why Brompton forks have such low trail?

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Freddie
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Re: why Brompton forks have such low trail?

Postby Freddie » 1 Jun 2018, 7:01pm

pjclinch, I'm sorry, that just reads like excuses for bad design. There are designs that it is nigh on impossible for anyone to ride consistently in a hands off position. This is not the same thing as riding a unicycle and is not a skill to be learnt (as riding a unicycle is).

A bicycle that has a mind of its own is a danger to the rider. A bicycle that cannot be controlled by lean input (which is what no hands riding is), is a machine that needs more attention than necessary and is liable to chuck its rider off at a moments inattention. Geometry is a known quantity, it is known what would make the Brompton (and many other folders) more stable, namely more trail in the fork.

Cars and motorcycles that oversteer are considered dangerous and unfit for the road. Because the novelty of folding has been added to a bicycle frame, that does not discount the necessity of it being a safe and stable ride.

Randy_Butternubs
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Re: why Brompton forks have such low trail?

Postby Randy_Butternubs » 1 Jun 2018, 7:35pm

Freddie wrote:pjclinch, I'm sorry, that just reads like excuses for bad design. There are designs that it is nigh on impossible for anyone to ride consistently in a hands off position. This is not the same thing as riding a unicycle and is not a skill to be learnt (as riding a unicycle is).

A bicycle that has a mind of its own is a danger to the rider. A bicycle that cannot be controlled by lean input (which is what no hands riding is), is a machine that needs more attention than necessary and is liable to chuck its rider off at a moments inattention. Geometry is a known quantity, it is known what would make the Brompton (and many other folders) more stable, namely more trail in the fork.

Cars and motorcycles that oversteer are considered dangerous and unfit for the road. Because the novelty of folding has been added to a bicycle frame, that does not discount the necessity of it being a safe and stable ride.


Given that you say you haven't ridden one I think you are drawing too-extreme a conclusion based on what the geometry looks like. Good handling seems to involve a few factors and be fairly personal so I don't think there is a good way to make a judgement on a bicycle without trying it yourself.

I'm not a fan of the Brompton particularly but I do like how they handle - to the extent that I'm keen on trying other low trail bikes. I didn't find it required any particular effort or concentration once I had got used to it. It certainly wasn't dangerous.

You've mentioned steering by lean-input a couple of times. This is not how I ride at all - all input is to the handlebars which then determines lean angle and steering. I'm skeptical that anything other than small course-correction is possible by just leaning given my (limited) knowledge of how single-track vehicles turn.

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pjclinch
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Re: why Brompton forks have such low trail?

Postby pjclinch » 1 Jun 2018, 7:54pm

fossala wrote:
Mick F wrote:Dunno what the Moulton's trail is.
I have tried in No Hands and it's no easier or harder than Mercian.

I'll have a go at measuring them both later.

I was thinking this last night, riding Moulton with no hands is easy. I also had a Brompton for a bit, couldn't ride it without hands even for 2 seconds.


I can ride my TSR no-hands for a (typically) a few hundred meters. I can ride my (old short wheelbase) Brom no-hands for (typically) tends of meters. I can ride a Dutch opafiets no-hands for kms, and am happy with hands in my pockets or changing gloves etc. Don't think I'd try that on the TSR (though doubtless some could do it easily).

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fossala
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Re: why Brompton forks have such low trail?

Postby fossala » 1 Jun 2018, 8:09pm

pjclinch wrote:
fossala wrote:
Mick F wrote:Dunno what the Moulton's trail is.
I have tried in No Hands and it's no easier or harder than Mercian.

I'll have a go at measuring them both later.

I was thinking this last night, riding Moulton with no hands is easy. I also had a Brompton for a bit, couldn't ride it without hands even for 2 seconds.


I can ride my TSR no-hands for a (typically) a few hundred meters. I can ride my (old short wheelbase) Brom no-hands for (typically) tends of meters. I can ride a Dutch opafiets no-hands for kms, and am happy with hands in my pockets or changing gloves etc. Don't think I'd try that on the TSR (though doubtless some could do it easily).

Pete.

I don't do it at all on my AM-18 currently as the headset need new bearings and is a bit stiff. Normally though I can go as long as I need.

Randy_Butternubs
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Re: why Brompton forks have such low trail?

