Torsional rigidity--measuring and increasing [Archive]

Chevy

04-26-2009, 12:42 PM

I have a lot of mods to my '68 Camaro, but haven't done anything yet for stiffening up the chassis despite autocrossing regularly for over a year now and steadily improving my times. I just ordered DSE integral subframe connectors as well as Al solid body mounts and front struts from the firewall to subframe horns from Chris Alston. I intend to install these three elements and most likely also the tiger cage (working on the budget) and measure the increase, if any, in torsional stiffness as i go.

Since the car is assembled and will be raced roughly monthly i may also be able to comment on performance by way of improvements each outing, if all goes well (both with installs and my driving)!

For starters i'm interested in suggestions on how best to measure torsional rigidity in my garage with simple equipment and without dissassembling the entire car. One issue i have in making an accurate measurement is that my front suspension (DSE coilover conversion with adjustible Konis and their tubulars) has a noticible amount of sticktion--if you press down on the front of the car and release it slowly so it doesn't bounce back up, then pull up on the front end and release slowly so it doesn't bounce back down, there is a difference of 9/16" as measured at the front wheel well sheetmetal. This makes figuring a baseline number a little more complicated. Also i'm not sure if this is normal?

I'm also interested if anyone has an opinion on the order of the mods. Obviously the body mount bushings are easiest and i could have done them already but am waiting to make some careful measurements first, so i planned to do them first once i get some baseline numbers. For the front struts, on the passenger side it'll actually probably be pretty easy, but i don't see yet how i'll be able to put the driver's side strut in with my brake booster (although the salesperson at Chris Alston assured me i would be able to).

Thanks in advance for your suggestions!

WS6

04-26-2009, 12:58 PM

The torsional stiffening only deals with the frame. So you'll need to remove the suspension from the equation by putting the car on jack stands or some other type of rigid platform. What you can then do is level the frame as much as possible. From there, put a jack under the front corner on the frame and start lifting. Measure how much you lifted that corner and then how much the corner on the same side lifted. You'll also want to keep an eye on the corner across from the lift point. It may start to lift as well. That's good but it depends on more than rigidity. You should notice that with the parts in place, the car bends less and the whole side lifts more evenly with the jack under the one corner.

GetMore

04-26-2009, 05:41 PM

One thing I'll add to the advice by WS6 is that you can just measure the distance from the frame to the floor for each corner of the car and then lift it and remeasure.
Make sure the points you use for the measurement can be found again so when you remeasure you will be at the same place. This way you will eliminate one set of variables.

You can also use a second person to watch the opposite end of the car (but on the same side) to see when the frame starts to lift there and then set the car down just enough for it to be touching there.

aosborn

04-26-2009, 06:37 PM

Try this, set up the rear of the frame on jack stands, with tires clear of the ground, as close to the rear axle centerline, or the point where suspension loads are introduced to the chassis. Jack up the front end and do the same with two more jack stands. Install a couple of concrete anchors in the floor near the rear stands, screw in an eye bolt into each anchor and secure the car to the floor with chains or straps (no flex allowed). Find a spot to set a level across the front end of the car preferably over the area where the jack stands are located and take a reading (works great with a digital angle finder). Now, jack up one corner of the front end just enough to remove one stand and lower the jack. Measure how much if any the corner dropped. Do your mods and recheck. If the car doesn't move, add a lever and a load to measure twist. Multiply the load by the lever length to get your resistance. I usually use lbs per degree of twist. I have done this many times on a bare frame and it works well, it will be a bit more challenging on a completed car.

Andy

David Pozzi

04-26-2009, 07:02 PM

Herb Adams outlines how to measure and calculate torsional rigidity in his book.
You have around 4000 ft lbs per degree with your current combo. Added bracing could possibly raise that to around 6000.
David

silver69camaro

04-27-2009, 05:44 AM

To give you an idea where you're at:
1966 Mustang: 4200lb-ft/degree
Ford GT: 21400 lb-ft/degree
Ferrari 360: 16000lb-ft/degree
Audi TT: 14000lb-ft/degree
Porche 996: 12160 lb-ft/degree

jackfrost

04-27-2009, 10:38 AM

To give you an idea where you're at:
1966 Mustang: 4200lb-ft/degree
Ford GT: 21400 lb-ft/degree
Ferrari 360: 16000lb-ft/degree
Audi TT: 14000lb-ft/degree
Porche 996: 12160 lb-ft/degree

so what's the difference? are these all unibody cars?

jaybee

04-27-2009, 11:51 AM

I think the difference is old vs. new. In 1966 the standard was much lower for torsional rigidity.

cluxford

04-27-2009, 11:59 AM

As David and Matt have said it's standard around 4,000.

