Stability

Shadow121

Active Member
Okay but the bikes trail doesn't change by laying a bag potatoes on the rear rack eh ;) ?


I rather prefer to solve causes than trying to live with consequences.
Also, in this case the consequence comes without and goes with a bag potatoes, and last time I checked I didn't see a switch on a muscle for it.
Fact is that the design of my other older now first spare bicycle must have been a better trade off, since I did the same things with it as with the current newer one, for years and twitchy behaviour ment a broken rack, spoke, brake or stick between the spokes slamming the fork, not a chosed design.
Luck.... is for sheep that hope.
The world isn't built by hoping ppl.
There, some psycho talk on sunday. :biggrin:
Am afraid you will have to live with the consequences you are experiencing
or design / solve yourself a bike, and when your done you will still have to live
with the consequences only this time you will be completely responsible for them.
 
OP
silva

silva

Active Member
Location
Belgium
If the bike doesn't work for you, then sell it on. It's no good whinging on here it won't change anything.
So far every bike I've got had problems, the last one about the worst, and these experiences brought me to fixed gear, to be able to DIY. On which basis then should I expect yet another bike to be a different story? It will be just another story, with same and new problems, and a repeat of all the work. Do you see any benefit in that? I don't.

I made the bike work for me, I found causes and solutions for the problems, and this topic is just that.
First causes have to be identified, then solutions have to be found, that's what I do and when I'm "whinging" it's to make clear exactly that, in cases this point is still not recognized.
To give another example (so blame me for "whinging"): at some point in the production stage of the bike, the dealer sent me an email that the bike was about ready, only that the chainline wasn't 100% straight but that they found a solution for that.
A year later, with the strongest and most wear reducing chain available (basically a 1/8" chain with 3/16" plates) mounted, that chains parts hung tilted nearly 45% in opposite directions. The dealer showed a baffled face and said he had never seen that before and that he had no idea how it came.
I decided to post the problem on a forum. The first answer I got was that the chainline must be quite wrong, and I was given instructions/tricks how to measure it (a direct measurement is not possible). I found the chainline as 5 mm wrong, and also that the rear hubs spokes flanges center was that amount offcenter, so that the spokes should be tensioned so that the rim/tire remained in the line of the front tire.
I mailed that forums topic to the dealer. He answered he "had followed my measurements and that they were correct", and by doing that directly contradicting his year-earlier claim that he had found a solution to achieve a 100% straight chainline.
Clearly his highest priority was selling a bike, if that bike would be what the customer wanted was lower priority and he lied to achieve the sale.

So the Nth problem now is that instability. It's not a big problem since I usually have some kilo's on top of the rack, but knowledge is where solutions start and hence my attempt here to pinpoint a precise reason for this rather serious handling difference dependent on load location.

My bike is parked outside now. Just arrive d back. If I now take off the basket with the standard luggage and the added today, and do a ride, the bike will act alike a horse that wants to throw off its rider. That MUST have a specific cause and that MUST be certain distances/ratios in the frame geometry. But which ones?
Maybe I should think "loud" here, as to give an idea of what kinda answer I'm hunting.
Imagine the rear rack was constructed so that its top would be 50 cm higher. Which effect would that have on the handling response? Or 50 cm lower?
Or some approach like this: I put 1 kg on the rack and to a test ride. Then 2 kg. Then 3 kg. And so on. To discover what weight change causes which effect on the bikes response. A precise weight could give a clue in a weight balancing problem.

My frame size is 65 cm

Geometrie Santos.jpg


"ZITBUIS LENGTE" is 650 mm
"OVERSTAP HOOGTE" is 896 mm
"BOVENBUIS LENGTE" is 620 mm
"BALHOOFD HOOGTE" is 960 mm
"BALHOOFD-DROPOUT" is 662 mm.

And so on...
 

Attachments

OP
silva

silva

Active Member
Location
Belgium
But it does change the bikes moment of inertia.

