Suzuki Burgman modification (aerodynamics + gearing mods)

[janvos39]

Last year I started modifications on my Suzuki Burgman 385 cc to look for a better fuel efficiency.
Inspired by the work of Graig Vetter I bought this Burgman early August 2008.
Riding it for some weeks unmodified to measure fuel usage. This appered to be 4.3 to 4.4 L/100KM. (54 MPG) Not bad for a scooter of this power to start with. I have a fixed route in driving to work. Mixed highway (75 MPH), road with 50 MPH limit and city driving with stop-go situations.
On my wishlist for modifing was also comfort. I like to sit upright so that I can ride without saddle or backpain over longer distances.
With the modifications as shown on the pictures this is already filled in. You hardly feel any wind which translate in more comfort certainly at colder days.
This is a big difference with unstreamlined bikes. Also some light rain is hardly noticed driving with streamlining like this.
The MPG improvement is not that big. I typical measure at filling the tank at the gas station that I have a 4L/100 KM (59 MPG) average.
I expected better, but realised that although I need less throttle the rev's stay the same and the specific fuel consumption per HP is worse with lower load.
The plan is for improvement of this to add an extra gear which will act as an overdrive. Gears are already cut but still to be implemented. And the gear shift mechanism must stil be made. Available time is at this moment the limiting factor. But this story will be continued when gearing is changed.

Two questions where somebody might have the answer.
Is there a MPG reader available in the market for a Suzuki Burgman of 1999?
Does somebody know where a BSFC map for Suzuki can be found?

Jan

[The Atomic Ass]

Since that's a carb'd bike, I don't think you'll be able to get an MPG display for it. As for gears, you can look into one of the aftermarket CVT options, I forget which one, but one of them reduces RPM's at highway speeds by 500 or so. You'd gain a LOT by slowing down from 75 to 65. Even more going down to 55.

I'm assuming you've already done the routine maintenance stuff on it, oil change, air/CVT filter cleaning, belt change, valve adjustment? The belt change is the big one. My Burgman is only getting down in the 50's in the winter temps, during the summer I was into the 70's (with poor aero, as mine was wrecked and never fixed). And I still need to do a valve adjustment and replace the belt and CVT. (CVT pulleys seem to get worn down from the belt itself, the aftermarket units don't exhibit this problem I am told).

Very interesting work you've done thus far, are you planning on dog-housing the front wheel? I imagine that would make for a big increase in efficiency.

[MetroMPG]

Welcome to the forum, Jan.

Interesting to see your mods. I've been following Vetter's latest project, and he also didn't achieve the large improvement he was expecting.

If I'm not mistaken, he blames it partly on the CVT on his bike: apparently the old Honda he's working with can't be geared any taller.

Please keep us informed!

[Frank Lee]

I'm tempted to put mail in the back of it.

Cool project!

[blueflame]

While at the scooter shop 2 days ago a guy was buying a high speed pulley for his Burgman, maybe with a slightly wider performance belt the ratios would upgear considerably.... Gear up kits for the final drive should be available too? Quite simple on a CVT scooter, just 2 small shafts in the rear axle.

Larger diameter rear tyre too...

A lot of drag in that scooped body area behind the front wheel...

[janvos39]

I am thinking of a way to improve on the dog house or also called scooped body. That will come after implementing other gears. The new gearing will be first.
The standaard 14 at 31 step 1 and 14 at 39 step 2 gears will be replaced by 14 at 29 (step 1) and 13 at 37 teeth.(step 2) All spur gears, home made.
Additional I will be able to shift to a second ratio for step 1 with 16 at 27 teeth .
I will add later some pictures of the gear sets. So gearing drops approx 20 %.

[The Atomic Ass]

Originally Posted by blueflame

Larger diameter rear tyre too...

Impossible. The current rear tire has less than 1" of clearance from the rear of the engine block as is.

[The Atomic Ass]

Originally Posted by janvos39

I am thinking of a way to improve on the dog house or also called scooped body. That will come after implementing other gears. The new gearing will be first.
The standaard 14 at 31 step 1 and 14 at 39 step 2 gears will be replaced by 14 at 29 (step 1) and 13 at 37 teeth.(step 2) All spur gears, home made.
Additional I will be able to shift to a second ratio for step 1 with 16 at 27 teeth .
I will add later some pictures of the gear sets. So gearing drops approx 20 %.

I think you might find that large a drop to basically kill the clutch usability. On mine the clutch will not fully engage until 15mph, with those gears it'll be around 20mph. That will make for very unfriendly clutch activation in the city.

But when you say you'll be able to shift to a second ratio... Do you mean you're making it shiftable while riding, or that you'll be able to swap to even higher ratio gear if you feel it's needed in the future?

[janvos39]

Indeed I'll make it shiftable with a dual cable connection so it can be shifted by hand. Like an old type of gearshift on a steeringwheel.

[janvos39]

You are right of course on the speed of 20 Mph for full clutch engagement. Therefor I intend to shift to the second gear at approx 40 Mph outside the city.