Brian Ratliff

Awesome. You linked your google search. Bravo.

Tell me. Have you read any of that stuff you linked to? Did you understand it? That first paper has me diving for my dynamics textbooks from college. Are you fluent in the subject? Eigenvalues and stability regions? Enlighten us. Please.

It is definitely not a simple model. But still, the bike is a pretty simple machine. Enlighten us with your thoughts about how a list of half a dozen design variables contemplates such a complex system.

Here's a hint. Yes... the system is complex to describe in its entirety. But a few design variables, trail and flop being two of them, are probably sufficient to fully describe a bicycle handling characteristic as is proven out by experiment. The modern bicycle is a stable and robust dynamic system, which is why the operating space of the design variables is so large. Maybe that's my response to the OP; for the road, these design variables have a wide range. But still, and it is extremely apparent on the track, these design variables play an important role in how the bike behaves and "feels". I've ridden bikes that are basically unrideable at speed on the banking. I've almost lost control of bikes that paired a track frame with a road fork, creating a short trail. Not fun to have the steering start oscillating in the middle of a 35+mph sprint on a 43 degree banking.

Brian Ratliff

To be completely fair to the OP, The book "Bicycle Science" does not, in fact, mention flop at all. I just checked. The chapter on bicycle stability is pretty thin and is sourced mostly from research done in the 70s. There's a tabulation of the trail on way outdated bike models and some mention of pretty simplified linear dynamics models and that's pretty much it.

The book itself is comprehensive but in sort of a random fashion. At one point he is talking about powercranks and power generated pedaling backwards. As an overview of the history of bicycle science, it is interesting. As a current day textbook to lend insight into modern bicycles, it is not great.

RollCNY

Please read the original post, including the Rolo bikes link. They essentially state that Flop dictates a bicycle's ability to hit the apex of a curve, and to adjust that line while in a curve.

The point of my little story is that regardless of Flop, the rider adjusts. The line I take through a curve has not changed, despite Rolo's assertion that it would.

Hey, wow, you're a track rider. Was that the purpose of your track comments?

RollCNY

OP, my reply was snide, and was unwarranted. I do not ride with my hands off the bars, so I would not have noticed if that attribute changed. Had I realized that was the sole point of debate, I would not have commented. I stated my experience only to say that differences in trail (and therefore flop) are extremely easy to compensate for.

For a given HTA, trail and flop are linearly related. So I don't see how one can determine what is impacted by flop, and what is impacted by trail. The only way I can imagine to actually isolate flop would be to have a bike with a variable HTA and variable offset/rake, so that you can adjust the same bike to have identical trail at different HTA conditions. The wheel base would also have to be adjustable, to keep that constant. Maybe then flop could be isolated as a sole variable.

Campag4life

I think it maybe important to consider what flop and trail are mathematically to better understand their relationship. All flop is...its a function of trail relative to head tube angle. Trail is also a function of hta as well. So Flop simply is trail with a greater onus on head tube angle versus fork rake. Both as it turns out are a function of one another. Trail is also referred to as 'castor' which addresses the centering or restorative nature of handling. Flop is related but mathetmatically places greater emphasis on hta. So they are highly related and the contrived parameter or even concept of flop is a slightly more what I would call confounded variable of frame geometry...trail being more fundamental as flop is a function of the more elemental construct of trail.

Where empirical assessment of bike handling gets dicey is...many factors influence a bike's handling characteristics and yes that includes stack and reach, wheelbase and even bottom bracket drop. Flop is simply a derivation of the concept of trail but with further involvement of head tube angle which is already a function of trail. So flop adds another level of complexity to determining how a bike handles. More terms could be described that say may include wheelbase...and/or bottom bracket height...or even rider CG relative to seat height. More concepts could be derived. We could call that 'steering turn in' which could be function of all the afore mentioned. So all depends on how intricate the mathematical relationships you want and at the end of the day what is really learned from it relative to how a bike actually performs. The reality is, the handling of a bicycle can not be distilled down into a meaningful equation. That equation is too multi variant and too complex. A human being however can qualitatively crunch this equation by riding a given bike for example...say the often compared difference between a Tarmac and Roubaix. Perhaps some inferences could be derived by this comparison by comparing dimensional relationships. But these would only be extrapolations and if one dimension is changed, say in the example of Tarmac to Roubaix, a 20mm difference in head tube length which places more weight on the hands of the Tarmac rider, this dramatically influences steering response. Include shorter Tarmac wheelbase and/or chainstays and further difference...independent of concepts or dimensional focus on flop or trail. Even sta affects rider fore/aft weight distribution and handling or dip/turn into the apex of a corner...flop and trail are only part of the equation.
Motorcycle racers know this instinctively by changing suspension height front and rear which changes handling dramatically...same flop and trail.

