On my mtb I try to get my seat a little nose down but can't do it. It can't be lowered more than horizontal position. It's a 1 bolt clamp.
Is it a known problem?

It looks to me that your seat tube is angled back so far that your seat post's intended 'nose down' position is now horizontal. Try getting a different seat post or saddle maybe?

You are right. But what seatpost should I look for?
Is there any specification? I want to order online.

It's the kind of issue I'd personally take to a bike shop. I have no idea if there's a specification, but if you take the old one with you to your LBS at least you'll be able to see if the potential replacement has a greater angle sweep for the saddle.

Adjustment a Notchy interface surface on post head?
it is with cheap seatposts of that type..
shop for another seatpost..

what is the diameter? need that data..
and perhaps length

want to shop online ? use a search for "seatposts"
Will probably be shipped from Europe..





...

I prefer two-bolt seatposts for better angle adjustment. Kalloy makes one (~$40 IIRC), or you can get the pricey Thompson version.

To order either, you'll need the seatpost diameter. Worth a trip to your LBS for a precise measurement. (Go ahead and let them order the Kalloy one for you -- what you save in shipping will likely cover the shop's markup.)

If you haven't already tried this:

1. Loosen your seat clamp binder bolt.
2. Tap on the bottom of the clamp with a hammer or something. Make sure it comes free from the fixed part of the seat post.
3. Now try readjusting your seat tilt.

Sometimes the bottom portion of the seat clamp doesn't come loose from the fixed part of the seat post. When that happens, the seat goes back to where it was as you tighten the bolt.

I know it sounds screwy, but is it possible the clamp is on backwards?
I mean maybe the slot is asymmetrical ......

If you're anyway handy, you could elongate the slot in the lower clamp plate to give yourself more range. It's likely aluminum, so a Dremel or circular file will go through it easily

It's a cheap seat post. Looking at the 2nd pic the bolthead looks like the rocker part it is as far back against the bolt as it will go. It is probably a 27.2 mm post go on ebay and look for one with 2 bolts one in front and one in back this set up provides a lot of tilt adjust and is easy to do by loosening one bolt and tightening the other.

Check the seatpost diameter.

Some brands of seat posts have a side mount option that should give you a full 360 degree rotation. Not that you necessarily need the seat upside-down.

This is a pretty large in diameter post, but an example.

https://www.ebay.com/itm/specialized...gAAOSwCBtbeadq

The problem they may not be as strong for holding the seat in place as some of the newer 1 and 2 bolt posts.

Aluminum can develop stress risers at any scratch or grind if it is a stressed part. It is new post time and I would go with a two bolt type. Make sure is can be adjusted from below.

I use a Nitto S83, but the Ritchey Classic,the VeloORANGE Grand Cru Long Setback, or Thomson Elite Setback were my other choices. From the images you posted you will want a post with setback as you are already past the max setback marking on your seat rails. The Nitto S83 is 20mm setback, The Ritchey is 25mm, the VeloOrange is 30mm, and the Thomson is 16mm.

That what I did. I think it's good enough now.
Thank you all for the answers!

Why is the saddle so far "maxed" rearward?

I always suggest possibly using a longer stem so as to move the handlebars forward in lieu of moving the saddle rearward to accomodate a rider's torso length.

The rearward saddle position stresses components and takes weight off of the front wheel, which invites flighty steering response.

A rearward saddle also requires the rider to bend more sharply at the waist to achieve a given amount of weight ahead of the pedals or to achieve an aero profile, which limits the amount of power that one can comfortably sustain.

And a rearward saddle position requires a much greater energy-wasting "heave" to get out of the saddle (in order to attack hills, cross road defects or effect acceleration).

So there are good reasons why bikes are not sold with their saddles forced to their rearward limits.

I often encounter riders with saddle set rearward because they found they were sliding past the rear edge of the saddle, which is actually the first symptom of too low of a saddle height.

I disagree a bit here - the only goal of saddle height- and fore/aft adjustment is to set the rider in the correct position wrt the BB, based on leg length, KOPS, comfort, efficiency, whatever one's yardstick is (I'm disregarding crank length here for simplicity, but obviously should also be considered). All other considerations are secondary. If the saddle is maxxed rearward once that ideal position is determined, then the rider should look into a seat post with more setback, or, as a last resort, a frame with a slacker seat tube angle, to achieve that saddle/BB positioning without slamming the saddle. AFTER THAT, the cockpit length should be addressed, generally through a combination of handlebar reach and/or stem length. If a comfortable cockpit can't be attained with a reasonable stem length ("reasonable" being in the eye of the beholder, of course - but I think anything in the 10-14 cm range would be reasonable). Anything outside that range would suggest that a frame with a longer/shorter top tube might be considered. What I wouldn't do is adjust saddle position to tweak cockpit length, unless it can be done without compromising that all-important saddle/BB positioning.