Why excessive wheel width may decrease handling performance!
Page 1 of 2 12 LastLast
Results 1 to 15 of 28

This is a discussion on Why excessive wheel width may decrease handling performance! within the Suspension & Wheels forums, part of the Tech & Modifying & General Repairs category; The typical myth that you can slap 17x12 wheels on a car and achieve 1.2G of grip in the corners ...

  1. #1
    zax
    zax is offline
    ¯\_(ツ)_/¯ zax's Avatar
    Join Date
    Nov 2008
    Location
    Neverland Ranch, Maryland
    Posts
    11,718
    I Support ClubWRX I Support ClubWRX

    Why excessive wheel width may decrease handling performance!

    The typical myth that you can slap 17x12 wheels on a car and achieve 1.2G of grip in the corners is just that, a myth. The maximum wheel width that a car can support while maintaining 100% contact patch is fixed from the factory by scrub radius, LCA length, and other geometries within the suspension. At a certain wheel width, the suspension will no longer be able to maintain a consistent contact patch, resulting in poor and inconsistent cornering performance. The exact width of wheel (and therefore tire) that reaches this upper limit is not directly known, since it depends greatly on suspension alignment, wheel offset, and geometry. However, going excessively wide on wheels (and therefore tires) is highly unrecommended. For those who are interested, here is an excellent write-up regarding the dangers of excessive wheel width:4

    Wheel Tech, Part II: Width Matters | Tuner University

    Unfortunately, there are a number of enthusiasts out there that by following typical forum/magazine myths about wheel sizing, have put us all in danger. Many of these myths have been around for literally decades.

    You see, what I’ve found is that if enough people say something long enough and loud enough, everyone begins to accept it as fact even if it’s not necessarily true.

    This is certainly true of the general rules of wheel size selection that you get on forums and even in magazines.

    Here are some of the myths you probably have been led to believe:

    Larger rims with lower profile tires handle better
    Wider tires give better grip and thus better handling
    Both of these are (for almost all enthusiasts) entirely incorrect.


    In this particular article, we’re going to discuss wheel width. Next time we will talk about wheel diameter.

    “But how could this be? Of course wider wheels handle better! The tire is wider so you’ve got more rubber on the road!” I hear cried from a member of the peanut gallery.

    Another member of the forum certified expert crowd shouts: “All supercars have super wide tires and low profile tires, if they’re doing it – of course it works!”

    Unfortunately, both are only true in limited circumstances, and for most people reading this, they’re never true.

    The point that both of these claims miss is that the cars they are looking to and learning from, were designed with those wheel sizes in mind, before hand. It’s not so much that wider tires do not give more grip – it’s that if you do not also have the suspension to match, you may actually be creating a very dangerous situation indeed.

    Think about it, have you ever seen a factory tuned car that came with significantly wider wheels or significantly larger wheels? You may have seen an inch or just over added, but no factory tuner worth their salt has ever gone much more than that – without also altering the suspension.

    The primary reason, is fitting a car with a wheel or tire combo that has a different offset or width will affect camber, toe, and caster angles in the suspension. Lowering a car will also have a similar effect. These changes have significant impact on the handling of the car and can even make it downright unstable.

    Even where the alignment is corrected, there can be significant changes in the scrub radius of the vehicle and unfortunately, in almost all production cars, scrub radius cannot be directly adjusted.

    In order to compensate for the change in the suspension geometry you introduced with the new size wheels, you would need to completely revisit the suspension geometry and this would require extensive modifications in most cases, far outside the resources of the average home mechanic. To correctly address these changes, you would literally need access to an alignment rack and the ability to fabricate custom control arms, and other suspension pieces.

    Danger of Wheel Width

    Which brings me to the first main point of this article. Given most people’s suspension tuning abilities and resources – straying far from the original tire and rim size will result in worsened handling and acceleration. In some cases, even downright dangerous handling characteristics at the limit , or in the event of a tire blow out or single wheel brake failure.

    I’ll go ahead and brace myself for the “but Nathan!s”, but stick with me and I’ll explain why getting this point will put you miles ahead of everyone else on the street – and even save you a good bit of money and possibly even your life.

    Wheel Width

    Simply put, this is where everyone goes wrong. The actual tire width isn’t as important as the OFFSET of the wheel in this case however. Small changes in tire width are sometimes acceptable, though they still alter scrub radius, a key figure that determines how stable your car is, or isn’t at the limit.

