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Old 11-17-2011, 11:20 AM   #1
haberkorn
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Default Carbon fiber vs Aluminum drive shaft

I've had an interest in this discussion but never really had anyone with facts as to rotating mass, horsepower difference etc. My family owns a shop locally that does aluminum, steel and moly drive shafts and I was just curious so I found this study and figured I would post it up as I see the aluminum driveshaft question arise fairly regularly on here.

It's pretty interesting if your thinking about going to a carbon/composite driveshaft.

Here's the link to the study:
http://www.engineer.tamuk.edu/depart...ign_report.pdf

If you don't want to read the entire thing, basically at the end they determine that the carbon drive shaft was a waste of money over an aluminum shaft and didn't produce any performance benefits.
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Old 11-17-2011, 11:30 AM   #2
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but its carbon... it cost me XXX more so it HAS to be better.

Only thing i can see Carbon being better for would be for driveline shock absorption.
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Old 11-17-2011, 12:03 PM   #3
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The big difference ive sen is the the CF ones are generally smaller in diameter causing fewer fitment issues. I had to clearance a few things to get my DSS aluminum driveshaft to fit.
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Old 11-17-2011, 12:23 PM   #4
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Quote:
Originally Posted by tom@kartboy View Post
but its carbon... it cost me XXX more so it HAS to be better.

Only thing i can see Carbon being better for would be for driveline shock absorption.
That's the common ricer train of thought for sure. I can see that being a benefit as well.

Only thing I had to clearance with my 3" aluminum shaft in my sti was I had to take off the diff protector to make room for the bigger OD. It took about 5 minutes on a hoist. I don't remember having to clearance anything else.
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Old 11-17-2011, 12:46 PM   #5
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There was about a papers width of clearance between the driveshaft and the saddle the comes off the diff cradle, and it rubbed on my rear shifter bushing. Granted perhaps its just because mine is a 00 RS with a WRX swap.
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Old 11-17-2011, 12:51 PM   #6
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Both are dumb when you can have a 2.75" single piece steel DS made for $275. That's what I did. It's fits perfect. And it's a smaller diameter than the Al one. It's only about 3 lbs heavier. Static weight means NOTHING on a DS. But it is a smaller diameter so its comparable to an Al ds in rotational inertial.

It's a HUGE improvement over the stock STi 24.5lb unit...
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Old 11-17-2011, 12:54 PM   #7
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So I don't have to retype this, here are some previous posts of mine on my experiences:

http://forums.nasioc.com/forums/show...&postcount=442
Quote:
Originally Posted by kpluiten View Post
I also had a one piece driveshaft made to replace the two piece STi one. I've read many good things about single piece shafts and the responsiveness they add to the car, but I didn't have the money for an aluminum one ($500) or a carbon fiber one ($1200) so I opted for a steel unit made locally. The advantage to the steel unit is that while it weighs marginally more than the aluminum or carbon units, it is significantly cheaper than the other two, fits much better than the aluminum one, and has a smaller diameter than the aluminum one.

In a drivetrain system, static weight is far less important than rotational inertia. In this case, the steel shaft is 3 lbs heavier than the aluminum one, but it is 2.75" in diameter vs the 3" diameter for the aluminum unit. While I have yet to do the math, I would expect the steel unit to have the same or less rotational inertia than the aluminum solution because it has a smaller diameter and thinner wall thickness. 3lbs static weight difference is really nothing in the scheme of things, especially considering how heavy the stock shafts are. Mark and I did some unofficial measurements and compared it with other driveshaft solutions on the market. This is what we found.

Stock 5MT DS: ~21.5lbs
Stock 6MT DS: ~24lbs (my application)
PST Carbon 6MT DS: 14.4lbs
DSS Al 6MT DS: 14lbs
Steel 1 piece 6MT DS: ~17lbs

Additionally, unlike the stock DS, this new unit has fully serviceable/rebuildable u-joints.

Here are some photos:

Top to bottom: OEM 6MT, OEM 5MT, 1-piece Steel 6MT


Serviceable/replaceable u-joints:





Mark also had a good idea to use the stock center carrier bearing from an OEM shaft as a make-shift driveshaft loop just in case a joint broke. The tail joint of the DS is pretty well encased by a factory part, but nothing but the exhaust would really hold the front up. Since I have a ton of spare 5MT DS's sitting around, I cut one up just to try.

