Stability issues

General Discussion about electric bicycles.
Paul   1 mW

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Stability issues

Post by Paul » Sep 17 2018 12:25pm

Hi,

My converted e-bike feels unstable if I ride it. The front wheel does not feel to 'lock' to a straight line. It feels nervous when I travel at speeds of max 35 km/h. What could be an option to give my bike more self-stability or balance?

What I already did is deflate the front wheel tire a little. That helped to diminish the nervousness of the steering wheel quite a bit.
I also connected a steering turn limiter (a spring) from the fork to the frame to keep the front wheel more straight. The spring causes the front wheel to be pulled back to a straight line. This seems to help a little bit.

But at this point I am not happy with the result. It is safe so far, but I dare not relax while riding it. Has anyone a helpful suggestion I could try out?

This is the 'trekking hybride' I converted to an ebike. https://www.pegasus-bikes.de/produkt/pe ... -586-61848
The motor is a Bafang 48V 500W rear wheel hub motor. I installed a 48V battery on the rear rack. This is the end result: Image

Thanks, Paul.

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fechter   100 GW

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Re: Stability issues

Post by fechter » Sep 17 2018 1:32pm

To me it sounds like the steering head angle is too steep resulting in not enough trail. Unfortunately this is hard to fix. One possible solution would be to use a different front fork that has more trail. On one of my A2B bikes, I took apart the fork and flipped the crown around 180 degrees so the front axle is now a bit further back. This improved the stability a lot. It looks like the brace on yours would prevent this from working.

If the fork has any kind of preload adjustment, crank it up so it doesn't compress as much.

I'm sure someone will also suggest moving the battery further forward on the frame so it's in the triangle. This might help too, but the bike should be able to carry a load on the rear without being unstable.
"One test is worth a thousand opinions"

Jon NCal   1 kW

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Re: Stability issues

Post by Jon NCal » Sep 17 2018 2:06pm

Some things to try, is check headset for condition and proper adjustment. Lower handlebars. Move saddle back a few inches.

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Chalo   100 GW

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Re: Stability issues

Post by Chalo » Sep 17 2018 2:20pm

My best guess is a headset problem. Too tight, assembled wrong, or worn with dimples in the bearing races. If the front end doesn't turn freely, the bike can't do its job self-correcting and staying under you.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 17 2018 3:02pm

fechter wrote:
Sep 17 2018 1:32pm
To me it sounds like the steering head angle is too steep resulting in not enough trail. Unfortunately this is hard to fix. One possible solution would be to use a different front fork that has more trail. On one of my A2B bikes, I took apart the fork and flipped the crown around 180 degrees so the front axle is now a bit further back. This improved the stability a lot. It looks like the brace on yours would prevent this from working.

If the fork has any kind of preload adjustment, crank it up so it doesn't compress as much.

I'm sure someone will also suggest moving the battery further forward on the frame so it's in the triangle. This might help too, but the bike should be able to carry a load on the rear without being unstable.
Thanks for your suggestions!

Perhaps the front fork is indeed a bit unstable by itself. Maybe I will change the fork, but that would be more of a last resort option for me, I guess.

I agree that the weight distribution is not optimal. I thought the bike could handle this configuration.

Nevertheless, I took some weights from my fitness gear just now and hung it from my bike. Image (Sorry for the poor photo quality, but it is dark now in The Netherlands. ) This improves the balance and stability enormously! So that is something to explore further. Maybe I can take the battery and hang it from the top tube. That is an experiment that can be done quite easily.

