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the jerk's advice: stems getting longer
Our pal the Senor is a cleaver fellow, as we know, and I have recently experimented with his notions of stem length, to wit, I have added some length, on the order of 1cm, and moved (just a tiny tad) forward on my saddle. Since I routinely sit way, way, way behind the spindle (some 3cm in some cases), I can easily come forward. To work this experiment I chose two bikes that are designed as true race bikes, which in my mind means a saddle/bar drop that places slightly more weight forward and into the front end. The drop I have in mind is about 3cm or so. I also am happy to be even a bit more stretched out. I hate feeling "short" or cramped in any way and I can _much_ more easily adjust to being longer in the front. The bikes are my French blue Sachs and my silver Rivendell. Both got Nitto Pearl 12cm stems which are more like 12.7cm because Nitto measures on the side (side of the stem to center of the open clamp) rather than across the top (from bolt to center). These are long stems but not silly long. They are well down below their max line. The Sachs shows more post than the Rivendell and is slightly quicker up front.
The results are all very positive. The ever so slight bit of weight forward makes the Sachs even more direct, steady, and rock solid. The extra reach gives me the chance to push my butt waaay back onto the saddle (this being very good for the lower back, btw). I put the saddle forward less than 1cm, so that's not much of a change, but I still feel like there is a bit more forward weight. The Rivendell in comparison just feels longer, with no change I can perceive in the way that it handles. The Riv ordinarily wears the fatboy Dugast 28c silk tubulars so it is impossible, imho, to improve on the ride. But I am even more comfortable just one centimeter more extended though I can't surmise any difference in the front end. The Sachs is clearly the more "pure" racer and it's happier bike for this move. Actually I did this on the TdF CSi awhile ago but forgot to mention it: in that case I didn't lower the stem or the saddle, I just made the bike longer and that was a good thing. I love being long in the cockpit, I suppose. To each his own. I just got a 13cm Ibis stem for my Ibis, now by a longshot my smallest bike (originally listed as a 55cm but c-c, so more like a 57). Report (a better one than this) to follow. The moral of this story: your stem is too short. I hear you, Senor jerk. dbrk |
#2
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Incredible,....
....I had been thinking of writing specifically on this topic! Today I installed a Cinelli Grammo threadless stem onto my Croll, the one for which DWF last year created a new fork.
What a difference it made!!! I had had a 13 cm Ritchey WCS. In addition to looking out of place on the bike, it was a bit too short and a bit too high. The Grammo is a 14 cm and sits a bit lower on the bike. There are no spacers. It is perfect. I really feel like it is a racing bike again. I get low and aero and have no pain anywhere. The only thing I need to do now is to work on the ol' beer gut thing..... The handling is improved, as the Jerk says it should be. DBRK is right when he says that the Jerk is right! |
#3
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Stem Test Proposal
Is my stem long enough?
Before spending money on expensive, and sometimes painful, stem enhancement from ITM, Deda, Ritchey, Nitto, or Cinelli, try this simple test: Drop a plumb line (or yardstick-length carpenter's level) from *two* locations: the center of the brake hood, and the curve of the drop. If the plumb line for the curve of the drops bisects the front hub axle, or (ideally) falls up to, say, 1 cm in front, and the plumb line from the hoods falls 1-2 (?) cm in front of the hub, your stem is long enough to put sufficient weight on the front wheel, and your steed will handle like a racing bike (unless it is made by Giant or by a small Russian company trying to make use of leftover titanium tubing from recycled MIGs, and is simply junk to start with). If the plumb line falls behind the front hub, forget it. Your stem is too short, or your top tube is too long, and it ain't gonna handle like a racing bike cause yer pushin that front wheel around like a Wal-Mart shoppin cart. Now, this is just a *proposed* test... The Doc couldn't sleep last night, and started goofing around with photoshop with some pro bike pics from cyclingnews.com, and observed the relation of the curve/hoods to the hub...got the Doc thinking that if your hands are over or in front of the hub, there's enough weight there for it to handle like it should...so the test would be to see where that contact point with the bike lies with relation to the front hub...but then again, the doc got D's in science classes, and although he is a Doc, he is a Doc of Literature, which, last time we checked, got nothin to do with bike design. Dave Kirk? ERitchie? Jerk? Does the test pass muster, or have no validity at all...? Last edited by Dr. Doofus; 07-03-2004 at 08:53 AM. |
#4
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I think stem length has become is a phallic symbol around here
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#5
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Dr., how many on this board are racing their bikes?
Not too many posts on the board from racers it seems. So what is the formula for stem length for the vast majority of serious recreational riders? I really enjoy riding 50 miles on my Rex/Walmart shopping cart. I fail miserably at the plumb line relative to front axel formula. With relaxed seat and ht angles, 8 bb drop, and level to saddle bar height, 9 cm stem; the shopping cart is wonderful riding cycle.
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#6
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Exactly Eddie. Its only an issue if you want to ride fast. If you lack the flexibility to ride in a low position, your bike won't handle like a racing bike anyway, and if you lack the flexibility, you're not trying to see how fast you can take a corner, because, as you accurately point out, that's not why you're riding.
We can talk about rake, trail, and front center until we're blue in the face, but the weight distribution of the rider is a crucial part of the picture.... If one is a "serious recreational rider" I and he think that the formula is "does my back hurt or not" -- becuase if you can't get the weight on the front wheel due to flexibility, its a total non-issue. |
#7
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Dr.,thanks for the clarification
All points of view appreciated.
