Would you agree with me?

rrsodl

I have been suffering from lower back pain after riding my new bike and I think I have figured out what is causing the problem.

I have two road bikes, old bike is built around a Reynolds 351c and it is very comfortable, however, my new bike with a Ti frame , which is set up with the same measurements as the old bike. I have double, triple, etc measured the settings of the two bikes and they are nearly the same.

The differences are very minor.

The cranks are 5mm longer on the new bike

The crank set on the old bike is a 39 - 52 and on the new bike is compact ie 34 - 50

I think I have been riding with too high cadence and I keep bouncing on the saddle. The new bike has a Swallow Ti rails while the old has a Swallow Chrome rails. I'm finding difficult to adjust to the compact crank set. The Ti saddle definitely bounces much more than the standard one.


Now that I have figured that out I will make sure that next time I go riding I will not ride in too high cadence.


So, would you agree that the lower back pain could be caused by the bouncing on the saddle?

declan1

If you're bouncing on the saddle, your saddle height is probably wrong, in addition to your cadence being too high.

I used to have lots of lower back pain, but since lowering my stem as low as it will go it has gone.

P.S. I think you're meaning Reynolds 531?

rolf_f

Not sure why you should think you are in too high a cadence on the new bike. You should tend to ride the same cadence whichever bike you ride. The only way that the new bike might force you into a higher than customary cadence is if you are spinning out in top - which is reasonably unlikely.

At all other times, the crankset config shouldn't make much difference.

It could be something subtle. For a start, when measuring the two bikes did you take frame angles into account? Have you tried swapping the saddles round? And as Declan says, bouncing on the saddles is often a symptom of too high a saddle. The longer cranks would require the saddle to be proportionately lower as well. And did you check stem length and handlebar reach?

cougie

I doubt its that.

Your cadence shouldnt change really - just because you're on a compact - the gear you select on the cassette should bring your cadence back to your usual level. And its easy to know your cadence - all you need is a stopwatch and count the revs.

If you find yourself bouncing - go up a gear and increase the resistance ?

I'm sure the frame angles will be different too - and what about the wheels and tyre pressures ? Are they the same ?

displacedaussie

If your cranks are 5mm longer you'll need your saddle 5mm lower (as your leg needs to reach 5mm further at the bottom of the pedal stroke).

Bozman

When I swapped from a std chainset to a compact my cadence increased, after spending 18 years on a standard it took ages to find my natural rhythm again and my cadence has risen, I was generally plodding along on a 53/19-18 and now I'm 50/19-18 when you'd expect it to be lower.
A mate has just made the swap after 25 years and he really can't get on with it, the new Moda is in the garage and he's back out on his old Bianchi and the chainset gets swapped next spring.

rrsodl

Bozman wrote:

When I swapped from a std chainset to a compact my cadence increased, after spending 18 years on a standard it took ages to find my natural rhythm again and my cadence has risen, I was generally plodding along on a 53/19-18 and now I'm 50/19-18 when you'd expect it to be lower.
A mate has just made the swap after 25 years and he really can't get on with it, the new Moda is in the garage and he's back out on his old Bianchi and the chainset gets swapped next spring.

It's a bit strange the feeling of riding a compact and it does take some get used to. I still feel I don't know how to ride a compact.

The new bike's top tube is 1 cm shorter that the old one, hence a stem that is 1cm longer. The handlebars are identical.

Angle from nose of saddle to BB are the same. Distance from nose of saddle to bars is the same. Angle from saddle to handlebars is the same ( Bars are 1" lower than the saddle)

Both bikes have a 73 deg headtube.

The saddle high was measured as I do on all my bikes. Sitting on the saddle with the crank perpendicular to the floor and the s small angle between ankle, knee and hip of about 20 to 25 deg.

It makes sense that a saddle too high might contribute to the bouncing, having said that, the Swallow Ti is known to be quite bouncy. In any case I will lower the saddle a little bit and see how it feels.

I might lower the bars too at some point. Sheldon Brown suggest an arched back http://sheldonbrown.com/pain.html which does make sense to me.

If I had a turbo trainer I could video me riding and compare both bikes.... A good enough reason to tell my wife why I turbo trainer would be a good idea

I don't know what it is but both bikes don't feel the same, there is a very small difference which I'm jet to find. My old bike has a broken in Swallow that feels like a sofa the Swallow Ti is not quite there yet so that is the first think I notice when I get off one and mount the other.

