Killing Engine Efficiency

As we’ve said many times, don’t expect improved performance, good gas mileage and
long engine life if you have increased aerodynamic drag and overall weight followed by
over-gearing your big single; especially if that big single has one spark plug like the

A surprising number of KLR650 riders are still changing from 15/43 (stock) to 16/43
sprockets. In the case of the DR650, a magazine actually recommended going up one or
two teeth in front and this on a big single that comes equipped with a very high 5th gear.
You can be sure of one thing; anyone who recommends these sorts of changes is
certainly not an expert, but worse yet, doesn’t know what the hell he’s talking about.

Kevin Cameron of “Cycle World” magazine, the top technical and engineering expert on
motorcycles that I Know of, has most recently dealt with the above subject as late as June
2009. He and other top experts such as the late Gordon Jennings all agree. If you want
the best performance and gas mileage out of your motorcycle, don’t increase the frontal
area and gross weight.

As for gearing: You should put yourself somewhere near the middle of the power band.
To paraphrase Mr. Cameron, “As four stroke engines are throttled down (like when over
geared), their pumping losses increase. As pumping losses increase so does fuel
consumption. As four stroke engines turn higher and higher RPMs they once again use
more fuel. Ideally, you would want an engine that is twice as powerful as required to
maintain the cruising speed you desire that puts you in the middle of the most economic
operating range.”

Do yourself a favor and obtain a copy of the June 2009 “Cycle World” magazine. If you
already have one, re-read Kevin Cameron’s article on “MPG Economics”.

My Christian Missionary wife Pauline Read and her leader Tina Jones (President of
Mission Vida Nueva) recently asked me to take some money to a village in Baja Sur 160
miles south of our home. I knew my maximum cruising speed would be 60 to 65 mph and
there would be stop and go driving in Tijuana and Ensenada, plus a two way, 15 mile,
rough dirt construction zone south of Ensenada. I decided on 14/43 gearing for the trip
(DR650 stock gearing is 15/42).

Upon completing my trip I filled the IMS tank and figured my mileage for the 315.7 mile one
day ride. Corrected mileage for the trip was 55.1 actual miles per gallon. That’s what
happens when you follow the advice of real experts like Cameron and Jennings. Keep
your frontal area as small as possible and gear your mount close to the middle of the
power band.

Where’s the Weight?

The 08/09 KLR650 (E model) has only one piston and approximately 34 rear wheel horse
power (the old “A” model has 37.1 rear wheel H.P.) and yet people load them like big Jim
Bellach (“king of 1000 V-Stroms”) might load one of his big twins in preparation for a long
trip north or south of our borders. Jim has two 1000 V-Stroms, one with over 100,000
miles on the clock.

What’s left of Jim Bellach’s old KLR650 has been in my garage since the last century.  Jim
and Kurt Grife both lost engines due to balancer failures about two weeks apart and not
long after I had warned them of potential balancer problems. But I digress.

I’m always amazed that some folks don’t understand that it’s important “where” you add
weight to motorcycle. If you ride off road you better keep extra weight aft of the pilot.

I’ve always gotten a kick out of the weight shedding crowd who throw away perfectly good
stock mufflers in an attempt to shed 12 pounds. Usually the new muffler is louder, doesn’t
fit well and requires service. Additionally, it was 12 pounds that aided rear suspension
plushness and didn’t have a noticeable negative effect on handling.

The DR650 has the most beautiful stainless muffler I’ve had on a motorcycle and it’ not
very restrictive. The one on my dirt DR650 has 40,000 miles on it and is still in perfect
condition. As far as I’m concerned there is no replacement for it, or my KLR650 “de-
tweeted” factory muffler.

If you plan to add, subtract or move weight on your motorcycle be sure the change won’t
negatively affect chassis dynamics and handling. For your own off-road safety and riding
fun, keep the weight off the front.