There is a definite difference. JASO (Japanese Automotive Standards Organization) developed its own set of tests specifically for motorcycles, resulting in oil formulas with additive packages designed for motorcycle engines which share its oil with the clutch and transmission.
Maybe. They might be better for your bike, but so far, I haven't seen any conclusive test that actually shows there is a difference. That Sport Rider article certainly isn't it. I read it several times, looked at their data and the best conclusion I can make is that they wanted to make a point and used the data that was convenient to show it and ignored the rest.
A few examples:
The motorcycle OEMs felt that lower levels of phosphorous and the introduction of more friction modifiers (aimed at higher fuel economy in cars) was not in the best interest of motorcycle engines. Since phosphorous is an important antiwear component, lower levels could reduce the ability of oil to protect transmission gears, since motorcycles share engine oil with the gearbox.
If you look at their data:
There is a difference of about 200 ppm for phosphorous and maybe 50 for zinc (the two anti wear additives of choice). Is that significnat? I don't know, but it doesn't seem to support this theory that there is a huge difference between auto and moto oils in wear protection due to not being JASO MA compliant. Look at the moly content. Higher on some bike specific oils than on the auto ones.
Don't substitute a higher API designation oil like SL, because it will contain less of some additives like phosphorus, and it may contain other additives that will yield higher fuel economy in a car but could cause slippage in your clutch.
Mobil 1 is SM/SL rated. It scores highest on viscosity retention, has a very high base number and a very good additive package (acid neutralizers, anti-wear). The phosphorous content is average, but it's supplemented by a large amount of zinc. The only potential drawback is the moly content. Does that last detail make it unsuitable for use on a motorcycle? Mobil 1 is the oil of choice for many people and I don't remember hearing complaints about slipping clutches.
Four-Ball Wear Test
With an eye toward evaluating oil's ability to lubricate under extreme pressure conditions, we picked a few candidates and ran them through the "Four-Ball Wear Test" (officially designated ASTM D-4172).
This test is used to determine the wear properties of engine oil in sliding contact (such as a piston sliding against a cylinder wall).
The smaller the wear scar, the better the protection.
And here are their results:
First, where did the Castrol GTX come from? They get to the most important test they are doing (everything else is a simple lab analysis of the oil) and they introduce an oil that wasn't evaluated at all previously?
Now this is the interesting part, this test is very simple, the smaller the scar the better the protection, right? When the GTX score better than the other two, it's inconclusive, but a few ppm of one additive or another make for a "significant" difference? Give me a break.
Tapered Roller Shear Test
We decided to conduct some additional testing aimed at evaluating an oil's ability to withstand the shearing loads present in a motorcycle gearbox (but not in the typical automotive engine). One of the claims made by most motorcycle-specific oil producers is that motorcycles present a different set of conditions than typical cars do, and that therefore you should spend more money to get oil formulated specifically for this environment. The meshing of transmission gears is said to shear or tear oil polymers over time, resulting in the degradation of oil viscosity and severely reducing its performance. As we stated earlier, this may not be so critical if you frequently change your oil. However, if you run longer than standard intervals, this oil property is something to strongly consider.
Alright, now we are getting somewhere. I agree, this is an important test. So what do they choose to compare, a standard auto mineral oil to 3 synthetics...
The curious part is that Motul 300V 5W-40 doesn't perform any better than Valvoline 10W-40, even though it's one of those Group V oils - "Motul 300V, however, uses 100 percent ester as its base oil, and is one of the more expensive oils." If they had thought this through, they would have at least compared Mobil 1 to MXT and maybe some of the Castrol products, to see if there was a real difference between automotive and motorcycle oils. Another missed opportunity or maybe they worried that the results wouldn't support their argument?
We did, however, unequivocally answer a few questions. For one, most name-brand motorcycle-specific oils are indeed different than common automotive oils, even within the same brand, debunking a common myth.
Yes, some products are different. What they didn't manage to answer was whether this made a real difference when used in a motorcycle engine...
Back to square one.