Postby Randy_Butternubs » 1 Jun 2018, 8:26pm

This is an interesting blog post on the work of Jim Papadopoulos, who is also active in the comments. Papadopoulos seems to be the foremost expert on bicycle self-steering as far as I can tell.

https://janheine.wordpress.com/2011/04/ ... -together/


Key excerpts from Jan Heine, commenting on Papadopoulos' work:

"New theoretical research in bicycle stability shows that many parameters interact to make a bicycle stable. No single parameter (e.g.: trail, head angle, wheel size, weight distribution) determines whether a bicycle is stable or not. When one parameter is altered, then the other parameters may need to be changed to arrive at a stable bicycle again."

"...they discovered that neither trail nor gyroscopic forces are required to make a bicycle stable. To test this, they built a bicycle with negative trail and a second set of wheels that spin in the opposite direction and cancel the gyroscopic forces of the wheels."

and direct from Papadopoulos:

"I would like to summarize some other ‘big ideas’ that we feel arise from the work:

1.We have shown that simply having negative trail is nothing to be frightened of, in itself. It could possibly be part of a good design.

2.We have shown that the two main arguments used to justify trail are incomplete at best:
A.The first is that trail supposedly encourages the steering to turn into a lean, and this is often demonstrated by holding a bicycle at a lean angle and noting that the steering responds as desired. But this is a flawed argument and demonstration. If the bicycle (at rest) is released to FALL, especially if there is a proper mass distribution representing the rider, the steering might turn TOWARD, might turn AWAY, or might NOT TURN. It all depends on mass distribution.

B.The second is the idea that caster (trail) governs the flipping around of the front wheel, just as it does for a shopping cart. We have seen no evidence of that, so we have surmised that casters operate very differently in leaning systems."


and

"After making my long comment above, I realized that I may not have emphasized one key point. I feel, and I’m sure my co-authors agree, that self-stability is not the same as nice handling qualities."

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pjclinch
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Re: why Brompton forks have such low trail?

Postby pjclinch » 1 Jun 2018, 8:50pm

Freddie wrote:pjclinch, I'm sorry, that just reads like excuses for bad design. There are designs that it is nigh on impossible for anyone to ride consistently in a hands off position. This is not the same thing as riding a unicycle and is not a skill to be learnt (as riding a unicycle is).


Your implication is that a bike that is not easy to ride without the handlebars is necessarily poor design, but since the handlebars are designed to be used then as long as the bike is stable when they are used that's a bit, well, hatstand.

Freddie wrote:A bicycle that has a mind of its own is a danger to the rider. A bicycle that cannot be controlled by lean input (which is what no hands riding is), is a machine that needs more attention than necessary and is liable to chuck its rider off at a moments inattention. Geometry is a known quantity, it is known what would make the Brompton (and many other folders) more stable, namely more trail in the fork.


But a bicycle that is easily controlled with minimal input from the handlebars doesn't have a "mind of its own", and will not be liable to chuck off its rider at a moment's inattention (I've not come across any cyclists who just forget to hold on to the bars at all, no matter how much they've zoned out).

Freddie wrote:Cars and motorcycles that oversteer are considered dangerous and unfit for the road. Because the novelty of folding has been added to a bicycle frame, that does not discount the necessity of it being a safe and stable ride.


Oversteering on cars and motorbikes is nothing to do with whether there is a minimum handlebar steering input on a pedal cycle to keep it directionally stable. As already noted, one person's "twitchy" is another's "responsive". I have actively chosen to do most of my urban riding on small wheel bikes (a Brom and a TSR) because I like the nippy steering the small wheels allow. That doesn't prevent them being safe and stable, just as long as I have at least one hand on the bars. My 'bent won't do no-hands (at least for me) but that's not a problem: I didn't buy it to ride no handed, I bought it to allow relaxed riding all day, and as long as I've got as much as one finger on one bar it does that.
On the TSR today I was doing about 25 down a hill changing lane, looking over my shoulder and signalling right. I hit a particularly prominent cat's eye without warning (what with looking the other way) that gave me quite a start. But with one hand on the bars I didn't deviate from my path. Had the handlebars come off I'll grant you I'd have been better off on my MTB, but they didn't...

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pjclinch
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Re: why Brompton forks have such low trail?