I just had mine rigidity tested by a qualified engineer about 4 week ago.

Here is the vitals....

68 Camaro
Art Morrison C5 front clip
full new rear frame rails (narrowed)
4 link rear with a panhard
DSE sub frame connectors. Welded in but bolted to the front clip not welded.

With no engine or trans in the car, and no interior or anything else (pretty much a stripped car). the rigidity test results can be seen below.

I am no engineer and cannot talk through this report in detail (maybe others can). All I do know is it now is just over 8,000 Ft/degree (on both sides of the car).

Note I have a full custom metal dash and console that is spot welded and runs all the way to the rear parcel shelf PLUS a metal hood liner that is also welded the entire way around the roof line. These are important as they will add a small amount to torsional rigidity.

https://static1.pt-content.com/images/pt/2009/04/TRT-1.jpg

Chevy

04-27-2009, 12:43 PM

Thanks to all who replied, this is a great discussion.

David, i was looking at Herb's book, i assume you mean Chassis Engineering. On page 96 he describes having someone stand on a 2by4 wrapped through the front frame, but this is impracitcal for a built car. I was wondering if anyone had any clever ideas of doing something similar with regular-guy shop tools with an assembled car?

Also hate to rain on your parade Cluxford but the readout you attached was in newton-meters rather than foot-lbs. Still, you have a pretty stiff chassis because with the conversion you are right about 6,100 lb-ft/deg (depending on side, they varied a little bit). This is the range David mentions getting to with properly-prepared first gens.

So if i "fix" three ends by putting them on jack stands, what is the easiest way to apply a known torque to an assembled car so i can get a number that could be compared to these other numbers?

Thanks!
Paul

cluxford

04-27-2009, 12:47 PM

Good catch...sorry I did know it was Newtom Metres (but 5am over here in Oz when I posted...hadn't woken up properly).

Chevy

04-29-2009, 05:20 AM

Still working on this, does anyone have an opinion once you fix the three corners whether you should load the fourth in bump or rebound?

Thanks again!
Paul

jackfrost

04-29-2009, 09:59 AM

please note I have no idea what I'm talking about, just sort of thinking out loud here:

it seems like you could set a torque wrench to a known value, like 200 ft-lbs, put it on the 4th corner and measure how far it takes to get it to click. then do the math with the length of the torque wrench and the distance traveled. maybe? :hmm:

WS6

04-29-2009, 10:09 AM

Paul,

How accurately are you wanting to measure? My response was in thinking you just wanted to see your parts working and to see what else you might be able to do. Is this about right or do you want specific weights and measurements?

Chevy

04-29-2009, 03:37 PM

Ideally i'd like to measure accurately enough that it was repeatable and you could measure the difference before and after mods--if in fact there was a difference. I have a background in engineering and understand the physics and measurements that need to be made, but i don't have a lot of practical experience in how to make the measurements-which is why i'm calling those experienced guys out for some help.

There are way too many claims of "substantially increases torsional rigidity" with no data to substantiate the claims!!! I haven't seen these data from any of the manufacturers and think it would be useful for all if someone did these mods systematically and made careful measurements as they went.

As a specific example, the issue of subframe connectors has been beat to death here, but frankly has never been resolved because even in the giant sticky thread there is not a single scrap of data on subframe connectors that someone could use to make their own subjective decision. What SN65 did with the stang was amazing and well documented and measured, but frankly it didn't get to the heart of what i think a lot of folks would like to see--what about the bolt-on parts that 90% of us are running? The vendors are either not making these measurements to substantiate their claims or they are not publishing them. If i am wrong and even one of the ten or more sponsors that manufacture subframe connectors that claim they substantially increase torsional rigidity have published the data, i'd love to hear about it, and will probably start patronizing them immediately.

