Has anyone installed the BT Brace on the 2006?

<div class='quotetop'>QUOTE(jbarnhart @ May 9 2006, 01:24 PM) [snapback]252220[/snapback]</div>

i'm not asking for expensive instrumental testing of its performance. i'm asking for just paper napkin analysis of HOW the product was supposed to be an improvement.

i'm not the first. i read the link posted by docvijay and there were already skeptics before.

the problem is that there is a competing theory to account for the observations of those who bought the product. and this theory explains the observations (which btw range from "completely changed handling" to "no observable change") better. this theory is the "placebo effect" theory.

 

<div class='quotetop'>QUOTE(DocVijay @ May 9 2006, 08:34 AM) [snapback]252138[/snapback]</div>

Hey Doc, I've enjoyed every single one of your posts in your extremely long mods thread, and you seem very careful in your analysis of each of your mods. For instance, you've convinced me that Tom's fr suspension brace can really help steering feeling.

A few people including myself only have been asking for the same rigorous testing and data analysis we hold every news reporter to that drives the Prius and says it sucks on MPG, or it's going to cost more to own it in the short or long run. We break down the numbers and challenge them.

Do we not do that here? I'm not talking about twisting forces or such, just how much better/faster the Prius can handle with Brian's obviously stiffer plate, and a simple double-blind time or G-Tech test. Is this that difficult?

A good example is how I had doubts about Brian's rear spoiler's effect, but 200volts airflow analysis placed a high-pressure area right where that spoiler is, and that really helps to visualize how a little spoiler could have a big effect.

I'm not a structual engineer, but I'm allowed to ask questions unless this is Soviet Russia. I just know from building balsa bridges, and learning about how the Twin Towers were built, that to counteract any twisting forces, build cross-braces that compress or expand, or build a core of very stiff material. How are bridges built? With a variety of stiff cross-beams, and a lot of cross-bracing that are designed to compress or expand. Look at frame of your house. Does it not fall over because it's using stiffer wood, or because it's using a lot of compressional cross-bracing?

How is this brace from Tom's mounted? If it's mounted parallel to the bottom of the Prius, I would more tend to believe that it's designed to counter some cross-flexing in the body and suspension.

So, how is the Prius flexing? If it's compressional/expansion parallel to the rear axle then either brace will do the job with Brian's doing better for compression. If it's twisting/side-to-side orthogonal to the axle, then I don't see how either brace could counter that.

I think we have standards here, and it's only simple real-world test data I'm asking for. I really want to improve my Prius's handling, but I want to be able to rigorously validate any add-on.

<div class='quotetop'>QUOTE(jbarnhart @ May 9 2006, 10:24 AM) [snapback]252220[/snapback]</div>

vs pseudo-scientific feeling? So, breaking this down, you've all observed a phenomena of improved handling, and formulated the hypothesis that the brace works. However the lacking next steps is quantitative predictions, while there is a lot of followup independent verification. I'm only asking for step 3. Being truly scientific, you have to be open to the possibility that the hypothesis is wrong. I'm quite satisfied to be proven wrong quantitatively.

 

<div class='quotetop'>QUOTE(efusco @ May 9 2006, 02:08 PM) [snapback]252248[/snapback]</div>

i didn't say "paper napking test". i said "paper napkin analysis". Meaning i want an explanation of the mechanism how the brace is supposed to work better. I don't care so much about actually performing the test. That will come later, after i understand HOW the product is supposed to work.

Begin by describing what is the direction of the forces relative to the brace that the brace is supposed to counteract.

 

below is a picture with arrows for the possible force directions.

yellow - sideways expanding force
red - sideways contracting force
green - twist around the vertical axis
blue - twist around the front-rear axis.

tell me which force is the brace supposed to counteract?

 

<div class='quotetop'>QUOTE(electricity_guzzler @ May 9 2006, 04:37 PM) [snapback]252338[/snapback]</div>

Hi Elec. Guz.

I like your diagram. You left out one force mode. De-planarization (came up with that word, not an ME). That is,what happens if the screws on one side move so that that end of the plate changes planes. The new plane may still be parallel to the unforced plane, but displaced vertically.

The BT plate has less deflection for a given moment presented in sideways (both) twist (vertical axis, f/r axis and l/r axis), and deplanarization than the original plate. So its difficult to know which its helping specifically.

I look at the rear of the Prius as a upside-down U section that is in the horizontal of a large right-side- up U section. As the plate is in the area where the hatchback starts, and the hatchback door provides no bridge across the top of the right-side-up U. In front of the hatchback are the rear doors, so, there is no Box section there either. And they say four-door cars are safer!?

