Where's the flex?
10-25-05 | 10:17 PM
#1
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From: Seattle, WA
Bikes: LOOK 585, Colnago Masterlight, Gunnar Crosshairs
Where's the flex?
I am having a serious problem with front-end flex (particularly when I'm out of the saddle) on one of my two road bikes and I'm trying to figure out what is the primary source -- frame, fork, or wheel. The bike that I'm having trouble with is a Litespeed Teramo (compact geometry, lower-end frame, G.E.T. tubing but not double-butted) with a Real Design fork (Litespeed house brand - not sure who makes it but I'm guessing Mizuno) and Easton Circuit wheels. Any guesses as to the primary source of flex?
My other bike is a Merlin Magia with an Easton EC90 SLX fork and Campy Neutron wheels. This bike rides as if it has its own energy source. It is a joy to ride -- and I don't have a problem with front-end flex. Given the lightness of the Magia frame, I'm guessing the problem with the Litespeed is not the frame (although what do I know? -- maybe it is). My next step is to put the front Campy Neutron on the Litespeed and see if the situation improves.
In the meantime, any theories/ideas you might have would be quite welcome. Thanks!
My other bike is a Merlin Magia with an Easton EC90 SLX fork and Campy Neutron wheels. This bike rides as if it has its own energy source. It is a joy to ride -- and I don't have a problem with front-end flex. Given the lightness of the Magia frame, I'm guessing the problem with the Litespeed is not the frame (although what do I know? -- maybe it is). My next step is to put the front Campy Neutron on the Litespeed and see if the situation improves.
In the meantime, any theories/ideas you might have would be quite welcome. Thanks!
10-26-05 | 12:53 AM
#3
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From: Mesa, AZ
Bikes: Moots RCS, tandem, beach-cruiser, MTB, Specialized-Allez road-bike, custom track-bike
When are you experiencing flex? Out of the saddle climbing? Or sprinting?
The handlebars and stem will flex about 1.0-1.5" around the axis of the stem. Test that out by being out of the saddle with your hands on the hoods and not yanking on anything. I've snapped stems and handlebars before, so they do experience a lot of strain.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
The handlebars and stem will flex about 1.0-1.5" around the axis of the stem. Test that out by being out of the saddle with your hands on the hoods and not yanking on anything. I've snapped stems and handlebars before, so they do experience a lot of strain.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
10-26-05 | 05:42 AM
#4
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From: Maryland
Bikes: 2011 Giant TCR Advanced, 2010 Motobecane Fantom Cross Pro, 2011 Redline Monocog Flight 29r
Originally Posted by DannoXYZ
The handlebars and stem will flex about 1.0-1.5" around the axis of the stem. Test that out by being out of the saddle with your hands on the hoods and not yanking on anything. I've snapped stems and handlebars before, so they do experience a lot of strain.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
10-26-05 | 06:16 AM
#6
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From: Seattle area
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Originally Posted by DannoXYZ
When are you experiencing flex? Out of the saddle climbing? Or sprinting?
The handlebars and stem will flex about 1.0-1.5" around the axis of the stem. Test that out by being out of the saddle with your hands on the hoods and not yanking on anything. I've snapped stems and handlebars before, so they do experience a lot of strain.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
The handlebars and stem will flex about 1.0-1.5" around the axis of the stem. Test that out by being out of the saddle with your hands on the hoods and not yanking on anything. I've snapped stems and handlebars before, so they do experience a lot of strain.
yeah, the tyres alone have about 0.2" of flex and the wheels about 0.5-1.5" depending upon the lean angle and how hard you're pushing. Frame-flex at the BB tends to be about 0.3-0.6" laterally with a 100kg force on the pedals. Fork flex is about 0.2-0.3", but will be higher when the bike's leaned over or under braking.
Handlebars & stem flexing up to 1.5 inches
Wheels flexing up to 1.5 inches
BB flexing more than 0.5 inch
Danno -- Where did you get that data? Sounds like your ride and mine are different.
10-26-05 | 10:57 AM
#7
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Joined: Jul 2005
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From: Mesa, AZ
Bikes: Moots RCS, tandem, beach-cruiser, MTB, Specialized-Allez road-bike, custom track-bike
A lot of general data from Damon Rinard's research and I devised my own very rough tests to simulate out-of-the-saddle riding at 20-30 degree bike-lean in a sprint.
1. Handlebars are easy. Just straddle the front-wheel with your legs (looking back at the bike). Grab the bar-ends and alternately push down on one end while simultaneously pull on the other. This isolates the upper-body forces from the legs. also keeps the bike-stationary for a frame of references. I can only apply about half the load of a sprint with my upper-body alone, but the bar-ends will flex close to 1" as it is.
