Indeed sir, cant wait for my monster to arrive
Rear Torsion Bar Upgrades...worth it?
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This is a sticky topic.
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Mods I don't have:
cage
stripped interior
chassis braces
cam
big turbo
new internals
....pretty much everything else
Sponsors:
Eurocompulsion
AAD
Cipher Auto
Pending:
Megan Racing (coil-overs)- Top
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For normal daily driving, either the Neu-F or the RRM bar will be an improvement to stock. They are both easy to install, whichever one ends up being cheaper should be your choice. There might be some on the classifieds soon with people replacing their bars with Ron's bars.
Now that we have Ron building custom torsion bars, we can start experimenting with them to dial in the rear suspension for racing applications.CPR 2013 NERO 500T (frankenstein) CPR ENGINE COVER , CPR TUNNEL BRACE , CPR INTERIOR X BRACE , E and D TUNE , BOOST FIX , MEGAN RACING COIL OVERS , 2 1/4"DROP, CUSTOM BORIS STRIPES , V4 , GTR RIMS /FALKIN RT613K TIRES , rear seat delete , CPR weld on rear torsion bar assembly.- Top
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As others have pointed out, for a given material the torsional stiffness of a circular cross-section is given by the Polar Moment of Inertia, J
For a circular x-section J = (PI*r^4)/2 or (3.1416*r^4)/2 , where r is the radius of the cross section. So in comparing the stiffness of a 25 mm torsion bar to a (stock) 22 mm bar, calculate the numbers and compare the ratio.
The ratio is 390625/234256, or 1.67
This means that the 25mm bar (if made of the same material) is 67% stiffer than the stock bar. If comparing two bars made of steel, one alloy may be stronger than another but the Shear Modulus, G doesn't vary by much. Hence a round bar of mild steel will be as stiff in bending and in torsion as the equivalent bar of alloy steel ( it won't be as strong though).
Steel has an elastic modulus and shear modulus that is about three times greater than Aluminum ( it also weighs three times as much). Consequently for this application Steel is what is used for these bars.
Having said all of that, what constitutes the OPTIMUM bar diameter for our cars is not so easy to figure. Most reports I've read about the Abarth say it under steers a bit, so I felt it would be a pretty low risk to put on a 25 mm bar. I haven't had any problems with this bar. At some point I should take the car to an empty lot, shut down ESC and drive a constant radius turn at increasing speed until it under steers, over steers, or is pretty neutral. So far as reducing body roll, the thicker bars will help with that although at some point there will be a diminishing return.
So have fun. Realistically, for daily driving you probably won't notice much of a difference, but it's a pretty easy mod to accomplish that can improve the car.- Top
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As others have pointed out, for a given material the torsional stiffness of a circular cross-section is given by the Polar Moment of Inertia, J
For a circular x-section J = (PI*r^4)/2 or (3.1416*r^4)/2 , where r is the radius of the cross section. So in comparing the stiffness of a 25 mm torsion bar to a (stock) 22 mm bar, calculate the numbers and compare the ratio.
The ratio is 390625/234256, or 1.67
This means that the 25mm bar (if made of the same material) is 67% stiffer than the stock bar. If comparing two bars made of steel, one alloy may be stronger than another but the Shear Modulus, G doesn't vary by much. Hence a round bar of mild steel will be as stiff in bending and in torsion as the equivalent bar of alloy steel ( it won't be as strong though).
Steel has an elastic modulus and shear modulus that is about three times greater than Aluminum ( it also weighs three times as much). Consequently for this application Steel is what is used for these bars.
Having said all of that, what constitutes the OPTIMUM bar diameter for our cars is not so easy to figure. Most reports I've read about the Abarth say it under steers a bit, so I felt it would be a pretty low risk to put on a 25 mm bar. I haven't had any problems with this bar. At some point I should take the car to an empty lot, shut down ESC and drive a constant radius turn at increasing speed until it under steers, over steers, or is pretty neutral. So far as reducing body roll, the thicker bars will help with that although at some point there will be a diminishing return.
So have fun. Realistically, for daily driving you probably won't notice much of a difference, but it's a pretty easy mod to accomplish that can improve the car.
You are easily smarter than I am..LOL still all that"smart stuff" breaks down to the diameter to the 4th power, and I used numbers instead of percentages to show the drastic differences, 1.67 times compared to 234,000 to 390,000 All rounded numbers of course
Het when did they start teaching physics in SC Im from West Virginia and they havnt started "new math" yet HA HACPR 2013 NERO 500T (frankenstein) CPR ENGINE COVER , CPR TUNNEL BRACE , CPR INTERIOR X BRACE , E and D TUNE , BOOST FIX , MEGAN RACING COIL OVERS , 2 1/4"DROP, CUSTOM BORIS STRIPES , V4 , GTR RIMS /FALKIN RT613K TIRES , rear seat delete , CPR weld on rear torsion bar assembly.- Top
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Ron is the best. If you are going to be buying a new bar, definitely get it from Ron/CPR. I have one of his awesome torsion bars right now and will be installing it this weekend. I will be providing impressions next weekend at my next autocross event.Last edited by nilfinite; 08-16-2014, 04:33 PM.- Top
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As others have pointed out, for a given material the torsional stiffness of a circular cross-section is given by the Polar Moment of Inertia, J
For a circular x-section J = (PI*r^4)/2 or (3.1416*r^4)/2 , where r is the radius of the cross section. So in comparing the stiffness of a 25 mm torsion bar to a (stock) 22 mm bar, calculate the numbers and compare the ratio.
