not a good enough reason IMO. it is, technically more robust to the elements than outboard bearings, but they are a PAIN to replace if something goes wrong. outboard cransk are much easier to replace, more versatile, and less likely to damage your frame on installation. same goes for PF30, and to an extent, BB86 and BBright as well. shimano will also make less money. so I DO see why they would not support BB30.
BB30 is popular among frame manufacturers because it saves them money. it's much faster and cheaper to purchase an OE spec bearing and press it into the fram than having to machine out steel threaded inserts and bond them into frames. it's a simple case of frame manufacturers versus shimano here. but shimano is sticking to their guns and as the major industry player, they have evrey right and clout to do so.
the 4 arm design may LOOK weird, but it offers tangible engineering benefits. the 4 arm design has been on shimano MTB cranks for awhile now. 4 arms are lighter than 5 arms, and shimano claim that the crank still retains the same level of stiffness. in addition, the new 4 arm design makes 110 or 130mm BCD pointless. you can put a 50-34 on that crank. you can also put a 53-39 on the very same crank. this is a game changer. cuts down inventory that stores need to hold ( you don't neeed to carry both compact and standard cranks anymore.) it also streamlines manufacturing. these savings may eventuaklly be passed down to the consumer if enough people follow their 4 arm standard and make chainrings for 4 arm cranks. ( shimano chainrigns are great but exoensive.) the problem here is that most other crank or chainring manufacturers are 5 arm, so they are trying to revolutionize the game here. My feeling is that this is a real game changer. once you get used to the 4 arm design, it actually looks pretty cool.
the new crank is certainly an impressive bit of techy kit and I'll be trying to get my hands on one as soon as ultegra 6800 comes out.
4 arms road crankset, for compact and no compact is a great idea if you use shimano expensive hollow chainrings. Those chainrings are very stiff, and they are extremely expensive to produce for shimano, imagine how expensive they would be for another manufacturer who won't produce a few millions of them... Quite a big shit is what i would call these new cranks. Not only that they are ugly as hell, but that they make 3rd party rings kind of impossible.
It's amazing to me how some people has such a little engineering manufacturing knowledge, and still write these pointless opinions with no reservations... welcome to planet earth i guess...
I'll have you know I am a mechanical engineer. I do know about manufacturing. I was putting it in understandable terms for those that MIGHT not understand. so before you spout off such accusations, get off your high horse. we might differ on opinion, but I challenge you to completely say that my post has completely no basis and no grounding in engineering knowledge.
shimano uses a special cold forging technique to make their chainrings. only shimano and praxis works forge their chainrings, which is inherently better than CNC machining for chainrings because of the grain alignment in the metal making a stiffer chainring. the start up cost for forging is REALLY high, which is why very few industry players use it. on a per unit cost basis, it actually isn't that expensive once your machines and tooling have been paid for.
the 4-arm design's main advantage is the ability to swap out the wide range of chainrings. weight savings and stiffness? minimal impact.
yes, it makes sense for a manufacturing point of view to just make one BCD pattern crank. it also makes sense for consumers and shops who have to keep less inventory on hand. But it is a business risk as it alienates aftermarket manufacturers from making compatible chainrings ( I'm not sure if shimano have patented the 4-arm design, or if they wish to license it.) . it's not a really big risk, as they are the biggest industry player, but it is still a risk.
