Why is the adjustable front boom curved on the S40 and V20?

[Neilsky]

I'm a newbie considering buying a Cruzbike S40, and I was wondering why the boom is curved at the BB? I think it looks interesting, but there must be an engineering reason to go to the expense of bending the aluminum tubing on the 2 top end models but not on the 2 less expensive models in the lineup. It looks like there would be enough adjustability in the headtube washer stack to give proper knee clearance with the handlebars if the boom was straight.
Thanks,
Neilsky

 

[ak-tux]

In short it was to allow the front derailleur to adjust independently of the boom length changes.

And now the the long version: The first version of the Silvio version 1.0 or the predecessor of the S40 and the vendetta had the boom straight and front derailleur attached directly to the boom. However, since these bikes were designed to be a "one size fits all", whenever the boom was adjusted for a short (than average) or very tall rider the front derailleur would no longer shift correctly because the angle relative to the chain would change significantly.

The curved nose allowed for a small stem to be welded on to the chainstay to mount the front derailleur and maintain a constant position irrespective of the boom adjustments.

 

[benphyr]

The curved nose allowed for a small stem to be welded on to the chainstay to mount the front derailleur and maintain a constant position irrespective of the boom adjustments.

Thank you for the concise, clear explanation. I have wondered and guessed, but it is nice to know.

 

[hurri47]

Gee, I always thought it was mostly to lower the handlebars and the little shifter stalk was a by-product. My Silvio 1.0 shifts fine in at least two of the four rear derailleur mounting location (for with and without the chainstay extension), but the bars are too high for both of them.

-Dan

 

[ak-tux]

Gee, I always thought it was mostly to lower the handlebars and the little shifter stalk was a by-product. My Silvio 1.0 shifts fine in at least two of the four rear derailleur mounting location (for with and without the chainstay extension), but the bars are too high for both of them.

-Dan

I think the curve also reduces that problem. I remember John Tolhurst talked something about fit for a wider range of people.

 

[dtseng]

The stalk for the brazed-on derailleur hanger is a bit too long; only good for 52-tooth chain ring. The hanger should be lengthened at least 10 mm more to accommodate smaller chain rings such as 50/48 tooth.
Also the cable stop and pulley should be moved to the left side.