The small upside-down U section is the main vertical force resisting structural member. This is seen in your picture where the exhaust pipe runs. But it is weak in resisting horizontal forces, as the open mouth of this U can collapse. The horizontal force resisting members are the flat plates to the left and right of the small U on the horizontal section of the the large U. These prevent sideward bending, and the U's hold them flat to do this work. But have little co-planarity restraint or any side force relative position restraint provided to the large flat floor plates. The little U will just collapse across its opening when a side force is applied, and so will the large U. Or the two U's can rack.

Now this is all VERY simplistic, as the exact alignment of the rear suspension attachments and the doors and the plate and the hatch opening are all somewhat offset. But the metal tying these things altogether can twist, as its only a thin sheet as well.

If the two flat sections of the large U displace, but stay horizontal, one wheel will be higher than the other in the rear. The car will tend to follow the circle of the highest rear wheel. Now if this reverses sudenly, the car will suddenly dart the other way. I believe this has happened to me driving my Prius in cross wind situations. With the plate installed, its much less, and the car tracks well even when its rocked by cross winds.

Figuring how much all these things will really twist is a problem that would take $100 to $500K worth of engineering facility/personel time.

If you expect anything more from this forum than presented so-far and above, you are just trying to rip-off engineers to give you a freebee worth more than most Las Vegas Slot Machines deliver. The cost of the plate is minimul for what it is, the market for it and the level of production. Still too cheap - think you can make one piece for less? - I doubt it. I think you will spend more money in doing the CNC code than the cost of this plate, let alone the lot charge for the one-piece you are going to get anodized or powder coated.

 

Hi Donee, your previous analyses that the brace is a better vibration dampener for the random side-load oscillations than the stock brace that collapses the small-U makes sense.

Would it be fair then to postulate that some of the de-planarization of the two sides of the big-U causing forward steering instability would be better counteracted with stiffer rear shocks/springs as well as a stiffer rear anti-roll bar instead?

 

<div class='quotetop'>QUOTE(donee @ May 9 2006, 08:14 PM) [snapback]252452[/snapback]</div>

any complex force direction can be broken down into additive forces along the given axes. the "deplanarization" you are suggesting is basically the blue force component but more in a shear motion rather than a twist motion. However,

1) does this really happen in the real world? the sides of the car are suspended. if you raise one side beyond the ability of the suspension to absorb the force, that side would just simply elevate. but why would the other side remain parallel to the ground. the whole floor would raise on a angle. i don't see how the two sides of the car could deplane since there's nothing holding one side to remain parallel to the ground when the other side rises.

2) even if the condition you describe happens, do you think the brace can prevent this at all? no way. the screws holding the side of the plate is aligned in a front-rear direction, and since the force of rotation is around this axis, it would just act like a hinge. the only thing on the brace that can prevent the shear or rotation are the strength of the screws. and i don't think the BT screws are any more strong than the OEM screws.

just look at the picture. and imagine how the brace could counteract each of the drawn forces. you will see that really it can only work with any efficacy against the sideways compression and contraction forces because those forces are along its length. in these conditions it is exactly acting like a brace.

but in the other conditions it is just acting either like hinge (up/down rotation or shear), or like a lever (front/rear rotation or shear).

in the case of the front/rear rotation or shear, try this: remove the screws of one end of the plate. then give it a kick along the front/rear direction (green arrow). do you think you might dislodge it? if you kick strong enough you can. the only force counteracting your kick is not the stiffness of the plate but the screws holding the plate.

 

<div class='quotetop'>QUOTE(NuShrike @ May 10 2006, 12:15 AM) [snapback]252596[/snapback]</div>

why should the BT brace be better than the stock brace for side-load that tend to collapse the U? do you think the side-load can overwhelm the stiffness of the OEM brace along its length? i bet you can take the OEM brace, stand it along its length on asphalt and hammer its end. it will chisel into the asphalt before you can buckle it. if you ram a prius on its side with an SUV, the whole prius would probably be thrown sideways first (if the force is slowly applied) or the screws will snap first (if the force is quickly applied) before the OEM brace will buckle.

now, regarding dampening, that's a different animal. if damping vibrations was the problem, then a rubber brace glued across the U would be better. no, damping is not the problem that the brace is meant to solve. in any case, steel is a better damper than aluminum.

 

<div class='quotetop'>QUOTE(electricity_guzzler @ May 10 2006, 12:43 PM) [snapback]252842[/snapback]</div>

You are forgetting one thing, mass. If you jack up one corner past the suspensions limits, that corner will indeed elevate. What keeps the other corner parallel? Gravity. the weight of the car pulls everything down. A car WILL flex unevenly. The best example is a convertible. All convertibles have extra reinforcement to prevent flexing. Take a cheaply made convertible and drive over a bumpy piece of road. You will get what the magazines call cowl shake. THe suspension does absorb 90% of the forces imparted on the car, but hte other 10% is through flexing of the cars chassis. If you think the Prius is so ultimately rigid that it doesn't flex at all you are sorely mistaken. Every time a model is re-engineered they always advertise something like "now 75% stiffer than the previous year." All car frames flex.