So the notion of flop which is a more complex way of looking at trail maybe an interesting academic exercise but nothing more.

Ridelots24

my brain just low flopped itself...

Campag4life

Really funny stuff. You should be a comedy writer!

redfooj

and what if the fork was Smartwelded

bakes1

Your multiple sniping of other posters is derailing this thread as much as or more then anything else. Seriously...
And are you so sure the dude just wants to talk about frame geometry?
Because I just re-read the OP and it kinda seems like the dude just read a couple of articles and wants to show off a bit and use some news terms he just learned but doesn't really understand.
But don't take my word for that. Just check out post #36 where he corrects himself and more telling, post #'s 48-51 where he is again corrected and this time what he got wrong was pretty much the basis for everything he was trying to enlighten us all about.

Campag4life

That would affect the concept of bounce steer through a corner Smart-alec

Campag4life

Actually, you are further derailing this thread. Brian is one of the smartest bike guys here. No, nobody is always right and each entitled to their opinion.
If you have something to add relative to the not widely acknowledged construct of flop, please do so. Otherwise don't troll...

Brian Ratliff

But doesn't flop have a role to play in bike cornering? Seems like it might. Flop is simply the front end of the bike lowering in response to the wheel turning. Some flop is obviously desirable, otherwise we'd all ride bikes with 90 degree headtubes and backward raked forks. Too much flop is probably bad too, which is why the headtube never gets more shallow than about 65 degrees. Is it not such a horrible thing to want to know why this is the case and what to do about it?

Flop will tend to lock you to a cornering line. Thinking about it, it is probably the reason why you are most stable cornering with weight on the inside handlebar. It's probably why, on a sharp corner, the bike feels like it "grooves" into the cornering line and takes some effort to get back straight.

And, yep, I'm a track racer and it's interesting to this discussion because whereas a road rider can adapt to almost any frame geometry (as you say, the rider adjusts) a track racer does not have that luxury. The physics are all the same, but I've got to ride a line a foot wide through a banked corner at 35-40mph. When is the last time you sprinted, at full power, around a corner on a line a foot wide? Bike handling gets real on the track, which is why I brought it up. All these things about flop and trail are magnified when you start putting demands like that into the equation, so the track becomes a test lab of sorts for these geometry considerations. You better believe it that track racers put some thought into this.

Bandera

No doubt about it, but we drew some inappropriate conclusions "back when" about handling and frameset construction that resulted in the 70's dedicated "Criterium Bike" fad.

A teammate who was a force on the track and a threat in any short flat-ish road race reasoned that the qualities of nimble, precise handling and a stiff efficient frame that made his track bike a joy to race on the track would translate to make a superior Criterium machine. A local builder produced what was essentially a copy of his track frame w/ a derail hanger and brake fittings.

Although he continued to be successful in Crit races on the radical new machine he eventually admitted that it rode like a lumber wagon on rough surfaces, was twitchy in cross winds and nervous on descents. Not ideal road bike qualities, but it was a highly specialized tool and no one could argue w/ his results.

My point?
The track and the road are different environments.
What works well on the banking may not on chip seal road descents into a decreasing radius off camber corner at pace.

Another point?
Get on the track if at all practical.
There is no better place to learn/hone essential basic cycling skills.

-Bandera

RollCNY

I have no idea whether flop plays a role, and it genuinely seems like a contrived measurement to simplify a complicated process. Flop is the amount of height change between a wheel parallel to the frame and perpendicular to the frame (90°turn). Turning the wheel 90° either forces the frame to lean away from the turn at the HTA, or you hold the frame vertical and alter the trail. But in an actual turn, you lean the frame into the turn, not away, and not forced vertical.

Oh, and turning the wheel lengthens the wheelbase. How does that factor into turning? The rate of change is dependent on trail.

To me, the mechanics of turning are very iterative, with a great range of variables impacting the outcome. The Rolo link read to me like they were definitively saying that flop was the primary determinant. I believe that to be a gross oversimplification.

I understand the "groove" feeling, but don't see that as relating to flop.

Brian Ratliff

Let me put it another way with a "food for thought" type question...

Why do we have stems on bikes? Why not just extend the frame, put the head tube angle at 90 degrees, and run a fork offset to the rear? Eliminate the stem. Eliminate the flop, keep the trail.

