I've recently gotten a new bike. My old bike has a nice super-adjustable/traditional rear rack. I'm thinking of trying one of the seatpost mounted quick on/off rackes to hold just a rack pack (that's what I use on the old bike 99% of the time) - I ride for 2-5 hours at a time so I like to have the essentials for longer rides.

My thought is that these seatpost mounted racks will have a vibration factor ... because of the single mounting point. Who has experience with these - what are your impressions?

TIA,

-D

I have the following:

http://www.topeak.com/products/rack_001.html
http://www.topeak.com/products/bag_013.html

The bag slides on the rails and locks in place. No straps or anything. I keep all my tools and a Crank Bros. mini-pump in one of the side pockets. When I lock my bike, I just slide the bag off and take it with me. It's a dream setup.

which fits the same bag system. It would hold the load with a lower center of gravity which (for me) would be a good thing. YRMV.

I've seen a seat post mounted rack (not this Topeak) which twisted. It had triangular legs hanging down (that functioned only to hold pannier bags) and one side was perilously near the rear wheel.

I've recently gotten a new bike. My old bike has a nice super-adjustable/traditional rear rack. I'm thinking of trying one of the seatpost mounted quick on/off rackes to hold just a rack pack (that's what I use on the old bike 99% of the time) - I ride for 2-5 hours at a time so I like to have the essentials for longer rides.

My thought is that these seatpost mounted racks will have a vibration factor ... because of the single mounting point. Who has experience with these - what are your impressions?

TIA,

-D

All racks will have a vibration factor, which is why loctite, or nyloc nuts, or both, are a good idea for any rack.

That said, I see no sense at all in seatpost racks for road riding. Really - what's the benefit? By design they are heavier, since the cantilever beam and clamp surface must be larger and stiffer than a traditional 4-point rack (which benefits from a truss structure). And given their higher weight, the seatpost racks also have lower load ratings. So don't stop at the market on the ride home because groceries might exceed its rating. Essentially, any hardware failure will constitute a rack alignment failure - whereas a 4-point rack can successfully be used with only 3 points solidly attached (in a pinch, like on my mtb camping trip last weekend. i forgot loctite for the hardware).

Another issue to consider - many frames (road and mtb) are sized "compact", meaning that the frame is lower and the seat tube longer. Within a certain envelope, the seat tube-to-seat post connection is designed for a person's weight acting downward and slightly to the rear. If you put a seatpost rack on this type of frame, you are exerting a large lever-arm (torque) on your seatpost and seat tube. Perhaps your frame was designed for such an unusual load, especially if an mtb, but more likely you're entering a grey zone where frame failure is possible.

The only reasons I can imagine for getting a seatpost rack, assuming you're a roadie and not on full suspension, are that (1) it's an aesthetics issue and so your personal choice; and (2) you just want to spend money on something new to distract you for a while...

All racks will have a vibration factor, which is why loctite, or nyloc nuts, or both, are a good idea for any rack.

That said, I see no sense at all in seatpost racks for road riding. Really - what's the benefit? By design they are heavier, since the cantilever beam and clamp surface must be larger and stiffer than a traditional 4-point rack (which benefits from a truss structure). And given their higher weight, the seatpost racks also have lower load ratings. So don't stop at the market on the ride home because groceries might exceed its rating. Essentially, any hardware failure will constitute a rack alignment failure - whereas a 4-point rack can successfully be used with only 3 points solidly attached (in a pinch, like on my mtb camping trip last weekend. i forgot loctite for the hardware).

Another issue to consider - many frames (road and mtb) are sized "compact", meaning that the frame is lower and the seat tube longer. Within a certain envelope, the seat tube-to-seat post connection is designed for a person's weight acting downward and slightly to the rear. If you put a seatpost rack on this type of frame, you are exerting a large lever-arm (torque) on your seatpost and seat tube. Perhaps your frame was designed for such an unusual load, especially if an mtb, but more likely you're entering a grey zone where frame failure is possible.

The only reasons I can imagine for getting a seatpost rack, assuming you're a roadie and not on full suspension, are that (1) it's an aesthetics issue and so your personal choice; and (2) you just want to spend money on something new to distract you for a while...

I'm a distance/fitness road rider. A wedge just doesn't have enough capacity for rain gear, lunch, cell phone etc. I've been using a standard rack with a Delta rack pack for the last couple years. In truth, I like the stability/strength of the traditional rack, but problem is transporting the bike in the trunk of my Taurus... just a real PITA, so since I don't carry ALOT, the beam rack seems like a good alternative, and it comes right off -> easier to get in the trunk... also yeah it is aesthetics - it's a new Lemond Sarthe. I'm not using the thing as a grocery transporter, but thinking of getting a 29'r for everything else, so I'll put a standard rack on that baby when I get it.

The main question that I hoped someone could answer, is if they feel any vibration from the cantilever and if any how does it manifest itself - big bumps only, or a constant "buzz" regardless of speed. So it's my presumption that a beam rack with 10 lbs max. isn't going to stress the frame/seatpost in the least, though I'm definately going to replace the carbon seatpost with AL for sanity's sake.

Anyone else have any experience? - I'm planning on using the Topeak with my existing Delta, since they do have one that's about 400g, and plaenty of capacity. If I find it does vibrate, I'll find an AL welder and add a reinforcement.

-D