Aero aids in Classic Modified open

[wobblywalrus]

The basic frame class is Modified (M).  A subset of this is Modified Partial Streamliner (MPS).  One can imply, although it is not directly written, that items specifically permitted in MPS are not allowed in M.  Some wind deflection tricks like a big headlight are not specifically mentioned in the MPS regs and are not prohibited by the M rules.  Arguably this could be considered to be legal in the M class.

The Open class is another subset of the M class.  The basic rules are for M class with the requirements noted specifically for Open bikes.  Something should be legal for Open class if it meets the M and Open class rules and is specifically permitted in the MPS class.

That, humbly submitted, is my interpretation of the rules.       

[gowing]

One can imply....Arguably...my interpretation.     

yep !

[wobblywalrus]

There should be a "not" in the last sentence of my post.  Something specifically listed as permitted in the MPS class can be implied to be not allowed in the other classes.

The AMA rules need to be redone for modified classes to give clarity.  Personally, I could not interpret the M or Open rules with any confidence that my views would be the same as an inspector.  The bike was run as an MPS.  Finally, the AMA screwed around with the rules enough that I decided to be an FIM entry.  It was an easy decision.  Their requirements are relatively easy to figure out, more consistent from year-to-year, they have classes for twin cylinder bikes, and they offer insurance.

[gschuld]

I?m with you there.  I wish the AMA rules were a bit less ambiguous.

You are seeing only 2 total classes in Modified though right?

M and MPS

With M being the Open non streamlining class and MPS with the full fairings.

George

[gowing]

I wish the AMA rules were a bit less ambiguous.

yep !

[Koncretekid]

For your consideration, here is a frontal view of my TR25/BSAB25  250 MPG bike that set a record of 100mph at Loring and 95 mph at World of Speed (SCTA). It should also be legal at AMA and would exceed the record, but I don't go to that meet any more.
 


What is important to realize is that there are two aspects of aero drag which are frontal area and coefficient of drag.  In this view, you can see that a headlight in front of me, although legal, would not decrease the frontal area.  What is important is to get your hands, back, top of helmet, and feet tucked in to decrease that area.  And as you can see, my feet are sticking out in the wind, which is not good.

But coefficient of drag is dependent on shape and on anything that can drag in the wind.  So I should be able to decrease my aero drag by getting rid of those cables, getting my feet tucked in, and getting rid of the gauges which are all creating drag. I am contemplating adding a headlight with the tachometer mounted into the back of it.  This is not specifically disallowed, and remember, don't anticipate a rule that is not written.  Just make sure that you are prepared to remove something if necessary to satisfy the inspectors.   

The rear end of this bike has no aero improvements except enclosing of the rear wheel (wheel discs).  The rules are different between AMA and SCTA, so there are several improvements I can try at the back.

So I will be back (when they open the borders!)

Comments are welcome.

Tom

[gschuld]

Thanks for the comments.

Yes, clearly a headlight would not reduce frontal area.  In your situation, having a gauge or two, idiot lights, etc mounted cleanly into the backside of a large headlight bucket would offer the incoming air to more cleanly split around the sides and top.  It?s frankly what I had in mind if I knew it was OK in the open class.  I can?t imagine it would be a huge improvement however.

From what I?ve researched, on open bikes, rider positioning and what happens behind the rider has a comparatively large effect on total drag.

Your feet, as you already mentioned, are exposed directly as small air brakes.  It?s not an easy to thing tuck in though, and you should have pretty dirty air by that point anyway.

George

[bones]

Hey George
   The picture of the A bike *1444 with the ram air intake is mine.
   I rode it at BMST as in the picture. No problems with Tech and the inlet.
At WoS there was a BIG discussion about it being aerodynamic. I had 6 people around me
discussing it. Three for and 3 against (tech guys) Tech won and I cut it off at the triple clamp.
I set records at both meetings at the same speed.

cheers   Bones