"weight problem!" I thought that was junk mail so I didn't read it. If you
post something like that it may be a good idea to include Baja somewhere in
the subject line.
What is the difference between ASTM A36 and ASTM 53?
Last year we switched to 1.25 dia x .049" wall tubing for our frame. It
lasted through one season alright. I actually couldn't spot any damage to
the tubing at all after competition. When you design your suspensions, how
high is the frame off the floor when bottomed out? We are somewhere about
three inches. At Midwest I know we were bottoming out the rear suspension a
lot more than we should have been, we still didn't have any problems with
crushed tubing. Their is little reason to build a competition vehicle that
lasts more than two years anyways... Perhaps I should hold my tongue until
the car has been rolled a few times.
Another arbitrary number: Our frame weighed 75 pounds when I weighed it. At
that time I had about half of the brackets and tabs on it. I was really
surprised at how light the rollcage was. In Solidworks the frame itself was
only 60 lbs. As we got closer to competition, we had less time to fabricate
lightweight parts, so the weight did increase to make our car about average
weight.
Forget about the frame, the best way to cut weight is to be more intelligent
about how all that stuff is mounted to the frame. Why use thick material
when you can bend a piece of sheet metal to be just as stiff. You would be
surprised at how little metal it actually takes to support an engine or a
driver's seat if you use structural shapes instead of .25" plate. If the
rollcage were designed around the parts inside there would be no need for
large awkward brackets.
Until you get the rest of the vehicle in good working order, loosing a few
pounds here and there will not have a very large effect on performance.
Eric Hutchenreuther
Kettering University
----- Original Message -----
From: <susantoa@pdx.edu>
To: <mini-baja@Autox.Team.Net>
Sent: Friday, November 12, 2004 8:00 PM
Subject: Re: weight problem!
> Please take into account that when people tell you what the weight of
> their frame/roll cage is you can't really compare them directly. You
> need to know whether they're giving you the weight of the roll cage
> with or without the mounts, is it just the cockpit area or the
> complete frame, how big is the car, etc. If you can weld it and you
> don't mind the frame be a "throwaway" frame, use 1.25x0.049 in ASTM
> 53, considering the same frame it will save you around 20% in weight.
> We used A36 in 1.25x0.049 and it locally deformed (not bent but
> crushed) where we hit obstacles. It last through two competitions,
> but now it's pretty shot.
>
> Our frame with 1.25x0.049, complete front to back with all of the
> mountings weighed around 90lbs or so. A different year's frame with
> 1"x0.083 weighed around 75lbs or so but it was a smaller car. Total
> vehicle weight in the last 4 years have been anywhere from 450lbs to
> 520lbs. Then again we used pretty big tires (24x9 in 12 inch rims)
> and each tire/wheel combo is around 27lbs by themselves.
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