Effects of different weight distributions

[Kim]

I've seen lots of people do a decent job with some old inner tube to protect the paint and jubilee clips. So long as you don't use a hydraulic torque wrench to stick them on I don't think it'd be suicidal, products like http://bikepacker.com/gorilla-cage-system-review/ seem to do the same thing.

I've got a gorilla clip attached to the boom of my tourer using the supplied cable ties and rubber padding, to make up for HPVelotechnik's blind spot for sensible bottle mountings.  It mostly gets used for a fuel bottle, but a Gorilla Cage of something slightly bulkier is a possibility I haven't needed to explore yet.

I'd be reasonably confident using one on a fork, as long as the diameter was towards the MTB end of the spectrum^[1].  A non-circular cross-section would help prevent rotation.


_{[1] At which point you're messing things up by adding unsuspended load.}

[Brucey]

the reason it is dangerous to have band-on clamps on forks  is that the fork is constantly flexing, and (rubber or not) the clamps will very probably come loose eventually. When (not if) this happens, one of two things occurs
a) the thing swings into the wheel and pitches you off the bike
b) the thing slides down the fork leg and then jams in the wheel, pitching you off etc.

because fork blades are tapered, the slightest slackness or movement  in a band-on fitting soon turns into a major problem.  Bottle cages mounted at funny angles see loads that they don't normally; since they break with monotonous regularity anyway, the sideways wobbling just makes breakage even more likely.

BITD it was common for riders to fit lamps etc  to the fork blades using a bolt on clamp.  For a time if you didn't have a boss, there would often be a 'pip' brazed on the inside of the fork blades; this was there purely to stop a loose clamp from sliding down the fork blade (some bikes with roller lever brakes had a similar feature).  Rotation was less of a problem, because the clamps were rigid in that sense and the fork blades were at that time a pronounced oval shape.

So this is very much a known problem and there is absolutely no need for a whole new generation of cyclists to 'solve it' again....

cheers

[Kim]

The fork on my Vagabond has mounting bosses for a rack mid way up the fork, and another boss by the drop out. I use a wolftooth BRAD[1] between the mid fork boss, and the drop out boss. I then attach the double bottle cage adapter[2]. The Gorilla cage goes on the front, and a bottle cage goes on the back. I've used this in winter with approx 600g in the front, and a 500ml nalgene bottle full of water on the back.

It looks something like this:



It works well, even off road, but I was careful to balance the weight round the fork.

My question here stems from what happens if the weight is all behind the fork (i.e. just the bottle cage, without the gorilla cage full of warmth in front of it). The BRAD setup allows me to move the weight up and down a bit. How would moving the weight relative to the drop out effect the handling of the bike?

That's a slightly more subtle question rather that the "how big a deal is attaching stuff to the fork, and how balanced does it have to be" that I think most of us thought you were asking.

I'd suggest you're in a better position to get a better answer by means of a bit of trial and error than you will by asking around.

[Karla]

To be honest you've been making noises about bottle capacity for long enough - not just on this thread - that it's obviously a big issue for you, so it's probably worth going for the long term solution and getting a sensibly sized frame, i.e. one that doesn't have miles of seatpost showing, so you can fit more stuff in the main triangle, whether that be a bottle on the seat tube or a bigger frame bag that allows you to free up space elsewhere.

[quixoticgeek]

That's a slightly more subtle question rather that the "how big a deal is attaching stuff to the fork, and how balanced does it have to be" that I think most of us thought you were asking.

I'd suggest you're in a better position to get a better answer by means of a bit of trial and error than you will by asking around.

My questions are becoming increasingly obscure and specialist I fear.

The question was primarily about the balance between the two sides (I've only ever used both sides full, or both sides empty, I've not had an imbalance), as well as the balance front to rear, and finally how moving it up/down.

Trial and error is one way to work it out. *BUT*, it's likely only to manifest Bad Stuff™ at high speeds, which until I goto the effort of a trip somewhere with more contours, I won't be able to easily test. More over, if it's a Really Bad Idea™, then there is risk that such a test results in unscheduled lithobraking, which would be considered bad.

In my head this would be a case of me ask question, someone wise will then come along and say "Yeah, that's gonna be an issue at speed, you may get wobble" or "Nah it'll be fine, the gyroscopic impact of the front wheel will be more significant the effect of a couple of kg, so don't worry" or maybe "yes, but keep it as close to the axle as you can".

I need to get better at asking questions...

