aeromoding shaft drive motorcycles

[redyaris]

I have a 1983 Honda VT500 that I will be aeromoding to see what can be achieved. The challenge is not being able to change the final drive. I suspect that getting into the 70mpg range should be fairly straight forward the real challenge will be getting into the 80mpg range at 70 mph on the interstate, or under the Vetter Challenge conditions. Low&Slow has already started on his Yamaha 550cc Verago V-twin. I suspect there are others out their with shaft drive motorcycle who could take up the challenge. The nice thing about the VT500 is that in 6th gear on the highway the slitest hill or head wind forces you to shift down a gear. At present the engine turns 5000rpm at 120km/hr [75mph], the improved aero would make highway cruising in 6th gear that much better.

[alvaro84]

So the VT500 transmission ratio is pretty similar to that of Teresa (4000rpm at 100km/h in 5th, 5000 at 125). And I can't change it either, I don't know about different belt sprockets available for the F650CS, so in this sense a belt drive is similar to a shaft.

On aero: wow, the Virago is more like a piece of art, not designed with merely function in mind, that seems harder to aero mod to me! The VT500 has a more 'solid' look (if it's the VT500 I googled). I might be wrong, though

[redyaris]

Originally Posted by alvaro84

So the VT500 transmission ratio is pretty similar to that of Teresa (4000rpm at 100km/h in 5th, 5000 at 125). And I can't change it either, I don't know about different belt sprockets available for the F650CS, so in this sense a belt drive is similar to a shaft.

On aero: wow, the Virago is more like a piece of art, not designed with merely function in mind, that seems harder to aero mod to me! The VT500 has a more 'solid' look (if it's the VT500 I googled). I might be wrong, though

I have learned quit a bit from the mods on my other bikes so this one [VT500] will start from a better starting point. What I like more and more is the behind the rider aero-cargo "box", the utility of the bike is greatly inhanced with this aeromod. The saddle bag area behind the riders legs seems to have deminished in importance and volume. It seems that only by actualy building something can you find a better way of doing it next time. Just thinking about it leaves you stuck in a rut.
The sides of the aero-cargo box will be curve as will the top. The sides and bottom will be Aluminium and the top may have to be foam and fiber glass, to accomidate some compound curves. It will be 36" long, 16" or 18" wide at the front and 4" wide at the rear. I selected these dimensions because they are close to what I did on an other bike that has been riden in cross winds of more than 60km/hr [37mph] without any problems.
The front fairing will be unconventional in shape, made from aluminium sheet, foam and fiber glass.
Some of the ongoing problems are keeping it accessable for sevice and repair and reversable so that it can be return to stock configuration if i should want to sell it.
An other consideration for this design is getting more weight onto the front wheel for better handleing after aeromods.

[low&slow]

Redyaris, I hope to provide some push in this friendly competition but must acknowledge the inherent drawbacks we'll face. Aeromods are a definite opportunity but the gearing up for lower cruising rpm is much harder than on chain-drive bikes. My Vision is geared much lower than your VT500 ( 5300 rpm@ 60mph ) and has only 5 gears. I may see if I can find a European Vision rear end gearset as they were set up for higher speed cruising. They are very rare and hard to find. If I can't get this I'll upsize my rear tire .
Reversibility is an important factor for me too. I'll probably never sell my Vsion but I do like to get together other other classic Japanese motorcycle riders and my mods would be considered heresy unless I could return it to stock configuration.
This will be fun, game on.

[redyaris]

Game on!
2012 Vetter Challenge will be the day of reckoning, when we see whos' mpg is bigger. It would be quit impresive if we could get into the 80mpg range.
What I am thinking is that cars are being aeromoded with very good result without access to changing the final drive gear ratios. Most cars start with much lower Cd's around 0.4 - 0.3. the average motorcycle has a Cd = 0.7 - 0.8. BMW got one of there production bikes down to Cd = 0.4 - 0.5. I would not be overly surprised if we could get down to the Cd = 0.4 - 0.3, at which point we could be in the 80mpg range without a change in final drive gear ratios. It will take time with lots of trial and error, but it is posible.

[Christ]

Someone could try getting another drive shaft and carrier, and modding it with a .75 inline gear set, or lower.

Fail the obvious inefficiency, it could probably be done.

[alvaro84]

Originally Posted by redyaris

Game on!
the average motorcycle has a Cd = 0.7 - 0.8. BMW got one of there production bikes down to Cd = 0.4 - 0.5.

With or without rider? And how does it change with the size of this rider? And what about a passenger?

Anyway, a tail section which can be used as a topcase sounds like a good idea to me. (Did you mention it here or in another topic, I wonder.)

[redyaris]

Originally Posted by alvaro84

With or without rider? And how does it change with the size of this rider? And what about a passenger?

Anyway, a tail section which can be used as a topcase sounds like a good idea to me. (Did you mention it here or in another topic, I wonder.)

The references for better understanding of this matter are; Aerodynamics of Road Vehicles Edited by Wolf-Heinrich Hucho Chapter 10 Motorcycle & The Racing Motorcycle A technical guide for constructos by John Bradley sections 4.3 & 4.4.
I believe this Cd figure [from Hucho] is with the rider. Generaly the Cd does not change with the size of the rider, what does change is the frontal area and the total drag force. In the same way that two sheets of plywood of diferent sizes being pushed through the air have the same Cd but the larger peace will require more force [due to its larger area] to go at the same velocity.
The affect of the Pasanger is all over the map; if the passange sites high bend the rider they will add to the frontal area and may also add to the Cd. If the passanger is tucked in beind the rider they may lower the Cd.
The Cd is the affect of the shape of an object; a flat peace that is square has a Cd of 1.17, a parashut has a Cd of 1.4, a cylinder parallel to air flow has a Cd of 1.1 to 0.83 depending on its length, a fully streamlined body has a Cd of 0.04, a large bird has a Cd of 0.40...
The Cd of a tree changes with respect to wind speed; the higher the wind speed the lower the Cd!

10m/s Cd = 0.43
20m/s Cd = 0.26
30m/s Cd = 0.20

isn't nature interesting?

[redyaris]

I have measured the throat of the Keihin D64A carbs on the VT500 [28.8mm x 32.6mm] which would be equivelant to a 30.8mm diameter throat. This should be better than the 34mm on the Suzuki GS500, and its almost the same as the Kawasaki Ninja 250 [30mm].
The Yamaha V-star 650 has 28mm carbs. which could be adapted to a Vision if they are smaller.

[low&slow]

RedYaris, Thanks for the suggestion, I'm still working on refining my streamlining and have made some noticeable improvements in the handling in windy conditions. Alan Smith advised me to lower and round off my windscreen and sine finishing it have noted a marked improvement in wind buffeting around me and in steering deflection from side winds. I also rounded th face of my front wheel fender . Next I'll clean the air filter replace the plugs, check the valve lash and do and oil change. Other steps are: modify the mirrors and turn signal lights. I should have a pretty good tank currently as I hit 200 miles and still haven't moved the petcock to the reserve position.
all the best L& S