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Author Topic:   IMCA door bar rules
Dirt Freak

Total posts: 252
posted November 22, 2001 07:13 PM
IMCA requires only 3 drivers door bars of 1 1/2 inch tubing and no minimum thickness is specified. Is this a safe rule? Could some of the chassis builders out there give me your opinion on this. My car has 1 1/2 by .090, but there are some cars out there that have .083.

Dirt Freak

Total posts: 464
posted November 22, 2001 07:36 PM
1 1/2 min of .083 for DOM and min of .065 for moly

Dirt Freak

Total posts: 390
posted November 22, 2001 08:20 PM
Some builders use .090 because of the variance in tubbing........if you took a cross cut of .090 and mic the thickness you will see anywhere from .084-.090 and if you take a cross section of .083 you will see some areas of the tube are .077 now is .083 save enough.......?

I personally run 3 bars of .090 some builder will use 4 bars and use all depends on the rest of the the bottom rail is attached, the X under the car, the height of the middle a complete chassis....not just a door bar system.......generally speaking yes, .083 is fine.........

Dirt Maniac

Total posts: 193
posted November 23, 2001 08:04 PM
Plus, wont the 18 gauge door plate IMCA requires also help.

Dirt Full Roller

Total posts: 61
posted November 23, 2001 08:49 PM
The door plate is far from a plate. It is about .050 - .060 thick, not much thicker than the aluminum doors you run now, and about as thick as many knife blades.

I would recommend using the term "minimum thickness" as just that, an absolute minimum. Anyone so concerned with weight that their safety comes second, might want to consider another hobby.

Most chassis builders are smart enough to build a car SAFE. Trouble is many home builders read the rule and think that all they need is inch and a half exhaust tubing.

I saw a Kraft chassis at a recent shop visit and the main cage was made primarily from 2" tubing, and had several braces...I was impressed to see that in a modified. And the car was not that much heavier than many others I have seen that were built with fewer bars and of lighter materials.

Pain as it is, I have to have my drag chassis certified every 3 years. The guy from NHRA comes to my shop (for a fee), sonic tests all the bars for thickness and diameter, verifies all required braces and restraints are in place and affixes a sticker to the rollcage. If the car is ever involved in an incident that causes damage to the cage, the safety crew immediately will destroy the sticker and you have to have the car recertified after it is repaired.. Now I understand the impractibility of this in weekend dirt racing, but it gives a perspective on the differences in the sanctioning bodies.

And belts are the other thing that bother me...after a few times soaked at the car wash, baking in the sun, the nylon gets weak. I have to replace my dated belts every year, and I spend $100 buck to do it...many that replace theirs sell them at swap meets or auctions to racers like you guys who buy them up at a bargain will never buy my used belts, if I don't feel safe running them I wouldn't sell them to anyone else.

I guess Bell's helmet ad said it best..everyone griped about their prices inthe 70's, they replied "if you have a $5 head buy a $5 helmet".

Dirt Freak

Total posts: 390
posted November 24, 2001 12:54 AM
The sheet steel in the door bars add a bunch of strength......take a couple or 2X4 pine boards, nail them together in the corners. You can twist and bend this around very easy. Now add a 1/8 sheet of plywood and try the same becomes very strong.

Indy cars have used this method of adding great strength to weight ratio.......As long as some builder don't start to use thinner tubing to off set the weight this is great.

The drivers compartment should be strong as heck, the front and rear clips should bend to absorb energy in a crash. If the car is too strong in the front or rear all the energy is absorbed by the drivers body.

And Mike you are right on the mark about used belts and the like. How about a good seat, I know people will spend $10,000 on a motor and $69.95 for a seat.....why not just weld in a old wheel to sit on.......LOL

My helmet is a watermelon ryne........what's my head worth.........about .29 a pound.

Dirt Maniac

Total posts: 135
posted November 24, 2001 04:02 AM
Back when they first started legalizing the 1 1/2 in. roll cages and the guys were putting the "exhaust"tubing in the cars at a driver/rules meeting,we were debating the best way to check the chassis,one suggestion was to have the builder bring one of his cars to the track get in and strap up,helmet and all,then the car would be picked up with a crane about 40 feet and dropped to the ground,if the builder survived,or was'nt hurt so bad that he could walk away on his own his chassis would be legal,but nobody wanted to try it.

Dirt Full Roller

Total posts: 40
posted November 24, 2001 09:13 PM
I think the door plate rule was made because the cut off rear bumpers (without nerf bars) could protrude through the alum. door to easily.

Dirt Full Roller

Total posts: 37
posted November 24, 2001 09:36 PM
Part of what to look at on drivers door bars is the size of the crush zone between the driver side and the door bars. Some cages have almost a foot of space betwwen the bars and driver while others barely have room to move your elbow. Crush zone and lighter bars ( within reason) actually make for a safer car as energy in absorbed instead of being transfered though the car to the driver. Remember the rib cage is not designer for side impacts but to withstand front ones.

Dirt Full Roller

Total posts: 61
posted November 25, 2001 09:14 AM
the thin plate offers strength to the cage in that it does make the door area more ridgid, but the thickness does very little to slow down a bumper or other object from poking through it. And if you slide a 2500# mod into the door of a competitor, and all the impact is absorbed by an area the size of a 1 1/2 or 2 inch bumper end, it is gonna poke a hole in the steeel. And not a clean hole, a jagged knifelike one.

Like I said, I guess the required minimum is better than nothing, but I sure would rather have seen it made a thickness that did more good. If you make a rule change the magnitude of this one, that affects all previous amd future chassis, MAKE IT COUNT.

Hey, what is the snell rating on a watermelon ?

Dirt Freak

Total posts: 390
posted November 25, 2001 10:14 AM
guys showed up every week with old motorcycle helmets and snowmobile helmets..
And You and I both know they are NOT approved for car racing, So I figured on painting my Simpson RX8 to look like the watermelon with a sign stuck in the back showing the .29 a pound.
Simpson says the snell is 95, but this year I will be replacing it with a new helmet and paint job.
I agree with you assement of the door bar area, but how thick would be good enough to keep a 2500 pound car from SPEARING threw this area............We both know it depends on the angle and diameter, wall thickness, of the tube doing the spearing......

Where I race we have plate over door bars and same thickness steel for the interior on the drive shaft side. 28 inches tall.......but only in the street stocks and super stocks.....NOT in the modifieds????? go figure, they must think the modifieds are not going to run into each other like the streets and supers.

I personally don't understand a safty rule for one class and not the other........
That makes as much sense as making the late models wear helmets and not the streets....

How about the number of guys racing WITHOUT a sub (crotch) belt???????/ where are the tech (safety) people..........

Dirt Maniac

Total posts: 101
posted November 26, 2001 08:56 AM
When I put my doorplate on I used 12 ga. material. (about .105 thickness) Twice as heavy but it is on the left side of the car anyway. Lets just say that my doorplate and a dirtworks got together one night and my doorplate faired better than his rear clip.

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