Helical style diff on the steering axle

Helical, Torsen, Quaife, Truetrac, whatever. The ones with the worm gears.

How do they behave on the steering axle? Do they transfer torque across the axle when the wheels are turned to either enhance or fight turning?

They're not too noticeable in terms of handling, they feel a lot like an open diff...just without the one-wheel-peeling.

Quaifes are very popular in FWD applications and they are only noticeable in how they get the power down vs open

They are pretty benign.  I have one in a Civic that has maybe 10k track miles on it, it put power down smoothly, reduces torque steer under boost, and if anything when you are at the under steering limit and ease into full throttle the car will tighten up slightly in the turn.  In low speed situations it is invisible. 

I'm actually mostly interested in loose surface behavior - snow, sand, mud. Will it help the vehicle turn, fight it or make no difference? Sonic, your comment makes me think that it's transferring power to the outside wheel and helps it turn.

Car: Ford Focus with supercharger, 223 FWHP.  I had a Torsen installed the same time as the supercharger.  My only experience with loose surfaces was with snow.  It felt like it was easier to power out of understeer conditions than before the modifications.  The extra may have helped but I feel that the diff was the main factor there.

That’s what it feels like, though we are talking about a different surface.  When driving that same race car in the snow to get it out of the garage on dead 200tw tires, it does spin both tires at similar rates, so it seems from the drivers seat. 

Find someone with an EVO VIII RS. Came with a torsen in the front case from the factory.

I've been racing our PF SRT4 in rallycross for three years now and the helical most definitely pulls you around the corner faster in loose conditions. You just have to learn the correct amount of throttle input to get this behavior. Too much throttle and you'll overpower the outside wheel and understeer. Too little and you don't get the benefit. I would judge the correct input to be between 50-75%, but I've never data logged this.

I can get the same behavior out of my Cobalt SS turbo on pavement in autocross.

Keith Tanner said:

I'm actually mostly interested in loose surface behavior - snow, sand, mud. Will it help the vehicle turn, fight it or make no difference? Sonic, your comment makes me think that it's transferring power to the outside wheel and helps it turn.

The hummer uses helicals on both axles... That should be a pretty good vote. 

The Hummer was built to a very odd set of specs, I don't like to look at it as the best way to do anything.

There's a Torsen in the front of the Ford Raptor, and that seems to work great.

A lot of off road specific vehicles will use a locker or clutch in the rear and a helical in the front, because it allows the vehicle to actually turn corners when compared to a clutch or locker front diff. 

Actually, i was really curious about how the torque was distributed as the relative wheel speeds changed and my brain wasn't telling me.

Thanks everyone!

I'll find out the first time we get snow, as this will be the first winter with the torsen in the front axle of the Jeep.  This torsen does have some preload, so it there is a little extra self-centering in the steering on pavement.  Might cause a little understeer off-throttle in tight turns on a loose surface, but I expect it to be pretty benign. 

Keith Tanner said:

Actually, i was really curious about how the torque was distributed as the relative wheel speeds changed and my brain wasn't telling me.

Slower wheel gets more torque.

Driven5 said:

Keith Tanner said:

Actually, i was really curious about how the torque was distributed as the relative wheel speeds changed and my brain wasn't telling me.

Slower wheel gets more torque.

That should fight the turning motion, IIRC.

FWD cars typically have negative scrub radius to counteract such tractive torque based self-steering effects, such that if anything it might even help the steering input slightly.  Beyond that, I believe the general effect is that the outside tire getting less torque longitudinally allows more of the grip to be used laterally, and that with the outside tire holding the desired line the inside tire getting more torque helps pull in the direction the tire is pointed.

I put one in my rallycross Neon when I switched to a 2.4.  I didn’t really notice much of a change in handling, maybe a touch more understeer, but traction, both in straights and coming out of corners was significantly improved.  

Keith Tanner said:

I'm actually mostly interested in loose surface behavior - snow, sand, mud. Will it help the vehicle turn, fight it or make no difference? Sonic, your comment makes me think that it's transferring power to the outside wheel and helps it turn.

They seem to be magic on Evo Xs.

1way for fwd, 1.5 or 2 way for anything else. A 2 way under a fwd would be hell when not on throttle, entry would be full understeer. 

In reply to Trackmouse :

You're describing clutch diffs.  The 1-way/2-way stuff is related to how the ramps that the crosspin/cross are shaped.

Helicals are just open diffs with worm gears instead of spider gears.  When you have one tire spinning, effectively the nonspinning tire is backdriving the differential.  Since you cannot backdrive a worm gear, the effect is that the differential biases torque to the wheel with the most grip (spinning the least).

So if you're unloading the inside front and it starts spinning, the effect is that it is driving the outside front harder.

I think it depends on the quality of the diff. I put a Peloquin diff (it's a VW specific Quaife clone) in my VW GTI VR6 many years ago. It changed the handling of the car, power on in a corner and the car would tuck into the turn nicely. Driving in snow (Edmonton, AB, Canada) had fantastic grip, kept up with a few surprised Subaru drivers. This might have been in part to the massive amount of front weight that car had, something like 68% front weight bias.

Clayton

Knurled. said:

In reply to Trackmouse :

You're describing clutch diffs.  The 1-way/2-way stuff is related to how the ramps that the crosspin/cross are shaped.

Helicals are just open diffs with worm gears instead of spider gears.  When you have one tire spinning, effectively the nonspinning tire is backdriving the differential.  Since you cannot backdrive a worm gear, the effect is that the differential biases torque to the wheel with the most grip (spinning the least).

So if you're unloading the inside front and it starts spinning, the effect is that it is driving the outside front harder.

But technically a helical is 2way, right? Just very uncommon to be applying vastly different brake torque to one wheel vs the other.

I guess 1 way 2 way makes sense only when referring to speed based limited slips, not torque based ones.

Helicals do nothing until there is enough torque input. The gears effectively have to jam into the end of their slots in the case before they'll transfer any torque. 

I have a helical diff in the front of my Caravan and havent noticed any ill effects at all. I have spun tires trying to climb dirt hills with it (believe it or not, i've driven it to the 'back acres' lol) and it worked for that. I have never turned under heavy throttle while on a loose surface but logic and other ppls experience here says it works the same, just changes how much input torque you need to 'activate' it vs pavement. 

In reply to Vigo :

Some helicals do have a bit of preload, so there's some resistance to slip even without torque input.  These ones are also more effective when lifting a tire than one without preload.