    You see, in order to fit wider wheels, typically folks use smaller offset wheels to accomplish this. The lower the offset, the closer the wheel face is to the hub. The opposite applies for those who fit larger offset wheels to push the tire edge out towards the fender.

    In both cases, the scrub radius of the car is altered. It either becomes smaller or larger. Both can create dramatically different handling characteristics at the limit, and for the street especially, all of those are highly undesirable.

    Symptoms of modified scrub radius include the tendency for the steering wheel to ‘rip’ out of the hands of the driver during hard braking or turning. The wheels will also tend to react violently to imperfections in the road surface, especially when being pushed.

    Aside from safety, it should also be noted that given a stock suspension setup, or a simply lowered one, you will not gain any additional rubber on the road.

    Think for a moment about an inflated balloon. When it is sitting on a table, there is no weight on the balloon and the air pressure inside the balloon is constant. If you let air out of the balloon, more of the balloon will touch the table. If you put more air in, less and less will touch the table. Think of that as tire pressure. Then, apply pressure with your hand. You’ll notice that you get more balloon on the table, the harder you press.

    The point of this illustration is to illustrate that the rubber on the road is mostly a function of air pressure and weight on the tire. The actual tire size matters minimally.

    Disclaimer (Added 7/25): Tires are infinitely more complex than a balloon. While the physics are at the very basic level the same, due to the complex construction of a tire, the basic physics are not a great model of what happens in the real world. It would take an extremely complicated simulator to even approach accurate predictions of tire width’s effect on a car especially at the limit. That said, the suspension geometry argument holds water. Contact patch is a little more debatable but from the data I’ve seen and from first hand experience, it seems that wider tires give more contact patch to a point, but then it goes backwards (less grip). It also is not easy to model or predict. The best method to find out if you’re competing is TRIAL AND ERROR, period. There’s no free lunch or general rule here. If you are not competing, then the advice given in this article is probably as close to accurate as it can be.

    How can that be? Well, when a vehicle is sitting at rest (easiest to illustrate) , regardless of the size of the tire, the same amount of tire will be in touch with the ground, given the same vehicle weight and tire pressure. The only difference will be the SHAPE of the contact patch. This is an oversimplification and yes there are other factors such as tire construction that play a role – but stick with me.

    Wider wheels will give you a more rectangular patch, while thinner wheels will give you a narrow yet longer more square patch. The thinner wheels will therefore be better (and of course there are extremes in both cases) for straight line acceleration and braking. The wider ones, because of the direction of the forces on the tire tread in the corners, will be better for cornering at the expense of some straight line acceleration. Unfortunately, it’s not quite that simple for say road racing as whatever gains you get in cornering, you’ll probably give up in the ability to get back on the throttle early. Something you would need to test and tune for sure, no guaranteed rule of thumb there.

    In other words, wider wheels do not always net an increase in actual grip, but they can under the right circumstances with the correct suspension to go with.

    As a matter of fact, the number one place you can pick up GRIP is in the tire tread and compound you choose. A 6″ wide tire, if it is appropriately sized and chosen for the application can handle over 1g of force if you use the right tire. You do not need a 14″ wide tire to achieve that kind of grip.

    We’ll talk at another time about other ways that grip can be increased, just know for now that raw grip is not directly (and sometimes not at all) related to the width of the tire. Especially when we’re dealing with modified production cars.

    As a bonus, thinner wheels tend to be lighter as well. You can gain a lot of wheel and tire weight by going wider.

    There’s a lot to say about this topic, and I’ll probably go in much deeper detail when I do my Braking & Handling online course coming up in I think May is when we’re going to do that.

    The big takeaway from this article is to stay as close to the stock width as you can. You will want to try to stick with the same offset wheel (possibly a few mm out or in, but try to stay at the same offset). Look at factory wheel sizes, especially optional sizes to get an idea of what offset and widths are appropriate for your car. Be sure when comparing wheel sizes and offsets from other vehicles to see if there are also suspension differences.
    2015 CWP WRX STi on order ... But how did I get roped back into an EJ motor?!
    Zax' Shaggin' Wagon Build Thread Now tuned for 99% pure Unicorn Jizz!

