Rear chassis member brace - Lexus IS Forum
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post #1 of 27 (permalink) Old 08-03-2011, 03:29 PM Thread Starter
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Rear chassis member brace

I have a 2011 IS 350 F Sport on the way and am looking for opinions on F sport suspension mods. I am wondering if I should get the rear chassis brace or the front and rear sway bars, or both! Opinions? Im not a gear head but love agressive driving.

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post #2 of 27 (permalink) Old 08-07-2011, 11:11 AM
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Sways are awesome easily the best mod u can put on the car

Chasis brace is dead useless weight
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post #3 of 27 (permalink) Old 08-08-2011, 03:00 PM
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Quote:
Originally Posted by Knightshade View Post
Sways are awesome easily the best mod u can put on the car

Chasis brace is dead useless weight
Funny, the braces do more than you think. I don't know how many customers of mine love the fact that their sunroof stops making noise now and their exhaust doesn't hit when backing out of a driveway.

D
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post #4 of 27 (permalink) Old 08-10-2011, 12:50 PM
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Originally Posted by is300soon View Post
Funny, the braces do more than you think. I don't know how many customers of mine love the fact that their sunroof stops making noise now and their exhaust doesn't hit when backing out of a driveway.

D
I'd be willing to bet if we take my car to a track and have an objective 3rd party run it with and without the brace they'll find no measurable difference in times.

That's what I mean by it being useless dead weight versus the sway bars that actually, measurably, improve performance.

Then again, my car doesn't have either problem you describe your brace solving in the first place.
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post #5 of 27 (permalink) Old 09-13-2011, 08:35 AM
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I have a hitch installed onto my car for transporting bicycles. Do you think the f-sport chassis brace offers any advantage in this situation? I'm assuming it would help reduce the chassis twisting caused by wind drag or an evasive turn with a bicycle. I use the vehicle for road trips (8-9 drives) transporting the bicycle.
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post #6 of 27 (permalink) Old 09-13-2011, 03:52 PM
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Quote:
Originally Posted by Knightshade View Post
Sways are awesome easily the best mod u can put on the car

Chasis brace is dead useless weight
subtle I don't know much about structural dynamics post.
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post #7 of 27 (permalink) Old 09-13-2011, 05:14 PM
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Originally Posted by APynckel View Post
subtle I don't know much about structural dynamics post.
Get back to me when you have some actual lap test times showing a bolt-on rear chassis brace doing anything measurable for a 2is, especially on street tires.

Now, on race tires, after you've already done sways, lightweight wheels, an aftermarket LSD, and corner-balanced coilovers? There you might be able to measure a difference from a bolt-on rear brace.. (though in 4+ years of reading the 2IS forums I've yet to ever see anyone do so... but I've seen a number of threads where folks dropped the $ on the F-sport brace and reported anything from "I can't even tell the difference" to "I think the back might feel slightly stiffer... but it doesn't make a real difference like the sway bars do")... but for the OP in just aggressive street driving, or pretty much 99.9% of folks who ask? It's dead weight.

Last edited by Knightshade; 09-13-2011 at 05:53 PM.
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post #8 of 27 (permalink) Old 09-16-2011, 05:23 PM
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Quote:
Originally Posted by Knightshade View Post
Get back to me when you have some actual lap test times showing a bolt-on rear chassis brace doing anything measurable for a 2is, especially on street tires.

Now, on race tires, after you've already done sways, lightweight wheels, an aftermarket LSD, and corner-balanced coilovers? There you might be able to measure a difference from a bolt-on rear brace.. (though in 4+ years of reading the 2IS forums I've yet to ever see anyone do so... but I've seen a number of threads where folks dropped the $ on the F-sport brace and reported anything from "I can't even tell the difference" to "I think the back might feel slightly stiffer... but it doesn't make a real difference like the sway bars do")... but for the OP in just aggressive street driving, or pretty much 99.9% of folks who ask? It's dead weight.
So what background do you have in structures to be able to discount it outright?
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post #9 of 27 (permalink) Old 09-16-2011, 07:47 PM
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Originally Posted by APynckel View Post
So what background do you have in structures to be able to discount it outright?
I asked first- where is your real life data on measured improvements from this mod on a 2is?

Show me that and then you get to ask about my resume

Given in >4 years on the boards I've never seen any evidence of measurable improvement from this brace (versus the sways where we have lots mention the large improvement- including guys who have done both and found the sways a big improvement, the brace not so much, I'll stick with my origInal reply to the OP and again ask you to back up your insult of my knowledge with some real world data
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post #10 of 27 (permalink) Old 09-16-2011, 08:54 PM
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Originally Posted by APynckel View Post
So what background do you have in structures to be able to discount it outright?
Knightshade is right here. If you have a background in structures you should know that the less stiff bits bend more (and before) the stiffer bits. Anyway, he's saying that the chassis is stiff enough without the rear member brace because of the compliance in a stock suspension and less grippy street tires, among other things.

