Chassis stiffness

[Revvdmedia]

In my OPINION, the chassis in the Stinger is acceptably rigid. The "driveway test" which does exert torsional twist on the chassis could be a measure of chassis rigidity, but can also be obscured by suspension compliance as well. I'm not an engineer, but I am gifted with the ability to reverse engineer and use analysis to understand the workings of complex mechanisms. Using my skills, I use the "driveway test" as my qualitative measure of torsional rigidity. I have used the same driveway daily for 3 years with 3 vehicles. Vehicle #1, and not very relevant in this test other than design similarities (hatch, 4 doors, big sunroof) is my wife's 2013 Hyundai Santa Fe. When ascending or descending the driveway, the vehicle does exhibit some flex. How much of this flex is suspension movement and how much is chassis movement is difficult to discern, but it is noticeably less stiff than Car #2 and Car #3. Car #2 was a 2015 Ford Mustang GT with the base suspension package and no other chassis stiffening added. When performing the driveway test, the Mustang is noticeably stiffer than the Santa Fe, but did exhibit some compliance or flex. Car #3 is the Stinger GT. When performing the driveway test, I feel the chassis is stiffer than the Mustang GT. When going up the driveway, it feels as though the underpinnings of the chassis remain rigid, as if the floor remains completely straight and solid, more so than the Mustang ever felt. All things being considered, I feel the suspension stiffness between the Stinger GT and Mustang GT is very similar when driving over the same sets of roads with bumps, seams and frost heaves. This comparison was running 19" wheels on both cars, but the Mustang's were wider but with a taller sidewall, and Pilot Super Sport (Mustang) vs. Pilot Sport 4 (Stinger). I feel the Stinger is at least as rigid as the Mustang was, if not even more. I don't recall many complaints on the 2015+ Mustang GTs regarding a jiggly chassis.

 

[MerlintheMad]

I don't recall many complaints on the 2015+ Mustang GTs regarding a jiggly chassis.

But "noise"? This subject came up because of "pops" "creaks" and "rattles" from the doors, hatch and sunroof. The asserted culprit has been the Stinger's "flexing chassis", which "needs" stiffening: and then the complaints/observations increase that now the sunroof is noisy "one hundred percent of the time", after the mods already applied; which tempts the fiddler/modder into further indiscretions to eradicate the new or increased noises.

 

[Revvdmedia]

But "noise"? This subject came up because of "pops" "creaks" and "rattles" from the doors, hatch and sunroof. The asserted culprit has been the Stinger's "flexing chassis", which "needs" stiffening: and then the complaints/observations increase that now the sunroof is noisy "one hundred percent of the time", after the mods already applied; which tempts the fiddler/modder into further indiscretions to eradicate the new or increased noises.

Honestly, commenting on noise in the Mustang cannot lodge any comparison to the Stinger. As commented by the review from Youtuber Savagegeese on his 2015 Mustang review, the Mustang - including mine - was quite literally a "symphony of creaks and rattles." Door panels creaked, dash panels cracked, driveline popped, and the rear end started creaking badly before I traded it. It was a fun car to drive spirited, but not fun to commute and travel in. All these complaints surfaced from the first year and became worse by the time I traded it at 20K miles.

I don't feel my Stinger (which only has about 500 miles so far) has any noises attributed to major chassis deficiencies. I will get a very occasional "tick" which sounds like it comes from the door frame, but I believe the felt padding as noted in the DIY section of this forum would fix it. The door striker spacer would likely also help. Compared to what I came from, this Stinger is almost completely silent. I sure hope it stays that way.

 

[MerlintheMad]

Compared to what I came from, this Stinger is almost completely silent. I sure hope it stays that way.

LOL! My previous daily drive was a '94 Voyager with five on the floor. Imagine the contrast for me.

 

[TigerGrillz]

A lot of good, useful information here. The thing I don't like is how the car's rear end can get upset over bump in the road and how disconcerting it feels in corners, on the street. I don't track my cars, they are my daily drivers but I like to have some fun at times and there are some places that the car rear end bounces more than I want it to.

I've only had my Stinger for 3 months - this does concern me too.
In AU the only GT available is RWD and I'm surprised how easy when going around a curve and running over a lump or seam in the road the rear end noticeably swings out and re-grips.
This and the chassis stiffness got me a little worried - all my cars prior (last one was a 2006 Mitsubishi 380 (aka Galant) and it had MUCH more stiffness than this.
Do you think this extra flex will in time damage the chassis/fittings/seals?
Will this happen during its 7 year warranty?

 

[Stinger GT SS]

I've only had my Stinger for 3 months - this does concern me too.
In AU the only GT available is RWD and I'm surprised how easy when going around a curve and running over a lump or seam in the road the rear end noticeably swings out and re-grips.
This and the chassis stiffness got me a little worried - all my cars prior (last one was a 2006 Mitsubishi 380 (aka Galant) and it had MUCH more stiffness than this.
Do you think this extra flex will in time damage the chassis/fittings/seals?
Will this happen during its 7 year warranty?

