Winter wheels and tires

[IndyIan]

This typically is only applied to your true AWD/4WD setups where the front and rear wheels are locked together so that no one set of wheels is free to just lock up while the others continue to rotate. Think of your typical FWD setup where the rear is lighter and so on a slippery surface those wheels can lock up, engaging the ABS where as the fronts didn't need it. With true AWD/4WD, the front wheels rotating mean the rear wheels rotate so things are kept "in synch", warding off ABS engagement until it is actually needed more globally.

I believe that's the theory.

Like Jetronic pointed out, all cars have a lot of front brake bias and front heavy cars have more, which is optimized for braking on dry pavement to have the front and rear tires engage ABS almost at the same time with all the weight transfer to the front. On snow, that weight transfer never happens and so for ideal braking the rear brakes could be doing more than the bias allows. Now alot of cars have Electronic brake force distribution which in theory should be able to optimize rear braking forces for the amount of grip the surface has. But I doubt any manufacturer dares to tune a decent amount of rear bias into their software on slippery surfaces, and certainly not the perfect brake bias effect of 4wd...
I found the braking with a no centre diff 4wd system was much better on snow and ice as its also mechanical ABS and helps keep the tires rotating at the same speed regardless of temporary losses of grip at each tire. In a short wheelbase vehicle like my 03 Tracker, you also had to watch the back end as the rear tires are now doing as much braking as the fronts with less weight on them so threshold braking in a corner would initiate a nice 4wd drift.
Our Outback and most part time AWD vehicles don't actually have a centre diff anymore, just a clutch pack which I'm sure is programmed to decouple the axles as soon as braking activates ABS or stability control to allow the systems to promote understeer effectively. It would be interesting to be able to shut off all the electronics and just choose to lock the clutch pack and drive that way. I'd think it would actually be faster in a rally stage situation but not as forgiving in a normal driving accident avoidance situation.

 

[SwampSurvivor]

I don't know if studded tires are the end all be all. There's some lines dug into my old apartment's parking lot from an ice storm. I *did* make it up the hill into the partking lot, but after a lot of spinning on those old studded winterforces. There wasn't much ice but I definitely didn't have enough traction.

With that said, my Focus made it up the hill with the studded winterforce and a lot of others did not.

 

[UG_Passat]

You don't see chains on this Audi quattro.. it's studded tires.

 

[Jarlaxle]

I wish I had them installed by now.

Of course...I wish I was driving my Challenger instead of a rental car. Should get it back this week, hope to get the tires on Friday.

 

[Jetronic]

Like Jetronic pointed out, all cars have a lot of front brake bias and front heavy cars have more, which is optimized for braking on dry pavement to have the front and rear tires engage ABS almost at the same time with all the weight transfer to the front. On snow, that weight transfer never happens and so for ideal braking the rear brakes could be doing more than the bias allows. Now alot of cars have Electronic brake force distribution which in theory should be able to optimize rear braking forces for the amount of grip the surface has. But I doubt any manufacturer dares to tune a decent amount of rear bias into their software on slippery surfaces, and certainly not the perfect brake bias effect of 4wd...
I found the braking with a no centre diff 4wd system was much better on snow and ice as its also mechanical ABS and helps keep the tires rotating at the same speed regardless of temporary losses of grip at each tire. In a short wheelbase vehicle like my 03 Tracker, you also had to watch the back end as the rear tires are now doing as much braking as the fronts with less weight on them so threshold braking in a corner would initiate a nice 4wd drift.
Our Outback and most part time AWD vehicles don't actually have a centre diff anymore, just a clutch pack which I'm sure is programmed to decouple the axles as soon as braking activates ABS or stability control to allow the systems to promote understeer effectively. It would be interesting to be able to shut off all the electronics and just choose to lock the clutch pack and drive that way. I'd think it would actually be faster in a rally stage situation but not as forgiving in a normal driving accident avoidance situation.

It's even worse, Indylan. EBD can only reduce rear brake pressure so you are dependant on the sizing of the brakes for the maximum rear bias (ie EBD does nothing).

AWD with clutchpacks disable the AWD as soon as you start braking actually.