Paul

WS6

04-29-2009, 07:36 PM

You'll find that a lot of the claims come from doing simple tests like what I mentioned. Doing the mods and then jacking up the car in a specific manner will easily show that the parts work. To give you actual data though would require them to measure like you're doing and they aren't really interested in that because it takes time, money, and either they don't know it well enough or they know that 90% of the people out there don't know it well enough to care about numbers. I'm like you though. I'm coming into my last year as a mech engineering student. I prefer numbers and evidence to back up claims.

I was planning with my own car to do what I described. Only I was going to use a dial indicator to measure. It would be a while before I would need to get a lever arm and heavy weight onto the frame and measure accurately like Adams mentioned in Chassis Engineering. I'm expecting my Ttop car to twist easily for a while.

I'm not sure where the post is as it's been that long ago. However, XV posted some videos of the testing they did in developing their parts. One of them was a simple test in which they ran tape diagonally across the engine bay to form and x. They had the car on a shaker rig and to watch the x spread apart was amazing. After their parts where on it, the x didn't spread apart so much and the video easily showed this. You could replicate this type test with your car and just using a jack instead of a shaker rig. You may not be able to get hard numbers of x pounds per degree this way. To be able to say the tape used to separate this much but no only separates this much would be very beneficial to you. You could try out different front end braces to see what helps with this simple test.

Bjkadron

04-29-2009, 07:37 PM

JRouche

04-29-2009, 09:42 PM

--what about the bolt-on parts that 90% of us are running?
Paul

I think thats the reason these aftermarket dealers are not going through the steps. They may think if you are using bolt on frame connectors you are not concerned about torsional stiffness.

Cause really, thats the weak link. Even if you pay attention the proper high torque specs for the fasteners it is still a slip fit for the connectors. Read SLIP fit. Slip will happen. Welded in connectors that are mended to the pan also provide much more torsional stiffness.

And even then its a matter of cross bracing. I welded in some beafy 2x4 heavy wall tubes to connect the rear to the front. Fully welded seams all along the pan where they met. Additional cross bars of the same 2x4" tube, fully welded to the pan and the rockers. And it still is not as stiff as it could be cause simply, Im still tying into the stock rockers, they are weak. . Thats where the weakness is. The frame is sufficiently stiff. If you were to do a jack test on the four corners of the suspension it would show some stiffness. But the problem is the body is still supported at the rockers.

So even though the frame shows some rigidness, buy itself, the body is still able to flex outside of the frame.

A quick check of that would be to jack the car up on the rockers. You may see some sag cause the body is not completely linked to the frame.

Maybe why some of the new cars with engineered uni-bodies are stiffer, they take the body and pan and make it ONE.

A way to combat that with our old cars is to make sure you have enough side bracing off of the center frame. They have to reach out to the rockers to support the body.

And when you do that you will have a solid platform, the "pan or plane" and the entire car will be supported by the horizontal pan. Then you can adjust the suspension to interact with the road from that plane. I look at it as a platform.

You have a few different horizontal planes. The base where the suspension pieces are located, bottom plane. The top, the roof line and the mid plane, belt line, where alot of your lateral weight transfer is. If you think about it spatially and tie the two panes (mid and lower) together then you have a great starting point to tune the suspension. JR

Chevy

05-01-2009, 02:57 PM

I'm gonna keep working on this, thanks for the comments and ideas. I will post up here when i figure out a practical measurement method and get your opinions. Gonna try and resist the temptation of the bolt-ons until i figure out a method to measure the changes.

Cluxford, can you describe the set-up that the shop that prepped your chassis used?

Thanks,
Paul

crashbox455

05-03-2009, 02:42 PM

Note I have a full custom metal dash and console that is spot welded and runs all the way to the rear parcel shelf PLUS a metal hood liner that is also welded the entire way around the roof line. These are important as they will add a small amount to torsional rigidity.

pics of this?

cluxford

05-03-2009, 09:41 PM

Here are a few....

https://static1.pt-content.com/images/pt/2009/05/IMG_0239-1.jpg

https://static1.pt-content.com/images/pt/2009/05/IMG_3445-1.jpg

https://static1.pt-content.com/images/pt/2009/02/IMG_3888-1.jpg

https://static1.pt-content.com/images/pt/2009/02/IMG_3897-1.jpg

https://static1.pt-content.com/images/pt/2009/02/IMG_3898-1.jpg

https://static1.pt-content.com/images/pt/2008/09/IMG_3450-1.jpg

https://static1.pt-content.com/images/pt/2008/09/IMG_3451-1.jpg

https://static1.pt-content.com/images/pt/2009/05/IMG_3891-1.jpg

David Pozzi

05-03-2009, 11:48 PM

This is a really cool topic. I'd be interested in the results when your done.

