Crankset design: Why not attach chainrings to back of crankarm?

[drewellison]

Back in the day when every crankset was a five arm spider design, all the mounting bolts were accessible and it was easy and simple to change the rings without removing the crank arm. Makes good sense.

Then when chainring setups got standardized, the five arm spider was rotated so there were four arms and the fifth attachment was to the back of the crankarm. That seemed to make a lot of design sense, with probably less material and seemingly more robust attachment design.(At least in Campy World where I live.) It made it more difficult to change chainrings, but so what?

Now Campy has gone back to four-arm spider design but all the chainring ring attachments are independent of the crankarm and bolts are not easily accessible for changing rings.

Wouldn't it make more sense to use a 3 arm spider design and make the fourth attachment to the back of the crankarm?

Am I overthinking this?

[FlashUNC]

If anything I think the four bolt design is easier for changing rings. Don't have to swap sides with one bolt facing one direction and four others facing the opposite direction. Its one less bolt to boot. Yeah, you gotta take the small ring off to get to the big ring bolts, but you had to deal with that nonsense anyways with the old design.

When has changing chainrings not been a pain in the butt?

[David Kirk]

I would assume that the loads taken by the back-of-the-arm bolt would be very low considering the phase of the power stroke and that they put the 4 arms where they are the most effective.

dave

[carpediemracing]

I would assume that the loads taken by the back-of-the-arm bolt would be very low considering the phase of the power stroke and that they put the 4 arms where they are the most effective.

dave

+1

I think the chainrings need support when under most stress. The Shimano arms were optimized for this, hence their odd but mirror spacing.

[oldpotatoe]

Back in the day when every crankset was a five arm spider design, all the mounting bolts were accessible and it was easy and simple to change the rings without removing the crank arm. Makes good sense.

Then when chainring setups got standardized, the five arm spider was rotated so there were four arms and the fifth attachment was to the back of the crankarm. That seemed to make a lot of design sense, with probably less material and seemingly more robust attachment design.(At least in Campy World where I live.) It made it more difficult to change chainrings, but so what?

Now Campy has gone back to four-arm spider design but all the chainring ring attachments are independent of the crankarm and bolts are not easily accessible for changing rings.

Wouldn't it make more sense to use a 3 arm spider design and make the fourth attachment to the back of the crankarm?

Am I overthinking this?

yes. Take the crank off..easy to access cr bolts. Both shimano and Campagnolo. Remember, the trend for 4 arm stuff(Campag and shimano) is to make one crank for almost any chainring combo..specifically, 53 to compact of 34, w/o a new crank.

[unterhausen]

I was convinced this was the greatest idea ever back in the '70s when I was a weight weenie. I never had one of the cranks built this way, but I think people didn't like wrenching on them. I'm surprised there aren't any strong anti opinions in this thread

[Pastashop]

If anything I think the four bolt design is easier for changing rings. Don't have to swap sides with one bolt facing one direction and four others facing the opposite direction. Its one less bolt to boot. Yeah, you gotta take the small ring off to get to the big ring bolts, but you had to deal with that nonsense anyways with the old design.



When has changing chainrings not been a pain in the butt?


The Mavic "Starfish" crank?.. Bolts directly into the arms? But probably better to have a modular, 5-arm set-up. Actually, the 3-arm Rene Herse set-up ain't bad either. The White Ind. VBC seems nice (never used one), but I'm out off by the large-ish (?) Q-factor.

[classtimesailer]

The crank arm flexes some which over time tends to loosen that one bolt. Before I was informed of this phenomenon, I had to replace that missing bolt. Thereafter, sure enough, I could regularly re-tighten that bolt.

Are you guys replacing chainrings or exchanging them. If I'm replacing a worn chainring, I figure it's time to dismantle the whole mess and check into my BB situation anyway.