Gear Reduction

Motor speed reduction is accomplished via primary gears in which 27 teeth drive 75 teeth for a 2.777:1 reduction at the countershaft sprocket.

The secondary utilizes a DID 428 NZ gold chain with 128 links in which 11 teeth drive 57 teeth for a 5.182:1 speed reduction.

This yields an overall reduction of 14.39:1.  The rear tire has a measured circumference of 82" (when weighted rolling on the ground).  This results in a speed of about 5.39 mph per 1000 motor rpm.  So the claimed top speed of 43.5 mph would require a motor speed slightly in excess of 8000 rpm (which seems surprising based on the motor's performance graphs ending at 6000 rpm).  I would be really impressed if the SiliXcon is performing “field weakening” to get the extra rpm.

2024 Gear Reduction

The 2024 Race and Comp have different reduction ratios than earlier models.  The primary is now 25 teeth driving 75 teeth for a 3.00:1 ratio.   EM's literature says, The transmission case on the 2024 Epure Race is lighter than in years past, but still plenty strong.”  Was this new case design needed to accommodate the smaller primary gear?  Or is there enough range in the eccentric adjuster mechanism to accommodate it?  If so, it would seem the 25T gear could be retrofitted to earlier models.  But I am unsure of the benefit.

The change in the primary reduction ratio means the clutch basket will be turning about 8% slower (25 / 27 = 0.926) than in earlier models.  As a concrete example, say the motor has a maximum rpm of 8200.  With the old 27T primary gear, the clutch basket would be spinning at 2952 rpm.  With the new 25T primary gear, the clutch basket would be spinning at 2733 rpm.  This slower-turning clutch implies 8% greater torque multiplication, making life more difficult for the clutch plates.

Additionally, the clutch basket itself is also a flywheel of sorts because it has inertia.  The energy stored in any rotating system is a function of the square of its rotation speed.  This means the slower-turning clutch basket will store less energy than earlier models.  

The secondary ratio is different too, at 10 teeth driving 53 teeth for a 5.30:1 ratio.   Quoting EM, “[ This ] supplies a smoother chain effect for better behavior of the rear shock, resulting in improved traction.  The smaller rear sprocket also provides better clearance from rocks and other hazards than its larger predecessors.

Thus the overall ratio gear reduction changes to 15.9:1 from 14.39:1 for about 6 percent shorter gearing.  I feel this is a step in the right direction too.

The 10-tooth sprocket is part number OP422-25428-10-00.  This would yield 10 percent shorter gearing when replacing the 11T front sprocket fitted to the earlier models.

Front Brake

I like the front brake!  It's more powerful than any of my other trials bikes.  The caliper is a Braktec Monobloc with a large pad surface area.  Unfortunately, my favorite pad supplier, EBC, does not make anything that size so I had to look elsewhere for spares.  Galfer's FD511 G1805 “red” compound is probably OE.  Their G1395 compound is the more aggressive sintered compound.  Chris Pearson at SplatShop recommends the “red” compound saying that the more aggressive sintered compound would only be better if one were riding in very mountainous terrain and it certainly would be harder on the rotor.