Just a note the 380 has a shorter wheel base by 160mm, although I do agree on the rear end wiggle that’s why I’m fitting Eibach front & rear sway bars I’m hoping this with greatly reduce or eliminate this issue.

 

[Dick Dastardly]

Interesting thread and covers a lot of bases. From my perspective:

- The creaks and noises from the doors / sunroof seem to be temperature related and can be heard even when washing the car and pressing on panels. So for me the noises are not about structural rigidity but the quality (or otherwise) of the plastics / rubber.

- For a long vehicle, with 5 doors and rear folding seats I think the chassis stiffness is pretty good and for fast road driving I can not feel any kind of flex but have not yet tried it on a track (but that is not why I bought it!).

- Rear movement on my car seems to be related to the LSD and is actually more marked since I had the diff oil replaced. I actually like that but again not sure if that has anything to do with chassis stiffness. Too little movement makes a car in my opinion rather clinical and soulless but probably faster. Guess this is the difference between a GT and Sportscar.

- Suspension on the car overall is good. I can not feel a huge difference between Sport and Comfort mode but certainly can not feel any difference in terms of effect this has on chassis flex in either mode.

Overall I think the balance between comfort and stiffness is well judged and the car does what it was sold as, being a long distance comfortable GT.

 

[Stinger GT SS]

Interesting thread and covers a lot of bases. From my perspective:

- The creaks and noises from the doors / sunroof seem to be temperature related and can be heard even when washing the car and pressing on panels. So for me the noises are not about structural rigidity but the quality (or otherwise) of the plastics / rubber.

- For a long vehicle, with 5 doors and rear folding seats I think the chassis stiffness is pretty good and for fast road driving I can not feel any kind of flex but have not yet tried it on a track (but that is not why I bought it!).

- Rear movement on my car seems to be related to the LSD (Limited Slip Differential) and is actually more marked since I had the diff oil replaced. I actually like that but again not sure if that has anything to do with chassis stiffness. Too little movement makes a car in my opinion rather clinical and soulless but probably faster. Guess this is the difference between a GT and Sportscar.

- Suspension on the car overall is good. I can not feel a huge difference between Sport and Comfort mode but certainly can not feel any difference in terms of effect this has on chassis flex in either mode.

Overall I think the balance between comfort and stiffness is well judged and the car does what it was sold as, being a long distance comfortable GT.

A good summation on this & I agree with most of your comments except, I have not experienced creaks & noises & In OZ the suspension has been specifically tuned to our conditions & sport mode is considerably firm than comfort which makes a great variation of styles when driving.

 

[Dick Dastardly]

In OZ the suspension has been specifically tuned to our conditions & sport mode is considerably firm than comfort which makes a great variation of styles when driving.

Interesting to hear that and would have been good here in the UK where we have big differences in road surface quality. For me the biggest difference between modes is the gear shifting / throttle response which is very noticeable (+ve).

 

[Waynerm002]

I'll agree the difference doesn't feel significant when going into Sports mode however, I can feel the firmness and when you hit bumps it is enough that you feel it and it can cause the rear end to bounce. In sport mode this is more pronounced if you are going fast and in a turn, it is a bit disconcerting to me. Now, I'm not pushing the car hard on most of my drives but at times when I want to, this is when things get that way. Waiting for my rear sway bar to see how that does.

 

[Dick Dastardly]

I'm surprised how easy when going around a curve and running over a lump or seam in the road the rear end noticeably swings out and re-grips.

I notice this as well but I think what is happening is that the limited slip is allowing a certain amount of oversteer and then the ASR is cutting in.
In sport mode the drift should be more pronounced before ASR cuts in.

I seem to remember the Galant used to have 'active yaw control' fitted to reduce this effect, which might be the difference between the cars?

 

[Tonkabob]

@CaliSting and @eflyguy, you two guys made my day. Thanks for the comments and personal observations. This is what I was hoping to hear: gearheads talking from a lot of experience. It's one thing to talk about how much the driver determines how well the car does. And it is germane to the topic of chassis "torsional rigidity" to point out that making a chassis more rigid is justified by lower lap times, but not to pursue higher performance at the expense of a good ride as a daily driver. I especially like the observation that heavy testing and practice are the only ways to determine if a car is working out. Start with a really good driver and then throw cars and changes at him (her?).

This all started by some assertions that the Stinger needs to be stiffer to reduce extraneous noise, implying that Kia somehow cheaped out where they shouldn't have. I'm even further convinced, after these few responses on this thread, that there is no basis for such assertions; that stiffening, chassis and suspension, is more likely to take a well designed car and Ef it up, creating noise where there was none before, and/or worsening noise that was already there.

