>>Let a vendor say that they have proof that the stb helps and watch folks jump on him like a pack of hyenas on a waterbuffalo carcass.
>>

no, not like a bunch of hyenas, like a bunch of professional engineers and technically knowledgable people who use these forums to gain and to give technical information. that includes debunking or or at least questioning claims claims that may not have a rational, scientific basis.

and "proof" in this case means at least repeatable measurements of your claim.

flyboy2160

 

ok, i'm into this.

here's the ultima chassis
http://www.ultimacars.com/fra_gallery.htm

where did the strut bar go? is this structure stiffer or more flexible than the mini unibody?

my point is still that you can't just say "strut bars make it stiffer" without knowing exactly what you're starting with.

flyboy2160

[edit] and a point of logic: one of the rules of logic is that "the onus of proof is on he who asserts the positive." it's illogical for someone to claim "there is a herd of reindeer living at the center of the earth making 1000 pound 400 hp mini coopers. i don't have to prove it - you have to prove it isn't true."

 

the stiffer bushings will transmit more road vibrations in general (which is why Mini chooses to luxuriate us with softer ones; after all, it is a BMW) and the response to steering moves will be crisper and more direct. A good thing.

changing the motor and trans mounts helps for acceleration related movements ans here stiffer ones will produce more cabin vibration at idle. it goes away jsut aove 950 rpm, below that it is an annoyance you can live with.

Flyboy: i'm going to steal your "onus..." quote for my sig line.

 

>>ok, i'm into this.
>>
>>here's the ultima chassis
>>http://www.ultimacars.com/fra_gallery.htm
>>
>>where did the strut bar go? is this structure stiffer or more flexible than the mini unibody?
>>
>>my point is still that you can't just say "strut bars make it stiffer" without knowing exactly what you're starting with.
>>
>>flyboy2160
>>
>>[edit] and a point of logic: one of the rules of logic is that "the onus of proof is on he who asserts the positive." it's illogical for someone to claim "there is a herd of reindeer living at the center of the earth making 1000 pound 400 hp mini coopers. i don't have to prove it - you have to prove it isn't true."
>>
>>

Wow, did you even read the post before you wrote this?

Nowhere in my original post did I say they simply added a strut bar to the Ultima chassis to stiffen it up... they re-engineered the chassis, after determining the flex with a custom jig. Therefore, this was simply a commentary on what a jig can do to measure rigidity AND that you CAN make a chassis stiffer - not necessarily with a strut bar, but that you can, in fact affect the torsional rigidity of a chassis with bracing. I also stated that this was on a tube chassis car, which means that it is NOT applicable to the MINI.

The strut bar example in the student paper shows the baseline unibody vehicle he drew and rendered. Then, he added the strut brace into that baseline model. Running a simulation on both, the theoretical gain was shown quite handily, I believe. Does it not show that the chassis WAS stiffer with the addition of the strut brace? Yes, yes it does... and quite handily.

Does that mean the MINI would benefit from a strut brace? NO. I stated that quite clearly. This is still waiting on proof...

However, I did state that all unibody cars have flex - it's inherent in their design. If you really want proof, simply search around the web and you'll find plenty of information. I don't have to prove it because it's an understood fact and there's a ton of information out there to prove it for me. I'll guarantee that the MINI has chassis flex - all vehicles do. I don't know what it is, but I'll guarantee it has it.

If you're going to start quoting maxims on logic, make sure you read and understand the post before you say I have the burden of proof...

 

My theory on why the Mini's chassis is so stiff is due to it's unique proportions. Unlike any other vehicles out there, the shotgun rails are extremely short because of it's abreviated front end. It is so short that the firewall in essense is acting to prevent shock tower flexing. In theory, if the shotgun rails were any shorter, the firewall it self would be the STB.

My 02 cents.
Sid

_________________

 

> "there is a herd of reindeer living at the center of
> the earth making 1000 pound 400 hp mini coopers"

. . . which look suspiciously identical to a Caterham R500
by the time they get done with all the mods.

Off topic, I know, but couldn't resist.

http://www.caterham.co.uk/showroom/s...superlight.htm

My next toy, as soon as I win the lottery.
Until then, my MCS is serving nicely.

