Grabber AT2 performance in snow

[Trevor]

Interesting performance, Grabbers running at 38PSI and have incredible grip on inclines and anything in a straight line. But corners are puzzling, understeer at very low speed which I wasn't expecting.

I have finished braking before turning in and appreciate my 120 weighs in at about 2.8 tonnes but unless I'm doing 5MPH or less then the front end just doesn't turn. Now I don't expect to drive like a loon in this weather and this is the first snow experience in my Cruiser but I was expecting more grip.

What are others experiences?

Trev

 

[Chris]

Trevor, I would say that this is basic mechanics really. In a straight line the tyres are digging you along, but when you come to turn, the tread doesn't act in quite the same way and you are then pushing the turned front wheel across the snow. It's under-steer. Just about any vehicle will do this. That's why on a 4x4 rally car they corner with all the wheels spinning under power so the front wheels are not being passively pushed, but are spinning and biting to pull the car around. With the car then sideways, it is then actually describing a series of short straight sections to get round. Do you have the centre diff locked. I find that this helps as it means the some of the drive has to go to the front even though you may only be in low revs. Not suggesting that you power slide every corner in town by the way.

Chris

 

[andyw]

I would say that 38psi was a bit hard for these conditions, maybe try around 34psi.

 

[fridayman]

I would say that 38psi was a bit hard for these conditions, maybe try around 34psi.

I'm running 32psi and my AT2's have performed perfectly.

 

[sae70]

I know I have a very different tyre But I to would say that 38psi is a little on the high side When I had my tyres fitted rescently (255/85/16's) the tyre shop asked to what pressure I'd like them pumped & I replied 'well I used to run my last set of tyres @ 24psi mostly unless on a run when I'd pop 'em up to 28/30psi' to wit they looked @ me with raised eyebrows To be fair they were 31" on a Vitara Diesel mind & these are 33's on a Collie if that makes any difference They suggested a pressure of 34psi that I agreed to After my rescent afternoon playing in the local lanes & with the inpending threat of 200ft of snow I felt that the pressure was a little high so I went round all four checking the pressures to find that they were all infact around 36psi with one @ 37 Not even close to 34psi then So I've now reduced them to 30psi on the fronts & 32psi on the rear for starters I'm happy to report that they are performing awsomely in all conditions & that I'm very happy So to sum up let some air out Maybe not as much as I have as your vehicle is heavier but why not try 34psi

What size tyres are you running

 

[Crispin]

Trevor, I've not had the same. Mine are 35psi and when they have slipped on a corner, it was expected. Even then, the TC does a fine job of getting things right again.
A lot of the time I have been surprised that they have not slipped.

As for driving with the CD locked, I don't actually think it is a good idea with the 120 unless you are stuck. The traction control is amazing in how it gets the car straight again. Overcook it in a bend and the dashboard beeps at you, noises from each corner and you can feel it working things out. Lock the CD and all that is gone as VSC is turned off. Electricery - I like it.

I found a hill where the Grabbers were fighting for grip. VSC was also working hard but I was not going anywhere fast. A dung beetle came hurtling past me. Lock the CD and I was off with much less fuss...

Compared to my old Grandtreks - Where the Grandtreks works hard and almost not at all on my local hill, the Grabbers did a bit better. Not as much as I thought they would though. But, surely sheet ice is ice, regardless of the pretty pattern you have on your tyre...

 

[Trevor]

Tyres are 265 17 70, have not yet tried lower pressures but will give it a go. This was on compacted snow rather than ice, VSC has kicked in a couple of times but not in time to save the slide. it's worth mentioning that this is on corners of 70 degress or over in 2nd gear high ratio and no CD engaged.

 

[sae70]

I would drop the pressures to 34 & give that a go What does the book say the pressures should be for standard fit tyres

 

[Andy Harvey]

The Landcruiser is heavier at the front than the back so given a normal road and no stability controls it will most likely understeer give drive gong to all 4 wheels. Now rear wheel drive cars tend to oversteer under power because the back wheels slip but often if you don't put power on they will also understeer, especially with a big engine. Front wheel drive cars tend to understeer due to power and weight being against them - the heavy end tends to the straight on.

Now it does depend on tyre pressure to some extent, if you can get good grip from the edges of the tyres - agressive tread etc - and you have lots of weight on the front then a vehicle with a heavy engine in the front can tend to at certain speeeds oversteer but generally because of the fact that the weight at the front makes the front reluctant to turn and tend to the straight ahead you will always tend towards understeer on front engined cars that don't have ridiculously powerful engines.

