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Torque Biased Diff


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#1 DeadSquare

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Posted 16 September 2019 - 10:12 AM

I have a kit car with a 1275 S engine in the back that has a tendency for the back end to step out on corners and I have been wondering if a limited slip would help curtail the habit.

 

Last week I got the chance to drive a Cox with a fairly hot 1340 and a limited slip.

 

I'm not sure what sort of diff it was, but it wasn't that nice to drive round twisting lanes, sometimes sticking like glue powering through, sometimes wanting to plough on,  although to be fair, I'm not used to the car.

 

Are torque biased diffs available for a Mini, and if so, has anyone here got experience of how a torque biased diff behaves in a similar rear engine set up ? 



#2 Moke Spider

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Posted 16 September 2019 - 10:18 AM

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.



#3 DeadSquare

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Posted 16 September 2019 - 10:46 AM

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.



#4 MiniMadRacer

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Posted 16 September 2019 - 10:57 AM

Hi, it should make things more predicable and you should be able to do the Mk 1 / 2 Escort driving style of steering with the rear, but a rear wheel drive with an LSD as Moke has said will make the car "more" tail happy but in a more predictable style.

 

I assume you have a rear engine rear drive car which will be Porsche / Hillman Imp handling which will always be a little rear unstable in my view.

 

As said check out the suspension as that is going to be very key to any decent handling in this sort of setup



#5 Bobbins

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Posted 16 September 2019 - 10:58 AM

 

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.

 

 

It will .... if you just intend to power slide everywhere! 

 

You'll probably need to address your spring weights, shocks and anti-roll bar (if you have one fitted), maybe all 3. You're likely running too stiff causing it to be tail happy, if they're adjustable try initially just backing off your shocks and see if it makes a difference. My experience is with Caterham's not rear-engined cars but the drive is fundamentally the same, the characteristics you're describing would suggest a waaaaaay too stiff rear end.

 

When you get it soft enough that pushing hard causes the inside wheel to spin, then you need either an LSD or ATB, in the meantime as Moke Spider says, fitting one will just make it worse!



#6 Moke Spider

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Posted 16 September 2019 - 11:07 AM

 

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.

 

 

What sort of Kit Car are we talking here and what is the suspension systems used along with a an idea of what the weight split front / rear is ?



#7 Steve220

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Posted 16 September 2019 - 11:09 AM

I have a Quaife ATB diff in mine and it makes the driving experience much more enjoyable through the twisties! However, I have upgraded suspension and better tyres.

#8 DeadSquare

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Posted 16 September 2019 - 11:24 AM

 

 

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.

 

 

What sort of Kit Car are we talking here and what is the suspension systems used along with a an idea of what the weight split front / rear is ?

 

 

It is a Unipower GT with coil over all round.



#9 DeadSquare

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Posted 16 September 2019 - 11:51 AM

I have a Quaife ATB diff in mine and it makes the driving experience much more enjoyable through the twisties! However, I have upgraded suspension and better tyres.

 

Presumably it is in a Mini, so any slight misbehavior at the front can be corrected by touches of left foot braking.

 

What does your upgraded suspension entail ?



#10 DeadSquare

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Posted 16 September 2019 - 11:57 AM

 

 

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.

 

 

It will .... if you just intend to power slide everywhere! 

 

You'll probably need to address your spring weights, shocks and anti-roll bar (if you have one fitted), maybe all 3. You're likely running too stiff causing it to be tail happy, if they're adjustable try initially just backing off your shocks and see if it makes a difference. My experience is with Caterham's not rear-engined cars but the drive is fundamentally the same, the characteristics you're describing would suggest a waaaaaay too stiff rear end.

 

When you get it soft enough that pushing hard causes the inside wheel to spin, then you need either an LSD or ATB, in the meantime as Moke Spider says, fitting one will just make it worse!

 

 

Letting the back end out, with a front engine, isn't quite the same as the pendulum effect of a mid mounted lump of cast iron.