I do have a suggestion about how you could attach the lever described in herb adams book. I'm not exactly sure of how the camaros are but I think you could chain around the subframe on the unsupported side and slide the 2x4 through. As long as the chain was fairly tight it would act like it was pressing down on the top(because of the chain) so it would measure the same. Just a thought.

This is what I did, the sway bar area is the best place to position the rectangular tube on a fully assembled chassis, then stand on the end and measure either angle change or use a dial indicator and measure deflection and calculate angle change. If you use an digital angle finder, you need one that reads to two decimal places, - .00° a block of wood can be placed between the rec tube and subframe to protect it on the short end, and chain around the hanging lever end. Just use jackstands in the rear near the spring perches, but do not put so much load on the lever that the car lifts off the stands. I use a floor jack under the exact center of the front sub, it's nice to have something narrow for the sub to teeter on. Lever length is from where you apply weight, to the car centerline. do not place the angle finder on the engine, it must be on the subframe near the axle centerline.
David

Bjkadron

05-04-2009, 09:57 AM

WOW! I never thought that David Pozzi would be quoting my stuff in agreement! Cool!

Norm Peterson

05-05-2009, 05:58 AM

I think you'll find that increasing torsional chassis stiffness ends up being a 3-D sort of problem, because of the nature of the torsional moment itself. Meaning that all of the effective ways occupy/enclose a lot of volume.

Big closed-section sill structures, a la E-type Jaguars
Large transmission tunnel at least partially enclosed on the bottom (Herb Adams Silverbird)
3-D tube frame with straight load paths and numerous diagonals running in skew directions

If you've noticed, the sills and A-pillars (at least) of most new cars are much larger (read: considerably more rigid) than their 1960's counterparts. That may be mostly due to safety standards involving rollover protection and passenger cell integrity, but the performance-improvement aspect is a nice side benefit.

See if you can get hold of a copy of Omer Blodgett's "Design of Welded Structures" (Lincoln Arc Welding Foundation), as there's a pretty good section in there about designing for torsional loading. Mostly practical, not centered around theory. Any reference that's good enough to have been used as guidance in the design of US Navy warships and nuclear power plants ought to be good enough to help anybody understand how to stiffen up a hotrod.

Norm

Chevy

05-26-2009, 08:10 AM

This is what I did, the sway bar area is the best place to position the rectangular tube on a fully assembled chassis, then stand on the end and measure either angle change or use a dial indicator and measure deflection and calculate angle change. If you use an digital angle finder, you need one that reads to two decimal places, - .00° a block of wood can be placed between the rec tube and subframe to protect it on the short end, and chain around the hanging lever end. Just use jackstands in the rear near the spring perches, but do not put so much load on the lever that the car lifts off the stands. I use a floor jack under the exact center of the front sub, it's nice to have something narrow for the sub to teeter on. Lever length is from where you apply weight, to the car centerline. do not place the angle finder on the engine, it must be on the subframe near the axle centerline.
David

Thanks David that sounds way easy compared to the best i came up with!

Thanks for everyone on this thread, i'm going to get started today so hopefully post some numbers soon.

Paul

PS Awesome pics Cluxford! Do you have pics of the car finished?

cluxford

05-26-2009, 05:20 PM

Far from finished. Just started paint prep this week.

Here is an updated interior and cowl pic

https://static1.pt-content.com/images/pt/2009/05/IMG_0569-1.jpg

https://static1.pt-content.com/images/pt/2009/05/IMG_0567-1.jpg

Chevy

05-30-2009, 06:20 PM

Bet you can't wait to get her finished!
Thanks for sharing!
Paul

Chevy

05-30-2009, 06:32 PM

Folks, Thank you all for your input, it helped a lot!

I did a Herb Adams-esque measurement with the chain. I built a simple jig by scewing a 4 foot 4X4 to a 10 foot 2X4. This fit nicely under the front horns of the subframe and allowed me to place a jack stand under one corner and then put a skinny polack (thanks Dad!) on the 2X4 to apply a torque.

