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Thread: How To: Tire Stretching - The Ultimate System Guide

  1. #1
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    Default How To: Tire Stretching - The Ultimate System Guide

    One and a half decades ago I started my tire stretching journey and about a decade ago I came up with a system for myself which has been continuously confirmed over 10 years. I'd like to share this with my friends and everyone in the car community that might need help with this. Seasoned tire stretchers will likely know all of this already, but I'm certain this may help a person or two; at the very least my own brother who still doesn't know fuck all about tire stretching after a decade of doing so. The disclaimer here is, tire stretching is not an exact science but I will do my best to explain the majority aspects to tire stretching including terms, technicalities and kinks to be encountered.

    When I first started playing with tires and looked at cool cars on the internet I desperately tried to make sense of how tire stretching works. Since then a built a massive picture library for myself with examples of different stretches with various wheel and tire sizes. Let’s go.

    First and foremost, the diameter of your wheel does not matter in my calculations. Everything you read below will be applicable from 13" to 23" wheels. I will use 18" mainly for explanatory purposes but later on I'll also throw in a few different diameter examples to make a point.

    Second and.. also foremost, both the width and the height of your tire have an effect on the desired stretch in the end. Very important to remember.

    Let me run you through my 'Stages' of stretching.

    Baseline:

    18x10 wheel with a 255/35 tire has always been my baseline because it is the easiest to remember. The 18 as said is irrelevant but the 10J is what matters here - 10 inches equal to 254mm which incidentally is (almost) exactly the width of a 255 section tire. Now this is where it gets fuzzy - as a 35 sidewall is 1/3 of the section width I found this to be the most 'neutral' height on any tire; anything less than 35 will result in a more stretched look, and anything more than 35 will result in a less stretched look. This is due to how section width in a tire is calculated - as you know the number on the side of a tire does indeed describe the section width and it's important to notice that this is NOT equal to the tread width (see pic below). The bulge in which the section width is calculated can get substantially bigger if you have higher sidewalls. That's why I found 1/3 sidewall to section to be the most neutral as I mentioned above.



    Still with me?

    Good.

    The baseline is Stage 0 - it's a neutral stretch, now every time you change the size of the width or the height you will move through the stages of stretching. Section changes in intervals of 10, and sidewalls change in intervals of 5. Each interval of either number will change the stretch stage you'll achieve. First example:

    255/35 on a 10J wheel is Stage 0

    245/35 on a 10J wheel is a Stage 1 stretch (mild stretch)

    235/35 on a 10J wheel is a Stage 2 stretch (solid stretch)

    225/35 on a 10J wheel is a Stage 3 stretch (full stretch)

    225/40 on a 10J wheel is a Stage 2 stretch (solid stretch)

    So you see what just happened? We've gone through the sections widths and every time we decreased the size by 1 we increased our stretch, vice versa we increased the sidewall height by 1 and that decreased our stretch by 1 stage.
    I will go into more detail how every stage of stretch manifests later on but there is 2 more very important things you have to understand.
    First, the different stages of stretch describe a stretch "angle" of the sidewalls. Take our example above, I described both the 235/35 and the 225/40 as a stage 2 stretch. That is because the angle of the sidewalls will be the same even though the 235 has a wider section, but the 225 has due to its 40 sidewall a higher circumference. Check out the picture below and focus on the angle of the sidewalls. You will also notice that the 225 goes 'higher'.



    Now if you're still reading let's add another layer of complication: Every interval of wheel width is also changing the stretch of any given tire. Wheel width intervals usually are 0.5 inches. Quick example

    I showed you above a 225/40 on 10J is a Stage 2 stretch, if you increase the wheel width by 1 size to 10.5J the 225/40 will turn into a Stage 3 stretch. Again, vice versa if you decrease the wheel width by 1 to 9.5J you also decrease the stretch to Stage 1 with the 225/40.
    So, if you've been reading all the gibberish above and are indeed a smart cookie you might wonder how does it compute that 0.5 inch of wheel width has the very same effect as 10m of section width. Half an inch are 12.7mm, this is a fixed value that changes every time you change the wheel width, BUT with a tire you also have to consider the sidewall. The sidewall number is a percentage of the section width, and every time you go up 1 section width you also increase the sidewall size which offsets the discrepancy between the interval sizes of wheels and tires (mostly).

