How do you set seat angle/saddle fore-aft?

datsunman

Probably a very silly question, but I'm stumped.

I had a bike fit a while ago and was told to use a 73deg seat angle, thing is, I'm not sure how I do it! I was given a saddle tip to bar measurement, but my saddle is different to the one we were using, so unlikely to help.

How can I determine where the neutral position/centre of the saddle is, do the numbers on the saddle rails actually mean anything or are they just for reference once the saddle is mounted?

Smokin Joe

The general rule of thumb is that when your cranks are horizontal you should have a straight line from your knee to the pedal spindle. If you are tall and long legged or prefer a slow cadence sitting a little further back will probably be better.

balthazar

The 73 degree seat tube angle refers to a nominal characteristic of an actual frame, and cannot be changed. That it can be accounted for by moving the seat forwards and backwards on its rails, or by fitting a different design of seatpost, shows how arbitrary this stuff is, though it is a useful point of reference. The KOPS (Knee plumb Over Pedal Spindle) fitting method has no scientific credibility, but is a good enough starting point. Adjust until you're most comfortable.

Monty Dog

73 degree is the seat tube angle on the frame, which is pretty standard on a lot of road frames. Saddle angle should be horizontal - maybe a touch nose-down but trouble if you have it pointed up. In terms of lay-back, there are a number of factors including riding style, femur length and muscle-strength. I prefer a lot of layback as it means I can apply maximum power through my quads whilst seated

ynyswen24

I've never found any justification for the knee/pedal spindle plumbline thing. It would mean you're only 'correct' for 1/360 of each pedal rev and never if going up or down any kind of gradient. You move forward on the saddle when sprinting and back when climbing so unless you fit a buttplug on your saddle to hold you in the'correct' position that aspect of fitting is dynamic rather than static.
Monty Dog has it correct, make sure your arms aren't stretched or too constricted but remember that as you move your saddle fore and aft to find what suits you best that you'll need to recheck the saddle height to make sure this remains constant.

redddraggon

djbarren wrote:

Sorry to jump in on this thread but ! question have is,

When you change your saddle from a stock saddle to a sexier one and the height from the centre of the rails to the top of the saddle is different. What is the best way to re-set your height?

Undo the seatclamp and move the seatpost up or down until you are at the right (original) height. Then tighten the seatclamp up at the recommended torque.

redddraggon

I do distance BB centre -> bit of saddle where you sit. As long as that distance is the same when you change saddles it'll be fine.

Or measure the stack height of each saddle, and alter the seatpost insertion appropriately.

datsunman

Thanks all, I possibly didn't put my point across well enough though.

I know that the seat angle is essentially a frame measurement, but if the saddle is neutrally positioned and your frame *is* 73deg then, in theory, you would be running that seat angle which would then give you the same KOP position. (Be that over the spindle or not). If you then moved the saddle forward/backward 9-10mm you'd be very roughly a degree up or down from your seat angle. I think!

Since my bike is 73.6 (or maybe 8 can't remember) I have to move the saddle slightly further back to get the same effect.

Basically, I have the following numbers and I'm trying to dial them into my current bike.

ST Length 575
ST Angle 73
TT Length 560
Saddle height (top saddle to bb) 77.3
Tip saddle to bb 7.5

If I had an Arione I could simply measure tip of saddle to bb, but as I have a different one I need to figure out another way of doing it. Anyone have an Arione they want to measure for me?

dennisn

Monty Dog wrote:

73 degree is the seat tube angle on the frame, which is pretty standard on a lot of road frames. Saddle angle should be horizontal - maybe a touch nose-down but trouble if you have it pointed up. In terms of lay-back, there are a number of factors including riding style, femur length and muscle-strength. I prefer a lot of layback as it means I can apply maximum power through my quads whilst seated

Have you noticed that by sitting further back you seem to SIT(have more of your weight) on the saddle than by having it further forward???? Thus letting the saddle support more of your weight and taking pressure off the arms and hands??? I've been messing around
with the saddle further back ever since I first read Keith Bontrager's article "The Myth of KOPS". He makes some good points in saying that knee over the pedal spindle is not the way to go(still, it should get you close - unless you're a triathlete).
Just wondering..

balthazar

I think that what you are attempting is a category error. Seat tube angle is a meaningless term when applied to anything other than the frame itself. I've never seen a bikefit chart which intended it to be read any other way. Saddle position is referred to and measured differently, usually located as x distance behind the BB.

If you are translating a position from another bike with a different saddle, then you might use the depressions that your pelvis (sit-bones) make, as a point of reference (instead of one or other end of the saddle, which is an arbitrary length).

sampras38

dennisn wrote:

Monty Dog wrote:

73 degree is the seat tube angle on the frame, which is pretty standard on a lot of road frames. Saddle angle should be horizontal - maybe a touch nose-down but trouble if you have it pointed up. In terms of lay-back, there are a number of factors including riding style, femur length and muscle-strength. I prefer a lot of layback as it means I can apply maximum power through my quads whilst seated

Have you noticed that by sitting further back you seem to SIT(have more of your weight) on the saddle than by having it further forward???? Thus letting the saddle support more of your weight and taking pressure off the arms and hands??? I've been messing around
with the saddle further back ever since I first read Keith Bontrager's article "The Myth of KOPS". He makes some good points in saying that knee over the pedal spindle is not the way to go(still, it should get you close - unless you're a triathlete).
Just wondering..