I took this part off (cut the rubber and metal out):


And was left with this:


Painted up:


Everything installed on the car:




This is the only area where I am slightly concerned with fitment (between the DS and the t-member). There is about 0.25" between the two and very little should flex in this area, especially with the upgraded differential and outrigger bushings.


Overall, the fitment was great and it was sized perfectly. It should be balanced to 7000 rpm which is a around 140mph with my final drive. The shop seemed pretty confident it would do better than that to. I guess we'll see soon. I'll be testing this to see if it has any strange vibrations or the like before I have anymore made for others.




This thread has some discussion as well:
http://forums.nasioc.com/forums/show...php?p=34287785
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Old 11-17-2011, 01:09 PM   #8
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Back when i did my swap we had three DSS alum shafts from them. all were within 1/2" of each other!!! WTF QC? none were balanced. Granted this was back in 07. hopefully they've gotten better.
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Old 11-17-2011, 01:18 PM   #9
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Bah...1/2 inch is close enough. Just stretch the thing Tom.

I agree with you kpluiten, a small diameter steel shaft is the easiest way to go. That being said, the 2.75 will reach critical mass and cause a vibration. But if its a street car it should never see that speed/rpm combo. Your drive shaft loop is sweet by the way.

The 3" shaft in my will vibrate like all hell is breaking loose around 170MPH, in which case you have to go to a 4" shaft and re-tin the interior of the car heh. We do 4" diameter shafts for quite a few local mid 6-7 second doorcars and they are nice and smooth at 200+ mph.

Last edited by haberkorn; 11-17-2011 at 01:25 PM.
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Old 11-17-2011, 03:09 PM   #10
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170?! Wow! Yeah, I haven't driven in the triple digits in years. I did 140 WAY back in the day when I first got the car. And promptly promised to not do that on the street ever again... to the officer. So yeah, 2.75 should work fine for me!

90 is my max these days. And I can do that on any on-ramp around here easily. I would be curious to see just how fast I could go before vibration took over.
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Old 11-17-2011, 05:07 PM   #11
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Haha! I don't have the balls for 170 in my subaru, hell I've only been 165ish in my race car. I can't go faster in the street car than I do in my race car, that would be some sort of sin.

We did the figuring off the balancer speed and rpm at the driveline shop. I did however have a swapped rs 35r car locally hit about 165 with a 3" aluminum shaft in it at a mile long race here and he called me frantically asking if the driveshaft fell apart heh. I told him to not drive so fast.

I bet the 2.75 shaft would be probably just north of 130 -140 you'd start with the constant vibration down the center. I would assume the critical speed is linear, so if a 3" shaft is good till 160-170 and 4" is good to 200+, 3/4 of an inch and a heavier wall can't be more than 20-30 mph difference I wouldn't think.

Last edited by haberkorn; 11-17-2011 at 05:16 PM.
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Old 11-20-2011, 06:49 AM   #12
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...yeah

Last edited by Uncle Scotty; 11-20-2011 at 06:55 AM.
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Old 11-21-2011, 09:44 AM   #13
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With the smaller diameter dss cf driveshaft it says its safe to 180mph. Is this different from the norm due to material?

Last edited by todeswalzer; 11-21-2011 at 01:14 PM.
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Old 11-21-2011, 11:45 AM   #14
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Could be a difference in materials sure. I've never had a carbon shaft in our shop to test it.
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Old 12-06-2011, 12:44 AM   #15
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Nice write up but interested to see the difference between 4" Al, ~3" steel and the CF ones.
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Old 12-28-2011, 09:50 PM   #16
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I had a local reputable shop, blumenthal transmission in OKC, fab up a one piece 2.75" steel drive shaft for me. I figured out why the Japanese didn't go with a single piece steel shaft in the first place.... after all, it would have been lighter and way cheaper for them to go this route. I have a very obnoxious resonance from ~75-95 mph that peaks right in the middle. It goes away over 95 mph. This means that my problem is NOT a balance issue, which would behave with a squared function to the shafts rpm. I suspect this is the reason the Aluminum shafts are larger in diameter. Carbon is very stiff and can get away with smaller O.D. I just wanted to throw my experience out there so people understand that they could throw $300 away on a shaft that has a resonance issue. Have a 6 speed swap on my 04 wagon btw.
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Old 12-30-2011, 12:38 AM   #17
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I find it funny that the OP references a College Engineering Student's senior design report as their reference. Speaking from experience, anything generated by a college senior in engineering is barely worth the paper it's written on.

