Cheap Chassis Bracing Bits You Can Buy And Bolt In

[MrStabby]

On 2/28/2014 at 10:40 AM, GTSBoy said:

Almost anything that goes flat across the underside of the car can only do precious f**king little. If you do not box something in in 3 dimensions, then you are adding almost no resistance to twist. And twist is what YOU want to get rid of. And all those braces are pretty much only 2D.

/engineering.

Question about chassis rails then; do they do fark all WRT chassis rigidity? AFAIK they're just shallow box sections running front to rear, so I cant see how they would provide much resistance to flex in any dimension compared to the contribution of the roof. And if that's true, then the defects you get from bashed up chassis rails is wankery...

[GTSBoy]

52 minutes ago, MrStabby said:

Question about chassis rails then; do they do fark all WRT chassis rigidity? AFAIK they're just shallow box sections running front to rear, so I cant see how they would provide much resistance to flex in any dimension compared to the contribution of the roof. And if that's true, then the defects you get from bashed up chassis rails is wankery...

On their own they're not very stiff.  Welded to the floor, which is welded to the pillars and the bulkhead and boxed by the roof, they certainly do add to the overall rigidity.  The shape that they are helps lot too.  They have the arches up and over the rear axle area which is worth something.  You'd certainly notice a car being a lot more flexy with them not there.

But yes.....defects for dents in the underside is the cops/RTA having a bit of a rub.

 

[hardsteppa]

from what I've seen since I started looking at brace designs, large areas of the car seem to just be pressed/shaped sheet metal. So nothing in them really to stop twist once any kind of load is put into the chassis. So putting a brace with very little flex from one solid point to another across the car then creates a bridge anchoring the 2 points rather than it just being the thin sheet metal. It won't make it 'immovable' like a 3d-rollcage structure would but does do a lot to reducing the bendiness overall.

The R33 (and prob 32's and 34's) have a ladder-type brace/boxed section running across the floorpan going across at the front of the front seats which stops at the transmission tunnel. I made a small brace that goes underneath the car and joins these 2 sections crosswise across the car (also creating a square-boxed section at this point of the trans tunnel) as well as spot-welded the crosswise box sections along their length and this small mod made a noticeable difference to the flex feel of the front half of the car when cornering, holding the car much flatter.

[hardsteppa]

ok so finished the latest brace; this runs crosswise under the car at the end of the transmission tunnel. Replaces the piddly brace(?) thing that's standard on r33 gtst's, and mounts there and also at each end in 2 places. I feel I've kept an open mind trying to avoid any bias or placebo effect but goddamn....rear end feel like it's glued to the road now, it's seriously planted. It's made in 2 pieces to fit under the tailshaft and over the exhaust, and bolts together to form one piece when fitted. Just needs 1 8mm hole drilled next to the stud that's already there to make a total of 4 mounting points in the middle, other than that it bolts to existing factory points, total of 6 mounting points across the car.

[MrStabby]

Very nice. Would be cool if you went to the track and got some mates to randomly add or remove the brace without telling you before each session, both of you keeping notes, then compare at the end to see if you can pick it. There's no escape from confirmation bias. But testing like that is too much work, so maybe just compare track times?

[260DET]

One feature I find a bit lol is strut bars that connect to the strut tops via rod ends. yet they are so common. I'm all for bracing, depends on the model of car of course but generally laterally and vertically where the front chassis rails butt against the firewall is worth doing. Did a triangular engine bay brace back to the firewall horizontal rib on the Zed and that certainly changed the handling, took a while to get used to but all good.

[MrStabby]

1 hour ago, 260DET said:

One feature I find a bit lol is strut bars that connect to the strut tops via rod ends. yet they are so common.

They're not completely dumb, as long as they have a turnbuckle in the middle and they're tensioned up after the install. Pulling the upper arm mounts together makes them more rigid.

[GTSBoy]

1 hour ago, MrStabby said:

They're not completely dumb, as long as they have a turnbuckle in the middle and they're tensioned up after the install. Pulling the upper arm mounts together makes them more rigid.

 

Well....no.  If there are pin connections at each end of a strut brace, then said strut brace has no ability to prevent both towers moving in the same direction.

