Wheel Flop Q

[merckx]

I have a question about wheel flop. I have a frame that really dives into a turn and not in a good way. It feels like the front end wants to collapse when turning. If the front end wanders while riding no handed, it will take a dive to the ground. I'm trying to figure out why this is occurring and maybe find a solution. It is a sportif style frameset with 47/57 brakes and clearance for mudguards. Here are the specs:

seat tube: 61 c-c
top tube 585 c-c
head tube:178
bb drop: 80
rear center: 440
front center: about 60
sta: 70.5
hta: 71.5
rake: 51
trail: 60

The trail feels like it is 70mm and not the actual 60mm the way it flops into corners. I was wondering if a fork with a 56mm rake (and trail of 55mm) would correct it. The front center would slightly increase but that may be a better balance with the longer chainstays. Thoughts?

[AngryScientist]

how long of a stem do you have on the bike?

[Dude]

X

[Lewis Moon]

how long of a stem do you have on the bike?

My thoughts are that, if it occurs while riding hands off, it's a bad geo issue rather than a stem issue.

PS, you should also ask the wags on V-Salon.

[FastforaSlowGuy]

how long of a stem do you have on the bike?

Why would stem length affect wheel flop when riding no-hands? Doesn't that take the bar/stem issues out of the equation?

[AngryScientist]

Why would stem length affect wheel flop when riding no-hands? Doesn't that take the bar/stem issues out of the equation?

you know, it's a good question, but i find, perhaps through coincidence that my bikes that use a longer stem are way easier to no-hand than those with a short stem. that may infer something about the rest of the bike geometry and my position on the bike, but i've never really thought about it too hard. anecdotal evidence from me though.

[merckx]

The stem is a 120 fwiw. It's not the stem, imho. Just wondering if a bit more rake will straighten it out.

[David Kirk]

Hey -

A trail number of 60 mm isn't normally associated with wheel flop and like you suggested it's usually more toward 70 mm that things get as bad as you are reporting. 60 mm is a bit long for a race bike but for a sport or general use bike one would think it to be fine.

I have two questions -

- is there a handlebar bag or front rack on the bike?

- are the numbers you listed numbers you measured or ones that were listed on the build sheet or in the catalog?


dave

[merckx]

Hey -

A trail number of 60 mm isn't normally associated with wheel flop and like you suggested it's usually more toward 70 mm that things get as bad as you are reporting. 60 mm is a bit long for a race bike but for a sport or general use bike one would think it to be fine.

I have two questions -

- is there a handlebar bag or front rack on the bike?

- are the numbers you listed numbers you measured or ones that were listed on the build sheet or in the catalog?


dave

Hi Dave,

Thank you for lending your expertise. I don't have a handlebar bag attached to the front end. No rear bag either. Tires are 25c 4000s. As far as I can tell, the bike is built to the spec noted above. I used a Wixey digital gauge to measure head angle and it seems to be on spec or close. The front center seems on spec too as I measure it so I assume the fork rake is good, no? Hypothetically speaking, if the HTA was off a 1/2 degree, say 71, would that throw a spanner in the works?

[wallymann]

bb drop: 80

this spec stands out.

i have a similar sized merckx (58tt) with a similarly low BB but my HTA is alot steeper, like +74deg. it also has wonky handling compared to everything else i own, both classic and modern -- at least when i'm fresh off my other bikes.

the merckx's handling is...deliberate. when the front end goes to one side when riding no-handed, it doesnt want to come back to center unless i give a very *exaggerated* hip shift.

while my first couple of rides i really didnt like it, i've gotten used to it after while...it's just different.

http://majortaylorcycling.org/bikes/thumbs/walter_merckx_corsa-os.jpg (http://majortaylorcycling.org/bikes/walter_merckx_corsa-os.jpg)

[merckx]

Dave, I'm wondering if the weight distribution is off. Maybe the front center is too short relative to the rear center? Also, if I have a fork built with a 56mm rake, will it add to the "flopishness" of the front end because it telescopes the front wheel out further even though the actual wheel flop measurement (and trail) is reduced (if that makes sense)?

[David Kirk]

Hey Mr. Merckx -

I'm having a hard time coming up with a reason why the bike would feel the way it does based on the numbers you've shared. Yes the c-stays are long and that places more weight on the front but the front isn't short at 60 cm.

I don't feel that 1/2° of head angle would make or break the deal. I also don't see the 80 mm of BB drop being much or a factor.....plenty of bikes out there with a drop of 80 that have no issues at all as long as the steering numbers are good.

