SCCA Autocross setup thread

Discussion in 'Fiesta ST Autocross' started by AlanBDahl, Oct 21, 2013.

  1. AlanBDahl

    AlanBDahl Active Member

    Des, you're running a 225/45-17? Tire Rack says that's 25 inches in diameter, quite a bit taller than the stock 23.5. I was thinking either a 225/45-16 or a 215/40-17 both of which are slightly taller than stock but closer to 24". Also both tires are 2 lbs lighter than the 225/45-17 which should help too.
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  3. Nik17

    Nik17 Member

    If you look on the previous page, he's running a 215/45/R17 on the stock wheels. You'll also see why he didn't pick the 215/40. Tire rack told them that the 215/45s he bought wouldn't fit, but magically they do without any rubbing at all
  4. Des

    Des Active Member

    Alan, my aim was definitely to increase diameter. The 215/45 is 24.7 inches tall, and as Nik17 notes, fits OK.

    A lot of folks were already going to test 16-inch sizes, so I wanted to see if this was also an option. It definitely is, and has the additional benefit of being cheap because I can use stock wheels. I certainly don't mind shifting after owning the S2000, CR-Z and FR-S, but given the choice would avoid it.

    Third in the Fiesta feels tall to me ...

    None of which means I won't swap over to 16s if you guys find it to be faster. You of all people know that I'm just guessing.

    We'll run the Focus and Fiesta, both drivers, back to back on Sunday and I'll update this then.
  5. AlanBDahl

    AlanBDahl Active Member

    When looking at the Tire Rack page on the D2 I failed to note the 215/45-17 when I made my size list, oops. I’m looking not just at outside diameter but also total weight of the wheel/tire combination, the distribution of the weight within the tire/wheel (since mass on the outside of the rim is worse) and the sidewall height. I’m still not 100% sure I’ll go with 16’s, it depends on what I can find in lightweight wheels in both sizes. Either way I’m aiming at tires around 24” tall, I don’t think I want to go any taller than that if I can help it.
  6. Slowclimb

    Slowclimb Active Member

    The more I am thinking about this the more I am considering sticking with the 17's for this year. Sort of wait to see what happens this season, who runs what and which is faster before I dump money into a set of 16s that I really don't want anyway. At this point I would lean to Team Dynamics...but if I stick with 17's I think it opens up some other options.
  7. AlanBDahl

    AlanBDahl Active Member

    I understand that Team Dynamics are popular with Ford folks because of their support of the Focus but I can’t see how they make sense when their lightest wheel is over 16 lbs while the OZs are luck lighter. The only potential advantage I can see is that they come in a 45mm offset if for some reason you rub on the outside with 42s. Is there something I am missing here?
    Cligedy likes this.
  8. Slowclimb

    Slowclimb Active Member

    The Ultraleggera 17 x 7 is 16 pounds according to Tire Rack, the Team Dyamics Race 1.2 is 17 x 7 is 17.3 pounds according to North American Motor Sports

    I can get a set of Team Dynamics for nearly 750 dollars while the OZs will run over 1K...the 1.3 pound difference is driver noise at the level I am driving...if you read this article from GRM (look down a couple posts on this forum for a scanned copy of the article) it gives some insight into why I have come to this conclusion...that plus trying different wheels out on my mini and finding almost not time gained with aftermarket light wheels as compared to the stock 16s that I ended up with.

    In Short Grass Roots Motorsports used two wheels one weighing in at 19.5 and the other weighing in at 15.6. Same tires, same air pressures, same drivers. While the drivers reported that the lighter wheel felt faster the timing gear showed the run was .1 second slower. The articles goes into a bunch of discussion about the results that I won't rehash, but suffice it to say I am not convinced that 5.2 pounds over 4 wheels is worth 3 to 4 hundred dollars....that is nearly another set of tires for me....
    Mr UFO likes this.
  9. Slowclimb

    Slowclimb Active Member

    They also adjusted for difference in offset with spacers.
  10. AlanBDahl

    AlanBDahl Active Member

    IMHO the effect of light wheels depends a lot on the torque of the car involved so they might have a bigger effect on an RX8 or S2K than a Corvette.

