55cm top tube and 140mm stem vs 57cm top tube and 120mm stem?

[yzfrr11]

Assuming all else being equal, which combination would be more stable (less prone to head-shake)?

I have been running the 57, 120 combination for 2 seasons on relatively flat terrain. While descending a mountain pass in Colorado last month, I had my first experience with head-shake. I would like to prevent this in the future!

[Smiley]

Look at the combo head angle and fork rake , hence TRAIL and get a frame with a longer trail that for one will help .

[dirtdigger88]

I am sure some will chime in and disagree-

but

I would say if you have to run a 140 stem on a 55cm bike- your frame is too small for you- the 140 would put TOO much weight on the front

a 120 on a 57 sounds right to me - but what do I know

Jason

[yzfrr11]

I am sure some will chime in and disagree-

but

I would say if you have to run a 140 stem on a 55cm bike- your frame is too small for you- the 140 would put TOO much weight on the front

a 120 on a 57 sounds right to me - but what do I know

Jason
That's what I was thinking. But a longer stem seems more stable. Too much front wheel weight is unstable - like you said.

[dirtdigger88]

If the 140 feels better- your bike may be too small

You may need the 140 to get into proper position but you cant be balanced on the bike

Jason

[Fixed]

bro that is a hot topic here if you can bend over enough without having the stem pointing stright up try it ,you know your bars will lower on a 55.Look at saab and the jerks bikes and see if you can ride on that setup I do on my race bike.their bikes are in the gallery. a lot of pro riders ride on 140's .Cheers :beer:

[Dave]

All responses are pure speculation with what little info you've posted. If you don't know the weight balance of your current bike, then listing the TT length and stem length is worthless info. If all else remained the same, the front center with a 55cm TT would be 2cm less and the weight on the front would increase by about 2% or less than 2 pounds.

FWIW, I've had as little as 42% of the weight on the front wheel (with my saddle far back) and never encountered a problem on Colorado mountain descents. I've moved my saddle forward about 2cm this year, which should have increased the weight on the front to approximately 44%. The bike does seem to negotiate the high speed corners better with this setup.

Head shake or speed wobble is more often caused by frame flex and often reported by riders of large frames.

More trail might help, but once again, without knowing the current amount of trail, who can say that you need more? Trek's don't have a lot of trail, but the Discovery riders seem to get down the mountains on them. If you have less trail than a Trek, then maybe less fork rake (more trail) would help.

Colnagos have lots of trail and while this makes the bike track a straight line at high speed, it also makes it difficult to change your line in a high speed turn. I like less trail and more responsive steering myself.

[Registered User]

Assuming all else being equal, which combination would be more stable (less prone to head-shake)?
!i assume you mean speed wobbles or shimmying.
I say there's only a slight increase in stability with a longer stem.

Don't forget head-tube length and handle bar height. Chances are, the smaller frame will have a shorter heard-tube, so your bars will have to be lower, unless you wanna use a lot of spacers.

[jeffg]

or anything similar and both my bikes are 55X57 with an 11cm stem. Many pros ride 13+ stems, several ride 11cm stems.

The main thing is that the frame is designed correctly. Kelly B. & Steve Hampsten know what they are doing. Nuff' said

[bluesea]

55cm top tube and 140mm stem vs 57cm top tube and 120mm stem?

Aren't there other variables involved? If you are comparing identical frame models, will the sta remain the same? I don't think that you can assume moving down 2cm in top tube will absolutely require a 2cm longer stem.

You need to define "headshake" more clearly. It sounds like you are describing a high speed shimmy in a straight-line descent. A longer stem will not affect or correct this, unless that shimmy comes from your being uncomfortable with the quickness of the steering characteristics of your bike at speed. In the latter case, a longer stem will slow down steering "input" by requiring slightly more handlebar movement for a given movement of the front wheel off it xy axis.

I agree with Dave on not enough info being provided, and on the importance of the actual weighing of front/rear weight distribution. A 13 or 14 stem can be appropriate in many situations. One does not automatically move down 2 frame sizes simple to remedy "headshake". A decrease in wheelbase (if any) will also have an effect on high speed handling.

