Question for the real chassis fabricators..

"Grindintosecond" (Grindintosecond) 01/14/2014 at 10:30 • Filed to: None

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will a roll cage solve the most flexible issues of cars out there? Example, caging a cavalier vs. caging a golf....will both be just as stiff? Im asking because of a project in theory. One car is light but a bit flexy, and the next generation of it is stiffer but 2-300 lbs. heavier...will a cage make both just as stiff and the lighter car the pick? or is origional stiffness still a difference?

Arch Duke Maxyenko, Shit Talk Extraordinaire > Grindintosecond 01/14/2014 at 10:36

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There are chassis braces, lighter and less costly than a cage, too.

Casper > Grindintosecond 01/14/2014 at 10:37

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That really depends on how the cage is built and how it ties to the car as well as where the weak points of the car actually were. If it's just a bolt in cage or welded in to a couple points, it will help, but it won't solve all the flex issues. If you are going 100% with it and doing a full cage (6+ point) and doing stuff like stitch welding and really buttoning up the flaws of the chassis, they will probably both be beyond stiff enough for anything you are doing. The cage is only part of what most people consider "stiffness" on the chassis. There's also the boxing at the front and rear of most cars such as the engine compartment and the underside in the suspension components that play into the overall feel. The passenger compartment maybe very stiff, but the front wheels still might be moving nearly as much as before simply because the flex wasn't in the area caged.

There is a tipping point where the original rigidity of the chassis isn't as relevant as the cage, but that point varies from vehicle to vehicle.

Bob Loblaw Made Me Make a Phoney Phone Call to Edward Rooney > Grindintosecond 01/14/2014 at 10:39

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Just as a point: the cage is going to add relatively significant weight to the car.

BJohnson11 > Grindintosecond 01/14/2014 at 10:40

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Original stiffness will definitely make a difference. Imagine in the extreme example if one of the chassis was made out of spaghetti. If you add a chromoly cage to that, the result will be less stiff than if the chassis was originally steel.

Like Arch Duke said, there are other ways to gain stiffness than by using a roll cage. Sub-frame connectors, boxing the frame, and stuff of that nature can help depending on what the original chassis construction is.

Tentacle, Dutchman, drives French > Grindintosecond 01/14/2014 at 10:41

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Total vehicle stiffness will be the result from the cage and car both. How much will be contributed by the cage and how much by the car depends on the roll cage design and where and how it mounts to the car.

The older lighter car will not become as rigid as the newer heavier car if it gets an identical cage.

DSimms777 > Grindintosecond 01/14/2014 at 10:43

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With everything the same, the stiffer car to start out with will always be stiffer. A less stiff shell with an elaborate cage incorporating suspension points and drivetrain mounting will be stiffer than a basic 4 point cage in a more stiff shell. It all depends on the extent to which the cage is made.

Casper > Bob Loblaw Made Me Make a Phoney Phone Call to Edward Rooney 01/14/2014 at 10:47

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I was thinking the same thing when I was writing my reply. If he's worried about a couple hundred pounds, he probably shouldn't be looking at a cage serious enough to fix his rigidity issues. Cages add a ton of weight depending on how serious they are, I have to guess the NHRA style cages can be somewhere around 200 to 300 lbs depending on the car and material.

Grindintosecond > Casper 01/14/2014 at 10:59

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this is a good point, let's compare application. NHRA vs. Rally/rallycross. Now there's some twisting of drag racing or constant twisting and impacts of the stage rally. Would a stiffer chassis go best for rally building and the lighter flexible chassis would be better for the drags where some cage "band-aids" can help it out? Am I wrong in that thinking?

Casper > Grindintosecond 01/14/2014 at 11:06

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In drag racing there's a lot of twist that happens in faster cars. The cages do help in both performance and safety. In drag racing you don't have to worry about cornering though, and corners actually can be helped by having a little looser setup and less rigidity at times. Of course you can compensate with suspension, mess with sway bars, etc, so you can always get back there. Personally a lot of the drag cars I have played with have had much more rigid setups than the rally cross cars I have driven. Rally cross is much less about rigid performance and more about predictable responses.

I wouldn't call things like subframe connectors or bracing/boxing "band-aids". They are more of a progressive thing. If I wanted to stiffen the wife's BRZ up (which I do) I wouldn't go straight for a cage. The first things I will try will be things from the underside and tower bars, then work my way more serious from there.

Bob Loblaw Made Me Make a Phoney Phone Call to Edward Rooney > Grindintosecond 01/14/2014 at 11:09

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It's an incredibly nuanced question that can have a lot of different questions.

At the end of the day, the first and foremost application of the cage is to comply with the regulatory body with which you race. NHRA/SCCA/etc. regulations often differ from one another, some more lenient, some less lenient, some not more or less lenient but rather stress different protection zones/structures as opposed to another form of racing.

After that, you get to chassis considerations, which then brings you to figuring out just how stiff any one car is and how much cage you think you need for the kind of racing you're doing. There's not a magical formula out there for balancing rigidity and weight, and there's not one magical car that has better balance than another; the question is just incredibly nuanced.