Thanks for your suggestions.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 17 2018 3:04pm

Jon NCal wrote:
Sep 17 2018 2:06pm
Some things to try, is check headset for condition and proper adjustment. Lower handlebars. Move saddle back a few inches.
Thanks! I will try that out. The condition of the bike is okee I guess as it is brand new. I will try it out with a lower handlebar setting and move the saddle a bit back.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 17 2018 3:09pm

Chalo wrote:
Sep 17 2018 2:20pm
My best guess is a headset problem. Too tight, assembled wrong, or worn with dimples in the bearing races. If the front end doesn't turn freely, the bike can't do its job self-correcting and staying under you.
The bike is brand new. The front wheel can move freely from left to right. I think it is maybe a design flaw, like fechter also suggested. Apparently the extra weight at the back has quite an impact on the stability of the bike. If only I had known when I bought the bike.

I hope the shifting of the weight of the battery to the front will give a satisfying solution.

Thanks for your help!

2old   100 kW

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Re: Stability issues

Post by 2old » Sep 17 2018 4:15pm

Looks like a "tail wagging the dog" problem. I think your situation would be resolved by transferring the battery/rack from the rear to the front of the bike.

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MadRhino   100 GW

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Re: Stability issues

Post by MadRhino » Sep 17 2018 6:53pm

Three factors are affecting nimbleness, I believe in your case all three are wrong.

Trail
Cockpit tuning
Weight distribution

The steer angle is designed for a rider positioned well on the front, I’d say one who has the hadlebar set lower than the saddle, a tall guy who has his head on top of the front wheel. Yet it should be handling, if there wasn’t some other problem.

You tuned the rider’s posture upright, cruiser style, on a frame obviously not made for this. But, it should be handling if there wasn’t another problem.

You have put lots of weight on the rear, to make it even worse. That, is another problem, but it should be tuneable to handle if there wasn’t another problem.... Find it. Fork, headset, wheel.. All suspect.

I will give you a hint about geometry and tuning: If you can’t ride it without the hands, it is wrong.

Then, if you can coast it at 50 Mph down to almost stopped without the hands, it is built and tuned damn good.
Make it fool-proof, and I will make a better fool.
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SirLongAss   100 mW

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Re: Stability issues

Post by SirLongAss » Sep 17 2018 7:28pm

Maybe you're wheel isn't true'd or perhaps the wheels need to be balanced. Both are very easy to check.

My gf's bike is like yours. I can get it going 55km/h and still be fairly stable.

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Re: Stability issues

Post by Paul » Sep 18 2018 9:43am

Thanks for all your suggestions. I tried a couple of things.

I moved the handlebars to a more forward and downward position. This did not improve stability. In fact it felt a bit worse. I tried the most upward position, but that is also not OK. So it seems around 40 degrees is for this bike a good compromise. Or the best I can get, at least. ;-)

I removed the rear rack and moved the battery to the frame. That improved stability, but not as much as I hoped. Therefore I moved the battery and controller to hang from the handlebars. This improved steering stability quite a bit. See this picture: Image.

My guess at the moment is that the front fork with suspension is not a good idea for a e-bike. By accelerating or maintaining speed, the front wheel gets a bit lifted. Because of the (weak) suspension, this is apparently quite a lot. Because of the lack of pressure on the front wheel, the steering feels too light and not safe.

If one pedals along, more weight is transferred to the front because one is leaning more on the handlebars. But if I just push the button and ride like a scooter one tends to sit in a more upright position, thus moving the weight and pressure away from the front wheel.

So at the moment I think I will go with the battery hanging from the handlebars. This gives continuous pressure on the front wheel and balances the accelerating power from the rear wheel.

What I still want to do is ask an expert opinion from a bike shop nearby. After all, I don't think I would like to ride this bike without my hands on the handlebars at 50mph (or 20 mph for that matter), even without a motor or ebike-kit. Perhaps there is indeed a tuning or balancing problem with the bike.

Thanks for your helpful suggestions!

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Re: Stability issues

Post by Paul » Sep 18 2018 9:45am

SirLongAss wrote:
Sep 17 2018 7:28pm
Maybe you're wheel isn't true'd or perhaps the wheels need to be balanced. Both are very easy to check.

