madteg
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| posted on 19/12/15 at 10:21 AM |
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What LSD is best
I am on lookout for a new LSD, at the moment i have a viscous type and find when accelerating hard the rear of the car steps to the left. Would a
plate diff or a torque bias diff make any difference
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MikeRJ
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| posted on 19/12/15 at 11:48 AM |
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They would give better traction, but if the car is stepping to the left all the time I'd check the corner weights to start with. Do you have
IRS or a live axle?
Plate diffs tend to be superior for track work, but can be a bit annoying in a road car, they tend to make banging/knocking noises when cornering at
low speed and can promote understeer. A torque biasing diff is silent in operation, has negligible effect on the handling but won't give the
traction of a plate diff in really slippery conditions, or when kerb hopping on a track.
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Doctor Derek Doctors
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| posted on 19/12/15 at 02:19 PM |
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Again I would say that a car skipping to one side under acceleration needs a suspension geo' check first. As well as checking all the bushes
springs.
Designer and Supplier of the T89 Designs - Single Seater Locost. Build you own Single Seater Racecar for ~£5k.
Plans and Drawings available, U2U or e-mail for details.
Available Now: The Sports Racer Add-On pack, Build a full bodied Sports Racer for Trackdays, Sprints and Racing.
www.t89.co.uk
www.racecarwings.co.uk
callan@t89.co.uk
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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OliilO
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| posted on 19/12/15 at 04:04 PM |
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If it's IRS then check all the wishbone bushes. I had something similar last year and it turned out one of the bushes was a bit loose causing it
to distort and change the geo when under load.
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phelpsa
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| posted on 19/12/15 at 05:34 PM |
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All Lsds allow some sort of torque difference side to side, which can cause the car to yaw one way or another. On the road the surface camber will
generally cause this to be clockwise (ie rear goes left). This can obviously be compounded by compliance or corner weighting issues.
As for which kind of LSD is best, they all have their advantages but the best one is the one that's set up to match your car and usage. This is
generally easiest with a plate type LSD as preload and ramp angles can be adjusted.
[Edited on 19-12-15 by phelpsa]
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CNHSS1
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| posted on 19/12/15 at 06:58 PM |
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ATB such as the quaife is vice-less, as has been said bugger all effect on the handling, superb in all conditions.
Plate diffs CAN be superior, but only if setup correctly for the car and conditions. A plate diff setup for max attack out of the corners in the dry
on slicks will be very tailhappy in the wet on wets. Good thing wiyh plated diffs is that you can alter the characteristics on and off throttle. In
the jap scene they call them 2 way ( same ramp and preload on and off throttle) 1.5 way (essentially softer action off throttle) and 1 way (o ly locks
up on the gas, essentially open diff off the throttle).
Viscous isnt bad, but in pure competition terms they are a little slow to react, ie when one wheel stats to spin up the diff reacts and then tends to
lock up spinning both tyres up. Can also overheat the fluid pack on heavier high powered cars.
For general track work in all conditions ATB is the best ive used. Plated is better in the dry but if set tight does have understeer
characteristics.
Good luck :-)
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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CNHSS1
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| posted on 19/12/15 at 06:59 PM |
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Oh and the pulling one way is highly unlikely to be the diff, more like corner weights or wear (or driver favouring the pies in my case lol)
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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phelpsa
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| posted on 19/12/15 at 08:33 PM |
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quote:
Originally posted by CNHSS1
ATB such as the quaife is vice-less, as has been said bugger all effect on the handling, superb in all conditions.
Plate diffs CAN be superior, but only if setup correctly for the car and conditions. A plate diff setup for max attack out of the corners in the dry
on slicks will be very tailhappy in the wet on wets. Good thing wiyh plated diffs is that you can alter the characteristics on and off throttle. In
the jap scene they call them 2 way ( same ramp and preload on and off throttle) 1.5 way (essentially softer action off throttle) and 1 way (o ly locks
up on the gas, essentially open diff off the throttle).
Viscous isnt bad, but in pure competition terms they are a little slow to react, ie when one wheel stats to spin up the diff reacts and then tends to
lock up spinning both tyres up. Can also overheat the fluid pack on heavier high powered cars.
For general track work in all conditions ATB is the best ive used. Plated is better in the dry but if set tight does have understeer
characteristics.