Newer cars are generally going to be stiffer, but that stiffness often comes at the cost of weight, and vice versa for an older vehicle. Other considerations are whether you're dealing with a body-on-frame vehicle or a unibody vehicle, which complicates the situation to a degree.

Tl;dr: it's a question that raises a ton of questions in and of itself, but the answer is that the answer will be differently for every situation and for every pair of cars you compare.

Grindintosecond > Casper 01/14/2014 at 11:12

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I see...I had chassis connectors i put into the 79 volvo and it was remarkable what it did. Made it quite responsive compared to before. And the thicker sway bars too...

So, how would you approach the application then based on the dilemma of the two choices? Example 1g car lighter but more flexible and 2g stiffer and a bit heavier? In rally/rallycross would this not matter so much since as you said the stiffer cage actualyl works better for the higher powered drag cars?

Casper > Grindintosecond 01/14/2014 at 11:23

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In reality most people doing rally/rallycross won't be at a level driver wise to get the most from a perfect setup anyway. I would personally think of the cage side of the equation as a safety issue more than a performance one. The weight from the cage will probably more than offset any real gain you would get, especially if you aren't racing some 500HP+ pro car. It should be there to keep you from having a tree invade your personal space in a very rude fashion.

What have you done so far and what cars are you actually considering? A Golf and Cavalier? If that's the case, you might be better off dealing with tower braces, connectors, and playing with sway bar thicknesses. If you are serious about it and going to do some real rally events that have a risk of roll over or high speed into something unforgiving, I would strongly suggest thinking of cage or roll bar for basic safety.

Grindintosecond > Casper 01/14/2014 at 12:22

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Until the 79 mini restoration is done. nothing yet. (long post here) After that project who knows what space ill have for the next one.

If I did pick this rally/rallycross as the next project, this is something to consider as the car i'm thinking of is not the stiffest but it has the cheapest possible parts. It may be a moot point now. this idea came up when I lived in western NY state. Since I moved to Colorado the closest stage rally is now 800 miles one way to get to. That and the cost of doing multiple (4-5) events in a year to make such a build useful is cost prohibitive not including the schedule that work will not let me have. So i'm thinking of rallycross now, with possible future of stage if they were ever to get that program going again in state or elsewhere closer. so this question I asked earlier came up when re-visiting the idea. No not a cav. Not a Golf. they were just examples.

My idea was a 2wd rear drive car. It's what I really learned to drive in anger. Heck my old Volvo was amazing in that regard. But when I saw great video of Mark Utecht's 383stroker group-5 mustang being awesome in Rally America, the wheels spun in my head. In a brief email conversation we had, it was the most fun he had ever had racing a car, (until he torque rolled it out of a culvert bending it) including the subaru he ran years ago . It was relatively cheap to build,except for the engine and t600 transmission, because he used 'junkyard' parts for suspension bits and pieces. like Ford LTD springs in the back and the like. Stock 15" wheels with the smallest goodrich offroad racing truck tires (rally tires would be "burned off in 15 miutes" he said) It worked and was extremely competitive in the 2wd class. In fact he beat, on a few of the fast stages in Idaho, the open awd class guys. Also mentioned that 450+hp and tq was completely unnecessary and overboard but was too much fun to pass up. The only car starters would back away from during the count down. Anyway, I have not the funds for a project of that magnitude but considering what a 2wd ...RWD rally car really needs in power and ability, a 3.8 230hp engine would fit the displacement limits of the regs, have beefy manageable torque (240lbs all ove rthe place) and be just fine for that task. Given the parts of the fox chassis being so interchangeable and cheap, it would be a great exercise in budget racing because as Mark proved, thinking ahead and using factory parts already existing can be just as good as expensive custom parts that do the same job. Now, the stiffer chassis of the sn95 is 200 lbs heavier, but if caged I'm not sure it would be that much of a benefit and that was my question I asked about. I know that a cross car caged is kind of a waste but I asked the question as if it were to be a full stage competition car for the group-2 2wd class....at 2700lbs max. and 230hp and 250 tq it would be competitive against group-2 and group-5 and in rallycross it would be a ball of fun. In rallycross the classes they run don't allow engine swaps unless its basically a full stage prepped sort of car...reason for a 3.8 swap would be similar power to the 5.0 but over 100 lbs lighter and the CG moved quite a bit further back...beneficial to a cross car. there's other thoughts and ideas on chassis makes to use for a 2wd rwd car but overall cost of build and enjoyment/$$? Fox keeps winning...

Anyway, since the move it has become a back burner idea since stage events are not logical anymore for me. but at least the idea is still there and it would be a great budget exercise. thought i'd see what reasoning i'd need to justify a cage or not. I did find my answers tho. thanks to you and the other guys for your insights!

Casper > Grindintosecond 01/14/2014 at 12:28

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I actually prefer RWD cars for pretty much everything. It all depends how serious you think you can maintain. I never made enough events to be able to justify building a rally/rally cross car, but I enjoy doing it casually like autocross. I think going the Fox route would actually be pretty good. Maybe you could find a chassis already with a cage and basic work from a retired racer and just build from there. They are pretty common in most racing since they are so cheap/easy to coax power from, odds are in your favor.