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Thread: Wheels, wheels, and more wheels

  1. #1
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    O.k., o.k. I know we've discussed wheel sizes in the "other" thread quite a bit, but still have questions related to how a wheel diameter impacts performance overall. I also recognize there are some tracks where a 205 tire is faster than a 225 regardless if it's mounted on a 6 or 7 inch rim. For the sake of this argument, let's assume that a person has access to plenty of 6" and 7" rims regardless of the bolt pattern.

    I've often heard (from some very intelligent people might I add) that if a car goes down from a 7" rim to a 6" rim, the car would see a decrease in handling performance, again overall. In the "other" thread, it was mentioned that a 7" rim will weigh more than a 6" rim and therefore the 7" rim isn't better. I also stated while only somewhat being a PITA why isn't a 5" rim better than a 6" rim if that were true? Obviously there is an optimum point based upon g-forces, horse power, ect. but I'm unsure where that is.

    Here we go again!



    Dave Gran
    Real Roads, Real Car Guys – Real World Road Tests
    Go Ahead - Take the Wheel's Free Guide to Racing

  2. #2

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    Don't ya just hate it when the answer is it depends? I'll use a formula car at Pocono for one extreme - narrower tires are most likely faster because there will be less mass in the air stream. This was also true for a GT-5 Nissan even though it had fenders. At the other extreme, let's say you are autocrossing. It's likely the same car will be faster on a wider tire. So the speed vs the width of the tire will often depend on the track, and somewhat on the car. However (you knew that was coming I hope), there are drawbacks - like footprint and braking. A wider tire should brake better than a narrow one. So again we're back to the individual track configuration. As to rim widths, part of the answer has to do with the tire. Some are designed for a narrower tire (like a cantelever design), and some for a wider rim. A tire designed for a formula car front (often somewhat narrow rim) can be quite different than one designed for the rear (often wider rim). And weight matters - both the weight of the rim AND the weight of the tire!

    The best solution for you isn't easy - have some of your favorite tires mounted on each size, and participate in practice days that provide enough time to play with the various options. Of course it helps to be consistent enough to be able to feel the differences, they may be a bit subtle, and a data acquisition unit isn't a bad idea either.

  3. #3
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    I'll bite. Here's something that looks a LITTLE like data, but isn't...

    I finally got the chance to do a back-to-back test of 205s and 225s at the Ultimate Track Car Challenge NASA weekend. All new, all on the same kind of wheels, all in very similar conditions in sessions about an an hour apart. Both had effectively the same diameter, according to Hoosier (although I didn't measure them).

    SUBJECTIVELY, the narrower tires were easier to drive. The car turned in better and felt more "unhooked" - more inclined to change direction. Unscientifically - since I still have never looked at the DL1 data because I keep being a dumbass and leaving the race computer with the car rather than bringing it home to West B. G. Virginia) I saw more revs at the end of the straight.

    Net result according to the watch was that the difference between the two options was small enough that it was lost in the noise of my lap-to-lap variability. No difference.

    Now, put someone with actual talent in the car and maybe they'd realize a difference. Or they'd be able to take full advantage of the better grip of the 225s. Don't know.

    But on the strength of that test, we tried 225s in the front and 205s on the back for the Nelson 24 hours - and LOVED it. Rear tires realized better temperatures and didn't pick up like 225s do. Car had a better overall balance, I think. Of course, Nelson is kind of a special case.

    For what it might be worth.

    K

  4. #4
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    I'll bite. Here's something that looks a LITTLE like data, but isn't...

    I finally got the chance to do a back-to-back test of 205s and 225s at the Ultimate Track Car Challenge NASA weekend. All new, all on the same kind of wheels, all in very similar conditions in sessions about an an hour apart. Both had effectively the same diameter, according to Hoosier (although I didn't measure them).

    ....
    K
    [/b]
    A little off topic, but I saw that you won 2nd place for the JV class. Congratulations.

