The Gates GT4 Primary Belt 640-8MR-25MM is a Gates PowerGrip GT4 primary drive belt, sold here at GritShift, a direct OEM replacement and performance upgrade for the Sur Ron Ultra Bee. 25 mm wide for the flanged primary pulley, high-torque synchronous design, ethylene elastomer, developed through GritShift R&D with Gates engineers, built in the USA, 0.24 lb.
Specs verified October 2026 against the live GritShift product page.
Specifications
| Belt | Gates PowerGrip GT4 640-8MR-25MM |
|---|---|
| Type | High-torque synchronous primary drive belt |
| Width | 25 mm |
| Pulley system | Flanged primary pulley of the Sur Ron Ultra Bee |
| Tooth profile | Optimized GT4 profile that maintains correct clearance on flanged pulleys |
| Compound | Ethylene elastomer, resists stretch and wear |
| Role | Direct OEM replacement and performance upgrade, stock or high-power builds |
| Development | GritShift R&D with Gates engineers |
| Made in | USA |
| Weight | 0.24 lb |
What bikes does the Gates GT4 640-8MR-25MM belt fit?
- Sur Ron Ultra Bee
Why upgrade the Ultra Bee primary belt to the Gates GT4?
Load distribution. The 640-8MR-25MM spreads drive load evenly across its 25 mm width, which reduces heat buildup, minimizes friction and prevents premature failure on the Ultra Bee's flanged primary pulley. The PowerGrip GT4 construction pairs a high-torque synchronous design with an optimized tooth profile that keeps correct clearance on flanged pulleys, so the belt tracks stably. The ethylene elastomer compound resists stretch and wear, which is what gives it a long service life on stock and high-power builds alike.
When should I replace the Ultra Bee belt?
Either when the stock belt fails or before it does. GritShift positions this belt for both cases: a direct replacement for a failed belt, or a proactive upgrade ahead of time for riders who want the drivetrain sorted before a high-power build or a long season. It is a direct OEM replacement for the Ultra Bee primary pulley system.
Who makes the 640-8MR-25MM belt?
Gates. GritShift developed the application through its own R&D testing with Gates engineers, and the belt is manufactured in the USA. For the Sur Ron Light Bee X and Segway we sell the narrower Gates GT4 Power Grip Belt 560-8MGT-16MM, and for the E Ride Pro-SS 3.0, 4.0 and SR the Gates GT4 Power Grip Belt 560-8MGT-20MM; the Ultra Bee takes only this 25 mm belt.
Where can I buy the Gates GT4 Primary Belt 640-8MR-25MM?
Right here. We sell the Gates GT4 Primary Belt 640-8MR-25MM at GritShift, made by Gates. Browse every GritShift part we carry in our GritShift collection.
