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  1. #1
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    New wheel advice

    The wheels on my A4 1.9TDI 130 are corroding pretty badly and the tyres need replacing so was thinking of buying a new set of alloys and tyres. Current size is 205/55 16". The MPG is amazing at the moment, easily 55mpg on a run and i dont want to compromise this, but I like the RS6 style alloys.

    Any advice of what size wheel & tyre to go for that wont eat fuel?

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  3. #2
    swarcup's Avatar
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    I believe these are available in 17 or 18 easily as original and even 19 from a genuine rs6(not to sure though) 18 are a popular choise for the ones who are a bit scared of what they believe will be a bumpy ride. I bought 19 inch ones and dont have any problems with the ride even with the sports suspension.The tyre costs do go up the lower the profile you get. The change in what your car will look like also will amaze you. As for the mpg issue i dont see how changing your wheels can affect this, apart from the extra weight of the wheels of course but if there is an issue i stand corrected.The wheels will of course be wider than what you have now also. The tyres on my 19 inch wheels are 235x35x19 so i suppose on 18 inch wheels will be 235x40x18 or 23545x18 but let someone with 18's say for sure
    2.5tdi Avant Q S 180 - 19" RS6 reps - chrome mirrors - ambient light package - cruise and dis retrofit - chrome side repeaters - front sline lowr conversion with cupra r splitter - rear lower valance with twin cut outs and exhaust tips - rs4 rear antiroll bar - puddle and footwell lights - sline door blades - fully colour coded - b8 autodimming mirror on custom window adapter - geuine aero wiper upgrade - genuine heated mirror upgrade

  4. #3
    BahnStormer77's Avatar
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    Keep the rolling radius the same* or try to stick to the OEM specs for the tyres and you'll be fine.

    * TyreCalc Tool

    Don't use your existing specs as a baseline though! 205/55 16" is actually NOT OEM for Audi, but a popular and perfectly acceptable choice since they are very close and a lot cheaper since those are the same size for a lot of Golfs, A3's, Focuses, etc... 215/55 16" is what you should be running on 16" - I bought mine off an Audi mechanic who was running 205/55/16's on mine and his other A4 quattro sport (1.8T).

    Currently your speedo will be under-reading by a few percent more than it should be and you will be clocking slightly higher mileage and mpg than you are doing in reality, but again, only by a few percent.

    18" OEM spec is 235/40/18 and with 8j(?) and ET45, it gives the car a nice solid stance without looking excessively aftermarket, RS6 alloys are the only ones I would really consider if I was to replace my S4 Avus's and the 17" versions of those are top of my list if I ever need to replace my 16" winter wheels (215/55/16, 0.36% difference between my 18" spec and 16" spec).

    If you're going for 17", I believe there are two options, one with a wide tyre, with 45 profile or a much thinner with a 50 profile: both will work and give the same rolling radius, but one is more stretched and will have better fuel economy... and the other will give your wheels better rim protection... we are only talking a few % on the economy, so I'd go with the rim protection and less stretched look, but each to their own.

    235/45/17 (-0.29%), 205/50/17 (-1.3%) and 215/50/17 (+0.25%) are all very close to the 18" OEM spec.

    % ratings in this post are all relevant to OEM standard of 235/40/18, which has my speedo and odometer VERY accurate compared to GPS stats on my SnooperLynx)... I think 215/50/17 would be EXACT on my car, but might actually under-read the speed slightly (most speedo's over-read the speed by around 3%-5%).

    For comparison, your 16" tyres at present are -2.06% compared to the 235/40/18's: anything within 2.5% is normally fine - but if you're going into the +ve territory you run more risk or rubbing or having a speedo that UNDER-read - which is dangerous in the world of Gatso's, Truvelo's, SPECS and Speedcurbs that we live in... the rubbing is only of concern on significantly lowered cars... I'd be more worried about a speed that under-reads significantly (remember you should have around 3%-5% to "play" with).
    Last edited by BahnStormer77; 4th May 2011 at 19:10.
    LostBok/BahnStormer77
    A6 (C7) Avant 3.0TFSI, DSG, rain and light sensor pack, LED headlight pack, MMI touch, SDS high, AMI, 360deg sensors + auto-park, Dunlop SP Winter Sports / Pirelli P Zero's.

  5. #4
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    Excellent reply, thanks very much. Tyre prices certainly shoot up from the common size i have now to any of those suggested 17" tyres!

  6. #5
    BahnStormer77's Avatar
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    I know what you mean: reasonable (Hankook) 205 width tyres can be found for about £75 a corner (based on Blackcircles.com, fitted and balanced) and just changing to the less common 215 width and you're looking at £90+ for the lower end of the "reasonable tyre" price range!

    Last time I replaced them, my Vredestein Wintrac Xtreme's 215/55/16 were about £95 a corner and my summer 235/40/18 Toyo Proxes T1-R's were £135 a corner (fitted and balanced*).

    *I know that "balanced" might seem to be an obvious part of fitting tyres, but I've had some tyre fitters do a static "balance" on tyres (as if they were motorcycle tyres.... which was NOT good!
    LostBok/BahnStormer77
    A6 (C7) Avant 3.0TFSI, DSG, rain and light sensor pack, LED headlight pack, MMI touch, SDS high, AMI, 360deg sensors + auto-park, Dunlop SP Winter Sports / Pirelli P Zero's.

