Alligator build discussion
 

The Dan Gurney Alligator was a limited run bike of about 30 units. He is a legendary man with a colorful racing history and serious design and fabrication skills, along with his team.

The Alligator concept strives to reduce horsepower requirements to go fast by reducing wind drag. If I remember right they did 140mph on about 70hp, not in a tuck. This efficiency concept obviously also applies to reducing fuel consumption.



I thought I'd start this thread to discuss how one would go about building a version of this bike except with fuel efficiency as a priority. Some key points to discuss could be:
-Ergonomics. Would you fit on it. Handlebar location could be an issue
-Suitable donor bikes.
-Swappable parts to donor bikes.
-Fabrication hurdles/solutions.
-Why or why not this is a stupid idea. Not IF it is.
-Fairing ideas.

Anyone interested?

Oh, I almost forgot. The thing that drives this is a LOW seat height to get out of the wind. I think it is about 17" above the ground. This corroborates desired values on the FFWeb discussions from those who've experimented and now know. Apparently the sweet spot is like 12"-17". But much lower than 17" runs into clearance issues with the swingarm with motorcycle wheels and adequate suspension travel.

First check your state laws on motorcycle seat height. Many states like NY require a 27 inch seat height for two wheelers and a 20 inches for trikes. There are some good designs on FF bikes on craigvetter.com

What I look for as a candidate for this type of bike is one that has a bolt on rear subframe so that I can try various versions without giving up the ability to return the bike to its original configuration. Both my WR250 and my KLR650 have bolt on rear subframes. I have purchased a used WR250 swing arm from ebay, that i will be extending after I have built a jig to hold all the peaces in place for welding.

You can't really tuck on a bike like this, can you ?
:D

I believe that Gators are ridden in the "pike" position...;)

That looks like a very comfortable rider postion with built in back support...:thumbup:

The only problem is no b i t c h seat. Which now that I think about it, may be a problem solver...;)

>

So building one of these will most likely require cutting, welding and fabbing the rear frame section, sacrificing the original bike. The bolt on rear subframe bikes like the WR will be exempt for the most part. To make room for the rider the swingarm probably will need extending at least 4", which is commonly done on a range of bikes so is probably not a big deal especially if working with steel vs. aluminum.

Ergonomics:
Humans need small bike cross sections directly in front of the crotch in order to fit without splaying knees out in the wind. When seated just above the swingarm the rear loop of the frame is directy in front of the rider. Perimeter style frames are widest at this point so it will require modification or a narrow section here.

Hands and feet when seated in a semi-reclined position typically require that the feet be forward of the hands to reduce knee angle and reduce reach to the bars. Forward foot controls and rearward handlebar placement is then desired. More fabbing to place foot placement as far forward as possible without interfering with the front wheel. Additionally, a "tiller" style bar to reduce reach.

Electrics: The battery on most bikes is directly under the seat. The open space between the (now forward) footpegs is a good relocation area. It also helps keep the center of gravity low.

Air box: This also is usually under the seat. Hmmm, maybe a short cone filter or piping the intake to another location will work.

Fuel tank: This is tougher if it is to be relocated. Leaving the donor bike tank in place keeps the CG high but may be worth it. Fabbing a tank to fit into the cavity created by the extended swing arm could be a solution also helping keep CG low.

Rear suspension: A single shock system is desirable as it is compact and doesn't require an especially strong rear subframe, easing fab requirements. Dual shock systems reduce swingarm loads, easing extension fab requirements and open up the center of the bike for other uses like a fuel tank, air box or battery.

Donor bikes I'm looking at are 250cc as they have outstanding MPG potential and really need aerodynamic drag reduction to do well at higher speeds. Cheap is also good, so finding a lightly damaged bike is a possible route.

250 Cruiser bikes already have a low seat height, small diameter wheels (lower swing arm height) are pretty common and cheap.

The Ninja 250 is really common, may be even cheaper but bars and frame mods may be more extensive. Attached are some pix of a mod started by an ecomodder that wasn't finished (search for it).

Here is a dualsport DR350 that was bobbed. The seat is low but rear wheel will hit the seat when fully compressed.

This sounds like something I would love to do on my sr185. it's already so narrow you wouldn't need to change that any, but the old school rear suspension would be a little tough to modify. I would think a 200cc single would be the perfect candidate, maybe a dual sport or converted dirtbike as they typically have the monoshock setup, and narrow profiles.