My gf's bike is like yours. I can get it going 55km/h and still be fairly stable.
Thanks for your comment. Gives me hope it is possible to improve stability!

Could you please elaborate a bit about the configuration of your gf's bike? What is the power of your motor? Where is the motor/battery placed? What position did you chose for the handlebars?

Thanks!

2old   100 kW

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Re: Stability issues

Post by 2old » Sep 18 2018 10:59am

Why not try a front rack where the weight is even lower? My 1000w DD is configured with the battery on a front rack and handles well.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 12:12pm

2old wrote:
Sep 18 2018 10:59am
Why not try a front rack where the weight is even lower? My 1000w DD is configured with the battery on a front rack and handles well.
That is a great idea. Thanks!

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MadRhino   100 GW

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Re: Stability issues

Post by MadRhino » Sep 18 2018 12:17pm

Suspension is a good idea, and a must for a fast bike. But, like any other components, suspension need to be installed and tuned properly.
Make it fool-proof, and I will make a better fool.
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Trek Session 10 mod. Variable geometry. 70mph
Dirt:
Santa Cruz V10. 50mph

AHicks   100 W

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Re: Stability issues

Post by AHicks » Sep 18 2018 12:26pm

My first conversion used a rear rack mounted battery (because it was easy), and I considered that a disaster when it came to riding it. Next attempt used the water bottle mounts on the forward down tube, mounting it as low as I could. That move turned the previous disaster into a winner. With weight distribution further forward, and CG lowered, it made all the difference in the world.

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motomech   1 GW

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Re: Stability issues

Post by motomech » Sep 18 2018 1:43pm

It's hard to know w/out actually measuring it, but I agree w/ Fecther, the steering stem angle looks awfully steep to me.
Feeling "unstable" is, of course subjective, but doesn't necessarily mean it's ready to go out of control. Perhaps, as hr.s are accumulated, the feeling will be less pronounced.
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'07 GT Idive 4 4.0, Q100H 201 frt. mounted, 14S Multistar LiPoly, elifebike 9-FET 20A controller. Mean Well HLG-320H-54A, Crazy Bobs on Alex DM32's 21 to 22 MPH. viewtopic.php?f=3&t=28151&p=1373714&hilit=Idrive#p13737

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Chalo   100 GW

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Re: Stability issues

Post by Chalo » Sep 18 2018 2:05pm

The head angle looks normal to me, after accounting for parallax in the photo.

My first two e-bikes had heavy lead battery packs on rear racks. They were shaky pretty much all the time. Most cargo racks have very poor lateral bracing and act like springs to make a hard mounted load wag from side to side.

If you put the battery in a pannier on the side of the rear rack, you get two benefits. You lower the center of mass for a smaller swaying moment, and you decouple the battery from the bike's frame, which would tend to quickly damp out wagging motions.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 3:26pm

AHicks wrote:
Sep 18 2018 12:26pm
My first conversion used a rear rack mounted battery (because it was easy), and I considered that a disaster when it came to riding it. Next attempt used the water bottle mounts on the forward down tube, mounting it as low as I could. That move turned the previous disaster into a winner. With weight distribution further forward, and CG lowered, it made all the difference in the world.
Thanks for sharing. I am probably on the same track.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 3:34pm

motomech wrote:
Sep 18 2018 1:43pm
It's hard to know w/out actually measuring it, but I agree w/ Fecther, the steering stem angle looks awfully steep to me.
Feeling "unstable" is, of course subjective, but doesn't necessarily mean it's ready to go out of control. Perhaps, as hr.s are accumulated, the feeling will be less pronounced.
Today I took my previously converted e-bike for a ride. It is a standard city bike with a front wheel hub motor and a battery on the rear rack. Now, it also felt a bit unstable to me, which I never experienced when riding it before. I guess I have become a bit over-sensitive on this stability-thing since I got this new bike.

