Back pain and stem length/saddle position

I'm on a Supersix which has the same geo as the CAAD 10 having moved from a Synapse. The Supersix is a 50 and the Synapse was a 54 which looks like a massive change in sizes but the top tube difference is only 15mm. The cannondale racing geo is stretched out so a 56 CAAD 10 could well fit you for reach as well as a 58 Genesis. The head tubes are relatively short however and I've found I've swapped upper back discomfort for lower back discomfort! Happens after the ride not during though, which I take some comfort from.

It seems in my case the reason is quite a steep increase in saddle to bar drop, which I am hoping will resolve itself by getting all the spacers under the stem and working on strength and flexibility before trying to move it down. Your situation sounds similar in some ways and those things are free to try first if like me £100+ on a bike fit is out of the question.

I had the same problem on both of my bikes with back pain after riding for about 1h. If you are getting back pain when you are riding it may be an idea to get your back checked out.

Any chiropractor should be able to asses your back and sort out the problem in a few sessions .......

If you're looking for a Retul and are in the Midlands, give dynamic rides a try

Lower back pain is generally caused by cramp in the supportive muscles at the base of the spine.

Now the reason they cramp is because they are working harder than they can sustain.

As highlighted here, there are two answers to your problem; 1. make the muscles stronger so that they can resist the workload being asked of them, 2. change your position to lessen the strain on the muscles.

option 2. is by far the best route in the short term.

In my experience, the pain is caused when the angle in the hip is too extreme, and isolates the stabilising muscles at the base of the spine. This can be caused by a host of reasons, from the saddle being too high, too far forward, more than likely too far back, or indeed the bars being too far away and too low. It can also be that the saddle is too low, and in a way to counter this, you move your body position back, which in turn then makes the hip angle more acute.

So... without seeing you on the bike its hard to say.

it could also be that the bike fit has simply allowed you to engage those muscles in the back for the first time and they are going to need some time.

What you mention about the shoes is interesting...

What size feet do you take? When on the bike, do you hang off the back of the saddle or sit in the middle?

I'm interested in the hand numbness... that is generally because the saddle is too far forward, or the reach is too long... which is kind of counter to the cause of lower back pain... unless you were super stretched out. Which your comments of feeling like the bike is small, kind of goes against.

My 2d-worth: my Cervélo also gave me severe lower back pain when first set up for me. (I do suffer from back pain generally, but this was severe.)

Of all the tweaks tried, by far the best was to swap to an inline seatpost (a Syntace P6). This has pretty much banished the pain.

I surmise the problem with the standard setback post was that I was sticking my arse out too far backwards.

I had exactly the same problem on one of my bikes, with lower back pain after an hour or so in the saddle.

I replaced the standard 120mm stem with a 90mm one (a big change) and that has sorted the problem out.

I'm not expert on bike fit, always relied on trial and error tweaking, to get bikes 'just so'. What you describe to me sounds like being stretched out too much (ie having to bend the lower back more to reach the bars), so a smaller frame and a shorter stem would be better. Your LBS recommending moving the saddle back but shortening the stem seems paradoxical to me, one will stretch you out, the other will let you be more upright.
I don't have time to look them up just now, but what are the relative head tube heights of your various steeds? Again a taller head tube (normally on a larger frame) will sit you more upright, requiring less bend and hopefully less pain.

Retul fittings like Mooleur suggested have a good reputation might help, though if your frame is the wrong size in one way or another, there is probably a limit to how much can be done even with different stems etc.

To add to the comments already posted, can I suggest adding a routine of situps, superman and plank core work? I've found that the stronger my core is the better I've been at adapting to my bike postition (e.g. as I've gradually lowered my stem). The exercises really do work and can completely elimate back pain.

check the handlebar width, my CAAD10 is a 60cm and it came with gigantic 47cm bars, which gave me shoulder and neck pain. Cannondale seem to scale the bar width pretty rapidly. The saddle to bar drop is pretty big too, as the head tube is pretty short. when it fits it's a great frame, I've raced it, ridden 100 miles plus many times and ridden it through the alps and pyrenees three years running.
In terms of lower back pain, a brilliant stretch is to work out your glutes is this one
http://vimeo.com/13350756
I do this about once a week and after hard rides, particularly racing and it really helps, can feel quite amazing in fact.

A CAAD10 will have a different head tube to your Charge & Genesis, probably much shorter, giving a lower drop from the saddle to handlebar. Is the stem slammed? Do you have the stem angled down? Bringing it up might help.

First thing to do is to measure up the bike that is comfy and set your CAAD10 to the same dimensions: reach, bar drop and saddle setback are the things that resolved the issues I had with lower back pain. 10mins with a tape measure and a plumb line will let you know where things need to be moved and dictated what stem you need to buy.

That and doing plenty of hamstring stretches!

EDIT: I'd also recommend a Retül fit. I've not had any problems whatsoever since getting it done. http://road.cc/content/blog/88098-get-fit-get-bike-fit-experiencing-ret%...

I struggled with proper fit after having a regular fitting at my LBS a couple of years ago. Constantly tweaking here and there.

I know it's kind of expensive but I can't recommend Retul fitting enough, if you shop around you should find someone (usually not an LBS but a lot of coaching services do it) that does it.

I'd particularly struggled after damaging my knees and shoulders after a couple of altercations with iron horses, despite the bike being fitted no amount of fettling seemed to ease these issues. Got a Retul done and lo and behold all pain just disappeared, even my power output was higher.

On the saddle, I find if my lower back is hurting it's usually a wee spot too low...but I'm no Dr or expert so probably don't take my advice there! Everyone is different.

I've since bought a new bike and I've tried to fit it the same myself and it's just horrendous, I'll be taking it back for a Retul fit asap!