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#8
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I use a somewhat substantial saddle to bar drop and stem length. I've been toying with brining it up a bit. The biggest hammer in my district sits relatively upright as did Indurain. Maybe you guys are talking about bars that sit up much farther than I'm seeing in my minds eye, but from where I sit, wattage is the key.
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#9
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The reason I mentioned "low" was that low and *long* tend to go together -- its hard to run a long stem with the bars even with the saddle, unless the top tube is pretty short.
We're not talking about aerodynamics. Wattage is also a dead issue here -- its not speed while pedaling here, its how much speed can the bike take while still giving the rider a feeling of control while *coasting* through a turn (pleeeeease don't say fast guys pedal through corners -- the only reason pedaling through corners is the fast way in the U.S. is because if you actually take the fast line through the turn you move out of the draft, because you have to follow all the idiots who have never taken a corner flying like hell in a kermesse *where they don't pedal through corners*). We're talking about handling. As for Indurain, yes, he had a fairly upright position for a pro. He also ran a stupidly long 150 stem to keep the front end of his bike short and to tear down those descents as fast as he hammered up them (but more about that later). When most people talk about stem length and handling, the first thing they think about is steering axis, and how a long stem makes a bike "steer" slowly. Indeed, a 140 or 150 stem gives an articulated feel when you turn the bars (you don't need to go that long unless you're riding a 58 or bigger, and depending on what handling you're shooting for). However, that's just part of the picture. The length of the stem also affects the amount of weight over the front wheel, which is another part of the handling stew, along with rake, trail, and head angle. Weight behind the hub, you're pushing the bike and the front end will feel loose in bad way, like the wheel is drifting (because it is). Weight too far in front of the hub, and you'll have an equally screwed up situation.... Look at this picture: Bike A: 58 cm seat tube, 57 top tube, 73 head angle, 43mm of rake, 130 stem Bike B: 58 cm seat tube, 59 top tube, 73 head angle, 43mm of rake, 110 stem The same rider could "fit" on both bikes. They have the same length from seat to stem center. They could have identical stack heights. Bike B would steer like a dog, while Bike A would be a responsive race bike. Why? Bike B is going to be longer in the front-center, and because of the short 110 stem, the rider will have less weight over the front wheel, regardless of bar drop. Bike A will be shorter in the front center, and have more weight on the front wheel. A very talented builder informed me that trail is a bit more important than f-c, and I'll take his expert word for it. However, if two bikes have identical trail, and one has your hands well behind the hub, and the other has your hands over it, the latter bike will handle more responsively and securely, tracking and "sticking to the road" better. Look back in ProCycling when Marcel Wurst rode Moncoutie's Decathlon. For some sick reason, Moncoutie ran a long top and a 110 stem, giving his 58cm bike a 60cm f-c. Wurst said he was scared to push it on a descent, and that a climber (and allegedly poor bike handler) like Moncoutie must not worry too much about handling switchbacks, only getting up them.... Think of it this way. Stem length isn't a fit issue. Top tube length and head tube length should set the front end of the bike up so it fits. Stem length is a handling issue -- how much weight do you want over the front wheel and why. Obviously, a tourist and a racer (or a club racer) have different desires for how the bike should handle. I wouldn't do a double century on my CSi with a 130 stem and 9.5cm of drop. I wouldn't take a Rambouillet to a crit. I may be off base here -- if I am, I hope jerk/kirk/ritchie will correct me.... Last edited by Dr. Doofus; 07-03-2004 at 06:17 PM. |
#10
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My Legend is 58 X 57, 73 + 73, 120 mm stem with a -10 deg rise. My plumb bob (a toenail clipper hanging from three feet of dental floss; my daily display of adaptability) shows that the center of the brake hoods is about half a centimeter in front of the hub axle, and the front of the drop is half a centimeter behind it.
So at least I'm not riding a shopping cart... Last edited by ericmurphy; 07-03-2004 at 10:34 PM. Reason: typoes |
#11
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Eric, I find this geometry/fitting stuff really interesting
Sounds like we might be about the same dimensions in body and bike. How tall are you, what length sleeve and pant legs do you have? Just curious to find out if I was more flexible if I'd ride a similar bike to yours.
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#12
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Please compare and contrast this with the greatest rider of all time and his insistance that a well balanced bike have a 110 stem. What other factors contributed to this...longer chainstays?
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#13
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Quote:
I'm amazed that the dimensions on my Serotta are so close to the dimensions on my previous bike (within a cm or so for most dimensions) and yet the fit on the Legend is infinitely better. Amazing what a difference such minor dimensional differences can make. BTW, my bars perfectly obscure the front hub when I'm on the hoods. That's supposed to be a good rule of thumb for stem length. |
#14
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Quote:
Hey, I and he said it was all speculative.... Anyway, the colnago charts have Eddy on 120s.... |
#15
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thanks for coming to the dark side kids. told ya the jerk is always right...
front center and balance....race bikes are designed around long stems...that's the deal they handle better with'em and handling is more important than just about anything including fit....you need your hips rotated forward to use the most powerful muscles in your body (try to stand up out of your chair without bending forward.....can't do it? how the hell are you supposed to ride a bike balls out looking like the wicked witch of the west?) so for the jerk low, long and the front wheel nice and tucked....not that it's going to matter on the painfully slow century the out of shape jerk is doing tomorrow....but my bike does have a 140 stem on it...
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