    Shit, if you could follow me this far the rest will be a walk in a park.

    Lemme now explain the different stages now in a bit more detail.

    Stage 0 (Baseline)

    I explained the baseline above and I just want to give you a couple examples so we're on the same page.
    All of these are Stage 0, pretty much no stretch, and while some already call this a mild stretch, I don't.

    18x10 255/35


    18x9 225/40


    18x9 235/35



    Stage 1 (mild stretch)

    The mild stretch is usually the maximum legal stretch you can get away with for example at the German Tüv because that is what you'll receive a certificate from the tire manufacturer for, saying what the widest wheel is that you can mount a certain tire size on.

    This stretch is a widely used stretch for people that are not looking for an extreme fitment but being able to comfortably tuck the tire away under the fender under compression thanks to its slightly angled sidewalls.

    Another interesting thing to note is that it appears that some autocross drivers swear by a mild stretch on their cars because it supposedly stiffens the sidewalls on a non-detrimental level and gives them more feedback and response from tires.

    Examples:

    18x10 245/35


    17x11 255/40


    18x9.5 225/40



    Stage 2 (solid stretch)

    This was for me the 'standard' stretch since I started doing this because this is when the tire starts reaching the maximum stretch angle it can get but without or only slightly exposing the edge of the wheel depending on the tire. I will get into different tire brands and types specifically later.

    Examples:

    18x10 225/40


    18x12 285/30


    15x9 195/45



    Stage 3 (full stretch)

    This is the maximum stretch I recommend ever doing. This stretch you can recognize by the tire exposing almost the entire rim of the wheel and but is still just about touching the sides of the wheel on the inside so it does not expose the barrel.

    Examples

    18x10.5 225/40


    19x14 315/30


    16x11 225/45



    Stage 4+ (no.)

    From this stretch forward you may start to expose the barrel - that means the sides of your tire under the rim protector may no longer touch the side of the wheel (again depending on if your tire runs wide or narrow). Unfortunately that is bad for a couple factors that I'm sure you knew already. First of all the tire may tend to slide from side to side, oh and it also might not be the best idea if you want to hold air in the tire for a longer period of time.

    This technique is mostly used on show cars that want to tuck their fender between the tire and the rim of your wheel with the help of air suspension. These mostly have to have air put in every couple of days.

    Please read again: From this stage forward you run an exponential risk of debeading your tire while driving.

    Examples:

    18x11 225/40


    14x12 255/35


    18x12 255/35



    Now that we discussed the stretched stages I want to quickly go through meaty tire setups, let's call them the negative Stages of stretched tires to make sure everything is covered. I'll make this short.


    Stage -1 (meaty)

    This is a setup that is used on endless track cars that want to maximize grip for competitive purposes. The picture below is a R888 setup that I will go into more detail later.

    Example

    18x9.5 255/35





    Stage -2 (super meaty)

    Many times this is what tire manufacturers recommend for their tires.

    I reckon some people would think this should be the baseline to a tire stretching guide, but you know what, fuck it. Using Fahrenheit over Celsius is just as retarded.

    Anyway if you go beyond this level of using a much wider tire that is recommended for your wheel size you may experience adverse effects like less response due to the wobble effect of too meaty tires as well as unnecessarily increasing unsprung weight not being able to utilize the increased grip any more.

    Example

    18x10 285/30





    Hope everything is clear.

    We ain't done yet though. Let's get into different brands and types of tires.

    Certain brands/tires are known to run notoriously wide like the Federal 595 SS and others are known to run extremely narrow like the Nankank NS2 or the Falken 452. It's important to note that this may affect the desired stretch, as a normal vs a narrow/wide running tire can easily be the difference of half a stage. A 595 and a NS2 will have a full stage of stretch difference in them at the same sized tire due to their designs.