To be honest you've been making noises about bottle capacity for long enough - not just on this thread - that it's obviously a big issue for you, so it's probably worth going for the long term solution and getting a sensibly sized frame where you can fit more stuff in the main triangle, whether that be a bottle on the seat tube or a bigger frame bag that allows you to free up space elsewhere.

That would require a lot more money than I currently have.

J

[LittleWheelsandBig]

QG’s proposal should work well enough. The fork blades rake forward a little, so having the cage behind the blade brings it closer to the steering axis than if the cage was on the side of the fork blade.

You can have an astounding difference in lateral loading before the handling becomes dangerous, provided you are comfortable with the bike’s handling generally. I think you should actually get comfortable/ familiar with descending fast before loading your bike with various detritus. If you are scared descending fast with everything perfect, it doesn’t much of a wobble over a bump to result in panic.

[Kim]

the reason it is dangerous to have band-on clamps on forks  is that the fork is constantly flexing, and (rubber or not) the clamps will very probably come loose eventually.

That makes sense.  'Eventually' may be acceptable, if this is for a one-off event.  (I'm firmly of the opinion that if you're making a habit of carrying Stuff, you're better off with proper bike luggage.)

BITD it was common for riders to fit lamps etc  to the fork blades using a bolt on clamp.  For a time if you didn't have a boss, there would often be a 'pip' brazed on the inside of the fork blades; this was there purely to stop a loose clamp from sliding down the fork blade (some bikes with roller lever brakes had a similar feature).  Rotation was less of a problem, because the clamps were rigid in that sense and the fork blades were at that time a pronounced oval shape.

The only fork I've ever used band-on attachments with is a horrid alloy thing that's about three times wider than it is thick.  Even a plastic band would struggle to rotate around that.  (It's currently sporting lowrider racks that are anchored to the solitary mudguard braze-on at the dropout, so there's no scope for vertical slippage.  Looks naff, but it stays out of the wheel.)

[quixoticgeek]

QG’s proposal should work well enough. The forks rake forward a little, so having the cage behind the blade brings it closer to the steering axis than if the cage was on the side of the fork blade.

Excellent.

What impact would height relative to the axle have?

J

[bludger]

the reason it is dangerous to have band-on clamps on forks  is that the fork is constantly flexing, and (rubber or not) the clamps will very probably come loose eventually. When (not if) this happens, one of two things occurs
a) the thing swings into the wheel and pitches you off the bike
b) the thing slides down the fork leg and then jams in the wheel, pitching you off etc.

This does make sense. Perhaps I could use these bolts to make fork mounted gubbins more secure https://yacf.co.uk/forum/index.php?topic=112187.0

To be honest I've not reached the point where I'd want to be mounting stuff on forks yet. For me that's definitely a sign that the kitchen sink approach is going a bit far, for audax at least.

[Kim]

What impact would height relative to the axle have?

I reckon the most significant effect would be one rate of sheep-shit accumulation at the bottle-rider interface.

[LittleWheelsandBig]

Height of bottle would make little difference. I’ve ridden with lowrider front racks and with modified lowrider racks mounted just below the fork crown for off-road pannier clearance (it kept the panniers close to the steering axis, unlike conventional front racks). There was little difference in handling, except when ‘throwing the bike’ while climbing out of the saddle.

[Bolt]

Speaking from experience, it's easy to over think this sort of stuff and end up straying a long way from what you're actually trying to achieve. 15 years ago and with no real distance experience, I commandeered my brother in-laws old mountain bike for a fully self supported JOGLE. The first day I rode the bike fully laden was day 1 of the ride, for sure it was a bit scary at first with all the weight at the back, but after 10 miles it all became perfectly normal and predictable.  I also still have the bike, which is for sale, for very little money

[Kim]

Yeahbut overthinking this sort of stuff can:

a) Be fun (especially if circumstances don't allow you to go for an actual bike ride).

and

b) Marginally improve your chances of having less to worry about when you do get round to riding.  Brucey's point above about the dangers of band-on attachments to forks is a case in point.


I agree that if everything's staying put and there isn't a terrible shimmy or massive load imbalance that prevents something important like braking or steering from working, you can generally get used to weird bike handling.

[bludger]

It's when you start trying to carry 30 ciabatta rolls in one of these that things get tasty!

[Phil W]

What are your rear lights ? Looks like you can get a good angle with them even when the seat stays are far from vertical.

[quixoticgeek]

What are your rear lights ? Looks like you can get a good angle with them even when the seat stays are far from vertical.