I read though the report and noticed several problems in their methods and testing. The conclusion is at best suspect, and more than likely incorrect.

A well made CF drive shaft in a true racing application would be worth the extra $$ IMPO. As it has been stated earlier, the real difference is the rotational inertia of the drive shaft. I have complete confidence that a well designed and well made steel, aluminum, or carbon fiber drive shaft will perform almost equally on a car due to their relative possions ratio's and their compressive strength per weight. A titanium drive shaft I think would blow them all out of the water. It would also cost more than the CF drive shaft, so if cost was (and it really always is) a consideration, it would not be worth it. This will change in the next few years (if it hasn't already) with advances in CF and resin technology that will make the CF drive shaft superior to all others. At that point we will start seeing CF drive shafts in production vehicles.
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Old 12-31-2011, 01:20 AM   #18
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i have a carbon, and LOVE it.
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Old 12-31-2011, 02:23 PM   #19
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I'd have to agree with the general assumtion that CF will be better than Alum or Steel. However, seeing as many high performance supercars these days still come stock with Alum instead of CF, I'd be willing to wager that gains seen from the latter are mostly applicable to a closed circuit with a clock running.

Wasn't the torque tube and CF driveshaft on the newest SLS AMG a huge deal because of it's materials?
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Old 12-31-2011, 10:04 PM   #20
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Thank you for posting that up

We did similar testing on our 2011 STi and found good gains. Not astonishing power level wise, however the drivability, and response of the car greatly improved

We actually increased the power output by switching to a PST carbon drive shaft, again not huge gains. But as you can see both tq and hp improved as a result of reduction of rotational mass.
No other changes where made between the tests, and the ambient temp was within 5 degrees on both runs, same tank of gas, same ECU map (not even reset), and so forth.
http://forums.nasioc.com/forums/show...27&postcount=1



Nissan is also using carbon on may of their new cars, the GT-R uses them, and if I am not mistaken so does the 370Z.

The issue with aluminum is the diameter has to be much greater compared to composite unit, and also the critical speed is lower. For instance DSS says to not spin the aluminum STi shaft past 155MPH do to vibration issues that can arise. Where as for example the critical speed of the PST composite same shaft is above 190MPH.
Huge benefit to carbon is how it fails. If you break the shaft anywhere between the yokes the carbon will separate and do minimum damage to the under carriage along reducing harm to the occupants.
Weight wise the Aluminum shafts where actually a hair lighter then the carbon units.
Another thing is that the carbon shaft has a much larger torsional rotational angle that it can be put through prior to failure compared to a aluminum unit.

Fine Line Imports also did a test with a carbon shaft and found similar results to our findings as well.

http://fliblog.wordpress.com/2009/02...iveshaft-test/

Kirill
RallySportDirect.com

Last edited by RallySport Direct; 12-31-2011 at 10:11 PM.
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Old 01-10-2012, 10:06 AM   #21
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Carbon fiber drive shafts provide high strength at low weight. In racing applications where everything counts, it's worthwhile, however it's also true that there are definitely places where you'll get better bang for your buck if you're just building a fun car for the street.
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Old 01-11-2012, 03:20 PM   #22
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what other kinda fitment issues are people having with the dss aluim

thinking of buying one from my friend for a good deal
I already had the pst cf and it vibrated like crazy at 120kph so i sold it
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Old 01-11-2012, 08:54 PM   #23
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That's what I feel at the same speed, I thought it was expected with a one piece. To me, it is acceptable but I can see how it won't be for others.
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Old 01-12-2012, 01:14 AM   #24
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Quote:
Originally Posted by kenliu84 View Post
That's what I feel at the same speed, I thought it was expected with a one piece. To me, it is acceptable but I can see how it won't be for others.

which drive shaft are you running
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Old 01-12-2012, 11:55 AM   #25
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PST carbon fiber
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