improving eBike road handling?

[jag]

I built an eBike on a pretty stiff CrMo frame, with reasonable weight distribution (rear hub motor, batteries in front triangle. See build post earlier this spring:
http://endless-sphere.com/forums/viewtopic.php?f=4&t=9549&p=147520&hilit=stumpjumper#p147520)

However handling is pretty sloppy. I realize it can't be as crisp as my roadbike or regular MTB due to the increased weight, but I'd like to improve it as much as possible. In particular when steering it feels sloppy. Doing tight curves at speed, it feels like the rear end is going to slide away like an oversteered car. When twiddling the steering left and right, it can start oscillating. Likewise riding no hands it also is prone to steering oscillations.

I'm already working on a solution to replace the cloth battery frame pack with a rigid frame mount box.
I've made sure all the bearings (headset, wheels) have no slop.

I'm wondering what other things I should focus on to improve handling?

Tightening up suspension fork? Wider rear rim? Stiffening rear wheel? Other ideas?

Original construction of the Manitou V fork looks decent. However fork struts are sloppy from wear. Not sure if I can fix that. Frame takes a 1" fork, and I don't see high quality forks in that size anymore.

Rear wheel is pretty significantly dished to be centered. I can bring it back a bit off center, and thereby maybe get a bit more even spoke tension. Would this help?

 

[Drunkskunk]

frame ossilations, also known as death wobble, can be caused by a few things. The most prominate is a loose or sloppy front fork.

they can also be caused by too soft of a suspension setting on the fork, and too much or too little castor angle on the front fork.

Having the bike feel like the back end wants to drift can also be a symptom of the castor angle. Unfortunatly, some Big Box store bikes were designed for ridgid forks, but had Suspension forks added post design. the extra heighth of the fork means the castor angle changes, and at speeds higher than the bike was designed for, can cause some handling issues. Having some free play in the fork is only going to make that worse.

 

[spinningmagnets]

D-skunk, soundslike you have studied this. I'm seeing a lot of MTB's converted to electric on the web (I have an MTB myself) fat tires, full suspension, and a front disc brake are why I bought one. I have converted to a more comfortable beach-cruiser seating/handlebar geometry, but I also am unhappy about handling at higher speeds on downhills.

If I was making my own frame, what would be a good front fork angle, with straight up-and-down being zero, and 45 degrees being a "chopper" styled bike? (my MTB head tube appears to be about 15-deg away from vertical)

 

[Drunkskunk]

Its not as simple as just the head angle. to design a frame, you need to know the head angle, called the rake, the leingth of the fork under compression, and extension, as well as resting leingth, the distance of the contact patch behind the centerline of the steer tube, and the weight distrobution.

 

[Toorbough ULL-Zeveigh]

definitely under the heading of 'other ideas'; a hub battery in the front wheel.
the supposed unsprung weight is a barely noticeable trade-off for the improved handling.
altho u may feel different so b4 u try it, a test drive on an E+ would help u to decide if it's 4 u.
since ur packs not that big just as an experiment temp mount the batts on lo-rider front pannys, see what that does for ya.
at a min tho, just moving ur pack lower down to where ur controller is now i think would make a big difference.

 

[jag]

frame ossilations, also known as death wobble, can be caused by a few things. The most prominate is a loose or sloppy front fork.

they can also be caused by too soft of a suspension setting on the fork, and too much or too little castor angle on the front fork.

I'll try to stiffen the suspension a bit. The elastomers are exhangeable, and I can also increase the preload on them.

The springs under the elastomers are somehow stuck, particularly on one side. I tried to take them out when I R&R:ed the bike in preparation for e-conversion.

What keeps a suspension fork tight? Some kind of bushings? I'll will look more carefully next time to figure out if there is something I can replace.

 

[jag]

definitely under the heading of 'other ideas'; a hub battery in the front wheel.
the supposed unsprung weight is a barely noticeable trade-off for the improved handling.
altho u may feel different so b4 u try it, a test drive on an E+ would help u to decide if it's 4 u.
since ur packs not that big just as an experiment temp mount the batts on lo-rider front pannys, see what that does for ya.
at a min tho, just moving ur pack lower down to where ur controller is now i think would make a big difference.

I have a low rider rack and panniers from my days of long distance touring, so I could try that. Of course, one reason I got the front suspension bike was to be able to have a low unsprung weight. I can also try to move the CG around a bit by relocating batteries within the frame triangle.

I'm however a bit confused to why a low CG is good. On the recumbent groups I read that a high CG recumbent is easier to ride than a lowrider, low CG recumbent.

 

[Tiberius]

I'm however a bit confused to why a low CG is good. On the recumbent groups I read that a high CG recumbent is easier to ride than a lowrider, low CG recumbent.

Jag,

You are quite right. A high CG is better when riding; a low CG is only good when parking the bike.

Looking at the picture, your weight distribution seems ok. So the problem is more likely to be some sort of flexing or unwanted movement. The obvious place to look of course is the forks, but it might be worth checking how smoothly the steering operates - a sticking headset might cause such symptoms.