Baseline measurement was 3820 lb ft/deg on the driver's side and 3780 lb ft/deg on the passenger side. This is a little less than the 4000 lb ft/deg David mentioned, but looks like i may have measured further forward on the subframe so perhaps that's not unnexpected...

First mod was solid bodymounts from Chris Alston. And...drum roll please...driver's side went to 4290 lb ft/deg. That's over 12% stiffer for a simple bolt on. Needless to say i was pretty happy with that.

I'm in the middle of installing DSE's subframe connectors, i'll post here the results, hopefully tomorrow...

Then i need help adjusting my suspension to take advantage of the new stiffness!

Thanks,
Paul

anthonys 69

05-30-2009, 08:05 PM

I'm going to install 69 camaro convertibles bracing on my 69 camaro coupe for added stiffness I don't plan to use a roll cage.

Chevy

06-01-2009, 03:22 AM

I got the DSE subframe connectors in yesterday, and as promised, here are the data:

3820 lb ft/deg Starting Torsional Rigidity
4290 lb ft/deg With Solid Body mounts from Chris Alston
4750 lb ft/deg with body mounts and DSE Subframe Connectors.

Total 24% improvement from baseline. Of note, solid body mounts take about an hour to change and cost about $100. Integral subframe connectors took about two days to install on a finished car and cost about $200.

Forward struts from Chris Alston are next--i have the passenger side in already, but the driver's side will be a little trickier, we have to work around the brake booster and i'll need to re-run some brake lines so i'm bending new lines, running to hardware store, bleeding brakes, etc.

Best,
Paul

Ripper

06-01-2009, 03:57 AM

3820 lb ft/deg Starting Torsional Rigidity
4290 lb ft/deg With Solid Body mounts from Chris Alston
4750 lb ft/deg with body mounts and DSE Subframe Connectors.

Great research and wonderful that you take time to share!

I'm going to seam weld my entire gen2 shell after the summer, and was planning to share that too.

Bjkadron

06-02-2009, 05:42 PM

Cool! Thanks for taking the time to post your findings. I'm seam welding my duster and doing custom designed sub-frame connectors this summer. I'll let you know how that works out.

BillyShope

10-27-2009, 02:54 AM

By mounting laser pointers, aimed at a wall in your shop, at both ends of the car as it is positioned on wheel scales and jacking one corner, you can measure torsional stiffness directly.
http://www.racetec.cc/shope

Bryce

10-27-2009, 05:55 AM

GOOD IDEA Billy. that would be very acurate. But maybe not a wall but a board placed vertically near the laser pointer.

Jasons72

11-20-2009, 09:08 AM

Awesome thread, ive wondered what my subframe connectors and solid body mount bushings did for my nova, i'm assuming my gains would be similar to yours.

BillyShope

11-20-2009, 10:09 AM

...near the laser pointer.
The nearer you get, the poorer the accuracy. The only problem with the wall is that, if your work area is like mine, you'd have to climb over a pile of junk to get to the wall and make your measurements.
http://www.racetec.cc/shope

sik68

03-09-2010, 08:30 AM

Hey Paul, have you gotten around to making those chassis stiffness measurements for the forward struts? Do you have any pictures of the struts? Thanks a lot!

Here is a forum thread (http://www.germancarforum.com/test-data/12334-list-torsional-rigidity.html) of chassis torsional stiffness for various cars.
(NOTE: 1000Nm/deg = 738ft*lbs/deg)