Consider a 4 foot piece of steel rebar. It's plenty stiff and straight. Now fix one end, and hang 100 pounds off the other, it will bend. Suddenly not so stiff any more. Cars are the same. When you jack up one corner and lift it off the ground, the frame is flexing. It may not be by a large amount, but it is. One way you cn check is to find a nice body line near the middle of the car. Stick something flat into the crease that fits in nice and snug, but still comes out easily. A quarter (or two stacked) will do nicely. Now jack up the corner of hte car till it's off the ground by a good couple of inches. Now go look at the body seam. The quarter will either be impossible to remove or it will have fallen out on its own. Flex.

In the real world, the forces that are actually acting upon the plate are ALL of those you mentioned.



<div class='quotetop'>QUOTE(electricity_guzzler @ May 10 2006, 12:53 PM) [snapback]252853[/snapback]</div>

As for the stock brace being as strong as you suggest, I think you are a bit optimistic. That thin piece of stamped steel would NOT survive a side impact from an SUV. It is stiff in your hands, yes, but to the forces generated by an impact, even simply by driving are significantly greater than what you could exert with a hammer. Asphalt is very soft, so driving it into that would mean nothing. I could drive a fork into asphalt.

To see how things work you have to think of the car in a dymanic environment. You cannot simply jack a car up on one corner and assume that taking a freeway off-ramp will impart the same, or even similar forces. You need to take weight transfer, grip differential between tires, angle, and a multitude of other factors before you can make any assumptions.

Continuing witht he off-ramp example, when you take one at a moderately high speed, you will feel yourself pushed into the side of the seat. The forces are not simply up and down now. They are at angles. If a front ire has more grip than the opposite back tire, the car will, in effect, try to fold itself betweent hose two corners. Of course, no car will actually fold itself inhalf, but those are the forces acting on it. You must also consider the center of mass and ceneter of gravity to further figure out the magnitude and vector of each force acting on the car. The suspension is effectively decoupled from the main mass of the car, so forces acting upon it and it upon the car are all different also.

Finally, the four bolts holding the plate to the car are more than sufficient to hold the plate on AND control the forces exerted upon hte plate. Remember, bolts hold much of hte car together. If they were so weak, a car would fall apart at the slightest bump. The bolts used in cars have shearing forces in the hundreds of thousands of psi. That is a LOT of force. THe bolts included are grade 8 bolts, which are the strongest generally available. The amount of force that would be necessary to shear the bolts or pull them out would be those on the level of being broadsided by an SUV. IF that is the case, the LAST of your worries will be the bolts on the brace!

Anyway, like I and others have said before. If you don't think it will do anything, then don't buy one. It's that simple. If you want proof, buy one and try it. If you determine it doesn't do anyhting for you, you'll find someone here that will buy it. And if you try it and decide you like it, no one here will rub it in.

 

your seam example is actually illustrative. the U around the exhaust pipe is like an enlarged seam. this is what the brace is well, bracing (against. but now tell me how the BT brace is better at bracing this seam than the OEM brace? Is the OEM brace not stiff enough along its length? is the OEM brace sufficiently stretchy that it will not hold the seam?

btw my point about the bolts is that the brace is stronger along its length than the bolts. do you agree?

 

<div class='quotetop'>QUOTE(electricity_guzzler @ May 10 2006, 04:11 PM) [snapback]253035[/snapback]</div>

Well from my own experiences, and also of others, seems to show that in fact the stock brace is NOT stiff enough. It does reduce flexing, but the BT brace further stiffens the car. But is it strong enough? Well, yes, it would have to be, ot Toyota would have made a stronger one. But it is also likely the minimum necessary to remain on the good side of the accountants. It, like other parts of the Prius, can be improved.

Is the brace stronger than the bolts? Which brace, the factory or the BT? Either way I really couldn't say. I know that grade 8 bolts are INCREDIBLY strong, and it takes quite a lot to break one. I know someone torqued the head off one, but that is a different force than what it would experience once installed. That is a question for a mechanical engineer.

Personally I think that the stock plate would bend before a grade 8 bolt would fail, but the BT would not. I also think the BT plate may actually fracture rather than bend if exposed to a strong enough force. But this is just speculation based on my very limited ME knowledge.

 

<div class='quotetop'>QUOTE(NuShrike @ May 10 2006, 12:15 AM) [snapback]252596[/snapback]</div>

Hi Nushrike,

I am not an ME! But here goes anyway. May Mother Nature (the queen of all engineers) forgive me. I do not think stiffer springs will change anything. The forces get transmitted to the chasis the same. In the crosswind situation the springs are not levered by the force, and stronger springs will compress less, but the force flows through the car body in series with the springs and supporting forces from the tires and road.

