# Aggressive Geometry Instability?



## Roadie41 (Sep 18, 2009)

I just purchased a new Giant 2009 TCR Advanced 3. I like most aspects of the bike such as weight, power transfer, ride position, and asthetics, but I'm having trouble getting past the instability I feel at times in the steering. I've ridden and raced a Trek 5000 for 10 yrs and it's been completely stable albeit with more relaxed geometry. With the Giant I've had some experiences where I feel a pull to one side or the other then a sudden release causing eratic steering. The problem is inconsistent and only seems to appear about 10%- 20% of the time during each ride. The problem is of course a bigger issue at higher speeds of 30+mph, but it's sometimes noticable at lower speeds (mid to upper teens) as well. When stationary there are no signs of any notching or looseness in the headset or elsewhere.

I rode the bike on my rollers and after about 25 minutes started feeling the effect creep in at about 22mph. Almost feels like a gyroscopic force starting to pull one way for a little while then a sudden release.

I've heard bikes with more aggressive geometry described as twitchy or nervous, but this seems excessive. I bought the bike to do more racing, but at this point wouldn't feel comfortable racing in a pack on it.

Anyone else have this kind of experience with aggressive geometry road bikes?


----------



## PJ352 (Dec 5, 2007)

Roadie41 said:


> I just purchased a new Giant 2009 TCR Advanced 3. I like most aspects of the bike such as weight, power transfer, ride position, and asthetics, but I'm having trouble getting past the instability I feel at times in the steering. I've ridden and raced a Trek 5000 for 10 yrs and it's been completely stable albeit with more relaxed geometry. With the Giant I've had some experiences where I feel a pull to one side or the other then a sudden release causing eratic steering. The problem is inconsistent and only seems to appear about 10%- 20% of the time during each ride. The problem is of course a bigger issue at higher speeds of 30+mph, but it's sometimes noticable at lower speeds (mid to upper teens) as well. When stationary there are no signs of any notching or looseness in the headset or elsewhere.
> 
> I rode the bike on my rollers and after about 25 minutes started feeling the effect creep in at about 22mph. Almost feels like a gyroscopic force starting to pull one way for a little while then a sudden release.
> 
> ...


IMO this has nothing to do with the bikes geo. The way you describe it, I'd suggest having the headset checked out as well as the front hub (bearings). I know you said the headset exhibits no unusual problems when stationary, but unless you're sitting on the bike at the time, there's no weight load on the front end, so you're not really duplicating road conditions. 

Also, if one side of the front bearings is binding it could cause these symptoms, but that's easier to diagnose simply by replacing the front wheel, test ride and see if the problem continues.

I view it as a potentially hazardous condition (and possibly indicative of a defect), so I'd have it checked out.


----------



## Roadie41 (Sep 18, 2009)

I do have another wheel I can try out, so that'll be the easiest first step. Thanks for the suggestions!


----------



## PJ352 (Dec 5, 2007)

Roadie41 said:


> I do have another wheel I can try out, so that'll be the easiest first step. Thanks for the suggestions!


Yup, I would do the same. Let us know how it goes.


----------



## Roadie41 (Sep 18, 2009)

PJ352 said:


> Yup, I would do the same. Let us know how it goes.



It isn't the wheel. I went out on a 22 mile ride and went most of the way feeling only a little of the effect and was almost convinced the wheel was part of the issue then it suddently started acting up. I immediately pulled over and turned the bike almost completely sideways before the front wheel/fork/handlebars gave into gravity. Steering was noticeably stiff, then I rotated the handlebars from side to side and few times and it loosened up. I started riding again and things were fine for the final 1/2 mile back to the house.

What would cause a gradual stiffening/tightening of the headset? 

I'm bringing the bike back to my LBS tomorrow to have them check it out.


----------



## PJ352 (Dec 5, 2007)

Roadie41 said:


> It isn't the wheel. I went out on a 22 mile ride and went most of the way feeling only a little of the effect and was almost convinced the wheel was part of the issue then it suddently started acting up. *I immediately pulled over and turned the bike almost completely sideways before the front wheel/fork/handlebars gave into gravity. Steering was noticeably stiff, then I rotated the handlebars from side to side and few times and it loosened up. * I started riding again and things were fine for the final 1/2 mile back to the house.
> 
> What would cause a gradual stiffening/tightening of the headset?
> 
> I'm bringing the bike back to my LBS tomorrow to have them check it out.


