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[RightRudder]

As a new FX owner I enjoyed reading the Too Much Torque thread.  I also was surprised on my first few rides how different the throttle response can be on an electric bike compared to an ICE engine even though having owned a Ducati years back I thought I understood about low end torque.  Not that I have had a mishap yet but certainly felt the edge of that boundary where a fun ride can turn into a bad day real fast.  Going uphill and encountering wet mud along a forest service road on the stock tires certainly gave me reason to consider turning around when I found the next dry spot.  It is common to talk about power to weight ratio but reading that thread prompted me to think with electric motors maybe it makes sense to think in terms of torque to weight? 

If I take the 274lb empty weight of a modular FX divided into its 78ftlb of torque it comes out at 0.315.  For comparison the SR/S with 140ftlb and 518lb empty weight comes in significantly lower at 0.217 so the lowly FX has considerably more torque available for its weight than the SR/S.  However to be more meaningful the rider weight needs to be included which brings the numbers for a 180lb rider to 0.200 for the SR/S and 0.182 for the FX illustratingthat the SR/S throttle demands more respect for the average rider than the FX.  With a lighter rider such as myself at 150lb the gap narrows to 0.209 for the SR/S and 0.196 for the FX.  A 110lb woman riding each of these machines would result in 0.222 (SR/S) and 0.218 (FX) which is almost equal.  But consider a small woman on an FX compared to a 180lb male on a SR/S.  She would actually face more potential for loss of traction on the FX than the heavier rider on an SR/S, and when you consider normal force on the rear wheel which is the main factor in traction, the lghter rider on an FX definitely has a handful (no pun intended) to deal with.

[T.S. Zarathustra]

You also need to take into account that torque is measured at the motor. Gearing will change it considerably. 

[RightRudder]

Yes that's very true and the wheel radius also comes into it, but I think the two are pretty similar between the motor and rear wheel aren't they?  Maybe a few percent difference but I think the main point I was trying to make still stands, that a light rider on an FX with a single battery has quite a lot of potential for surprises if they are unfamiliar with the character of it.  Given that the FX looks very small and light the potential to grossly underestimate its ability to break loose is even greater.  I've heard some stories that tend to support this.  Even at the dealer where I got mine two people sepatately tried to warn me to go easy on the throttle because when they got their first bike which was an FX, a very experienced rider from their staff went down in the parking lot within a few seconds the first time they took it outside for this very reason.

[TheRan]

The FX has 18/90 gearing versus 20/90 on the SR/S, but also a larger diameter tyre so it's probably close.

Another thing to consider is the torque curve, despite being electric the older bikes without TC don't give you full torque from 0rpm. It's limited until a little over 15mph. I don't know how the SR/S works, whether it can give you maximum torque from a standstill if you turn off TC.

[T.S. Zarathustra]

Another thing is that torque is power. So torque to weight ratio is power to weight ratio. There is a simple formula to convert torque to horsepower or watts.
Also lighter vehicle (including rider or not) will have less resistance to speed (inertia) changes, thereby reducing the potential loss of friction.

But more powerful vehicle will always have more potential for mishaps. It might be nice if all bikes would come with a training mode where power will increase slowly. I remember when I was going from 50cc to bigger bikes a friend of my fathers (who had some racing experience) said "roll the throttle open, don't snap it open", "feel the power increase and sense the grip", "while riding be aware of all your environment all the time", "train yourself accelerating and doing emergency stops on different surfaces". He said some more stuff that I have forgotten but I have tried to follow most of that and (except for one time when I was nearly frozen on the bike, rode over some wet fallen leaves and lost the front) have never had an accident.

[RightRudder]

Another thing is that torque is power. So torque to weight ratio is power to weight ratio.
SNIP

Actually that's not correct.  Torque is force at a radial distance in a rotating system.  Power results when that force does some work by rotating that system and energy is consumed over a period of time.  Torque can be applied and if the there is an equal resistance there will be zero rotation and therefore zero power and energy consumed.  So torque does not equal power.

But torque is the thing that applies the force where the rubber meets the road and that is what determines, given an amount of friction, whether the tire will grip or there will be slippage.

All I was trying to suggest in this thread is that traditionally motorcycles and other performance machines have been evaluated by a power/weight specification (among other things) and when comparing internal combustion powered bikes it's an apples to apples comparison, which will give you a sense of its performance.  Electric bikes can certainly be evaluated that way too, but since the character and the way an IC engine develops torque is drastically different than an electric motor,  I just felt that perhaps in this case a torque/weight spec might be more meaningful.  I think in the absence of traction control, a number for torque/weight gives a more intuitive sense of what the rider is holding in the right hand, but just my opinion.

[rayivers]

My FX was almost a different bike in the dirt with one or two batteries.  With one, torque was the same as two up to about 30-35 mph but it accelerated faster (less weight), hooked up better (weight farther back), and wheelspin was limited (less hp).  The opposite was true with two batteries, though obviously it was much faster over 30 mph with greatly increased range.  I almost never used two.

[RightRudder]

Rayivers,

I had the same experience as you with one vs two batteries.  The bike is definitely livelier with one and I'm only a 60kg rider so the extra battery is quite a change in overall weight, but one question though, you said weight farther back, I am running with single battery up front which I figured would help with keeping the front end planted.  I had not tried with a single battery in the rear.  Have you tried both ways?

[rayivers]

One of my bikes has the single battery up front (only for street), the other in back (mainly for dirt).  I don't think I could really ride the dirt bike any other way, the front would just seem too heavy (and it would undo all my efforts to make the front end lighter-feeling).  The street bike handles fine with the front battery, and probably would with the battery in back too.