View Single Post
  #20  
Old 09-09-2020, 06:04 AM
andrewwynn's Avatar
andrewwynn andrewwynn is offline
Member
 
Join Date: Jun 2015
Location: Racine, WI
Posts: 10,818
andrewwynn will become famous soon enough
Wife's plate is parked behind the garage. Has been for months.

Will not cause any catastrophic problem but the car jiggles like crazy without it in comparison.

Here's how I know: I used to own a convertible Z28 and my X5 feels rigid and firm like my Z28 with the top up. Hers feels wiggly and jiggly like the Z28 with the top down. Maybe I will take some g-force readings to demonstrate but the flex is maybe 3-5x as much it's quite noticable. If you can't feel it you aren't a performance driver. I feel the shake ripple though the car at every pothole. It took me a while to make the association but I think it was going over a railroad track when i felt the body twist and felt the rebound spring/giggle it felt exactly like the Z28 with the top down.

In addition the big risk is defomation in a crash. If wife's car hits something solid on one corner it's screwed. There is virtually nothing to keep the car from turning into a parallelagram. The "thin plate" can handle at least 50-70,000 pounds of shear strength and that is enough to keep the car rectangular in a minor crash.

Now: onto the bolts. If you reuse them and don't torque them you will not get the main point of the plate; stiffening the body. The bolts are designed to be torque to yield to achieve about 10,000# of clamping force per bolt. 60,000# total. If you just snug them you will get 500-2000# each or 3000-12000# total which is meaningless as a stiffening plate and will just be a skid plate.

I did destructive testing on a few bolts and they withstood the full torque to yield about three more times before internal failure and broke in half at 5-6 times. One guy suggested use 45° vs 90 to achieve a decent tightening force which seems reasonable but probably is half or less the design force dropping to 20-30,000#. Probably enough to improve the suspension handling but not enough to help in an accident.

A better option is to use bigger bolts. Upgrade to 12mm or 1/2" and normal torque (Unlimited reuse) will achieve the clamping force needed to achieve the design requirements and you can buy the bolts for $2@.

Also there is nothing special about the bolts to make them so expensive save the captive washer and flareed head. The nuts are squashed to make them locking but you could do the same with a vice and new nuts as well.

If memory serves, they are M10-1.5 10.9 50mm length. If you can find 12.9 same size you can also achieve the 5T force without damaging the bolt and re-use then as often as you want.

So: now your are actually Informed. Use the new information as you wish and stop guessing. After at least 6-7000 miles my wife's car is not coming apart at the seams without the plate it's just wiggly and giggly. Re-use of the bolts can be done to some extent but after about 4 total applications they will fail to apply the design force and stop doing the job of the active part of the suspension.

I have driven the X5 with "snugged" bolts and did in fact notice: still jiggly and also noticed when I replaced and torqued the bolts that the plate had moved around under the bolts because they weren't tight. That awesome "feels like a sports car" feeling of tight suspension comes largely though the stiffening plate which does exactly as the name suggests.

Those are the facts. Other suggestions are mere unsubstantiated speculation. No the car won't self destruct without the plate, yes the bolts will self destruct after about 4-5 applications at factory torque specs. No the plate will not do its job with the bolts snugged tight.

I had my plate off for about a week and I couldn't stand the wiggles and had to put it back on. Wife not a performance driver and doesn't notice.
__________________
2011 E70 • N55 (me)
2012 E70 • N63 (wife)
Reply With Quote

Sponsored Links