Driving in the snow

[GrasB]

[QUOTE 1714963, member: 45"]That's all very clever, but the reason no bmw or Mercedes gets up our road in the snow is because they're rear-wheel drive, have fat tyres are have the accelerator welded to the floor, while normal cars crawl past them. Regardless of whether they have wired pedals.[/quote]
I'll call you on this one because you're not getting the point:
Car 1 -
Power: 452bhp @ 6300rpm
Torque: 437lbt @ 3100 rpm
Weight: 1037kg
Driven wheels: rear
Drive tyres: 245/40R18
Can be driven in snow with relative ease

Car 2 -
Power: 215 @ 6100rpm
Toqeue: 199lbft @ 2400-4200 (that's less than the above car is producing across this range)
Weight: 1505kg
Driven wheels: rear
Drive tyres: 255/45R17
Very difficult driving in snow.

Care to explain this please?!

 

[Linford]

[QUOTE 1714963, member: 45"]That's all very clever, but the reason no bmw or Mercedes gets up our road in the snow is because they're rear-wheel drive, have fat tyres are have the accelerator welded to the floor, while normal cars crawl past them. Regardless of whether they have wired pedals.[/quote]

I've seen this 'fat tyred rear wheel drive are hopeless on gradients in the snow' argument so many times. My Shogun has fat tyres (265's), is a big old lump with most of the weight over the front end, and unless I put the box into 4wd, the car is for all intents and purposes a 2wd car like any of the Beemers and Mercs. The only difference realistically is that it has all terrain tyres on it. I've only ever admitted defeat once whilst with all the diff locks on whilst climbing it on a hill, and that was on a 1 in 3 section on Bushcombe lane last year which had about 18" of standing snow on it with a layer of sheet ice underneath on the road surface itself (this lane is on the Hell of the North Cotswolds route in Woodmancote, Bishops Cleeve), and no other car had actually got up to that point before my attempt - people weren't even walking it at that point, and I consider this to be the steepest gradient in Glos county on a public road.
I'd be happy to put it to the test with both 2wd and 4wd on a slope if we get some really slippery conditions again to lay this one to rest as I can't see the argument dying without any proof either way ?

 

[GrasB]

I cant imagine a situation where you would left foot brake in icey low speed conditions, care to expand?

When you've got almost no grip applying the brakes while applying the power checks wheel spin by adding extra friction to the driven wheels. It's easier to control the throttle when the engine has load. I was in the situation were at idle in 3rd & 4th gears the front wheels would spin with any resistance to the car moving forwards. Applying the foot brake was giving enough extra resistance to the engine to not overwhelm the front wheels.

 

[GrasB]

[QUOTE 1715009, member: 45"]15 year old BMW -can't get up the hill
New BMW -can't get up the hill
15 year old fwd Ford - can get up the hill
New fwd Ford -can get up the hill[/quote]
Er... & this answers my question how? I can explain cars not getting up hill by driver incompetency. Your challenge is to explain why one wide tyred RWD car can be driven in icy conditions & another can't.

 

[GrasB]

Ah OK... not tried that... Going straight to 2nd gear always works for me and if your losing traction in 3rd and 4th then I would argue your going way too quick for the conditions.

This was pulling away!

 

[Linford]

[QUOTE 1715015, member: 45"]Tractors are rwd with fat tyres linf -you know what people mean when they use the term you're choosing to argue.

I'll give you a ring next time it snows and you can come and watch out of our dining room window with me. Or even join us pushing -you get a lot of time to read the name on the boot lid beside your gloved hands.[/quote]

Mine wasn't to argue to the point, but to clarify better. I guess the best test would be to directly compare mine and a LWB Landrover with the 4wd disengaged on both (if you can do this on a defender ?) to see the differences between a fat and skinny tyred car tested side by side.

Unless they have limited slip differentials on these luxury cars, they are going to be on a hiding to nothing - come to think of it, I think my Shogun has one of these though on the back axle.

