Driveline vibration

http://hpwizard.com/rotational-inertia.html

Here you go, you're looking at around a 10-15% 'bonus' by taking weight out of the drive shaft rather than body in terms of power and acceleration. Going from the Coz listings you're dropping ~8kg:equiv going from stock to aluminium for $500. It's not exactly at the top of the list for value for money power adders but once you've done the basics (Big turbos and E85) it's probably not too bad. Again assuming they actually work properly and aren't reduced to a modern art installation on your first proper launch.

Wheel/tyre assemblies are a fair bit more impactful with 50-100% 'bonus'. Harder to come up with good estimates though having such irregular weight distribution.

 

Driveshafts dont have offset weights and flying arms like a crank, they are not percentage balanced to suit an rpm.
What rpm they are balanced at is largely irrelevant.
Id go as far to say that claim of highspeed balancing is sales blather. If they dont shake at 3000 rpm, they wont shake at 5000rpm or 10,000 rpm, UNLESS they were incorrectly balanced in the first place

E

 

There is information available on the net concerning tailshafts, as an example:

In practice, all rotating shafts contain some imbalance or misalignment.
Depending on the 'out of balance' and the flexibility of the end supports, some vibration will be present.
Critical speeds are those at which a tail shaft displays excessive whirling.
As the rotation speed approaches the 'critical' speed of the shaft, the imbalance will result in increasing lateral deflection or 'whirling' and possible self-destruction.
To prevent this, the shaft length and stiffness must be chosen to have a sufficient margin between the maximum operating speed and the shaft's 'critical' speed.

All rotating shafts undergo deflection during rotation.
The magnitude of deflection of a dynamically balanced shaft is dependent on the stiffness of the shaft, rotational speed, distance between supports and magnitude of the secondary couple.
The stiffness of the shaft is based primarily upon tube diameter and thickness.
The speed at which maximum deflection occurs is called the critical speed.
For any given shaft there are an infinite number of critical speeds, however for practical reasons we are only interested in the first order critical speed.
Running at or near the critical speed will cause the shaft to vibrate excessively and ultimately fail, which can severely damage the driveline and surrounding components.
It is important that a tail shaft operates sufficiently below its critical speed.

The tailshaft will spin at 7,000rpm in top gear at redline in a stock TT.
The synchro's in my OS Giken gearbox limited the rpm to 9,000rpm.

Carbon fibre tailshafts are factory fitted in the R35 GT-R.

Sydney Driveline Service (the subject of the original post)balance the tailshafts at 3,000rpm & state they are good for 5,500rpm.

 

Mate, this is all very interesting but its old news.
Look at the very first point.

You might have missed my post further up about my engineer cobbers here who do a custom/one-off tailshaft building service.
They have NEVER had to balance a tailshaft. ive watched them do several. They do the whole job in a large lathe with additional steadies for the tube, the spigots on the ends have a slight step machined into them and the tube ends machined true, pressed together paying a lot of attention to phasing of the yoke ends.
The whole show is slowly spun with a dial guage used from end to end to look for runout, and welded.

No balancing necessary.

E

Its this attention to detail that makes most of the spiel above largely pointless.. IF the job is dont right to begin with.

 

If they genuinely don't need balancing and are being used in high speed, short final drive ratio vehicles and are lighter than a stock unit I would have to guess they are using top shelf base components. Most castings and extrusions wont be of uniform density. I bet for your buddy doing less work than other tailshaft shops his products aren't any cheaper. So not a disagreement 'if it's done properly' but obviously most people dont think that approach doesn't pass a cost/benefit analysis.

 

Re: Tailshaft balancing

https://www.youtube.com/watch?v=tm7DhP3M4AA

https://www.youtube.com/watch?v=Uw-VrpYmuz0

 

The only "high-end" components my mates use are the correct type of tubing for the job. other than that, the yokes and so-on are just off the shelf clobber.

E

 

These are interesting vids.
Well worth watching.

E

 

Carbon Fibre vs Steel.

https://www.youtube.com/watch?v=hjErH4_1fks

 

Well thats real interesting...I think

So, we compare a (circa) 5000, yes, five thousand dollar tailshaft against a 250 dollar steel shaft!!!
They didnt describe the steel type, the thickness. Just compared, what looked remarkably like stainless steel food grade tubing, to a hideously expensive custom item destined for a million dollar plus supercar.

There was no repetitive, high speed cycling, there was no, sudden impact loadings, there was no heat cycles, no additional vibration... nothing.

Im mean.. really mate, what exactly does this largely pointless comparison actually achieve in the real world other than to pull the wool over the ignorant populations eyes?

Why not just, move the engine to the back, transversely mount it and do away with the tailshaft altogether.
For the amount of folding stuff required to buy something decent like that, you could have your car modified to do away with the tailshaft altogether.

Yep, Im convinced..... That that video is no more than a thinly veiled advertisement.

