Bicycle front tire wobble due to weight on the back of the bike

[Lgo]

TL;DR Summary

Not sure what the "Prefix" means...Is it my experience or the level of experience I think I need to get my issue answered. Trying to get help with a balance issue on my bicycle

I am a bit overwhelmed with your forum site. I was not sure where to post my question...Here goes-

Full details…I have an e-bike. It weighs about 55 pounds. I have ridden it for the last year with a canvas bag attached to the rear flat book carrier. The canvas bag measures 19” long, 9” tall and 6” wide. Because it was limp and hanging down, I built an inner skeleton to keep the bag firm when it was empty. In the bag were several items including a folding lock that weighs about 4 pounds, a plastic bag with tire changing equipment, (also about 4 pounds) and a few random items weighing about another 5 pounds. I also had a heavy bike chain that weighed 8-9 pounds that was wrapped and attached along the outside of the bike carrier rack. When I would take my hands off the handlebars my front tire would wobble. I brought the bike in to check my wheels and they were both “true.” After removing the heavy chain my bike no longer wobbles. I realized that the chain was wrapped one and a half times around the carrier. So, there were two lengths of chain on one side and only one on the other. The difference in weight on one side was causing the wobble.

I found that I did not have enough room using the canvas bag and wanted something larger. I purchased a plastic toolbox. It weighs 2-3 pounds and measures 19” x 10” x 10”. I put a thin piece of rubber about a quarter of an inch thick between the toolbox and the rear carrier. I attached it firmly at six points. The toolbox is very secure. I put the contents of the canvas bag into the toolbox and found an extreme amount of front tire wobble with my hands off the handlebars. Since the toolbox was less than half full, I used foam rubber along the sides and lined all the contents in the center of the toolbox running from the front to the rear. This made very little difference in the wobble. I then moved the contents to the front portion of the toolbox, (just behind the bike seat). So now I have the heavy items tightly packed together in the front 25 percent of the toolbox and the wobble is down by probably 75 percent.

My question to this forum is A) Why am I having wobble now and did not have any with the canvas bag. B) Does anyone have any suggestions to reduce the wobble down to zero?
Thanks,

LGO

 

[Baluncore]

Welcome to PF.

What is the frequency of the front wheel wobble, is it speed dependent, once per turn of the front wheel, or is it a higher frequency?

When did you last replace a front tyre? Is the front inner tube the correct size, or is it too big? Did you check the wheel mass balance, or only check if the geometry was round and symmetrical? An old tyre can become asymmetric, when the spokes are adjusted to pull it geometrically true, it develops a hidden mass imbalance and wobble. Check that the tyre bead is seated correctly on the rim.

There may be an invisible crack in the frame. Has your bike ever been involved in a minor accident?

 

[jack action]

https://bikecommuterhero.com/bicycle-feels-wobbly-5-possible-fixes-with-pictures/
https://cyclingtips.com/2020/07/bicycle-speed-wobbles-how-they-start-and-how-to-stop-them/

 

[256bits]

TL;DR Summary: Not sure what the "Prefix" means...Is it my experience or the level of experience I think I need to get my issue answered. Trying to get help with a balance issue on my bicycle

I brought the bike in to check my wheels and they were both “true.

You can check that yourself.

for a no-load test.
Just lift the bike off the floor and spin the wheel.
As the wheel rotates:
check for any out of round ( radial ) differences,
check for any sideways ( lateral ) differences.

while riding, you can check the radial and /lateral movements at low speed and at high speed.
Attach something that just barely scraped the rim, and see while riding if there are any differences.

The no-load test is with no stress on the wheel.
The riding test is with your bike weighted and the frame under stress and some strain.

 

[Lgo]

Welcome to PF.

What is the frequency of the front wheel wobble, is it speed dependent, once per turn of the front wheel, or is it a higher frequency?

When did you last replace a front tyre? Is the front inner tube the correct size, or is it too big? Did you check the wheel mass balance, or only check if the geometry was round and symmetrical? An old tyre can become asymmetric, when the spokes are adjusted to pull it geometrically true, it develops a hidden mass imbalance and wobble. Check that the tyre bead is seated correctly on the rim.

There may be an invisible crack in the frame. Has your bike ever been involved in a minor accident?

