Key Factors Affecting RT MPG
So here's my compendium:
Highway vs. town driving: On highway one-up, I get 32 mpg, maybe a little more. Around town (e.g. backroads commute to work), I'm down to 26-28mpg. I've since begun taking more four-lane highway routes to work if I want to save fuel.
Yes, the Windscreen: As many repeat, the RT windscreen and faring are like pushing a barn door down the road. The lower the windscreen, the lesser the drag, which could improve mileage somewhat, but it will be negligible, unless ridden that way over a few tanks of gas. Given our hot summer in MD, I've found riding with the windscreen all the way down more a matter of comfort than stellar fuel savings. I sometimes muse as to whether there might be some practical after-market modifications for the front end of the RT, produced by such folks as Vertika Trykes Canada (V.T.C) that might improve aerodynamics and flow-through. I would also not mind seeing an after-market replacement for the rear top case ... an assembly that could actually be removed and re-installed, like a Harley Tour Pack; thus reducing weight and drag. I belive LAMONSTER has posted something on a lower-profile wind screen he has mounted on his RT. He described its highest adjustment as equal to the stock windscreen's lowest adjustment. Interesting ... but I'll tell ya ... when I rode 286 miles back from VA in pouring rain, my full-size deflector shield was a dream.
Shifting: You're out on the back country roads ... rolling hills, twists and turns ... or in the mountain twisties. When I ran the Blue-Ridge Parkway this past may, I was down to 24-26 mpg. When I returned on I-81, I was back up to almost 34 mpg at times.
Lugging: Whether SM5 or SE5, don't lug the engine. On streets, keep the engine happy in 3rd gear at around 32-3500 rpm. On the road, avoid 5th gear until you're up around 50. The popular acclaim is that on the highway, the engine isn't happy until it's resting at around 5000 rpm. The 998 Rotax (as are all Rotax motorcycle engines) are european high-rev designs (made in Austria, of course). If you are trying to duplicate the blop-blop-blop feel/sound of a Harley on your Spyder, the result will be an air-starved, over-heated engine and over-consumption of fuel.
Loads: Two-up with trailer? Everyone's reporting in the mid-20s with both, and in the high twenties on open road two-up, which can vary up or down depending on the individual/aggregate weights of your passenger and trailer, respectively; also the recency of your all-you-can-eat breakfast buffet.
Tire Pressure: The lower the tire pressure, the more drag. I keep my fronts at between 19 and 20 psi; the rear at 32 psi. I've not yet been able to figure out the basis for BRP's original specification for "13-17psi" in the front tires. However, now that I am replacing my front shocks with Elka Stage 1+'s, I've learned that the stock RT Shocks ain't that hot (technically; my ride has been fine), and that dyno testing of the stocks showed the majority of buffering is taken up by the external spring of the shock, vs. the shock itself. Hmm. This might mean hat BRP's intention was to compensate the flakey buffering with low tire pressure. Still, I've had better performance and mpg running at higher tire psi.
Engine Air and Fuel: If one is using anything less than 93 Octane, it's going to make the engine run richer, which consumes fuel. An immediate improvement I'm making is replacement of the stock air filter with a good one from K&N. My jury is out on moding my exhaust in the near term; however, there might be some valid theory that by replacing the stock exhaust (takes up to 13 pounds off the bike), with greater combined flow through from the air filter and exhaust, the slightly-reduced weight, more efficient air supply and slightly increased horsepower, might have a positive effect on fuel consumption.
Power to Weight Ratio: The highest mpg I've ever seen on my Spyder (or heard of here for that matter) is 34 mpg. The lowest mpg I've seen reported on any spyder is 24 mpg. I look at it this way: We're getting about the same mpg as a Toyota Corolla under reciprocal conditions. 1000cc v-twin/929 pound bike vs. 2.4 ltr four cyl/2822 lb car. I truly feel my only desired improvement is the power-to-weight ratio. If BRP/Rotax could partner on adapting a 1200 cc version of our v-twin without increasing engine or transmission weight, I'd be a fan. Note: Rotax does have an 1125 cc V-Twin used in the final year of Buells on the 1125R. I don't know how adaptable its form factor is to the Spyder, but it is described as a lightweight engine that can crank out up to 146 hp, vs. the 991's 100 (in the RT). Why BRP didn't feel the 1125cc was appropriate for the the Spyder I don't know.
PS this is why a 6th and slightly over drive final gear would help these trikes greatly but BuRP just doesn't want to spend the money to make it right. The Aprila has 6 speeds and gets better fuel mileage by the way.
