Anyone have significant handling issues with FWD?

John in CR

100 TW
Joined
May 19, 2008
Messages
14,954
Location
Paradise
I had a front wheel drive ebike for a few months back in 2008, and didn't note any problem issues in handling. If anything, in loose stuff like dry sand it was a benefit to handling. I do recall the tendency for it to make the ebike go upright more quickly when accelerating out of curves, which did put me closer to the center of the road after the curve than I would have been with a RWD.

I ask because I'm building a high powered 2wd mostly for trail riding, and want to make sure I'm not missing anything in terms of handling. I'm getting too old for taking hard falls. The only potential problem I foresee is when I'm powering through loose stuff where both wheels are throwing off rooster tails of small rocks or mud, if the front wheel suddenly gains traction with the handlebars turned at all, then a high side would immediately result.

I don't have much off road experience, so am I looking at it right? Can any of you FWD users confirm the risk? Any other issues, other than the obvious:
1. Be sure to let off the throttle when any wheel gets air.
2. Don't use slip charge regen (regen braking activated by letting off the throttle).

I'm planning for 8-10kw peak input to the rear motor and 4-6kw up front, through 4" wide knobbies that are only 16.5" in OD, so the target is something along the lines of a bipolar Hanebrink on steroids. :mrgreen: I just want to make sure it's not a pain inducing machine. I've always though that 2wd would be the holy grail of dirtbikes.
 
I ran about 1800w in the front and 3.5kw in the rear. The torque from the back wheel unloads the front one, so the front slips much more than it does with FWD on its own. Mine high-sided in a straight line on tarmac, so make sure that you have tyres that give plenty of grip.

I've got a feeling that 2wd is OK for low power, but may bring more disadvantages than advantages as the power rises.

Another thing to look out for is that a heavy motor in the front wheel stops the front suspension from working properly because of the adverse effect on the ratio of sprung to unsprung weight.
 
When I ran my X5305 in a 700c wheel on 36V/35A, I had no particular handling issues other than those related to the mass of the front wheel.

Even at that modest power level, I experienced wheelspin when climbing steeper than 10% grades in wet conditions. The front wheel would break loose with every pedal stroke, catching again when pedal pressure lightened. Handling and maneuvering were normal, though. I imagine that if I had tried to turn at those times, the front wheel would have spat out from underneath me. In practice I was always grinding straight up the hill without attempting to change course.
 
The more power you want to drive through the front, the more weight you'll need over that wheel.

I've ridden FWD bikes that wheel spun easily and others which you had to work hard to make them spin out. Frame geometry, wheelbase and body position will play a big roll in how effectively you can use the power up front.
 
I don't see you having any major handling problems until you are riding steeper than 10% grades.

Then as Chalo said, you will end up with so much of your weight transferred off the front and to the rear, that you will start spinning the front tire a lot easier. At that point, hub weight up front will help prevent wheelies that throw you off.

Charging the bars enough can help, but you can't do that enough and remain seated. When the trail gets really rough I stand the pedals rather than try to ride it seated.

I say go for it, like me you won't likely be doing that much of trying to climb a wall. And if you do get some front wheel spin, you still have a rear hub pushing, so it won't be that big a deal. The only issue will be possibly wearing out front tires faster than you'd expect.
 
Thanks guys. Despite being for the trails it will have a longer wheelbase than a mountain bike, so I should be able to keep the front pretty well weighted.
 
Costa Rica must have nice trails that you will soon be confident with, and I know that you like speeding John. FWD is dangerous in the mountain for anything but slow technical riding. Riding the mountain trails you will soon discover that a light weight front end is a must, and that is why we are willing to spend a lot of money on light weight forks, brakes, wheel, stem and handlebar; as a compensation for battery weight so the bike can easily be wheelied in acceleration and the front can be handled very quickly. You want to be strong with the front, so a very wide handlebar and a short stem are making you a better rider like magic.

Trails are unpredictable, one day it is clear and the next you find a tree fell across the trail right after a turn that you got used to take fast. Your bike geometry and weight distribution has to be set to make the bike an aggressive wheelie machine, you want the power on the rear and a lot of it, enough to throw rocks 50ft behind when climbing. When you need weight on the front, it has to be your own weight and your posture makes it all. Ideal wheelbase for power riding the mountain trails is between 48 and 51 inches, shorter makes it difficult to control the wheelie, longer makes it difficult to control in cornering. A slack steer angle is also a must when you are speeding on the rough, a variable headset is a very good safety addition that makes your bike much safer to jump and brake. Front brake has to be top and tuned with large pad surface, you can't afford to be cheap with the front brake.

I know that you want to try riding mountain trails for a long time. Make it so you can do it safer and learn faster. With the adequate bike setup, you will soon love it, with minimal pain.
 
You can also look at how people use the Rokon 2WD for some idea of how their configuration might be similar to yours.
 
MadRhino,

I only go fast in straight lines with visibly clear road ahead. Trail riding is going to be slow going for me with both wheels on the ground. ie have a big honkin battery, maybe a backpack full of solar panel for a long midday break, and go exploring. I think I'll end up somewhere between a Rokon and a Christini. I have a parallel build in the works that will be more capable of the riding you're talking about with 15-20kw geared low and mounted to the swingarm near or in the pivot point.

The 2wd is something I feel compelled to do with hubmotors to see the advantages and disadvantages first hand. I'm actually doing 2, one that's Hanebrink-ish for trail riding, or transportation for people who live beyond the reach of paved roads, or maybe a useful single track vehicle for hunters. The other is a cheap moto conversion using 2 of the motors in 17" moto rims that Luke used when he was down as just a single motor. The goal there is to have a 60mph moto using bargain motors in full size moto wheels with the load split in half and double the cooling, so even the steepest hills aren't an issue using stock hubmotors even with a large rider and and carrying a long range 74V60ah battery pack.

As long as that pulling front wheel doesn't cause high sides (or some other serious handling issue), then I think both will be successful builds. I was running less than 3kw on my original FWD ebike and never noticed anything but benefits on the street other than the one quirk powering out of curves. Once accustomed to it, getting deeper in curves was actually fun and the motor help right the bike. I hope the result is like this review of a street 2wd Yamaha http://www.motorcycle-usa.com/269/4240/Motorcycle-Article/Yamaha-R1-Ohlins-2WD-Review.aspx, but we shall see.

John
 
Back
Top