How securely are the batteries mounted? Do they move around?

Nick

 

[jag]

Looking at the picture, your weight distribution seems ok. So the problem is more likely to be some sort of flexing or unwanted movement. The obvious place to look of course is the forks, but it might be worth checking how smoothly the steering operates - a sticking headset might cause such symptoms.

How do I check a headset? There is no slop in the bearing. It feels smooth when swinging left-right stationary. Can something go wrong so it sticks under the loads when cycling?

How securely are the batteries mounted? Do they move around?
Nick

Batteries are in a bag. They do swing a bit. This surely amplifies oscillations. Not sure if it will start oscillations. I'm working on a rigid mount in the frame triangle.

 

[Grinhill]

I agree that rigid-mount of the batteries may improve things. Include some cushioning such as closed-cell type foam to absorb shocks.

 

[fifthmass]

I had a similar situation briefly. One of the rear rack support bolts down by the rear axle sheared and my 30 pound battery bag was wobbling side to side. I felt as if the rear end wanted to go out from under me. Fortunately the battery rack was still supported fine by the remaining upright stay until I got to work and found out what the problem was.

I would not be surprised if your loose battery support was the cause. How heavy are your batteries?

Regards, Bill

 

[huskydave]

I think your frame is flexing and this is effecting your handling. Unless you upgrade the frame their is little you can do. I had this problem with my original bike it only had front suspension. I looked for a bike with a solid wide heavy rear swingarm and it helped a lot but it still has a bit of side wobble on acceleration but is way better than the other frame I had. I installed a downhill front fork this year and I could not believe the differance in handling. It feels secure and I feel much more confident now. Your bike looks balanced to me but you may benifit from a stiffer frame imo.

 

[adrian_sm]

I have a similar set-up to you, rear hub motor, batteries in the frame. Although I did make a rigid bracket for the battery (with some cushioning foam of coarse). The batteries I mounted as low as possible. My front fork is nothing fantastic, a bit sticky in it's motion, and I do get some shudder under braking, but that is likely to be movement in the rim brake bearings. Apart from that it feels rock solid on the road. Definitely not as nimble as prior to the conversion, but feels quite balanced. I have never had any issues with oscillations, so I agree with the others, start off by securing the batteries would be my first move.

You can see my bike and battery mount pics here if you are interested.
http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=9627#p158382

 

[huskydave]

That still looks like a nice bike. If you sell it you can look for something stiffer. The money I spent on a full suspension frame was well spent. When I added the 170mm + travel front fork, disk brake and dialed it all in I have a very forgiving bike. I use about 4" of travel just on heavy braking the rest is for going over potholes going off curbs and the tripleclamps that I have feel much more secure but over time I slowly spent money the more I used my bike to make it more comfortable.

 

[jag]

I would not be surprised if your loose battery support was the cause. How heavy are your batteries?

Thats probably at least part of the cause. As mentioned, I'm working on a rigid mount solution.
Batteries are 12kg, hub motor wheel is 7kg, so the e-conversion added nearly 20kg to a 12kg bike.
Had I gone for a lighter setup (4kg geared motor and 3-4kg battery), maybe attention to detail in
the build would have been less critical.

 

[Toorbough ULL-Zeveigh]

I'm however a bit confused to why a low CG is good. On the recumbent groups I read that a high CG recumbent is easier to ride than a lowrider, low CG recumbent.

explaining that could get involved & as usual the whole story is not a simple generalization.
not necessarily a low CG but low-er one at least, anything that can b done to offset some of that high mass of the rider to restore some balance can only help.

personally i have little choice but to ride all winter long as it lasts about 8 months out of the year around here & on ice with a high CG the bike constantly wants to go tits-up.
riding on ice is the same as riding on dry pavement as far as the bikes tendency of motion goes.
the bike will react the same way as it approaches the limits of adhesion in either case.
only the traveling velocity at which it happens will be different, an icy surface just makes it more readily apparent.

You are quite right. A high CG is better when riding; a low CG is only good when parking the bike.

just the opposite actually, high CG is beneficial at near dead stop only to make it easier to balance, whereas u have the gyro effect to help out at any kind of cruising speed, at least according to Tony Foale.

"Low weight & a low motorcycle center of gravity both facilitate good balance."

 

[Drunkskunk]

the debate over High V.S. low center of gravity is on going.

But I'll point out, its nearly moot when you sit on the bike, as you add your 240lbs to the top of the seat and handlebars, you make the bike inherently top heavy.

and your 10 pounds of battery isn't going to effect your handling much, unless you tape it to the end of a 10 foot pole, and hang it off to the side of the bike or something.

I use the same bag as you, and while the batteries can move a little, there isn't enough material for them to move far enough to cause the problems you describe. Thats also just about the ideal spot to mount batteries with a rear motor.