Left hand side: B&M Secula dynamo

Right hand side: B&M Secula permanent

There's a cateye TL-LD560 on the seat post too, below the saddle bag.

What impact would height relative to the axle have?

I reckon the most significant effect would be one rate of sheep-shit accumulation at the bottle-rider interface.

That's the main reason for not using the BRAD setup to put a bottle on the underside of the down tube.

My personal preferred solution is to stick 2 bottles under the saddle, with the WOHO anti sway thing. It's a great idea. But I've had 2 bottles cages rattle lose, one of which jettisoned when going over block paving. I've also had the the whole thing rattle lose. Even with nyloc nuts, and loctite. It's a shame, as it's a really good idea.

If I could find a way to make the woho anti sway not be crap, I'd use that by preference.

It's when you start trying to carry 30 ciabatta rolls in one of these that things get tasty!

Except you don't use that at 70kph downhill in the alps...

J

[grams]

If I could find a way to make the woho anti sway not be crap, I'd use that by preference.

Replace the bolts with cable ties.

[Kim]

What impact would height relative to the axle have?

I reckon the most significant effect would be one rate of sheep-shit accumulation at the bottle-rider interface.

That's the main reason for not using the BRAD setup to put a bottle on the underside of the down tube.

Just in case it's not obvious, the splatter problem can be worked-around by:

a) Bottles with a cover over the spout.  These are faffy to drink with, particularly when wearing gloves.  If it gets properly splattered, you probably need both hands to prevent the cover depositing mud on your nose as you drink.  Works fine for mountain biking.

b) Unscrewing the lid and decanting water to your stays-reasonably-clean bottle when it becomes empty.  I reckon this is a better solution, as it's only slightly more faffy than the cover, but you only have to do it once per bottle.  Fringe benefit that only one bottle has to have a lid suitable for drinking on the go.

I've made use of both approaches in different contexts.  (And have a variation on (b) for the fast recumbent, where one bottle is equipped with a hydration hose for access on the move, and the other has a regular bidon lid for access when stopped.)

[Cudzoziemiec]

Mounting things on forks without bosses: I had a low-rider pannier rack mounted on the suspension fork of a MTB using P-clips. It stayed rock solid with loaded panniers including mild off-road. But I only used it for a year or was it two years? There is, as Brucey says, always eventually... though refitting every couple of years might indefinitely postpone this?

Asking questions: Yes, QG you need to get better at asking more precise questions! As TBH do we all – not to mention sticking to the point and addressing (including identifying) the question that has actually been asked, rather than digressing on things which are connected but don't answer the question (see above).

[Zed43]

Dune suit.

Kinda appropriate that this is suggested by a guy named Paul 

[mzjo]

the reason it is dangerous to have band-on clamps on forks  is that the fork is constantly flexing, and (rubber or not) the clamps will very probably come loose eventually. When (not if) this happens, one of two things occurs
a) the thing swings into the wheel and pitches you off the bike
b) the thing slides down the fork leg and then jams in the wheel, pitching you off etc.

because fork blades are tapered, the slightest slackness or movement  in a band-on fitting soon turns into a major problem.  Bottle cages mounted at funny angles see loads that they don't normally; since they break with monotonous regularity anyway, the sideways wobbling just makes breakage even more likely.

BITD it was common for riders to fit lamps etc  to the fork blades using a bolt on clamp.  For a time if you didn't have a boss, there would often be a 'pip' brazed on the inside of the fork blades; this was there purely to stop a loose clamp from sliding down the fork blade (some bikes with roller lever brakes had a similar feature).  Rotation was less of a problem, because the clamps were rigid in that sense and the fork blades were at that time a pronounced oval shape.

So this is very much a known problem and there is absolutely no need for a whole new generation of cyclists to 'solve it' again....

cheers

Just to complete the comment I will put a figure to "eventually". 50kms. On a pre-war tandem with humongous great fork blades! That do you? DAHIKT
Of course QG has bosses on her fork so this is not an issue, if she's sensible about it.

[Brucey]

I worry about bottle cages failing by fatigue anyway; there are very few that appear to be able to withstand, say, and actual bottle being in them for very long..... and that is even though the loads are mostly in a central plane.   Once mounted on the side of a fork at a jaunty angle I'd expect many such fittings to be a (fairly short lived) fatigue experiment. 

