Rules clarification on tube frames and hood modifications

[billj935]

1985 911; Two questions 1. Full rollcage, tied into front and rear suspension, Will I be considered to have a tube frame if I replace the rear arch containing the shock mounts (crossmember) with a tube connected to the stock sheet metal tubes running the length of the car in the rear?

2. Can I vent the oil cooler through the front hood? bill j

[JSG1901]

Hi Bill,

 

The litmus test for whether or not a car should be considered to be tube framed is whether or not removal of the tubes renders the car un-driveable. If it does, it's considered tube-framed.

 

NOTE: the paragraph above was modified 7/22/13 for better readability.

 

I can't completely understand what you're saying you want to do, but that's the test you'll have to pass or fail.

 

As to venting the oil cooler through the hood, sure.

[garbageman]

I see the paragraph in the rules about what constitutes a tube frame. But I am unclear if the rules allow tube frame or not.

Thanks

[JSG1901]

The rules DO allow tube frames but the power-to-weight ratios are different. You can see this in section 5.1 where you'll notice that, for instance, the GTS3 ratio for tube-frame cars on slicks is 14.5 : 1 whereas a non-tube-frame GTS3 car on slicks would only need to be 12:1.

 

So, while there's an advantage going with the full tube frame, there is a weight penalty associated with it, too.

[garbageman]

Cool. Thanks again.

[cstreit911]

1985 911; Two questions 1. Full rollcage, tied into front and rear suspension, Will I be considered to have a tube frame if I replace the rear arch containing the shock mounts (crossmember) with a tube connected to the stock sheet metal tubes running the length of the car in the rear?

2. Can I vent the oil cooler through the front hood? bill j

 

Bill,

 

Modification of the rear cross-member with a tube to support the shocks was/is fairly common on the 911's and was never considered to be a tube-frame. It offered no performance advantage per se, just installation of coil-overs in the car that was not setup for them. That said, your car will take coilovers without doing this, you just need to reinforce the cross-member. Fairly common mod.

 

Oil cooler vent perfectly fine.

[gisqc]

I would like a clarification with the statement about being able to drive with the tubing removed.

 

First, if one mounts an engine or transmission on a new place, most likely maybe a tube reinforcement, which means without the tube the car can't drive is it still a tube frame car OR "Modification of suspension and drivetrain mounting points alone does not constitute a tube frame." applies?

 

Or would one need to mount anything on a part of the body and then reinforce it with a tube around, meaning it could still "drive" without the tube (altho it would have no rigidity at all in certain cases?)

 

I'd like to swap the rear subframe of my bmw with something custom, that alone is fine with the rules since it's bolted to the chassis, but if I want to modifiy the mounting points of that subframe I would most likely have to tie it to some tubes since the floor in that area is very weak beside the oem mounting points. Would that be a tubeframe or it would be ok? Suspensions points are all using factory sheetmetal (cage reinforced) but those would be only a few "driveline" mounting points.

 

Thanks

[JSG1901]

The problem here is we're trying to answer a hypothetical without anything to actually see, so it's all a bit of a guess. Having said that, let's go back to the objective.

 

We all know that you can make a faster racing car if you build it all from tubes and toss on a body than if you work with the factory unibody. The spirit of this rule is to both acknowledge that fact and to provide a way that people running true tube-framed (German) racing cars can compete in GTS, albeit with a penalty.

 

To that end, I wouldn't consider reinforcements made from tubing to constitute a tube-frame car, at least they way I understand what you've written. If you were to cut away substantial portions of the unibody and replace them with tubes, then maybe it is.

 

Acknowledging that a completely stock factory car would not be considered tube-framed, and that a car that is nothing but tubes with a shell of a body thrown over it is, clearly there is a continuum between the two that constitutes a gray area. At some point, enough modifications can be done that what began as a factory car becomes what we'd consider to be a tube-framed car. But, because there are probably a thousand ways you can modify the car, I don't know how exactly we can say what is and what isn't tube-framed with a whole lot of specificity. It's not like there's a point where everyone in GTS can agree that if you add one more tube of any kind, suddenly you've crossed the threshhold into tube-frame territory.

 

I'm reminded a little of Justice Potter Stewart's characterization of hard-core pornography when he said, "I know it when I see it." The goal here is not to be unnecessarily restrictive but neither is it to allow any possible modification without penalty. If you have actual engineering drawings of what you're trying to do that you would like a ruling on, I'd be happy to take a look and discuss it with my technical people. More likely, you're like most of the rest of us and this is being done a bit more informally. I think the question you need to ask yourself is "Would a reasonable group of uninterested competitors consider what I've created to be a tube-framed car?" because, at the end of the day, that's pretty much the standard that will be applied.

 

If I properly understand what you've described about the modifications you hope to make, I don't think they would constitute a tube frame. But, having said that, I may not be fully grasping the implications of your words and what they will result in in the actual metal. So, while I think you're okay, I would also say it's possible you're not, depending on the work you actually do.

 

Sorry I can't be more specific.

[autodoctor911]

I would assume that if someone were to run a real DTM car, it would be considered tube framed, even though it is based on a series spec carbon monocoque tub, not a tube frame. I guess in GTSU, it doesn't much matter anyways, but they might run it at a lower weight to power, in which case, it should definitely be penalized against stock framed cars. Now is a 991 RSR a stock tub? not that you'll see one of those in GTS, but from what I could see of how it's constructed, it has been pretty much turned into a tube frame car now, where as the 997 RSR would definitely have been considered a stock tub. The front end of the 991RSR in particular, has been completely reworked with upper control arms and coil over shocks replacing the factory struts, all mounted to tubes coming out of the firewall, with no factory sheet metal visible with the carbon front bodywork removed.