Motor position

[Phil the drill]

Hi
I'm curious to know why most folk seem to think that the rear wheel is the best place for a huib motor.
In most bikes this means a vast concentration of the weight over the rear wheel - this taking most of the weight of the rider, motor, luggage and battery. Leaving the front largely unloaded, and relatively light. I have heard many say that this improves the bikes handling, but I have to say I'm a little sceptical about this. I still ride off road motorcyles (despite the ramblers association's best efforts to ban me and my colleagues from all but the widest of tarmac surfaces - bless them) and a fundamental principle of keeping control of a motorbike off road is to keep your weight up front and maintain control of the front wheel at all times. Rear wheel slides and skids can be easily tamed with a little experience and indeed can be fun, but to loose the front wheel usually means having a meaningful discussion with the earthworms. Surely keeping some weight on the front wheel of an ebike (like the hub motor for instance) helps with maintaing control in poor conditions, especially on corners and at speed.
My old Powabyke had a centrally mounted battery, and front hub motor, not withstanding that it was generally very overweight, its actual front/rear balance was good I never felt that the front end was uncomfortably 'light'. (I use the term 'light' advisedly, since we are talking about an old Powabyke here!). In the case of my new Wisper I am still a little uncertain of this aspect of it's design. The weight is very much biased to the rear, even unloaded and although I have never had a significant problem with the handling, I am never the less just a little unsure about how it will cope with very challenging conditions. Fortunately I have not yet had to test its front wheel adhesion in serious anger as it were, but the season of mud, leaves, slurry and manure on the roads is about to come upon us, and I confess to being a little more nervous about it this time.
Perhaps it may also be worth considering ditching the standard Chinese tyres also.....

Phil

 

[Mussels]

Surely keeping some weight on the front wheel of an ebike (like the hub motor for instance) helps with maintaing control in poor conditions, especially on corners and at speed.

Keeping traction at the front wheel is all important as you say which is why in a fast corner I wouldn't want to double (at least?) the unsprung weight of the front wheel to make it jump around on a bad surface.

 

[Phil the drill]

Keeping traction at the front wheel is all important as you say which is why in a fast corner I wouldn't want to double (at least?) the unsprung weight of the front wheel to make it jump around on a bad surface.

Surely increasing the weight will reduce the jumping around of the front wheel? On an off road bike you move your own position right up over the front wheels to increase the weight over them and unload the back slightly. That can put much more weight over the front than just the motor on its own can do, surely?
Sorry I still don't quite get it!
Phil

 

[flecc]

I prefer the rear hub motor having extensively ridden both with various bikes Phil, even to the extent of the considerable difficulty of converting my Torq 1 to a rear motor location.

While I totally agree with you about motorbikes, bicycles for some odd reason respond very differently to front weight, and behave themselves better with a light front end. It's probably something to do with the dynamics of a very light vehicle and a comparatively very heavy rider, where those two weights are much closer and often reversed for motorbikes. Because of the body's absorption properties, it is in a sense an additional layer of sprung weight, as opposed to the unsprung weight of the bike's front assembly, or whole bike in the case of a rigid one.

Some front-motor bikes have notoriously unpleasant characteristics, the Torq 1 particularly, the motor weight etc leading to very hard hammering up into the bars on rough surfaces. Many with that model have gone to great lengths to fit highly absorbent handgrips and modify their riding position to more upright to take pressure off the arms. Having sprung forks hides that characteristic to some extent on many models, but the additional bounce can still be evident, though not felt.

The rider's weight tames the weight of the rear motor, battery etc, leading to less effect on handling. My Q bike has most of it's weight concentrated on it's rear wheel, but the other benefit of that is the security when towing the very heavy trailer loads that I commonly do with it. For towing substantial loads with a bike, the two worst things are rear suspension or a light back end on the bike, both making it possible for the large load to take command of the rear wheel. With the firmly planted rear of the Q bike, over 30 mph downhill with a heavy load on a very large trailer is very stable, actually straight lining better than when solo on the same bike.

There's a theoretical benefit of two wheel drive on front motor bikes, but that's largely offset by the potential loss of front wheel traction in wet, icy or loose surface conditions, particularly when uphill and even more certain when towing a load.

Also good is centre motor as on the Panasonic units in the Kalkhoffs etc., weight in the middle and low, but still not as safe for towing. Some examples:

Q bike and trailer load

Q bike for shopping

Trailers general

The ex-Torq T bike
.

 

[flecc]

Surely increasing the weight will reduce the jumping around of the front wheel? On an off road bike you move your own position right up over the front wheels to increase the weight over them and unload the back slightly. That can put much more weight over the front than just the motor on its own can do, surely?
Sorry I still don't quite get it!
Phil

As you see from the above reply Phil, the motor weight increases front wheel jumping. The weight distribution and tyre grip on motorbikes is very different. Extra weight and motor drive on the front easily promotes sideslip on bike tyres when heeled for a bend, something motorbike tyres are much better at coping with. Just look at the timid 30 degree lean angles of top race cyclists compared to the up to 65 degrees of top race motorbikes, a very different world.
.

 

[Tiberius]

Hi Phil, and flecc,

Its a complex but interesting subject. There is a good section in Wikipedia about cycle dynamics and handling. There is also a thread running right now on endless-sphere about it. Spooky that the same subject should come up simultaneously and independently in both forums, though the debate on ES started over battery location, which is usually a bigger mass than the motor.

I have a Torq (front hub motor) and I have built myself a rear hub motor bike. I prefer the handling of the rear motor, though there are so many other differences that a straight comparison is impossible. One of my theories is that it is to do with location of the weight relative to the roll axis, but rather than repeat the debate here, I'll give you a link Endless-sphere.com • View topic - Mounting your battery, Center of Gravity.

Nick

 

[Phil the drill]

Hi
Thanks Flecc and Nick for a very comprehensive answer, I think I follow your reasoning now and of course I can see the very obvious advantages of rear wheel drive when towing heavy loads - avoiding the loss of traction that may otherwise occur.
As I said, I haven't actually had a problem with my Wisper's handling, I was just wondering whether or not to expect it! I feel I may have been a little hasty in pre-empting a possibly non-existant problem!
Thanks again,
Phil

 

[wibble]

I've noticed the front wheel sliding out slightly when going around corners. I just dismissed it as crap tyres, but after reading this thread I'm wondering if it's the front motor. umm...

Food for thought!.