If there is any freeplay at all in the front fork, there is your problem. There is no adjustmernt for how tight those fit, as it's a machined part, and if it's lose, its worn or stretched out.

The first thing I would try is getting another fork. garage sale bikes are cheap, and it should be easy enough to swap forks. Not much point chasing other possabilities when there is a known problem.

 

[GTA1]

Here is what I would do:

Get a set of strain gauges, and laser pointers / scales.

Rig it up to measure deformation at different parts of the system: frame, forks, wheel/hub.

At the same time, get an accelerometer to measure forces on the frame in 3D.

Get all that data into a logging device and then see where it is bending / flexing, what is moving around where.

Issues can be deformation as well as dynamic balance.

If you have some good engineer friends, see if some of them will lend you a Finite Element Analysis Software suite.

The hard part in a vehicle is to simulate not only the frame, but the centrifugal forces created by rapidly spinning mass --- Especially one like the wheel / hub that distorts depending on whether it is accelerating, decelerating, bending from turning, etc.

Then add to that the bouncing / up and down motion, momentary contact / loss of contact with road and its loads as it grips or not grips the surface....

-------------------

Without doing any science, off hand, my first suspect of causes of your issues is the front fork / wheel combo bending under the strain.

Temporarily replacing the fork with a stiff (unsprung) fork and see if that makes a difference.

Or try a much stronger front wheel (with much beefier spokes and rims).

Or both....

Without science, basically you end up doing diagnostics by a process of elimination.

 

[adrian_sm]

One other thought. The only time I have had my rear end feel loose like you describe is when I got a flat.

I was riding along happily, then went though one corner, and thought that feels a bit loose. Then through some chichanes (sp?) and nearly lost it. Back end was all over the place.

So you might want to check what pressure you rear tyre is at, or maybe even spoke tension.

 

[jag]

One other thought. The only time I have had my rear end feel loose like you describe is when I got a flat.

I was riding along happily, then went though one corner, and thought that feels a bit loose. Then through some chichanes (sp?) and nearly lost it. Back end was all over the place.

So you might want to check what pressure you rear tyre is at, or maybe even spoke tension.

I'm guessing rear tire/wheel flexibility is perhaps the number two or three cause (after swinging batteries and loose suspension fork). Lacking rear suspension, I ride a pretty big tire (1.95" Tioga city slicker) at low pressure. The rim is the narrow original rim that comes with the NineContinent hub and wheel.

I'll do a little bit more of the "process of elimination", since I'm already working on a fixed battery mount, can easily pump up the tire to see if that is the cause. I've been looking for a 1" steerer tube fork, but haven't seen anything better than what I have yet. Most of the 1"-ers seem to be low end forks.

All else fails, I can explore the laser pointer measurement idea (thanks for the tip). I'll stay away from the detailed FEM modeling of bike dynamics.

 

[GTA1]

Another commonly used engineering technique is to paste black and white squares on parts that are moving fast (rim, etc.) and then either photograph it with a high speed video cam (fast frame rate) or use a strobe light to slow it down so you can see what it is doing under certain conditions.

Something is deforming / bending is my guess.... and Rear wheel is as good a suspect as the front fork/wheel.

What diameter are your spokes?

Have you tried beefier tires that have more plies, are stronger and more resistant to deformation at speed?

 

[Mathurin]

City slicker at the rear, yeah that may be why your bike feels tail happy. These tires ride real nice, spool up fast, got low rr and seem to last forever. Yay! But, in cornering they feel like the bike wants to wash out under me, not the most confidece inspiring. Suggest getting german, french or italian rubber on there, also something bigger then what you have now would be nice (or, narrow the front to balence).

 

[EVnewbie]

Since you have a one inch fork, just swap out a solid fork cheapie to test. I'd take a bunch of bungie cords and tighten up the battery pack mount and take it for a spin. Granted, you don't want a solid fork for riding but it will take the suspension fork out of the equation. If it is the fork, take it apart and put stiffer elastomers and springs inside and lubricate the tubes and seals with Judy Butter. I've been using Judy Butter on suspension forks for years and it keeps them smooth and supple over the miles. Good luck!

 

[Takemehome]

Did you check for cracks in the frame at the soldering points ?
I know it doesn't happen often, but it does,and it's very dangerous if it wield at high speed.

 

[jag]

Over the past month I've tried several of the ideas. Here's what made the most improvement:

Weight balance. Any load in the rear panniers make handling worse.

Tire pressure. I was running the rear tire fairly low (for smooth ride on the hardtail MTB). After pumping up the tire pressure the ride is harsher over uneven pavement, but the handling is so much better.

I stiffened the front suspension fork a bit. It was already on the max using the adjusters, so I replaced one section of elastomer with a 1.5 times longer wood plug. Maybe helped a little bit, and keeps fork from bottoming out. I guess it wasn't designed for 12kg of NiCd up front...

Now the bike rides about as good as one can expect from a 30kg eBike. Still not as precise and fun as my 10kg bikes, but quite acceptable.