Good luck :-)
I wouldn't say the torsen diff is viceless, in low traction conditions they are often barely better than an open diff. And the fact that they
can't be used to change on and off throttle balance could be called a major vice. I have an ATB in my daily and I wouldnt change it for my usage
(particularly for Fwd), but the additional potential of the plate diff for tuning handling characteristics is a major plus in a lot of applications.
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phelpsa
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| posted on 19/12/15 at 08:39 PM |
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I should probably add that viscous Lsds are very predictable and progressive, working well in most conditions. I've always run one in the Locost
and found it to be a good all rounder. You just have to remember not to lift off when the inside wheel lights up, the faster it spins the faster the
diff works!
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Theshed
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| posted on 19/12/15 at 08:46 PM |
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Such an interesting title to the post.....must be my age
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coyoteboy
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| posted on 20/12/15 at 12:36 AM |
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http://www.pistonheads.com/features/ph-features-tech/born-slippy-all-about-limited-slip-differentials/25275
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CNHSS1
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| posted on 20/12/15 at 01:56 AM |
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ATBs and the low grip myth doesnt really compute on track. Ive used all three types btw, so its not just theory. For the ATB to exhibit its fault, the
grip needs to be near zero (think ice) or one wheel in the air and no forward motion. In reality if a wheel lifts off the ground when kerb hopping you
have a good measure of forward speed anyway so the effects are near zero, according to the logger. Agree plate diffs can be better, dont dispute that,
but they are just as likely to be worse. A tight plate diff in pi55ing rain isnt funny. As for not influencing the handling as a vice, i guess thats
down to how you like to drive, power available, tyre grip etc. If running hillclimb slicks then you have about as much tyre (mecha ical) grip as is
available. On 1Bs or road tyres id humbly suggest that a less aggressive diff is quicker. My cars also turbo charged so the torque can ramp up very
quickly, +100ft/lbs in a matter of feet, so again easy to get initial understeer power on quickly followed by snap oversteer as both rear tyres are
lit up.
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
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MikeRJ
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| posted on 20/12/15 at 09:30 AM |
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quote:
Originally posted by phelpsa
I wouldn't say the torsen diff is viceless, in low traction conditions they are often barely better than an open diff. And the fact that they
can't be used to change on and off throttle balance could be called a major vice. I have an ATB in my daily and I wouldnt change it for my usage
(particularly for Fwd), but the additional potential of the plate diff for tuning handling characteristics is a major plus in a lot of applications.
The fact that you can go from an open diff to a torque biasing diff and notice no change to the car other than improved traction is what makes it
viceless. Plate diffs undoubtedly offer superior traction in low grip situations, but compared to an open, viscous or torque biasing diff they
clearly change the handling and often have other undesirable characteristics (e.g. noise). Those are vices.
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phelpsa
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| posted on 20/12/15 at 10:33 AM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
I wouldn't say the torsen diff is viceless, in low traction conditions they are often barely better than an open diff. And the fact that they
can't be used to change on and off throttle balance could be called a major vice. I have an ATB in my daily and I wouldnt change it for my usage
(particularly for Fwd), but the additional potential of the plate diff for tuning handling characteristics is a major plus in a lot of applications.
The fact that you can go from an open diff to a torque biasing diff and notice no change to the car other than improved traction is what makes it
viceless. Plate diffs undoubtedly offer superior traction in low grip situations, but compared to an open, viscous or torque biasing diff they
clearly change the handling and often have other undesirable characteristics (e.g. noise). Those are vices.
The ATB does change handling characteristics, but can't be tuned (so you're stuck with whatever it does) and can only bias so much torque
side to side (good for minimising torque steer on fwd cars). Hence its effects are limited in all respects, which is the vice of the torsen. However
if it matches your car and application then perfect.
The viscous LSD won't change handling characteristics until there is a critical wheel speed difference.
A plate diff has an extremely useful and tuneable effect on car balance and can bias torque completely under certain situations. They can be noisy if
set up aggressively with lots of preload, but pretty mild if not. I would suggest that if you had one in a car and found it snappy on throttle in the
wet then you could probably have done with less preload. A lot of diff suppliers recommend playing with different ramp angles, but in low grip
conditions the preload becomes a major player. A plate diff with low preload behaves in a very similar fashion to an ATB, but is fully tuneable and
can still transfer 100% of torque under some conditions.
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jeffw
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| posted on 20/12/15 at 10:43 AM |
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I use a ATB for sprinting. I don't have the race team available to change axles/diff between runs hence why a plate diff doesn't suit.
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