For the motorcycles transmissions, gear durability is key meaning that that lubricant shear stability is critical. A 10w30 viscosity grade lubricant and a proper selection of viscosity index improver (vii) are suitable in order to minimise oil shear down in the transmission.

In terms of friction performance, the motorcycle’s wet clutch applications involving multi-plate and centrifugal, require unique frictional properties and viscometrics. Low friction oils may hurt “wet” clutch performance such as clutch slipping which can cause poor drivability, power loss, and starting problems. The frictional characteristics of the lubricant need to remain stable over drain intervals to maintain shift feel and clutch performance. The higher fuel dilution in motorcycles is also a normal phenomenon and it increases wear severity.

The emerging challenges in motorcycles are similar to those of cars. Upcoming exhaust emissions regulations and more stringent emission standards triggering an increased demand for newer, cleaner engine designs resulting in more stress on lubricants even in emerging markets. In India, for example, the Bharat Stage IV standard for two wheeled vehicles introduced in 2017 is similar to the European Euro IV standard. From 2020, India will introduce the new Bharat Stage VI standard for two wheeled vehicles which is similar to the Euro V standard, in essence bypassing the Bharat Stage V standard. The aim of these standards is to reduce greenhouse gases causing climate change, improving fuel economy and reducing CO2

emissions. In terms

of fuel economy, Original Equipment Manufacturers (OEMs) have moved towards the use of lower viscosity grades to achieve higher fuel economy. Currently in motorcycle engine design SAE 10W-30 is considered as low viscosity, although in future SAE 5W-30 and 0W-30 may also be introduced. The formulating challenge this presents is a potential trade-off between fuel economy on one hand and durability or improvement in anti-wear performance on the other. Lower friction oil may lead to clutch slippage. An ideal friction modifier should reduce metal-on-metal friction while maintaining high paper-on-steel friction to ensure optimal clutch performance.

If we look at the impact of passenger car motor oil with associated fuel economy claims then we can see that fuel economy for passenger car motor oil can be achieved with friction modification which can cause clutch slippage and loss of engine power

and subsequently overall driving performance. Low viscosity, specifically High Temperature High Shear viscosity (HTHS) is related to oil film thickness. High HTHS is good for durability or wear protection, however low HTHS is good for Fuel Economy. In response to some of these concerns, JASO (the Japanese Oil Standard) T903 has been implemented in 1998 to address the concerns on the use of low viscosity and low friction passenger car engine oils in motorcycle applications.

The following changes occurred between JASO T903 2016, and 2011 versions. For friction properties, there are four classification limits MA/MA1/MA2/MB. The classification is characterised by three frictions characteristics indices looking at Dynamic Friction Index (DFI), Static Friction Index (SFI) and Stop-Time Index (STI). The reference oils used are JAFRE-A and –B. The clutch material is a friction plate and test procedures are used and measurements taken based on calculation methods of coefficient of friction and stop time Index. The report of Molybdenum content in the lubricant is mandatory in any JASO T903 test report.

We can judge the performance of dedicated motorcycle oil against passenger car motor oil through rigorous testing. Firstly looking at an engine oil durability test using Oronite’s proprietary test, we can assess 10w-40 viscosity oils in Group II base oil to compare passenger car motor oil performance against motorcycle oil performance formulated with Oronite motorcycle oil additive. The parameters evaluated included detergency, the oxidation to piston and land ratings, the increase experienced in Total Acid Number, or TAN, (ASTM D664) and the Viscosity increase (ASTM D445). Continued on page 12


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