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[evtricity]

I've always been intrigued by how low the trail figures are on Zero bikes - 80mm on the SR/DSR/S/DS with a relatively common 24 degrees of rake (steering angle).

With most sports bikes running around 95mm of trail I would expect the Zeros to be very twitchy at only 80mm but I don't find that when riding my SR. I suspect that the lower centre of gravity of the Zeros (versus gas bikes) contributes to an increased stability and less willingness to turn so perhaps the shorter trail has been chosen to counterbalance that.

What do you think about the low trail figure - does it make the Zeros twitchy compared to sport bikes you've ridden?

While the Zeros are relatively light I've always found my SR still needs a good push (countersteer) to get it really leaned over i.e. more than 40 degrees.

Does the low centre of gravity change its dynamics with respect to cornering e.g. harder to lean over?

[rayivers]

I've always been dismayed by how low the trail figures are on nearly all modern bikes.

I think the '15 SR I rode last October had both front brake and tire-inflation issues - I had to countersteer it to keep the front tire from scrubbing, even in very slow corners. According to one article I read online, this may be caused by excessive triple-clamp offset, which creates oversteer that increases with lean angle.  The '15 FX and R6 I rode earlier that day both tracked fine, along with the vast majority of street bikes I've ridden since the 70's, although that '64 Ducati 250 was a little twitchy.

AFAIK - and all else being equal - lowering the vertical center of gravity increases stability in every axis, making wheelies, stoppies, and dropping quick & hard into corners more difficult.

Every time I've increased the effective fork rake of my MX bike, both straight-line stability and cornering performance improved.  The changes have been small so far, but I'm working on it.

Ray

[evtricity]

Thanks Ray, that's very interesting.

Another Zero rider racing a 2015 SR commented that his bike pulls into bends when he uses the front brake at lean (trail braking) into corners. While I don't trail brake a lot I've never felt this oversteer on my 2014. Since the 2014 and 2015 are supposed to have the same geometry perhaps this relates to the Showa suspension which may be a bit soft, quickening the steering more significantly under front braking.

[spacetiger]

I do not have a Zero yet (perhaps in a year or so) but am studying the bike and like what I see.  Zero is doing an awesome job with design and manufacturing.  They are also putting in some really quality hardware, especially suspension and braking to go along with what they are doing in the power department. 

I like this new thread because someone out there is also looking at the geometry and asking a good question.  I don't know if I can answer the question, but thought I'd post some graphics from data I kept from another bike project (CB700sc) involving common bike metrics.

Pic 1.  Rake vs Trail.  A somewhat tight "V" design relationship.  Zero S/SR is the black dot with cyan ring.  I consider the Zero a naked bike (black dots).  The sport bikes are the red dots and the cruisers are the magenta dots way out there.  I would say Zero is in the V, but the low trail number makes it stand out.



Pic 2.  Wheelbase vs. Weight.  The tightest "V" design relationship I found; Zero picked a safe spot for the S/SR but low down the V.



Pic 3.  Trail vs. Weight.  A loose V design relationship and Zero S/SR is a bit of an outlyer because of the low trail but it still is in the V.



Pic 4.  Rake vs. Weight.  Another loose V and Zero S/SR is low in the V but in the middle.



Pic 5.  Trail vs. Wheelbase.  A "//" design boundary relationship(?).  Here the trail number doesn't stand out but looks like it is in the middle.  That said, the other manufactures seem to like the left side boundary.



Pic 6. Rake vs. Wheelbase.  Like pic 5 above, Zero S/SR is safely in the middle. 



So yes, the trail numbers are low, but not out of the norm.  The Zero numbers show they designed the bikes to be agile performers and they have given them quality components and a drivetrain that can really make the bike a great riding machine. 

You guys indicate the Zero has a low CG, but my visual inspection suggest the heavy batteries are high up in the bike, so I really wonder how "low the CG is on the bike.  What I would suggest on the bike is that it has has a tighter CG, that is it has a lower polar moment of inertia design, so the rake and trail numbers could reduced to take advantage if this design aspect to produce a nimble machine. 

As a side note, the 2011 S had a rake and trail of 22.7 degrees and 2.8 inches - MUCH smaller than the 2015 Zero S/SR.  They got away with these tiny numbers because it had less battery mass (even tighter CG / low polar moment of inertia).

If the tighter mass is an advantage to the electric bike, I would guess as power improves, it will overcome the gas powered bike in [short] races because it can out handle the gas bike.

Just a thought,
Jerry

[evtricity]

Wow, great analysis Jerry.

The reason I say the Zero SR/S/DSR/DS has a low centre of gravity is that the battery almost completely sits below the main chassis spar.

If you don't have a power tank then compared to a gas bike that will have the top of the motor and the fuel tank at or above the main spar it must have a lower centre of gravity.

[spacetiger]

Agree on placement of the battery, but look at it this way.  Draw an imaginary line between the wheel axles.  You will find the drivetrain primary mass very close to the line.  On the gas engines, some designs have the heads up higher, but they are relatively low mass compared to the case, crank, shaft drive (if you have that).  The gas tank has moved down on many bikes, although many still have it up top.  But 4 gallons x 7 lbs/gal = 28 lbs + tank.  An engine can weight 200-300 lbs, so the gas is light.

On the Zero, the battery is notably above the imaginary line.  The additional power pack is even further away.  But, the mass centralization of the Zero is clear as the heavier bits are close to the CG.  When they can change the shape of the battery pack to get it lower in the bike frame, the bike will handle unlike ANY gas powered bike.  Hope they get there before I buy...

Jerry

[evtricity]

Good points.

I actually lowered my SR almost an inch when I  changed the top triple clamp to a flat custom one. I also removed the bash plate and charger so its CG is definitely lower than stock.

With the higher discharge and capacity of the 2016 battery, switching to the 9.8kW pack would lose one of the modules in the top of the battery pack (monolith), lowering the CG while still providing enough power to support the SR motor peak power.