 

[Pew]

AWD with clutchpacks disable the AWD as soon as you start braking actually.

If you mean the center diff opens, you are correct. Cars with center diffs will almost always be unlocked unless it detects slip, in which the AWD system will do it's thing based on the algorithms and start clamping down on the clutches. Unless you're in a car that you can "lock" the power distro, like an STi I believe.

For example, the Evo (X) is always at a 50:50 torque distribution so it's never disabled. Based on the accel, yaw, wheel speed, and steer angle sensors, the center diff will still lock to maintain it's 50:50 torque split. So if you're braking into a turn very hot and the rear starts stepping out, the center diff will still clamp down (but not too much since the driver is still trying to turn.) It's interesting to be able to feel this happen when the car is driven to the limit of the tires.

 

[Jetronic]

i'd call an evo and sti 4x4 for that reason.

The evo does even more, it will change the torque split in the rear diff from 50:50 in those cases... torque vectoring is very useful indeed

My fwd has torque vectoring on the front wheels and you can feel and see it aswell. When you're on the edge of grip and adding more power should be introducing understeer, the car tightens it's turning circle again

 

[edyvw]

i'd call an evo and sti 4x4 for that reason.

The evo does even more, it will change the torque split in the rear diff from 50:50 in those cases... torque vectoring is very useful indeed

My fwd has torque vectoring on the front wheels and you can feel and see it aswell. When you're on the edge of grip and adding more power should be introducing understeer, the car tightens it's turning circle again

I think current VW Golf R in addition to AWD has vectoring diff. in front.

 

[UG_Passat]

I think current VW Golf R in addition to AWD has vectoring diff. in front.

No it doesn't. It has open differentials front and rear.

FWD GTI with the Performance Package has the vectoring differential aka a Haldex clutch to the right of the open differential.

 

[edyvw]

No it doesn't. It has open differentials front and rear.

FWD GTI with the Performance Package has the vectoring differential aka a Haldex clutch to the right of the open differential.

Ah OK, I was under assumption they implemented that on R in addition to AWD. Atleast I read that somewhere (would nto be surprised if it did not find its way here in the US).

 

[UG_Passat]

Ah OK, I was under assumption they implemented that on R in addition to AWD. Atleast I read that somewhere (would nto be surprised if it did not find its way here in the US).

The last time Borg Warner (haldex) had a torque vectoring differential with AWD was the Cross Wheel Drive (XWD) that was found in Saabs and some GM products. It was a Gen 4 haldex with another haldex clutch on the rear differential.

There's rumors the MK8 Golf R might get an updated XWD setup.

 

[Jetronic]

it was between freezing and thawing this evening, and the ground was wet from fog falling down. it's been a long time since I've seen the ESC light on my car, but today I did.

Also had use for the torque vectoring in places, haven't felt that since I uprated the rear arb. Must've been more slippery than I thought. Explains why nobody was over the speed limit....

 

[Kestas]

I remember my car in high school, 1973, driving in the winter with bald tires. It made me develop some good driving skills.

 

[Jarlaxle]

Winter tires are on. So far, so good.

 

[Fattylocks]

I remember my car in high school, 1973, driving in the winter with bald tires. It made me develop some good driving skills.

Best way to develop tail out drifty driving skills.

 

[Rand]

The last time Borg Warner (haldex) had a torque vectoring differential with AWD was the Cross Wheel Drive (XWD) that was found in Saabs and some GM products. It was a Gen 4 haldex with another haldex clutch on the rear differential.

There's rumors the MK8 Golf R might get an updated XWD setup.

The 2022 Volkswagen Golf R Has 315 HP and Torque-Vectoring AWD

We may not get the standard Mk. 8 Golf, but the most powerful production Golf will make it to our shores next year.

www.roadandtrack.com

The 2022 Volkswagen Golf R Has 315 HP and Torque-Vectoring AWD​

looks like rear axle torque vectoring. on awd setup?

 

[Jarlaxle]

Pretty impressed with the snows on the Challenger. Traction is excellent, wet grip is very good. Noise is less than I expected. Main limiting factor of the car now is the very low ride height.