can someone explain car tyre sizes

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  • can someone explain car tyre sizes
  • PeterPoddy
    Member

    Diameter will be slightly smaller so the overall gearing of the car will be lower – i.e. higher revs for a given speed and possibly higher fuel consumption and brisker acceleration at the expense of top speed

    Lower profile may also give a harsher ride.

    It might also be modification that needs noting on your insurance, as they have a habit of checking things like this to wriggle out of claims.

    jimw
    Member

    you will have approx 9mm lower ride hight, 3.4% reduced rolling radius so the same 3.4% speedo error compared to original if this website is to be believed

    http://www.willtheyfit.com/

    Premier Icon Rusty Mac
    Subscriber

    By going narrower you also have to stretch the tyre to get it to fit which is not ideal for the tyre and would further reduce the overall diamiter of the wheel.

    As well as all the things PP mentioned it will also throw the calibration of your speedo out a little.

    PeterPoddy
    Member

    Rusty, it’s not narrower is it? Both 195 width?

    195 is width
    55 is the sidewall height expressed as a percentage of the width
    15 is the rim size

    oh and as for difference in the real world, none.

    b r
    Member

    What difference does it make in the real world.

    You fitted the wrong tyres, and since they are both lower in profile and cheaper – are probably a worse quality tyre over the ones you should have fitted…

    mrmo
    Member

    if my car has 195/55r15s and i fit 195/50r15s which cost less. What difference does it make in the real world.

    Premier Icon Rusty Mac
    Subscriber

    PP I was sure i read 195 v 190 oops my bad.

    Premier Icon Del
    Subscriber

    the dimensions may not be the only difference. did you check the speed rating too? this may account for the price differential.

    PeterPoddy
    Member

    Ahh. I wonders if there was some sizing thing I wasn’t aware of! 🙂

    Also remember if you only fit 2 at front say it can play havoc with ESP ABS and suchlike.

    mchlptchr
    Member

    Not much difference other than the slight Speedo issue mentioned above (assuming they’re on the wheels with the speed sensor).

    b r – they’ll most probably be cheaper as they’re a more popular size.

    have done exactly the same thing in the past. Same tyre, slighty different size, cheaper.

    Premier Icon pictonroad
    Subscriber

    None at all, you’ll feel more difference by changing the psi a bit. It’s not stretching the tyre, you really won’t tell. I always changed 55 profile tyres to 50s, much cheaper for 205 and 195 usually.

    mrmo
    Member

    I haven’t done it, just noticed that 50’s are much cheaper than the 55’s that the car is fitted with. Been looking at exactly the same tyre and it seems to be of order £20 per tyre cheaper to go for a 50 than a 55.

    So basically no real difference, but change all 4 to be safe?

    As someone else mentioned make sure they are an appropriate size in the manual of the car, if they are different to the sizes specified as suitable for the car then I would think any insurance claim might not go your way and they won’t pay out. Comes under modifications to the vehicle iirc.

    Premier Icon mboy
    Subscriber

    So basically no real difference

    Errrrr… CHECK with your insurance company first… Seriously!

    I say this because I know that many people have been caught out here as fitting different sized tyres (even just a profile lower) is classed as a modification, and insurance companies have refused to pay out as a result…

    Sorry to be the bringer of bad news, but I figured you’d rather find out now rather than when your insurance company doesn’t pay out! Of course this may not apply to all insurance companies, but I’d find out first…

    In the real world though, insurance company aside, as someone who’s done this (had a Peugeot 306GTi-6 years ago with 195/55/15 and fitted 195/50/15’s to it), I wouldn’t recommend it to be honest. Fine if you want a lower ride height for track use, but it throws the speedo out by a good few percent, your fuel consumption goes up (cos the car is now geared lower), and the ride will be slightly less compliant. It’s not massive changes agreed, but remember that your car will now sit lower to the ground by 10mm or so, but that the spring rates haven’t changed so it will bottom out on speed bumps and potholes much more easily now.

    A far better bet is to change where you get the tyres from, and find somewhere that supplies good quality tyres at better prices…

    http://www.blackcircles.com/
    https://www.camskill.co.uk

    Hope I’ve helped

    coffeeking
    Member

    I run 195 50 15s in replacement for 195 55 15s. Two notable consequences over the maths above:

    Fuel economy dropped minutely.
    New size mostly comes in a lower load rating (still well within the plate specs for the car so no issue with insurance) but makes them more susceptible to pothole damage.
    Handling is no different.
    Speedo is barely any different.
    On any car that’s not a road legal track car you’ll not bottom it anyway.

    Reasonable trade-offs for a car doing lower miles and when the tyres are 50% the cost.

    Personally never had an issue with insurance, they usually sound totally bemused when I Itell them.

    ell_tell
    Member

    Have a look at this. Perhaps 205/50/15 might be better?

    http://www.etyres.co.uk/tyre-size-calculator.htm

    ell_tell
    Member

    I changed from 195/50/16 to 205/45/16. Resulted in a slightly smaller diameter but it meant I had far more choice of tyres and ended up getting a decent(ish) brand – Vredstein – instead of a cheapo make and I the ride quality is now far better than on the budget Accelera it had on before.

    The slightly wider tyre also offers a bit more side wall protection against kerbing etc.

    Premier Icon Northwind
    Subscriber

    I fitted slightly taller tyres to the mighty focus- they were £20 cheaper per corner for the same make/model, and they upgeared it slightly, both of which I was happy with. And it already cornered like a spacehopper so no real downsides. Insurance didn’t really understand why I was calling.

    I don’t know if it’s the same for car tyres, but for motorbikes the sidewall numbers are more a vague estimate than a statement of fact, there’s wild variations.

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