Home Forums Autocross / Solo 2 Fastrack December

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    • #17141
      Alan Sheidler

      There are several proposals in the December issue of FasTrack.

      Please be an active participant and send your thoughts to the SEB via http://crbscca.com/
      Of particular interest to me is this one:
      #12430 KM Tire Proposal

      The KAC is seeking member feedback for the following change to 19.1.B.2.A – allowing rear tires up to 8.0” wide.

      Tires must be no larger than 12.5” in diameter and no smaller than 9.0” in diameter as imprinted on tire. Tire width is limited to 5.5” for the front and (7.1) 8.0” for the rear as imprinted on tire.

      The rationale for this change is to make it possible to again run 6 inch diameter rims.
      There are few if any 7.1 rear tires in the 6″ rim diameter.  But there are several
      brands at 8.0, including a Hoosier tire.  If competitors want the option of running
      something other than the unofficially spec 5″ MG, then this proposal should make
      sense.  What is not stated is when this could be implemented.  2014 would be
      ideal, why wait?  That will be part of my reply on the subject.  Without that being
      specified, the soonest the change could take effect is January 2015.

      Other proposals include the specific addition of the Rotax DD2 to the KM class
      for 2014.  I personally see no reason not to vote for that one.  Two drivers were
      planning to run one at Lincoln this year, but were afraid of a protest against the
      kart because of a rule book issue.  So, one driver ran another class, and one
      ran another kart.

      The safety-related FJ proposal makes sense, but it only has me asking:
      how is the word “vicinity” going to be applied?

    • #17303
      Tim Walsh

      Devil’s advocate:

      So what we’re doing is trading a major shakeup in wheels,tires, testing, stability and possibly package availability, for maybe a couple of theoretical entrants?  I’m just not seeing the advantage to solo karting.



      The DD2 proposal seems like a no brainier to me.

    • #17363
      Larry Andrews

      One more advantage to the 6″ setup is additional ground clearance.  While this does change chassis performance, it’s a huge benefit to enhancing chassis longevity for kart guys on rough courses.

      Here in SFR, we have exactly zero lots where repeatedly bottoming out isn’t a fact of life.  I haven’t autocrossed very often (just twice in 3 years) because I’m not willing to bend a new Tony roller.  Additional ground clearance (even just 1/2″) would be welcome.

      ymmv, etc and so on…

    • #17414
      Alan Sheidler

      AFAIK, it has never been attempted or deemed necessary in SCCA solo competition for any regular class.  Having a single maker and size set as a spec tire has advantages in some racing series, based on advertising, regulatory needs, availability, etc.  Even in more tightly controlled Solo classes such as CM and FM, there has never been a specified tire, to my knowlege.  I do not know of anyone who competes in either of those classes who might be in favor of a spec tire.

      Please don’t confuse the issue for an open class by comparing with FJ.  The rationale for MG Red as a specified tire has much more to do with safety and cornering capability than anything else, besides helping to limit costs for parents.  Remember also, that FJ is not a “normal” class, but a restricted one without a National Championship.

      This request for a change in the rule is about opening up the possibility of actually using the already-legal 6″ rim, by adjusting the legislated size number to encompass those which are actually available.  Currently, the listed 7.1 number effectively legislates that 5″ diameter rims must be used.  Changing that to 8.0 means that the always-legal 6″ rims can also be used.


      Let me ask this of those who compete in, or who are interested in KM for SCCA Solo competition: Would it be a more appropriate request to delete tire size references altogether, and instead regulate only the rims?  For ALL other SCCA Solo classes, it is the RIM size which has specifications and limitations, not the tire.

      From my research of a large number of wheel manufacturers, both specialty/aftermarket and OE suppliers, there is a fairly narrow range of Metric wheel sizes which are used on racing karts.  I investigated VanK, Douglas, Burris, DWT/MagTech, Oryx, in addition to Tony Kart (OTK), CRG, Birel, and others.  Wheel widths at the bead seats for fronts vary from 120 to 140 MM for fronts, and 180 to 214 MM for rears.  Most kart racers/autocrossers assume them to be 5″ for the fronts, and 7.75″ to 8″ for rears.  For rear rain treaded tires, 6 or 6.5″ rims are commonly used.  But the inch sizes appear to be a simplification, with metrics being more precise.

      If the rim is regulated, and not the tire, it would certainly serve to control the tires which can be effectively mounted, but it would give competitors a wider choice in which tire to run.  Note that the numbers molded into a tire do not mean that it will be identical in actual measurements to one marked the same from another manufacturer.  For rims, conformity to a standard is easier.

    • #17432
      Scott Boito

      Unofficially I think I like that idea better than playing with the tire size.