It's like trying to balance a pencil on your hand.
It's difficult with a plain pencil because it moves fast and twitchy and once started over it's hard to correct.
Now attach a weight to the top of the pencil and it become easy because it's feels a lot more stable.

That what has happened on the bike.
The sack of potatoes acts in part as a mass damper and has slowed any fast side to side oscillations into a range you find easy to control.
The higher the weight is sited on the bike then the more the moment of inertia changes and the more you feel the effect.
That's why it works well on top of the rack and not so much in side panniers.

How twitchy a bike is an interaction between it wheelbase, headset angle, trail and even the bottom bracket height.
As you've two bikes, one stable and one twitchy, then measure all the distances and angles on both.
The draw a scale diagram of both from the same starting point and you'll easily see how and where they differ.
Ok, that's an idea, as soon as I have the chance I'll measure my previous bike, the data for the current I've found on the web.
The end goal is to determine what can be done to make the bike respond the same with a mass of zero on the rack.
 

YukonBoy

The Monch
Location
Inside my skull
You are a tall rider on a big frame. You will have a high centre of gravity. With long limbs you can shift that centre of gravity (COG)) quite a lot. The bike is light in comparison and has no damping. So these shifts in weight can make it seem unstable. I wonder if the weights you add to your bike are acting like dampers, lowering the overall COG, giving the bike inertia and less affected by your weight shifts.

A recumbent of course would massively lower your centre of gravity and bring it somewhere in a line close with the wheels. Have you tried a recumbent as your solution rather than repeated mistakes with diamond frames?
 

snorri

Legendary Member
- rear light has no switch, meaning that when I park it at a shop it draws attention to my bike for like 10 minutes without any benefit, probably just to save the cost of a switch despite the small thing costing 50 bucks..
This is a totally unjustified complaint, many people including myself would consider this to be an extra they happily pay extra for. A light that stays on for a period, either at traffic lights or when coming to a stop at night is a safety feature as it helps other road users to see and avoid you. Not having a switch improves reliability of your lighting system for no extra charge, and has nothing to do with cost savings. Besides, why did you not ask the supplier to adapt the lighting system to suit your requirements before placing your order if unhappy with the basic provision?
I don't think you mention front luggage, could it be the load needs to be better balanced between front and rear?
Here's a video of a Santos Traveller 3+ road test, the reviewer gives it his seal of approval making it difficult to understand your catalogue of complaints regarding frame design.

View: https://www.youtube.com/watch?v=dcDnWHhrupI
 
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fossyant

Ride It Like You Stole It!
Location
South Manchester
It does worry me that you've had issues with every bike. You may have a balance issue, and loading up the bike will make it more cumbersome.

I've never had a bike that had bad stability, even a Raleigh Chopper that's known to be poor handling.
 

Tigerbiten

Veteran
You are a tall rider on a big frame. You will have a high centre of gravity. With long limbs you can shift that centre of gravity (COG)) quite a lot. The bike is light in comparison and has no damping. So these shifts in weight can make it seem unstable. I wonder if the weights you add to your bike are acting like dampers, lowering the overall COG, giving the bike inertia and less affected by your weight shifts.

A recumbent of course would massively lower your centre of gravity and bring it somewhere in a line close with the wheels. Have you tried a recumbent as your solution rather than repeated mistakes with diamond frames?
You have that the wrong way around.
Adding weight to the rack moves the CoG up.

A basic rule of thumb or recumbents is the lower the seat is and/or the more reclined you are, the harder it is to balance because it gets more twitchy.
Which is why it's best to start with a recumbent with a fairly relaxed upright position and only go more extreme once you get used to it.

