Space Saver Tyre

Faults and Technical chat for the Volvo XC40
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Tartansporran
Posts: 20
Joined: Tue Dec 04, 2018 4:08 am

Post by Tartansporran »

I recently fitted my space saver spare tyre due to a puncture. I know these are a skinny get you home tyre with multiple restrictions. However, I was surprised to find it was also a much smaller diameter which would obviously cause that wheel to rotate quicker than the other wheels for a given speed. The manual says this is ok despite various vague and conflicting warnings. The manual also states ‘On all-wheel drive cars, the drive on the rear axle can be disengaged’. Anyone know what this means, and why, and how do you do it on the all-wheel drive XC40 if at all?
XC40 D4 R-Design Pro First Edition, Osmium Grey, 19” Wheels

Deleted User 3629

Post by Deleted User 3629 »

These are temporary to get you to a garage or home and are usually one size for each model, yet each model can have various size wheels/ tyre combinations - the main thing is that they clear the brake calipers and they are only used for emergency reasons to cover a small distance at low speed - under these conditions they are ok to use even if the diameter is slightly different.
Tartansporran
Posts: 20
Joined: Tue Dec 04, 2018 4:08 am

Post by Tartansporran »

Thanks Oldie, yup, pretty much what the manual says and what I eluded to. However, have you an answer to the question re all-wheel drive cars? Red Herring? Complete tosh? Cut and paste from another manual not applicable to the XC-40?
XC40 D4 R-Design Pro First Edition, Osmium Grey, 19” Wheels
Deleted User 3629

Post by Deleted User 3629 »

Modern drive systems don't seem to like different diameter wheels on the same axle - some even question fitting a new tyre on the same axle with a worn one - but this then would be a combination expected to cover 1000's of miles - not an emergency space saver expected to cover no more than 50 or so miles.
Felindre
Posts: 777
Joined: Wed Dec 23, 2020 2:19 pm
Location: South Wales, UK

Post by Felindre »

The haldex AWD system is a part time on demand system. There's an electronic controlled fluid clutch taking drive to the rear that only engages when required, so most of the time it's running as a 2WD car. It only comes into play when pulling away, when it detects wheel spin or when you select the drive mode (which is only at low speed).

So having one smaller wheel isn't a big issue.
B4 AWD Inscription , Fusion Red, Blond interior. Drivers Assist, Climate, Tinted rear windows and Towing pack.
Ordered 14 Dec 20, delivered 10 March 21
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