 

I can cope with promoting the former, it just gets rather wearying wondering if the next bend will induce the latter.



#11 Cooperman

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Posted 16 September 2019 - 12:25 PM

Going back to my days of Porsche driving, I recall that to promote over-steer a thicker rear anti-roll-bar was fitted. This was ideal for forest/gravel rallying. To reduce over-steer a thinner rear anti-roll bar was fitted. An alternative would be a bigger diameter anti-roll bar on the front should reduce over-steer.

A LSD will not, by itself, reduce over-steer but it will make it easier to keep it in a stable over-steer slide with power on. I do recall testing a 911 with a LSD and a fairly thick dia rear anti-roll bar and it just wanted to go straight on at every sharpish corner.

In this case it would be a good idea to experiment with anti-roll bars. They are probably the key to this.



#12 Bobbins

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Posted 16 September 2019 - 01:29 PM

 

 

 

Limited Slip and Automatic Torque Bias Diffs are available for Minis, however, if you are running an Open Diff now and the back comes out, it would be worse with either of these.

I'd look to the suspension set up and settings first.

 

I was hoping that it would make things more predictable.

 

 

It will .... if you just intend to power slide everywhere! 

 

You'll probably need to address your spring weights, shocks and anti-roll bar (if you have one fitted), maybe all 3. You're likely running too stiff causing it to be tail happy, if they're adjustable try initially just backing off your shocks and see if it makes a difference. My experience is with Caterham's not rear-engined cars but the drive is fundamentally the same, the characteristics you're describing would suggest a waaaaaay too stiff rear end.

 

When you get it soft enough that pushing hard causes the inside wheel to spin, then you need either an LSD or ATB, in the meantime as Moke Spider says, fitting one will just make it worse!

 

 

Letting the back end out, with a front engine, isn't quite the same as the pendulum effect of a mid mounted lump of cast iron.

 

I can cope with promoting the former, it just gets rather wearying wondering if the next bend will induce the latter.

 

 

Yes agreed, and what you're asking the suspension to achieve is exactly the same .... keep the back end in check with as great a lateral force as achievable whilst enabling the driven wheels to propel the car forwards. Your current setup is losing lateral grip and therefore also traction - once you get the suspension controlling the grip you can then decide whether you need a different diff to maintain propulsion.



#13 Steve220

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Posted 16 September 2019 - 03:21 PM


I have a Quaife ATB diff in mine and it makes the driving experience much more enjoyable through the twisties! However, I have upgraded suspension and better tyres.


Presumably it is in a Mini, so any slight misbehavior at the front can be corrected by touches of left foot braking.

What does your upgraded suspension entail ?

We're in mini chat, so yeh 😂

The front of my car doesn't 'misbehave', the rear used to kick out on high speed cornering but I have controlled that through the shock absorber settings. I have protech shocks, adjustable bottom arms (poly bushed) and tie bars (poly and rubber), rears I have KAD toe and camber brackets. The car is very predictable, with the ATB, it has reduced torque steer and I'm not afraid to give her more power through the corners now 😎

#14 DeadSquare

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Posted 16 September 2019 - 04:45 PM

Unfortunately there is no rear anti-roll bar.  A  Mini front one doesn't fit because there are Formula type parallel links in place of the tie rod, but I think I'll make a link to attach it to the lower wish bone, and try one.

 

I have played around with the damper setting, which does made a difference to the grip, but also means that when it brakes away, it is harder to catch.

 

I'm going to cut through a couple of lower wish bones to weld in 3/8" and try that.  I'd also like to test a set of reproduction SP3 tyres, as the old Dunlops were nicely predictable.

 

Thank you all for your thoughts on this matter, they are more helpful than my wife's, which is to drive more slowly ! Ugh.



#15 Orange-Phantom

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Posted 16 September 2019 - 05:22 PM

Could this be of any help?

 

https://kentautodeve...r-anti-roll-bar






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