  7. #6
    S3 GAZ's Avatar
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    If you're going for 17", I believe there are two options, one with a wide tyre, with 45 profile or a much thinner with a 50 profile: both will work and give the same rolling radius, but one is more stretched and will have better fuel economy... and the other will give your wheels better rim protection... we are only talking a few % on the economy, so I'd go with the rim protection and less stretched look, but each to their own.
    Think you got it mixed up 45 and 50 profile will give different rolling radius. The profile is the hight thickness of the tyre not the width. 45 is thinner than 50 so the rolling radius is less

  8. #7
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    45 and 50 does relate to the height of the wall of the tyre, but this number is a percentage of the width of the tyre.

    A 235/45/17 size has a tyre wall height of 45%x235=105.75mm and a 215/50/17 tyre has wall height 50%x215=107.5mm. Similar overall diameters, hence similar rolling circumferences.

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    S3 GAZ's Avatar
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    Quote Originally Posted by pj123 View Post
    45 and 50 does relate to the height of the wall of the tyre, but this number is a percentage of the width of the tyre.

    A 235/45/17 size has a tyre wall height of 45%x235=105.75mm and a 215/50/17 tyre has wall height 50%x215=107.5mm. Similar overall diameters, hence similar rolling circumferences.
    Ah. Didn't know that. Every days a school day lol

  10. #9
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    have a look on edition 38 in the classifieds there loads of sets of nice wheels, you will need a few post before you can look in there.

    you'll find 18" wheels generally come with 225/40/18 which is a lot more common and cheaper tyre than 235/40/18 makes little difference to overall speed, but if you really want to know differences look here
    TYRESAVE: Tyre Size Calculator

    2ndly if economy is important then stick to oem wheels and not reps of them as they weigh much more and will bring the mpg down
    Silver A4 wagon on porsche splits

  11. #10
    BahnStormer77's Avatar
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    thanks PJ133

    Don't worry Gaz, very common mistake!

    Hence why most people do a double-take when you tell them that completely difference "profile" tyres can be fitted to the same rims and have an almost identical rolling radius (although NOT close enough to run different spec across the same vehicle, especially if it's a quattro!!!!!)*.

    235/45/17 (-0.29%), 205/50/17 (-1.3%)
    * although personally, if I had a FWD, I'd be tempted with putting the narrower ones on rear, which is how the new Polo GTI is apparently setup... likewise, I always used to run nice deep, new tyres on my old Golf GTI's fronts and borderline legal ones on the rear... as the fronts got "dubious", I'd shuffle them back and put a new set on the front

    Back to the tyres: Because of the price difference, lots of people end up with the wrong rolling radius (and real-world lower fuel economy) because they go for narrow tyres (either in an attempt to keep tyre costs down or to improve fuel economy)... what actually happens, which only exacerbates the issue is that the INDICATED economy goes UP, even if you compare fuel usage versus the odometer readings, this will also show an improvement.... but the actual amount of fuel used on any given A to B journey will actually be higher!

    The reason being that the very slightly smaller (narrower) wheels are actually recording more miles for that same A to B journey!

    But the car is actually geared very slightly lower, so certainly for a long motorway haul, your actual economy will be slightly worse!

    And on the other economising aspect: narrow tyres = more chance of wheelspin/skid/drift, which although more fun, will mean you wear tyres out a lot faster!

    Personally, I go for the other extreme and save my summer tyres from going brittle and wearing prematurely* by never using them when the ambient temp is <4deg C (I normally change as soon as it's consistently below 10deg C since winter compound is better than summer below 7deg C). Conversely: Winter tyres are not to be used over 20deg C.... those tyres are like sticky warmed up track tyres when they're sat on your drive at -10C, so they get REALLY soft when the weather warms up!!

    *Summer tyres apparently wear 40% faster in winter than they do in summer due to being so much more brittle and due to the increased risk of any wheel spin / sliding / skidding - although I think that stat is North American, so probably not as extreme in the UK!

    edit: I always find is slightly funny that I post those using the "Post Quick Reply" button
    Last edited by BahnStormer77; 5th May 2011 at 13:00.
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  12. #11
    BahnStormer77's Avatar
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    Quote Originally Posted by matttrs View Post
    you'll find 18" wheels generally come with 225/40/18 which is a lot more common and cheaper tyre than 235/40/18 makes little difference to overall speed, but if you really want to know differences look here
    TYRESAVE: Tyre Size Calculator
    Sorry - I should have stated: the 235/40/18 is OEM spec for the S4 - as Matty has stated, the 18" upgrade option normally came with 225 width...

    Quote Originally Posted by matttrs View Post
    2ndly if economy is important then stick to oem wheels and not reps of them as they weigh much more and will bring the mpg down
    **big thumbs up**

    The only "reps" worth buying are good wheels, from a good manufacturer that are the same design, don't go for these £500 for wheels+tyres packages... there's a reason why the package is nearly the same cost as the tyres would normally be!!

    e.g. Ronal actually make the S4 Avus III wheels and they are badged with the four rings and "Ronal"... but that means there is a Ronal wheel out there that looks identical and doesn't cost £550 a corner
    LostBok/BahnStormer77
    A6 (C7) Avant 3.0TFSI, DSG, rain and light sensor pack, LED headlight pack, MMI touch, SDS high, AMI, 360deg sensors + auto-park, Dunlop SP Winter Sports / Pirelli P Zero's.

 

 

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