    STU BMW Z3 2.5liter

  5. #5
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    Distant second but thanks! We knew going in that it wouldn't be hard for someone to show up with some swapped beast that fit the class rules and kick us all over the place but it was REALLY interesting to see what the "track car" concept has morphed into. There were no fewer than five pseudo-factory Nobles there, with plates from all over the country and a semi full of crew and hospitality area for the drivers.

    I kept thinking during the weekend that an ultra-light MkII Golf with an ABF Gr A rally engine and sequential 'box would be pretty interesting...

    K

  6. #6
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    . At the other extreme, let's say you are autocrossing. It's likely the same car will be faster on a wider tire. So the speed vs the width of the tire will often depend on the track, and somewhat on the car. ....... [/b]
    And even that depends!

    Same car, two drivers, same rims..5.5", the 175-70-13 Yokes were 1 full second faster than the 185-60-13s. Same OD. For both drivers. YMMV.....

    But, with that in mind, I'd love to see data on a 225 stuffed on a 6" rim that proves it's as effective as it would be on a 7" rim, as it is reputed to be by some in that other thread.

    Thats a case of "prove it" in my eyes....
    Jake Gulick


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  7. #7
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    Then, you also have to consider "overheating" the tires at the end of a race. May not have any bearing in a light ITB car, but it will in ITA.

    I'd buy what ever is cheaper!
    Jeff L

    ITA Miata



    2010 NARRC Champion

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  8. #8
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    But, with that in mind, I'd love to see data on a 225 stuffed on a 6" rim that proves it's as effective as it would be on a 7" rim, as it is reputed to be by some in that other thread.

    Thats a case of "prove it" in my eyes....
    [/b]
    Couldn't agree more... I think in most cases, you're going to be better off on 205's with the 6" rim. I tried Hoosiers in both sizes on my car, and you'll never convince me that 225's are the right tire. On 205's the car drives better (more predictably), and the tires heat up and wear more evenly. And yes, the car is a little faster on the narrower tire... about a second per lap quicker at Hallett as I recall. And keep in mind, the Volvo is a 2640 lb car, not exactly a lightweight. The only disclaimer I'll make here is that this "data" was gathered using the older (S04/S05) tires; things may be totally different with the R6, but not likely IMO... there are now even larger differences in section and tread widths between the two sizes. I Haven't used any new R6's yet in either size... I've currently got a pretty good supply of SM take-offs. Like Jeff, I can't pass up cheap rubber!

    Gary Learned
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  9. #9
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    Im extremely jealous right now! I could have a never ending supply of sm tires, but cant use them..... eh, first year of the car is somewhat developmental anyways. see you all in the northeast next year!

    Marc Rider
    Itb vw GTI

  10. #10
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    I am also thinking of trying the 225's on the rear and 205's on the front, though i am not sure if it will be a win. You would expect it would, w/ the rear weight bias of the fiero. However, i get a bit of understeer on entry, w/ the car being fairly even/balanced after i get the G's going. So, w/ the 205's on the front, i am worried i'll get even more understeer.
    Scot Mac - Mac Motorsports
    88 ITB Fiero #41, SFR, NWR, ICSCC

  11. #11
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    Or maybe the front will grip better, as the carcass isn't rolling and distorting the tread, making the 225 less effective than the 205....
    Jake Gulick


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  12. #12
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    And even that depends!

    Same car, two drivers, same rims..5.5", the 175-70-13 Yokes were 1 full second faster than the 185-60-13s. Same OD. For both drivers. YMMV.....

    [/b]
    Two different drivers makes for too much variableness in the test.

    I was running 205's previously, and and now running 225's, and the 225's are definitely faster. However, again, there are too many variables. The 205's were old hankook's, and the 225's are new r6's, and the driver is getting more used to unique handling characteriestics of the car.

    I would like to do a more controlled study, but can't afford it. So, anyone want to donate a set of new 205's, 225's, and an extra set of 14x6" spinwerkes wheels, for the *cause*??

    (though the spinwerkes are somewhat optional, since i could swap the tires)

    Scot Mac - Mac Motorsports
    88 ITB Fiero #41, SFR, NWR, ICSCC

  13. #13
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    Two different drivers makes for too much variableness in the test.
    [/b]
    You may want to read Jake's post again... I think he's saying that both drivers were 1 second faster on the narrower tires.