I've used the plumline method as a starting point and then tweaked it from there, adjusting until I have more weight on my saddle than the bars. i think i've got it pretty much perfect now.

There are so many theories and techniques out there and most of them have some substance, but mostly they just get you to a good starting point.

datsunman

balthazar wrote:

I think that what you are attempting is a category error. Seat tube angle is a meaningless term when applied to anything other than the frame itself. I've never seen a bikefit chart which intended it to be read any other way. Saddle position is referred to and measured differently, usually located as x distance behind the BB.

If you are translating a position from another bike with a different saddle, then you might use the depressions that your pelvis (sit-bones) make, as a point of reference (instead of one or other end of the saddle, which is an arbitrary length).

The bike fit chart wasn't saying that I should be using 73 degree as an angle, it was saying that my setup was based on a 73 degree angle with the saddle in a neutral position. So I figured my saddle position was at 73 degrees relative to the floor, as per the seat angle of the frame.

Anyway, I haven't got either the test frame or the test saddle to compare to, think I'll just play on the trainer until I get it somewhere near correct.

dennisn

sampras38 wrote:

dennisn wrote:

Monty Dog wrote:

73 degree is the seat tube angle on the frame, which is pretty standard on a lot of road frames. Saddle angle should be horizontal - maybe a touch nose-down but trouble if you have it pointed up. In terms of lay-back, there are a number of factors including riding style, femur length and muscle-strength. I prefer a lot of layback as it means I can apply maximum power through my quads whilst seated

Have you noticed that by sitting further back you seem to SIT(have more of your weight) on the saddle than by having it further forward???? Thus letting the saddle support more of your weight and taking pressure off the arms and hands??? I've been messing around
with the saddle further back ever since I first read Keith Bontrager's article "The Myth of KOPS". He makes some good points in saying that knee over the pedal spindle is not the way to go(still, it should get you close - unless you're a triathlete).
Just wondering..

I've used the plumline method as a starting point and then tweaked it from there, adjusting until I have more weight on my saddle than the bars. i think i've got it pretty much perfect now.

There are so many theories and techniques out there and most of them have some substance, but mostly they just get you to a good starting point.

I think the part in Keith's article that made the most sense to me was his theory that the critical dimension for seat fore and aft positioning
is the horizontal relationship between your body's center of gravity and the bottom bracket. Unfortunately, it seemed that that was as far as he could take it. At least at that time.

dbrooksbank

I seem to be having exactly the same problem for positioning my saddle. I can get the height sorted without too much trouble, but the fore/aft placement appears to be just trail and error?

I've had a go at the kops method and it just doesn't work. My knee position is always in front of the axle by about 20mm or so? so my plan is to line the centre of the saddle with the centre line of the seat post as my starting point, and work from there?

I'm taking the centre of the saddle as the mid point along it's length, as the rail numbers don't make any sense.

Is it a case of just experimenting until you find the most comfortable seating position, and then keep a record of the BB spacing? at which point you can then start on the stem length??

JohnnyAllez

I always use a spirit level across the top of the seat and set it level with the bike on the deck (on a level surface obviously)

balthazar

dbrooksbank wrote:

I seem to be having exactly the same problem for positioning my saddle. I can get the height sorted without too much trouble, but the fore/aft placement appears to be just trail and error?

I've had a go at the kops method and it just doesn't work. My knee position is always in front of the axle by about 20mm or so? so my plan is to line the centre of the saddle with the centre line of the seat post as my starting point, and work from there?

I'm taking the centre of the saddle as the mid point along it's length, as the rail numbers don't make any sense.

Is it a case of just experimenting until you find the most comfortable seating position, and then keep a record of the BB spacing? at which point you can then start on the stem length??

I think trial and error is the best way of ascertaining bike fit; the calculation methods are only aggregates of other riders' positions which they judged comfortable. They may give you a starting point but you have one of those already.

As has been mentioned, KOPS is discredited, so don't be concerned by it. If you feel comfortable with the saddle/BB position, but still think you may prefer the handlebars to be closer/further away, then try a different stem. Bike shops sometimes loan stems out, or make a small hire charge, redeemable against a new stem. A change here may make you reconsider saddle position, so be prepared to back-and-forward a bit.

You can pick any feature as your point of reference, as such data serves only you. I measure from the depressions that sit-bones make in the saddle, if possible: that way you still have a useful measurement if you change the saddle. Once you are fully comfortable on your bike, which may take hundreds or thousands of miles to ascertain, then you have a reference position which you can transfer to any other.

darren H

Personally I have the seat set just tilted slightly up. I set it level with a spirit level then angle it back a fraction and i mean a fraction. I find if I set it dead level that im sliding forward a bit.
I have always tweaked my bike a bit over many rides. It does take a while to get the correct set up.


New riders often think that they are not correctly seated when doing long rides. A pro once told me that its just simply something you get used to. Yes a correct position is itally important but lots of riding is as well.

Most riders who are uncomfortable have too big a bike