Could you change the power split front to back eg 70% rear 30% front

[Davezj]

Well as the title says, is it possible?
could it be done, if so, what would be involved.
what is the best power split to kill the massive understeer we have in the VR4, (50-50, 60-40, 70-30, 80-20, etc)
i know you could say just go into the corner at a slower entry speed, but that is not what i am asking.

this is another one of my what if, is it possible threads.

let the discussion comence, what are your thoughts.

[Chris.W]

If I remember rightly the 8g VR4 although 4wd is biased towards the rear anyway. Somewhere between 60-40 & 70-30.

[Nick Mann]

On rolling roads the rear wheels do see more power than the front. It seems to be a 50:50 split until the power levels climb, then the difference is more noticeable. The vr4 is too heavy to turn in fast, the 4wd lends itself to a slow in fast out approach and the ayc helps that too.

[Davezj]

i was under the impression the split was something like front 48 and rear 52.

i am not sure but if someone knows for sure let it be known.

[SGHOM]

The vr4 is too heavy to turn in fast, the 4wd lends itself to a slow in fast out approach and the ayc helps that too.

Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

[Davezj]

entry speed is dependant on grip, and i would have thought the more power you put through the front wheels the less grip you have.
i would have thought once you have finished the turn in and have started to apply the throttle on the way out of the corner you could put more power through the front wheels to pull you out of the corner.

i understand the slow in fast out approch, but i was more talking about chaging the actual power split like the audi R8 20 front 80 rear, could it be done and with what. i presume it would be some other kind of center diff.

[Nick Mann]

Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

That's a piece of string length question! Vicky had a 206 GTi for a long time, so it is easy for me to compare that and the VR4. The 206 would turn in and change direction at phenomenal rates, but you couldn't plant the throttle round the corner, you had to feather it. The 206 would turn in a lot better and at higher speed, but the VR4 would exit most corners faster I'd say. The VR4 slingshots out of a corner. I'm not known for being slow on track, so I'd say my approach is not a bad one.

[scott.mohekey]

You can replace the center diff with a Cusco Tarmac which alters the bias towards the rear. Kenneth has one I believe.

[Louis]

Hmm??

thinking about that, taking the perfect corner, what do you think should be your entry speed... apex speed... & exit speed?

It also depends on the car.
Rear wheel drive, front wheel drive, and 4 wheel drive are all slightly different approaches.

Also the answer to the question is:
S AYC

[Louis]

Also, personally I would not agree with VR4 's being prone to massive under steer!.
Any more than any other car!
If anything I would say they were a lot better than a lot of cars on the understeer.

What tyres are you using?

[SGHOM]

Sorry for the slightly off topic comment, but I spoke extensively to Richard [physician] about this.
As a track day driver, as you know, he was superb. He also bought the book...studied the theory... & put it to good practice.

His thoughts & learnings were.... regardless of car, ie; fwd. rwd. or 4wd...... the entry speed, apex speed & exit speed should be exactly the same to take the 'perfect' corner.

So therefore, would changing the bias make any difference? It's surely the way you drive?




ok..... coats on

[Louis]

entry speed, apex speed & exit speed
So: 50, 45, 50.
For every car and every corner, problem solved???!!!.

So a 4wd sports car has No advantage in a corner over a 1000cc front wheel drive Nissan???.


(Cat, pigeons)

[Louis]

There are videos out there (and on here) that show the advantages of SAYC over other diffs. They also explain in basic terms how to make the most of the system when driving.
Have a look at them.

Doesn't matter what your driving, if you go in too fast for a particular car, you will get understeer.

[SGHOM]

Doesn't matter what your driving, if you go in too fast for a particular car, you will get understeer.

Exactly my 'off topic' point ! every car has different characteristics. the point I'm trying to make is to take a corner perfectly, you need to know how the particular car will take it ! so going in too fast will cause understeer. slow in... fast out?? still not the right way !

If, for example, redgate [donington] is a 60 mph corner max for a certain car.... that should be the max throughout the corner. 50 mph for some cars.... maybe 90 mph for some !!

do you get my point?

[Kenneth]

Your maximum speed through every part of the corner is determined by grip. However with changes in force direction, weight transfer and all that other stuff the amount of grip you use for lateral adhesion (not running off the tarmac) vs acceleration can change dramatically.

Our cars suffer a asymmetric weight distribution. Because the back end is lighter, the lateral grip used to turn a corner at a certain speed is less in the back than in the front (force being a product of mass and acceleration). Therefore, you should be able apply more forward acceleration in the rear before exceeding traction.

