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Winter tyre pressures and observations

7K views 10 replies 7 participants last post by  JiggyJag 
#1 ·
Having managed to got halfway home in the XE the other day in the snow, all was going rather well until with no major issues starting/stopping/cornering until I had to stop at some traffic lights at a double humpback bridge near home. Despite multiple attempts using my lightest right foot (AND I still had all-surface progress control and snow/ice mode engaged), I couldn't get up the final slope. I gave up and decided to reverse back down to the nearby pub car park but started to skid sideways as well and ended up stuck very near a wall/fence on the wrong side of the road! I tried everything to get it moving even slightly (even got the rear mats out!) but it was no use... Fortuitously I was right next to a pub and the kind landlord came and towed me out... (was very nervous about traffic coming over the bridge the other way too fast and into my car!) For reference, the towing eyes are LEFT HAND THREAD! Car abandoned in pub car park and collected by visiting Brother-in-law in Disco Sport... In conclusion, while it managed ok on slight inclines and general driving on virgin snow, on compacted slushy snow and any sort of decent incline it was pretty useless (NB I have driven both my RWD XKR and various FWD cars in snow before and had a lot less trouble!), basically despite all the fancy new technology/modes, I can only conclude that all-season or winter tyres are very much necessary in these conditions.

ALL GOING WELL



GOING NOT SO WELL (TYRE TRACKS ON FAR RIGHT ARE MINE!!)



As it's forecast to be a cold/snowy/icy few months and having loved our set of Conti WinterContact tyres I bought for our Octavia for winter 2010/11 (I since discovered they don't fit the vRS though - so straight on EBay!), I decided to get some for the XE as I need to be able to get to work late and night and early in the morning, without fear of ending up in a ditch. I'd already been less than impressed at the lack of grip on cold/wet mornings, so decided to hunt down some wheels and tyres. In the end I got a bargain set of used (but pretty much perfect) front and rear 19" XE S wheels off EBay, a set of TPMS sensors and some new Pirelli Sottozero tyres (wanted Michelin PA4s but they went up £100 EACH overnight!)... All now fitted and ready to rock...

So the question is what pressure should they be inflated too... Jaguar manual is utterly useless on the subject:

http://www.ownerinfo.jaguar.com/document/4N/2017/T19987/20731_en_GBR/proc/G1877932

Found this random Topix document (looks like it is for an older model of Jag, not sure what) which recommends 32 psi -

https://topix.jaguar.jlrext.com/topix/service/procedure/538455/PDF/cb40813c-9a0f-4222-9f03-2d1444dc159a/en_GB?

Text is the same as the XE manual but the critical table on pressures is missing in the XE manual...

Conventional wisdom is that winter tyres should be inflated to about 0.2 bar/3 psi above summer pressures so have gone for 40 psi as a starter for ten... (37 is the standard)... anyone else got any actual information about what pressure they should be (bearing in mind Sottozero's are OEM fit!)


WINTER WHEELS



SPOT THE DIFFERENCE! (#DUNLOP SLICKS!)

 
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#2 ·
My reading of the Michelin advice on this is that you use the standard car makers correct pressure, as written on the B pillar, but if you're checking the tyre pressures in a warm garage then add 3psi to compensate for the drop when the air temperature is around zero; or pump them up out in the cold to the car's correct pressure.
 
G
#3 ·
richmond said:
My reading of the Michelin advice on this is that you use the standard car makers correct pressure, as written on the B pillar, but if you're checking the tyre pressures in a warm garage then add 3psi to compensate for the drop when the air temperature is around zero; or pump them up out in the cold to the car's correct pressure.
That's good advice. Just for interest I checked my pressures the other day with the car one side in the sun the other in the shade. The sun side showed 35psi and the tyres felt warm. The other side felt cold and the pressures were 31 psi. Ambient outside temp was 4C.
 
#4 ·
I have avoided heavy snow driving here in NY last winter, both because I was new to the car and to Rear-Wheel drive, but also because folks here in Northeastern US cities can't "drive" for love of heaven, and hit EVERYTHING, the dog, the mailboxes, the electrical posts, that garden shed you've got way in your back yard-
They get scared in RAIN, but hardly think of altering their reckless driving at all when going through SNOW.

I can't remember the manual's instructions about the ASPC, so I'm not sure if it said you should shut down ICE/SNOW mode before activating ASPC (not running them simultaneously)…

But regardless, experts have proven, NO modern electronic transmission-modifying program yet, and NO all-wheel drive transmission on All-Season tyres, helps a capable driver better than a quartet of good winter tyres on a car. Tests have even been done that surprised the editors, where winter tyres were allowing some RWD cars to beat their AWD versions mounted with good all-season tyres.

