Getting way ahead of myself - let's talk about skid plates

I don't even have my Saab C900 on the road yet and already my brain is filled with rallyx fever dreams, so naturally it's time to talk about skidplates. In keeping with the Challenge-compliant budget, cheap is good and cheaper is better. I want a plate that is 12x48" - that should cover the vital bits. I know I'm unlikely to need such a thing for rallyx, but if I'm building something that bears a passing resemblance to the decrepit shell of something that might once have looked vaguely like a rally car, it's going to have skidplate, dammit.

I understand that ideally I'd use something like 1/4" aluminum, but that's probably going to be expensive and difficult to shape. So to questions:

- Solid plate vs. a grate of bar stock welded to 2 or 3 crossbars. The latter is probably easier to fabricate, but will it protect effectively? How wide is too wide for the gaps? For plate, what's the minimum thickness needed to be effective (remember, rallyx, not stage rally)? How about vertical bracing or other strengthening? Any other brilliant ideas for how to set this up?

- Attachment points. How many do I need? The factory plate, which covers the front from the valance to the crossmember, mounts with five bolts, though I'm not sure what sort of loads this plate is intended to absorb. If I extend back to cover the remainder of the transmission, will another two bolts at the rear be sufficient? Regardless, I'll probably have to weld in an additional piece of square tubing to attach the rear of the plate.

- Speaking of the factory plate, would it be madness to just weld some additional metal to it to extend coverage back to the firewall? It seems reasonably strong, probably enough for rallyx.

- Any suggestions for cheap materials that might work here? I scoured the metal pile on the last town dump day, but I couldn't find any sheet metal that was more than appliance outer shell thick. I did grab some 3ft sections of roughly 1" square steel tubing , but I don't think that's ideal, as it would be hard to bend and reduce ground clearance.

Just remember a steel skid plate of that size will be 75-80lbs in 3/16th and a 1/4" aluminum one will be like 35lbs

How about none?

If you need a skidplate, the course designer berked up and the safety steward should not have signed off.  Per the RXR, courses should be safely navigable by any stock vehicle.

(I have a skidplate not for rallycross, but for street driving - I do not have/cannot use a swaybar, which was also the thing Mazda used to keep stuff from hitting the oil cooler.  Stuff hitting the oil cooler is a world-ending event.  So, skid plate, oto prevent highway litter from putting my car into statue mode)

Knurled. said:

How about none?

 

If you need a skidplate, the course designer berked up and the safety steward should not have signed off.  Per the RXR, courses should be safely navigable by any stock vehicle.

 

(I have a skidplate not for rallycross, but for street driving - I do not have/cannot use a swaybar, which was also the thing Mazda used to keep stuff from hitting the oil cooler.  Stuff hitting the oil cooler is a world-ending event.  So, skid plate, oto prevent highway litter from putting my car into statue mode)

^^Pete has a skidplate on his rallycross car that could probably survive driving over an anti-tank mine, regardles of what he *says* its for, he doesn't take it off for rallycross, even though it weighs a metric ton. :D

that's nice in theory, but a poor strategy in practice. Courses change, rocks get uprooted, ruts get created. 

Our venue is pretty smooth and doesn't rut up much at all. I don't think I've even made contact with anything on my skidplate. That said, another e30 (guys who have run for 10 seasons in that car and never broken an oil pan) somehow smashed their oil pan WITH a skidplate on last week. I was the next car and saw the oil trail's location. They were somewhat off the line and hit a rock that the previous car had apparently kicked out of the ground. It was just bad luck (not a course issue, as we have stock miatas and stuff running with no issues). If you rallycross, you may not always be right on the course (depending on your skill). And not all rallycross courses are on farm fields like Pete runs on ;)

Rallycross courses have to be safely navigable by stock vehicles (i.e. it has to be able to get around safely if the driver drives at a reasonable competition pace).  "safe" /= "not able to damage your car no matter what." That's called "autocross" lol. Any rallycross can damage your car if you do something wrong, go off course, whatever. It's the nature of rallycross.  

IDK what the underside of that engine looks like, but a 48" long skidplate seems ridiculously excessive. My stage rally plate (1/8" stainless) is only 36" long, and that's protecting an inline-6 and the transmission bellhousing on mine. For a rallycross car, really the only thing worth "protecting" is the lower oil pan itself. not sure how big that is on your car, but whatever the smallest size plate you can make to JUST protect that is more than sufficient for rallycross. 

definitely solid plate. The bar idea sounds like a terrible idea, honestly. It will allow rocks to get wedged up in there or get on top easily, and if one gets wedged between the bar and the oil pan and you hit much of anything, goodbye oil pan. 

crossbar probably is overkill for your purposes. 

Go find an old stopsign or something and cut it up / done. 

what is your stock plate like? A quick google search seems to show that car has a subframe that appears to protect the oil pan fairly well, so you may not need anything thicker than a "slider plate" so to say.

