Frame wobble - custom built bike
I've recently had a Roberts hybrid built - it's suffering from frame
wobble/shimmy. It's a custom built Reynolds 725 hybrid, based on the Audax Compact (see http://www.robertscycles.com/products.html). FWIW, I'm 5'11", 84kg. Wheels are 36 spoke XTR hubs with Mavic T520 rims, Conti Travel Contact tyres. My question is - is frame wobble acceptable on an expensive custom built bike? Roberts have tried adjusting the headset (which didn't help). Is this just bad luck - am I stuck with it? How far should Roberts go in trying to put this right? Thanks for any advice - I genuinely don't know what I should expect from the framebuilder on this. |
When the steering begins to wobble press your knee against the top
tube. Experiment with your seat position. Try to put less weight on your rear wheel. |
"Kenny" wrote:
When the steering begins to wobble press your knee against the top tube. Experiment with your seat position. Try to put less weight on your rear wheel. Or more weight. It's a harmonic situation; pretty much any structure has a frequency at which kinetic energy inputs from the rider or the road surface will cause and/or increase an oscillation. So the fix is to change the frequency of oscillation. Any number of things will do that, and it's easy to alter the weight distribution of the rider, as Kenny pointed out above. If you habitually carry stuff with you, try shifting it from, for example, from the back to the front. -- Ted Bennett Portland, OR |
"jcb1973" wrote:
I've recently had a Roberts hybrid built - it's suffering from frame wobble/shimmy. It's a custom built Reynolds 725 hybrid, based on the Audax Compact (see http://www.robertscycles.com/products.html). FWIW, I'm 5'11", 84kg. Wheels are 36 spoke XTR hubs with Mavic T520 rims, Conti Travel Contact tyres. My question is - is frame wobble acceptable on an expensive custom built bike? Roberts have tried adjusting the headset (which didn't help). Is this just bad luck - am I stuck with it? How far should Roberts go in trying to put this right? Thanks for any advice - I genuinely don't know what I should expect from the framebuilder on this. Did you spec the geometry and/or tubing? I've had customers make some fairly outrageous requests in terms of geometry, and have made clear that if there are problems with the handling as a result, it's not a "warranty issue". Normally a customer will just know what they want in terms of the bike's "mission statement", and I'll figure out how to optimize the handling around the necessary "fit points" (the saddle, crank and bars). If I did that and the bike had a significant handling issue, I'd stand behind it 100%. If the customer laid out an odd geometry (against my advice) and it didn't work, that'd be another thing. I couldn't find anything about the Roberts geometry on their website, so it's hard to say if there's anything odd about their "standard" geometry. Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame |
jcb1973 wrote:
I've recently had a Roberts hybrid built - it's suffering from frame wobble/shimmy. It's a custom built Reynolds 725 hybrid, based on the Audax Compact (see http://www.robertscycles.com/products.html). FWIW, I'm 5'11", 84kg. Wheels are 36 spoke XTR hubs with Mavic T520 rims, Conti Travel Contact tyres. My question is - is frame wobble acceptable on an expensive custom built bike? Roberts have tried adjusting the headset (which didn't help). Is this just bad luck - am I stuck with it? How far should Roberts go in trying to put this right? Thanks for any advice - I genuinely don't know what I should expect from the framebuilder on this. well, the good news is that you've got what should be a shimmy-resistant wheel setup - the xtr hub has a much better bracing angle than a standard road hub. beefy rim too. the bad news, imo, is that unless you're running a funky rack on the rear or some other unusual device, i think it's a function of tube set and therefore not something that can be addressed easily without getting a different frame. two weeks ago, i finally got around to building up a steel bianchi vigorelli i'd bought. i got it because it was essentially the same as my bianchi pista which is an utterly great bike & superbly stable. the two frames come out of the same taiwanese factory, use the same external diameter tubes, etc. they even appear to have the same frame angles when held side by side. only real difference is the pista's higher bb & much cheaper tube set - reynolds 520 vs. 631 on the vigorelli. the 520 has thicker walls as evidenced by a 26.8 seat post vs. 27.2 for the 631. result? the vigorelli is a complete noodle & a shimmy nightmare. now, some of the shimmy could be the wheelset. i experimented with a badly shimmying frame a while back & was able to tune out some of the resonance with a stiffer rear wheel [straight gauge spokes drive side & hub with a fractionally better bracing angle] - improved the ride substantially, but the frame still had the propensity to shimmy. same with the vigorelli, even with a straight gauge spoked rear. in your situation, unless you have really skinny spokes like revos, the better bracing angle of xtr should cover any improvement vs thicker spokes on an ordinary road hub. a different frame completely cured any shimmy i had on my first bike, with whatever wheelset. if you order another, i recommend a "cheaper" heavier gauge tubeset with as large a diameter as possible on the down tube & top tube. or go aluminum. of the 3 aluminum frames i have, all are excellently stable with no shimmy characteristics whatsoever. others in this thread mention ways to handle shimmy if it occurs. they are correct and offer good advice, but imo, having to cope with the problem in the first place is unacceptible, especially when appropriate frame design can eliminate it. |