Imagine a square made up of simple lines.  The top line of the square is the strut brace, the bottom 3 lines represent the steelwork of the car.  At all 4 corners you have pin connections that permit rotation.  The top 2 pins represent those that are in the ends of the strut bar, the bottom 2 pins represent the lack of complete rigidity in the car's steelwork that is the reason why we want to add a strut brace.

Now simply push the top corner of the square sideways.  This is the same as putting loads into the suspension/body of the car such that both towers are forced in the same direction.  Because all 4 pin joints freely allow rotation, the square will fall sideways into a rhombus, then fall flat.  If you replace the top 2 pin joints with fixed joints that do not allow rotation, when you push the top sideways, these joints resist the force you're applying and prevent the square deforming.  The weak joints at the bottom would be happy to let the top move around, but the top won't.

Therefore pin joints at the end of strut bars are a silliness, and also therefore MOST strut bars are a silliness because most of them are thus equipped.  It's true, such bars do keep the tops of the towers the same distance apart, but what they don't necessarily do is keep the tops of the towers in the same place relative to the lower suspension pickup points.

Edited December 21, 2016 by GTSBoy

[MrStabby]

Agreed, if the assumption that the lower joints can be considered pins, but they will have some resistance as they are not pinned. I guess I should correct myself and say that pinned strut bars are "not useless", rather than that they're "not completely dumb", because it is dumb to pin something that's better not pinned.

I am assuming that the flexibility in the tower is non-linear, and that the preloading pulls the towers up to a point where stress vs strain is higher than when not preloaded.

[GTSBoy]

I just made the lower joints pins in the thought experiment so it was clear that the bottom half of the structure had flex in it that we were trying to box up.  So the car isn't as flexible as pure pinned joints, but if it has enough flex in it to warrant a strut bar, then it has enough to warrant doing the strut bar properly.  Pinned strut bars are at least as much for cosmetics as they are for anything serious.

All this is also ignoring the fact that Skylines don't even have struts so only gain a small portion of the benefit available from a strut bar.  All the suspension pickups on a Skyline are sufficiently close to the frame rails that the subframe is what keeps them apart. The only strut bar I have time for on Skylines is the one that goes back to the firewall - which also has fixed ends.  And even that is not because it stops the top of the towers moving from side to side so much as it adds to the longitudinal vertical stiffness of the front of the car, somewhat like those A-pillar inner guard braces do.

[MrStabby]

Re: A pillar inner guard braces, worthwhile? These right (UR-FD3-188 in the link below)

http://www.uniqueautosports.com.au/Parts-Shop/ultra-racing-front-strut-bar-and-fender-bars-588.aspx

[GTSBoy]

I've not had an opportunity to compare a car with/without them, but I'd be willing to be that the A pillar bars would do a reasonably good job of adding stiffness into the front of a lot of cars.  So long as they are nice and stiff in themselves, they look like they should prevent the front end going up-down relative to the firewall/floorpan, which can only be a good thing.  Ideally the strut bar that goes with it in that kit would also go back to the firewall centre.

[260DET]

3 hours ago, MrStabby said:

Re: A pillar inner guard braces, worthwhile? These right (UR-FD3-188 in the link below)

http://www.uniqueautosports.com.au/Parts-Shop/ultra-racing-front-strut-bar-and-fender-bars-588.aspx

Will be fabricating something like those for the project Z, will be welded in place though.

[hardsteppa]

the pin/hinge type strut braces -  there is friction there (with mounting bolts being tightened) so not like they're free to just pivot freely. However I don't like them cos you're wanting to add stiffness but yet add flex-points into the brace? A one-piece item is a much better option.

As for a-pillars, yes noticed a much more solid feel to the car at higher speeds with this although also fitted a 1-piece strut brace on the front at the same time. I would imagine most benefit came from the a-pillar braces though.

[dr phil]

Just tried to fit a R33/34 GTR 3 piece floor brace to my R34 GT Four, the one that goes under the rear seat, and under the tailshaft. Despite the GT4 having the outer bolt holes, and 4 studs near the tunnel (3 used from factory) - the GTR brace DOES NOT fit.

2 things are different, the studs in the body are larger diameter in GTR, and they have a slightly different spacing.

Mr Nissan does not want you to turn your GT4 sedan into a GTR without a fight!