[dannyboy2233]

Hello all,
I'm new to this forum, and recently purchased a used 2007 Cannondale Carbon Rush 2, with primarily stock components. I've been looking at dropper seatposts, but I'm unsure as to which ones would fit my bike. The idea of "exposed seat post" confuses me, as I'm not sure to which measurement it is actually referring. I do, however, know that the diameter of my seatpost currently is 27.2 mm, so I know that there are options out there. If anyone could explain to me that measurement/make recommendations as to my size of seatpost, I'd be super grateful. Thanks in advance!
Danny

 

[Bro]

Exposed seatpost is the seatpost that you can see between frame and saddle.

 

[dannyboy2233]

So then what sort of measurement should I be looking for? If you look at the gravity dropper website, for example, it talks about exposed seatpost measurements, and I'm not entirely sure how to interpret it. If you could help, that'd be great. Thanks!

 

[ChainChain]

Go measure how much seatpost is sticking out of your frame right now with the seat at the correct pedal height. That number should be greater than the distance that the dropper drops plus whatever flange or what have you at the top of the dropper that doesn't fit in the frame.

 

[dannyboy2233]

Sweet, thanks so much. So for a dropper post, the "low" setting should be at my regular pedaling height, correct?

 

[ChainChain]

Droppers have three settings, up, down, and somewhere in the middle. Some may travel further then others. The point of the "exposed seat tube" number is to get a dropper that when it is all the way up you can still reach the pedals. With a dropper fully extended there is a limit as to how far into the frame you can put it at the seatpost clamp.

Odds are if you have a frame that fits you, it shouldn't be an issue, but some droppers have 100mm of travel and some have 125mm. and you may want less travel if height is an issue.

You don't want the length of the green to be less than the red or you won't be able to utilize the dropper properly

 

[dannyboy2233]

Let's just say, for the sake of making it easy for me, that the dropper's only got two settings; up and down. In terms of ease of pedaling, what should the spots be? i.e. should the top setting be nearly the equivalent of me standing up & the bottom one be my regular pedaling position?

 

[jetboy23]

How tall are you and what size is your frame? I'm 5'10" with a 34" inseam (longish legs). I ride a large frame with a 19ish inch seat tube. Both of these frames have a 400mm long seat post with 100mm of drop. I have never needed more than the 4" drop. But, i also have most of the static portion of my seat post inserted into my seat tube.

If you're looking into Gravity Dropper (since not many other options for 27.2 seatposts) you will want to decide if you want a 4 or 5 inch drop. A 400mm total length is about average and will allow both of those drop lengths. Any shorter and you're really only cutting a few grams, or, unless you had a bending seat tube that can only accept a shorter insertion length. No need since your seat tube is straight. If you have a smaller frame and have long legs, you might want to go for the 425mm with a 5" drop.

I hope that makes sense. If you still feel like a 4" drop and 375-400mm total length won't work for you, give GD a call. They will be happy to help you pick the perfect dropper. Or, X Fusion has the Hilo in a 425mm total length and a 4in drop. They take most of the options and confusion away. lol.

 

[dannyboy2233]

Ok. I'm 6'1 with ~34" inseam. The X-Fusion sounds good, as I like the infinite adjustment. Do you know anything about compatibility with the Cannondale Rush Carbon 2 from 2007?
Thanks!

 

[ChainChain]

The only real compatibility issue is seatpost diameter. You say it's 27.2mm so buy one with that diameter.

When the seat post is up, it should be at the properly adjusted height for efficient pedaling, as is your current seatpost. When it's down it is just out of the way.

Go measure the "green" measurement seen above on your bike with the saddle at the proper height. That information will help determine if you get the 4 or 5 inch dropper.

 

[jetboy23]

X Fusion only has the 4" version in the 27.2 seat post size. That is the one that's compatible with the 2007 Rush. Gravity Dropper, you have the option of 350 or 375 total length for 4 inch drops and 400 or 425 for 4 and 5 inch drop.

Infinite adjustment is nice, but, not a game changer. I have one dropper with infinite adjustment and one without. I am usually a full drop or full up rider. Once every 20 rides or so i will do a slight drop on rolling terrain. My other dropper is a Up, down 2", down 4". I'll use the 2" down as much as the slight drop on the infinite dropper and notice little difference. All up to your personal preference.