# What makes a bike stable? Or twitchy?



## Zipp0 (Aug 19, 2008)

My '01 steel Lemond Tourmalet is a fairly traditional geometry road frame, with 16 3/8" stays, and an aftermarket carbon fork with rake identical to the original steel fork. For the life of me, I cannot ride that bike no-handed.

Over the winter, I picked up a Taiwanese AL frame, compact geometry, 16" stays, and a straight blade carbon fork. It's a somewhat "racier" frame than the Lemond, I'd say. I can jump on that bike and ride no-handed all day.

This seems a bit counter-intuitive to me. Are compact frames generally more stable? Enlighten me.


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## laffeaux (Dec 12, 2001)

Compact or not has no effect on how a bike handles.

The two greatest factor's are head tube angle (HTA) and fork offset (or rake). Together, along with the wheel radius, they create a measurement called "trail." Do a search for "trail" and you'll get a better understanding of what makes a bike steer the way that they do.

Generally though, if you move the front wheel forward by decreasing the HTA, the bike becomes more stable. Conversely, if you move the wheel forward by increasing the fork's offset you make the bike less stable.


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## darkmother (Feb 18, 2009)

As mentioned, trail is a factor. I've found some bikes that I have owned become difficult to ride with no hands if:
1) the saddle nose is tilted downwards
2) the saddle is way back behind the BB shell. 

Also if your frame or fork is out of alignment, it may pull to one side or the other making hands free riding difficult.


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## fallzboater (Feb 16, 2003)

laffeaux said:


> Generally though, if you move the front wheel forward by increasing the HTA, the bike becomes more stable.


I'm sure you meant to type "decreasing the HTA."


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## Fredrico (Jun 15, 2002)

*Check wheel alignment!*

While a steep head tube angle makes a bike steer quickly, "twitchy," combined with a short wheelbase, any bike can be ridden hands free by simply aligning the two wheels in the same track. :thumbsup:

I have such a bike, 39" wheelbase, 74 degree steering angle, 75 degree seat tube, short 41 cm chainstays, classic road race geometry. When I lean it into a corner, it goes, sometime faster than I want it to. But I can peel a Powerbar wrapper with both hands and the bike forges straight ahead as if on a rail. It descends mountains like a motorcycle.

I have another bike, 40" wheelbase, 42 cm chainstays, with a 73 degree steering angle. I have to deliberately lay it into a corner. It wants to go straight ahead at all times. This is great no hands. I can even steer it left or right with no hands.

Take a long straight edge and hold it up along both front and rear rims. Can you get it to touch on two spots on each rim? If not, the frame is out of alignment, the fork is bent sideways, or most likely, the rear wheel is out of dish, rim no longer centered. This happens when the drive side spokes, tensioned more than the non drive side spokes to get the rim over to center, loosen up first when the rear wheel rolls along, "ovalized" by the torque and rider weight. The rim creeps over to the left.


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## Richard (Feb 17, 2006)

I don't think the intent of the OP was to discuss "frame alignment."

The ability to ride a bike "no hands" (absent a bent frame or fork) is almost always a "trail" issue. I have a hard time explaining to people that the steeper the head tube angle the less fork rake is desireable.

The worst handling bike in my stable from a "no hands" standpoint is my 1972 Raleigh Supercourse with a 73 degree head angle and a 50mm fork rake, despite the long wheelbase.

The best has always been my Falcon with a 74 degree head angle and a 43 degree rake fork, despite a very short wheelbase and a very short "front center."


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## Peter P. (Dec 30, 2006)

Compact frames have nothing to do with twitchiness or the ability to ride no handed.

Your wheels may not be dished correctly on the LeMond. The headset could be pitted. The fork may have too much rake and thus too little trail, requiring more "constant" correction to keep a straight line. The LeMond could have a steeper head angle than the AL frame. The LeMond frame could be out of alignment.


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## Hank Stamper (Sep 9, 2009)

I'd guess fit (where you body weight is in relation to the wheels) plays a role too.


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## ZoSoSwiM (Mar 7, 2008)

Is your center of gravity the same? You could be more top weighted on one bike than the other making it harder to balance.

Can you ride with no hands if you scoot forward or backwards on the saddle?


Check the headset as well.. if it's overly tight or loose it'll give you plenty of trouble.


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## nce (Aug 7, 2009)

I had a similar problem with my bike. When riding no handed the bike would always go to the right. Turns out that the cable housing on the left was long enough to push the bike to the right. I shortened it and am now able to ride no handed.


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## Kerry Irons (Feb 25, 2002)

*Intent*



Richard said:


> I don't think the intent of the OP was to discuss "frame alignment."


