Bicycle stability question
 

I have a question about the riding characteristics of one of my bikes, and I figured the best person to ask about this problem would be a framebuilder.

I have ridden a lot of different bikes in my time, but all but one have been pre-90's. Colnago, Gios, Rossin, etc. The only newer bike that I own is a 2005 Fuji Professional which I bought new a few years ago, just so I would have something a bit newer.

My problem is that its ride is very unstable. It is very challenging to ride at slow speeds no handed. I know what you're thinking, it's an operator problem. But I don't have a problem riding any other bike no handed, just this one. I once rode my Rossin 26 miles, uphill, no handed, because my coach told me that I used my upper body too much. So I can assure you, I'm quite capable of riding no handed. This bike just seems to be unstable for some reason.

I've been thinking of getting a new bike that doesn't have this problem, but after comparing the geometry of most higher end bikes, the Fuji seems to be fairly typical. So any ideas about what's causing the instability? Is it a common problem with newer carbon frames?

I would go to my LBS and test ride a few, but where I live is fairly isolated, and I would have to travel about 400 miles one way just to test ride a bike, which I'm not about to do.

Any ideas about this problem, or any suggestions about a good choice of off the shelf, high end racing frame would be appreciated. What's a good all round racing frame, for someone who's still in fairly decent shape, and loves hills?

:wtf:

I doubt any of the later model carbon fiber frames are gonna ride as stable as the older steel frames you mentioned. Most all of them are just built as tight, light, and stiff as possible. The chainstays are short and the forks are getting so light its I very seldom lay on the front brakes hard. As a road racer I always loved the carbon frames because they are light and stiff and good for racing however after getting into building frames with steel I realized that there really is nothing that compares to the ride of a steel frame and fork. A steel fork truly makes a difference to me, of course I would have a carbon fork on my road bike just because I was trying to shave some grams, but the ride quality is lacking. I don't have any idea what the problem is with your bike. Have you checked it for any cracks or damage of any kind? It sucks that you live so far from any bike shop, its hard to believe you live that far from one. While every frame company has there own marketing strategies I personally think that alot of the carbon frames out there all ride similar and it would just be trial and error until you find one you like. They should all be more stable than what you are describing though. I don't have any beefs with carbon and am working on building some carbon frames when I get time but I don't think you will ever find anything to ride exactly like your older bikes. I would sell the Fuji for what you can and try another brand. I was always partial to Look frames but that is just my opinion. It mostly depends on what fits and feels good to you. Good luck with it. Chao.

I am not a frame builder, just a lurker trying to do as much research to learn about building a frame in the near future, but I may have some insight on your problem from past experience. Check out your headset. I had a bike that was parked for many years with the tire pointing straight, and it felt like there was a detent that would make the bike only want to go straight. Replaced the headset, and it handles so much better. I have herd that headset bearings, that are dry, worn, needing adjustment can make steering very sketchy.

This may be too obvious, but:

Is the rear triangle alignment OK?
Is the fork straight?
Does the bike have a really steep head tube angle?

meech151, carbon frames may indeed have a less stable ride than the old steel frames, I don't know, my Fuji is the only carbon frame I've ever ridden. But I can't believe the stability of my Fuji is normal.

As far as I can tell there aren't any cracks, and the geometry is fairly standard, except for possibly the head tube and the fork rake. I've noticed that most carbon forks have a slightly shallower head tube angle, and their forks have very little rake. Most carbon forks have a slight bend at the crown, but not what I would call rake. My Fuji's fork has a slightly steeper head tube and a bit more of a traditional steel fork bend. Kind of similar to a Scott. But the Scott's still have the bend higher up on the forks, and not the traditional rake. I'm not sure if this could be the cause of the problem.

The only other glaring difference is the top tube. Most carbon frames have the sloping top tube, but the Fuji has a horizontal top tube. This makes the seat stays a bit steeper. I don't know if that could put a bit more weight on the rear wheel then other carbon frames, when riding no handed. I was thinking that maybe that combined with less forgiveness compared to a steel frame, might contribute to the handling problems. But I don't know.

I was hoping a frame builder could give me some insight.

I know, it sucks to live that far from a bike shop. I don't just live far from a local bike shop, I live far from a local bike rider. I rode about 250 miles per week this summer, and only once saw another rider who could honestly be classified as a cyclist. Not a racer, just a wannabe tourist. Around here it's just kids and parents riding around town on cruisers and BMX bikes. It's 75 miles to the nearest bike club. Makes it difficult to stay motivated to train. But I try. I keep hoping that someday I'll get the chance to beat Lemond. I think now I could take him, he doesn't look like he's in too great of shape.


e3954is, thanks for the input, but it's not a headset problem. The headset doesn't seem to have any problems, turns smooth and free. Trust me, I've ridden quite a lot on bikes with pitted headsets. I was never much on bike maintenance when I was younger, which is why Ron Kiefel gave me the nickname "Shake n Bake". Because he said that I cooked without grease. But then my dad didn't own a bike shop. I had to pay for my bike parts. (Most of the time)



Al Criner, as far as I can tell everythings straight, and nothings cracked. The head tube is a touch steeper than a lot of carbon frames, which could have something to do with it. It also has a more traditional fork rake than the straight forks you see on most carbon frames. Do you think that could be a source of the problem?

So any ideas anybody?

Very well could be too much rake and too little trail. Get out your angle-gauge and measure the actual head-tube angle. Then measure the rake and calculate the trail.

BINGO!!!!!!!

Measured the trail on the Fuji and compared it to my other bikes. The trail on the Fuji is about half what it is on any of my other bikes. So I think you've nailed it Danno.

This gives me a means of determining the handling characteristics of any bike that I might choose to purchase online. Being so far from my LBS, and most likely having to make several trips to varying destinations in order to test ride all of my perspective choices, I needed some way of the determining the possible ride characteristics without actually doing a test ride, and this information certainly helps.

I didn't want to end up with another unstable ride.

Thanks Danno, and everybody. I figured framebuilders would be able to figure this out, and you didn't let me down.

Just out of curiosity, where do you live Leech?

So if most "stable" steel stage-race bikes have trail in the 55-60 mm range, your less than stellar carbon bike has trail around 30 mm? That is amazing, a very low-trail carbon road or sport bike!

How are you measuring trail, or calculating it? I've found it challenging sometimes to get a good measurement of offset. And if you don't have a straight-sided head tube (some carbons don't), it'll be hard to measure head angle.

I find that 55-65 mm trail is best for my type of riding, too. Below 50 mm and the bike starts feeling pretty twitchy. Getting a fork with less rake would help, but I doubt that you could make up 20 mm; forks only come in a limited range of rake values. A larger dropout-to-headset length on the fork would also help by changing the headtube angle. Also, I've had putting on a larger diameter front tire helps with no-hands operation. But these are all kludges- best to get a bike of the "right" geometry.