Until I get my rule book I thought I would ask you guys.. I am having the local short track guy weld in my cage over the Christmas break.. He needs to know what diameter tube and thickness to use? Any limitations on the 8.5 sec cert for door coverage? How about the distance of the tubes from the drivers seat, by the knees or behind the seat? Any good advice to pass on will be greatly appreciated!
I'm assuming NHRA and a car with a full frame. (Doh ou: The first word in the post is NHRA!) For mild steel it's 1 5/8 dia .118 wall, but due to tolerance most people use .134 wall to ensure that it's at least .118. Some of the .134 tubing I measured was only .125 thick. If I had ordered .120 wall it would have been under .118 I'm sure. I use 1 3/4 dia tubing instead of 1 5/8, and I think most round track cars use 1 3/4 but it's only around .090 thick. As for chrome moly it gets a little complicated because different bars can be different thicknesses, but if you used .083 for everything it would pass. For both mild and CM, the main hoop, roof hoop, forward cage bars (the ones that go from top to bottom near the windshield, door bars and sill bars need to be a min of 1 5/8". If the car has a perimeter frame the frame itself takes the place of the sill bar. The back brace bar and rear support bars (from the top of the main hoop to the rear of the car) need to be at least 1 1/4". If the OEM firewall has been modified more than 1 sq foot a dash bar needs to be installed between the forward cage bars. There's also specs for a swing out door bar, and if you want an X in the door instead of a single /, both bars can be 1 1/2 instead of a single 1 5/8. I'm not sure about cages, but for roll bars the rear of the drivers helmet cannot be more than 6" in front of the main hoop, and the top of the rear support bars cannot be more than 5" from the top of the main hoop. I just noticed that for the roll bar (not cage) they show 1 3/4" as the minimum. I can't find the info on the height of the door bar, but I think it's supposed to be somewhere between the shoulder and elbow. There's plenty more, but that should get you started!
Something I forgot! The shoulder harness mount is to be level with your shoulders (it's measured perpendicular to the seat) to 4" below, so position the back brace bar with that in mind.
I would suggest ordering and viewing the 7.50-8.49 specs from SFI, Spec 25.5 for your application.. you will find that it is not greatly different than the NHRA spec for 8.50, and any car is always safer and worth more at resale time if it is an SFI chassis, even if you never intend to go faster than 8.50. Here is the link http://www.sfifoundation.com/drag.html JW
Thanks Alan... I'm going to print this and share it with Mater, the cage guy. You are correct about the Circle guys using .093" 1 3/4" stuff. he said that is what he has lying around. Guess I'll use that stuff where i can for weight savings. I'll be reading your advise a few more times... Thanks again. If you think of anything else please write it, I'll be looking for it. Thanks again :TU: :TU:
Thanks Jim, kind of you to send me in the right direction! I'll order it today. Mater said he wouldn't charge much more for extra bars, so I'll more than likely make it overkill keeping the SFI resale suggestion in mind. Good stuff Thanks again :TU:
Ordering the SFI spec is a good idea, that's what I did when I put the cage in the wagon. The way I look at it, the more I can do to protect the driver (ME!!!) the better! I can always build another car! I looked at lots of cars to get ideas and to see how others had done things, there's many ways to build a cage. I'll add this, too. I like to lean the main hoop rearward a little to match the angle of the B-pillar, I think it blends in with the car better. Just remember that for mild steel everything associated with the cage must be at least .118".
Hey - that is too cool :bglasses: I'll send it to ya asap... I would have wrote sooner, been working on the switch panel wiring for six hours.... I'll call the NHRA boys and have them put the book on ice.. I'll join em at my first meet- hopefully in the spring uzzled: If you put your return address on the book I'll make sure your postage is returned :TU: Way cool - I'll owe you one. Mike