On topic: wouldn't the use strain gauges to measure flex before/after application of strut braces at least begin to answer this point?

 

The Caterham will have to wait until the lottery too

This is THE perfect example from a friend who beat me to it:




I do have a very nicely built 1/12 scale from Tamiya that will have to suffice for now.

 

>>
>>> "there is a herd of reindeer living at the center of
>>> the earth making 1000 pound 400 hp mini coopers"
>>
>>. . . which look suspiciously identical to a Caterham R500
>>by the time they get done with all the mods.
>>
>>Off topic, I know, but couldn't resist.
>>
>>http://www.caterham.co.uk/showroom/s...superlight.htm
>>
>>My next toy, as soon as I win the lottery.
>>Until then, my MCS is serving nicely.
>>
>>On topic: wouldn't the use strain gauges to measure flex before/after application of strut braces at least begin to answer this point?

Ahhh the Seven. When I was a kid, I thought I was going to be able to save up for a kit.

 

>>. . . which look suspiciously identical to a Caterham R500
>>by the time they get done with all the mods.
>>
>>Off topic, I know, but couldn't resist.

>>On topic: wouldn't the use strain gauges to measure flex before/after application of strut braces at least begin to answer this point?


isn't there some rule that hijacking the thread OT is ok if the OT is screamingly witty? and while we're OT, what kind of seats are in msfitoy's friend's caterham?

on topic: typically strain gauges measure very, very small deflections over their own small length. if you applied a bunch of them to say the sides of the shock towers, you'd know the deflection of those local spots and maybe could guess at what the whole tower was doing after some geometric calculation. a direct reading of the distance bewteen the towers is both better and much easier. those little strain gauges are a real pita to mount and to calibrate.

flyboy2160

 

His isn't a genuine R500 but built with the same specs. He's got a Rover putting out over 250 hp with a dry weight of around 1200lbs. Nothing could touch that thing. The seats are R500 carbon fiber.

 

(*sweet* Catterham. This month's EVO has an article on their latest creation.)

JLM. As always, thanks for sharing the skinny as you continue to tear apart & rebuild the rig. Awesome pics of the subframe in the other thread. (Is this gonna be a kit someday?)

OT. A lot of folks have made jigs to measure movement using a few simple parts. Basically a thin steel rod mounted at one end (on one tower) with the free end travelling through a loop at the other end. The loop, of course, if fastened on the other tower.

Slide a couple of o-rings over the rod, and snug them up to the loop (one o-ring on either side of the loop.) Any deflection causes the loop to bear upon one o-ring or the other, sliding it away. When you're done, the distance between the two o-rings (adjusted for their starting positions) is your deflection.

Not terribly accurate, but should be enough to give you your answer. Cost? About $5 at Home Depot.

Jeff in ATL

 

If a little strut tower bracing is said to be good (without any scientific evidence to back it up), then more must be better, right?

 

Andy, that brace looks great.

And, it probably adds JUST enough weight above the CG
to counteract any improvement dut to less tower movement.


On to the subject at hand. I've been drawing free-body
diagrams for a few days, and unless I'm missing something
COMPLETELY, it looks like the towers move in the same
direction when you corner really hard, so a tower-brace
the keeps the tops of the towers the same distance apart
won't actually do ANYTHING even if it works perfectly.

I guess the vendors have some "secret-sauce" they put on
or something.

 

Yeah, um, Andy, gimme one uh them ther GigantoBrace strut bars. Do ya make 'em outa steel? 'Cause I don't reckon the 'luminum be strong 'nuff or heavy 'nuff.

 

Andy, yet another great mod from you. I really like this one because you didn't add any additional weight. Just remove the front bumper support and mount it between the shock towers... Brilliant!

 

well it actually doesn't not just add weight, but removes weight...as you surely aren't going to get the hood closed with that on so just toss the hood - weight saved :smile:...plus now look at the great air flow you will get :smile:

 

* May require modification to the hood.

 

flyboy2160 wrote:

Force is exerted in a rearward and downward direction to retrieve the wallet from the pocket. Then, there is an upward moment arm removing money from the wallet. This is followed by a feeling of increased performance and a sense that the car is "smoother".