 

[Linford]

... not the most romantic of 1st dates

You are a card Smeggers

 

[GrasB]

Powers in all the wrong places. lumpy.

Actually that's how I'd describe the delivery of the car which could be driven. The main problem is that there's no way to hold 0 throttle on the engine, the act of loading up the engine causes the ECU to open the throttle producing a torque spike. Applying the hand brake, increasing the sensed load, on the modern car only serves to make the ECU open the throttle wider. Result is you seem like you're driving with a lead foot.

I found out about this stuff when I modded my Alfa. FBW throttle responded in a way where it expected the car to have virtually no torque at certain rpm where in fact it actually had near 300lbft, it was bad enough to often spin the wheels on a wet day let alone when snowing (& this is an AWD car!). It made pulling away very very unpredictable & often lead to impromptu 0-30mph tests . Now it's mapped to a flat semi-log response & all is well.

 

[Linford]

I'll call you on this one because you're not getting the point:
Car 1 -
Power: 452bhp @ 6300rpm
Torque: 437lbt @ 3100 rpm
Weight: 1037kg
Driven wheels: rear
Drive tyres: 245/40R18
Can be driven in snow with relative ease

Car 2 -
Power: 215 @ 6100rpm
Toqeue: 199lbft @ 2400-4200 (that's less than the above car is producing across this range)
Weight: 1505kg
Driven wheels: rear
Drive tyres: 255/45R17
Very difficult driving in snow.

Care to explain this please?!

What is this car with 452bhp which weighs barely a tonne ?

 

[Linford]

[QUOTE 1715081, member: 45"]Ok. Maybe when people talk about fat tyres they should be explicit about them being low-profile and designed for max grip on tarmac.[/quote]

Surely though, a tyre offering max grip on tarmac is going to be slick, or as close to ?

 

[Nigel-YZ1]

It's a known thing that the compound on standard tyres loses it's effectiveness below 7 degrees, which is an advantage of winter tyres.
Maybe the poor performance of some of the prestige cars is down to the relative compounds used on standard tyres in those price/performance brackets?

 

[Linford]

It's a known thing that the compound on standard tyres loses it's effectiveness below 7 degrees, which is an advantage of winter tyres.
Maybe the poor performance of some of the prestige cars is down to the relative compounds used on standard tyres in those price/performance brackets?

I ran for a little while with race scrubs on my old motorbike. On a day with a frost, they were absolutely lethal and had virtually no grip at all when the brakes went on when they had no heat in them. I was glad to get them off the bike, but I very much doubt that the compounds on any performance car is as soft as these. The surface went like chewing gum when up to temp and they had a very short life (Rennsports IIRC)

 

[Linford]

[QUOTE 1715099, member: 45"]Yes, exactly.[/quote]

I think consideration needs to be given to an LSD on a high performance car which GrasBs example most likely has. Most cars aren't fitted with them, and consequentially, as soon as one wheel spins up, you aren't going anywhere - such is the nature of the beast.

 

[GrasB]

[QUOTE 1715070, member: 45"]You claim that the main reason for rwd low profile tyred cars struggling on hills is down to the car's brain. It may be a factor in some cases, but more basic issues have much more of an impact. As clearly demonstrated in my last post.[/quote]
No your last post shows you can't deal with the fact that I, quickly, came up with a scenario your preconceived idea didn't actually deal with. It also doesn't deal with the fact I know 5 wide tyred RWD cars with control tyres (Toyo Proxes T1-R) making it up a snowy/icy 12% gradient over the weekend & not one of them on a single run failed to make it up. It just kind of puts your position in the range I call unsupportable.

What is this car with 452bhp which weighs barely a tonne ?

TVR Cerbera 4.5 weight reduced prepped & supercharged

 

[GrasB]

I think consideration needs to be given to an LSD on a high performance car which GrasBs example most likely has. Most cars aren't fitted with them, and consequentially, as soon as one wheel spins up, you aren't going anywhere - such is the nature of the beast.

From what I understand no LSD... unless the guy swaps it out when he does hill climbing (LSD's are prohibited in the class he runs)