The new bike looks about 3/4" smaller that the old one but that shouldn't make any difference I think.

Both on 23c tyres with 110 PSI.

unixnerd

If you're getting lower back pain I'd drop the saddle 10mm and give it a whirl.

rrsodl

unixnerd wrote:

If you're getting lower back pain I'd drop the saddle 10mm and give it a whirl.

Well, I re-checked the saddle hight for the N time and it's the same as in my old bike. In other words 5mm lower to allow for the 5mm longer crankset. Saddle hight measured from top-centre to BB.

Watching a video on youtube about bike fitting, one mentions that a saddle that is too far back would cause lower back pain, hence I pushed the saddle about 7.5mm to the front and I rode the bike for 10 miles. Not 100% sure the problem is gone as I still have some pain, however, I felt I could have continued riding, On the other hand, on my previous ride, before shifting the saddle forward, I felt the pain getting worse so I came back after 6 miles.

Hopefully I'm on the right track. I will try a 20 miler tomorrow if I can spare the time.

unixnerd

The knee over pedal spindle (KOPS) method isn't perfect but is a good first guess at saddle fore/aft position. I just assumed it was OK on my new bike and had a bit of pain (can't remember where!). KOPS adjustment solved it.

Camus

When I was setting up my new bike I had a bit of pain at the right side of my lower back that always appeared after 2 hours + in the saddle, I moved my saddle forward and it went away, so it could be that or perhaps your stem is too long?

rrsodl

Camus wrote:

When I was setting up my new bike I had a bit of pain at the right side of my lower back that always appeared after 2 hours + in the saddle, I moved my saddle forward and it went away, so it could be that or perhaps your stem is too long?

Well, the stem is 1cm longer than the one on my old bike, having said that, the top tube is 1 to 1.5 cm shorter on my new bike. So the overall length is about the same on both bikes.

I'm now more convinced that moving the saddle forward probably did the trick. About 8 hours have passed since the ride and the pain is the same I felt yesterday or the day before, if anything it's a little better.

colsoop

RRSODL wrote:

Well, the stem is 1cm longer than the one on my old bike, having said that, the top tube is 1 to 1.5 cm shorter on my new bike. So the overall length is about the same on both bikes.

I'm now more convinced that moving the saddle forward probably did the trick. About 8 hours have passed since the ride and the pain is the same I felt yesterday or the day before, if anything it's a little better.

If the stem is 1cm longer and the top tube is shorter your essentially slightly more stretched than the previous bike depending on the angles of seat post and head tube.

Moving the seat forward would alleviate this a bit but could also cause you to put more weight through your wrists and shoulders.

speshsteve

so the bikes geometry isn't the same then.....

I'd go and get a proper bike fit, 10 mm here or there makes a huge difference.

MountainMonster

You can't really measure things from 2 different bikes with different geometries and apply the same to each. You need to work with the frame.

rrsodl

colsoop wrote:

RRSODL wrote:

Well, the stem is 1cm longer than the one on my old bike, having said that, the top tube is 1 to 1.5 cm shorter on my new bike. So the overall length is about the same on both bikes.

I'm now more convinced that moving the saddle forward probably did the trick. About 8 hours have passed since the ride and the pain is the same I felt yesterday or the day before, if anything it's a little better.

If the stem is 1cm longer and the top tube is shorter your essentially slightly more stretched than the previous bike depending on the angles of seat post and head tube.

Moving the seat forward would alleviate this a bit but could also cause you to put more weight through your wrists and shoulders.

Well, it seems that moving the saddle forward was the right thing to do. I did 26 miles today and felt good. The pain is nearly gone by now, I can only feel it when lifting objects.

The difference between saddle nose to bars Centre is about on both bikes 4mm. The most important thing for me is that the bike feels good now, like I found the correct centre of gravity.

The next test will be to go for a 70+ miles ride. I'm now confident that I'll be OK.

FlacVest

RRSODL wrote:

colsoop wrote:

RRSODL wrote:

Well, the stem is 1cm longer than the one on my old bike, having said that, the top tube is 1 to 1.5 cm shorter on my new bike. So the overall length is about the same on both bikes.

