My stearing feels "twitchy"
 

A couple months ago I picked up a gently used older 49cm Specialized Roubiax. I really like the bike overall, but one thing I noticed is that the steering feels much more "twitchy" than either of my other two bikes (50cm Trek "Lexa" and WSD). I really don't know much about bicycle dynamics but I am pretty handy. The thing I did notice is that neck part, where the handlebars bolt to the fork tube, seems noticeably shorter on the Specialized. Is this why it feels the way it does? Would changing that part make it feel more controllable?

The part you're referring to is called the stem. If the stem on the roubaix you bought is shorter than what it came with, then yes, the bike would be twitchier.

Like smashndash said, if the stem is shorter than stock, the handling might seem twitchy. Since this is a smaller frame often ridden by shorter riders it is entirely possible that the previous owner moved the bars closer to the steerer tube by adding a short stem. Look up pics of your bike online and see if it compares.
Another thing that can seem to make a bike twitchy is if the headset is binding.

Before blaming a shorter than OE stem one would need to study the front end geometry of the 3 bikes in question. A more vertical head tube angle and shorter trail dimension could give the "twitchier" feeling.

This is very possible. The difference between a friends Specialized Roll and my Giant Sedona's steering Sensitivity is shocking. Both have stock stems but the Sedona has noticeably less fork rake and perhaps head tube angle. It is so much more twitchy then the Roll it takes a few minutes to get used to.

You have to experience it fist hand to appreciate how a small change in front end geometry can dramatically change a bikes handling.

I much prefer the Rolls increased stability, But the Sedona isn't a problem once you get used to it. There are probably benefits to faster steering, perhaps it's preferred for mountian bikes. The mountian bike my Sedona replaced also had fast steering. But I don't think that fast steering is best for to the average recreational cyclist.

+1. The Roubiax has more of a "race" geometry designed to handle quicker than your Trek Lexa & WSD (i.e. twitchier). A quick handling bike can be a fun ride too but some, like me, find it more tiring on a long ride having to make small steering corrections all the time. You may grow to like it after putting in some miles but don't spend a lot of money trying to make it something it's not. If you like the way the bike fits now changing to a longer stem will ruin the fit for you as well as possibly having no effect in improving the handling.

The first thing I would look at is how you are set up on the bike. Seat set back, bar/seat heights and reach. If these are different than some of the handling differences are from that. One trick I do every so often is to line up my bikes side by side with their seats even WRT to each other. Toe clip straps around the bars help keep the bikes from falling over. Standing from the side and sighting along the seat tops, tips than dropping down to the BB and cranks and ending at the bars one can see any positional differences quite readily.

Otherwise I pretty much agree with the other comments about stem lengths and steering geometry intentions. Andy

I changed the 100mm stem to a 70mm stem on my Tarmac and the bike did seem a little twitchier on twisty downhills, but I quickly got somewhat use to it. Three or so months later when I changed the 42 cm bars to 38 cm bars, I all of a sudden seemed more perfectly in tune to going down those twisty trails and making more rapid changes in my line for hazard avoidance than ever before and even when the bike had the 100mm stem and 42cm bars.

So while I've never heard it discussed before, I'm wondering if there is something to stem length vs bar width.

OK, based on the replies so far I went out to measure mine. Unfortunately, I don't have any measuring device that measures in metric units. However, fortunately, all three stems have the length stamped into them. All three are Bontrager. Both the ones on the Treks are 75mm, but the one on the Specialized is 70mm. Could that 5mm really make a noticeable difference? Or is it more likely the geometry? It doesn't really bother me too much but I would like for there to be less difference in the way they handle. I pretty much only ride paved roads and prefer a little more stability.

I've changed stem length by a lot more and not noticed a handling difference. I really like Andrew Stewart's idea. Line them up side by side with the front axles/wheels even and strap them together. Then start comparing set up, head tube angle, bottom bracket height/position and wheelbase length (another factor). I think you'll find some significant differences that will explain the feel of the bikes. I'd read this article before starting: https://cyclingtips.com/2018/11/the-...-the-steering/

Give it a few weeks, and keep riding. Years ago, my fancy new bike was quicker steering, "twitchy". But after some rides, I stopped noticing it. I think riders reflexes adapt until the bike feels normal. (Kind of like learning to ride! That's very strange and hard to do at first.)

