littlebear
Member
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- 2017 Mazda CX5
I've seen a front tower strut brace on a CX5. What do they do ?
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Front Tower Strut Brace
- Thread starter littlebear
- Start date
True. As a matter of fact, the CX-5 comes with a lightweight strut tower brace. It's located under a shroud just aft of the strut towers. Perhaps with racing rubber mounted and on a grippy surface this lightweight brace could be over-whelmed but for normal use it's more than adequate and it has been crash tested. A stronger aftermarket brace could conceivably compromise the frontal impact performance.
I had a medium clicking noise on hard cornering. It only happened occasionally but sounded like a "tick" or "tock" sound that happened sometimes shortly after initiating a sharp turn at slower speeds. I traced it down to the bolts holding the OEM brace to the strut towers. Tightening them up made the sound go away (and it hasn't returned in a years time). I suspect these bolts were too loose as the brace is bolted on after the car has been painted.
Could you post photos? I don't know which bolts you mean.
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- San Antonio, Texas
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- '15 CX-5 Miata AWD
They reduce flexing between the tower struts in cornering, which can help keep wheel alignment in check while doing a hard corner. Over time the little stresses can cause mm of movement in the shock tower (and if you keep your car long or drive it hard, could actually affect alignment). If you put a stb on a car, cut it down the middle and jack one side, on most cars the bar will become uneven; basically this is an illustration of what a rigid (not hinged) stb does, on a much smaller scale. It's not something you put on your car and notice a huge difference like say a stiffer sway bar (on a worn out old car probably but not a new one). They (braces) also become an absorber in an impact. Potentially preventing/lessening chassis damage depending on the bar location/hit.
I don't think you can say that about every car; I noticed it very distinctly when I put one on my 2001 Maxima. But then, it had a chassis as stiff as Sbarro spaghetti.
This CX-5 has a very rigid chassis with an (not very attractive but quite functional) STB boxing the front suspension very nicely. To your point I am very doubtful I'd notice any more stiffness in that area without some very good rubber on the corners. I was very impressed when I even found my 2011 M3 i-Touring sedan had a factory STB in place. Mazda is truly serious about enhancing the driving experience.
But after-market STB's can be very eye-catching when the hood's up. That I would notice, if it was important to me!
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I don't have a photo but I'm talking about the bolts that affix the OEM strut brace to the strut towers. They are located under a plastic shroud that is at the base of the windshield. The shroud is a little tedious to remove due to the number of plastic fasteners and that the windshield wiper arms must be removed first.
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- San Antonio, Texas
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- '15 CX-5 Miata AWD
he is talking about the black bar. It doesn't connect with the strut itself though, just the welded tab on the inside of the tower. It seems to be more for supporting the cowling.
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Actually, it's not just the single welded tab visible in your photo but also a second, beefier tab on the backside of the tower. Bolting a strut brace to the strut tower is the same as bolting it to the top of the strut because the strut tower is very stout and integrated into the rest of the chassis. There will not be significant flex between the OEM bolt location and the aftermarket mounting location (which was chosen for convenience as there is no need to weld mounting points on the tower itself). That is some beefy metal formed into a very strong 3D shape and wrapped into primary chassis members.
I found the picture below in another thread. Based on the size and number of fasteners it's obviously designed as a structural chassis member. A simple shroud support would not use such beefy welded mounts or such large fasteners.
Lifting the cowling you'll see the black bar is much more substantial than that picture alone suggests. It joins to form an angled bracket that is attached with two more bolts to the white flange with the two spot welds on the shock tower, between the two rear-most shock mount bolts in your picture but underneath the cowl. That angled piece then runs across the top of the firewall, bolted in three or four places to the firewall, to the other side tower where the mounting is repeated. The metal is quite substantial, much more substantial than needed for the job of attaching the cowl! Being joined to the shock tower in three places each side, angled and bringing the firewall into the structure via the firewall bolts it's forming a much stronger box-frame of the suspension than might seem obvious.