You have your answer. Most likely as you ride and there's weight put on the front end (by you and road irregularities) something is binding. If I had to guess, it's the fork crown race, lower bearing and/ or the lower head tube/ crown interface. 

Normally these types of problems are caused by something in the lower portion of the HT. If where the bearings seat inside the HT is molded CF, it could be malformed, but you'll know that if after the LBS repairs it, the problem returns. For now, your plan to return the bike to them to check out is a good one. Needless to say, it's a warranty issue.


----------



## Hooben (Aug 22, 2004)

I have the exact same bike and it rides like it's on rails. It steers itself with no issues at all. Perfect balance, and no pulling to any side what so ever. Have the LBS check it out.


----------



## Roadie41 (Sep 18, 2009)

PJ352 said:


> You have your answer. Most likely as you ride and there's weight put on the front end (by you and road irregularities) something is binding. If I had to guess, it's the fork crown race, lower bearing and/ or the lower head tube/ crown interface.
> 
> Normally these types of problems are caused by something in the lower portion of the HT. If where the bearings seat inside the HT is molded CF, it could be malformed, but you'll know that if after the LBS repairs it, the problem returns. For now, your plan to return the bike to them to check out is a good one. Needless to say, it's a warranty issue.



Took it to my LBS and they took apart the headset and reassembled. Said they didn't notice anything wrong, but I've been on two rides since of 27 and 17 miles and it's completely trouble free so far. 

I'm REALLY liking this bike right now.

Thanks for all the input!


----------



## PJ352 (Dec 5, 2007)

Roadie41 said:


> Took it to my LBS and they took apart the headset and reassembled. Said they didn't notice anything wrong, but I've been on two rides since of 27 and 17 miles and it's completely trouble free so far.
> 
> I'm REALLY liking this bike right now.
> 
> Thanks for all the input!


Glad it worked out for you. It's safe to say it was the headset, but still a mystery as to what it was, exactly. It'll probably be fine, but if the problem does resurface, you'll know what to focus on.


----------



## Magdaddy (Feb 23, 2007)

*interesting read*

I have/had a similar problem with my 09 TCR Advanced SL0. After about 1200 miles, the front steering tightened up significantly. At first I thought the effect was the cross winds on the Zipp 404's...kinda a similar feel. After stopping and lifting the front of the bike, it was readily apparent something was wrong.

My shop took the headset apart, repositioned some spacers, and it was good to go...On the first ride back, I noticed the bars a little a drift. So I stopped, loosened the top cap(was really kinda loose)loosened the stem, and retightened. With the steerer tube tightened-the stiffness came back. While I didn't have my torque wrench on the ride with me, I certainly didn't over tighten it. After loosening it a "little" the stiffness went away. I put 60 miles on it that day, and it seemed fine.

Heavy into cross season here now, and I just built up a new crosser, so I have not been back on the roadie for a few weeks now. Gotta get back on it for a couple of nice fall rides, and see if all is still ok.


----------



## PJ352 (Dec 5, 2007)

Magdaddy said:


> I have/had a similar problem with my 09 TCR Advanced SL0. After about 1200 miles, the front steering tightened up significantly. At first I thought the effect was the cross winds on the Zipp 404's...kinda a similar feel. After stopping and lifting the front of the bike, it was readily apparent something was wrong.
> 
> My shop took the headset apart, repositioned some spacers, and it was good to go...On the first ride back, I noticed the bars a little a drift. So I stopped, loosened the top cap(was really kinda loose)loosened the stem, and retightened. *With the steerer tube tightened-the stiffness came back. While I didn't have my torque wrench on the ride with me, I certainly didn't over tighten it. After loosening it a "little" the stiffness went away*. I put 60 miles on it that day, and it seemed fine.
> 
> Heavy into cross season here now, and I just built up a new crosser, so I have not been back on the roadie for a few weeks now. Gotta get back on it for a couple of nice fall rides, and see if all is still ok.


I know you said you didn't over tighten the headset, but from your description that's exactly what you did. 

There could be something in the headset design that's prone to binding. As to exactly what, who knows, but I've heard of this before. At least now if the problem resurfaces, you (and the OP) have some experience as to the cause.


----------

