Layback seat post and distance to BB

eddiefiola

I went for a bike fit and the guy fitted me at 778mm saddle height and 85mm saddle to BB distance (along with some other changes like stem length).

Unfortunately this never shook the pain i get in my shoulder after riding for more than an hour or so.

I've still been moving things around and ended up with the saddle height slightly higher and the saddle to BB distance is now 97mm.

I feel like this increase in moving the saddle further back has balanced me more and that is removing more pressure from my arms.

My question is how far back from my fit 'measurement' is too far? In order to move the saddle back further from the BB to balance me more I need to buy a layback post as the saddle is now as far back as it can on mine.

This is what I have already does this look like its layback already?

gavbarron

Looks layback already.

One question though, why go for a bike fit if you were going to disregard it and do your own thing?m seems a waste of money? Did you tell them you have a shoulder issue so they could account for this in the setup?
I'd assume that going further back would put more strain on your core which will fatigue quicker and this put more work on your arms again. Also by moving the saddle around you are affecting how you sit relative to cranks and your power output, as well as knees. If you needed a longer reach then stem may have needed to be a bit longer.
Why don't you try getting a bike fit to get the right position...

eddiefiola

Hey Gav, the disregarding came after trying their fit and it still not having any affect.

Their other change after this was trying some smaller bars, 46cm > 44cm and changed from Ergo to compact/shallow drop.

I only have one issue after the fit or even now after me tweaking things, which is the pain top of my right arm.

I believe this is due to incorrectly using KOPS as the determining factor for the saddle nose to BB distance rather than being balanced.

"I'd assume that going further back would put more strain on your core which will fatigue quicker and this put more work on your arms again."

If i'm more balanced surely this will put less pressure on my arms?

"Also by moving the saddle around you are affecting how you sit relative to cranks and your power output, as well as knees.

Agree, but the only issue so far is my arm, if anything moving the saddle back further than the fit measurement has made things feel better in the power & knees department.

Of course i'm self diagnosing and as many wanna be amateurs and could be making things worse.

And i'm not trying to be a smart arse by quoting each point above I appreciate any discussion, I've made nearly 3500kms since starting in April this year and this is the only thing that I don't enjoy about being out on my bike so will do anything to fix it.

gavbarron

Being balanced is the general idea unless you were being setup for a low aero fit but what I meant was that if you sit further forward, the angle between your back and arms and to the bars will be steeper and so they are stronger. If you sit further back the angle opens up and so your back and arms take more load. Think of a comparison of the plank position and how much easier it gets if you bring your bum up into the air. This isn't definitive knowledge, more my interpretation of mechanics and bending moments (I'm an engineer and not in any way sports qualified so to speak to please disregard my thoughts).
I would think that even more important is the height of the bars relative to the saddle, if too low them your arms and shoulders will take more of the load. Try a spacer and bring them up a bit to see how it goes.
I'd also suggest have a sports therapist or such like having a look at your shoulder, pains after just an hour would suggest something more than a bad fit being the issue, even with a bad fit I would expect to ride for longer than that before issues propagate

Monty Dog

FSA do a seatpost with 32mm layback - but to use that amount of saddle setback does require a degree of flexibility as it puts a lot of stress on your lower back.

No surprises on folks not getting on with bike-fits - there's a lot of snake oil merchants out there.

Herbsman

If your bike fit didn't make you comfortable on the bike then you need to go back and get the person to re-fit you at no extra cost, or give you a refund. Do it as soon as possible.

eddiefiola

@Monty Dog Thanks been looking at that FSA K Force not cheap though ;-O

@Herbsman tbh I don't think they did a bad job they just used a system from Specialized which I don't think 'fits' everyone, the post isn't about the money

styxd

Eddie, it sounds like you;re on the right lines. I think my saddle setback is somewhere around the 110mm mark!

According to maths, if you move your saddle back, you should also probably move it down a touch aswell (since moving it back increases your pedal stroke). However, what's to say the fitter got it the right height in the first place!?

Your current seat post has setback, not sure how much by looking at the picture, probably 15-20mm.

gavbarron wrote:

Also by moving the saddle around you are affecting how you sit relative to cranks and your power output, as well as knees.

Not quite sure what this means? I imagine your power output would increase by moving the saddle back, since you wont be having to battle a constant pain in your shoulder!

Herbsman

eddiefiola wrote:

@Herbsman tbh I don't think they did a bad job they just used a system from Specialized which I don't think 'fits' everyone, the post isn't about the money

That's the problem, they shouldn't be using a 'system' as such, they should do the fitting based on how comfortable the rider feels, not based on some numbers that have been 'calculated'