TheRX7Project HalfDork
2/9/20 4:18 p.m.

Is this in a Challenger?

Jvella36 New Reader
2/10/20 11:12 a.m.

In reply to TheRX7Project :

No, BMW E36.

John Welsh
John Welsh Mod Squad
2/10/20 11:18 a.m.
Jvella36 said:

I have a custom made 4 point roll bar which is made out of Chromoly and the dimensions are 42mm x 2mm and the feet of the roll cage are 3mm, I did not fabricate the roll bar myself so I'm just asking here what you guys think about it.

My question back to you is, "what does your sanctioning body think about it?" 


Also I was wondering if it would be ok to use 8.8 grade bolts since I couldn't find any higher grade bolts.

Granger or Fastenal should be able to get whatever you need.  See recommendation above of sanctioning rules.  


Ransom GRM+ Memberand UltimaDork
2/10/20 11:31 a.m.
Jvella36 said:

In reply to TheRX7Project :

No, BMW E36.

I believe he's asking whethis this is for a car for the GRM $2000 Challenge, not whether it's a Dodge Challenger. Yet another reference to "what sanctioning body's rules are you trying to meet?"

Robbie GRM+ Memberand MegaDork
2/10/20 2:16 p.m.

Considering the tube is specced in mm I'm assuming the op is not in America and very unlikely to be building a challenge car.

Jvella36 New Reader
2/16/20 6:22 a.m.

I am not trying to build a competition car, this car is mostly used on weekends and maybe some autocross nothing huge.

I'm just trying to confirm if the dimensions of the roll bar are correct and if I can use 8.8 grade bolts, that's all.


79rex Reader
2/16/20 7:41 a.m.

The bolts are something to look into, but what its bolting to is really important.  plates underneath it? Reinforced somehow?  A bolt will mostly be as strong as the threads they are going into

BoxheadTim GRM+ Memberand MegaDork
2/16/20 11:10 a.m.

In reply to Jvella36 :

If you're not trying to build a competition car, why the half cage? It's usually not something you need for street driving and autocross, and can cause additional problems on the street.

I'd also try to find stronger bolts (like grade 12.9), the last thing you want is that the safety device becomes a projectile in case of an accident. And I'd also like to second and third 79rex's question about how the cage is generally mounted. Is it a bolt-through design with spreader plates, or one that is designed to be welded in? In the latter case it likely doesn't have the spreader plates to mount on the outside of the car and you can't just bolt it in instead if it's designed to be welded in.

Knurled. MegaDork
2/16/20 11:12 a.m.

If it's just a street/autocross car, I agree, remove it and don't worry any more about it.   Outside of a convertible, modern chassis don't really benefit from a 4 point roll bar the way older cars did. It's just added weight and added pain in the ass.

BoxheadTim GRM+ Memberand MegaDork
2/16/20 11:33 a.m.

In reply to Knurled. :

Or a pain in the back of one's head .

The one reason I could see is if you wanted to run four/five point belts as the rollbar has a harness bar, but I don't think that's too hot an idea either unless you run seats that are equipped for harnesses. One of the reasons I finally decided to not run bucket seats in my occasionally tracked S2k.

Jvella36 New Reader
2/17/20 11:12 a.m.

The roll bar has reinforcement plates underneath.

Olemiss540 Reader
2/17/20 11:34 a.m.

I am fairly certain my kirk rollbar did NOT have grade 10 hardware. 4 grade 8.8 bolts on each mounting point (floor, floor, wheel arch, wheel arch). Just a data point. 

If the force is enough to shear 16 grade 8 bolts, than the day is over for any bolt in solution I am afraid.....

Just use as wide, long, and solid footings as possible as that bolt location in the floor of an e36 is flimsy as E36 M3. Try to tie it into the corner where the 3 panels come together if possible somehow. You want to try and prevent the bar from punching THROUGH the floor where the main hoop mounts.

Here was my previous rollbar:

You can see it didnt have the back X, but did have a cross bar to the main hoop to prevent collapse. Worth looking into this if possible.....

Knurled. MegaDork
2/20/20 8:25 a.m.

What keeps the harness bar from being able to fold in the middle or rotate up/down?  It looks like it is not secured to anything but the main hoop, where it is attached in the middle of a span.  If that is the case, it's essentially worthless as a safety device.


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