    • #17543
      Tim Walsh

      Regulating the rim size seems much more logical to me. It’s a number based on reality, vs. tire manufacturer wishy washy logic. Yep, it’s more of a pain to police, but certainly within the realm of doable.  That does mean that someone’s going to try the 6.0 width tires on the front, but I think that’s an acceptable tradeoff to using hard restrictions on rims.

    • #17702
      Scott Boito

      FYI, we have received only a few letters on the tire proposal so we need more input either way before we can decide anything.

      And if the rim instead of tire width sounds interesting, we need someone to write that up and submit.


    • #17775
      Alan Sheidler

      At least you are expressing an opinion, and that is good.

      I hope I can explain a couple of things.

      With only the exception of the non-national championship FJ classes, there has never been a spec tire for ANY class that I am aware of.  For SCCA solo, doing that would be a major step/paradigm change from a Solo tradition and fact: In nearly every class, there are a variety of vehicles which compete fairly and closely against each other, while having tire manufacturer and size options as part of the mix.  It is up to the developer/tuner/driver to choose what works for him or her, based on many factors.  Among those is the fact that different vehicles perform better with product having slightly different tire carcass construction and tread rubber compound/chemistry.

      To someone fresh to the KM class, all the karts “look alike”.  To someone with experience in the class, nothing could be further from the truth.  For some chassis, a soft 50MM axle will be best, along with maximum available caster and a soft sidewall tire.  For others, it is a hard 40MM, six seat struts, minimum caster, and a stiff sidewall tire.  What works for one will not necessarily work for another.

      Wheels and tires are so much a part of that in autocross.  As far as there already being a defacto spec tire in the class: Of course you are right.  People tend to play “follow the leader”, particularly if there are few other options to choose from.  For some of those drivers, only the advent of a blatantly faster “miracle” tire would get them to change, because people become complacent and set in their ways.  For the guy at the front, there is zero incentive to shuffle the deck and re-deal.  For everyone else, there really should be.  It is all about the options, and what will make each kart work the best it can, at the direction of the person squeezed into the Tillett.

      The point is that what is “the fastest” can differ between chassis and driving style, if there are real options to be explored.  Right now, there do not appear to be any in tires.  I have mentioned earlier that the 5 and 6 inch rims have always both been legal in F125/KM.  That is a fact, and it was not brought in from thin air.  When karts were first proposed for Solo, the rules set came from basically a combination of IKF, WKA, and SKUSA.  At that time, it was possible to run the 6″ rims with them.  The change to only 5″ for sprint W2W came through several influences that benefitted national series.  Tech inspectors did not need to deal with variety there, and sponsorship influx was a big factor.  Part of that had to be from the European chassis manufacturers influence: Their products are designed with specific rubber in mind for sprint racing in specific classes.  Other uses are adaptations, and Autocross is pretty much as far as you can get from the factory, unless you throw in Ice Racing.

      Do a little research, and if you dig deep enough you’ll see that in the earlier days of F125, competitive drivers used Firestone YFA’s in 6″ (Including Paul Russell, ask him, or look up the results from 2003) and Maxxis (also 6″), MG, Bridgestone YEX, YFA and YFB in 5″, plus Burris, Vega, Dunlop, and… I forget the others, but there were some.  Don’t be fooled into thinking that the competiton was ruled by one tire or driver, or that the class was still so embryonic that tires did not matter.  It was really difficult to get an edge, and there were a lot of options for hunting one down.

      Am I asking for change?  Not really.  I’m asking to be able to use the 6″ rims which I’ve owned for a decade, by legalizing the tire  size currently in production that fits.  And, that have an outside chance to work, as I develop a new-to-me chassis which just hit the ground in September.  I’m asking for options.  Like used to be available.  The fact that a company which has a stake in, and a history of support for SCCA Solo makes a potentially workable tire is icing on the cake.

      If KM were to be truly a spec class, then why not sealed Rotax Max, + Tonykart Krypton + Mojo D2 tires?  Oh, this isn’t W2W?  Well then, how about keeping open ALL of the options?

    • #17819
      Jason Vehige

      I still think you should try the 5″ R50  :)  I would have stuck with the latest gen of this great tire but with a brand new to me Chassis in 2013 I wanted one less variable to deal with so I went with the MG …

      I am still convinced the HoHo is faster on asphalt…  I plan to try the R50 again on concrete once I have the chassis dialed in a bit better on the MGs and adjust from there.


    • #17832
      Scott Boito

      Alan, according to the Hoosier site, the R45 and R50 have approx the same durometer.  I wonder how much of a difference, if any, there is between the two tires.  Of course the sidewall flex could make a difference between the 5″ and 6″ wheels/tires, so there is still some data to be gleaned there.

