Two sizes of carbon rails

16/04/25 23:01 Filed in: Gear

Why bike industry? Why??
The seatpost that Trek included with my replacement frame - very nice of them too - was the RSL "flexy" carbon post. This ships with 7x10 carbon rail "ears". I discovered that the seat mast that shipped with my original Checkpoint used the same identical ears, but were for 7 mm round rails (ie, metal rails). I quickly put those pieces into play to mount up my Fizik saddle. And a couple of others. None of which I really liked.
Then, as I've noted previously, I tried out some other Bontrager saddles. They use a 7x10 mm oval rail in carbon.
When I decided to try the Ergon saddle, I didn't even consider that the rails might be different. Twenty-five hours of riding and listening to the seatpost head snap over bumps and I had the epiphany while on the bike - the rails are 7x9 mm and therefore too small for the ears. It explains a lot. Tightening does hold the saddle in place, but doesn't feel like it's "tight". And the bottom of the ears touch the actual post - which doesn't seem correct.
I've got the proper ears on order and will report back. Before this epiphany, I was contemplating buying a different post, since I think I like this saddle.

As a side note, I can't believe how expensive these ears are. On the Ergon post (also sold for less money with Canyon branding) they are sold with round rail ears and the 7x9 oval ears are the only other option. Trek sells the RSL post with the 7x10 oval ears installed and will sell you either of the other sizes. All of these things sell for about $60. For two bits of aluminium and a bolt (2 bolts in the Ergon post).
I ask, what was wrong with the 2-bolt post heads that all the lightweight posts used for many years? They could accommodate most any rail size - at worst with longer bolts. I don't feel like these eared posts are any better at retaining or supporting the saddle rails, and in some ways could be worse.

Fingers crossed, the new ears quiet the bike back to pure silence.

Michael Hanslip Coaching

If you want to go faster, you have to pedal harder

Two sizes of carbon rails