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A3 Black Ed. tyres (R18): 225/40 to 225/45 for comfort?

Discussion in 'A3/S3/Sportback (8P Chassis)' started by mockendo, Mar 5, 2013.

  1. mockendo
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    mockendo New Member

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    [Mar 5, 2013]
    Hi,

    Just registered and thought I'd try out the forum for a burning question! Not long purchased an A3 Black edition (60 plate) and think it's a cracking car. Only downside is the slightly hard ride, and part of this is probably down to the low profile of the tyres (225/40-R18).

    It seems that just increasing the tyre profile increases the air volume in the tyre and could have a significant impact on comfort. So my question: is there physically enough space on a standard issue A3 black edition to take a 225/45 R18 tyre vs the standard issue 225/40-R18? I'm not looking to make any modifications to the car or change the rims, just the tyres.

    It seems there'll be an increase in the circumference of approx 3.5% from this calculator (TRC Calculator)

    Any experience appreciated!
    Mark
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  3. deanshaw24
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    deanshaw24 Member

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    [Mar 6, 2013]
    I think you would have to go 225/45/17 as the whole size of of wheel will increase by 5cm! Which will put the speedo out, not sure about the wheel arch gap. And the car will sit taller
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  4. daz5182
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    daz5182 Member

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    [Mar 6, 2013]
    No expert but you'd be changing the dimensions with bigger tyres, would fit though i should as rs3 have 19s.... As for speedo just click it on sat nav before and after
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  5. deanshaw24
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    deanshaw24 Member

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    [Mar 6, 2013]
    Yeah but the rs3 has 35 profile to compensate for the 19s, so it's still the same size wheel?
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  6. Shadowman
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    Shadowman Member

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    [Mar 6, 2013]
    If you fit what is a 'taller' tyre on the car whilst keeping the original wheel size, then you change the rolling radius and therefore the gearing and the speedo will be altered as deanshaw24 correctly says, which is a p-in-the-a just for a smoother ride.

    Why don't you adjust the current tyre pressures as a starting point, as they are set very high as standard ?

    Don't go mad as there are obviously safety limits to consider, but you could adjust them by a couple of psi all round without too much of an issue and that may be enough to make the ride tolerable ( and it's free )...:arco:
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  7. mockendo
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    mockendo New Member

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    [Mar 8, 2013]
    I'm not too worried about speedo (would double-check against satnav afterwards) or gearing changes, just interested in whether it's physically possible without the wheel coming into contact with the bodywork, and whether anyone has tried it. As you say the R19s generally have /35 tires to keep the total size similar. So:

    225/40 R18 = radius 299mm stationery (309mm @ 60km/h) [existing tyres]
    225/35 R19 = radius 303mm stationery (311mm @ 60km/h)
    225/45 R18 = radius 308mm stationery (320mm @ 60km/h)

    So worst case is an extra 11mm extra radius (NB not diameter) vs existing wheels, and extra 9mm vs 225/35 R19s - anyone got these fitted and could check if there's any clearance?

    Here's hoping!
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  8. miw615
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    miw615 Member

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    [Mar 8, 2013]


    Hi Mark

    I have a similar car to you with 225/40 R18 set up compounded by the stiffer suspension with the S-Line spec.
    I don't want to change tyre size (speedo set up etc) so have narrowed my tyre choice to ...............

    Goodyear Efficient Grip Performance 225/40 R18 92W or Dunlop SP Sport 01 225/40 ZR18 92W
    Speaking to the manufacturers they both claim to run quieter and to choose the 92W loading - what tyres are you on at the moment?
    #7
  9. Rom
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    Rom Member

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    [Mar 8, 2013]
    Going to 225 / 45 would lose you 11.25mm arch gap clearance, and 11.25mm ride height gain. Whats the current gap like ?

    45s would be roughly 71mm rolling radius increase, speedo will under read 3.41%

    Im running 35s on 19s, lowered 40/50, and i could probably afford the 9.8mm arch loss swapping to 225 /45 / 18 would give me. So i would guess a standard, non lowered car should be able to. But measure to be sure.
    As an idea, my rolling radius is 9mm more than your 40 / 18.

    What about dropping to 215 / 45 / 18 ? Gives about 42mm rolling radius increase. I went from 225 / 40 / 17 to 215 / 45 / 17 purely because i got a deal on decent tyres :)

    I used this site Online Wheel & Tyre Fitment calculator. Offset, Tyre stretch and Rolling Radius calculator
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  10. Shadowman
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    Shadowman Member

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    [Mar 9, 2013]
    I don't want to be a stick-in-the-mud, but be careful with insurance. If you are staying with tyre options which are available on other versions of the 8P, then fine but if you stray away from the manufacturers options, then you may find issues with the insurance cover if anything happens.
    They look for any loophole these days, and a tyre/wheel combination that isn't manufacturer recommended may be enough for them to invalidate the cover.
    I know lots of people do it, and I have myself in the past, but it's something to bear in mind.
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  11. alfiejts
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    alfiejts Member

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    [Mar 9, 2013]
    It may or may not help, but I know that 245/40-18s rub very badly on an A3 8P.

    ( I was trying my daughter's TTS winter wheels to check theyd been balanced OK by the garage.....)

    They ran OK with just me driving on smooth roads & motorways but four-up I had major rubbing noises from the back over any small bumps in the road....

    I'm assuming that was down to the extra width, but it might have been down to the extra diameter....
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  12. miw615
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    miw615 Member

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    [Mar 9, 2013]
    Good point - I have spoken to my insurance company and they are okay with changes - must put it writing though!
    #11
  13. markm3006
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    markm3006 Member

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    [Mar 10, 2013]
    I have 205/55/16 winter tyres on my 2012 Black Edition & the ride is just as firm as it is with the standard 18's on it :wtf: :wtf:
    More noisy too :mad:
    Woke up to this
    [​IMG]
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  14. gixerson
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    gixerson Member

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    [Mar 11, 2013]
    Just to reiterate that choosing tyres to soften the ride is like wearing gloves to keep your feet warm.

    Tyres do flex to maintain contact with the road surface, but the amount tyres deform is extremely little compared to the amount of travel you have on your suspension.

    Some tyres do have a softer sidewall, the Toyo T1's are a prime example, compared to many other tyres they have very soft walls, but still this has very very little feedback through anything other than steering.


    Some things i'd check.

    1/ The shocks.
    Leaking shocks have very little resistance or damping, so shows through with a very rough ride, although it's unlikely you will have 4 shocks all equally knackered, still if 1 or 2 are faulty it will upset the ride of the car.

    3/ Springs
    If you have aftermarket springs on these will often be a fair bit firmer than stock, often at the expense of damping.
    If lowering springs are fitted this makes matters even worse as the lower the car the less suspension travel you have available, to compensate for this springs have to be firmer.

    As i say, fitting taller or softer walled tyres will have very very little effect on how stiff the car feels over bumps, the only thing you'll loose is feel on initial turn in.
    #13

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