Winter car tyres, go down a rim size?

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  • Winter car tyres, go down a rim size?
  • Premier Icon matthewmountain
    Subscriber

    My wife is getting a new to her car and I had a quote from a tyre/wheel specialist for winter tyres and rims. The existing car tyres are 205 50 R17, but they have recommended going for 205 60 R16.

    Partly because they are cheaper, but more importantly for better handling in winter conditions. He also said the car would not need to be recalibrated as reducing the wheel size would mean the tyres would have a larger profile and hence be the same size, so the overall rolling radius is the same?

    I would also need tyre pressure monitors installed, well I don’t need them but the car has them fitted for some reason unknown to me. I asked ford if it could just be switched off but apparently it can’t!

    So how on earth does a tyre valve connect to the computer on a car? Would the car know it was an after market valve ?

    jimw
    Member

    As long as the rolling radius is the same, you are likely to get a more comfortable ride and less likelihood of rim damage. Not sure about the handling aspect. The Skoda I had went from 18″ to 16″ rims with winter tyres and it did loose some of the initial bite on turn in but that could simply be to the tread blocks moving around.Still much improved grip in wintery conditions

    Premier Icon tthew
    Subscriber

    The 50/60 numbers in the code indicate the profile, i.e. the height of the sidewall as a percent of the width, (205mm) so yeah, they will be pretty much the same outside diameter.

    Tyre pressure monitors are a type approval requirement now. Not sure when that started, but all new-ish cars will have them fitted.

    Vader
    Member

    The car handbook should list the permitted tyre/wheel combinations and also the recommended tyre sizes for winter tyres.

    If you google ‘tyre size calculator’ there are several sites which will calculate overall diameter of each tyre size and allow you to compare – heres one for example. IME it is unlikely to be the same diameter

    cant help you on the tpms question

    trail_rat
    Member

    Tpms not being in our winter wheels means an orange light comes on in the dash and we get a dialogue saying tire pressure not monitored

    As we don’t have run flats we do the same thing we have done for 20 years and that’s walk around the vehicle before the journey to observe a flat tire or not- I’m not paying 250+ quid for valves to make that shite work(different if I had run flats) -note you will fail not with this light on…..so we mot in summer with our summer tires on…or I could plug in lexis and disable it if I really wanted.

    We went down a rim size to give more sidewall for the potholes that always appear in the severe freeze thaw that pushes shitty patches on the road out.

    Garage talks sense.

    Premier Icon Northwind
    Subscriber

    Depends what you mean by “better handling”. Smaller wheels and taller tyres works the same on cars as it does on bikes, more or less- but what you want from winter tyres might not be the same as summer. More volume can protect the rims a bit more from potholes/bumps, could come in handy if you slide to a kerb. Never really given it much thought, other than to make sure they’ll fit over my brakes.

    Spot on with the rolling circumference, though they’re not quite identical in this example… 205/50/17 is 805 revs per mile, 205/60/16 is 786 per mile. Though that’ll probably just make your speedo a wee bit more accurate.

    Can’t speak for pressure monitors, never had them

    nbt
    Member

    This site is a good reference

    https://www.wheel-size.com/

    Certainly when i got winter wheels for the Volvo, i went down from 17 to 16, and the tyre size went up to compensate, from 205/50R17 to 205/55R16. You seem to be jumping two sizes there?

    Premier Icon matthewmountain
    Subscriber

    Thanks for the information. By handling I don’t mean driving like the stig, I just mean is it more likely to get up a snowy road!

    Would changing the wheel size affect the warranty?

    Vader
    Member

    You need to check the vehicles handbook to see what the permitted wheel/tyre sizes are for it. There will probably be 2 or 3. Also as a guide, look inside the petrol filler flap, the tyre pressure sticker (if there is one) will probably list the recommended pressures for the different tyre sizes allowed on the vehicle.

    Changing to sizes outside those in the handbook is potentially a modification, which your insurance company might be interested in – there are hours of threads on petrol heads et al about this sort of thing!

    mattyfez
    Member

    Would changing the wheel size affect the warranty?