I hate to say that most of the distances ....
"ZITBUIS LENGTE" is 650 mm
"OVERSTAP HOOGTE" is 896 mm
"BOVENBUIS LENGTE" is 620 mm
"BALHOOFD HOOGTE" is 960 mm
"BALHOOFD-DROPOUT" is 662 mm.
.... Have no real relevance to how the bike handles, just the size of the bike.
The ones you need are the headset angle, trail and wheelbase.
Here -> https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry is a good article on how changing these can alter the handling of a bike.
Hope that helps .......... :biggrin:
 
OP
silva

silva

Active Member
Location
Belgium
Have you thought you just might not be used to a lighter handling bike. Or are too used to a laden bike ?
The bikes response difference based on a presence or nonpresence of a few kilo's on the rear rack is just way too big to consider normal. I have had 30 kilo on the rear rack, about 10 times as much, and I hardly notice the response difference with that few kilo. So more is no problem, less is a problem.
It's like a few kilo's more brings some balancing above or under a treshold. Or in other words, the weight distribution of the design was chosen close to some margin value.
Remember, when I ride an older bike, without anything on its rack, I don't notice any response difference, only that accelerating goes faster.
 
OP
silva

silva

Active Member
Location
Belgium
This is a totally unjustified complaint, many people including myself would consider this to be an extra they happily pay extra for. A light that stays on for a period, either at traffic lights or when coming to a stop at night is a safety feature as it helps other road users to see and avoid you. Not having a switch improves reliability of your lighting system for no extra charge, and has nothing to do with cost savings. Besides, why did you not ask the supplier to adapt the lighting system to suit your requirements before placing your order if unhappy with the basic provision?
I don't think you mention front luggage, could it be the load needs to be better balanced between front and rear?
Here's a video of a Santos Traveller 3+ road test, the reviewer gives it his seal of approval making it difficult to understand your catalogue of complaints regarding frame design.

View: https://www.youtube.com/watch?v=dcDnWHhrupI
Since you name what I experience as a pain an "extra", we clearly have different opinions.
I cannot agree with yours, you may have missed some points.
- I don't want my bicycle drawing attention from thieves due to a rear light that I cannot switch off.
- I have had rear lights with a switch for a couple decades in situation home work shop, never had malfunctioning switches, also because I always took precautions "in case", alike taping off the circumference and protecting the button / switch against water. Little effort, in case.
- I want to have the CHOICE, and that is what a switch provides. No problem with the light staying on when I stop for a traffic light or so, IF I have selected that. But I ALSO want to be able to select OFF.
- the rear lights parking light is an electrical load stored in a capacitor. Imagine in winter, dark. Possible snow. I have to stop for some reason. To walk with bike at hand, I don't need light. But if I want to see something for which it is not clear enough, that electrical load is available. IF it wasn't wasted for nothing. Without a switch, it is.
- The supplier never told me that the rear light had no switch. I discovered it after delivery. The supplier also didn't tell me that he had mounted a 3/32" chainring (Surly stainless steel) instead of the asked for 1/8" drivetrain. I discovered it after a month, when the thing got worn down to sharkfins while on my previous bike the 1/8" chainring of alu 7075T6 lasted a year and half (and more if I had continued). There were quite some things untold to me. After over a year I discovered the reason for my very weird chain wear (it hung tilted under 45 degree angles). The chainline was 5mm out. The supplier had said that it was "100%" straight. But wait, I started to "whine" again here, so please forget it. Friendly wave.
- True, I should have some luggage on the front (I should try a bag in front of the handlebar but there is little room due to shape of the handlebars. And the brake fluid lines sit in the way. But the reason for front luggage is just to prevent the bike from tilting over to the back when alot weight, not to improve its response when steering. Can't even imagine how that would have any effect - it doesn't now (earlier this year I tried a bag at the front but I experienced it as a hassle and it limited my view on the road (sometimes I don't step off the bike when having to wait, I keep the bike in balance, standing)
Also, remember, it's not a front/back load difference that causes that hard handling, but a drop under a certain weight on top of the rear rack. I can put whatever in the bags hanging under the rear rack, and whatever in a bag on my back / backpack, and whatever along the horizontal tube (in my avatar pic you can see a steel U profile/rail mounted along the horizontal tube, its length was from front handlebar till a meter after the rear light.