The ratio is 390625/234256, or 1.67
This means that the 25mm bar (if made of the same material) is 67% stiffer than the stock bar. If comparing two bars made of steel, one alloy may be stronger than another but the Shear Modulus, G doesn't vary by much. Hence a round bar of mild steel will be as stiff in bending and in torsion as the equivalent bar of alloy steel ( it won't be as strong though).
Steel has an elastic modulus and shear modulus that is about three times greater than Aluminum ( it also weighs three times as much). Consequently for this application Steel is what is used for these bars.
Having said all of that, what constitutes the OPTIMUM bar diameter for our cars is not so easy to figure. Most reports I've read about the Abarth say it under steers a bit, so I felt it would be a pretty low risk to put on a 25 mm bar. I haven't had any problems with this bar. At some point I should take the car to an empty lot, shut down ESC and drive a constant radius turn at increasing speed until it under steers, over steers, or is pretty neutral. So far as reducing body roll, the thicker bars will help with that although at some point there will be a diminishing return.
So have fun. Realistically, for daily driving you probably won't notice much of a difference, but it's a pretty easy mod to accomplish that can improve the car.
I got a 30mm bar from Ron tapered down to 22mm on the ends. It'll probably be somewhere around 100% stiffer than the stock bar.Last edited by nilfinite; 08-16-2014, 04:33 PM.- Top
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Thanks for the replies everyone. So I have tally'd up the replies to this thread and these are the types of replies so far (and yes I'm paraphrasing):
"I haven't installed a bar yet but looking forward to it." x1
"I have installed a bar but haven't driven alot yet to comment." x1
"ZOMG! The BAR is BEST! MUST HAVE!" x1
"Installed bar but with other/supporting mods." x2
"Miscellanious comments." x10
"Yes I installed the bar. yes I like it. No reason not to install it." x2
I started a fresh thread to find out the Pros/Cons to installing a bar from those that have them on their Fiat500/Abarths. I'd like to hear more from people that have installed a bar and what they noticed if anything.
Which bar have you installed on your car. and what difference did you notice?
Here's a perfect example: I purchased a certain "shifter accesory" that was getting rave reviews on the forums and websites. No one said anything negative about it. What a great mod.
As soon as I purchased it someone made a new thread and asked if anyone else was experiencing the same negative effects they were. All of a sudden numerous people were coming forward with their similar problems.
I ended up seling the part at a small hit to my wallet. I don't want the same thing to happen if I purchase a larger rear bar.Last edited by slowbird; 08-16-2014, 05:35 PM.👍 1- Top
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My answer to your question was one of the first responses, that being - yes it will affect ride quality. Positively, indeed it will tighten up the rear of the car.
Question to you: How much do you want to tighten the car prior to other suspension mods?
A little - go with a 25mm
Moderate - 28mm
With that in mind, what other mods are you interested in that will relate to suspension?
The negative side of all this? The car will get stiff fast with suspension mods, but it won't wander all over the road whrn its windy or you hit a small bump.
You really need to drive a car with just a new rear bar on it, it is easier to understand once you drive a car with it installed.Last edited by shadowshaggy; 08-16-2014, 05:37 PM.Mods I don't have:
cage
stripped interior
chassis braces
cam
big turbo
new internals
....pretty much everything else
Sponsors:
Eurocompulsion
AAD
Cipher Auto
Pending:
Megan Racing (coil-overs)- Top
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Comment
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Driving wise, mine will be uncomfortable daily duty; the 25mm is good daily and good for a spirited drive. The 28mm is a little stiffer, so I would recommend, for example, the CPR 25mm with new brackets. That way you get a solid 25mm bar with new brackets, not tapered to the 22mm mounts.
IMO the ride is too bouncy, twitchy, and rough as it is. I f I were to do anything it'd be adjustable Koni's front and rear.Last edited by slowbird; 08-16-2014, 06:02 PM.- Top
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See pm, I will butt out of this conversation.Last edited by shadowshaggy; 08-16-2014, 06:59 PM.Mods I don't have:
cage
stripped interior
chassis braces
cam
big turbo
new internals
....pretty much everything else
Sponsors:
Eurocompulsion
AAD
Cipher Auto
Pending:
Megan Racing (coil-overs)- Top
- Bottom
Comment
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I recently drove an Abarth with Bilstiens and on anything but smooth surfaces I found the ride Bone Jarring. I couldn't live with that as a daily driver but boy did it look nice.
Everyone has different preferences...hence my request for everyones experiences with an upgraded rear bar.- Top
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If you are wanting to tighten the steering and not worried about racing etc I would buy a lower chassis brace and a set of the RRMS corsa chassis braces RRMS has the corsa on sale for $189 and I sell the lower brace for $100 shipped, it would be worth while to ask as you have here about the effect on understeer
I have over 30 of the lower braces on the road including tweaks car I am confident that you will here nothing negative about the quality or performanceCPR 2013 NERO 500T (frankenstein) CPR ENGINE COVER , CPR TUNNEL BRACE , CPR INTERIOR X BRACE , E and D TUNE , BOOST FIX , MEGAN RACING COIL OVERS , 2 1/4"DROP, CUSTOM BORIS STRIPES , V4 , GTR RIMS /FALKIN RT613K TIRES , rear seat delete , CPR weld on rear torsion bar assembly.- Top
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