I'd imagine a lot more effectively than one single flexy-beam FSTB across the open expanse of the engine bay; certainly more efficiently since as you pointed out it's performing more than one job!
I've never seen this attention to chassis rigidity on bog-standard, economy (I have one on my M3 too!) trim level of any other manufacturer's automobiles. Mazda engineers went to quite some bother to economically make this chassis very rigid and a joy to zoom-zoom right out of the box. I believe that's part of the SkyActive chassis design philosophy.
Incidentally, those three bolts on each side were loose on my CX-5 when I first got it, leading to a creaky/knock noises as the suspension shifted load in turns and bumps. I had to take the cowl (partly) off to find all the bolts and tighten them. That's how I am quite familiar with this area!
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It's a small point for standard use, but it's not the same.
In one application the force is transferred directly from the strut to the brace to the other strut = Simple.
In the other application (OEM) the force is expected to follow a load path from the strut to the tower through the tabs into the "OEM brace" and vice versa on the opposite side. The OEM brace is not centered on that load or the load path, neither are the connection points. All of which create eccentric loads in those members. That is not optimal for this application, and can create problems with fatigue over time.
A direct strut brace would be MUCH better.
It's pretty obvious to me you don't have a good idea of the forces involved or the strength of the components at hand. If you did have a grasp of what's involved here, you might take issue with the rigidity of the OEM brace itself. But to suggest that the mounting location is at risk for metal fatigue is just absurd.
By your reasoning, the strut brace Chris installed has a worse issue with eccentric loads on the centers of the strut towers. If you compare the photos above you will notice that the OEM brace transfers the load directly in line with the center of the strut while Chris's brace does not. But this matters not one whit due to the rigidity of the entire area at the top of the strut towers.
* I said possible fatigue of the members (the brace is a member, as are the towers).
* How are these cars driven? On what surfaces? At what rate of speed? Over bumps? Rocks? Sand? Without all of this (and more) data neither one of us fully understand the forces at play.
* I never stated that I knew what the forces were. I didn't calc them, so you're right on that part (but I don't really want to either). I also don't need to calc them in order to see that the design is not optimal from a purely structural standpoint. Didn't say it won't work, but it's far from the best design out there. Mazda had to contend with a number of factors when coming up with their design - cost/ ease of manufacturing/ potential use/ secondary uses (cowl mounting point) / the list goes on. I'm sure they did their best to come up with a solution that is a great compromise though.
To be clear, I wasn't making an argument for Chris' brace in particular, but most aftermarket brace design is aligned directly with the strut towers (at least those that I've seen) for a direct load path between the towers. But, if we look at the photo Chris posted, you will see that:
* his brace is mounted directly to the studs = direct load path -vs- OEM which is bolted to the rear corner and one secondary tab on the strut tower = forces (whatever they may be) need to traverse the tower and gather at those points in order to be transferred to the brace itself. Or a portion of the load is simply transferred through the rigidity of the tower itself. That's a good compromise design, but is it ideal...nope.
* With the aftermarket brace, the bulk of the mounting material is concentric to the vertical centerline of the strut itself. Although the load path after that point is off center to the strut. That is not ideal, but the cross section of the bar likely makes up for it. Assuming the (aluminum?) brace is made of thick enough material. -vs- OEM, the engine side mounting point is aligned with the load path, but the rear mounting points are not. The tower itself is carrying that load and transferring it to the brace. Again, good compromise considering the secondary use of the brace but not ideal.
* the horizontal mounting flange (where the mounting bolts are located) also overlaps a good portion of the strut tower, adding rigidity to that steel section. - vs- OEM which is just a welded tab (although it appears they beefed up the section at the tabs). = Point load. This will likely never fail, but it's far from ideal.
Like I said earlier, with standard use, none of this will ever be an issue. But, you never know what people are doing with their CUV's these days. (rofl2) And I think these differences make it clear that the OEM and aftermarket braces are clearly NOT the same, although they perform the same function to a point.