      If I had more than two asphalt events planned in 2014 I would buy a set of R50s to play with.  9 planned National events on concrete, so MG is where I’ll be p(l)aying.

    • #18037
      Larry MacLeod

      Although I have a set of 6 inch rims…. What about everyone else?   Can you still buy 6 inch rims from the usual Karting speed shops?




    • #21889
      Scott Boito

      Last chance to submit letters on these topics. We’ve received little feedback…

    • #17311
      Alan Sheidler

      So what we’re doing is trading a major shakeup in wheels,tires, testing, stability and possibly package availability, for maybe a couple of theoretical entrants? I’m just not seeing the advantage to solo karting.

      Major shakeup?  Perhaps you do not understand about the 6″ wheels.
      At the inception of the KM (F125) class, and for some years after, there were several options for tires in both 5″ and 6″ rim sizes.  A popular and successful tire was the Firestone YFA, a 6″ rim diameter slick.  Seen on karts at major national events were tires from Maxxis, Bridgestone, Dunlop, Hoosier.  Even later, when the YFA tire carcass was apparently altered for specialized use in oval racing, there were options.  Many of the early competitors still have the 6″ wheels.  They are easily available.  Yep, they are legal, and have been since the beginning.  But without the tire allowance, they can’t really be used.
      For the years at Heartland Park, the Vega tire was highly competitive.  As in… Winner.

      Since then, what has become essentially the “spec” tire for autocross is the MG YZ or “Green” racing slick.  “One size fits all” is not really true, I don’t believe.  There are differences in chassis, and in driving styles, for which the MG is not the best tire, and 5″ is not the best rim diameter.

      So, how much of a change are we talking about here?  My primary interest is in the Hoosier R45 “Superkart” rear tire, part # 22800.  The front tire numbers meet the limitations posted in the current rules .
      Based on the Hoosier Factory specifications, the 6″ R45 tire is 0.25 inches wider at the tread, and 0.5 inches larger in circumference than the 7.1/11.0 – 5″ tire.  Those numbers compare closely when matched to the currently popular MG tire.

      My measurement of the rear MG tire (mounted, inflated) indicate an approximate tread width of 6.4 inches when measured from the edges of the contact patch, 7 inches when using the shoulders of the tread.  Diameter measures 11 inches, with a circumference of 34.25 inches.  Note that the measured tire has 13 runs of approximately one minute each on abrasive concrete.

      My measurement of the Hoosier R45 tire # 22800 (mounted, inflated) indicate 6.75 inches to the edges of the contact patch, 7.25 inches if carried around the shoulder of the tread.  Diameter measures 11 inches, with a circumference of  34.75 inches.  Note that the measured tire has 12 runs of approximately one minute each on somewhat abrasive concrete.

      Based on a hands-on comparison of two tires, the Hoosier shows an increase of approximately 5.5% in the direct contact patch width over the MG.  Additionally, the circumference of the Hoosier measures approximately 1.5% larger than the MG.

      Visually, the tires are very close, with the most obvious difference being the shape of the sidewalls.  Mounted on the same width rims, the MG has a rounded sidewall, whereas the Hoosier’s has a more square or flat profile.  Part of that appearance has to be due to the difference in rim diameter, 5″ vs 6″.

      Legalization of the tire size will allow an option in the KM class where few, if any, exist on a practical basis today.  There are certainly no guarantees that the proposed tire size would be competitive.  As with all changes to any competition vehicle, additional tuning and adjustments would be required before the full level of competitiveness could be evaluated.

      One more IMPORTANT thing:  Hoosier is a strong supporter of SCCA Solo, and has been for many years.  Hoosier offers contingency for successful use at National events.  Try and get anything out of MG.

    • #17412
      Daniel Wendel

      Why not just have a spec tire. If the SCCA can talk to Hoosier and get them to offer contingency and a good suppler. Why not declare the Hoosier “22370” and “22150” in the R50 compound the spec tire?

      FJ uses spec tires and so do most W2W classes, why not KM?

    • #17770
      Daniel Wendel

      Still think the tire/rim size rule is stupid.  Just go spec Hoosier R50 to make the people who want their free tires happy.
      No matter what rule you put in place kart tires and rims are cheap enough that what ever is the fastest people will go out and buy. It is going to be a “spec” tire even if the rules say you can use what ever you want. All 33 KM&L drivers at the 2013 nationals had MG tires. In 2012 all 31 drivers used MG tires. In 2011 only 2 karts had Hoosiers everyone else lets guess… MGs. 2010 had one kart with bridgestones all the rest MG. SCCA is broken for anything before 2010, so I can’t get the data. It seems like the MG is the “spec” tire currently with no rule in place whist other tires that are legal are available such as the Vega XP and Hoosier R50 and others.


    • #18243
      Alan Sheidler
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