Weld-in roll cage

I was bad last winter. Didn't read the new GCR very carefully, didn't read these boards too much. I got caught without the required second door bar on the passenger's side.

It would be easy enough to find a local guy to put in that second bar and be done with it, but why not use this as an opportunity to get rid of that old, heavy Autopower bolt-in cage and have a custom cage welded in. I don't have $1,000+ burning a hole in my pocket, but it's been a while since I did much to develop the car.

The question is, how much will I gain? The car is an '87 GTI in ITB. It's about 30 pounds overweight, and usually runs mid-pack although that depends on who else shows up. Will I lose any significant weight? Will the extra chassis stiffness amount to anything like a second a lap on a 1:37 course like Grattan maybe? I'm looking around for a chassis shop here in West Michigan, but I want to know what the return on my money will be before I commit.

Looking forward to your comments!

For whatever this is worth, my friend and I run identical looking '72 Datsun 510s in ITC. Mine has a welded-in Autopower cage that we put in two years ago. His has a custom cage similar to a few other 510s that we run with out here in N California. His car is about 85 lbs lighter than mine after adjusting for driver weights. With driver weights included, I'm net 110 lbs heavier.

It seems hard to believe that my cage could be that much heavier than his, but I don't know where else the weight could come from. He has the same sidebar configuration as mine, but he has two x's behind the main hoop, where I just have two down tubes going from the top of the main hoop to the top of the rear wheel wells. Both cages are .120 wall thickness.

However, on the track, the cars could not be more closely matched, both in straight line speed and in and lap times. We regularly run within tenths of a second of eachother at each of the three tracks out here.

Based on all of this, I would tell you to just add the bar and use the money for something else.

When I went from an Autopower bolt in to a Joe-Dog custom welded in cage I gained lots of stiffness, and had to add ballast, and re-installed carpeting/sound deadening to make weight.

You should get right down to weight and the car will be safer - more crush space w/door bars and stiffer structure.

I highly recommend it.

If all you're looking for is stopwatch value for your investment, the return on a weld-in cage is going to be pretty low. Spend the money elsewhere on the car, or simply run 3 more races this season.

If you put any value in the save-your-a$$ quotient, your return could be (hopefully you never have to find out) pretty high.

I think a properly designed and installed welded cage can be safer, stiffer, and lighter. You have to ultimately decide what the priority is: safety or speed.

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I think a properly designed and installed welded cage can be safer, stiffer, and lighter. You have to ultimately decide what the priority is: safety or speed.
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Excellent point and IMHO in amateur racing safety wins every time.

I am welding in an old Autopower cage now. It is very heavy. I have always made my own and many others. It is easy to look up the tube weights from any vender. The 1.5 x095 is about 2# per ft, maybe. The big fat 1.75x ? erw is about a third more. 40- 50 pound reduction, is about right@ 120ft.
The autopower is bolted to a very weak area of the car, unless you have added large load spreading pads.
I invented a "crush box" for floor pan mount cars . It is very simple. Make a large100sq in, pad, that wraps up to the sill. weld it only on two sides( or spot the edges) to the floor pan itself . Build a .080 to 095 riser box that is about 4 in square and 1in tall, weld it to the floor pad . Now weld the tube to the center of the riser/crush box. Do this at any floor points.
What this does, is to spread the load to the other floor mounts and to the rear post, as the box is crushed, without pushing thru the floor. The whole cage is very lightly loaded, as opposed to a point being very heavy loaded, as in a sharp , high, tumble.
The large pad is welded on two sides to reduce the floor pan "Punch" outline. The floor is very weak after a contiual bead around a heavier pad. You can also spot for about 1in along the edges of the large pad.

I have researched the patent and it is open. Not much of a market tho.

Use gussets for the down tubes to the rear and the front. These help the load spread.
The boxes can also be a piece of 1x6x .095. Is is important that the cage tubes are not directly above the box edges, IE there needs to be some area to bend, not stack.
I also will tab the tubes to the sill. at all options.
If anyone wants the front the cash for a patent. The reasearch has been done and I'am all ears.
Mike Ogren [email protected]
I dont think that the weldin cage will make your car faster, if you are only over by 30#. The added stiffness has very little affect on the FWD cars.According tot he chassis books. I dont tie the rear struts togther anymore as a result. I dont want a totaled car just because it got hit inthe rear quarter and shifted/ twisted the whole car. I would rather cut the tube,pull the corner back out. Rather than cut off the back end.
MM

I should have prefaced my answer not to replace the cage with the excellent point that was made on safety. I was only answering based on the question of lowering lap times.

I bought my car three years ago with an existing cage and after looking at it, decided it needed to be replaced before I would put the car on the track. The welds were horrible and the base of the hoops was welded to very weak floor pan structure. I'm not sure that if the car went upide down that the floor pan would even support the car's weight.

The new Autopower cage was installed with nice strong, quality welds done by a certified welder. We added lots of support at the bases of the hoops, we put in the optional dash bar across the front and the (then) optional two door bars on the passenger side. I also supported the door bars with three down tubes between them. I think I have a pretty safe cage now, but I wish I would have made the seat mount part of the cage so the seat would move with the cage. I may change that.

If I'm not mistaken a GTI in ITB has a minimum weight of 2280. That means your choices for tubing are as follows.

