Euro: VSA

Yeah. I first read about it in one of Porsche's old "fake" LSD software. Usually the inner wheel spins because there is less resistance than the outer wheel during turning. By braking the inner wheel, it creates a situation where the outer wheel would have less resistance and so the torque goes there. But being only an open diff, at max 50% of torque can be sent to the outer wheel, no way close to a real LSD. But I guess for the heavy Euro, with no LSD and robbed of 1000rpm hi-cam range, we have to take what we get. :)

That's some great information there.... I think most VSA systems work pretty much the same on newer cars these days, although probably what matters most is how much the reaction time is!


ABS is not actually part of the VSA however, because ABS is purely and can only be activated by your foot. It is not an automatical function.


However, they are separate but RELATED in a way, as I have already mentioned earlier on regarding E.B.D. (electronic brake distribution), because VSA uses the ABS/EBD computer to work out how to brake each wheel individually when VSA is automatically activated due to various reasons, and it is required to steady the car.


E.B.D. itself is an extension to A.B.S. but it too isn't automatically activated because it only comes into action when you are braking yourself, and that's braking very hard on slippery surface or crappy tyres.

V.S.A utilizes this as well as power-cut-off traction control. It is on top of everything, but if you turn V.S.A. off the car will still have E.B.D. and A.B.S. readily available when you brake hard enough!




Also, braking one individual wheel when there is one wheel spinning - might seem to have similar effect as a helical LSD or AYC system, but it doesn't. It is not an LSD equivalent because it did not TRANSFER torque to the outside, less-spinning wheel.


In fact, it reduces the torque on the wheel in concern, which doesn't give the car more traction going through the corner like a proper LSD would, on say a Civic or Integra Type-R, but barely reduces the car's speed so it is still within traction limits and isnt sliding around any longer!

It won't increase the cornering speed or ability of a car like an LSD would. :)

EBD and VSA utilise the underlying ABS system. That's the primary link between them guys.

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Originally Posted by Omotesando

Also, braking one individual wheel when there is one wheel spinning - might seem to have similar effect as a helical LSD or AYC system, but it doesn't. It is not an LSD equivalent because it did not TRANSFER torque to the outside, less-spinning wheel.


In fact, it reduces the torque on the wheel in concern, which doesn't give the car more traction going through the corner like a proper LSD would, on say a Civic or Integra Type-R, but barely reduces the car's speed so it is still within traction limits and isnt sliding around any longer!

It won't increase the cornering speed or ability of a car like an LSD would. :)

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AYC works like the VSA braking, but instead uses clutches to transfer torque between the left and right. It's similar to the VSA one but it works without needing to wait for slip to occur. Edit: I just found out, AYC is very similar to the ATTS that was in the Prelude VTi-R ATTS. Any members with experience on the ATTS?

The braking of one wheel does transfer torque to the outer wheel, so you do get an LSD effect. The difference is that Helical LSDs like the one used in the Type R can PREVENT inner wheel spin since the outer wheel is balanced in torque as the inner wheel BEGINS to want to spin. VSA on the other hand has to DETECT the wheelspin first before braking. So VSA is slower in reaction compared to LSD.

The 2nd thing is that the Euro still has an open diff, so with the VSA braking the inner wheel, the maximum torque that can be transferred to the outer wheel is 50%. You're right that it won't corner as fast as compared to when you are not spinning your inner wheel, but in situations where you are spinning the inner wheel, it tries to improve it as much as possibe.

The original invention of a Differential was so that the car can actually turn into a corner as the two driving force tyres would have to trace a different radius of a circle, as the outer wheel needs to rotate slightly faster. Impossible on a solid front axle of course.


The problem on an Open Diff vehicle is that the diff actually wants to transfer more torque to the more freely spinning wheel. When you turn in, the car's loading, thereby grip advantage, is actually all on the outer wheel, making the inner wheel wanting to Slip (or spin).... eventually the open diff will act counter-actively by transferring even more torque to this wheel..... making the car understeer.



On a Limited Slip Differential this is the opposite.

Through a limited slip device such as a Viscous Diff, Helical Diff or a Clutch Type Diff, what happens is as soon as the inner wheel sense a slip, it does the right thing by instantly transferring greater torque to the wheel which has more grip, the outside wheel.



