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Saddle rail diameters(3 posts)

Saddle rail diametersGMS
Sep 27, 2002 1:32 PM
Recently we've read that some saddles, like the Fizik Aliante, have "big" rails that don't necessarily fit in some seat post clamps. This puzzles me, because seat rail diameters are not standard (obviously, as in this example), yet the manufacturers never seem to list the diameter of the seat rails on their saddles.

How can we have a non-standard component that doesn't specificy anything about itself?

That would be like buying handlebars and performing a trial-and-error test for compatibility with your stem.

Anyway, if the only classifications we have for seat rail diameter are "big" and "not big," what is a "normal" seat rail diameter?

Thompson's web site insists that you use none other than 7mm seat rails. It's unclear to me how one would find out short of buying a saddle and measuring... or just jamming it in the seat post and praying it works.

Furthermore, Thompson is the only seat post manufacture I have seen to list what seat rails diameters it is intended to work with. Many people have indicated that the USE Alien clamps don't take as large seat rails as other clamps... but nothing indicates this before purchase.

In any event, is there any way to gain knowledge of seat post/saddle rail compatibility short of trying it physically?

Thanks.
calipers...C-40
Sep 27, 2002 3:12 PM
When all else fails, measure the rails with calipers or a micrometer. I've never encountered this problem in 20 years of cycling. I've also never seen anyone advertise the diameter of their seat rails.

I measured six saddles that I have and all were the "standard" 7mm diameter.
Ti and CrMo rails = usually 7 mm diameter, but carbon ...Markus_B
Sep 28, 2002 1:58 PM
rails have larger diameters (some not even round) and can be problematic.

I think most seat post respective saddle manufacturers haven't realized the problem.

As they haven't realized the problem that some saddle's rails (without slope = fi'si:k Pavé, fi'si:k Nisene, e.g.) make reasonable tilt adjustment impossible in combination with some posts (Tune, Thomson with 0° clamp, e.g.).

I would recommend trying it physically if saddle rails are made of carbon or if the rails have (almost) no slope towards the nose of the saddle.

Why don't you specify your favorite combination? Maybe someone out there can tell you if works?

P.S.: Flite, Pavé. Aliante Ti = 7 mm