    Zach | Moderator -- Mid-Atlantic States, Tech & Modifying & General Repairs
    The REAL 'WTF Tuning?!' Progenitor
    Rollin' with the Bugeye Mafia #302 | N.E.R.D. Subject Zero | Blobeye Synd. #Tree-Fiddy
    Facebook me here

    Your Mid-A local board: http://www.clubwrx.net/forums/mid-atlantic-states/

  2. Remove Advertisements
    ClubWRX.net
    Advertisements
     

  3. #2
    MAINEiac 11blackSTi's Avatar
    Join Date
    Nov 2012
    Location
    Portland, ME
    Posts
    2,371
    I Support ClubWRX
    Zax - I think it was you that told me to not go to a 9.5 inch wheel. It is information like this that makes me appreciate finding this forum

    But don't get me wrong...I also enjoy reading about v6 honda accords

  4. #3
    Registered User Heide264's Avatar
    Join Date
    May 2010
    Location
    Pittsburgh, PA
    Posts
    4,154
    I Support ClubWRX
    Good article Zach.

    I personally find suspension geometry very difficult to wrap my brain around time to time. The only book I have read in it was extremely difficult to get through and aimed at kit cars. Most principles still apply, but they are ones you don't see on forums frequently.

    I personally am not confident enough to write an article on most of the suspension topics... however that article above is great.
    Quote Originally Posted by Trainrex
    He was throwing balloons filled with sulfuric acid and shrapnel at the swat team. They finally had to take him down with rubber bullets.
    2011 STi Build Log
    -Part 1 - Reading, Data Logging, and Analyzing Data
    -Part 2 - Turbocharger 101 & Basic Boost Control
    -Part 3 - EcuFlash, Experimental Defintions, and a Drive By Wire Intro

  5. #4
    Moderator rage-wrx's Avatar
    Join Date
    Aug 2010
    Location
    Yonkers/NYC
    Posts
    10,717
    I Support ClubWRX
    Zach, I am shocked you would post something like this. This belongs on Stance Nation

    But seriously, great article.
    T0ny
    2011 WRX
    2012 FXT

    The Big 2011/2012 Mod Thread


    Ooh,hang on. That is the throb of a turbocharged flat four engine. A sound which,all over the world,heralds the imminent arrival of a moron - JC.

  6. #5
    and the Funky Bunch Calvinball's Avatar
    Join Date
    Jan 2012
    Location
    Philly Area
    Posts
    5,902
    Zach, it makes me sad that you posted this...





    because I'm locked out from repping you again.
    - Will
    First Mods: What to do and what not to do
    Current Car: 2014 Golf TDI
    Previous Cars:2012 WRB WRX Hatch, 2004 RSX-S, 1998 Grand Prix GTP
    "Isn't it amazing how smart you feel when you just aren't being stupid?"

  7. #6
    Dimensional Drifter Rambo's Avatar
    Join Date
    Oct 2010
    Location
    Planet Express
    Posts
    4,669
    I Support ClubWRX
    As a followup, if anyone is seriously interested in suspension design, we read this book during my college senior project designing SAE Forumula and Baja cars:
    Tune to Win: The art and science of race car development and tuning: Carroll Smith

    My senior project focused on driver ergonomics (seat design, controls layouts, etc), so I mostly skimmed this book, but the suspension design guys referenced it constantly.
    Isaac -- 2003 WRX sedan Stg II - Gave its life for mine 6/2013.
    2007 Outback 3.0R wagon
    Proud owner of a N.E.R.D, Member 1.38×10-23

    He who shall be last, shall be sideways and smiling... - Jeremy Clarkson

  8. #7
    Hell on Wheels Rodman's Avatar
    Join Date
    May 2012
    Location
    CT
    Posts
    217
    I Support ClubWRX
    Great info!
    Rod
    2014 WRX SWP Premium sedan
    Stink-Eye Mob #57
    "Just remember, with great power comes great responsibility" - rarrior

  9. #8
    Registered User Orestes85's Avatar
    Join Date
    Dec 2012
    Location
    NC
    Posts
    48
    I didn't see mention of anything about the heat of the tires, however. A wider tire will heat less quickly than a narrow tire. Ultimately you have to take both into consideration as a reasonably wider tire maybe be better for certain applications.
    The Turboturtle Build Log
    Spec Ops Motorsports
    ETS GTX3576r -- GSC S2 -- 9:1 Compression Motor

  10. #9
    Registered User oguitar's Avatar
    Join Date
    Nov 2009
    Location
    Albuquerque, New Mexico, United States
    Posts
    1,014
    Also wider tires increase rolling resistance.
    Life is like riding a bicycle in order to keep your balance you must keep moving.