Alfa 159 - 31.400Nm/degree
Aston Martin DB9 Coupe 27,000 Nm/deg
Aston Martin DB9 Convertible
15,500 Nm/deg
Aston Martin Vanquish 28,500 Nm/deg
Audi TT Coupe 19,000 Nm/deg
Bugatti EB110 - 19,000 Nm/degree
BMW E36 Touring 10,900 Nm/deg
BMW E36 Z3 5,600 Nm/deg
BMW E46 Sedan (w/o folding seats) 18,000 Nm/deg
BMW E46 Sedan (w/folding seats) 13,000 Nm/deg
BMW E46 Wagon (w/folding seats) 14,000 Nm/deg
BMW E46 Coupe (w/folding seats) 12,500 Nm/deg
BMW E46 Convertible 10,500 Nm/deg
BMW X5 (2004) - 23,100 Nm/degree
BMW E90: 22,500 Nm/deg
BMW Z4 Coupe, 32,000Nm/degree
BMW Z4 Roadster: 14,500 Nm/deg
Bugatti Veyron - 60,000 Nm/degree
Chrysler Crossfire 20,140 Nm/deg
Chrysler Durango 6,800 Nm/deg
Chevrolet Corvette C5 9,100 Nm/deg
Dodge Viper Coupe 7,600 Nm/deg
Ferrari 360 Spider 8,500 Nm/deg
Ford GT: 27,100 Nm/deg
Ford GT40 MkI 17,000 Nm/deg
Ford Mustang 2003 16,000 Nm/deg
Ford Mustang 2005 21,000 Nm/deg
Ford Mustang Convertible (2003) 4,800 Nm/deg
Ford Mustang Convertible (2005) 9,500 Nm/deg
Jaguar X-Type Sedan 22,000 Nm/deg
Jaguar X-Type Estate 16,319 Nm/deg
Koenigsegg - 28.100 Nm/degree
Lambo Murcielago 20,000 Nm/deg
Lotus Elan 7,900 Nm/deg
Lotus Elan GRP body 8,900 Nm/deg
Lotus Elise 10,000 Nm/deg
Lotus Elise 111s 11,000 Nm/deg
Lotus Esprit SE Turbo 5,850 Nm/deg
Maserati QP - 18.000 nm/degree
McLaren F1 13,500 Nm/deg
Mercedes SL - With top down 17,000 Nm/deg, with top up 21,000 Nm/deg
Mini (2003) 24,500 Nm/deg
Pagani Zonda C12 S 26,300 Nm/deg
Pagani Zonda F - 27,000 Nm/degree
Porsche 911 Turbo (2000) 13,500 Nm/deg
Porsche 959 12,900 Nm/deg
Porsche Carrera GT - 26,000Nm/degree
Rolls-Royce Phantom - 40,500 Nm/degree
Volvo S60 20,000 Nm/deg
Audi A2: 11,900 Nm/deg
Audi A8: 25,000 Nm/deg
Audi TT: 10,000 Nm/deg (22Hz)
Golf V GTI: 25,000 Nm/deg
Chevrolet Cobalt: 28 Hz
Ferrari 360: 1,474 kgm/degree (bending: 1,032 kg/mm)
Ferrari 355: 1,024 kgm/degree (bending: 727 kg/mm)
Ferrari 430: supposedly 20% higher than 360
Renault Sport Spider: 10,000 Nm/degree
Volvo S80: 18,600 Nm/deg
Koenigsegg CC-8: 28,100 Nm/deg
Porsche 911 Turbo 996: 27,000 Nm/deg
Porsche 911 Turbo 996 Convertible: 11,600 Nm/deg
Porsche 911 Carrera Type 997: 33,000 Nm/deg
Lotus Elise S2 Exige (2004): 10,500 Nm/deg
Volkswagen Fox: 17,941 Nm/deg
VW Phaeton - 37,000 Nm/degree
VW Passat (2006) - 32,400 Nm/degree
Ferrari F50: 34,600 Nm/deg
Lambo Gallardo: 23000 Nm/deg
Mazda Rx-8: 30,000 Nm/deg
Mazda Rx-7: ~15,000 Nm/deg
Mazda RX8 - 30,000 Nm/degree
Saab 9-3 Sportcombi - 21,000 Nm/degree
Opel Astra - 12,000 Nm/degree
Land rover Freelander 2 - 28,000 Nm/degree
Lamborghini Countach 2,600 Nm/deg
Ford Focus 3d 19.600 Nm/deg
Ford Focus 5d 17.900 Nm/deg

It think it's funny how the Corvette and Viper are among the noodle-iest of these cars.

Norm Peterson

03-09-2010, 10:02 AM

I've translated that table into an Excel spreadsheet, re-sorted it all, and added a column for lbf-ft/deg, which may make it more useful.

For Ferrari, 1000 kgf-m/deg = 9806.6 Nm/deg = 7233 lbf-ft/deg and 1 kgf/mm = 56 lbf/in.

But I'm a bit suspicious about that really low value for the Lamborghini Countach.

And somebody probably should double-check everything.

Norm

Bjkadron

03-09-2010, 02:58 PM

The Aston Martin one-77 supposedly is 22,000 lb-ft/deg. But that sounds incredibly high.

