Originally Posted by
DangerousDanR
For my R350 size XL my measurements are as follows:
Top Tube: diamond shaped 34.5 mm
Down Tube: diamond shaped 41 mm
Seat tube: round 36.5 mm
ST Thickness at top: 4.3 mm
Chain Stay: oval 19 mm X 25 mm
Seat Stay: Upper 17 mm
Seat Stay: Lower 16 mm.
These are approximate measurements taken with a so so digital caliper, but they are within 1 mm of correct.
I believe that the R300 uses a different alloy so it will be different. My frame may be more like the Helix Pro or the R500. I also have a couple of Lynskey Hard Tail mountain bikes, and they are also solid performers. I bought my first Lynskey for a winter commuter after a steel circa 1980 Ritchey, which I had powder coated, started to bubble and rust from the stuff they put on the roads here when it is above zero and it snows. That Lynskey bike has seen many years of hard use with not a single frame related issue.
Thank you for taking the time to measure. From those diameters I'd be very surprised if your r350 frame was not lots stiffer than my r330.
I added your measurements to my data from the other thread - each reading is now a quad of: cannondale sr1000, kona raijin, r330, r350.
tube diameter in mm: <sr1000, raijin, r330, r350>
Top Tube: 35, 35, 33, 34.5
Seat tube: 32, 36, 35, 36.5
downtube: 45, 44, 44, 41
seatstay: 19x26,19, 15, 16-17
chainstay: 25.5, 19, 20.5, 19x25
Your r350 has significantly larger seatstay and chainstay, than my r330 and that is significant.
I ran numbers for moi and find that each mm increase in diameter from 15, 16, 17 gives about a 22% increase in stiffness.
Comparing seat stay if a 0.9mm thick 15mm diameter tube has moi of 1000 then 16mm is 1220 and 17mm is 1480. Just eyeballing it looks like my frame's stiffness is held back by those tiny 15mm seatstays.
The 25mm height on your chainstays will be almost double the stiffness of my r330's 20.5mm chainstays (4700 compared to 2500), but I'm not sure how that will impact the frame stiffness wrt side loads.
The modulus of elasticity of Ti alloys doesnt' change much and it can't change stiffness by more than 10%, tubing wall thickness can cause a difference of 25% but you can see that diameter dominates. I believe the point of 6/4 is that it is stronger so you can make the tubing thinner for the same stiffness, so is potentially lighter or tougher, the stiffness is a myth.
Anyway, I'd guess if someone were wanting to estimate the stiffness of a frame they are considering they should ask the manufacturer, and if in doubt check those tube diameters.