No idea why you want to run it to the firewall. Even my stage plate doesn't extend that far back - there's nothing back there that's gonna get damaged at rallycross unless the Saab has a really, really weird engine setup. Rear mounts for my plate are the engine subfrane, just behind the steering rack (and it extends about 6" past that).  4 bolts, no problem. 

In reply to irish44j :

The SAAB does have a really weird engine setup - the transmission is the oil pan, the clutch is under a plastic cover up against the radiator, and the belt end of the engine is against the firewall.

I haven't heard of any stage rally plates that do more than protect the radiator and the front half of the oil pan or so.  Beyond that is unimportant, as you're going to be bouncing away from whatever it was you just hit.  If you high center on the plate, you weren't really going fast enough to hurt anything anyway...

side note, looking for pics I just came across this one from Great Lakes Div. Challenge back in 2014. That's Mr. pete right there...

on a side note, never sell stuff to Pete, unless you like $100 of quarters for payment

Knurled. said:

In reply to irish44j :

I haven't heard of any stage rally plates that do more than protect the radiator and the front half of the oil pan or so.  Beyond that is unimportant, as you're going to be bouncing away from whatever it was you just hit.  If you high center on the plate, you weren't really going fast enough to hurt anything anyway...

well, you HAVE heard that, lol....because mine is a stage rally plate on a stage rally car that has done a number of stage rallies, and it does protect farther back than just the front of the oil pan ;) Plenty of stage plates run "stingers" to protect the bellhousing and transmission. If you don't think it's possible to hit your transmission on stuff in stage, you're mistaken. Take a look at my passenger side rocker and it's about 4" higher than it used to be. Remember, on stage you can take a detour OFF stage, where it's nice to not break E36 M3 on a tree stump or big rock , so you can get yanked out and continue (ask Chris Nonack about that.....). On a stage car you can jump and land ON a rock that doesn't even hit the front of the oil pan, but smashes the back end of it (how we broke ours at NEFR last year). There are all kinds of ways to do damage on stage, trust me. My car has 3/16 HPDE sheeting over the entire underbody. Many cars have skids on their diffs too (especially Subarus), armor on trailing arms, etc etc. 

irish44j said:

side note, looking for pics I just came across this one from Great Lakes Div. Challenge back in 2014. That's Mr. pete right there...

on a side note, never sell stuff to Pete, unless you like $100 of quarters for payment

 

I was in a serious financial bind back then... at that GLDiv I was driving on snow tires because I didn't have access to my rally tires due to some housing difficulties.  And when I paid in quarters, I had literally no money at my disposal, I spent all of my remaining free cash getting to and from the event, and scraped up all the loose change I could find because I'd promised someone that I'd give them $100 that weekend and I prefer to keep my promises.

Extra fun was not being able to go to work the next week - no gas money.  That kind of turned into a big situation, and in a roundabout way I acquired the S40 because of it.

Of course, times are much more baller now.  Pimpin' the S60R, have two rallycross cars in nearly ready to go status and three more waiting in the wings for when those explode and die, a sweet secret lair to hide most of them, rally tires out the ass, etc.  Picking up a set of Compomotives for the RX-3 next weekend too, from a rallyist going to SOFR.  Going to pay him with foldin' money!

Thanks for all the feedback. As noted, the powertrain is on a C900 is oddly arranged. The engine is backwards and sits atop the combined transmission and differential, with a bellhousing of sorts and a triple chain drive sending power to the transmission at the front. 48" long would give me coverage of that plus a little at the front to angle it upwards.

Smashing a transmission known to be somewhat fragile is not something I would like to do, so a skidplade seems a reasonable idea no matter what. I'll see what I can find as far as materials. Should I happen to find a piece of 1/4" aluminum, how does one bend such a thing without a brake?

Knurled. said:

Picking up a set of Compomotives for the RX-3 next weekend too, from a rallyist going to SOFR.  Going to pay him with foldin' money!

Speaking of...he messaged the OVR facebook page asking for your contact info because he couldn't get ahold of you. If I knew they were Compomotives I would have swooped in to get them first. 

On topic. My 900 turbo had a factory skidplate. It looked like it would be sufficient for any rallycross. If you don't have one already you could probably find a used one. Looks like Eeuroparts doesn't stock them anymore. 

In reply to EvanB :

I have that factory skidplate installed. It may well be adequate, as it seems to be fairly stout, but it is also pretty small. A while back I found an old eeuroparts blog post about their rally C900 that showed a quick-and-dirty extension welded to the factory plate - that may be the route I go if I don't find something both better and cheaper.

I have a SaabSavior copy of the old Saab Sport & Rally skidplate on one of my C900s. You probably won't be able to find one for sale, but I'd guess there are some specs for them floating around on the internet somewhere. I could also probably take some photos and measurements after Carlisle if needed.

In reply to EvanB :

He has three sets for sale.

In reply to Powar :

I've seen photos of that skidplate and it looks great, though I suspect finding one at an even remotely affordable price - if I could find one at all - would be problematic. Measurements of yours would be nice to have - thanks for the offer.