Chevy

03-10-2010, 06:12 AM

mikedc

04-11-2010, 01:35 AM

I don't know about you guys, but I've never actually flung around a Bughatti Veyron's 60,000 Nm/deg chassis and tested how it feels compared to 34,000 Nm/deg Fararri F50.

Specific numbers on a few cheaper & older American rides might be a bit more relevant.

Tony Arnold

12-30-2010, 10:01 PM

What i noticed from the pictures posted of the chassis stiffners are that they do not provide any triagulation and do not strengthen the chassis where it sees the load. If you were to look at any NASCAR chassis you will see multiple bars going to the spring pockets. This help support the load that the chassis sees at the point it gets loaded. You will also see that most chassis builders will tie both front hoops or spring pockets together with either bolt in k or x bars. Keep in mind these are just my suggestions. One simple thing you could try is make a bar about 1 3/4 in dia and run it across both hoops to tie them together.

TheBandit

02-23-2011, 01:23 PM

I stumbled on this thread reading through the stickies today. I'd really be interested to see this kind of testing done for the Hotchkis Handle Bars.

https://static1.pt-content.com/images/noimg.gif

Thanks to all who've contributed to the thread. I will try to get similar measurements before & after on my Nova when the time comes.

andrewb70

06-06-2020, 08:10 AM

....I will try to get similar measurements before & after on my Nova when the time comes.

Better late than never :-)

Andrew

TheBandit

06-08-2020, 08:15 AM

Better late than never :-)

Wow I forgot all about this thread. Looking at the dates I was still a few years out from having my car back on the road at that time. I recently started a new thread on this topic, but decided to nuke it to keep the conversation going here since there is already a lot of good info.

I am preparing to install subframe connectors and I plan to get a baseline measurement on the torsional rigidity of my car, then see how much it changes. After reading through this thread I have a few ideas on how I'll go about it. Thank you for pointing me back here Andrew!

For reference, in addition to what's described in this thread, I came across another well-documented attempt at this here:
https://www.stangnet.com/mustang-forums/threads/torsional-rigidity-test-67-coupe.723029/

David Pozzi

06-10-2020, 07:56 PM

I recommend using a dial indicator instead of the angle finder that I used in my tests. Accuracy is rather poor with a .05 resolution angle finder. With a more common .0 resolution angle finder, it's very poor. Many phones can do angles but I think the resolution is not good enough.

TheBandit

06-19-2020, 07:17 PM

David I could not find inch on how you constrained, loaded or measured yours. Did you post an explanation here or on your website thanks for any pointers.

TheBandit

06-19-2020, 08:09 PM

Found a great video here

https://youtu.be/xTlj2XLEOF8

Norm Peterson

06-20-2020, 08:18 AM

When you're looking for effects in the 5%-ish range, I think you should be hanging barbell plates from a fixed position near the end of that bar. Bags of loose stuff distributed over a foot or more probably won't end up with their weights as evenly distributed from one trial to the next, or even be located in the same places every time.

The door bars can only improve torsional stiffness over their length within the chassis, so they may well have added 8% - 10% to that mid-section portion of the chassis. Everything in front of and behind that section is the same as before, so the overall effect would be one involving "springs in series" math.

But it is a good illustration of concept, despite the mention of strength rather than stiffness.

Norm

David Pozzi

06-28-2020, 07:56 AM

David I could not find inch on how you constrained, loaded or measured yours. Did you post an explanation here or on your website thanks for any pointers.

I tested similar to the Porsche video. Used a chain to support the square tube & apply torque. I did not tie down the other end. Just supported it on jack stands. It’s heavy enough That it did not move on a fully built car. On a shell it needs a counter balance Weight or tied down. I tested a Camaro with roll cage & nearly no stiffness improvement! The forward braces stopped near the steering box coupler which was required by the SCCA rules.

TheBandit

06-29-2020, 11:02 AM

Thank you David. Where did you position your jack stands? With a fully built car I am thinking both sides under the rear subframe near the front leaf spring perch and one side under the front subframe on the horn extending in front of the suspension. Then a chain over the other horn of the front suspension for the lever bar. Torque would be measured from the single jack stands up front to wherever the weight is applied. I would measure deflection at the unsupported frame horn.

I was thinking maybe instead of using weights, I could use a jack and put a bathroom scale between the jack and the lever arm. That would require chaining the opposite side of the lever arm.