[jerk]

Colnagos have lots of trail and while this makes the bike track a straight line at high speed, it also makes it difficult to change your line in a high speed turn. I like less trail and more responsive steering myself.[/QUOTE]




no it doesn't. the bb drop, wheelbase, front center make colnagos extremely responsive bikes. couple this with their great torsional rigidity, and you'd be hard pressed to find a better handling bike in any hard fast condition. this being said, like all proper race bikes this assumes a normal length stem (>110mm) for proper balance.

jerk

[bluesea]

no it doesn't. the bb drop, wheelbase, front center make colnagos extremely responsive bikes. couple this with their great torsional rigidity, and you'd be hard pressed to find a better handling bike in any hard fast condition. this being said, like all proper race bikes this assumes a normal length stem (>110mm) for proper balance.

jerk

Like you said...

I have close to ideal f/r weight dist. with a 13cm stem. Went down a size to account for shorter legs (and aesthetics), and the bike (MXL) is stiff and responsive. I've seen many comments about how Colnago's don't steer very well but I suspect this has to do with technique.

Can you explain what you mean by the Colnago's front center and wheelbase?

[oldguy00]

no it doesn't. the bb drop, wheelbase, front center make colnagos extremely responsive bikes. couple this with their great torsional rigidity, and you'd be hard pressed to find a better handling bike in any hard fast condition. this being said, like all proper race bikes this assumes a normal length stem (>110mm) for proper balance.

jerk


So jerk, a similar question.....with colnago geometry, all things being equal, would you recommend a 56 frame with a 120 stem and 3 cm of spacers under the stem, or would you go with a 57 frame with a 110 stem and 2cm of spacers under the stem??
thx!

[Dave]

Everyone's entitled to their opinion Jerk, but I rode C-40s for four years and I guarantee you they turn slowly. When I first moved to Colorado, I had a C-40 and a Fondriest MDC. They were like night and day when it came to cornering down the mountain.

Jerk, you're wrong on all counts about colnago's geometry. The BB drop is a standard 7cm in most sizes, the same as 90% of bikes on the market. The front center (and wheelbase) are long and the trail is larger than just about any bike on the market. These features do NOT make for an overly responsive bike. The 54cm that I rode has 67mm of trail and a 59.1cm front center. The LOOK that I ride now has 64mm of trail, which is still quite a bit, but a 2cm shorter front center. It's a much more responsive bike, but not as quick as the Fondriest, which had an even shorter front center.

I sold my Colnago because it handled too slow for my taste and sold the Fondriest because it was too twitchy in high winds. Other than that, the Fondriest would scream down a mountain.

[jerk]

So jerk, a similar question.....with colnago geometry, all things being equal, would you recommend a 56 frame with a 120 stem and 3 cm of spacers under the stem, or would you go with a 57 frame with a 110 stem and 2cm of spacers under the stem??
thx!


probably the former, but it may not be ideal and a bicycle built around a higher headtube might work better.

[jerk]

Everyone's entitled to their opinion Jerk, but I rode C-40s for four years and I guarantee you they turn slowly. When I first moved to Colorado, I had a C-40 and a Fondriest MDC. They were like night and day when it came to cornering down the mountain.

Jerk, you're wrong on all counts about colnago's geometry. The BB drop is a standard 7cm in most sizes, the same as 90% of bikes on the market. The front center (and wheelbase) are long and the trail is larger than just about any bike on the market. These features do NOT make for an overly responsive bike. The 54cm that I rode has 67mm of trail and a 59.1cm front center. The LOOK that I ride now has 64mm of trail, which is still quite a bit, but a 2cm shorter front center. It's a much more responsive bike, but not as quick as the Fondriest, which had an even shorter front center.

I sold my Colnago because it handled too slow for my taste and sold the Fondriest because it was too twitchy in high winds. Other than that, the Fondriest would scream down a mountain.


the jerk has only ridden colnagos in his size so he doesn't have first hand experience on what a c40 in a 54 would ride like.....but lots of the jerk's pals have ridden colnagos in that size and what you are saying, while valid, is not the experience of any of these folks. the bb drop is 7cm an the stays are super short and the bike wants the saddle pushed back and alot of weight on its front wheel....if you set up a colnago like this and you can handle the moderate to extreme saddle to stem drop the bike was designed around...a c50 corners and descends with the best of them.

there is alot more to bicycle design than trail. what length stem were you using? how big are your hips versus your shoulders? how much do you weigh? where did you have your saddle setback to? how much drop did you have?

the jerk believes you, but colnagos are reknowned for their handling and the people who push their bikes the most are almost universal in their praise for how the bikes corner.

jerk

[divve]

I have to agree with Dave that Colnagos tend to respond slower to steering input. It's clearly evident in their stock geometry as well. That doesn't necessarily effect the actual handling quality in a negative sense. More than anything, it's more a matter of personal preference in my opinion.