Thanks...It is definitely not the wheel. If I empty out the toolbox, I have no wobble. It is related to the weight in the toolbox.

 

[Lgo]

https://bikecommuterhero.com/bicycle-feels-wobbly-5-possible-fixes-with-pictures/
https://cyclingtips.com/2020/07/bicycle-speed-wobbles-how-they-start-and-how-to-stop-them/

Thanks...It is definitely not the wheel. If I empty out the toolbox, I have no wobble. It is related to the weight in the toolbox.

 

[Lgo]

You can check that yourself.

for a no-load test.
Just lift the bike off the floor and spin the wheel.
As the wheel rotates:
check for any out of round ( radial ) differences,
check for any sideways ( lateral ) differences.

while riding, you can check the radial and /lateral movements at low speed and at high speed.
Attach something that just barely scraped the rim, and see while riding if there are any differences.

The no-load test is with no stress on the wheel.
The riding test is with your bike weighted and the frame under stress and some strain.

Thanks...It is definitely not the wheel. If I empty out the toolbox, I have no wobble. It is related to the weight in the toolbox.

 

[Lgo]

TL;DR Summary: Not sure what the "Prefix" means...Is it my experience or the level of experience I think I need to get my issue answered. Trying to get help with a balance issue on my bicycle

I am a bit overwhelmed with your forum site. I was not sure where to post my question...Here goes-

Full details…I have an e-bike. It weighs about 55 pounds. I have ridden it for the last year with a canvas bag attached to the rear flat book carrier. The canvas bag measures 19” long, 9” tall and 6” wide. Because it was limp and hanging down, I built an inner skeleton to keep the bag firm when it was empty. In the bag were several items including a folding lock that weighs about 4 pounds, a plastic bag with tire changing equipment, (also about 4 pounds) and a few random items weighing about another 5 pounds. I also had a heavy bike chain that weighed 8-9 pounds that was wrapped and attached along the outside of the bike carrier rack. When I would take my hands off the handlebars my front tire would wobble. I brought the bike in to check my wheels and they were both “true.” After removing the heavy chain my bike no longer wobbles. I realized that the chain was wrapped one and a half times around the carrier. So, there were two lengths of chain on one side and only one on the other. The difference in weight on one side was causing the wobble.

I found that I did not have enough room using the canvas bag and wanted something larger. I purchased a plastic toolbox. It weighs 2-3 pounds and measures 19” x 10” x 10”. I put a thin piece of rubber about a quarter of an inch thick between the toolbox and the rear carrier. I attached it firmly at six points. The toolbox is very secure. I put the contents of the canvas bag into the toolbox and found an extreme amount of front tire wobble with my hands off the handlebars. Since the toolbox was less than half full, I used foam rubber along the sides and lined all the contents in the center of the toolbox running from the front to the rear. This made very little difference in the wobble. I then moved the contents to the front portion of the toolbox, (just behind the bike seat). So now I have the heavy items tightly packed together in the front 25 percent of the toolbox and the wobble is down by probably 75 percent.

My question to this forum is A) Why am I having wobble now and did not have any with the canvas bag. B) Does anyone have any suggestions to reduce the wobble down to zero?
Thanks,

LGOView attachment 317238

I tried to edit my post, yet the time allowed to edit it has ended...Let me add that I removed all the items from the toolbox and rode the bike and there was no wobble. This confirms that the tires/wheels are fine. Again, wobbles with items in toolbox, does not wobble when the toolbox is empty. -Thanks

 

[DaveC426913]

Is a giant rotating magnet part of your tool kit?

 

[hutchphd]

It is related to the weight in the toolbox.

More precisely it is due to the mass in the toolbox, how and where it sits relative to the rear wheel contact patch, and how the bike frame flexes.
My 1966 VW beetle wore out its steering damper and developed similar tendencies. A damper in the system would probably work here , but I do not see a good way to implement it. Maybe you could shock mount the box

 

[DaveC426913]

More precisely it is due to the mass in the toolbox, how and where it sits relative to the rear wheel contact patch, and how the bike frame flexes.

Would it be worth adjusting the contents so they are balanced ideally?

 

[Dullard]

This problem is also common for some motorcycles (I can testify that the 2000 Yamaha FZ-1 has it). I've been experimenting with it for about 20 years - a couple of observations:

When you take your hands off the handlebars, you also 'sit up' - that significantly changes the load on the front wheel and the geometry of the suspension.