Regarding stability and loading;  having mass attached to the fork ups the moment of inertia (MOI) in the steered part of the bike. This does make the bike handle differently but you soon 'get used to it'.  The one thing that may happen with an uneven load as you intend is that the bike could handle a bit weirdly over bumps; when viewed in the reference frame of the whole bike, the steered part doesn't always rotate around the central point; because the bike can be tipping to one side at the same time and accelerating (e.g. in exaggerated form if -say- the front wheel is going into a large pothole off-centre). Because the tyre is now on a camber the contact point changes and the steered part of the bike sees a lateral thrust  in addition to the other loads that arise.  The net effect of all this is that (instantaneously) the steered part of the bike may be turning around an axis that is offset sideways vs the steerer centreline.

Because the MOI is sensitive to this in the proposed arrangement you may find that the net effect is that the steering kicks faster to one side over bumps than the other.  You may not notice this or you may just 'get used to it' (there's quite a lot of that going on, on most bikes...). Note that if the view down the steerer changes between hands on and hands off, the bike isn't tracking perfectly (usually because of a frame geometry issue, sometimes uneven loading -which can be the rider-).  In this event every bump (even a head-on one)  is liable to give a little impetus to the steered assembly and this is exactly the sort of thing that can provoke a shimmy.

FWIW when assessing a new loading scheme/bike, it isn't a bad idea to ride no hands (or as close to it as you can) and then to deliberately perturb the steering by knocking the handlebar.  Try both directions, if you might have an uneven load or the bike might not be tracking perfectly for some reason. Also try this at different speeds.

You can mentally mark the whole scheme down if

a) the bike can't be ridden no hands, either easily or at all
b) the bike behaves very differently when perturbed in different directions
c) the bike behaves very differently at different speeds
d) you get a 'high energy shimmy' developing over a wide range of speeds.


All bikes will shimmy; its just a question of at what speed and how dangerously.   The energy contained within a shimmy varies, but the highest energy is when there is lots of mass that is coupled to the moving parts and not very much damping. When there is no damping, starting  the shimmy can be very speed dependant but once it starts it can carry on over a wider range of speeds.    Thus most  unladen road bikes can be made to shimmy violently starting at one specific speed but because the main mass in the system (you) isn't well coupled the energy contained within the shimmy is usually small; in the test I have described (with a road bike) you will usually find you can start a shimmy and it can be so bad it would soon cause the frame to fail if it were allowed to continue, but can be quelled easily by simply putting a hand back on the handlebars.  If you know what speed a shimmy can start at, you will know what it feels like and how (not) to hold the bike at that speed.

   If you start to get a shimmy developing in a bike with a load on the steered assembly, you are in a whole different problem; by its very nature it will be a high energy situation and some major effort /change may be required to bring it under control.  If you have an offset load as you describe one possible effect is that the range of speeds over which a shimmy might start becomes broader.

So I usually test road bikes until I get a shimmy and then see how bad it is and how difficult it is to get it back under control.  But with a touring/loaded bike I tend to make sure that in 'normal riding' I don't get a shimmy and then in use I stick within the range of speeds with which I am happy.  I have seen one or two loaded bikes start to shimmy and it was ugly; pretty dangerous in fact. However I have seen many more instances where the load simply wasn't attached well enough, and just started to come off, often because something broke or came loose. 

The vast majority of bolt-on schemes for attaching loads to  forks seem woefully under-engineered to me; the whole scheme ought not overload any one bolt (remember that the loads can be multiple and don't always add up in the way you expect) and ought to be proof against any one bolt/stay/clip breaking or coming loose.  Most schemes are not like this at all, and many of them I would not consider fit for riding down the shops with, let alone more lengthy jaunts on rough surfaces.

cheers

[quixoticgeek]

Brucey, your answer is a work of art. Thank you! Much food for thought!

J

[mzjo]

Don't forget to do your testing with all your intended tyre combinations. Motorcycle sidecarring has shown me at least that tyre width can play a huge part in setting up a steering oscillation. It may be that your fork loading will work fine with one tyre and not with another (in which we would all hope that the most stable tyre combination is also the most useful one for you when you want the extra storage).

[Cudzoziemiec]

My tourer laden with rear panniers, tent on rack, Gorilla bags on forks and bar bag, started a slow rear weave when it hit 53km/h as I plummeted down the hill into Lower Swell. Definitely a weave not a shimmy and definitely coming from the back, leaving the front stable. I'm blaming the sandwich I'd bought but not eaten, packing it into one pannier, in Stow at the top of the hill.