"jim beam" wrote:
... result? the vigorelli is a complete noodle & a shimmy nightmare. now, some of the shimmy could be the wheelset. i experimented with a badly shimmying frame a while back & was able to tune out some of the resonance with a stiffer rear wheel [straight gauge spokes drive side & hub with a fractionally better bracing angle] - improved the ride substantially, but the frame still had the propensity to shimmy. same with the vigorelli, even with a straight gauge spoked rear.... How about wrapping the tubes in the head tube/down tube/top tube are with carbon fiber composite to add some stiffness to the frame? -- Tom Sherman – Earth |
Tom Sherman wrote:
"jim beam" wrote: ... result? the vigorelli is a complete noodle & a shimmy nightmare. now, some of the shimmy could be the wheelset. i experimented with a badly shimmying frame a while back & was able to tune out some of the resonance with a stiffer rear wheel [straight gauge spokes drive side & hub with a fractionally better bracing angle] - improved the ride substantially, but the frame still had the propensity to shimmy. same with the vigorelli, even with a straight gauge spoked rear.... How about wrapping the tubes in the head tube/down tube/top tube are with carbon fiber composite to add some stiffness to the frame? like carbon cranks? sure, that would work. better off not bothering with the steel in the first place if investing that kind of effort though. honestly, i'd love to be a die-hard steel guy, but aluminum frames seem to be so much superior in this important regard, i do all my serious mileage on them these days. curved seat stays & carbon seat posts make the ride just as comfortable as steel. |
"jim beam" wrote:
result? the vigorelli is a complete noodle & a shimmy nightmare. now, some of the shimmy could be the wheelset. i experimented with a badly shimmying frame a while back & was able to tune out some of the resonance with a stiffer rear wheel [straight gauge spokes drive side & hub with a fractionally better bracing angle] - improved the ride substantially, but the frame still had the propensity to shimmy. same with the vigorelli, even with a straight gauge spoked rear.... Tom Sherman wrote: How about wrapping the tubes in the head tube/down tube/top tube are with carbon fiber composite to add some stiffness to the frame? Funny. Very funny. Sky Yaeger, Bianchi's designer actually did that! She spec'd an aluminum welded frame with 'carbon wallpaper' on the chainstays ( "rigid, yet flexible") as a joke - but Bianchi booked orders for it! Dealers actually believed it! No kidding. -- Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971 |
A Muzi wrote:
"jim beam" wrote: result? the vigorelli is a complete noodle & a shimmy nightmare. now, some of the shimmy could be the wheelset. i experimented with a badly shimmying frame a while back & was able to tune out some of the resonance with a stiffer rear wheel [straight gauge spokes drive side & hub with a fractionally better bracing angle] - improved the ride substantially, but the frame still had the propensity to shimmy. same with the vigorelli, even with a straight gauge spoked rear.... Tom Sherman wrote: How about wrapping the tubes in the head tube/down tube/top tube are with carbon fiber composite to add some stiffness to the frame? Funny. Very funny. Sky Yaeger, Bianchi's designer actually did that! She spec'd an aluminum welded frame with 'carbon wallpaper' on the chainstays ( "rigid, yet flexible") as a joke - but Bianchi booked orders for it! Dealers actually believed it! No kidding. One of the methods of increasing shear resistance in existing elevated roadway piers lacking (remember the section of freeway that collapsed during the 1989 Loma Prieta earthquake) is to wrap the piers with a fiberglass reinforced polymer (FRP) blanket. -- Tom Sherman – Earth |
On Thu, 24 Feb 2005 20:13:37 -0800, jim beam wrote:
well, the good news is that you've got what should be a shimmy-resistant wheel setup - the xtr hub has a much better bracing angle than a standard road hub. beefy rim too. the bad news, imo, is that unless you're running a funky rack on the rear or some other unusual device, i think it's a function of tube set and therefore not something that can be addressed easily without getting a different frame. This is hogwash. No one can predict which frame/wheel/component/rider combination will shimmy, and which won't. The biggest contributer to shimmy is that last bit, the rider. Both in terms of position/mass, and in terms of how the rider handles the bike, it can make a huge difference. A degree or two of "bracing angle" is totally irrelevant. -- David L. Johnson __o | What is objectionable, and what is dangerous about extremists is _`\(,_ | not that they are extreme, but that they are intolerant. (_)/ (_) | --Robert F. Kennedy |
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