1.5" x .120 at 1.769#/ft
1.625" x .120 at 1.929#/ft
1.75" x .095 at 1.679 #/ft

Guess which one I went with on the RX7 at the same weight and requirements. Also the rule is no more than 100 square inches per pad (.080 min) and no longer than 12" on one side. Use as much of that 100 as you can. Tubing/pabs can only be welded to the body structure in a maximum of 6 places or 8 if two run forward from the door hoops to the firewall. No "tabbing" allowed.

Speaking from the perspective of one who has watched that sky-ground-sky-ground... movie in the windshield, I would never cut corners on safety gear. That goes beyond cage construction and includes seat, seat mounting, harness, harness attachment, etc.

Well if the stiffness won't cut my lap times that significantly, I doubt that the 30 lbs. will. And despite what my wife keeps telling me, there's no way I'm going to lose 30 lbs.! I'm 5'10 165 lbs.

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...the base of the hoops was welded to very weak floor pan structure. I'm not sure that if the car went upide down that the floor pan would even support the car's weight...[/b]

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Mine is similar, except it's bolted to a very weak floor pan. This has been a concern in the back of my mind for a few years. Maybe because of the cost it's never quite reached the front of my mind.

Based on all this I'll look for a guy locally to build me a cage, definitely with big pads on the main hoop, but I won't go nuts with all kinds of extra bracing. If anyone knows of a good cage fabricator in West Michigan I'd like to hear about them. If not I may go to Izzy's. Hopefully my wife won't think it's cheaper to just buy more life insurance!

I appreciate all the feedback! :birra:

lenny,

if you are looking for speed, i would drop $1000 on data logging.

if you are looking for safety, i would go for a $1000 HANS.

if you are looking for less weight, convert the autopower from bolted to welded by getting rid of the sleeves and bolting and add the 100 sq. inches on the mounting points.

this should be very little money and give you some benefits of safety and stiffen the chassis some.

tom

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lenny,


if you are looking for safety, i would go for a $400 Isaac Link or a $800 Isaac intermediate.


tom [/b]

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fixed that for you...;)

Just a little equal time, LOL.

touche!

no problem! i have neither. i will like die of old age waiting to find out if NASA or SCCA will actually clarify to the point of knowing what i can do and stay "legal"

good luck with whatever you do lenny. sorry to have missed grattan last week but i am doing the nasa honda challenge race there next weekend instead.

tom

As much as I'd like to see you come in the door, update the doorbars and maybe convert the cage to a weld in if it's feesable. If you don't have a 1,000 burning a hole in your pocket, use it to get more seat time. That'll get you further toward the pointy end of the field than the trickest roll cage would.

Now... if the welds are questionable or your head/legs/arms are resting against the cage... that's a different story.

If the GTI's min. weight is 2280 then the IT tubing is 2100 which IIRC is 1.5x.095 @ 1.426 lbs pf.

You can tab to the 100sq in, sill/ floor plates. You may have to run a contious bead from the base to the tab.( to be 100% legal) I have never been advised that I had to reduce the safety at any SCCA event, and they are the worst. You cant tab to the door post or A pillar, and all that, like a stock car, of course.
You may be able to cut the floor post off of the Autopower and replace the bases with boxes that spread the load up to the sills.
If you dont think that you can pick the car up and drop it 15ft inverted, without busting thru the bottom of the car, you should park it.
50# is worth about 1sec at Sebring in my B car. 100# is 1.5 at 2:45. The fastest cars will be 5# over on the scales post race, IMHO. I am
MM

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If the GTI's min. weight is 2280 then the IT tubing is 2100 which IIRC is 1.5x.095 @ 1.426 lbs pf.[/b]

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The tubing sizes I quoted above can be found on page 89 of the 2007 GCR and are for IT cars weighing from 2201 - 3000#.

1.5" x .095 is OK for cars 1501 - 2200#.

And, unless something has changed in the latest GCR, IT tubing size is determined by min. weight MINUS 180 lbs.....

Hard to tell if we're on the same page or not Tom ;)

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And, unless something has changed in the latest GCR, IT tubing size is determined by min. weight MINUS 180 lbs.....[/b]

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I stand corrected and learned something new today.

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I have never been advised that I had to reduce the safety at any SCCA event, and they are the worst.
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I'm not sure I understand this statement.

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You may be able to cut the floor post off of the Autopower and replace the bases with boxes that spread the load up to the sills.
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This definitely sounds worthwhile, if I decide to keep the Autopower.

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50# is worth about 1sec at Sebring in my B car. 100# is 1.5 at 2:45. The fastest cars will be 5# over on the scales post race, IMHO. I am
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That's a longer track than where I go, but 30# should be worth a few thenths anyway. If I lose 50# I can run more fuel, so the weight distribution is better.

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And, unless something has changed in the latest GCR, IT tubing size is determined by min. weight MINUS 180 lbs.....
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9.4.1.F.4. For purposes of determining tubing sizes, the vehicle weight is
as raced without fuel and driver. The minus tolerance for wall
thickness should not be less than .010” below the nominal
thickness. Improved Touring roll cage tubing size are to be
calculated based on the published vehicle weight minus 180
lbs.
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That makes mine a 2100 lb. car. 1.500 x 0.095 should work.

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good luck with whatever you do lenny. sorry to have missed grattan last week but i am doing the nasa honda challenge race there next weekend instead.
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I didn't know NASA got up our way! Some day I may check that out. Do they have a place for an ITB car to play?