Not only that, depending on your tyre budget, you can benefit from having more acceleration in the back than the front, using tyre slip to rotate the rear of the vehicle at a higher rate than the front to increase turning speed. Not good for rear tyre life though.

With 65/35 rear/front torque split (got to add that I have front helical, rear plate but no centre LSD), my Galant still has a lot of difficulty in breaking traction in the rear on a good surface.

I am quite a fan of Richards. I am pretty sure what he said is the best overall strategy in terms of smooth and consistent lap times (some would say perfect laps) however not sure that you could categorise it as the fastest way.
Personally I do it mostly his way because I don't like crashing, the "fastest" way always comes at greater risk and things like trail braking, rear rotation give me the runs

On topic, yes you can run asymmetric power distribution. To do so you need a planetary gear centre differential.
A planetary gear has essentially 3 rotating parts. If you turn any part, the other 2 will turn at various speeds determined by the gear sizes etc. The interesting thing with a planetary gear is that if you lock together any 2 of these, the whole assembly must (but can) run at the same speed. As a centre diff, the outer housing (the planetary carrier) is connected to the final drive and so rotates at the final drive speed.
The inner (sun) gear is connected to the front, the annulus attached to the rear wheels.

When grip is good, the sun and planet carrier are locked by the road surface, therefore gear speed is the same across the entire gear assembly. Any change in speed across the front and rear causes the planetary gear to move to accommodate.
However due to the annulus having gearing advantage over the sun gear, any force applied to the annulus is distributed at 65% to the annulus and 35% to the sun gear (at least in the case of the cusco tarmac gear diff)

Fairly simple arrangement. Expensive to buy

Sorry for the slightly off topic comment, but I spoke extensively to Richard [physician] about this.
As a track day driver, as you know, he was superb. He also bought the book...studied the theory... & put it to good practice.

His thoughts & learnings were.... regardless of car, ie; fwd. rwd. or 4wd...... the entry speed, apex speed & exit speed should be exactly the same to take the 'perfect' corner.

So therefore, would changing the bias make any difference? It's surely the way you drive?




ok..... coats on

[Nick Mann]

So Derek, how come racing drivers on a circuit don't hold a constant speed round a corner? I know Richard was quick - I have had the pleasure of following him on track, as have you.....

In reality you are still braking as the turn starts and already accelerating before the turn ends. You need to use all the grip available at all points of this - you can turn tighter when you are not accelerating or braking, but getting on the power sooner gives you extra speed all the way down the next straight. I like this description:

The fastest approach to a corner will involve a little combined braking and steering at the entry to the corner, followed by acceleration combined with steering as the corner unwinds. While braking/accelerating the corner must have larger radius than when the tyres are providing cornering force alone, otherwise the total traction vector will exceed the traction limit

[Adam.Findlay]

what is the best power split to kill the massive understeer we have in the VR4,

The torque split is purely 50/50 on our cars stock, any one saying otherwise is only measuring slip in the center lsd when on a rolling road / hub dyno due to different loading on the front and rear axles. as when our centre LSD is active it limits the slip between front are rear output trying to maintain 50/50 split. hence why some people report bias to the front and other say bias to the rear...

changing the power split via use of a epicyclic (planetary) gear set such as a cusco tarmac gear like Kenneths will mainly only help you when accelerating out of the corner. as when you enter a corner you wont be on the gas.
so understeer on turn in can more or less only be cured by the addition of a helical front lsd, suspension setups and tyre choice (ignoring driver capability)

increasing the the torque applied to the rear wheels will more likely induce oversteer on corner exit but again it comes down to more than just the torque split. a good rear lsd is drastically cheaper than a tarmac gear and dramatically combats under steer, well from my experience it does.

[Davezj]

So if i fit an S-AYC rear diff (that i have spare in the shed) i will not gain any more power/torque to the rear, but as the S-AYC is supposed to shift about 30% more touque left and right than the standard diff, so it should feel likethe cars is smaller and more nimble in the corners

[Nick Mann]

It does give a slightly more rear wheel drive feel, but I suspect that is due to the extra torque movement. It makes naff all difference on turn in though!

[Davezj]

yes, i understand that that to fast in will induce understeer whatever car you are in.
but my initial thought was to do with, could you do something to allow you to enter the coner at a high speed without experiencing the understeer.
I supose one thing you could do is get stickier tyres, but is that the only thing.