I'm now more convinced that moving the saddle forward probably did the trick. About 8 hours have passed since the ride and the pain is the same I felt yesterday or the day before, if anything it's a little better.

If the stem is 1cm longer and the top tube is shorter your essentially slightly more stretched than the previous bike depending on the angles of seat post and head tube.

Moving the seat forward would alleviate this a bit but could also cause you to put more weight through your wrists and shoulders.

Well, it seems that moving the saddle forward was the right thing to do. I did 26 miles today and felt good. The pain is nearly gone by now, I can only feel it when lifting objects.

The difference between saddle nose to bars Centre is about on both bikes 4mm. The most important thing for me is that the bike feels good now, like I found the correct centre of gravity.

The next test will be to go for a 70+ miles ride. I'm now confident that I'll be OK.

Well it seems like you've found out the problem, but if I were to see this topic sooner, I would have instantly said to move your saddle forward. Moving it forward moves your center of gravity forward, which will put LESS strain on your lower back.

I have always had my saddles as far forward as they can go, due to my bars being flipped and spacers removed; I'm stretched out more, so I need to move the saddle forward to make up for this; this is the reasoning for the steeper seat angle on TT bikes. You have more weight up front, and moving that saddle "forward" allows for the CG to be where it needs to be; the aero position warrants this. (In lamens terms of course)

Seeing that the, what crank is longer and you had to move the seat down, you also have weight distribution of the bike; if the bike is lighter, then less force will needed to be pressed downwards to move it; simple physics. That upwards/backwards force the pedals put on your legs keeps you in the saddle.

If the bike is lighter, the newer bike, you WILL bounce if everything else is the same, because less force is needed to push the pedals; this with a longer crank will allow more torque on the spindle, which moves the bike further with each press, ALSO allowing LESS force for the same amount of forward push.

That might be why you bounce. But I just pulled that out of my butt, so feel free to pick this apart or disregard in any way.

Bozman

FlacVest wrote:

RRSODL wrote:

colsoop wrote:

RRSODL wrote:

Well, the stem is 1cm longer than the one on my old bike, having said that, the top tube is 1 to 1.5 cm shorter on my new bike. So the overall length is about the same on both bikes.

I'm now more convinced that moving the saddle forward probably did the trick. About 8 hours have passed since the ride and the pain is the same I felt yesterday or the day before, if anything it's a little better.

If the stem is 1cm longer and the top tube is shorter your essentially slightly more stretched than the previous bike depending on the angles of seat post and head tube.

Moving the seat forward would alleviate this a bit but could also cause you to put more weight through your wrists and shoulders.

Well, it seems that moving the saddle forward was the right thing to do. I did 26 miles today and felt good. The pain is nearly gone by now, I can only feel it when lifting objects.

The difference between saddle nose to bars Centre is about on both bikes 4mm. The most important thing for me is that the bike feels good now, like I found the correct centre of gravity.

The next test will be to go for a 70+ miles ride. I'm now confident that I'll be OK.

Well it seems like you've found out the problem, but if I were to see this topic sooner, I would have instantly said to move your saddle forward. Moving it forward moves your center of gravity forward, which will put LESS strain on your lower back.

I have always had my saddles as far forward as they can go, due to my bars being flipped and spacers removed; I'm stretched out more, so I need to move the saddle forward to make up for this; this is the reasoning for the steeper seat angle on TT bikes. You have more weight up front, and moving that saddle "forward" allows for the CG to be where it needs to be; the aero position warrants this. (In lamens terms of course)

Seeing that the, what crank is longer and you had to move the seat down, you also have weight distribution of the bike; if the bike is lighter, then less force will needed to be pressed downwards to move it; simple physics. That upwards/backwards force the pedals put on your legs keeps you in the saddle.

If the bike is lighter, the newer bike, you WILL bounce if everything else is the same, because less force is needed to push the pedals; this with a longer crank will allow more torque on the spindle, which moves the bike further with each press, ALSO allowing LESS force for the same amount of forward push.

That might be why you bounce. But I just pulled that out of my butt, so feel free to pick this apart or disregard in any way.

Slightly hijacking this post, but i thought that i'd read somewhere that - moving your saddle forward can lead to an arching back which will end up giving you lower back pain?(taken that you don't get a longer stem).