Actually, the OP didn't imply much about what he wanted to discuss. Other than the question about compact frames, the essence of his question was "why is one bike harder to ride no-handed than the other." I think that many bikes are hard to ride no-handed because the wheels are not properly dished or square in the frame, or the frame is out of alignment. Lots of people post here about how they have to mess with their wheels to get them to sit squarely in the frame, suggesting alignment to be a common problem.

I think Fredrico made a good point.


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## Zipp0 (Aug 19, 2008)

I'm not sure what it is, but it isn't the wheels, and the frame was recently in the shop of a world-class framebuilder, so I doubt alignment is an issue. And I recetly rebuilt the headset and all is well there. 

I think it just be the nature of the frame and fork combo. I like the frame, but just need to keep a hand on the bars 99.9% of the time.


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## thumbprinter (Jun 8, 2009)

i had a hard time riding no hands until i got a bike fit done and dropped my saddle 2 centimeters. all of a sudden it was easy....


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## nayr497 (Nov 8, 2008)

I've been thinking about something similar too. I'd have to dig up the HT angle and other measurements, but...

I have a Tommasini Diamante with MS Columbus tubing. It rides well and fits me well.

I have a Casati Laser with Genius Columbus tubing. It rides very, very nicely and just feels smoother than the Tommasini. I wonder why? The Tomma is supposed to be even nicer of a bike.

Some factors:
- Tomma is a 1990; Casati is 2005
- same general sizing/setup (saddles, bar levels, hood angles, saddle height)
- Casati does have Vittoria Evo Corsa tires, which are really damn smooth and nice
- Tomma has some Continental GP 4000's; also nice, maybe not as soft and plush

On the same roads, the Casati just feels smooth and nice while the Tommasini feels nice, but a bit more harsh when going over bad roads.

Could it be the wheelset? Both have 32 hole, box rims. Someone suggested the Tomma might have much tighter geometry, but both are pretty tight. Wheels on both right up against the ST. Both have steel forks as well.


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## Fredrico (Jun 15, 2002)

nayr497 said:


> I've been thinking about something similar too. I'd have to dig up the HT angle and other measurements, but...
> 
> I have a Tommasini Diamante with MS Columbus tubing. It rides well and fits me well.
> 
> ...


Everything about a bike, geometries, tubing diameter and thickness, alloy formulas, and sure, wheel and tires, affect the quality of the ride. That's the fascinating thing about bike riding, the intimate connection the rider has with his bike.

If angles are the same, and wheels too, could it be Genius tubing is slightly more "resilient" than the MS? I could be wrong, but seem to remember MS tubing was known for its stiffness, translation, lack of resilience, when compared to other tube sets. Wasn't it designed for heavier riders, or sprinters?

I have SL on one bike. It's really nice on a century, comfy as heaven, but also climbs like a bird. It magically springs back to meet your down stroke, spurring you forward, encouraging the effort.

Have SLX and SP mix on another bike. SLX has rifling inside near the lugs to stiffen it up, but its as thin as SL in the middle, 0.5 or 0.6 mm. SP is slightly heavier gauge tubing used for the chain stays. The heavier the gauge, the less "resilient." That bike accelerates like a bandit, and does everything the SL does, but at the end of a long ride, leaves me feeling a little beat up. It's most comfortable when loaded up with panniers, for which it was designed. Kind of like a truck with beefed up suspension. Carry a load it feels just right, but empty it's a little harsh riding.

Similarly, tubing might explain the difference in feel between your Tomma and Casati. I bet that Tomma rocks when going all out. Good race bikes are like that. They don't reveal their excellence until ridden hard. Lesser bikes start to flex and wander around.


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## TTCC (Feb 27, 2010)

Some bikes may be twitchy at slower speeds, but at higher speeds like descending, become more stable. It is a little trade off from the trail number result. 

As mentioned, rider weight distribution plays into it as well. If your weighted too much to the back, the front gets light ... usually you are upright when riding no-handed which adds to the imbalance.


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## laffeaux (Dec 12, 2001)

fallzboater said:


> I'm sure you meant to type "decreasing the HTA."


Oops... Nice catch. I edited my post.


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## Creakyknees (Sep 21, 2003)

Zipp0 said:


> I'm not sure what it is, but it isn't the wheels, and the frame was recently in the shop of a world-class framebuilder, so I doubt alignment is an issue. And I recetly rebuilt the headset and all is well there.
> 
> I think it just be the nature of the frame and fork combo. I like the frame, but just need to keep a hand on the bars 99.9% of the time.


so, assume you're riding along on nice smooth asphalt on a clear sunny warm day with no wind, feeling good, rolling along nicely, and you take your hands off the bars. What happens?