Postby pjclinch » 1 Jun 2018, 8:52pm

fossala wrote:
pjclinch wrote:
fossala wrote:I was thinking this last night, riding Moulton with no hands is easy. I also had a Brompton for a bit, couldn't ride it without hands even for 2 seconds.


I can ride my TSR no-hands for a (typically) a few hundred meters. I can ride my (old short wheelbase) Brom no-hands for (typically) tends of meters. I can ride a Dutch opafiets no-hands for kms, and am happy with hands in my pockets or changing gloves etc. Don't think I'd try that on the TSR (though doubtless some could do it easily).

Pete.

I don't do it at all on my AM-18 currently as the headset need new bearings and is a bit stiff. Normally though I can go as long as I need.


It's entirely possible that you're a better no-hands rider than I am. My point was more that even while a Moulton can be ridden no-hands by some of the people, some of the time, there are other bikes that are better for it.

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531colin
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Re: why Brompton forks have such low trail?

Postby 531colin » 1 Jun 2018, 10:22pm

Bicycle self-stability (when you push a bike and let it go, it carries on "on its own") is an interesting intellectual curiosity, but it has nothing to do with actually riding the thing......because a 20 pound bike can't keep an 11 stone rider upright.

People buy Bromptons because of the fold. That's it, no other reason. Let me see if I can remember it....back wheel flips under. frame hinges. handlebar mast hinges down. it clips together somewhere near the front wheel axle.

You could give it more trail keeping the frame length the same, or the front centre the same, or whatever you will, because you can manipulate either head angle or fork offset to give whatever trail you want, keeping one or the other constant if that's what the fold requires.
I'm quite certain I could re-design the Brompton to fold just as well as it does now and to steer a whole lot better; I'm equally certain that Brompton won't bother, firstly because they don't know any better but also because the customers are so fixated on the fold that they will put up with dreadful handling.
And the handling is dreadful. I have borrowed one on a couple of occasions to do a train-assisted day where we ride from York to Scarborough....by the time I get to Scarborough, I don't mind if I don't ride one of the damned things for another year.
Properly-designed touring bikes (and tandems) are completely unperturbed by random inputs (road surface lumps and bumps, side gusts, luggage swaying, foot coming off the pedal, etc.) which will send a Brompton careering towards the ditch, or the wrong side of the road. That's whats wrong with them, and whats tiring if you ride them for any length of time.

How a bike handles no hands is very relevant to how it deals with random inputs when you are riding hands on. A touring bike no hands should be quite difficult to divert from "straight ahead", requiring exaggerated angles of lean to negotiate a gentle bend no hands, and becoming more stable as speed increases.
A race bike should be able to slalom the cats' eyes riding no hands. I prefer a commuting bike to have handling nearer to a tourer than a race bike......the argument that fast steering gets you out of a tight spot doesn't cut it with me, because fast steering can equally get you into a tight spot if your attention is focussed on the traffic rather than the road surface.

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Re: why Brompton forks have such low trail?

Postby pjclinch » 2 Jun 2018, 3:28am

531colin wrote:
People buy Bromptons because of the fold. That's it, no other reason.


It's a combination of a tight fold with a very rideable bike. Otherwise cheaper alternatives like the Cresswell Micro and Strida would have sold in similar numbers.

531colin wrote:Let me see if I can remember it....back wheel flips under. frame hinges. handlebar mast hinges down. it clips together somewhere near the front wheel axle.


Close-ish but no cigar, as the rest suggests unfamiliarity with them.

531colin wrote:I'm quite certain I could re-design the Brompton to fold just as well as it does now and to steer a whole lot better; I'm equally certain that Brompton won't bother, firstly because they don't know any better but also because the customers are so fixated on the fold that they will put up with dreadful handling.


I don't think this is actually the case at all. I first tried one when a friend was after a folder for her mum, and I (somewhat surprisingly) located a very good condition second hand one at a good price. We went to have a look, and I gave it a go not knowing quite what to expect. And I was immediately taken with just how normal a ride it gave. Shame about the brakes (this was a Mk 2), but the ride was fine, and I said on the back of a few minutes riding to my friend that I'd buy it and if she still wanted it I'd sell it on at the same price and get one of my own (I sold it on to her shortly afterwards and bought another). And other owners I know got them because they rode fine, and happened to fold up small too. Mine goes for weeks at a time without being folded beyond the parking flip, but it does a substantial portion of my day to day riding.