If you put a fork with more rake in the frame you will certainly lessen the trail which might be a good thing (I say 'might' because I'm skeptical that the 60mm of trail you should have now is causing the flop issue.......I've owned and ridden many bikes with 60 mm of trail that do not flop) and it would also make the front center a bit longer which could also be a good thing. That said 5 mm of front center change can often be felt but would seldom completely change the bike and turn it from a bike with flop to a proper handling bike.

So with all of that said - I can't tell what is causing your issue and have no clear recommendation on how to fix it. Based on the numbers you give I would not expect the bike to feel agile or race-like but at the same time would not expect that it would be so overly stable that you experience dive or flop.

This is why I asked about racks and bags........I keep thinking there needs to be one more piece of the puzzle to solve it but I don't see any place where that piece is missing.

Has the bike ever been crashed or damaged in any way?


dave

[bart998]

[QUOTE=David Kirk;1619875]

Has the bike ever been crashed or damaged in any way?


^^^^
THIS.... I'll bet the blades aren't aligned or similar, structural problem.

[palincss]

Hey -

A trail number of 60 mm isn't normally associated with wheel flop and like you suggested it's usually more toward 70 mm that things get as bad as you are reporting. 60 mm is a bit long for a race bike but for a sport or general use bike one would think it to be fine.

I have two questions -

- is there a handlebar bag or front rack on the bike?

- are the numbers you listed numbers you measured or ones that were listed on the build sheet or in the catalog?


dave

But a 71.5 degree head angle generally is associated with a lot of wheel flop, is it not?

[tiretrax]

I was wondering about the fork, but what about the wheel - could it be out of true/uneven spoke tension?

[David Kirk]

But a 71.5 degree head angle generally is associated with a lot of wheel flop, is it not?

No - not at all. In fact a head angle means nothing on its own and only becomes relevant when it's coupled with a given fork rake to result in X amount of trail.

I think sometimes people can get the idea that a more shallow angle will result in flop because mass market bikes so often come with a one-size-fits-all fork rake (usually 43 or 45 mm) and this will give too much trail and result in flop. The end result being folks blame the head angle while completely passing over the fact that it't just the wrong fork for the frame.

A 71.5° head angle combined with a one size fits all fork rake of 43mm will give a nasty 68 mm of trail which will nearly guarantee flop. While on the other hand......if you toss that 43 mm fork onto ebay and put a proper fork with rake of say 53 mm then you get a trail of less than 58 mm and life is good.

dave

[merckx]

Thank you all for your contributions on solving this puzzle. The frame has not been damaged in any way and is not out of alignment as far as I can tell. It rides with no hands on the bars really well as long as it doesn't deviate from center. I may punt at some point and have a fork with a longer rake built. Fit and function on this frame is really swell.

[Peter P.]

My first question is, was the fork made specifically for the bike? If the axle-crown length is longer than what the frame was designed for, you'll experience wheel flop.

I had a Trek 660 which rode fine until I replaced the headset with a Stronglight roller bearing headset.

The lower cup had a taller stack height than a typical headset of the day (although when I refer to my Sutherland's Manual, the published numbers don't seem to reflect what I remember).

The result was a wheel flop which I could feel when leaning into corners. It was as you described; the front end felt like it wanted to "collapse" in corners. I could only tolerate it for so long when I switched it out for a more common ball bearing headset with a shorter lower stack height because I suspected that was the cause. Problem solved.

So the other problem could be the stack height of the lower headset cup.

[David Kirk]

Thank you all for your contributions on solving this puzzle. The frame has not been damaged in any way and is not out of alignment as far as I can tell. It rides with no hands on the bars really well as long as it doesn't deviate from center. I may punt at some point and have a fork with a longer rake built. Fit and function on this frame is really swell.

Cool - one last question out of curiosity.......... does it feel fine when going fast and you can easily ride no handed but at lower speeds it's sketchy?

dave

[moose8]

Cool - one last question out of curiosity.......... does it feel fine when going fast and you can easily ride no handed but at lower speeds it's sketchy?

dave

Now I'm curious because I've had a bike like that - what causes it?

[cmg]

Now I'm curious because I've had a bike like that - what causes it?

the more trail, the more stable the bike wants to be and have heaverier, harder to turn steering. It will tend to correct itself. As the trail decreases (fork rake increases) the more twitchy it becomes or steering becomes more sensitive. have a look at the diagram. pretty good website that tries to explain handling with calculator. http://yojimg.net/bike/web_tools/trailcalc.php i think the OPs geometry is off. the bike should be stable.