The battery on the handlebars made the new ebike a lot more stable than my converted city bike ever was. So I think you may be right. I just have to get more hours on the bike and get used to how it handles at higher speed.

SirLongAss   100 mW

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Re: Stability issues

Post by SirLongAss » Sep 18 2018 3:35pm

Paul wrote:
Sep 18 2018 9:45am
SirLongAss wrote:
Sep 17 2018 7:28pm
Maybe you're wheel isn't true'd or perhaps the wheels need to be balanced. Both are very easy to check.

My gf's bike is like yours. I can get it going 55km/h and still be fairly stable.
Thanks for your comment. Gives me hope it is possible to improve stability!

Could you please elaborate a bit about the configuration of your gf's bike? What is the power of your motor? Where is the motor/battery placed? What position did you chose for the handlebars?

Thanks!
My gf's bike is running a 1000w bafang HD and it is placed center and low.

This is her bike that I converted.
https://www.giant-bicycles.com/us/cypress-dx-2016

The handle bars are set up like yours, higher then the seat. More like a motorcycle.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 3:44pm

Chalo wrote:
Sep 18 2018 2:05pm
The head angle looks normal to me, after accounting for parallax in the photo.

My first two e-bikes had heavy lead battery packs on rear racks. They were shaky pretty much all the time. Most cargo racks have very poor lateral bracing and act like springs to make a hard mounted load wag from side to side.

If you put the battery in a pannier on the side of the rear rack, you get two benefits. You lower the center of mass for a smaller swaying moment, and you decouple the battery from the bike's frame, which would tend to quickly damp out wagging motions.
Thanks for your suggestion. I had also noticed this effect on the e-bike. By increasing the tire pressure, it was more manageable, but I could feel it pulling sometimes. Your pannier suggestion sounds great for reducing this.

However, at the moment, I think I will go with the battery hanging from the handlebars or placing it on a front wheel rack. I have made a few short trips today and I think I am going to be satisfied with this setup. Thanks!

Jon NCal   1 kW

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Re: Stability issues

Post by Jon NCal » Sep 18 2018 3:46pm

I'm wondering if you tried sliding the saddle back? Even 1 inch makes a big difference in handling.

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 3:50pm

SirLongAss wrote:
Sep 18 2018 3:35pm
Paul wrote:
Sep 18 2018 9:45am
SirLongAss wrote:
Sep 17 2018 7:28pm
Maybe you're wheel isn't true'd or perhaps the wheels need to be balanced. Both are very easy to check.

My gf's bike is like yours. I can get it going 55km/h and still be fairly stable.
Thanks for your comment. Gives me hope it is possible to improve stability!

Could you please elaborate a bit about the configuration of your gf's bike? What is the power of your motor? Where is the motor/battery placed? What position did you chose for the handlebars?

Thanks!
My gf's bike is running a 1000w bafang HD and it is placed center and low.

This is her bike that I converted.
https://www.giant-bicycles.com/us/cypress-dx-2016

The handle bars are set up like yours, higher then the seat. More like a motorcycle.
Thanks for your information. Yes, that bike looks a lot like mine. Nice. I have become more optimistic since participating on this forum that it is possible to get it right. Thanks for that! Maybe one day I will also move to a mid drive motor, as it has more power and better weight-placement.

I guess the two main factors for a stable e bike are weight distribution and my getting used to handling the new e-bike. I think I am on the right track now. Thanks!

Paul   1 mW

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Re: Stability issues

Post by Paul » Sep 18 2018 3:54pm

Jon NCal wrote:
Sep 18 2018 3:46pm
I'm wondering if you tried sliding the saddle back? Even 1 inch makes a big difference in handling.
Ah, that is a good one. No, I have not tried that yet, but will do that tomorrow. I had switched saddles the other day and later on put this original back on without much care for position. It is also angled a bit downwards, which makes it kind of uncomfortable. I will experiment with a few positions tomorrow. Thanks!

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