    I also want to quickly mention cheap vs premium tires, in both categories there are tires that stretch better or worse, it really is the same as with overall performance, just because you pay premium it doesn’t mean it will perform superior to a potentially cheaper tire. Please beware that there is definitely cheap tires that will perform horribly. For example, I made the worst experience driving on a set of Acceleras that came with the R32 back then, felt like I was driving on ice. But on the other hand do not be fooled by magazine tire reviews that get paid by tire companies or certain garages/mechanics telling you about tires that cost 2 or 3 times as much – they are not necessarily better than many reasonably price rubbers.

    Moving on, there is different types of tires and these will make a difference when stretching tires, I’m sure you have heard the term “semi-slick” thrown around frequently. When it comes to semi-slick tires it mostly comes down to the compound or more specifically to the treadwear. The lower the treadwear number, the softer the compound, the quicker they wear down (but also usually means more grip).

    From my experience the definition for semi-slick tires is rather loose. I’ve seen everything under treadwear 200 being called semi-slick and that is what I usually go by. A few examples for tires between 100 and 200 is the Advan AD08 (that I swear by), the Direzza Star specs, a Faken RT615 or Kumho KU36s. These tires are usually recognizable by the slightly lighter, dark greyish hue and appear bit more ‘matte’. What makes them special for stretching is that you get a very specific look that I find exceedingly appealing. These tires tend to have rather hard sidewall which makes stretching them not exactly easy but is well worth the effort.

    Here are some examples

    18x11 245/40 Direzza Star Spec


    18x12 265/35 Falken RT615



    All that said, usually the term for a true semi-slick tire is reserved for tires with treadwear 100 and below. As I briefly hinted at above the Toyo R888 is one of them. These tires have a very special look to them as you can see above, these do not feature a rim protector integrated into the rubber which is why they tend to be very aggressive looking and are a favorite for many show car builders, albeit expensive.


    Next up, J-stretch vs reverse J-stretch.

    The J is referring to the form of the sidewall while stretched; back to the 595ss vs NS2 example. Where the NS2 tends to take the J form, the 595ss tends to curve outwards.
    Keep that in mind and inform yourself about a tire, check first how it stretches in order to achieve a desired look.


    As you can see there is many different factors that have to be taken into account when you wanna do tire stretching right. Again, not an exact science but if you understand this guideline you should be good with anything from 155 to 355 section width.
    In the unlikely case you were able to read through all of that shit above AND understand any of it I would like to congratulate you to potentially be the first person that understands me. God knows I tried with my brother, my wife, friends and of course random strangers on the internet. I failed every time. Miserably.

    If you didn’t, but at least get what I mean with the different stages of stretch I shall include a list of all wheel width vs tire size combos I can think of below (I don’t deal in sizes below 9). That can help you to quickly identify how much of a stretch the desired setup would have. What you’ll do is simply press CTRL+F and type the desired setup with the following syntax: XXX_YYY_ZZ

    XXX= wheel width without the point or comma (i.e. 9, 95 for 9.5, 10, 105 for 10.5)

    YYY=tire section width (i.e. 255)

    ZZ=tire sidewall height (i.e.35)

    Try this: 105_225_40

    Found it? Awesome.