    You’d have to check the options for your car, my old Volvo came from factory with 16,17 and 18 inch options depending, so as long as you get the right speed rating and load rating or better, and sensible profiles it shouldn’t be a problem.

    nbt
    Member

    I listed alloy wheels as a modification on my insurance, it didn’t cost extra and i don’t want to find that I’m not covered because I’ve swapped wheels

    docrobster
    Member

    My wife drives a 67 plate kodiak. It came with 17 wheels and it was cheaper to get a set of steel 16s with tyres than 4 17 inch winters.
    The car has tyre pressure monitoring which works by comparing the speed the wheels are turning at rather than the actual tyre pressure. If you’ve got a soft tyre it will have a a smaller outside diameter and so it will rotate slightly faster and the system picks it up. When we swap the wheels as long as the pressures are right when they go on you just reset the system and it works fine.

    Premier Icon BadlyWiredDog
    Subscriber

    Thanks for the information. By handling I don’t mean driving like the stig, I just mean is it more likely to get up a snowy road!

    For normal, sensible, day-to-day driving it’ll make little appreciable difference from my experience. I run an inch smaller wheels with higher profile tyres in winter, the car rides slightly softer because there’s a little more air volume and the sidewalls are taller – if you drive into a crashy pothole it’s less crashy and less likely to ding the rim.

    The tyres will mean you’re more likely to get up a snowy road, but that’s more down to having rubber that remains soft and grippy at low temperatures, lots of sipes in the rubber and deep tread blocks. Mostly the car will just feel slightly softer and maybe a little less precise, but will be a lot happier in cold, wet, snowy conditions.

    They’re brilliant things for winter driving.

    Vader
    Member

    Like mattyfez my car has 3 wheel size options and 4 tyre size options listed in the handbook as standard. The 4th tyre size is if you want to use snow chains as you need to ensure clearance to the strut.

    trail_rat
    Member

    I listed alloy wheels as a modification on my insurance, it didn’t cost extra and i don’t want to find that I’m not covered because I’ve swapped wheels

    And by that logic do you phone them and tell them when you fit your winter rims ?

    andyl
    Member

    Your handbook should state winter tyre sizes. You may also have a range of sizes fitted to that car on the pressure sticker.

    Beware going smaller if it is a sports model with big brakes as they may not fit over the calipers.

    Premier Icon leffeboy
    Subscriber

    So how on earth does a tyre valve connect to the computer on a car?

    small radio transmitter afaik.   it doesn’t need to transmit very far or very often so the batteries will last a long time

    We’ve gone for the smaller rims, larger tyres for winter thing as well.  Don’t know if it works better than the same size rims but the tyres work brilliantly in winter so I’m happy

    jimw
    Member

    Oops, double post

    jimw
    Member

    And by that logic do you phone them and tell them when you fit your winter rims ?

    Yes, I always do, even though the company has said that they don’t need to know, they always note a modification and issue new documents each time, FOC.
    The winter alloys are genuine OEM and are listed as compatible with the vehicle by the manufacturer, after market ones might be different

    trail_rat
    Member

    I’ll remember that next time I have a puncture and need to fit my spare wheel.

    jimw
    Member

    If the spare is issued with the vehicle then to won’t need to.
    As you probably already knew…

    bear-uk
    Member

    My 14 plate Seat has a Winter tyre setting on the infomation display. So I assume it will recalibrate the speedo accordinly for the bigger circumfrence although it possibly is out anyway according to sat nav speed and dash speed.

    trail_rat
    Member

    My winter wheels are 4 spare wheels from the dealer when I bought the car With the same size tire as the spare.(yes the spares a size down with a deeper tire and without a tpms valve ….and the stock wheel nuts are alloy and steel compatible)

    Fwiw…..I discussed it with my insurance and they are not worried in the slightest unless they are alloys or not genuine steel wheels.

    As it stands 4 spare wheels as I use are type approved specifically for the vehicle so they have no issue with it.

    Genuine steels?

    So what about the steelies the like of Reifen sell?

    globalti
    Member

    A smaller wheel is definitely a good idea as it will improve the comfort and noise. I went from 18″ on my Passat B7 to 17″ on my B8 and was happy with the smoother ride and reduced noise.

    Winter tyres are fantastic and the slightly softer compound makes them even more comfortable so a set on smaller wheels will really transform the car.

