QuestionHi Dan,
I am working on designing a roll cage for a modified Triumph TR6. I have a basic plan, but a few of my design goals are conflicting with each other. I might be road racing the car in the future, but for now will be happy with driver's school, track days, and autocross. My design so far incorporates some of the SCCA guidelines (just for reference) but not all.
I'm trying to achieve the saftey and stiffening benefits of a full-blown cage structure with more of a partial stucture is the root of the problem. I've done a lot of amazing things with this car though, so I really think I can do it with good effort and solid engineering. Just have to figure out how..
I'd love to send you some pictures of a partial cage/ chassis stiffener in another person's TR6 that looks very much like my initial plan. If you're at all available to review the pictures I would really appreciate your help.
Thanks you very much in advance, Eric Sims
AnswerHi ERic:
Sure, you can send pix to < danL5454@aol.com >
The primary function of a cage is of course, safety of the driver. This aspect should trump all others. Included in the safety aspect is 'ease of exit'. This in case the internal environment becomes less than pleasant (on FIRE !) So, while building your cage, have your racing seat already temporarily installed where it will be in use, and place the main lengths of tubing in thier planned locations as well, and tack weld them. Now make a few practice entrys and exits, planning methods of egress through both the driver's door,and also through the passenger door.
It's very difficult to make an effective and safe cage look good in an open car. I've a friend that races TR-7's and the top of the cage follows the forward slope of the body at about the height of the windshield, doesn't look too bad either, though his normal entry is over the top. The TR-6 doesn't offer this slope, though it's a much more attractive car !
I think the most important part of any cage is the sturdiness of the four main mounting points. Many fabricators are happy with a 4" X 4" plate welded to the floor. If you'll fabricate those plates in an "L" shape to weld to the floor but continue up the side of the floor pan it just about doubles their strangth. If you can mount them in the front close enough that they can also rise along the front inner fender well, so much the better. To visulaize this, take a comon shirt box, place it on a flat surface and cut in half diagonally across the bottom. You now have a three-sided piece . That's the idea only make it fit the inner corner, and weld your secondary upright to that. In your case, the real chassis is too far inboard to attach the front hoop there without a lot of heavy fabrication, and don't forget , you gotta get your feet in there !
Most cars also have a 'step' in the rear behind the driver's seat. I prefer to mount the main hoop atop the step, with a pad that fits over the step, again welded to both a flat surface and at least one verticle surface. You'll want to locate the rear hoop as far back as possible. I'm a large man and have had to battle my way into and out of way too many race cars that left no room for a driver ! It may be possible for you to attach the rear (main ) hoop directly to the chassis. If so, consider cutting an appropriately sized hole all the way through the frame rail, and welding the tube in top and bottom with plates on both sides, super strong.
Your rear braces should go dirrectly to the chassis, plated and welded. The rear location should be no further back than the centerline of the rear wheels. Where possible the strongest structure is an equi-lateral triangle.
Now the side bars. Think long and hard about this. Mine always travel all the way from the rear strut towers to the front fender wells. From the pix of the chassis online, I don't see how you could attach them to the chassis in a practical way. Let me see what you've got in the way of pix and we'll dope it out from there.
Look forward to hearing from you !
Dan Liddy
Sarasota, Florida