When the front wheel is lightly loaded, almost anything (tread/wear patterns seem to matter in my case) can cause it to oscillate.

Bottom line: Keep your hands on the handlebars. Ride more, worry less.

 

[Baluncore]

Thanks...It is definitely not the wheel. If I empty out the toolbox, I have no wobble. It is related to the weight in the toolbox.

If the toolbox is loaded with asymmetric mass, then you will automatically lean your body sideways to keep the bicycle close to vertical.
Two possibilities:
1. There is insufficient load on the front wheel to make the contact patch big enough to stabilise the control of direction. Lean your body forwards to test if front wheel load is a factor in the oscillation. Try lowering the front tyre pressure slightly, but not by so much that the steering becomes heavy.
2. There is a flexibility due to mechanical instability in the frame, maybe loose bearings in the steering column or axles, or a fracture in the frame. Hang the bike off the ground, from its seat, then kick the frame in different places to find the source of the rattle.

 

[berkeman]

More precisely it is due to the mass in the toolbox, how and where it sits relative to the rear wheel contact patch, and how the bike frame flexes.
My 1966 VW beetle wore out its steering damper and developed similar tendencies. A damper in the system would probably work here , but I do not see a good way to implement it. Maybe you could shock mount the box

This problem is also common for some motorcycles (I can testify that the 2000 Yamaha FZ-1 has it). I've been experimenting with it for about 20 years - a couple of observations:

When you take your hands off the handlebars, you also 'sit up' - that significantly changes the load on the front wheel and the geometry of the suspension.

When the front wheel is lightly loaded, almost anything (tread/wear patterns seem to matter in my case) can cause it to oscillate.

Bottom line: Keep your hands on the handlebars. Ride more, worry less.

I don't think I've seen any steering dampers on bicycles yet (even MTBs), but they may exist. I absolutely have used them on my sportbikes and superbikes, and they can be lifesavers.

My introduction to steering dampers happened during an otherwise ordinary early morning sportbike commute here in Silicon Valley at about 6AM merging onto a freeway on my CBR600F4 at the time, and having to accelerate harder than usual because of the traffic pattern as I merged over to the leftmost commuter lane. I saw that I was way too close to an 18-wheeler behind me as I was merging left, so pinned it leaned over during the merge, which lifted my front wheel at about 60mph while I was leaned over a bit in the merge. As my front wheel came down briefly and skipped off the pavement with me at full throttle and leaned a bit, that set off a front end oscillation that turned into a full tank slapper. Fun times. 65+mph doing a tank slapper with freeway traffic all around you.

Luckily, the other cars near me saw what was going on and slowed a bit giving me some extra room, and also luckily I knew about the emergency response to a tank slapper (Spoiler box below). I was able to recover from that oscillation without getting ejected and run over, and it was enough of a wakeup call that I installed a steering damper on that bike the next week. It was also my track day bike at the time, in addition to being my commuter, and it was a lot more likely that something like that would happen at the race track rather than while commuting.

Anyway, to the OP, you are getting good advice so far in this thread. I would look at the debug suggestions offered so far, and if those don't help, relocate that toolbox weight among a couple different tool carriers closer to your bike's center of rotation/gravity.

Spoiler

If you ever need to recover a tank-slapper, clamp onto the bike with your legs and push forward with both open hands against the handgrips. That should stabilize the tank slapper, although it can take a couple seconds to damp out.

https://www.motorcyclistonline.com/mc-garage-video-motorcycle-steering-dampers-explained/

 

[Tom.G]

I too rode motorcycle for several decades. Here are the things I've found/discovered about a speed wobble:

Do NOT counter-steer to control wobble. Your reaction time has enough delay so that by the time you counter-steer the front wheel has already started moving back in that direction!

1) If it hits at speed:

Stiff-arm the handlebars! - - Do Not Use Front Brake until wobble stops

a) Stiff-arm the handlebars - that is lock your elbows straight. This supplies much damping that keeps you upright!
b) Slow down.