    Are you sure your wheels have pressure sensors? These are only fitted to the most expensive cars, most (VAG for example) work by comparing the average rotation speeds of the wheels using the anti-lock braking software and if they detect a wheel beginning to spin at a faster average speed, they signal a puncture.

    philjunior
    Member

    Smaller wheel will allow winters to work better. They do need more flexible sidewalls though, so turn in won’t be so sharp anyway (and will be less sharp still with smaller rims), and it won’t be as solid at speed.

    In wintery weather, you don’t really want to be turning in so sharply that the sidewall stiffness matters, plus your ultimate grip on snow etc. will be better with a smaller diameter rim.

    Obviously make sure the wheels are correct for your car or it might handle funny, rub the tyres on bits it’s not meant to, not fit over the brakes, or even end up breaking wheel studs etc.

    pedlad
    Member

    I agree that the winter tyres make a massive difference to the ride comfort around the pot-holed roads of Herefordshire and Gloucestershire where I do most miles. Down a rim size and bigger sidewalls plus softer compound.

    That reference to spare wheel got me thinking…it’s a space saver but non winter. So if (God forbid) we were to have a puncture half way up an alp in feb, would the narrower space saver cut through enough (like a thin mud MTB tyre) to give control or would 3 winters plus a space saver be a death trap!?

    Probably hypothetical unless you can buy a winter space saver….in which case that should really be OEM from the factory to cover this eventuality as they’re limited to 50 so not for summer performance as it stands.

    Premier Icon bruk
    Subscriber

    I run winters on both our cars usually and have gone down at least 1 wheel size for each. Personally I prefer the ride of the wife’s X5 with Winters on and it has the added benefit of much better tyre wear. It came as standard with stupid wide front and rears and they tended to wear at the edges no matter how well you got the tracking set up. Much narrow winters haven’t done this and worn very evenly in comparison.

    Just check the online places are right, I ordered winter for my 3 series and went with the smallest size offered but they didn’t fit over the bloody brake callipers.

    Premier Icon jairaj
    Subscriber

    Echo what others have said, smaller diameter wheel and taller side profile is in line with common wisdom but not always required. Double check in the car manual what is the range of correct sizes.

    205/60/R16 is 2.4% taller than original which is on the taller side, I think normally you want to keep difference no more than 1.5%. If you can get tyres in 205/55/R16 that would better as is only -0.8% difference.

    You may need to inform your insurer if you change the wheels and tyres. If the manual has specs for winter tyres and wheels then most likely your insurer will be fine with it as it is to original spec of the car.

    The tyre pressure monitors are electronic valves that send the pressure to the vehicle. Depending on the age of your car it may be an MOT requirement that these are working and functional. You could just get an MOT performed with the summer wheels and tyres so this is not an issue. Most tyre fitters will charge something like £60-80 per valve so it can get expensive for a full set.

    Premier Icon Rich_s
    Subscriber

    The car has tyre pressure monitoring which works by comparing the speed the wheels are turning at rather than the actual tyre pressure. If you’ve got a soft tyre it will have a a smaller outside diameter and so it will rotate slightly faster and the system picks it up. When we swap the wheels as long as the pressures are right when they go on you just reset the system and it works fine.

    Now that is worth knowing! Explains why I once had soft tyres but no tyre pressure warning on my last Skoda. Every day’s a schoolday. Thanks docrobster

    phil5556
    Member

    You might find that the recommended winter tyre size for your car is also actually narrower than what’s on it now.

    I think our Polo goes from 215/40r17 to 195/50r16. So down a wheel size and 20mm narrower. We stuck with the recommended sizes on that.

    I think my BMW also suggests a similar change of size, although I got the larger size for cheap so have gone against what’s recommended.

    Tyre pressure monitoring systems can either use a pressure sensor in the wheels or ABS sensors to monitor relative wheel speeds. The former is more accurate and better. My wife’s car has them and will set off when cold as the pressure reduces a bit with temperature so all 4 wheels will report as having low pressure and will actually report the pressure reading in each wheel. Clearly if your indirectly measuring it via differential wheel speed the it won’t register in this scenario as the system has no way of determining the actual tyre pressure.

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