E

 

With the popularity increasing the last few years of using aftermarket drive shafts , we wanted to go over some information in regards to the subject & cover some common questions that we see our customers ask us about.

Why?:

The reason to change out the drive shaft to a Aluminum or Carbon Fiber unit is quite simple, it is to reduce rotational mass & increase response.

By replacing the heavy stock steel drive shaft with a lighter 1 piece unit you save about 1/2 the weight in most applications, & allow more energy to go into rotating the tires instead of rotating dead weight.

Similar concept as doing a lighter flywheel & pulley, however other additional benefits are also to be had.

Many new modern cars are now coming equipped with light weight shafts for the reasons of performance, such as the GT-R & other high end exotics.

Aluminum Vs Carbon:

2 of the most popular materials to use when replacing the steel shaft will be either aluminum or carbon fiber.

Below I will cover some of these basics.

1)CF shaft is smaller in OD to handle the same torque capacity as the aluminum counterpart unit.
Means you have more clearance & requires less modification under the car to run a carbon shaft vs aluminum.
Some applications require modification to heat shields or transmission tunnels to allow adequate clearance for the larger OD Aluminum shaft.

Reason for the larger diameter of the Aluminum shafts is that these shafts are purchased as raw aluminum from aluminum manufactures.
These raw aluminum tubes are only available in certain sizes, so to get the adequate wall thickness of the tube to handle the torque the shafts are purchased in the larger tube size.
With carbon shafts they are able to be manufactured at a smaller diameter with the desired wall thickness to meet the requirements of the load application

2) The CF shaft has a higher critical speed.
For example an aluminum STi application shaft start to flex & vibrate above 155MPH due to the aluminum hitting its natural frequency.
The CF shaft is closer to 195MPH.
It might not sound like 40MPH is a big difference, but a Stg2 STi can get very close to 155MPH, to hit 195MPH you got to have a crazy fast car (well in excess of 500WHP to hit that, & only a small hand full of tracks in the world have straights to accommodate that).

3) Carbon Fiber has a much higher ability to withstand load in the application of fiber lamina direction compared to an equally as thick aluminum tube.
This makes the shafts much stronger due to a higher yield strength required to load the shaft beyond a point of failure.
This will directly apply to shock load capacity of the shaft without fracture or damage.

For instance your typical 6061 aluminum has a Tensile Yield Strength of 40,000PSI, which sounds very high.
Now Carbon Fiber is between 3,000psi-15,000psi (depends on the quality of the carbon, either industrial grade or military grade) in the fiber longitudinal direction.
So you now might think that aluminum shaft will be stronger, but wait.
The thing about carbon is you use more than 1 layer when creating a part, so after you stack 4-10 plies (depends on manufacture) you can see that your tensile yield strength x number of plies = sky high yield strength!
From there you can take into account the density of carbon fiber & can see the benefits.
*Please note there is much more that goes into these shafts than just sticking plies of carbon fiber pre-preg together, but it gives you the basic idea.

Directly from ACPT

"All driveshafts twist to some degree when torque is applied.
The resistance to this twist is measured as torsional spring rate.
Standard carbon driveshafts have a torsional spring rate a little less than aluminum and about half that of steel.
The advantage of a lower spring rate is less driveline shock & a reduction of stress on other drivetrain components, as well as increased traction."

If you are having issues breaking your rear axles, or ring & pinion this might be a good way to prolong the life of those parts.
Reason is that the carbon drive shaft will be like a rubber band, when launched hard it will twist slightly to absorb some of the shock & then spring back to its normal shape.
The twist would be minimal (only a few degrees 5-10) on VERY hard launches, however that twist is absorption of energy.
Thing that breaks many parts such as gears is shock to the part from abrupt and high application of power.
F=M*A, so if you slightly reduce the acceleration of the power application you prolong life of components.
*simple way of thinking this, you can put a 10lb hammer on your finger slowly with no damage, however if you slam the hammer you will do a lot of damage. Similar concept with the carbon shaft twisting slightly, as it slows down the application of the energy on the component.

4) When the CF shaft fails, the fibers will come apart and un-wind.
When an Aluminum shaft fails, well you have a 14lb sledge hammer spinning at over 10000RPM going to town under the side of your car & you just hope it does not penetrate.

The big concern many people have with the CF units is the CF shaft separating from the metal yokes.
The adhesive that actually holds the 2 together, how its assembled, & how it's cured is a trade secret of these manufactures, as this will separate many of the manufactures & really make or break a manufacture.

That was a big concern for us as well when getting into the CF drive shaft market, however after many conversations with PST about they have yet to have a failure of the carbon or the adhesive itself.
They state that the failure point is, the metal yokes actually.
Not something that they have seen on import applications much in the past, but more or less on 1/4 mile domestic applications.
And at that point they have a option to custom make a billet yoke if your car really needs it.

5) A equivalent CF shaft will be about 5-10% heavier than a Aluminum counter part.

6) Aluminum shafts are only about 30-50% of the price of the CF unit.

So what one to get?