With a VSA system intervening, you are basically trying to apply a single brake on the slipping inner wheel when it is receiving the maximum torque, trying to slow this wheel down forcefully and externally. Unfortunately unlike an internal LSD device which has Diff Oil to cope with the frictions involved, you are attempting to exert a large effort on a wheel receiving the bulk of the torque using only your 'brake pad', in order to try slow down the wheel enough so that it won't receive more torque as it slips further. The idea is not to transfer more torque to the outside wheel because your brake pad isn't designed to handle torque for torque and this is while you still have your foot on the accelerator!! You are losing a lot of energy anyway, plus wearing out parts. During the whole transition, the brake pad is still biting hard on the wheel which is constantly receiving some torque.


Whilst this could potentially make the car turn in better, though reaction time a bit slower than LSD, this still doesn't give it a normal LSD effect because VSA is a passive system that's only activated over the limit. On a longish, high speed corner where the inside wheel doesn't have anywhere near enough torque to break traction even if car is already understeering, the VSA simply wouldn't turn on. On an LSD equipped car the more active system will be much more sensitive, starting to transfer the correct amount of torque to the outside loaded wheel 'linearly' and 'gradually', pulling/pushing the car into the corner better.



Secondly and very importantly when launching the car in a 'straight line', a proper LSD will ensure that you can get the best tyre traction, no torque steer due to diff torque between the wheels and the ability to still spin both tyres just a tad to get the best acceleration. This is especially true launching in the wet.


On the Euro Accord the VSA system is linked with a power-off or braking-power traction control system, so whether you turn it on or off, you won't get the launching effect of a proper LSD equipped car... LSD isn't just for cornering afterall!





As for the Prelude's ATTS system, it isn't a very sensitively incremental system, certainly nowhere near the reaction time of the Mitsu Evo's active-yaw and acd system. Although it is definitely better than a VSA system that is only mean to work PASSIVELY!

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Originally Posted by Omotesando

With a VSA system intervening, you are basically trying to apply a single brake on the slipping inner wheel when it is receiving the maximum torque, trying to slow this wheel down forcefully and externally. Unfortunately unlike an internal LSD device which has Diff Oil to cope with the frictions involved, you are attempting to exert a large effort on a wheel receiving the bulk of the torque using only your 'brake pad', in order to try slow down the wheel enough so that it won't receive more torque as it slips further. The idea is not to transfer more torque to the outside wheel because your brake pad isn't designed to handle torque for torque and this is while you still have your foot on the accelerator!! You are losing a lot of energy anyway, plus wearing out parts. During the whole transition, the brake pad is still biting hard on the wheel which is constantly receiving some torque.

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Yes, the brake pads and discs take a beating. However the VSA system still tries to do that and do a half-hearted emulation of an LSD. I'm not arguing that the VSA is even 1/2 as effective as a torsen diff. Instead I am arguing that the VSA system does brake the inner wheel if it loses traction. Look at all the enthusiastic TSX drivers in the US who have warped rotors after just 30,000 miles without ever going on a race track. I suspect that the warpage is caused by the VSA braking the inner wheel when it loses traction. Those US guys do like to gun their cars on the freeway on-ramp after all.

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Originally Posted by Omotesando

Whilst this could potentially make the car turn in better, though reaction time a bit slower than LSD, this still doesn't give it a normal LSD effect because VSA is a passive system that's only activated over the limit. On a longish, high speed corner where the inside wheel doesn't have anywhere near enough torque to break traction even if car is already understeering, the VSA simply wouldn't turn on. On an LSD equipped car the more active system will be much more sensitive, starting to transfer the correct amount of torque to the outside loaded wheel 'linearly' and 'gradually', pulling/pushing the car into the corner better.

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Yup, the VSA system does not increase the turning limit like an LSD. As I said, the LSD is superior. VSA is a poor man's LSD.

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Originally Posted by Omotesando

Secondly and very importantly when launching the car in a 'straight line', a proper LSD will ensure that you can get the best tyre traction, no torque steer due to diff torque between the wheels and the ability to still spin both tyres just a tad to get the best acceleration. This is especially true launching in the wet.