    Incidentally, I confirmed via email today with Hoosier that the "recommended" rim widths in the A6/R6 chart are in fact driven by Tire & Rim Association standards and must be printed as-is. As I tried to point out a couple of times in the other thread, you have to read the Tire Care Tips page for the R6 to get the real lowdown on optimum rim widths. For the 225/50 R6, it's 8.8 inches, give or take a half inch (and it was the same story for the earlier S04/S05 tires, as well). Jeff Speer at Hoosier said his actual recommended rim width range for a 225/50 would be 8 to 10" if you want optimum performance. He also realizes that most people can't run those widths, and you should still get good wear and performance on rims as narrow as 7.5 or 7.0".

    So... according to Hoosier, the 225/50 R6 will work on a 7 inch rim, but that rim is apparently narrower than what the tire really wants.

    Gary Learned
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    http://www.youtube.com/user/denrael

  14. #14
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    In regards to the tires, I really don't think it's as simple as a 205 being faster than 225s on all tracks. In speaking with some of the guys at OPM, they did testing on various tracks and found some to be faster with the 225s and some to be faster with the 205s.
    Dave Gran
    Real Roads, Real Car Guys – Real World Road Tests
    Go Ahead - Take the Wheel's Free Guide to Racing

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    You may want to read Jake's post again... I think he's saying that both drivers were 1 second faster on the narrower tires.
    [/b]
    Oh, right...i read it that the OD was the same for both drivers! ;-)

    Incidentally, I confirmed via email today with Hoosier that the "recommended" rim widths in the A6/R6 chart are in fact driven by Tire & Rim Association standards and must be printed as-is. As I tried to point out a couple of times in the other thread, you have to read the Tire Care Tips page for the R6 to get the real lowdown on optimum rim widths. For the 225/50 R6, it's 8.8 inches, give or take a half inch (and it was the same story for the earlier S04/S05 tires, as well). Jeff Speer at Hoosier said his actual recommended rim width range for a 225/50 would be 8 to 10" if you want optimum performance. He also realizes that most people can't run those widths, and you should still get good wear and performance on rims as narrow as 7.5 or 7.0".

    So... according to Hoosier, the 225/50 R6 will work on a 7 inch rim, but that rim is apparently narrower than what the tire really wants.
    [/b]
    That is interesting. So, the "Recommended Rim Sizes" are NOT the "recommended" rim sizes. They are dictated by "Tire & Rim Association" standards? But their web site says that the "Measured Rim" is the one dictated by the "standards", and it is dictated by DOT. Hoosier's site says:

    The reason for the differences lies in the Department of Transportation requirements for publishing tire dimensions
    on any tire that carries a DOT certification. Each tire size has a specific rim that must be used when taking
    measurements ("measured rim") for tire comparison. This is intended to allow consumers a consistent way to compare
    tire sizes between brands.

    (Note, parens are mine)

    I'll give them a call.
    Scot Mac - Mac Motorsports
    88 ITB Fiero #41, SFR, NWR, ICSCC

  16. #16
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    OK, i talked to Jeff on the phone. Yes, he did say that the "Measured Rim" is dictated by DOT *and* that the "Recommended Rim" is from the "Tire and Rim Assoc" (TRA). He then went on to recommend 7.5" to 9.5" for the 225/50/14, but he admitted that his calculation didn't take into account the "lip" size (lip is mainly what supports the sidewall). And he agreed that taking into account lip size would make the recommendation 7" to 9" or 6.5" to 8.5", which is getting quite close to the T&R assoc recommendation. Also, that the smaller rim size would be better as the tire wears, since the shoulder will gradually wear away, creating a smaller tread width. Not sure how that jives w/ the sidewall, though.

    It sounds to me like they are willing to put that tire on a LOT of different rim sizes (approx 6" to 10"), in order to sell more tires (not surprising).