1) This variation on Slow down can be a little risky for stability so riders with low experience should not try it, and don't try it in a turn! A momentary hard application of the rear brake will cause weight transfer to the front and stop the wobble while also slowing you down. Do Not Use Front Brake! Front brake use can cause the steering to lock to one extreme.​

2) Causes (in no particular order, most have been mentioned above)

a) insufficient weight on the front tire
b) low tire air pressure
c) worn tire
d) bent rim
e) possible bent forks or frame causing misalignment (see 'f' below) or less caster of the front tire ('Caster' is the angle that the tire-road interface is forward of where a line thru the steering head axis meets the road.)
f) tracking (front-rear tire and steering head alignment (see above))
g) 'Rain Grooves' cut in the pavement (Common on California freeways)
​

You could also add some ballast near the front of the frame to get better weight distribution. When my wife and I took road trips with the luggage rack loaded, we had to pack some stuff in a tank bag to keep the front end stable. This was on a 650cc touring bike.

Keep the shiny side up!

May the wind always be behind you.
Tom

 

[gary350]

Utility trailers, camper trailers, RVs, trucks, cars, all have the same problem if the rear end is too heavy. Put 800 lbs of bricks in the truck of your car it will wreck once you reach a certain speed. I use to ride a bicycle with side saddle rear baskets too much weight in the rear especially if weight is behind rear axle bike will wreck when it reaches a certain speed. Every thing has a natural self oscillation, move weight or change weight oscillation frequency changes. Watch video.

 

[Baluncore]

When I would take my hands off the handlebars my front tire would wobble. I brought the bike in to check my wheels and they were both “true.” After removing the heavy chain my bike no longer wobbles.

Normally, your upper body weight is supported by your hands on the handlebars. That gives you three points of contact, the bars, the pedals and the seat, which fixes the plane of the bicycle frame and prevents oscillation.

When you take your hands from the handlebars, you also sit up straight, thereby transferring your upper body weight from the front to the back wheel. At the same time, you have removed one of the three points of contact, so the frame can oscillate with and against the castor of the front wheel. Castor oscillation is not a problem when you hold the handlebars, nor when you have a significant weight on the front wheel.

 

[gmax137]

This is why motorcycles use saddle bags rather than top boxes. Or at least, put your heavy stuff in the saddle bags and light stuff in the top box.

 

[JT Smith]

When I went on month-long bicycle tour some years ago the well respected owner of the shop I frequented insisted that it was better to put the weight up front, in panniers on the front wheel. That seemed counterintuitive to me. But I tested it out on the road and sure enough it made a difference in how well the bicycle handled. I don't understand the physics and I don't know if it has any bearing on your wobble problem, but I was convinced. I had only two panniers and put them on the front wheel. I had some stuff on a rack behind the seat as well but about 75% of the load was up front. FWIW.

 

[gary350]

When I went on month-long bicycle tour some years ago the well respected owner of the shop I frequented insisted that it was better to put the weight up front, in panniers on the front wheel. That seemed counterintuitive to me. But I tested it out on the road and sure enough it made a difference in how well the bicycle handled. I don't understand the physics and I don't know if it has any bearing on your wobble problem, but I was convinced. I had only two panniers and put them on the front wheel. I had some stuff on a rack behind the seat as well but about 75% of the load was up front. FWIW.

YES this is correct, always put heavy weight up front, trailer & vehicles. We belong to a nation wide camper group we keep telling people not to put heavy weight in the rear but they don't listen. They use there camper to haul 800 lbs of stuff to the camp ground, bicycles, kayak, ice chests, food, 400 lbs of firewood. They get their vehicle up to 60 mph it fish tails and wrecks, destroys the camper, vehicle upside down in ditch, family in hospital or dead. Engineers design vehicles & trailers to pull perfect empty, once you throw weight off balance it gets dangerous. Never haul heavy weight in the rear. Every thing has its own resonance frequency.

 

[berkeman]

but they don't listen. They use there camper to haul 800 lbs of stuff to the camp ground, bicycles, kayak, ice chests, food, 400 lbs of firewood. They get their vehicle up to 60 mph it fish tails and wrecks, destroys the camper, vehicle upside down in ditch, family in hospital or dead.

So this camping group has been steadily getting smaller?

 

[Baluncore]

So this camping group has been steadily getting smaller?

It would not surprise me if new members had to join as life members, rather than pay annual fees. It would then be more like a pyramid scheme, where members have an opportunity to deselect themselves from longer term membership, to the benefit of the greater community.