The entire field of engineering design is about collapsing complicated physical behavior into a limited number of design variables. To say "it's complicated" and leave it at that doesn't really do much for me. Flop is one of about six or eight design variables that every frame manufacturer plays with to affect bike handling. That's your "great range of variables" that a century of experimentation has given us. Now, everyone's complained about the Rolo link... nobody's actually answered to its logic except to say "it's complicated". That's a cop-out. The Rolo link is compelling. No data, but the logic is compelling, even if the numbers might eventually show it insignificant.

So, since you wrote the words that you "don't see [the "groove" feeling] as relating to flop"; expand on this. You have me intrigued. What's your thoughts or alternative theories? Don't go begging that "it's complicated". Of course it's complicated. But design variables are finite and each relates to bike handling with different effectivity. Why do you believe flop is not one of these effective variables?

Brian Ratliff

I agree. Track and road are different environments. And it could be that variables that are significant on the track do not have the same significance when on the road.

As to the other point: I like your thinking. I like the track.

Brian Ratliff

BTW, it's perfectly okay to go into the realm of "number of angles on a pinhead" type thinking when approaching these topics. It's how the raw material for creative thought and problem solving is generated. There is no need to be fully practical on an internet forum when opining on bicycle dynamics.

3alarmer 

...you should also read the link to "Poisoning the well of discourse" in the other FLOP thread. I doubt it will help at this point in your life of expertise and saving the internet, one post at a time, but it's still pretty interesting.

3alarmer 

...self professed expertise is the current currency of the bike forums. I have had full serving of yours, sir.

RJM

I knew this had something to do with Jan Heine.

The fact that he carries a load on the front wheel has something to do with his preference for low trail and I'm assuming that relates to some sort of "wheel flop" number.

Darth Lefty 

So far it's about five pages

3alarmer 

...#thnkU

McBTC

I think the mathematical relationships are pretty well understood. No one is arguing with the mechanics of the calculator in post 1.

Bicycle handling is important but looking into how the geometry influences bike handling is of interest only to a few. Those with an interest, however, are quick to agree that the amount of trail is the most important factor in bike handling so perhaps it is no surprise that current productions bikes all seem to have about the same amount of trail baked into their road bikes –e.g., everyone is doing the same thing so they must all be right.

No one seems to be questioning the tacit and yet unstated underlying assumptions being made by current bike producers in favor of the modern low-trail road bikes, despite the fact that the amount of trail was much larger in the past. And, the amount of trail nowadays also is quite a bit less than, for example, what you’d have on Dave Moulton’s "ideal handling bicycle.” So, Moulton’s design philosophy is now out of the mainstream. But why has the mainstream moved to shorter amounts of trail?

We know from Mouton’s spec when looking at the lowest HTA (71) on the graph where the amount of trail is at its max (69), where and the amount of wheel flop is correspondingly at its highest (21). Accordingly, according to Moulton, 21mm of flop should not be thought of in the range of an undesirable amount.

Given that, flops of 15mm cannot be the reason current bike producers are going with trail amounts in the 50s. Trail amounts could be in the 60-67 range (all with flops under 20) and maybe we’d all like that better. Some of us would.

No manufacturer I know of has articulated a reason why we should have fewer options in this regard –e.g., why we should have less and less trail in our road bikes. As we see in this thread, no one is asking for smaller and smaller amounts of trail. And yet, all we see on the market is HTA and offset relationships that would offer higher amounts of trail in a road bike are hard to find.

Campag4life

To me McBTC...your thesis is ridiculous. Not only are you considering trail and flop in isolation...say independent of chainstay length and wheelbase and also relative to sta and rider fore/aft weight distribution but no manufacturer is beholden to explain anything. Chevy in their Corvette marketing doesn't publish their steering ratios and knuckle lengths nor their pressure versus angle onsets for steering assist either. All manufacturers short of those that want to celebrate their differences thru marketing let their products do the talking. I have owned and ridden road bikes for 40 years. Your preoccupation with past spec's to me is irrelevant. Bikes are better 'by far' in every category than they have ever been. I have owned several from every decade. Bikes today handle circles around examples of the past...in no small part due to their stiffness which affects handling precision..aka Specialized cobra head tube and one piece top tube/head tube/down tube construction. It is quite possible that reduction is trail is partly tolerated for example by the stiffer bikes of today. Also bike have never descended at high speed better. Trails chosen today are chosen for the simple fact they work...values migrated to after 50 years of experimentation. The average road bike owner doesn't even know what trail is. They do know what weight is of course and why manufacturers sometimes and not always even advertise weight.

RJM

That isn't true.

Wheelbase, Trail, and other considerations -
Learn About Bikes with Rivendell Bicycle Works

Grant knows some things about bike design and has written about it, but this is a good, short article that touches on trail and wheelbase that is on the Rivendell site.

Basically, boiling this down to a single number doesn't work.