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I've got 3 bikes, cotic soul, ragley mmmbop and pace rc295. All same width bars and length stem. I ride the cotic the most, it's flat here so it's set up xc ish but it's the only one that gives me lower back pain. Did a 20 miler locally yesterday and tried saddle position, moving the seat forward and backwards and nothing seems to work. I ride either of the other two and have no issues whatsoever?
Anyone know what else I coidl try?
Cheers.
Stem length and bar width are a tiny part of the geometry puzzle. You need to look at TT length (This is what you'd be changing by shuffling the saddle around), Reach and Stack too.
If the Cotic is longer or shorter (in reach or TT) than the other two bikes then you could either be overreaching (too long) or hunching (too short). Is the stack height (vertical height from the centre of the BB to the top of the head tube) shorter on the Cotic, that would leave you bending forward too much.
Geometry geeks is a good place to start, search for your bikes and add them to the comparison and you can see where the differences are.
I also use bikegeo.net you have to type all the measurements in yourself, but it does allow you to play with spacer stack height and stem length angle to understand where the handlebars will actually end up.
I had a very similar thing (mid back, lower trapezius) with my 16.5 mk1 Switchback and I eventually conceded that I had it set up too short (effective reach) which was helping cramp up my back when I rode it. I've since stuck a very unfashionable cast ally Giant OE 60mm stem on and it's loads better, to the point I've now got it set up as my long distance trundler.
My skids and wheelies bike is a medium 2016 Trance which, along with the offending 45mm stem from the Switchback, is about the same effective reach.
I did start doing back strengthening exercises at the same time I swapped the stem for a longer one so there may be additional factors but I definitely think the major change was the longer stem, as soon as I rode it I felt less cramped. It's only 15mm or so but it makes a difference.
Also, what generation Soul? The early ones had really slack seat tube angles so work best with shorter (100mm) forks to keep the seat angle sensible even though they may technically be able to take a longer fork. Same as the earlier BFes too.
edit- maybe consider punting the Soul and just enjoying the other two?
it’s flat here so it’s set up xc
Raise the bars?
Do the bikes all have the same saddle? You might be sitting with your pelvis/hips in a different position to keep your crack'n'sack comfy, resulting in your sore back
Strengthening my glutes fixed my lower back pain. If your glutes are weak the lower back takes over the role of extending the hip thus it gets overworked and fatigued, which may be what’s causing your pain.
It's a mk 4 soul with 100mm forks on.
I did change the stem last year so maybe I'll try with the old stem.
Morning I'll have a look at those websites tomorrow, cheers for that.
Got different saddles on all 3, I had a supelightweight saddle on the soul which I thought might be causing it wo put a fabric scoop on and it's no different.
Are the seat tube angles and BB heights the same, and hence are your hips, knees and feet in the same relationship with saddle and pedals. If your feet are different fore/aft with relationship to your saddle you might have a different stress on hams and glutes.
You need to get out the tape measure on the lot of them and work out where there is a big differance.
I had a road bike that did the same to me. It was a reach/drop to handlebars issue for me. My eventual fix was I inverted the stem (angled up) with no change in length which brought the bars up and back.
I'm not sure it's the up and back that's the answer for you but the relative position of bars and saddle would be where I'd start looking for the causes of the back ache.
When making changes I changed one thing noticeably to get an indication of which way round things were wrong (in my case I tried a super cheap 20mm shorter stem still roadie way up). That was worse, so I knew it wasn't too short at that height. I then flipped it wrong way up for roadie - better but not right. Then original stem "wrong" way up. Bingo. It was a bit more faff than that as I also tinkered with handlebar rotation and lever position but hopefully that gives you the idea. With tiny increments at the start I'd have been less sure of the effects.
I always set my fore and aft saddle position relative to the BB as a baseline. I don't use it to adjust reach to any significant amount that's for the right length stem.
As an old barsteward, and a broke back, I can still ride both my road bikes that I've had since my early 20's - race positions. It's taken a while and a chunk missing from my spine, but both are comfy for hours. Tape measure and a bit of time and a note pad.
Seat angle is a big deal. For the same bar stem distance the slacket the seat angle the further forward your feet adding tension to your hamstrings and back
Or put it another way a steep seat angle is used on a time trial bike to rotate its position forward. More aero tuck for same back bend
I set my bikes up to be identical as near as I can get.
The bottom bracket is the starting fixed point. Get the saddle height and horizontal distance back from the bb the same as a comfortable bike.
Then get the handlebars the same distance from the saddle and the same height relative to saddle.
This article on bjke gitting is good. Road and touring oriented but much probably applies to other areas.
Sorry been working last few days. Will do what you suggest tomorrow, pad and paper and a tape measure. I'll use the BB to measure from and see where there's a difference.
Cheers for all the help and suggestions, I'll report back. (No pun intended)