Cannondale Hybrid Bike Vibration over Gravel Road

The orange block near the seat post is a Slam Stick X accelerometer. I recorded the frame vibration as I rode the bike over a gravel road adjacent to the Green River in Kent, WA at 10 mph. The time history and power spectral density from the vertical axis are shown below. I expected to see some sharp peaks due to tire imbalance, gears, chain, etc. I also expected to see some resonant peaks. Instead, the data have a relatively smooth, broadband characteristic.

I have mostly ridden this bike over paved paths. So far, I have had one broken spoke and one flat tire. But damage potential from travel over rough trails would be a concern and might cause fatigue cracks in the welded joints over time.

Here are the bike specifications before I changed the seat and made a few other modifications.

Best UseRecreational Cycling
Bike Frame MaterialAluminum
FrameQuick CX, SmartForm C2 Alloy, SAVE, 1-1/2″ to 1-1/8″ tapered head tube
Step-ThroughNo
Bike SuspensionFront Suspension
ForkSR Suntour NCX w/ lockout, 50mm, 1-1/2″- 1-1/8″ tapered steerer
Fork Travel50 millimeters
CranksetShimano Acera, 48/36/26
Bottom BracketFSA Cartridge
ShiftersShimano Alivio, 3×9
Front DerailleurShimano Acera 31.8 clamp
Rear DerailleurShimano Deore
Rear CogsShimano Alivio 11-32, 9-speed
Number of Gears27
Brake TypeHydraulic Disc Brake
BrakesShimano M315 hydro disc, 160/160mm
Brake LeversShimano M315 hydro disc
RimsDC 3.0, double wall w/eyelet, 32-hole
Front HubAlloy Disc, sealed, loose ball bearings, QR, 32h
Rear HubAlloy Disc, sealed, loose ball bearings, QR, 32h
Wheel Size700c
TiresPanaracer Comet Hardpack, 700x38c
Tire Width38 millimeters
Handlebar ShapeFlat Bar
HandlebarCannondale C3, 6061 double-butted, 12mm rise, 680mm
StemCannondale C3, 6061 Alloy, 31.8, 12°
Seat PostCannondale C3, 6061 Alloy, 27.2 x 350mm
SaddleCannondale Quick CX Ergo
PedalsCannondale Fitness Reinforced Composite
HeadsetVP Si 1-1/2″- 1-1/8″
ChainKMC Z99, 9-speed
Weight27 lbs. 3.2 oz.

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