A roll bar does not present large forces to the chasis. Only the restraining force on the torsion spring portion of the bar is presented to the chasis. A stiffer bar will have higher forces, but these are still smaller in comparison to the static load and dynamic disturbances. Typically one can hold the torsion spring portion of a roll bar in place with muscle strength as the car is rocked. The straps that hold torsion spring portion of the roll bar are probably only good for about 50 pounds. So, the car may roll less, but the chasis deflection will be the same.

Springs and roll bars have no damping effect. Indeed they are designed to return all the energy of need to compress or twist back as efficiently as possible.

 

<div class='quotetop'>QUOTE(electricity_guzzler @ May 10 2006, 12:43 PM) [snapback]252842[/snapback]</div>

Well, this is where the money comes in. Get yourself and your Prius over to a frame bender and measure it when the operator pumps the hydraulic ram. Don't forget to pay the body shop for its facility and personel time - proably about 1000 bucs. Oh and bring your own dial indicators.

I think deplanarisation is possible because the small U can roll. Its arch shapped and force up on one side of the plate will lift that side of the arch. The small U terminates into a plate towrds the rear of the car, which should prevent/reduce the roll. Note that the plate does not extend above the center of the small U very far before its bent over horizontal. At least that is how it appears in the picture. This plate seems to be insufficient and probably buckles in the zone above the top of the small U.

Without some real FEA modelling of the Prius structure, or laser measurement of the car on a ride simulator, this is all just prelimary. This stuff would be written down in a notebook, so that when the actual measurements (or computer model) are available, experiments could be comprised on the spot to methodically check out the hypothesis in the notebooks.

...

On your comment about the plate chiselling into the pavement, you are assuming there are no moments presented to the plate. The bolts and flat surfaces the plate mounts to can twist as well and push. In which case a forced buckling can occur that would not if the forces were purely axial with the plate. The BT Tech plate has been modeled to resist the moments better. In a structure as complicated as the Prius chasis, its prudent to consider there will be moment transmitted into the plate.

 

the tensile strength (strength against stretching) of a grade 8 bolt is 150,000 pounds per square inch. the shear strength (strength against the head of the bolt tearing off) is roughly 60% of tensile, or around 90,000 pounds per square inch.

if it is indeed the case that the bolts which ship with the bt brace are grade 8, then we can safely say that bolt strength is not a problem.

 

<div class='quotetop'>QUOTE(donee @ May 10 2006, 09:11 PM) [snapback]253215[/snapback]</div>

how about applying your reasoning the other way. assume that the stock brace is more than capable of the bracing job it is supposed to do. and since it is too expensive to prove that it is not, just believe it.

do you know if there is even one OEM plate that has been twisted or buckled ever?


<div class='quotetop'>QUOTE(samkusnetz @ May 11 2006, 03:50 AM) [snapback]253356[/snapback]</div>

i'm curious what is the grade of the OEM bolts?

maybe we should be replacing only the bolts if it is not strong enough.

 

<div class='quotetop'>QUOTE(DocVijay @ May 10 2006, 04:44 PM) [snapback]253058[/snapback]</div>

anecdotal.

i think it is not an improvement if you replace something that is just right with something that is overbuilt

 

You're getting tiring, Guzzler.

Nobody has a scientific analysis to "prove" the brace is better. Given the cost, no one ever will. You dismiss all first-hand experience as "anecdotal" and useless. You aren't convinced, yet you seem to want to convince all who HAVE the brace that we're fools.

Your arguments against the brace sum up to one point: you don't understand how it works. So what? Speaking for myself, I don't care if you understand how it works or not.

You are the most prolific, negative poster on the topic of the brace, and you've never even held one in your hands, let alone driven a car with one installed. Which I find... ridiculous. You have risen to the status of a troll. At least on the topic of the BT brace.

 

<div class='quotetop'>QUOTE(electricity_guzzler @ May 11 2006, 09:24 AM) [snapback]253432[/snapback]</div>

This has got to be one of the most idiotic statements I've seen in a long, long time. Improving is not improving?

I won't respond to you anymore, as this thread shows you're a troll, but...

who defines what "is just right" and "is overbuilt"? In the case of Toyota, it's the beancounters, not the engineers. The engineers engineer for safety, but are held in check by the beancounters before they truly get to what "is just right".

 

electricity guzzler, Why so hung up on the brace? No one is forcing you to buy one. If you don't think it's worth it, don't buy it. The brace is probably more cost effective (even if it doesn't do much) than the fog lights and voice recognition you did buy.