It is definitely the geometry. When I first got my Roubaix I wondered if I had screwed up buying a bike with a more race style geometry (less rake) because it felt super twitchy compared to my other bikes. But now that I've been riding it for a while I actually prefer the feel of it over the more relaxed geometry bikes. Of course, if I drink more than a pot of coffee in the morning before going out for a ride all of my bikes feel twitchy. Ride it awhile and it will grow on you.

Thanks guys. I'm not saying it's bad, and I'm certainly not going to alter or get rid of the bike because of it. But if "toning it down" a little was as easy as changing that stem piece out, I would probably give it a try just to see what happens. What I may do regardless, is just switch one of the 75mm stems on a Trek and the 70mm stem on the Specialized and see if that brings them closer together. That way I can get an idea of whether a change will be worth the effort with no investment. I'm thinking that would be really easy to do and cost exactly zero $$$.

actually, no. Roubaix's are known for their relaxed geometry and more compliant ride.

I'd vote for this first, not knowing what your other bikes are you are comparing to. What you call twitchy might be what some of us other's perceive as responsive. My '78 Raleigh Competition GS was way more responsive or sporty, than my Schwinn Paramount. The Paramount had a longer wheelbase and more trail on the front wheel, so it felt like a solid machine built for the road. But not something that I'd be comfortable in close quarters and having to maneuver suddenly. My new Tarmac is even sportier still and I like that.

You also might be just feeling the difference of the way the forks transmit the road surface too you and it's thrown off the way you feel the road.

Whether you might can change the stem length or bar width is only going to be an experiment that might not work for you. You'll also be changing your fit if you change the stem length. And for some a little might be a lot.

If you know the year, make and model and size of your bikes, then search for the geometries of them and then look at the trail, wheelbase and head tube angles.

There are some sites that have vast databases containing many bikes. And some let you compare side to side. Others will need to tell you what they are.

Of course being a used bike, do you really know that it's in the great condition you think it is in? Maybe the previous owner ran straight into a brick wall and something got knocked out of whack.

I looked over the Specialized pretty thoroughly because is my first CF bike. Not like I'm an expert by a long shot, but I saw no evidence of any damage. I'm sure it was laid down once, but besides scraping up the finish on a couple components, the bike is in near-new condition.

Again, it's not a big deal, and it's not something I feel I need to "fix". I'm just curious why this one feels the way it does. And if toning down that responsiveness was as simple as swapping out that stem piece, I probably will do it at some point just because.

I doubt that a 5mm difference in stem length will make a noticeable difference.

Pretty sure you have Caged Balls or Sealed Bearings in your head set but you may want to check. I had a twitchy head set on an old Peugeot and found the previous owner had used too many Loose Balls in the head set when he rebuilt it.

I never really gave the fast twitchy steering on my Giant Sedona much thought until I had swapped bikes with my friend's Specialized Roll. It was only then I realized how much difference the front end geometry can make in handling. I'm guessing the Roll, Being a comfort bike is designed to provide a more stable ride so It's not surprising it is so different.

As a recreational cyclist I don't find the faster steering to be any more fun, stable, or requiring any more attention then any other bike. It only takes a few minutes on the bike to get used to it, and after a few hours I just take it fore granted.

Yes, do that. But with a 5mm difference, don't expect to feel anything. See if you can get ahold of a 90mm stem, if only to make a significant enough change that you might be able to tell. You also might try a wider handlebar.

This is probably the handling characteristics of the bike. I wouldn't go messing around with fit/reach in order to adjust handling.

Have you taken measurements to make sure your bikes are all fit about the same way? Saddle height, saddle fore-aft (based from the bottom bracket), reach, etc.

And are you certain the headset isn't loose. I wouldn't think the already short stem came on that bike originally. So whomever replaced it may not have known how to properly adjust the headset bearings. If you are going to change the stem, then do you know how to properly adjust them?

No measurements. Eyeballed it. That's all I've done so far.
I have not. Guess I'll have to find a video on that.

The 70mm stem might be the original, the 49cm Roubiax had a short stem in some years.

Not if it's Bontrager branded.