  11. #10
    Registered User Ruh Roh's Avatar
    Join Date
    Dec 2011
    Location
    Pottstown PA
    Posts
    3,178
    good article

  12. #11
    Registered User xFalleNx's Avatar
    Join Date
    Nov 2010
    Location
    Voorhees, NJ
    Posts
    4,016
    My flat brimmed hat and 18x10 rimz say you're wrong and stupid. What do you know anyway?? A V6 accord is faster than your car.
    --Anthony 2011 DGM WRX stg2+sf intake WTFtuned

    Official Subie owner as of 01/10/11
    Stink Eye Mob #87

    Bye bye Bimmer
    Hellooo '11 REX

  13. #12
    Registered User Orestes85's Avatar
    Join Date
    Dec 2012
    Location
    NC
    Posts
    48
    Quote Originally Posted by xFalleNx View Post
    My flat brimmed hat and 18x10 rimz say you're wrong and stupid. What do you know anyway?? A V6 accord is faster than your car.
    I still say that proper 18x10 wheels with the proper suspension are no problem at all when run with the proper alignment. I posed this topic to a guy I know who runs his car on a track on a regular basis with 18x10s and 275/35 tires. According to him, there is only a loss in steering feel (in a 2008+, not a big issue since steering is relatively numb) and an increase in tramlining on the interstate. In short, a GR or GV chassis can effectively run a 275/35r/18 tire with the proper suspension and see good results and gains in handling.

    However. For a street only car then everything posted in that article applies, especially if you're on an OEM suspension setup.
    The Turboturtle Build Log
    Spec Ops Motorsports
    ETS GTX3576r -- GSC S2 -- 9:1 Compression Motor

  14. #13
    MAINEiac 11blackSTi's Avatar
    Join Date
    Nov 2012
    Location
    Portland, ME
    Posts
    2,371
    I Support ClubWRX
    Quote Originally Posted by xFalleNx View Post
    My flat brimmed hat and 18x10 rimz say you're wrong and stupid. What do you know anyway?? A V6 accord is faster than your car.
    I am pretty sure that VTEC compensates for added tire width.

  15. #14
    MAINEiac 11blackSTi's Avatar
    Join Date
    Nov 2012
    Location
    Portland, ME
    Posts
    2,371
    I Support ClubWRX
    Please critique me because this is what I am thinking, and I am sure I am wrong...

    I am going from 18x8.5 .55 offset (I am pretty sure that is stock offset) wheels with 245/40/18 tires (stock crap) to 18x9 .45 offset wheels with 255/35/18 tires (Michelin Super Sport awesomeness). My thought is that the added half an inch won't have much of an effect on contact patch, and the contact patch that is there will be better due to the much better tires (probably want new alignment?). The change in offset will be slightly offset be the fact that the tires are wider (10 mm = 5 mm on each side of center point of tire).

    Tell me what I am not considering!
    Last edited by 11blackSTi; 01-16-2013 at 09:48 AM.

  16. #15
    He simply abides. SD_GR's Avatar
    Join Date
    Jul 2002
    Location
    CA, US
    Posts
    21,897
    I Support ClubWRX

    Why excessive wheel width may decrease handling performance!

    Back when magazines were still somewhat relevant they would test tires. They'd typically show a contact patch for each model, and each patch would be different despite the sizes and pressures being equal.

    Usually, attempts to explain contact patch shape changes vs. wheel width changes will at least mention that their conclusions are over-simplified and depend on "all things being equal" and they will do so ostensibly in the spirit of helping the reader.

    I suspect they're actually helping the author instead.

    All things are not equal. Even if the pressure is equal when contact patch is measured, the volume of tire and gas and the operating temperatures are not considered. Nor is it usually mentioned that different brands will yield a different contact patch anyway.

    Far more complex subjects are discussed routinely and it's odd to me that authors state "I'm oversimplifying for your sake" without also stating "here's 1000 pages of complex math if you insist" because there are inevitable parallels with statements such as "pay no attention to the man behind the curtain."

    I wonder how much air the contact patch discussion really holds.
    WRX Info Links, Courtesy TheJ
    The world breaks everyone and afterward many are strong in the broken places. Ernest Hemingway
    I lied. I cheated. I bribed men to cover the crimes of other men. I am an accessory to murder. But the most damning thing of all... I think I can live with it. And if I had to do it all over again - I would. Benjamin Sisko
    DISCLAIMER: Opinions expressed are the author's alone and are inherently worthless.

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •