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Wheel weight and unsprung weight info

Discussion in 'A3/S3/Sportback (8P Chassis)' started by dunk, Oct 15, 2009.

  1. dunk
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    dunk Member

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    [Oct 15, 2009]
    some info that may be useful within a realistic budget

    oem rs6 7.5x18 et54 weigh 12.9kg
    oem s3 7.5x18 et52? 12.5kg
    bbs ch 8x18 et50 10.9kg
    bbs ch 8x19 et50 11.5kg
    reps rs6 8x18 et46 12.4kg (special soft and bendy version)
    ultraleggeras 8x18 et45 8.4kg
    race pro 1.2 8x18 et52 8.9kg custom made
    mtm 9x19 are 16.5kg for comparison

    i ignored the silly priced ultra light ones - such as folk etc etc which are generally £400-£600 per wheel

    i just swapped my oem rs6 for race pro 1.2 so lost 4kg per wheel - does it make a difference? surprisingly yes it does. there is less crash on bumps, the steering feels tighter and more precise with better turn-in, slightly lighter steering and the whole car feels much more nimble on the b-roads particularly.

    im not sure that oem to bbs 12.9kg to 10.9kg would be as noticable but then most people upgrade for the looks not performance... however bbs will cost you £1100-1200 where as race pro 1.2 can be had for £500-600 a set.

    other useful unspring weight savings can be had:
    1) s3/r32/3.2 front brakes have alloy calipers and are much lighter then the steel standards
    2) tt alloy front bottom arms are lighter and give the much needed negative camber
    3) s3 hubs are alloy and save a few kg each wheel and are quite cheap.
    #1
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  3. rickyquicky
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    rickyquicky Member

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    [Oct 15, 2009]
    :icon_thumright:

    thats some good info right there.
    #2
  4. devonmikeyboy
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    devonmikeyboy As far from JBS as possible !

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    [Oct 15, 2009]
    Copied from the Dymag alloy wheel site :
    Reducing un-sprung weight on your car is different than reducing weight from your cars body (sprung weight), reducing un-sprung weight by 1kg has the effect of reducing your cars body (sprung weight) by 6kg! This means that if one wheel is 2kg lighter than the wheel it replaces it is like removing 48kg from your cars body when you fit a set of 4 wheels. This improves acceleration, improves braking , reduces stopping distances, give sharper steering.
    #3
  5. Spin140
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    Spin140 Active Member

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    [Oct 15, 2009]
    The team dynamics represent excellent quality and value for money, I have a graphite set on order for this very reason, they aren't the best looking wheels around but great for track events etc..
    #4
  6. N8
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    N8 Kowalski Details VCDS Map User

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    [Oct 15, 2009]
    Good post and info!
    #5
  7. Kivinen
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    Kivinen Member

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    [Oct 16, 2009]
    Use narrower wheels. Little info from OZ page..
    7x17" - 6.94 kg
    7x18" - 7,38 kg
    8x17" - 7,74 kg

    7,5x18" - 7,92 kg
    8x18" - 8,00 kg
    9x18" - 8,73 kg
    8x19" - 8,99 kg

    Didn't those use bigger brake discs? Bigger disc = more weight.

    Some page says 1:4 and 1:8.. so 1:6 is good middle way :)
    Last edited: Oct 16, 2009
    #6
  8. dunk
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    dunk Member

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    [Oct 16, 2009]
    good suggestion, narrower wheels would be great and so would keeping to narrow tyres, its far better for the handling - but for most of us the oz wheels are too expensive, probably genuine bbs as well. most reps are heavy and not available in much other than 8x18

    unfortunately there arent that many suitable 5x112 7.5 or 8 x 18 choices in a decent weight with an offset of 45 to 50 or higher.

    the s3/r32/3.2 brakes are bigger at 345mm so the disks are heavier but the calipers are a large single pot alloy compared to the very heavy iron caliper of the smaller disks - overall the brakes are quite a bit lighter and also much better at stopping.

    up to about 8.5" the tyre is the widest bit of the wheel and so its only the offset that determines arch clearance with any kind of lowered springs

    et45 will work for most people with 225 tyres and probably 235 as well (worked with mine) but once you start to change cambers then things can get tight.

    the longer tt bottom arms create negative camber by widening the bottom track and this also move the top of the wheel closer to the arch so et45 stick out a bit, and at the back reducing the camber from factory -1.5 to -1.2 moves the top of the rear wheel out towards the arch as well - i wanted to use a 235 tyre all round because of my 360lb/ft fwd so needed an offset of about et50. fortunately team dynamics have an et50 casting for the race pro 1.2 and were happy to make a custom offset of et52 for me. im pretty sure that bbs et50 8x18 or 8x19 would have fit fine as well but they would have cost £1200 or so and be heavier anyway
    #7
  9. paddy
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    paddy Audi=No fault code, no idea

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    [Oct 16, 2009]
    The real advantage of losing some unsprung weight will be in ride quality, Im not sure how Dymag can claim "This improves acceleration, improves braking , reduces stopping distances, give sharper steering."...I would agree about the steering if it wasn't assisted but the rest i would think was minimal as a percentage of the cars power/weight/unsprung weight ratio.
    Where you really notice the difference is on a motorbike but there the unsprung weight is a much higher percentage of the overall weight.
    #8
  10. JeffY
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    JeffY Member

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    [Oct 16, 2009]
    Has anyone changed A3 hubs for S3 ones? Whats the cost?
    #9
  11. stokeballoon
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    stokeballoon Member

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    [Oct 16, 2009]
    I have a full set of S3 hubs in my loft. Will they fit the Ed30? If not will be up for grabs, This means I will have to take a look now.................
    #10
  12. stokeballoon
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    stokeballoon Member

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    [Oct 16, 2009]
    Disagree with the brake caliper part. The S3 caliper is made of 3 parts, an alloy housing which houses the piston (grey part), this is bolted to a large caliper frame (Black part), which is forged steel (again black), and the combination is bolted via guides to a caliper carrier, again steel and rather large. The weight of the S3 brake combination per corner is quite a bit heavier over the 312 Std GTI set-up. It is so much bigger and more substantial.

    [​IMG]

    GTI and S£/R32 side by side.

    [​IMG]
    #11
  13. stokeballoon
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    stokeballoon Member

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    [Oct 16, 2009]
    please bear in mind the R32 caliper carrier is not shown in the above comparison pic, whereas the GTI caliper is shown complete.
    #12

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