I’m a bit thick – anybody explain the idiot’s guide to how to decide what size drop, etc, to get?

I’m after a KS Lev to go on a Yeti ASR5C (therefore 30.9mm diameter seat tube).

Ta…

Easy
Look at your bike with your saddle up. Measure the amount of post showing from the frame to the rails. (Exposed Length)
Get the tech specs or find a post in the shop and measure how much length is taken up by the collar and a different head design. (Gubbins)

Then Exposed Length – Gubbins = Amount of Drop

You then need the right amount inside the frame.

Okey dokey, ta!

I’ve got one dropper with 4″ travel, and one with 5″. I would really recommend 5″. So much so, that I will probably sell my 4″ post and upgrade to a 5″. Others may differ obviously, but on my bike 5″ is totally out of the way for descending, while 4″ is still slighly too high.

The other thing is that one one of my bikes, in order to get the seatpost at proper, full up climbing height, the seatpost needs to be slightly higher than the minimum insertion point, which worries me. So I’d say that the thing you really need to look out for is the amount of seatpost inside the frame. I’m not sure I can offer any helpful advice about the right size, but I’d say it’s the most important issue.

Right, so after a bit more research and a slightly confusing inches – millimetres conversion from a fancy table somebody’s done on MTBR, by my maths and measurements:

215mm of post showing currently
125mm drop post is 385mm total length, min insertion 120mm/max 200mm
“Gubbins” occupies c35mm

Therefore:

125 (drop) +35 (“gubbins”)=160mm
215-160=55m of shaft showing as well as “gubbins” and stanchion
385-215=170mm of insertion (oo-er)

170mm sitting just over halfway between min and max insertion.

Whereas, doing the same calculation with the 150mm drop post – min insertion 120mm/max 226 and total length 435mm:

435-215=220mm

I.e. pushing the max insertion envelope a bit much for comfort…

So I should go for a 125mm drop post. I think. Would that be right…?

I asked a similar question of KS and they responded with this information.

“You need to measure from the top of your seat tube to the your seat rails when you seat is set up for flat ground riding. Once you know this dimension, you will know the total height.

You need to account for the collar height of the new LEV seatpost which is 2.0″.

So if you are looking at the 100mm LEV you are looking at about 4″ plus the 2.0″ for the collar totaling 6.0″.

The 125″ will be 5″ plus the 2.0″ or a total of 7.0″.”

Hope this helps