Dyno strapping points

[zaq123]

Where do you guys strap e30 for the chassis dyno run?

The last time I had it on the dyno, tunner did front wheels but the rear he was talking about taking the muffler off. Luckily we didn't have to do it and he strapped at the rear subframe. Was a pain sort of and took awhile to find good points as the rear control arms were on the way a little. Left control arm paint got scratched a little from the hook after the run, which isn't a big deal but still.

Are those towing tie down brackets that go between rear shock and the control arm good enough to hold the car down? What do you guys normally do?

garagistic steel tow tie downs

[zaq123]

anyone used these ?

[TobyB]

Is that a flat hook bolted in- between the shock and the trailing arm???

That looks... more than slightly terrifying, especially for dino-sawer work...

I've used the factory tie- down slots for putting the factory tiedowns in
(Turner had a sale, and I had TurnerBux)
and those are pretty robust. But that's just for trailering- I'm too cheap to dyno.
They engage well, and feel solid in the chassis.

Why can't you just strap the rear wheels???
(heh)

t

[zaq123]

Is that a flat hook bolted in- between the shock and the trailing arm???

That looks... more than slightly terrifying, especially for dino-sawer work...

I've used the factory tie- down slots for putting the factory tiedowns in
(Turner had a sale, and I had TurnerBux)
and those are pretty robust. But that's just for trailering- I'm too cheap to dyno.
They engage well, and feel solid in the chassis.

Why can't you just strap the rear wheels???
(heh)

t

Why terrifying? They recommend to have two 10000 lbs rated rear straps ~500hp car. I think 500 hp V8 car can produce like 3500-4k lbs of real world pulling force. Shear strength of e30 M12 8.8 shocks mounting bolt is 9500 lbs at threads (single bolt0. Those brackets are steel, not aluminum. So I'd think 2 of them should do the trick?

[TobyB]

Terrifying because it's some red metal bolted in- between the lower shock sleeve and the single- shear shock bolt at an angle.
And in the pic, it's not even aligned with the force that'll be put on it, so it's going to rotate when loaded.
And it has open hooks, too...

Will it work? almost certainly.
Will it break? most likely not.
As you say, that's all way- over- beefy hardware back there.

But from a force transfer standpoint, BMW didn't design that point
to take load in that direction, the bolt's being twisted by the off- axis load,
the shock sleeve is usually just a little wrap of sheet metal
(which limits clamping force on the bolt)
and it's pulling directly on the trailing arm, so the suspension is not available
to take the shock loading of an irregular wheel or roller.
(I'm thinking of the first year of wings in racing, when they did similar, and shit broke catastrophically)

For a tiedown in a trailer, where there's almost no real loads,
I'm sure they're fine. If one starts to distort, you'll catch it when you unload.
On a dyno, I watch too many 'dyno fail' videos, and when a strap loosens,
you almost always get to see a car slide off the side of the thing.

I'm probably overthinking it. I always do. But I'd come up with a different way,
just from personal preference, prejudice, and paranoia.
I break enough shit that I think is 100%....

Oh- also. This is for realz: gated hooks are sooooo much safer than the open hooks in that picture.
If it loses tension for a second, you don't want the hook to fall out!

t