Upright riding and stability -- a wife bike concern

[icepick_trotsky]

Mrs. Trotsky currently rides this Cannondale:

http://i.imgur.com/5RISOh6h.jpg

I built it up that way because she needs to sit as upright as possible due to a spinal fusion, but she also aesthetically prefers older bikes. And she has a bias toward aluminum for some reason.

This bike as built has a tendency to shimmy at low speed. It kind of feels wobbly, like it's being oversteered. She also describes feeling unstable while descending.

What's causing this? Does the fact that there is basically no weight over the front wheel affect handling or stability?

If I changed the frame, what should I look out for? My inclination is to get a cx bike with slacker angles and bigger tire clearance. I know a TCX with albatross bars would look weird, but might meet her needs better.

Before you tell me, he's not interested in a Rivendell style steel bike. She doesn't like the weight of a steel fork.

[JimmyTango]

I would bet that, as you guessed, there is not enough weight on the front wheel. I had a similar problem with a Soma Rush that my brother handed off to me recently-- he had it built with sparrow shaped bars and a 90mm long high rise stem (he is not a roadie and only used it for the occasional beer run) and it was a wobbly mess to ride. I put a slammed 140mm stem and bars with no rise and it rides like a bike again!

Considering your wife's fit constraints, maybe you could help things out on this bike by:

1) putting a shorter rake fork on it to increase the trail. Try to find a track fork that fits.

2) slightly shift a bit more of her weight forward without increasing hip angle (in other words- keep her back in the same position relative to the pedal stroke while shifting just a bit of weight onto her hands) by simultaneously moving the saddle forward (and up) a bit, the stem a touch lower and longer, and/or maybe some bars with less back sweep.

I think that if you can find a fork with 5-10mm less rake and switch the bars for something slightly less rearward swept (the "Noah's Arc" bars come to mind as an option that might still fit her style but provide a slightly more forward position) you'll make a noticeable difference.

[Ken Robb]

If she grasps the bars farther forward does it feel more stable?

[velofinds]

Shame the ride leaves something to be desired. Aesthetically you did a great job :banana:

[CNY rider]

I'm at work and the picture won't load.
But I have had similar symptoms with improperly installed or maintained headsets. May be worth checking.

[David Kirk]

My guess is not enough weight on the front wheel combined with the near zero offset of her hands relative to the steering axis. The lack of offset of the hands forward of the steering axis gives her less leverage over the steering. It also makes it so that a very small movement of her hands has a real effect on the steering angle. Picture putting a 140 mm stem on there and how much further her hands would need to travel for a given steering angle and you might see how it works.

These two things combined could make for a challenging package.

dave

[Mark McM]

My guess is not enough weight on the front wheel combined with the near zero offset of her hands relative to the steering axis. The lack of offset of the hands forward of the steering axis gives her less leverage over the steering. It also makes it so that a very small movement of her hands has a real effect on the steering angle. Picture putting a 140 mm stem on there and how much further her hands would need to travel for a given steering angle and you might see how it works.

I agree with those that mention lack of weight on the front wheel. The affect of trail is greatly influenced by weight on the front wheel - the less weight on the front wheel, the less stability that trail provides.

However, I'm not sure I agree that stem length is a problem. The steering action is different with a short stem, but it isn't necessary less stable. As an example, look at downhill MTBs: These typically have very short stems, and often use back swept bars, and yet these bikes are stable enough to ride at speed on very steep, rough terrain. (Yes, there are more difference between a downhill MTB and a road bike, but it shows that a long stem is not necessary for stability).

[yinzerniner]

I agree with those that mention lack of weight on the front wheel. The affect of trail is greatly influenced by weight on the front wheel - the less weight on the front wheel, the less stability that trail provides.

However, I'm not sure I agree that stem length is a problem. The steering action is different with a short stem, but it isn't necessary less stable. As an example, look at downhill MTBs: These typically have very short stems, and often use back swept bars, and yet these bikes are stable enough to ride at speed on very steep, rough terrain. (Yes, there are more difference between a downhill MTB and a road bike, but it shows that a long stem is not necessary for stability).

But isn't that why they also use super wide bars, so the offset of the hand position from the steering axis is as far out as possible for maximum stability?

[Mark McM]

But isn't that why they also use super wide bars, so the offset of the hand position from the steering axis is as far out as possible for maximum stability?

Yes and no. The wide bars are not so much to enhance the inherent stability of the bike, but to fight the torques generated on the wheel by rough terrain on wide knobby tires. For example, on smooth pavement I can descend on my road bike at 30 mph without my hands on the bars (zero steering torque). While I'm too chicken to go faster no handed, I regularly go up to 50 mph with my hands on the bar tops squeezing against the stem (very little steering torque). But if descended on a rough trail at the same speeds, the terrain would be continually grabbing at the wheel knocking it out of line, and I'd have to apply a significant steering torque to keep the wheel straight. (And this is true even though MTBs have substantially more trail than road bikes.)

[David Kirk]

But isn't that why they also use super wide bars, so the offset of the hand position from the steering axis is as far out as possible for maximum stability?

Yep. Wide bars and short stem work together on an MTB because you are still getting your hands far enough away from the steering axis to give the needed leverage.

Where do you instinctively put your hands when going fast downhill or on rough roads on a road bike? On the tops? Not usually....even if you spread your hands as wide as you can on the tops the offset or steering lever is still small. So you typically go to the hoods or drops and this is in part to lengthen the lever between your hands and the steering axis.