Chasis stiffening parts should be on in the next few days. I'll let you all know if the twist induced sun roof rattles are gone and if there is less noticable twist and in my off camber driveway. Re- paint is on week 3 but should have the car back today or tomorrow.
I know everone loves thier stingers as do i but, but there is no denying this is one flexy beast for a modern sporty car. Doesn't mean it still doesnt handle well. Stiffening the chasis will only do good things. Thats why kia tried to make it stiff but hard to do with one of the largest trunk / hatch openings around.

 

[Tonkabob]

I notice this as well but I think what is happening is that the limited slip is allowing a certain amount of oversteer and then the ASR is cutting in.
In sport mode the drift should be more pronounced before ASR cuts in.

I seem to remember the Galant used to have 'active yaw control' fitted to reduce this effect, which might be the difference between the cars?

I think the general consensus is the car is under damped and when you hit that mid corner bump the rebound un weights the back tires a bit reducing traction and giving a slight slide or about to slide feeling. And the wallow is unsettling in general.

 

[Waynerm002]

I think the general consensus is the car is under damped and when you hit that mid corner bump the rebound un weights the back tires a bit reducing traction and giving a slight slide or about to slide feeling. And the wallow is unsettling in general.

That's exactly the feeling right there.

 

[MerlintheMad]

Stiffening the chasis will only do good things. Thats why kia tried to make it stiff but hard to do with one of the largest trunk / hatch openings around.

It will only do good things to the handling and lapping speed. But noise-wise? I don't expect that stiffening will reduce noises in any way. But good luck! I only want the best experience for everyone. If something doesn't work out, you'll try a different approach. My approach is to leave the car alone, to quote again: "Just drive the damn car. Don't try and stand it on its bloody ear!" I want my car quiet and fast. And I am not a gearhead or member of the "mod squad". So, I go with what I got and trust it is well designed to perform the task we read about: comfortable, luxurious long distance driving with high performance at our fingertips.

 

[Ozstung]

I'll agree the difference doesn't feel significant when going into Sports mode however, I can feel the firmness and when you hit bumps it is enough that you feel it and it can cause the rear end to bounce. In sport mode this is more pronounced if you are going fast and in a turn, it is a bit disconcerting to me. Now, I'm not pushing the car hard on most of my drives but at times when I want to, this is when things get that way. Waiting for my rear sway bar to see how that does.

Like you im going to go down the rear sway bar route. The eibach springs had little effect on rear wallow. Not that they probably should have?

 

[Tonkabob]

Chasis stiffening parts should be on in the next few days. I'll let you all know if the twist induced sun roof rattles are gone and if there is less noticable twist and in my off camber driveway. Re- paint is on week 3 but should have the car back today or tomorrow.
I know everone loves thier stingers as do i but, but there is no denying this is one flexy beast for a modern sporty car. Doesn't mean it still doesnt handle well. Stiffening the chasis will only do good things. Thats why kia tried to make it stiff but hard to do with one of the largest trunk / hatch openings around.

Ok finally got my car back from repaint and got my mid/rear and rear Ultra racing chassis braces on. I had recently installed the front sway bar and noticed a significant increase in chassis flex on bumpy roads and off camber driveway - and with that additional creaking. The mid/rear braces front mount is right between the two doors and the rear brace most the way back behind the spare tire well. This is hard to measure, but the driveway twist is certainly not gone but i would say reduced by 30-50%. On bumpy roads the car is quieter as well. I think with the bracing i am less flexy than stock before i added the front sway. Not much, but slightly better. I was still noticing my sun roof noise on very smooth roads, so that one may not be chassis flex or is caused by very minor chassis flex that probably cant by fixed by stiffening. I did apply a fresh coat of silicone lube to the sun roof seals today (2nd time) and it is quiet again. There is a front 4 point brace that mounts around the transmission and that probably stiffens more of the sunroof area than the mid/rear brace that i did not buy.
Warning on the mid/rear chassis brace - its a tight fit with larger diameter aftermarket exhaust. I spent hours adjusting the brace and exhaust to get them not to touch and rattle. Driver side of my Ark exhaust was fine but passenger hung a little lower.

Installation notes: Rear brace - be sure to be on jack stands not ramps or the car body may disconnect from the sub frame! Mid/Rear brace can be done on jacks or ramps. On jacks the front mounting point shares a bolt with the brace under the exhaust and another diagonal brace. The chassis flex (from the jack points) was enough that i could barely get the bolt back in as the diagonal brace as it pulled away from the hole. So ramps probably better for the mid/rear brace.
Now if only anther $200 would fall from the sky so i could try that 3rd brace....

 

[Jwolf]

Like you im going to go down the rear sway bar route. The eibach springs had little effect on rear wallow. Not that they probably should have?

I can't say anything about sway bars as I don't have them, but I can say that with springs on the standard GT RWD (fixed suspension) the rear is planted. So it could be that stiffer shocks would do the trick too.