Cantilevered vs diamond frame design

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Hey, guys, having both frame styles, I got to wondering:
Other than aesthetics and weight, what are the advantages / disadvantages of cantilevered vs triangulated (diamond shaped) frames?
What strengths/ weaknesses between the two? A realy academic question, I know, but on a bike forum, I figure there might be an enthusiast with maybe a bit of engeneering background who could answer this for me. Anyone?
 
I guess the forward extensions of the seat stay could add some rigidity, but, I think looks is about it... :roll:
 
Since cantilevered bars do not actually rest upon weight bearing points in a bicycle frame, the strength they provide is negligible, in fact it is quite possible that cantilevered frames are less strong than diamond frames as they are heavier and lack the strict triangular gussets and joints.

However, from personal experience, I can attest the cantilevered frames are so similar in rigidity that it is purely an aesthetic choice. Most Rat bikes are not going to be used for excessive jumping or off-road riding, nor are they going to be raced in centurions or rallies so being extra light weight is usually not the paramount concern.

I believe the popularity of vintage canti-frames has more to do with the addition of cool looking accessories like tanks and light than they have to do with structure.

That said I recommend a canti-frame as they look great and provide more customization options.
 
I think that there are also some significant differences from one manuacturer to another in terms how strong or rigid a cantilever frame might be. From the bikes I have, I'd say that the Schwinn canti frames are built like bridges. The Columbia frames are almost as robust, whereas the Murray, Roadmaster, Ross & Rollfast frames that I have are a lot less so. Either the tubes are lighter and smaller or how and were they attach to the frame is weaker, or both. While you could get away with building a klunker from a Schwinn cantilever frame, I wouldn't bother attempting it with an AMF Roadmaster. So, not all cantilever frames are remotely equal from an engineering point of view...
 
Thanks, folks, I was just curious, is all. Looking at my frames again, I see the point about the cantis being maybe less robust, at least if all other factors were equal.
 
Back in my BMX days in the late 70's - early 80's I first built up a Sears (Murray) cantilever - no problems and lots of stunts and jumps.

I then built up a Ross cantilever and rode that like mad jumping fourteen 55 gallon drums. I even had the original Ross forks, it was built really well - no problems.

Then I built up a Schwinn Fastback with Tange forks and cracked the top tube in only a few weeks. It cracked at the joint near the head tube.

I had a Schwinn cantilever that I delivered newspapers on with a Ross 10 speed fork to allow the newspaper bag to hang off the bars and double clamp neck without hitting the front tire. That held up to years of heavy newspapers.

I would say that the cantilever design helps strengthen the frame but BMX and Mountain Bike frames were built stronger with straight cro-moly tubing and better joints and welds. I also would say that the Ross frames and forks were perhaps better than the Schwinn based on my experience. I also had a Ross Apollo that was built like a tank with square tubing.
 
For the most part its an aesthetic difference, rather than structural. More important would be to consider the frame construction techniques which would vary based on brand, year, model, etc. Many manufactures made similar looking frame designs, but used different manufacturing methods so its hard to compare. Fillet Brazed, welded, electro forged, soldered, external lugs, internal lugs, pinned lugs, etc. Most cruisers use fairly low end steel tubing, vs what you would have found on a high end road bike.
 
You can get adult size diamond frames all day long but the cantilever frames just don't come in "tall" sizes. I love my cantilever frame B6 and Phantom, but the reality is they were built for 12 yr. old boys. I'm 6' 2" and now am pretty good at making long, laid back seat posts. :roll: Gary
 
B607 said:
You can get adult size diamond frames all day long but the cantilever frames just don't come in "tall" sizes. I love my cantilever frame B6 and Phantom, but the reality is they were built for 12 yr. old boys. I'm 6' 2" and now am pretty good at making long, laid back seat posts. :roll: Gary
Click to expand...

See, I have the opposite problem. I'm 5'6" with proportionally short legs. Even a typical cantilever frame is borderline for me. I can stand flatfoot over it, but there's little clearance... I often have a tough time finding diamond-style frames that I can use comfortably. Most road bikes are too tall, even in the small frame sizes, if the top tube is actually horizontal and not canted some. I'm looking at buying a new Kona Dew, and find I'm at the very bottom of the size range they offer...
 
New school 26" BMX. The seat's practicalty on the rear tire. Or a 24" bike?
 

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