well recently i have noticed that my rpms have gone up when driving at a constant speed. for example in 4th gear at 50mph i used to be at 3000 rpms. Now when it sits at about 3100 rpms (4th gear at 50 mph). the rpms are being monitored on my vafc so it shouldn't be an issue with the tach being off. the MT fluid was changed 14,000 miles ago with Honda fluid.

I'm just wondering what could cause this?

 

Wind

 

change your tires? Tire wear could be the reason as well, or snow on the tires

 

I definetly need new tires, which will be bought soon with tax returns. any other possible reasons, out of curiosity?

 

well mechanically it's impossible. The final drive in a given gear makes a given speed given a stock tire diameter. So the only way it goes wrong is tire diameter.

Wind will make your engine work harder, but it shouldn't affect the rpms to speed.

 

As weird as this sounds...I think it is impossible to do that. I could imagine this with an auto tranny..but not on a manual. Once the clutch is let out....there is no slipping.

I have no idea what to tell you.

 

well 100rpm at the speed you're going (50mph) isn't a big difference

keeping in mind that stock tachs aren't entirely 100% precise, it's very easy to attribute such a small change to the shape of your tires, road conditions, winter conditions, wear, or dozens of tiny things you could come up with

for 100rpm i wouldn't sweat it.

500+ is another story though

 

your speedometer could be off a few mph.

David