2. wheels are very, very weak laterally. The more the bike is leaned over, the more the wheels bend at the contact patch. I clamped a wheel in Park truing stand and clamped stand in vice. Hung 100kg of sandbags off rim to simulate peak dynamic force on rim. Hang the sandbags near where the wheel goes between the arms of the stand. Measure gap between rim and arm for deflection. Used Flex=cos(LeanAngle)*MaxFlex to roughly estimate wheel-deflection where perfectly vertical bike experiences zero lateral wheel flex.
3. BB is kinda hard to isolate from the fork. Stand on left side of bike, hold front-brake, lean bike over about 20-degrees, stand on pedal with all your weight while holding same the bike-lean angle, notice BB's lateral deflection.
EDIT: Oops, wrong equation in #2, fixed.
1. Handlebars are easy. Just straddle the front-wheel with your legs (looking back at the bike). Grab the bar-ends and alternately push down on one end while simultaneously pull on the other. This isolates the upper-body forces from the legs. also keeps the bike-stationary for a frame of references. I can only apply about half the load of a sprint with my upper-body alone, but the bar-ends will flex close to 1" as it is.
2. wheels are very, very weak laterally. The more the bike is leaned over, the more the wheels bend at the contact patch. I clamped a wheel in Park truing stand and clamped stand in vice. Hung 100kg of sandbags off rim to simulate peak dynamic force on rim. Hang the sandbags near where the wheel goes between the arms of the stand. Measure gap between rim and arm for deflection. Used Flex=cos(LeanAngle)*MaxFlex to roughly estimate wheel-deflection where perfectly vertical bike experiences zero lateral wheel flex.
3. BB is kinda hard to isolate from the fork. Stand on left side of bike, hold front-brake, lean bike over about 20-degrees, stand on pedal with all your weight while holding same the bike-lean angle, notice BB's lateral deflection.
EDIT: Oops, wrong equation in #2, fixed.
Last edited by DannoXYZ; 10-26-05 at 03:49 PM.
10-26-05 | 11:28 AM
#8
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Joined: Jan 2005
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Originally Posted by DannoXYZ
A lot of general data from Damon Rinard's research and I devised my own very rough tests to simulate out-of-the-saddle riding at 20-30 degree bike-lean in a sprint.
1. Handlebars are easy. Just straddle the front-wheel with your legs (looking back at the bike). Grab the bar-ends and alternately push down on one end while simultaneously pull on the other. This isolates the upper-body forces from the legs. also keeps the bike-stationary for a frame of references. I can only apply about half the load of a sprint with my upper-body alone, but the bar-ends will flex close to 1" as it is.
2. wheels are very, very weak laterally. The more the bike is leaned over, the more the wheels bend at the contact patch. I clamped a wheel in Park truing stand and clamped stand in vice. Hung 100kg of sandbags off rim to simulate peak dynamic force on rim. Hang the sandbags near where the wheel goes between the arms of the stand. Measure gap between rim and arm for deflection. Used flex=cos(LeanAngle)*force to roughly estimate wheel-deflection where perfectly vertical bike experiences zero lateral wheel flex.
3. BB is kinda hard to isolate from the fork. Stand on left side of bike, hold front-brake, lean bike over about 20-degrees, stand on pedal with all your weight while holding same the bike-lean angle, notice BB's lateral deflection.
1. Handlebars are easy. Just straddle the front-wheel with your legs (looking back at the bike). Grab the bar-ends and alternately push down on one end while simultaneously pull on the other. This isolates the upper-body forces from the legs. also keeps the bike-stationary for a frame of references. I can only apply about half the load of a sprint with my upper-body alone, but the bar-ends will flex close to 1" as it is.
2. wheels are very, very weak laterally. The more the bike is leaned over, the more the wheels bend at the contact patch. I clamped a wheel in Park truing stand and clamped stand in vice. Hung 100kg of sandbags off rim to simulate peak dynamic force on rim. Hang the sandbags near where the wheel goes between the arms of the stand. Measure gap between rim and arm for deflection. Used flex=cos(LeanAngle)*force to roughly estimate wheel-deflection where perfectly vertical bike experiences zero lateral wheel flex.
3. BB is kinda hard to isolate from the fork. Stand on left side of bike, hold front-brake, lean bike over about 20-degrees, stand on pedal with all your weight while holding same the bike-lean angle, notice BB's lateral deflection.
