SCCA Autocross setup thread

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

  1. Couldahadav8

    Couldahadav8 Active Member

    Mr. Dahl,

    Have you done the calculations to see how short of a tire you would need to make 3rd gear usable? Dyno graphs suggest torque is fairly flat (204-220) between 2 and 4.5k rpm. Horsepower is flat, relatively speaking, between 4 and 6k rpm. I am not sure whether the Toyo would be small enough to get into the powerband for slower courses--at least in third gear. Any thoughts you have about this would be appreciated. Also, if you go with Toyos would you be getting them shaved?

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  3. WScottCross

    WScottCross Well-Known Member

  4. Couldahadav8

    Couldahadav8 Active Member

    Thanks. That is a great link. I have saved it. I have reviewed a similar calculator. I was really just asking Alan for the answer because I am lazy:) Since I am lazy and hamfisted, I do better if I don't have to shift more than once a run--in this case twice. The fact that the car makes different power in third than it does in second makes this a bit more complex than if the power was consistent in all gears. If power was the same in 2nd and 3rd, I would just go for the tallest tire.

    Perhaps the better question here is what rpm in third are we shooting for following the shift from 2nd. Is it 2000, 3000, 4000? And, how low can we go in the rpm in third so that the increase in power can make up for the gearing advantage in 2nd gear? My thought is that the rpm range to shoot for is between 3 and 4k, but if we can get by with running the car as low as 2000rpm in third without a huge real loss in multiplicative torque/power, then that changes things dramatically.
  5. Cligedy

    Cligedy Active Member

    I haven't done any datalogging yet for comparison, but I still think dropping below ~45 in third would cost time. Hopefully I can get some useful data from the Android dataloggers I plan to use. Or if someone has a legit setup, please share your info.
  6. AlanBDahl

    AlanBDahl Active Member

    The answer may be course dependent. For example if a course has a long third-gear section and the rest of the course is slow enough to not need third with short tires then the short tires would be better if everything else was equal. Temperature is going to figure into the equation as well as the Toyos are supposedly better in the cold.
  7. Des

    Des Active Member

    Alan, what did you eventually go with? (And hi! We raced together in NWR until a couple of years ago).

    I love the idea of a 225 but not so much the 50 ... Limbo, we'll be watching to see how you do!
  8. Nik17

    Nik17 Member

    Has anyone figured out the biggest size that'll fit on the stock wheels?

    The best bit of information I found in the winter tire thread which goes by diameter.
    It looks like we'd be trying to stay under 25" or so diameter to be safe.

    Do you think that means I can squeeze some 235/40/R17s Z2s on the stock wheels? TR lists the diameter as 24.4"
  9. Cligedy

    Cligedy Active Member

    I've put the the 225/50R16 rivals on. TireRack lists them as having a 24.9" diameter and they rubbed a bit at or near full lock. I'm using a wheel with a 42mm offset.
  10. Nik17

    Nik17 Member

    I just recently picked up my ST, so forgive my ignorance. Obviously that 42mm offset is smaller than the 47.5 of the stock wheel, so does that mean a 24.9" diameter with a big offset would rub more, or less? Or perhaps it depends on where it's rubbing.
  11. Cligedy

    Cligedy Active Member

    The wheel is pushed 5.5mm out from the center of the car. Given that I am running a tire that is 20mm thicker (hence +10mm on each side of the wheel) than stock, the tire should be 4.5mm closer to the center of the car. If you are trying to squeeze 235s on the stock tire, you will be adding 30mm of width, or 15mm on each side. By my measurements, you only have ~18mm before you start rubbing on the front strut. I didn't measure the rear.

