Hi all,

My bike (2009 KLX 250SF) used to go ~50mph at 5K rpms (6th gear).

After changing the oil from a non motorcycle specific oil (Mobile Super 10W-40) to a specific moto oil (Castrol 4T 4-stroke 10w-40) and changing the filter to a K&N, the bike now goes a few mph lower than 50 at 5k. We're talking ~3-5mph lower. That's what's indicated on the speedo, at least.

Is this a direct result of changing the oil and filter? Anyone experience this?

Your help is well appreciated,

Andrew

 

Probably just a perception or placebo effect of some kind. It's probably physically impossible to attain those results without something changing in gearing, tire size, or similar issue. If your speedo is operating correctly, the mechanical performance of the all the drivetrain and driveline components will operate exactly the same no matter what oil you use. Fuel mileage and in some extreme cases even performance could be affected at some tiny molecular level due to lubrication, but not the numbers from your true speed to rpm in the same drive components. The tranny will often shift a little smoother immediately after an oil change, but not speed to rpm.

 

Oil can effect lots of things but it would take a gearing/wheel size change or a slipping clutch (unlikely) to alter the rpm/speed ratio

 

Since the OP had non-moto oil in there this could be valid.

 

Yeah, but it would be inconsistent rpm to actual speed...not the consistent situation the OP believes he's experiencing.

 

Mechanically impossible unless the clutch is slipping with the Castrol.

Or something hokey going on with the speedo drive.

Then again with that stupid bar tach there could be enough difference going from one block to the next. I have no idea what each block is worth. If you run the low limit for the bar display versus the high limit.

Of course tire pressure change could alter it too - or tire wear. Heck I wouldn't get too wound up in it.

 

Bingo: Stupid bar tach....now that makes sense

 

Magic oil - that's the only answer.

 

Did you throw a new front tire on the bike while doing the service? Bald front tire to new front tire would equal about 3mph on the speedo!

 

Marvel Mystery Oil?