The bike IS stable, just like my previous bike, only that there is one exception: not any kilo on the rear rack and I ride like a drunk - really, I am unable to stay 10 meter on the white lines drawn near the edge of the roads. And near or in cities, with lotsa height differences and crap in the way, it's just scary. I have to slowdown just for this.
As soon as I find the time and I figure out how to put some luggage in the front side of the bike, that doesn't hinder me one way or another (1 idea is in the triangle of the frame close to the handlebar), I will put the highest weight/smallest stuff (spare chain, chain tool, water) there, that will surely help to avoid tilting over.
 

YukonBoy

The Monch
Location
Inside my skull
You have that the wrong way around.
Adding weight to the rack moves the CoG up.
Only if the COG is below the level of the rack. I'm referring to the COG of the bike / rider combo and would expect (for diamond frame) the COG to be above the height of the rack in such a case. I'm not referring to the COG of the bike alone.
 
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fossyant

Ride It Like You Stole It!
Location
South Manchester
My fixed gear was hard work when I started loading it up with stuff for the commute. Didn't notice it after a while, but oh my, did the fixed and the two other road bikes feel very different, ie. fidgety. I was used to a laden bike.

You might be too used to a loaded up bike.
 

Tigerbiten

Veteran
Only if the COG is below the level of the rack. I'm referring to the COG of the bike / rider combo and would expect the COG to be above the height of the rack in such a case. I'm not referring to the COG of the bike alone.
On a trike the combined trike-rider is important simply because you need to lean to the inside on a corner to keep that wheel on the ground.
On a bike, unless you're doing the likes of extreme MTB stunts, then the bike and rider move as one so I think the combined CoG is largely irrelevant. You don't normally move off the saddle and shift to the inside like you do when cornering fast on a motorbike.
But the bike's CoG and where the mass is situated alters the bikes moment of inertia.
Any increase the moment of inertia slows the bike natural twitchiness down and makes it feel more stable.
 

Shadow121

Active Member
To the OP, while it is nice to understand why and how things work,
given you bike is fine with a load in the right place, I would just enjoy
the bike.
When I was young I had the most expensive racing bike in the shop,
don’t even remember the make, and it was the most difficult bike to
ride, If you coughed you would change direction, the one I have now cost 200.00
second hand, it’s a treat in comparison, and super comfortable.
I have had goes on other bikes, expensive and not so, and everY one of them
rode differently, that’s just how things are, and why people who know will
always advise you to try before you buy, it’s the only way you can be certain
whether any bike is the bike for you.

Regarding your current situation, try a shorter or longer stem,
even try a fork that would leave the bike more similar to a bike
you have that does not have the issues you currently have.
Fork trail and stem length can play a huge part in how a bike behaves,
I once put an 80mm stem with 3 degrees more rise on an old bike instead of its 90mm stem,
everyone told me it would be even more twitchy, but I did it, the bike was
completely different, and to everyone’s surprise the twitchyness was gone,
the bike was twitchy because of me, it wasn’t turning in unless I gave it a quick pull
and I was overdoing it, the shorter stem did it for me.
 

Shadow121

Active Member
You are a tall rider on a big frame. You will have a high centre of gravity. With long limbs you can shift that centre of gravity (COG)) quite a lot. The bike is light in comparison and has no damping. So these shifts in weight can make it seem unstable. I wonder if the weights you add to your bike are acting like dampers, lowering the overall COG, giving the bike inertia and less affected by your weight shifts.

A recumbent of course would massively lower your centre of gravity and bring it somewhere in a line close with the wheels. Have you tried a recumbent as your solution rather than repeated mistakes with diamond frames?
I would agree, more weight is dampening the bikes response to the riders input and keeping it online,
take away just enough weight and the bike becomes twitchy. That’s why they put ballast into empty ships.
 
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