Jacking Rails Improve Stiffness???

[Radiation Joe]

Can anyone comment on the improvements in chassis feel/performance from welding in jacking rails?
Is the car stiff enough already that the rails don't make much difference? Way back when, I welded in "subframe connectors" that actually made a difference in my 1990 SHO. Do they make a difference in the S550?
Thanks.

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[WildHorse]

Jacking rails & Subframe connectors are entirely different.
SC are welded in as you said, JR are bolted in a couple places and will flex.

 

[paulm1]

Not sure about the S550 but I put the sub frame connectors / braces in my fox body way back when, it helped a lot. the s550 does not feel like it has a lot of body flex. What did help a lot though was the factory strut tower brace system up top and the g-track brace from steeda underneath. I put the stop the hop kit in the rear as well. Car felt a lot better after, turn in and response much better.

 

[MAGS1]

Having had the jacking rails on two different S550’s now (and having driven them both with and without the rails) it does feel like the rails provide a little more rigidity to the body, although I agree with the above that there’s not much body flex in the S550. I got them for the ease of jacking up the car to change tires, the added rigidity is just a plus for me

 

[tj@steeda]

It's a secondary benefit but not something we tout as part of the benefits of the Steeda Jacking Rails.

If you are interested in the Steeda unit, here are some differences on paper:

 

[bnightstar]

Can anyone comment on the improvements in chassis feel/performance from welding in jacking rails?
Is the car stiff enough already that the rails don't make much difference? Way back when, I welded in "subframe connectors" that actually made a difference in my 1990 SHO. Do they make a difference in the S550?
Thanks.

There is a noticeable difference in stiffness when you install Jacking Rails. And make the rear fill more connected to the front but not as much as a difference than say IRS Base kit. The biggest benefit is that the jacking rails make it easier to get the car in the air so any time you work on the car they help. Totally worth it upgrade for me.

 

[WD Pro]

OK, I'm going to be the awkward one, again ...

I struggle to see how connecting two points (with holes 1, 2 & 3, 4 on the below diagram), that are only separated by the same box section steel can have any noticeable benefit ?

There's no triangulation going on and no cross bracing from one side of the car to the other etc.

Are the chassis rails really moving enough in that plane to get a noticeable difference ... ?

It's a secondary benefit but not something we tout as part of the benefits of the Steeda Jacking Rails.

If you are interested in the Steeda unit, here are some differences on paper:

With reference to the above - if the Steeda's marketing guys haven't even jumped on it, I think that tells us all we need to know ...

@tj@steeda - If there is a genuine benefit, why not make a system where the jacking rail is truly full length (including your IRS mounting points and the empty hole behind them), that bolts on using all 7 holes per side and with a slightly modified IRS brace that bolts on through the rail using the existing holes (5 & 6) ?

If the rails genuinely add stiffness, the above suggestion would give you an improved fully braced rail and all the existing benefits of your IRS support braces

WD

 

[bnightstar]

OK, I'm going to be the awkward one, again ...

I struggle to see how connecting two points (with holes 1, 2 & 3, 4 on the below diagram), that are only separated by the same box section steel can have any noticeable benefit ?

Mine are full length ones for Kenny Brown and the do add noticeable difference in stiffness of the chassis. As I said you can feel what the rear is doing a bit more.

 

[S550 Recon]

No.....

 

[Cobra Jet]

OK, I'm going to be the awkward one, again ...

I struggle to see how connecting two points (with holes 1, 2 & 3, 4 on the below diagram), that are only separated by the same box section steel can have any noticeable benefit ?

There's no triangulation going on and no cross bracing from one side of the car to the other etc.

Are the chassis rails really moving enough in that plane to get a noticeable difference ... ?



With reference to the above - if the Steeda's marketing guys haven't even jumped on it, I think that tells us all we need to know ...

@tj@steeda - If there is a genuine benefit, why not make a system where the jacking rail is truly full length (including your IRS mounting points and the empty hole behind them), that bolts on using all 7 holes per side and with a slightly modified IRS brace that bolts on through the rail using the existing holes (5 & 6) ?

If the rails genuinely add stiffness, the above suggestion would give you an improved fully braced rail and all the existing benefits of your IRS support braces

WD

You're correct, there isn't any benefit from installing "jacking rails" OTHER THAN being able to jack up a vehicle WITHOUT crushing the "pinch welds" of where the body shell sheet metal is joined.

Knowledge sharing for others who are new to Mustangs:

The pinch weld is the location under the driver or passenger side rocker and is the junction where the floor pan meets the rocker - two entirely separate pieces of stamped/formed steel that is welded together to make part of the "unibody".

All Mustangs since inception have a pinch weld (as do other vehicles) and the Mustang is also a unibody design with no actual frame separate of the body.

By placing a jacking rail next to (or even if over) a pinch weld only provides a rigid base to jack the vehicle. It's NOT joining the front and rear floor pan "sub-frame rails" together as a sub-frame connector is designed to do.

The only other way a jacking rail could be a benefit would be if the car wrecked and the inertia or forces that be tried to bend the floor pan in half front to back where that rigid "bar" may not give - but if the forces were great enough, would just pop or rip the bar from its bolted location.

---

Sub-frame connectors for an unibody vehicle are designed to join the front and rear frame rails together, where there is a gap between the front and rear rails.

On a unibody vehicle like the Mustang and with prior models to the S197, the L & R FRONT rails are sometimes "box-like" and could be separate from or integrated into the floor pan. They are normally located about 12"+ inward from the rocker towards trans tunnel, extend from the base of the fire wall floor pan and terminate just before the driver and passenger seats.