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Of course I agree that the two braces are not the same even if they do perform similar functions. The brace Chris has installed is more rigid and has higher eccentric loading relative to the center of the struts. The main load path of the OEM brace is in-line with the struts. But neither one is compromised in any way due to eccentric loading up to forces great enough to start breaking wheels off the vehicle. This is because of the extreme amount of strength in the heavy welded end brackets of the aftermarket brace and the load path of the OEM brace that is in-line with the struts. And who cares about the strength of the brace once forces get so high that other parts of the vehicle are being destroyed?
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- San Antonio, Texas
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- '15 CX-5 Miata AWD
Well my bar is steel, so it's heavier (not that it's "heavy") but in comparision an aluminum bar of the same thickness will be about half as strong.
Considering you still have the stock brace in place, and added another steel brace, I'd bet you likely never have to worry about those towers moving (unless there's a catastrophic failure).
Hopefully things like that never come flying off, if they do then all bet's are off for sure.
I have to say, that since I'm not planning on racing my CX-5 (autocross or rally lite are possibilities for this car I think), or doing any "serious" off roading (some light duty trails are definitely on order though) then the stock brace would be just fine for me. But if I was going to partake of those activities, I'd certainly add a good heavy duty brace to keep things square. At the very least it's very good peace of mind.
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- San Antonio, Texas
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- '15 CX-5 Miata AWD
I saw the turbocharged mz5 getting some of the lowest times in a sasca autocross last month. All you need if the right mods and fine tuning.
Before anyone plans real off-roading they surely don't want to increase rigidity and stiffness. Off road you want flexy, compliant suspensions to which another STB would add nothing. If anything you'd want to take off roll bars, lengthen shocks and springs to increase travel and lift for ground clearance, air down tires that are hugely plus-sized to stock CX-5 low-profile rubber. Almost everything they do to make a vehicle better for off-roading, makes it worse for on-road performance. Even to the point of prefering SAS to independent suspensions.
Maybe your 'off-road' idea is different from mine, but I can't see a CX-5 ever seriously considered for off-roading. In the New Mexico national forests and desert mountains I used to roam there's a lot more to do to make a CX-5 even adequate... but never good or likely to go where I liked to because swapping the entire power train to a 4x4 with proper lo-range xfer case and rear diffie that takes over 50% of the torque is kind of not practical.
I'd totally limit any the CX-5 to 'lite off roading'... short trips across a level pasture to a picnic spot and excursions onto sandy beaches. The problem with most any off-road trekking adventure is you start off OK but things go south really quick, especially due to weather changes and trail conditions since your last trip. You have to be able to trust your vehicle to get you out, so you can't start off with a fair-weather 4-wheeler. It has to be up to the worst even if you don't plan on it. And oh yeah, your trail buddies are not going to enjoy pulling your sorry ass out of every mud puddle. They wanna trek, that's what they came for!
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I'd want my suspension to flex, not the frame.
Sounds like you'd want a nice solid body-on-frame, not unibody.
There are good unibody 4x4's out there (cherokee, FJ) but they're designed that way from the get go. A flexie STB is really intended to box-in the suspension to prevent geometry changes that makes handling vague. It won't stiff up the CX body enough to take off-roading abuse, you'll need to weld in gussets across all the corners to keep things together. Otherwise even if it flexes, so what? you're not worrying about speed here... just transiting the obstacle. With tires aired down to 5 lbs steering precision is pretty crappy anyway.
A really curious thing to do would be to drive two diagonal wheels up on an obstacle suspending the other two tires about 6" (or would be if the front tire was up in the air). Then open doors and tail gate... will they bind? rock the vehicle back and forth, alternately bouncing on those two tires. Will the doors still close with even gaps? If they do then the SkyActiv chassis stiffening doing a great job! If it can't pass this test then the chassis is completely unsuitable for off-roading in any serious sense, not without some gusseting.
If what you're talking is off-road rally racing: well, then you ARE thinking something entirely different, but I think the CX has a long, long way to go before being ready for that too.
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