    I checked and the OZs are 15.7 lbs or 1.6 lbs lighter. Personally for me at the prices we're talking the weight savings are worth it but then I won a ProSolo national championship by 0.002 seconds once so for me at least even a tiny advantage is worth it. Plus frankly $250 isn't much given how much money one spends traveling to out-of-town events.
  11. Slowclimb

    Slowclimb Active Member

    Luckily Torque is one thing our cars aren't short on...

    Yes I know what you have done...and if you had the same results they did in that article I directed you to maybe your win would have been by .1002 seconds ;)...But either way this is why I qualified my statement with "at the level I am driving".
    Still I have talked to a load of guys who are competitive at national events and they have also lead me to believe that the amount of savings we are talking about is noise. But then, opinions are funny things that we all have. Either way if I had the feeling I was going to step into a car and be seriously competitive in the first year I would be going to a 16 inch wheel..not sticking with the 17s.
  12. RodMoe

    RodMoe Well-Known Member

    This way you still have a upgrade path as your skills develop you can also upgrade the car to match .. just my opinion ;)
    Slowclimb likes this.
  13. Slowclimb

    Slowclimb Active Member

    Plus it buys a season to see where the car shakes out and who does what. Hopefully if the car picks up in popularity we will get some additional options for aftermarket as well.
  14. Slowclimb

    Slowclimb Active Member

    Funny thing on the OZs...silver are .3 pounds heavier then black according to tire rack...
  15. wash

    wash Active Member

    Rotational weight and acceleration are one thing but light wheels also have the advantage in unsprung weight which makes it easier for the shock to damp wheel motion and that means more grip if you tune for it.

    I'm going for light 16's because I want a bit more sidewall. So far the reports on 16" tires I've read say there is very little loss of turn in response so I think that's probably the right direction.

    I've heard some people will try 15's so we will have a lot of data to compare pretty soon.
  16. Slowclimb

    Slowclimb Active Member

    I think 16s are the way to go as well.
  17. Cligedy

    Cligedy Active Member

    Having a limited budget means I can't get every last gram out there. Having lost events by 0.004, I'll take every gram I can get though.

    With the 16" wheel, I can tell a reduction in steering response time vs the oem wheel /tire. For me, it's only enough to notice. With the car on oem springs, the body rolls so much that the extra sidewall flex is minor to irrelevant.
  18. AlanBDahl

    AlanBDahl Active Member

    Rolling isn't a bad thing if and of itself. My Audi 90 rolled a ton but was still fast because it stuck well.

    I've narrowed the choices down to 225/40-16 and 215/45-17. Both have the same weight and height when mounted the only difference is the 225s are 0.5" wider unmounted though probably they will be close to the same mounted. Will try to decide which way to go by Friday.
  19. Cligedy

    Cligedy Active Member

    Agreed. The car was very good. I just wanted to be clear that the sidewall flex from 16" tires isn't an issue.
    I've looked over the results from the test & tune, and I am stunned that my times looked so good compared to the rest of the field. I am way out of practice. The FiST made me look pretty good though.
  20. Cligedy

    Cligedy Active Member

    Des, have you run any other events with the 215/45R17 tires yet? Did you get zero rubbing with your setup?

    During my test and tune with the 225/50R16 Rivals (24.9"dia.) I had some rubbing. I finally got a look underneath, and the rubbing was worse than expected. After just 4 runs, I've worn a hole in the fender liner in 2 places. If you are running the 215/45R17 without rubbing, then I may be able to just have my Rivals shaved instead of trying to sell them and starting over. Thanks for your help.
  21. Des

    Des Active Member

    Yes, we ran today. Zero rubbing either on my 215/45/17s or on my buddy Josh's 225/45/16s.

    Can you shave enough to make it work?

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