    I don't have a good way to see if the tire is rubbing at full lock because of the height or the width of the tire. It is probably a combination. Whether the 235/40/17 would rub is uncharted territory at this point. Unfortunately, because of the number of variables with tires and mounting options, once it gets close, the only way to know is to try it. I'm sure lots of people would be curious to know, but somebody is just going to have to go first.
  12. AlanBDahl

    AlanBDahl Active Member

    Hey Des! :)

    I have not choosen a tire yet but if I go for the Z2 it’s likely to be the 225/45-16 or maybe even the 205/50-16 depending on how well the tires fit on the rims.

    Don’t expect a lot from me right off the bat as I plan on making my changes slowly over the whole year. Hopefully by Nationals I’ll have it well set up :).
  13. limbo

    limbo Active Member

    No pressure! Dixie will be my first ever "national" event and I've got <2 years in the sport so don't let my performance be indicative of what the car can do.

    I have much less time to get the car setup for Dixie and I'm not sure the car needs a bar as much as it needs some shock tuning. Rebound is set awful high from the factory and I think the car could benefit from it being toned down. I'm interested to see what you come up with, I'm probably just going to run it as is and we'll see how it goes.
  14. Des

    Des Active Member

    I ordered the 215/45/17 ZIIs last night. We'll get data on both combos that way.

    My codriver and I are going to run both the Fiesta ST and a Focus ST. We drove them back to back yesterday, the Fiesta on the stock Bridgestones with 200 miles on it, and the Focus on 245/40/17 RS-3s and a rear bar. Short-ish asphalt course had a couple of big-acceleration chutes, two slaloms and two thread-the-needle gates, but top speeds were no more than about 55 mph.

    Got the Fiesta to a 41.6. It didn't rotate at all until I bled the rear tires down to 30 on the last run. Just three runs.No wheelspin except at launch, and in general zero drama, which means there was a lot more time to be had.

    Fastest time in the Focus was a 40.1 (my co-driver; I was a couple of tenths slower), which was good for 2nd PAX overall of 240 drivers, behind only Bryan Heitkotter, who is scary. Getting that 40 was work: There is wheelspin everywhere, controlled drifts on corner exit with micro-corrections on the steering to get the power down, and ice mode reared its ugly head.

    The Focus is silly fast, that's for sure. Not sure the Hankooks are a good fit -- you're not sure where the tires are pointed, and on this car that hurts because of the e-diff. You wind up sawing back and forth a bit.

    Once the tires are on the Fiesta we'll get data to see what's faster where. The steering doesn't feel as good as the Focus's does, and the super short first gear sucks, but it was carving smooth arcs where the Focus was a wheelspinning mess.
    spangenb and Cligedy like this.
  15. Des

    Des Active Member

    Alan, hope we'll see you down in Crows, El Toro, San Diego, etc. And yes, we do expect a lot from you :)
  16. AlanBDahl

    AlanBDahl Active Member

    This lack of rotation is what I expect from the car which makes me think it will require a crazy-ass driving style with violent inputs to encourage rotation if a rear bar is not installed. But so far I've not raced it, this is just based on 6000 miles of street driving.
  17. AlanBDahl

    AlanBDahl Active Member

    I'll be at Crows for sure, SD or LA is less for sure if I can't find a co-driver as I have almost no vacation time.
  18. Nik17

    Nik17 Member

    Are you putting those on the stock wheels by chance?
  19. Des

    Des Active Member

    Yes. I won't buy wheels until we have some idea how 16s vs 17s plays out. Another guy here in SF, terrific driver named Josh Salvage, is getting an ST as well. He'll go the 16s route. Fastest guy wins.
  20. Nik17

    Nik17 Member

    Did you get confirmation from Tire Rack or somewhere else that those were the biggest ones that would fit?
  21. Des

    Des Active Member

    No.Tire Rack called to say they wouldn't fit. But they are just shorter than the 225/50/16s other folks are already using, and narrower to boot.

    I plan to mount these, see if and where they rub, in hopes of working my way up to a 235/40/17. That's 24.4 inches tall -- shorter than these -- but I want to see what kind of clearance there is.

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