Sure, the brace will make the chassis stiffer, but what use is that if your springs compress and tires break loose before the chassis flexes?
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post #11 of 27 (permalink) Old 09-17-2011, 08:49 PM
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Originally Posted by korinfox View Post
Knightshade is right here. If you have a background in structures you should know that the less stiff bits bend more (and before) the stiffer bits. Anyway, he's saying that the chassis is stiff enough without the rear member brace because of the compliance in a stock suspension and less grippy street tires, among other things.

Sure, the brace will make the chassis stiffer, but what use is that if your springs compress and tires break loose before the chassis flexes?

Exactly that... thanks for doing a better job summing it up than I was doing

It's kinda like putting a BBK on the car expecting the car to stop shorter... that won't happen unless you've taken other parts (the tires and road surface in that case) way way way beyond the specs any normal person is driving with... Making the chassis any "stiffer" than stock is only useful if the current stiffness is the limiting factor in anything you're actually doing with the vehicle... and on street tires, on any common bolt-on shock/spring combo, on normal road surfaces, it just ain't. So you're just hanging dead weight on the car with that brace.

You might notice a slight difference in the ride/feel of the car with the brace (reviews are somewhat mixed here from those who own the thing) but you won't see any measurable performance benefit.... maybe after doing the half-dozen other suspension/handling mods I mentioned earlier in the thread with a timed course and a stopwatch you might finally see a very very tiny benefit... but nobody has yet, so that's a big maybe, and it's not gonna help a normal driver in street use any.

As opposed to the sways (the other thing the OP asked about) which makes a significant and very noticeable improvement in feel and handling even on an otherwise stock 2IS.
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post #12 of 27 (permalink) Old 09-26-2011, 11:17 AM Thread Starter
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Knightshade has saved me $375 plus install as I was about to buy this thing. Not to create any sore feelings here, however, APynckel seems to be a believer in the mod. while Knightshade reasoning seem sound to me I would be interested in knowing why Apynckel disagrees (if that is indeed the case).

I have a 350 F Sport with front/rear sways and a new set of Hankooks. The F Sport already has lowering springs and stiffer shocks, however, I'd still like to stiffen up the handling aspects of this car.

My other car is a Cayman S so I guess I've set the bar fairly high in the handling department. That's why I was interested in the brace. Plus, I'd want to keep the car stock.

I appreciate/respect all opinions. I know crap all about cars other than which ones I like.
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post #13 of 27 (permalink) Old 09-26-2011, 01:16 PM
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Because rigidity of a chassis and the harmonics of a chassis are not the same thing.

Anyone who denies outright the beneficial aspects of a structural piece that more firmly ties together opposing sides of a vehicle (which would otherwise only be connected by an arch over a driveshaft) with a space truss, is not very well informed in the fields of structures or harmonics. There is flex that would be negated with this brace in place, and the overall harmonics of the car would be changed. Whether that's for the better, Lexus should test and release data (since they decided to release this part as an "upgrade").
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Last edited by APynckel; 09-26-2011 at 01:23 PM.
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post #14 of 27 (permalink) Old 09-27-2011, 07:25 AM
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Originally Posted by APynckel View Post
Because rigidity of a chassis and the harmonics of a chassis are not the same thing.

Anyone who denies outright the beneficial aspects of a structural piece that more firmly ties together opposing sides of a vehicle (which would otherwise only be connected by an arch over a driveshaft) with a space truss, is not very well informed in the fields of structures or harmonics. There is flex that would be negated with this brace in place, and the overall harmonics of the car would be changed. Whether that's for the better, Lexus should test and release data (since they decided to release this part as an "upgrade").
The fact they have offered no such data kinda supports my point it's a useless upgrade though.

Because it is.

Likewise throwing bigger brakes on a street car is a useless upgrade, despite the "theoretical" things bigger brakes can do. Because you're limited by the traction of your tires, which even the stock brakes are more than adequate for.

Just as in this case your handling won't improve, at all, by making the chassis stiffer because chassis flex isn't currently holding back handling at all.

Note I didn't say the brace didn't make the car stiffer, which you seem to be assuming. I said it was useless. Because the added stiffness doesn't make the car handle any better.

It's kind of like if you're building a building... your plans call for it to be able to withstand a 5.0 earthquake... you can spend a ton of money and make it more "structurally sound" to stand up to an 8.0... but if the strongest quake that has ever, or likely will ever, hit the building is a 3.0... that's a stupid waste of money. Doesn't mean the extra money won't make the building "stronger" but it's pointless to do it. Same thing here with making a chassis (where flex doesn't limit you in any way) flex less.

It's possible there'll be a subjective 'feel' difference (just as changing your brake pads can cause a 'feel' difference, but make absolutely no difference to the distance the car actually stops in)...Indeed the several threads from folks who have done this mod have varied from no-difference period to there's a (very small) feel difference, but nobody has observed any measurable improvement in anything.... and that's not really worth throwing an otherwise useless hunk of extra metal on the car IMHO.
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post #15 of 27 (permalink) Old 09-28-2011, 03:42 PM Thread Starter
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I have one question for Apynckel.

Did you buy it?
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