    So, the question for us is what is optimal or ideal, and then take the plus or minus 1" to give us a range (since Hoosier is BS'ing us). A good assumption is that it is zero sidewall angle (from vert). Using hoosier's published section-width, zero sidewall angle would be an 8" or 8.5" rim. Which gives us a range of around 7" to 9" (or 7.5" to 9.5"). Or ~1" greater than the TRA's recommendations.
    Scot Mac - Mac Motorsports
    88 ITB Fiero #41, SFR, NWR, ICSCC

  17. #17
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    Now 'fess up... I'll bet you wish you'd had that conversation with Jeff before you bought tires, eh?

    IMO when it comes to Hoosiers at least, you can plus or minus and wishful think until the cows come home... a 225/50 works best on something a lot wider than a 6" wheel, lip size be damned. For that matter, my money says the same applies to a 205/50. In other words, I'm betting the 205/50 Hoosier will perform better and last longer on a 7 inch rim, all else being equal. I hate to even bring up the category here in IT-land, but I have a hunch (having done zero research on the subject) that it's no accident the Spec Miata bunch is running that very combination... 205/50 on 7 inch wheels.

    Gary Learned
    MiDiv
    Volvo 142E
    http://www.youtube.com/user/denrael

  18. #18
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    I don't have any experience on my car with different width rims. However I am stuffing 225s onto 13x6" wheels, but mainly because the 225/45-13 gives me (I think) the OD that I want. To be honest, it is quite possible that a 7" wheel would perform better, or course it ain't easy finding either size in a 13.

    As much as anything, I am doing this to try something different and learn something that makes the car faster...or not. Either way valuable info.
    Chris Schaafsma
    Golf 2 HProd

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  19. #19
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    Now 'fess up... I'll bet you wish you'd had that conversation with Jeff before you bought tires, eh?

    IMO when it comes to Hoosiers at least, you can plus or minus and wishful think until the cows come home... a 225/50 works best on something a lot wider than a 6" wheel, lip size be damned. For that matter, my money says the same applies to a 205/50. In other words, I'm betting the 205/50 Hoosier will perform better and last longer on a 7 inch rim, all else being equal. I hate to even bring up the category here in IT-land, but I have a hunch (having done zero research on the subject) that it's no accident the Spec Miata bunch is running that very combination... 205/50 on 7 inch wheels.
    [/b]
    I think the analysis that i just did is correct. ie, that ~8" is optimal for the 225, and that 1" around it is "pretty good" (7" to 9"), and race usable.

    I haven't done the same calc's for the 205/50, but my guess is that 7" is probably optimal for it, and that 6" - 8" is probably a good range.

    And yes, knowing that Hoosier's "recommended size" isn't even THEIR recommended size (website is basically BS), is useful. I gave him some crap about it, and he took it pretty well, and said that they were thinking about putting YET ANOTHER SIZE on that spec chart for the REAL recommended size. That is obviously not the answer, just makes it even more complex. Since they already made an allowance for the standards organizations by making the "measured size" the DOT standard size, the should thus make the "recommended size" THEIR RECOMMENDED SIZE!!

    However, i still don't necessarily think that 205 are better than 225's, on 6" rims. I think it depends on the car, and the track. They are probably pretty close, which is shown by the fact that it appears there is good number of people running each of them, and some running both together.
    Scot Mac - Mac Motorsports
    88 ITB Fiero #41, SFR, NWR, ICSCC

  20. #20
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    However, i still don't necessarily think that 205 are better than 225's, on 6" rims. I think it depends on the car, and the track. They are probably pretty close, which is shown by the fact that it appears there is good number of people running each of them, and some running both together. [/b]
    Maybe, but you clearly have to admit that changing ITB to 7" rims could result in performance increases, due to some folks running 225s on a more optimal rim, correct?
    And that there are cars that are rim limited, and that some cars will acheive better results, either fr one lap or 20 while others will not, or can't....

    Which is NOT what you purported way back when you said any differences in performance between a 6" and a 7" were insignificant...
    Jake Gulick


    CarriageHouse Motorsports
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