The REAR frame rails were again similar to the front, but start at further rear point of the rear uni-body, run along the rear floor pan and again usually terminate just under or just after the rear seat bottom location.

The idea behind sub-frame connectors is that it creates a rigid and now structural join that reinforces the large "gap" under the floor pan, joining the front and rear unibody together. This is beneficial for forces placed onto the vehicle from extreme use as in drag racing, road racing or even auto-X where the body is susceptible to forces beyond normal daily driving - and forces that could (and in some cases do) warp, bend, contort or damage the sheet metal when NOT joined by sub-frame connectors.

Sub-frame connectors came two ways:
- straight tubular OR boxed steel that was about 4ft in length and could be bolted through the ends of the front and rear sub-frame OR welded onto and along the lengths of the front and rear sub-frames which crates the "join".

- same design as noted above, BUT the secondary design came with cross bars that could be bolted or welded to the floor pan under the front seats. That secondary rigid piece of steel once installed with the sub-frame connector created a "T" shape. The cross bar would be mounted under the front driver seat and front passenger seat (1 bar per side). The bar was secured through the front seat bolts that go through the floor pan and were approx 1.5ft in length. This extra bar provided rigidity and support directly under the front seat area by not only tying those bolts together for the seat, but it was against the floor pan under the seating area and created more rigidity to floor pan for when (mainly driver seat) sees extreme forces of body weight transition.

Sub-frame connectors and jacking rails serve totally different purposes and are 2 totally different designs.

I'm not sure how anyone who has purchased jacking rails can "feel" anything.... it's placebo. The rockers and the steel surrounding the rockers is quite rigid in itself, and is one of the stronger areas of the unibody design and floor pan ... You could take a wooden 2x4, cut a trench in it, place it over the pinch weld and still jack the car just as one could with steel bolted on jack rails - there's no benefit to tying a unibody together under the pinch weld like sub-frames. You're not strengthening any gaps or the floor pan of the unibody design - because the ROCKER and the join of the rocker and floor pan structure already serves that tie-in purpose.

Want to add purpose and true rigidity - tie in the front and rear unibody where it matters and counts.

 

[ice445]

It does make a marginal difference, it's easier to lift rear tires than on a stock car. My street has a very steep incline that's also rolled over, so traveling up it creates substantial twisting forces in the unibody. While the chassis is very strong by default, these rails seem to reduce some amount of droop when the front is on the ground and the rear is not fully supported by the ground.

If I had to guess it would be like a 5% difference, enough that I noticed something but not enough to where it's doing anything useful. The above explanation is comprehensive but ignores the fact that the entire unibody is subject to deformation from twisting forces. It's the same reason people have issues with the seams cracking on the corners where the rear glass is laid on some cars. I suspect that the bolt holes left by the factory robot carrier things are threaded far enough through that the jacking rail "boxes" the lower pinch weld reinforcement with another layer, probably one for side impact protection which ends up increasing stiffness fore to aft by some minor amount. But I'm no engineer.

 

[SH!FT]

Can anyone comment on the improvements in chassis feel/performance from welding in jacking rails?
Is the car stiff enough already that the rails don't make much difference? Way back when, I welded in "subframe connectors" that actually made a difference in my 1990 SHO. Do they make a difference in the S550?
Thanks.

Cobra beat me to it.

I have Steeda's Ultra-Lite Low-Profile Full Length jacking rails. Their super convenient for getting the front and rear tire on one side off the ground quickly with a pump jack. I'd go with their shorter version (exposes the factory jack points) if you have a legit lift or have a shop do work.

Check out Steeda's description for the 555-5754 IRS Subframe Support Braces. Sounds like more of what you're looking for.

Here's what I'm about to install:
Steeda 555 5532 Extreme G-Trac K-Member Brace
Steeda 555 4438 IRS Subframe Alignment Kit
Steeda 555 5754 Rear IRS Subframe Support Braces

 

[derklink]

Cobra beat me to it.

I have Steeda's Ultra-Lite Low-Profile Full Length jacking rails. Their super convenient for getting the front and rear tire on one side off the ground quickly with a pump jack. I'd go with their shorter version (exposes the factory jack points) if you have a legit lift or have a shop do work.

Check out Steeda's description for the 555-5754 IRS Subframe Support Braces. Sounds like more of what you're looking for.

Here's what I'm about to install:
Steeda 555 5532 Extreme G-Trac K-Member Brace
Steeda 555 4438 IRS Subframe Alignment Kit
Steeda 555 5754 Rear IRS Subframe Support Braces

What is the benefit of exposing the factory jack points (with the shorter version)?

 

[WItoTX]

Plenty of autox buddies have them, and say they do improve stiffness. I went the other direction, that the gain in weight is not worth it.

TBH, I don't think there is a right answer. A little more body flex for a little less weight sounds good to me, but others may want a little less flex. But my opinion, less weight > stiffness. I would deal with even more flexi-ness, if it meant my car lost another 100 lbs.

 

[Radiation Joe]

Thanks for all the replies.
When I ask about increased stiffness, I'm thinking about lifting a wheel when exiting a driveway at an angle kind of stiffness. Subframe connectors did that for the SHO. I think I won't see that kind of improvement on an S550. I've already got the Steeda 4pt in the front and semi-solid mounted subframe in the rear. Guess I should be happy with that on the street.

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