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But then, LSD will tend to put more torque on the wheel with traction, so you will get MORE torque steer since one wheel has more tractive force than the other. I think suspension design is a better way to deal with torque steer.

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Originally Posted by Omotesando

On the Euro Accord the VSA system is linked with a power-off or braking-power traction control system, so whether you turn it on or off, you won't get the launching effect of a proper LSD equipped car... LSD isn't just for cornering afterall!

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As I said, the VSA tries to do its best with 4 ABS channels and throttle control via drive-by-wire. I never said that the VSA could ever match an LSD. So why are we arguing over this? :)

To recap, I said that the VSA has an LSD-like effect, but it is a poor man's equivalent of the LSD, in other words, it's not as effective. The message I am getting from you is that the VSA doesn't carry out the action of braking the inner spinning wheel to transfer torque to the outer wheel. And that is the part that I disagree with. All your other information and comments about LSD vs VSA, I agree with 100%.

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Originally Posted by Omotesando

As for the Prelude's ATTS system, it isn't a very sensitively incremental system, certainly nowhere near the reaction time of the Mitsu Evo's active-yaw and acd system. Although it is definitely better than a VSA system that is only mean to work PASSIVELY!

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Of course it is no where near the performance of the AYC, because it was developed almost 10 years ago and not used in any car other than the old Prelude ATTS. Of course if you compared the modern version of the ATTS, the SH-AWD, then I'm sure even SH-AWD is better than AYC due to its torque split control.

My VSA light is on constantly. Im guessing its not working since i fitted the merc wheel hubs and brakes. But i dont even know what its for. Is it the traction control system?

You're asking for a whole world of issues with different brand hubs and brakes on your car.

Do a search on insurance or something on this site and you'll see the risks your exposing yourself to.

Have you checked to see if your ABS works??

Who fitted them for you... they deserve to be shot.

Sorry man but i cant help but shake my head

Large familiar roundabout, diesel/oil on the road, reasonable speed (circa 60kph).
Car further sideways than I ever wish to experience again (unintentionally anyway)
Forget arguable shortcomings or alternatives (eg lsd).
I am OK and the car is still showroom perfect.
Had there been no vsa the car would not have got itself out of the situation. I probably would have got us out of the situation, but what if I was a bit more tired or distracted?
I have read about how it works and I have tried to test how it works, and now I have seen it live and unrehearsed.
For me, end of discussion. Every new car sold should be fitted with this type of system.

PS no-one was around but if they were, the system worked so well that they would have assumed i did it on purpose!

hehe my EG civic now feels like a death trap with no ABS/VSA compared to my Euro.


In a sideways situation...

If the car is fishtailing sideways (arse is sliding left), does VSA brake the left wheel and accelerate the right wheel to neutralize the fishtailing?

If VSA equivalent is installed on all cars - it will help avoid many accidents especially when road is wet (or has oil) for certain. It is a passive system and as such it usually activates and only required when you're not expecting something!! A good LSD is more of a different primary device - it makes the car corner much better in a neutral manner, especially when power is applied.


If car is fishtailling left on a right hand turn corner/roundabout, the VSA should brake automatically the right rear wheel? and if you're on the throttle cut fuel a little bit? When I tested it deliberately I think that is what it does? Although I find that as the tyres are more worn, the VSA doesn't work as well as it should. I still slide way too much into the other lanes to the point of dangerous (understeer majorly) and it still doesn't activate sometimes. :(

EDIT: Not really sure how the brakes work... just guessing.

here is an easy way for you to test the VSA system take the car on a dirt road (hopefully fairly wide if your not confident on dirt) and try to get the car sideways and see what happens.

i have done this a few times and it is soo much fun it's as if there is an invisible rubberband attached to the car that flings you back straight again

the only way this system effectively works if is you DO NOT TOUCH THE BRAKES as this will apply brake pressure to all wheels and over ride the system i do quite a few mountain runs and some of the surfaces are sub standard and the best way to get full use of the system is is use or don't use the accellarator and definately don't use the brakes ( obveously there are situations where they are needed but most of the time being a front wheel drive car you can pull your self out)