This strictly will depend on your application & budget to be honest.
Overall both aluminum and CF are significant improvements over the stock unit.
But the CF will be better than Aluminum as it's safter, smaller diameter, has a higher critical speed, a better elasticity, & higher degree of torsion before fracture/separation.

However that is not saying that aluminum is a bad, as aluminum shafts have been used for decades before the composite technology got to the point where it was better & more affordable for this type of application.

Source:
http://theattack.rallysportdirect.com/2012/01/carbon-and-aluminum-drive-shaft-overview/

 

So whats the point of all of this?

Its an advertising blather, pure and simple.
The whole spiel is stating facts and truths in a way that suggests you have a shittonne of power available to you and that your driveshaft is thieving monster that robs you of your precious horsepower at the moment of sudden torque transfer and when ALL that horsepower is lost in twisting the shaft all that 5 to 10mm.

In the very same way that Video suggests that the CF tube is so much a better choice that the steel example.

Its marketing deception in its finest and purest form.

What happens to that lost energy as the torque delivery of the motor lessens as rpm and speed builds.....
Aaahhhh, well, probably a few thousanths of an mm/gram is converted to heat as the molecular structure of the metal is slightly distorted as the tailshaft is wound up, but, as it UNWINDS, a few more precious percentages of mm/grams is lost in heat and the rest stored as potential energy in the natural spring of the shaft, is released as a torrent of liberated horsies into the wheels for your motoring pleasure in addition to your fading torque from the engine.

I mean really, The notion that you will gain any useful power by reducing the rotational mass of a 3 inch tailshaft, that only accelerates or decelerates proportional to ROAD speed and then comparing that to a lightened flywheel that is many kilos heavier and many times the diameter, is as preposterous as it is laughable in the real world.

Its a mathematical equation for people a lot sharper than I am mathematically but someone work it out please!!!

Smoke and mirrors crafted carefully by very switched on marketing professionals, carefully fed with facts and figured from knowledgeable engineers, all combined to cruise as close to the winds of deception and lying as possible whilst still looking relevant to the masses. Bit like the media really!

In the very same vein as the proponents of aluminium radiators V's copper/brass because aluminium conducts heat faster than copper/brass/unobtanium... whatever you like to call it.
Its quite true, heat conducts significantly faster in ally than it does in...Ill call it copper, approximately 30% or so. I dont remeber the exact figure. Its circa 30% IIRC but work even 5% either way.
No dispute there. Its a fact.

Now, what they fail to tell you is that copper is actually circa 30% stronger metal that ally, altho similarly heavier as well, can in fact be made significantly thinner, so thereby decreasing the time it takes to transfer the heat, along with INCREASING water volume and airflow thru a similar sized core and still stay alive in the rather engine environment!!

So your precious fancy looking ally radiator your so proud of is in fact, usually, significantly LESS efficient that a copper radiator of the same dimensions!!!!!! Sure, go make it out of 0.5mm ally sheet and lest see how long it lasts!!!!!

In an attempt to bring things back to an even playing field, the aloominumb brigade will add depth/thickness to the radiator core in an attempt to compete with a copper job! Strangely, by about that circa 30%.... as a rule.

So, to say the same thing a different way, you could happily use a copper radiator more or less 1/3 smaller and still achieve the same heat storage/transfer delta.

Ill bet your PWR and whoever else radiator builders leave THAT part out of the ally sales spiel. Dont want to talk your way OUT of a potential sale do you!!!!!
I will concede that ally radiators look great and imply some"performance" visually so they please the owners and tyre kickers alike.

So, at the end of the day, there is NO practical/everyday benefit in spending a shittonne of money on both an ally radiator or a CF or ally tailshaft (think material density/strength ally tube needs to be significantly thicker walled tubing to maintain strength more or less nullifying the weight advantage)

Is why ally tube exhausts are not popular. Expensive, fatigue related failure prone and much more difficult/specialised to fabricate. All is NOT what it appears in the press!!!!!

Safety?..... Mmmm probably cant get past that. Pretty rare for a tailshaft to suddenly break whist driving along, pole-vaulting the road car into the scenery. They mostly break in high-powered drag and race cars off standing starts and as a result of lack of attention to inspection by either dye penetrant or mag fluxing.
Tailshafts are a bit like exhausts. Once installed, they dont get much thought at all until something fails.

E

 

Lucky I bought an ACPT shaft rather than a PST unit.

 

Here's a link concerning PST (fast forward to about the 8 minute mark)
It doesn't look like they manufacture the carbon fibre tube section.

https://www.youtube.com/watch?v=6WZ53rWXTsc

What was their response concerning the faiures you experienced?


Link to QA1 driveshafts.
https://www.youtube.com/watch?v=idtuqwv92NY

 

It's disappointing to say the least when you pay for a product that you would expect to provide better than normal service.
If it was an ongoing problem, you would expect there would be a noticeable reaction from consumers.
US manufacturers seem to follow up with customer service.