Minimum legal seat height?

[beatr911]

So in an effort to decrease drag on my project bike I'm working on ways to decrease the seat height. From the web research I've done so far it appears that the handling dynamics also improve when the height decreases below about 17" above the ground with the rider in the saddle. So that's my target. Because most new bikes have heights at a minimum of about 25" this will require some frame modification and fabrication.

The Dan Gurney Alligator was lower but I do not know if it was legal.

So my question is, why are most "low" bikes greater than 25". Is this a legal limit? I haven't been able to find a definition of seat height on any federal or state DOT web pages. They list handlebar height requirements but no seat height requirements.

If someone has this information, please provide a web address so I can check it out. Thanks!

[kawboyCAFE]

i dont know if there is a legal limit, but there is a danger factor if you get it too low. cars cant see, and you cant see everything you need to. plus the control and lean angle goes down the hill the lower you go.

[euromodder]

25" would be about an average person's lower leg length.
With a seat height lower than that, even with one's feet on the ground, the knees would be higher than the butt on the seat
Not exactly comfortable in a traditional seating / leg arrangement , and it leaves little leverage with your feet on the ground.

[JasonG]

Some states have a 24" limit. Cali and washington IIRC

[beatr911]

JasonG, Thats what I'm after! If you can possibly dig up where you found this information, it would be most helpful.

I did find on I think it was the NHTSA site, that the federal minimum engine size for freeway use is 150cc. Each state may have it's own stricter requirement which would bump it up to a larger engine displacement. I understand that California is 250cc. I saw nothing in the Washington Administrative Code (WAC) or the Washington State Highway Patrol site or links otherwise, so I'm guessing I'm safe with my tall geared 200cc supermoto on the interstate. (81mpg last tank, with much more left on the table!)

Kawboy, Yes I guess there is an additional danger factor with being too low. Maybe totally geeking out with a flashing light on top of my helmet would do, just kidding. I'm thinking that additional side panel area of a bright color may offset it enough, we'll see. Still in planning stages. Thanks for the reminder.


euromodder, butt comfort I think is a function of seat design and construction. With more weight on the seat it will become more critical and a larger component of the suspension system for rider comfort. With a much lower center of gravity, there should be less leg leverage needed. I'm curious see what that ends up like.

If anyone has ridden or at least sat on a Dan Gurney Alligator, please report. It would really be interesting to hear independent non-biased impressions and address the comments of those above.

[Frank Lee]

CA is 150cc

[Gasoline Fumes]

From New York's form MV-529B:
25" for 2-wheeled, 20" for 3-wheeled.

[Christ]

Pa Code Title 67 sub chapter H § 175.155. Chassis.

(c) Seats. A motorcycle shall be equipped with a seat for the operator which is firmly anchored to the frame or support. No metal spring shall protrude from the driver’s seat.

That's all there is.

[beatr911]

Hmmm. So the law isn't consistent between states, it exists in NY but may not exist in other states. Maybe there is a federal standard that I haven't found yet.