[FastforaSlowGuy]

Tom Kellogg has a great discussion of trail and its effects on handling.
http://www.spectrum-cycles.com/geometry.php

People always talk about a bike getting twitchy or sluggish, but as Tom points out, it's really about how it handles across the speed range. A neutral bike handles the same, but with high or low trail, its handling changes with speed.

[merckx]

Cool - one last question out of curiosity.......... does it feel fine when going fast and you can easily ride no handed but at lower speeds it's sketchy?

dave

At speeds above 18mph, the bike rides easier no-handed. Below that speed, it becomes more of a handful if road undulations or a little wind pulls it off line. I've had many framesets with trails at 57-60 mm and they were really stable at lower speeds. This one is a departure. The fork was made for the frame so no clues there. Also, the headset is a King and it perfectly adjusted.

[David Kirk]

At speeds above 18mph, the bike rides easier no-handed. Below that speed, it becomes more of a handful if road undulations or a little wind pulls it off line. I've had many framesets with trails at 57-60 mm and they were really stable at lower speeds. This one is a departure. The fork was made for the frame so no clues there. Also, the headset is a King and it perfectly adjusted.

It sure sounds like it behaves like a bike with too much trail.

I suspect that the fork does not have the rake you think it does. Even a few millimeters will change the trail and feel and my guess is that your fork has less than the stated rake.

Before you throw down for a new fork I'd pull this one from the frame and measure its rake. If you need any guidance to get a good measurement let me know.........there are simple ways to do this with just a ruler and a few blocks of wood.

dave

[witcombusa]

What is the type and condition of the headset? A slight amount of on center "detent" will cause exactly what you are experiencing.

Perhaps a great time to do some PM there and check things out. You also may want to go from a caged bearing set to loose balls (if applicable).

[witcombusa]

My first question is, was the fork made specifically for the bike? If the axle-crown length is longer than what the frame was designed for, you'll experience wheel flop.

I had a Trek 660 which rode fine until I replaced the headset with a Stronglight roller bearing headset.

The lower cup had a taller stack height than a typical headset of the day (although when I refer to my Sutherland's Manual, the published numbers don't seem to reflect what I remember).

The result was a wheel flop which I could feel when leaning into corners. It was as you described; the front end felt like it wanted to "collapse" in corners. I could only tolerate it for so long when I switched it out for a more common ball bearing headset with a shorter lower stack height because I suspected that was the cause. Problem solved.

So the other problem could be the stack height of the lower headset cup.

I don't think the problem you had was because of any minute difference in lower race height. The Stronglight roller bearing headset has more resistance to turning than a ball bearing headset. On some bikes it is enough to make the handling feel odd. I run one on my WitcombUSA without issue but have heard others have the same issue as you did.

This is also why I think it may be the headset on the OPs bike. They really can really disturb the feel of otherwise great bikes (and motorcycles too). Not just brinneling or gauling damage but even dried out grease can do it.

[seanile]

Also, the headset is a King and it perfectly adjusted.king is cartridge, not going to have an indexing with that.

[merckx]

It sure sounds like it behaves like a bike with too much trail.

I suspect that the fork does not have the rake you think it does. Even a few millimeters will change the trail and feel and my guess is that your fork has less than the stated rake.

Before you throw down for a new fork I'd pull this one from the frame and measure its rake. If you need any guidance to get a good measurement let me know.........there are simple ways to do this with just a ruler and a few blocks of wood.

dave

Dave, that is what I'm going to do, pull the fork and measure it. I think I can do it myself. I have a Park fork alignment jig. I'll fasten the jig to my vise, insert the fork, index it, measure the dropout ctr from the bench top, flip the fork around, index it, and measure again. Then do the maths. Sound correct?

Regarding the headset, it is a King, brand new, and adjusted perfectly.

[David Kirk]

Dave, that is what I'm going to do, pull the fork and measure it. I think I can do it myself. I have a Park fork alignment jig. I'll fasten the jig to my vise, insert the fork, index it, measure the dropout ctr from the bench top, flip the fork around, index it, and measure again. Then do the maths. Sound correct?

Regarding the headset, it is a King, brand new, and adjusted perfectly.

I think that should do it.

Let us know what you fit out.

dave

[merckx]

I'll report back. Thank you all for your suggestions.