I've used winter tyres so much in the past---even when the car was FWD, and the speed was 50 through a blinding unsalted fresh snow storm, no wheel spins. After a month of this kind of driving, the winter tyres would tear their treads apart and be ruined beyond use in any additional winter-but NO wheel spins, no sliding into hedges, no towing.

It's nice to have a button that engages SOME spiffy program to get the car working in your favor, but let those systems be your 2nd and 3rd level of snow protection. Make 4 winter tyres always your primary protection.
Getting stuck in the snow, and switching on the car's "save me" program never really feels like fun.
Slowly maneuvering around a poor truck that got stuck in the snow, while your car with snow tyres didn't get stuck….always feels like fun.
 
#5 ·
I drove to and from work the other day on icy roads with the temp below zero as my first test of the XE on winter tyres, it didn't miss a beat, no traction control flashes or anything. Near home I stopped for a quick Sausage and Egg McMuffin and did a couple of laps of the frost covered deserted car park to see where the limit of grip was, despite being deliberately coarse on the throttle and steering, it would not unstick (I didn't go too mad though as there were kerbs around!) so I was well impressed!

Of note, rain/ice/snow mode can be on at the same time as ASPC (makes sense as it will probably be one of the previous conditions if you are considering ASPC use), but it calms down the acceleration even more than in normal mode. From the manual:

ASPC operation is influenced by the current driving mode selection. For example, the rain/ice/snow mode requires gradual ASPC acceleration to help gain available wheel traction. The normal mode allows increased ASPC acceleration to help improve vehicle progress.
While I remember, I also tried the low friction launch when I was stuck and that didn't help either!
 
#6 ·
Back in the late 70s and early 80s my Ford Escorts and BMW 3 series never gave me any worries in snowy weather. My wife always managed to get home to North Leeds from Wakefield in her Mini.
I'm sure it's not rose tinted spectacles, but modern "summer" tyres, coupled with the virtually snowless years between the late 80s and 2009 that mean that very few drivers aged under 40 have much experience in driving in snow, that cause all the problems.
 
#7 ·
One important thing to note with ASPC is that you shouldn't use the accelerator.
Using any application of throttle will cut it out.
From the manual:

"The driver can override ASPC operation at any time using the brake pedal or the accelerator pedal. The instrument panel displays an ASPC override message."

So if you touch the gas or the brake it will turn ASPC off.
As posted above, depending on which driving mode is selected will determine how aggressively the car will try and accelerate, it doesn't mean how much gas you can give it.
The whole point of ASPC is that you set the speed manually and the car will then use it's systems to try and make progress.
You don't touch the accelerator.

Also regarding the low friction launch feature:

"If the low friction launch feature is currently enabled, it is disabled when the ASPC system enters full function mode."
 
#8 ·
How do you set 'low friction launch's - can't find it in my menus
 
#9 ·
JiggyJag said:
How do you set 'low friction launch's - can't find it in my menus
From the manual.
It seems there are a few criteria depending on vehicle spec.
Don't ask me to interpret this !
:lol:

Font Screenshot Parallel Number Web page
 

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#10 ·
PhilB said:
One important thing to note with ASPC is that you shouldn't use the accelerator.
Using any application of throttle will cut it out.
From the manual:

"The driver can override ASPC operation at any time using the brake pedal or the accelerator pedal. The instrument panel displays an ASPC override message."

So if you touch the gas or the brake it will turn ASPC off.
As posted above, depending on which driving mode is selected will determine how aggressively the car will try and accelerate, it doesn't mean how much gas you can give it.
The whole point of ASPC is that you set the speed manually and the car will then use it's systems to try and make progress.
You don't touch the accelerator.

Also regarding the low friction launch feature:

"If the low friction launch feature is currently enabled, it is disabled when the ASPC system enters full function mode."
My memory of using ASPC is that you can apply the accelerator or brake without coming out of ASPC mode.

From the manual:
" Light and gentle application of the accelerator pedal will temporarily override the current set target speed. When the accelerator pedal is fully released, the Progress control system will revert back to the previously selected target speed.

Light and gentle application of the brake pedal will also lower the target vehicle speed. When the brake pedal is fully released, the Progress control system will maintain the speed at which the brake pedal was released."


Interestingly, last year I found ASPC worked well. However this year I tried to use it while slowly entering a narrow, curved car park entrance with an icy high rubber speed bump. ASPC didn't work so I ended up backing up slightly and giving it some power to use the car's momentum to run over the speed bump.
 
#11 ·
PhilB said:
JiggyJag said:
How do you set 'low friction launch's - can't find it in my menus
From the manual.
It seems there are a few criteria depending on vehicle spec.
Don't ask me to interpret this !
:lol:

Screenshot-2017-12-31 Jaguar Owner Information.png
Thanks Phil - I looked at this also and gave up also :(
 
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