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Tuesday, April 07, 2009

Resistance is futile

Disclaimer: I am not an expert. All I know I learned from Google.

The weather has warmed up and the snow has melted off again so I got the motorcycle out and road it to work today. The forecast had called for it to be worm and dry all week but they are now forecasting a cool-down with chance of rain and snow on Thursday. Oh well, it's spring time in the Rockies.

I'm not getting the gas mileage that I should be getting. It started out getting 45mpg but it has dropped a little with each fill-up. It's down to 34mpg. Other C50 Boulevard riders report 45-48mpg city/50-52mpg highway. Something not right. Aside from mechanical problems there are several other factors that can affect gas mileage on a motorcycle.

Wind resistance probably has the biggest impact on gas mileage. Anything that sticks out (or up) into the air flowing around the bike as it's moving down the road causes wind resistance. The rider is typically the most prominent wind obstruction on a motorcycle. That's why a lot of motorcycles have a windscreen and fairing. I know this has a major impact at highway speeds but I don't know how much of an impact it has at city speeds. My motorcycle doesn't have a windscreen or fairing.

Tire pressure also has an impact on gas mileage. Too low of a tire pressure can can wear out the tread faster and ruin the tire, can make cornering more difficult, and reduce gas mileage. The specifications for my motorcycle calls for 33psi in the front tire and 36psi in the back tire (cold). Some riders will lower the tire pressure down a little for a smother ride. The streets around here tend to have a lot of ridges, ribbons and cracks in them; It's worse at intersections where cars apply their breaks or turn. I had lowered the air pressure in my tires down to 30psi and 35psi hoping it would smooth out the ride a little. I didn't notice any difference so I've pumped them back up.

Using the wrong octane of gas can also affect gas mileage. The specifications for my motorcycle calls for 87 octane - I've been using 85 octane. That doesn't seem like it should make too much of a difference until I factor in the fact that from September - February they sell oxygenated gas. Oxygenated gas produces less air pollutants but it also reduces the gas mileage! I need to be buying 87 octane during the summer months and the next higher octane when the gas is oxygenated. I could try a different brand of gas too.

Lugging the bike (running at too low an rpm for the gear) also affects gas mileage. My motorcycle doesn't have a tachometer on it so I shift based on what the engine sounds like and how the bike feels to me. This might not be a good gauge for shifting. I tend to shift into 2nd fairly quickly. I also use the friction zone a lot going in/out of the garage and when pulling away from stop lights so the engine might be lugging a little then. The problem is, I don't know what the rpm really is or even what it should be! I miss having a tachometer.

I've got the right octane in the gas tank now and have pumped the tires up to the right tire pressure. I think I will get a windscreen. I really don't know if I'm lugging the engine so I won't worry about it.