Drive Belt

From Unofficial Zero Manual
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Zero uses a belt for primary transmission of torque to the rear wheel. It's quiet and lightweight but is a proprietary design that can wear out. If you plan to put a lot of miles on a Zero or risk the belt often, buy a spare belt ahead of time and mind its maintenance.


Risks

Drive belts fail by snapping or by stripping the teeth.

On Landing
The most common situation for a belt snap is when going over a major bump or jump where the rear wheel leaves the ground.
  • If, while airborne, the throttle is not immediately relaxed, the rear wheel will rapidly spin up.
  • A wheel that is moving extremely quickly in the air will get jerked back to its regular speed on landing. This is transmitted to the belt through the rear sprocket and can easily strip teeth.
From Debris
Gravel or sand that gets thrown between sprocket teeth and the belt will force the belt to expand quickly under load, and can cause it to snap.
Reportedly, sand is a much more reliable path to belt failure than gravel.
The sprocket tooth design is meant to deflect gravel to the inside of the swingarm towards the wheel.
The bike has an upper debris guard made of soft ABS plastic, but does not have a lower guard.
From Mis-Alignment
An unaligned belt can wear really badly and break sooner.


Wear

Generally, watch for belt damage and try to anticipate when to replace the belt to avoid an incident on the road where the belt snaps.

What to Check
  • Check the teeth for wear and cracks.
    If you see cracks in the tooth forming, the belt is getting old.
    If you see deep cracks starting, it's time to replace the belt ASAP.
    Rear Drive Belt Wear Analysis
When to Replace
  • When it snaps.
  • When any teeth have been ground off.
Hard Skips
  • If the belt experiences a "hard skip" from debris between the belt and a sprocket, it is likely to fail soon after. Watch it carefully if this happens.
Tension with aging
Apparently, per forum user JaimeC, belts don't wear like chains.
As they get older they'll actually get tighter, not looser like a chain.
  • When a chain ages, the little bearing points between the links and rollers wear causing the chain to hang looser.
  • When a belt ages, the rubber on the inner/toothed side begins to swell.
Since the Kevlar belt on the outer circumference won't stretch, the inner circumference will shrink making the belt tighter around the sprockets.
Generally, you want to make sure the belt hasn't gotten any tighter since you brought it home.
References


Damage

Bumps
Belts are most commonly damaged by using the throttle in the moment that a wheel becomes airborne, over a bump at speed, say.
If the wheel spins up momentum in the air, regaining traction on landing will jerk the belt, causing a loss of belt teeth or the belt may snap entirely.
Debris
Gravel, road debris, or sand can damage or snap the belt if caught between the belt and the sprocket.
Sand seems to be the most sure to destroy a belt; gravel has a lower probability given some basic design protections that should scatter gravel out of or away from the sprocket.
Teeth loss tolerance
Missing belt teeth can be tolerated briefly until a replacement can be made by riding at low torques (easy acceleration, not too high sustained speeds).
The front sprocket has up to 28 total teeth, and only half of those can be in contact with the belt at any given moment, so a continuous sequence of stripped belt teeth might continue up to perhaps 12 but any length of missing teeth is riskier as it gets longer.
The teeth and inner surface of the belt can melt into the front sprocket if the sprocket slides where there are not teeth
If the front sprocket slides, the front sprocket will go fast and it will take out additional teeth as the wheel catches up
Eventually you will have to remove material from the front sprocket or replace it. And eventually the belt will break and you will be unable to climb a San Francisco hill (does this sound oddly specific?)
Scraping out the material with metal can damage the sprocket. Avoid it. A hardwood dowel or a polycarbonate rod, sharpened, is better. Acrylic is too weak.


Damage From Sprocket Debris

Drive Belt/Damage From Sprocket Debris

Specifications

Zero's final drive is a custom-designed Gates HTD (high torque drive) Poly Chain Carbon toothed carbon fiber belt.

  • It's never been available outside of Zero's parts system.
  • It's been the same part for 2012-2016 models.
    2017 models shifted to a wider belt that can accommodate more torque/loading.
Years Width Pitch Models Sprockets Number of Teeth Length OEM Part No. Photo
2010-2011 14mm 8mm S/DS 98T / 28T 200
30-02641
2012-2016 S/SR 132T / 28T 220
30-03673 (old logo)
30-08084 (new logo)
reference photo of belt
DS/DSR 130T / 28T
2017- 17mm 14mm S 13.0 130T / 28T
FX/FXS
DS/DSR
SR/S6.5
90T / 20T 158
30-08086
reference photo of wide belt
2020- 20 11 SRF 90T / 20T 151
30-08226
Part
Gates GT Carbon, 14mm wide, 8mm pitch, 220 teeth. It's only available from Zero.
P/N's are 30-03673 ("Belt Drive, 220T, 8mm Pitch, 14mm Wide") and also 30-08084 (same belt w/new Zero logo).
One rough match for reference: Gates 8MGT-1760-12 Belt
Another Gates product page that highly indicates a product/technology match: Poly Chain® GT® Carbon™ synchronous belts per Gates drive belts (EMF Thread)


Tension Check

Krikit Tension Gauge

Zero recommends the Gates Krikit belt tension gauge to check belt tension.

Krikit Tension Gauge invoice and box
Krikit Tension Gauge gauge and instructions
Video Guide
MostlyBonkers made a How-to video:
Tips
  • Turning the back wheel backwards before measuring will give different readout compared to turning the wheel forwards before measuring using the same spot.
    The difference may be significant to the (pre-2017) 20-30kg belt tension specification.
    For wide-belt 2017+ models, the tension specification is very wide (~25-75kg) and thus has a lot of leeway but seems worth a rotational check anyway.
  • The center of the belt can be reached from below, without removing the mudguard.
    This is described as a note in 5.14 in the 2015 manual
Steps
More detailed generic instructions for the Krikit deflection device
  1. Ensure the blue indicator arm is pressed down.
  2. Place the gauge in the center of the belt span, such that it is aligned longitudinally with the belt length.
  3. Place a finger on the blue pressure pad and depress this pressure pad.
  4. Keep pressing the blue pressure pad until you feel and hear a distinct 'click'. When this 'click' sound is heard, do not press any further.
  5. Remove the gauge and read the belt tension by observing the point where the top side of the blue indicator arm crosses the numbered scale on the gauge body.
  • Care must be taken to ensure that the gauge is not 'rocked' when pressing down on the blue pressure pad. The strap above the pressure bar is provided to attach snugly over the finger and prevent any 'rocking' motion.
  • Due to the fact that this device requires some amount of practice and operator skill, the accuracy and repeatability of the tension readings are not high.
Improvement
Because this procedure is not trivial to perform consistently, there is a modification to make the tension gauge easier to align
Gates' Carbon Drive mobile app
As of 2017, the Official Owners Manual also includes a procedure using Gates' Carbon Drive mobile app to check belt tension.
Usage
  • Use the application in a quiet environment.
  • Pluck the belt near the center of the lower belt span, so it vibrates like a guitar string.
Recommended Belt Tension
Belt Type Years Resonant Frequency Tension Range
Narrow 2013-2016 96.3 Hz – 124 Hz 20 – 30kg
Wide 2017+ (except S 13.0) 42.5 Hz – 73.6 Hz 25 – 76.5kg

The frequency can also be checked with instrument tuning apps such as Tuner-gStrings for Android.


References
Articles