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## SeattleRider (Jun 17, 2009)

question: am i being too detailed when asking the bike shop guy about trail? is it even something i should be concerned about? since i'm fairly new to road biking and i'm about ready to spend $3K+, i'm very sensitive to everything. 

why does the fork rake on bikes remain the same across the entire size range? some manufacturers do vary the rake in one model and but not another. for example on the tarmac, as the bike frame gets larger, the rake decreases otherwise you would end up with an unstable bike. the rake on a cervelo rs varies from a 49 on smaller bikes to a 43 on the larger. however, the roubaix fork rake remains the same 49 on all sizes and unless you are "average" size you are going to end up with a too much or too little trail. i've read that ideal trail is 5.8 - 6.0.

should trail be a deciding factor? for size 61, the scott i've deduced is 5.6 which seems fine but the size 61 roubaix is 5.3 which i've read can make a bike unstable at high speed. are there enough other compensating factors in the frame for this small trail such as longer chainstays? will this bike be unstable and twitchy in turns or at higher speeds? should i now be considering a new fork with less rake for the roubaix? can i even do that?

thanks.


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## fallzboater (Feb 16, 2003)

What it comes down to, is that you need to ride the bikes. Someone who is not close to your size and weight isn't going to be able to tell you how the bike is going to handle for you. The taller and heavier you are, and the more aggressive you are on technical descents, the more likely you are to experience the death wobble. One of my current frames is a 61cm SL Pro (I'm 6'-3", 195 lb), and the front end is very rigid and responsive, yet it's still twitchier than I'd like (the Roubaix should be more stable). Other bikes have had good stability, but death wobble on the brakes. So, trail is not the only factor. OTOH, if your riding doesn't include high speed descents with hairpins, you may never experience it.


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## Peter P. (Dec 30, 2006)

SeattleRider said:


> question: am i being too detailed when asking the bike shop guy about trail? is it even something i should be concerned about? since i'm fairly new to road biking and i'm about ready to spend $3K+, i'm very sensitive to everything.
> 
> why does the fork rake on bikes remain the same across the entire size range? some manufacturers do vary the rake in one model and but not another. for example on the tarmac, as the bike frame gets larger, the rake decreases otherwise you would end up with an unstable bike. the rake on a cervelo rs varies from a 49 on smaller bikes to a 43 on the larger. however, the roubaix fork rake remains the same 49 on all sizes and unless you are "average" size you are going to end up with a too much or too little trail. i've read that ideal trail is 5.8 - 6.0.
> 
> ...


Good question though yeah, I think you might be too detailed to be asking the salesperson about trail. Don't be put off if the salesperson has no clue about trail; it's a somewhat esoteric dimension the general public doesn't know about. Should you be concerned about it?-Sure; why not? The more knowledge you have as a consumer the more likely you'll purchase a bike you'll be happy with.

Even though you have an understanding of how trail affects the handling of a bike, since you're "fairly new" to the sport, you're really going to have to ride bikes with known trail figures and interpret the results yourself. Only after doing so on bikes with various front end specs will you know what specs and what resultant handling you prefer.

_"why does the fork rake on bikes remain the same across the entire size range?
_

Because it's cheaper for manufacturers to stock only one rake of fork.

People will debate what is the ideal fork rake. Generally speaking, 57mm is considered the middle of the trail figure continuum. +/-2mm won't be readily perceptible. but I can attest to the fact that 5mm certainly is.

There's no such thing as a compensating factor for a low trail bike. Longer chainstays or a lower BB won't mitigate it's steering. I couldn't see buying a new Roubaix and then switching out the fork. I agree with you that the trail figure is low even though the head angle is low for that size frame, which should slow down the steering a tad. I'd say ride the Roubaix if you can, otherwise, seek a bike with a higher trail figure.

My experience with low trail bikes (in the low 50mm range) is, they feel like they're on caffeine. When you are turning or cornering, the front wheel feels like it's on ice. Lowering the head angle to 72 degrees can overcome some low trail bikes' traits, but you're not likely to see such a head angle on a 60cm+ frame.

Most bike manufacturers design their front ends to appeal to the widest customer base possible so they can sell the most bikes, so you can be reasonably assured bikes like the Roubaix will be rideable. The question is, will you enjoy the handling? You'll more notice differences in trail once the bike is up to speeds above 20mph and you're steering the bike or carving turns. Also with low trail bikes you'll be providing more handlebar input to keep the bike in a straight line. If you tug on the bars a lot or your upper body is not still, the bike will tend to "snake" or "weave" down the road.


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