531colin wrote:And the handling is dreadful. I have borrowed one on a couple of occasions to do a train-assisted day where we ride from York to Scarborough....by the time I get to Scarborough, I don't mind if I don't ride one of the damned things for another year.
Properly-designed touring bikes (and tandems) are completely unperturbed by random inputs (road surface lumps and bumps, side gusts, luggage swaying, foot coming off the pedal, etc.) which will send a Brompton careering towards the ditch, or the wrong side of the road. That's whats wrong with them, and whats tiring if you ride them for any length of time.


I suspect that along with Freddie you're confusing "not what I'm used to" with "objectively worse".

The handling is fine, and I say this as someone who in 18 years of riding one has never been sent careering off line by any of the things mentioned above any worse than I've been on a drop bar tourer (of which I also have years of experience). In fact part of the reason I donated my drop bar tourer to the local recycler was I wasn't using it any more... a 'bent had replaced it for touring and for local work I found my Brompton had just usurped it as go-to bike. Mainly I prefer a more upright ride if I'm not in a comfy chair, finding it much easier to relax, but if the handling were terrible it wouldn't be the relaxed ride I find that it is.
My house is on unsurfaced road, Dundee has its share of cobbled streets (on hills), I tend to take off-road short-cuts, and none of this phases a Brom at all.

What I find tiring if I ride it for a long time is the effect of all my weight on a saddle for the day. No coincidence that I tour on a 'bent.

531colin wrote:How a bike handles no hands is very relevant to how it deals with random inputs when you are riding hands on. A touring bike no hands should be quite difficult to divert from "straight ahead", requiring exaggerated angles of lean to negotiate a gentle bend no hands, and becoming more stable as speed increases.


My touring bike is a 'bent, and that particular model I absolutely won't attempt no-hands. But one handed it's very stable indeed even with unexpected inputs , and as with a very upright bike having no lean on to the bars it's actually much more stable one-handed than a bike ridden in a forward crouch.

531colin wrote:A race bike should be able to slalom the cats' eyes riding no hands. I prefer a commuting bike to have handling nearer to a tourer than a race bike......the argument that fast steering gets you out of a tight spot doesn't cut it with me, because fast steering can equally get you into a tight spot if your attention is focussed on the traffic rather than the road surface.


The key phrase there is "I prefer". The Brom's steering has, in 18 years, never put me in "a tight spot". I ride my TSR in preference on some journeys for various reasons: the stiffer frame and front suspension means it's more efficient, it's got a bigger gear range in finer increments and it carries a bit more. But there's nothing broken about the handling that I want to fix.

I taught a complete non-rider to ride a bike using a Brom earlier this week. Another session a couple of days later I re-introduced another rider who'd not ridden since she was a wee girl (she's about to retire). Neither seemed to find my SWB Brom a problem after the first few minutes.

It's very unusual I see a post from you where I wonder where on earth you're coming from, but this is one of them. It just doesn't square with my experience at all. The only time I find the Brom handles poorly is going up a very steep hill, when it's hard to keep the front wheel down, or if there's a properly heavy load in the front bag.

Pete.
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Re: why Brompton forks have such low trail?

Postby Barks » 2 Jun 2018, 7:21am

This all comes across as the OP being one of the anti-Brompton crowd and is just looking to generate a wider consensus along those lines. I have had a Brompton for three years, did find it relatively ‘twitchy’ (to my hybrid with MTB tyres) when I first rode it but withinn a few minutes adapted accordingly. The Brompton is very responsive but this makes it very manoeuvrable which is fantastic in busy areas. Having a load in the front mounted bag does make the bike feel steadier. All design is a compromise you just have to trade off what you want from it - I wouldn’t be without my Brompton for day to day use in around towns and cities. If want to go further/faster, carry loads of stuff, etc, then I simply use a different design bike, just like someone who switches between a road racer and an off-road bike option.

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Re: why Brompton forks have such low trail?

Postby UpWrong » 2 Jun 2018, 8:03am

Bromptonites don't seem to allow alternative views. As I said, I abandonned Bromptons because of their handling. So the company lost my business and I will forever point people expressing interest in folding bikes in the direction of Terns. The difference in stability is night and day.

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Re: why Brompton forks have such low trail?