    Stage 0
    9_235_35 9_225_40 9_215_45 9_205_50 9_195_55
    95_245_35 95_235_40 95_225_45 95_215_50
    10_265_30 10_255_35 10_245_40 10_235_45 10_225_50
    105_275_30 105_265_35 105_255_40 105_245_45
    11_285_30 11_275_35
    115_295_30 115_285_35
    12_305_30 12_295_35
    125_315_30 125_305_35
    13_325_30 13_315_35
    135_335_30 135_325_35
    14_335_35

    Stage 1
    9_225_35 9_215_40 9_205_45 9_195_50
    95_235_35 95_225_40 95_215_45 95_205_50 95_195_55
    10_245_35 10_235_40 10_225_45 10_215_50
    105_265_30 105_255_35 105_245_40 105_235_45 105_225_50
    11_275_30 11_265_35 11_255_40 11_245_45
    115_285_30 115_275_35
    12_295_30 12_285_35
    125_305_30 125_295_35
    13_315_30 13_305_35
    135_325_30 135_315_35
    14_335_30 14_325_35
    145_335_35

    Stage 2
    9_205_40 9_195_45
    95_225_35 95_215_40 95_205_45 95_195_50
    10_235_35 10_225_40 10_215_45 10_205_50 10_195_55
    105_245_35 105_235_40 105_225_45 105_215_50
    11_265_30 11_255_35 11_245_40 11_235_45 11_225_50
    115_275_30 115_265_35 115_255_40 115_245_45
    12_285_30 12_275_35
    125_295_30 125_285_35
    13_305_30 13_295_35
    135_315_30 135_305_35
    14_325_30 14_315_35
    145_335_30 145_325_35
    15_335_35

    Stage 3
    95_205_40 95_195_45
    10_225_35 10_215_40 10_205_45 10_195_50
    105_235_35 105_225_40 105_215_45 105_205_50 105_195_55
    11_245_35 11_235_40 11_225_45 11_215_50
    115_265_30 115_255_35 115_245_40 115_235_45 115_225_50
    12_275_30 12_265_35 12_255_40 12_245_45
    125_285_30 125_275_35
    13_295_30 13_285_35
    135_305_30 135_295_35
    14_315_30 14_305_35
    145_325_30 145_315_35
    15_335_30 15_325_35
    155_335_35

    Stage 4
    10_205_40 10_195_45
    105_225_35 105_215_40 105_205_45 105_195_50
    11_235_35 11_225_40 11_215_45 11_205_50 11_195_55
    115_245_35 115_235_40 115_225_45 115_215_50
    12_265_30 12_255_35 12_245_40 12_235_45 12_225_50
    125_275_30 125_265_35 125_255_40 125_245_45
    13_285_30 13_275_35
    135_295_30 135_285_35
    14_305_30 14_295_35
    145_315_30 145_305_35
    15_325_30 15_315_35
    155_335_30 155_325_35
    16_335_35

    While I could continue on and on about tiny details I think this is a good point to conclude the guide.
    If you feel there should be something added, let me know and I’ll consider.
    Also if you think there is something wrong - however unlikely that may seem - feel free to also let me know.

    I hardly believe this is an enjoyable read, but I hope it was somewhat helpful anyway.

    PS: Yes, I have a fetish for tires (and wheels), touching new tires is my favourite spare time activity.

    Alex
    Last edited by h3llk1t3; 04-17-2018 at 03:28 AM.

  2. #2
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    Excellent guide and makes total sense to me!

    I just looked up the sizes I ended up running and both are stage 1, which confirms the same consistency of stretch!

    Thank you for taking the time

  3. #3
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    Thanks Alex,

    I hope everybody will read this and hopefully it will change the scene a little bit.
    Daily Driver: Volkswagen Golf Mk3 1.6 Europe Edition

    Showcar: W201 2.5-16 Evo1 Replica

  4. #4
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    Well written and takes some of the "black art" out of the stretching process.

    Cheers Alex!

  5. #5
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    Good stuff for sure!

  6. #6
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    this is actually very helpfull! thank you for posting!

  7. #7
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    Wow dude nice write up.

  8. #8
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    this is awesome thanks!

  9. #9
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    This is genuinely awesome Alex, many thanks for this!
    IG: @sebastienaudeon
    1974 Porsche 911S

    Quote Originally Posted by TRaNz View Post
    *pats Sebs head*
    there there.
    keep calm, go mash your face on a car window.

  10. #10
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    Shout out!! Saved me so much time from doing research and looking on tyre stretch, thank you

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