Rear engined cars tend to oversteer for the same reasons - the front is happy to change direction as it is light whereas the rear wants to go straight on - hense the seriously tail happy performance from Porkers until they got big enough tyres and wings and all that to force the back to grip more than the force of nature was trying to take the back into a hedge / wall / bridge etc.

With 38lbs in your tyres though on snow you will be getting less grip for a couple of reasons.

1. You will effectively be riding more on the middle of the tyres than the sides - you want the sides to grip when changing direction (skiiers will know that).
2. because you are in effect putting less tyre on the road (because it is mainly on the middle as the tyre ballons at higher pressures) you will generate less friction which will generate less heat which will mean that your tyres are cold and less deformable meaning that the tread pattern can't move around little variations in the surface and find grip.

Like with Mud and sand you need lower pressures in snow and ice but for snow and ice it is not just that you get more tyr contact on the road but also that you generate more heat which makes the tyres softer - the main reason for winter tyres apart from better tread is that the compound is softer and grips better at lower temperatures gievn the same tyre pressure.

 

[Crispin]

Would you / do you get a tyre which is good on ice? I'm not talking about soft snow or slightly packed snow but something like 4 day old snow which is now just solid ice. I can see how my Grabbers are better on fresh snow because they can displace some snow and hopefully find tar under it. But, on my slight hill test today, the Grabbers did not do much better than the Grandtreks. Regardless of tyre and tread, if you on ice then surely every tyre s basically equal. Only difference would be compound.
Could you get a compound which is better on ice? Any slip though and you would be on a thin film of water so no real contact?

What is the normal low working temp for tyres? I imagine it's pretty cold. Paul - In Siberia was there anything special you did or were they normal tyres?

 

[Andy Harvey]

Most normal tyres don't work well at temperatures below 0, winter tyres work below that.

Yep valid point, no tyre apart from a studded one work well on solid ice - only ice skates work well on that stuff.

 

[Chris]

That's when it's time to break out the chains. I have a set that now won't fit any of our cars. I shall have to get some more. They are fantastic on ice or snow. But I see now that there are all sorts of really clever alternatives to metal chains.

Chris

 

[AndyCook]

dont have that problem with my AT2
but have them about 34psi or less

yes if you cane it round a roundabout on snow they will slide, but not with sensible driving.

 

[Simon_LJ70]

My AT2's fitted a few weeks ago have been perfect so far, checked pressure and at 36 so will try them a little lower and see if I get any difference

 

[karl webster]

As stated before my at2s are also great in fresh snow. Playing in 18inches with no problem at all up or down hill at sensible speeds. The other night though it let go at 35/40 with no warning. Yet dave was in his 80 with his bf mud tarrains with no problem at all. I was struggling on the main road on the compact stuff. But fresh snow wouldnt want any other tyre.
karl

 

[24Seven]

In my totally unscientific tests in changing types of snow today.

a. Land Cruiser with BFG M/T's

b. Defender with KM2 BFG M/T's

c. Front wheel drive Escort Van with 155/65's whatever was fitted

The winner was c. The Escort Van was the most controllable and felt the safest IMO

 

[Jon Wildsmith]

 

[Chris]

I had a couple of mates arguing in the pub one day. My Rangie will go anywhere. Bet it won't go where my Shogun will. It's all about the driver not the vehicle. Right, I bet you.... Bet on! And with that we left the pub and headed to Marsh Green.

After some significant wheel spin and macho crap, we came to rest alongside each other in deep mud. Well, they both said, that seems to be a draw. Then we heard 'beep beep beep of a car horn'. We went to the rear of the two stricken 4x4s to see Mike (bless him, no longer with us) in his escort van, head out of the window shouting 'I haven't missed it have I, why have you stopped here?'

I miss him and his van.

Chris

 

[Cptsideways]

There's a specialist bit of equipment you need to use in such circumstances, its a mchanical actuator driver operated its down the side of the seat called











The handbrake


On second thoughts what you really need is my wifes Golf Tdi on proper winter tyres, last year & this year its been pretty much unstoppable, we have'nt found a local hill it can't get up!! & we've been trying! You can drive around like complete loon, its 100% completely predicatable & you can pretty much drive around at normal numpty speed quite safely. Also my old Audi A2 Tdi on snowies was just as good except it'd get stuck in the snow drifts when it bellied out.

ETA: You can get a snow version of those tyres in Japan with the little sipes in them

 

[Trevor]

So that's where I was going wrong all along