Postby pjclinch » 2 Jun 2018, 9:06am

UpWrong wrote:Bromptonites don't seem to allow alternative views. As I said, I abandonned Bromptons because of their handling. So the company lost my business and I will forever point people expressing interest in folding bikes in the direction of Terns. The difference in stability is night and day.


That different people interact differently with different bikes is hardly a surprise. So it's no surprise that just as you and 531colin don't get on with Brom handling, there's plenty (like me) that do. And for those that do get on with a Brom, that a Tern may be more stable is a bit of a moot point. A trike is easier to balance than any of my bikes, but if I don't really have any trouble balancing my bikes then the extra point of balance stability on a trike is really neither here nor there for me.

There are plenty of reasons to prefer alternative folders to Broms. I ride a Brom because for me, and what I want and do, the Brom is a good match. Do I consider alternatives to be heresy? No, I frequently recommend alternatives, and I also recommend people take test rides to see if they get on with stuff.

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Mick F
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Re: why Brompton forks have such low trail?

Postby Mick F » 2 Jun 2018, 9:19am

Still not measured the trails .............

However, I can ride some bikes almost permanently no hands, and others like my Mercian are difficult and twitchy.
What I have to do, is sit right back and vertically. It's all to do with weight distribution rather than solely on trail.

Mercian can be pushed by the saddle and the steering is easy and accurate and simple.
Moulton isn't easy. Once to go off course, it takes a great deal of leaning the other way to correct it, and often it's unrecoverable. I put that down to the small wheels rather than frame geometry.
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Re: why Brompton forks have such low trail?

Postby Freddie » 2 Jun 2018, 9:25am

pjclinch wrote:That different people interact differently with different bikes is hardly a surprise. So it's no surprise that just as you and 531colin don't get on with Brom handling, there's plenty (like me) that do. And for those that do get on with a Brom, that a Tern may be more stable is a bit of a moot point. A trike is easier to balance than any of my bikes, but if I don't really have any trouble balancing my bikes then the extra point of balance stability on a trike is really neither here nor there for me.
What you seem to suggest is that there is no such thing as objectively good handling and that all handling is dependent on the individual riding the bicycle.

Is that really true? Whilst there are people who can't ride no hands whatever the bicycle and even people that can't ride a bicycle at all, this doesn't discount the fact that some bicycles are more stable than others and there is a range in which a bicycle provides normal handling and outside of this range the handling is sub-optimal.

Why should somebody have to relearn how to ride a specific bicycle? Doesn't that suggest the design is flawed from the get go (save things like fixed gear, which is a different kettle of fish).

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Re: why Brompton forks have such low trail?

Postby Randy_Butternubs » 2 Jun 2018, 11:58am

Freddie wrote:
pjclinch wrote:That different people interact differently with different bikes is hardly a surprise. So it's no surprise that just as you and 531colin don't get on with Brom handling, there's plenty (like me) that do. And for those that do get on with a Brom, that a Tern may be more stable is a bit of a moot point. A trike is easier to balance than any of my bikes, but if I don't really have any trouble balancing my bikes then the extra point of balance stability on a trike is really neither here nor there for me.
What you seem to suggest is that there is no such thing as objectively good handling and that all handling is dependent on the individual riding the bicycle.

Is that really true? Whilst there are people who can't ride no hands whatever the bicycle and even people that can't ride a bicycle at all, this doesn't discount the fact that some bicycles are more stable than others and there is a range in which a bicycle provides normal handling and outside of this range the handling is sub-optimal.

Why should somebody have to relearn how to ride a specific bicycle? Doesn't that suggest the design is flawed from the get go (save things like fixed gear, which is a different kettle of fish).


I don't think he's suggesting that good handling is entirely subjective, just that it isn't entirely objective.

I don't think anyone has said anything about relearning, just that different people have different experiences. I was in London traffic within seconds of first getting on a Brompton and it was no danger and I was enjoying it within 5 minutes. As I said earlier I'm not particularly a fan of Bromptons as I find them rather flexy and extremely slow but I do like how they handle.

I'm not writing off those who hate the Brompton handling. That some people don't get along with them is news to me but I don't disbelieve them. Such differences are only an issue when someone stubbornly, or perhaps arrogantly, tries to enforce their experience as the one true truth (TM).
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