[Dave]

Colnago chainstays are on the short side (but only 3mm shorter than a LOOK). That's an accurate statement.

Short chainstays REDUCE the amount of weight on the front wheel. If the saddle is moved far back, this further reduces the weight on the front wheel. The long front center also reduces the weight on the front wheel. If a rider buys a Colnago and sets it up with the whatever his normal KOP is, then the bike is likely to have less weight on the front than many other brands.

If a Colnago "likes" more weight on the front, then the saddle would have to be further forward than normal, not further back, to compensate for the short stays and long front-center.

FWIW, I weigh 135. I've ridden a Colnago with the saddle anywhere from centered on the post to all the way back. I'm a short torsoed rider, so my stem length ranged from 100 to 120, depending on the saddle (KOP) position I was experimenting with at the time. I ride with a 9-10cm drop from the saddle to bars. On the 54cm, I used an 84 degree stem with no spacers. On my LOOK, I've got it setup another 5mm lower. This setup could position my torso as low as others riding a 120-130 stem with more spacers. Position is NOT all about stem length. Stem height relative to the saddle also has to be factored in.

http://www2.propichosting.com/Images/421571459/2.jpg

[Fixed]

bro you guys know a lot more about this kind of stuff than me but to me your bike looks like it is setup very nice for a small guy climbing in the mountains where as Mr. Jerk is more of a big strong classics guy i.m.h.o. it's all good cheers :beer:

[bluesea]

The C does steer a little slower, and it does hold a straight line more effortlessly. I'm thinking that what is being discussed boils down to technique and riding style. You may have to approach the apex in a different manner, maybe in terms of how smoothly or how aggressively you initially throw into the turn. This is a subtlety that is hard to explain, and even harder to quantify. The point is, the C should be able to handle any series of curves in a more than competent manner if ridden properly.

[Dave]

If your only ride is a Colnago, you'll get accustomed to what it takes to make it respond as desired. The problem I had was owning two bikes with drastically different steering while learning to negotiate high speed mountain corners, including 180s. There's more to it than negotiating a fast 90 on a city street in a crit. I found the quicker bike to be easier to ride. The Colnago took a lot of coaxing to correct my line, if I was drifting toward the centerline in a 180.

[jerk]

If your only ride is a Colnago, you'll get accustomed to what it takes to make it respond as desired. The problem I had was owning two bikes with drastically different steering while learning to negotiate high speed mountain corners, including 180s. There's more to it than negotiating a fast 90 on a city street in a crit. I found the quicker bike to be easier to ride. The Colnago took a lot of coaxing to correct my line, if I was drifting toward the centerline in a 180.


fair enough. the jerk has ridden alot of bikes and has always found neutral handling frames ideal in just about every situation. the jerk thinks maybe he wasn't understanding you; despite your clarity. maybe the jerk was just itching for a fight because he misses his c50.
jerk

[Grant McLean]

no it doesn't. the bb drop, wheelbase, front center make colnagos extremely responsive bikes. couple this with their great torsional rigidity, and you'd be hard pressed to find a better handling bike in any hard fast condition. this being said, like all proper race bikes this assumes a normal length stem (>110mm) for proper balance.

jerk


Jerk,

Aren't you are assuming that "slow steering" doesn't make a great handling bike? Pro's would likely beg to differ, that's why they like them colnagos.

I think the c40/c50 is _very_ slow handling, i've been riding a c40 for 2 years, and it's the most stable, slowest steering bike of the dozen or so I've owned in recent years. Not that there's anything wrong with that. Like Dave said in his post, if you ride a c40 all the time, you get used to it, and appreciate the versitility of the whole package. I'd never use the word "responsive" to describe the handling of a c40, and i'm not sure I'd want "responsive" if I were racing as pros do.

Grant


Grant