Stem length on a road bike is not just about fit or weight distribution.

dave

[Mark McM]

Where do you instinctively put your hands when going fast downhill or on rough roads on a road bike? On the tops? Not usually....even if you spread your hands as wide as you can on the tops the offset or steering lever is still small. So you typically go to the hoods or drops and this is in part to lengthen the lever between your hands and the steering axis.

But stability on a road bike (smooth roads) isn't about leverage on the handlebars. If it was, then the solution to a speed wobble would be wider handlebars. You mention going to the hoods or drops on rough roads - this actually does two things: As you say, it increases leverage on the handlebars. But it does something else perhaps more important - it decreases steering changes for a given hand movement. In other words, when you hit a bump, and your body and hands jerk, a smaller change in steering results for a given hand jerk.

With narrow tires, even rough roads generate little steering torque on the handlebars. The reason is simple - a torque is a force acting on a lever arm, and the contact patch of road tires is so narrow, that there is little lever arm to generate a steering torque. I've demonstrated this to friends by riding no-handed over a set of railroad tracks that are at a 45 degree angle to the road - the wheels go up and down over the tracks, but because the tire patch is so narrow, the front wheel turns very little. This is quite the opposite of wide knobby tires - when the side knobs grab the edge of a rut or rock, there is enough lever arm to generate a significant steering torque, and so a wide handlebar is needed to help the rider fight this torque.

[cachagua]

Wide bars and short stem work together on an MTB because you are still getting your hands far enough away from the steering axis to give the needed leverage...



I think there's another factor in play here. Getting your hands far away from the steering axis side-to-side is one thing, but in addition, getting your hands forward of the steering axis helps stability too. Your weight, as you lean forward on the bars, has a similar effect to trail at the other end of the axis: as the bar swings around, it lifts you, so it makes things tend to stay straight. Therefore I think a little more stem extension, all other things being equal, is going to calm a bike down more than a little less.

Also you're in a better posture to swing your weight from side to side when you're leaned more horizontally, in contrast to basically pivoting above the seat when you're completely upright. (Obviously most people's riding positions are somewhere between these extremes.)

But: what can you do about this little gem you've got? (I mean the bike.) I wonder if trying different bar heights, to find the place where the greatest extension is comfortable, might be a step toward optimizing things.

[OtayBW]

Considering your wife's fit constraints, maybe you could help things out on this bike by:

1) putting a shorter rake fork on it to increase the trail. Try to find a track fork that fits.

Increasing the trail would make the steering 'less certain' (e.g., more wobbly) at low speed, no?

[Mark McM]

Increasing the trail would make the steering 'less certain' (e.g., more wobbly) at low speed, no?

You might be referring to 'flop', the tendency for a wheel to want to turn further to side when it is steered off center, which is predominantly a low speed phenomenon? Yes, flop can increase with increased trail, but flop is also greatly affected by weight on the front wheel. Since the front wheel on this bike is under loaded, there will probably only be a negligible increase in flop with a moderate increase in trail.

[CMiller]

I would totally look for a cross bike instead. Older aluminum ones can be found affordably. Slacker geometry, longer top tube, slightly fatter tires, would likely all contribute to a more comfortable and stable ride. On my upright bikes I use a much longer stem too.

[smead]

It looks like the quill stem is a good 4" above the top of the fork/HT. If that is not one of those Nittos with a really long quill body, you might be getting some flex & instability from the quill not being far enough down in the fork. Either way it is high enough to make me believe that's part of the stability issue. A frame with a lot longer HT would probably fit her needs better.

[prototoast]

The simplest solution I can think of, that doesn't involve a new bike (or major changes to this bike) would be to buy a front rack and put something heavy on it.

[Ken Robb]

The simplest solution I can think of, that doesn't involve a new bike (or major changes to this bike) would be to buy a front rack and put something heavy on it.

The first post states that she didn't want the extra weight of a steel fork.

[yinzerniner]

The first post states that she didn't want the extra weight of a steel fork.

Also don't see how that would be in any way safer as it'll add more weight to the front but at a very high point, so while the shimmies might go away the bike will want to run off the road during turning and stopping.

[prototoast]

The first post states that she didn't want the extra weight of a steel fork.

I stayed within the letter of the requirements, but perhaps not within the spirit.

[Peter P.]

Obviously, you and your wife have found that a road bike geometry does not pair well with a comfort bike riding position.

You need to emulate the geometry of a hybrid or comfort bike.

[buddybikes]

How many levels did she have fused? I had my L4/5 fused and got back on my firefly just raising stem 5mm. Is she overdoing it? I certainly don't know her situation of course. May need my L3/4 done, but even then I am confident won't need much more than flipping stem or perhaps shorten it a bit.

If you really like riding together, work with a good fitter and/or framebuilder.

Good luck

[icepick_trotsky]

Pretty major. L2 to T2.

https://i.imgur.com/qJJu12Cl.jpg

[buddybikes]

Yikes! Invest in a fitting, one with medical background. Fitwerx (MA, VT, NJ) - Haven't used them but when I spoke regarding my issues (also diabetic neuropathy and the back issue) they seemed highly educated. Of course don't know where you are located...

[charliedid]

If she can't ride a road bike stop looking at road bikes and get her one of these.

Sorry for her pain.