Tuning tires for top tier times

Discussion in 'Fiesta ST Autocross' started by Cligedy, Jan 16, 2014.

  1. Cligedy

    Cligedy Active Member

    Because there was still some question about what tires could fit on the FiST, and because I have limited funding, I made the decision to buy a pair of the 225/50 Rivals and 225/45 Dunlop Z2. I liked the idea of getting a few extra mph at the top of second with the Rivals, but was worried that they wouldn't fit. Even though the Rivals rub near full lock, they should work just fine.

    If I had known for sure that the Rivals would fit on all four corners, I would have just ordered a full set. I don't think that running different tires is ideal, but I want to make the best of the situation. The performance of both tires should be similar enough that I don't think that the difference between the two makes will lead to any adverse handling conditions. Now I have an opportunity to effectively run two different tire setups just from swapping front to rear. The differences in tires are/ may be:
    • the gearing
    • responsiveness/ transition behavior
    • heat tolerance
    • performance in the rain (fingers crossed this doesn't matter all season)
    Even though they are both 225s, the Rivals clearly have a wider contact patch. The Rivals also give me about 2.5mph extra at the top of second gear. Does anybody have any thoughts on what I could do to optimize this situation? Is there anything I'm not thinking about?

    My club doesn't have a test and tune this season, and there are no close events in other clubs before our season opener. That means that I will be doing this by trial and error at points events. Any advice is welcome. Thanks all.
     

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  3. McRib 1s Back

    McRib 1s Back Well-Known Member

    I like your enthusiasm! If it were me, and I was determined to run taller tires, I'd match them. You won't know until you run it, but I'm betting you've introduced some healthy understeer in that configuration.

    Since the others are new, consider selling them and buying the matching set? Sorry, I know that's not what you want to hear. :/
     
  4. Cligedy

    Cligedy Active Member

    I bought the split set thinking I could sell off the pair of Rivals if they didn't fit, but knowing that they do, I'm curious if I can use this to my advantage. Such as the Rivals up front for faster courses and the Z2s for tighter courses. From what I read, the Z2s get greasy when they heat up, so maybe run them in the cooler months and switch to the Rivals during the hot months.

    I know there are tradeoffs, but I want to give it a try. What configuration do you think would induce understeer?
     
  5. McRib 1s Back

    McRib 1s Back Well-Known Member

    What I'm about to state is a gross oversimplification...

    My experience with past FWD tuning saw that increasing front grip over the rear as such, always produced more understeer. This was true when I dropped a monster sway bar up front alone, too. This was not true with internal bracing or strut tower braces.

    Anyhow, it illustrates the idea.

    Why not keep your idea/theme and buy two more of each! You're onto something here -- wheels and tires for different courses! :)
     
  6. limbo

    limbo Active Member

    I think you've got it backwards. Adding a monster front sway bar up front will decrease grip up front, inducing understeer.
     
    RodMoe likes this.
  7. McRib 1s Back

    McRib 1s Back Well-Known Member

    Perhaps, I have been known to do that! ;)

    Going from an old memory on my SE-R, changing nothing else, the big Stillen sway bar did induce more understeer. True story. It wasn't until I went big on the back, relaxed the front, that I had neutral handling!

    It made me wonder if there was something in common, given they are both torsion beam cars (though the scissors link on the SE-R was different).

    Don't let that corrupt my example! Back to the tires. More grip up front, and you end up with more understeer.
     
  8. Cligedy

    Cligedy Active Member

    I doubt that there is a huge delta in grip between the two brands. I expect the Rivals may have the edge due to the wider footprint. I do expect there to be differences in steering feel and responsiveness. Also, heat tolerance and gearing will be factors.
     
  9. limbo

    limbo Active Member

    No. More grip up front = less understeer.

    I don't think you'll notice much difference in overall grip levels, either.
     
  10. McRib 1s Back

    McRib 1s Back Well-Known Member

    Sorry, rushed response...

    Let me say it this way, softening the front and increasing the rear has been what I've seen work on FWD cars when faced with entry and exit understeer problems. This was sorted out with track testing, not anecdote. Some of this is certainly counter-intuitive.

    Ultimately both seek to IMPROVE front end grip. I knew this was a potential can of worms, and happy to talk further about it.
     
  11. Cligedy

    Cligedy Active Member

    The more I think about it, I'm worried that the tires may come up to their operating temperatures differently causing balance issues. I've never had a front wheel drive car before, is this a problem others have had?
     
  12. RodMoe

    RodMoe Well-Known Member

    With a FWD car just remember as you lift in the corner the back end should also rotate out for you and yes bigger in back or less bar in front is the rule of thumb for wrong drive cars as some i know tend to call them .. personally i like the challenge :)
     
  13. Cligedy

    Cligedy Active Member

    Yeah, that's the other thing; I am learning how to drive a fwd car. I've only ever driven a fwd at autocross once. That was a nationally prepped sts civic, one run, 5 years ago. I'm looking forward to learning, but this is gonna be different than what I'm used to for sure.
     
  14. RodMoe

    RodMoe Well-Known Member

    Oh Fun it will be lets hope that back end won;t come around too fast before you get the feel ;) Been there Spun that LOL
     
  15. Cligedy

    Cligedy Active Member

    I can catch it...
    I can catch it...
    I can still catch it...
    SPIN
    +4 cones, fuuuu!

    In a spin, both feet in :cool:
     
    Firesail likes this.
  16. RodMoe

    RodMoe Well-Known Member

    So true mine sin wasn't so much the cones as the two tires off a dnf.. I just was a over achiever and put 4 tires off just to make sure ...
     
  17. wash

    wash Active Member

    A stiff rear bar (or twist beam) let's you three wheel which puts more weight on the inside front wheel which means more front grip.

    When you go big on the front bar, you lose that and the grip of your outside front becomes the limiting factor.

    Spring rate, CG height and the anti-sway bar all contribute to roll stiffness so there are a lot of knobs to adjust.
     
    Mr UFO likes this.
  18. Slowclimb

    Slowclimb Active Member

    I've seen some guys run monster front tires on FWD cars to increase front end grip...leaving more stock sized tires on the rear. I am not sure but think it was Daddio in a neon who ended up with FTD...so it is not unheard of to run different sized tires front and rear. I recall some VWs running in DSP that did the same to help cure their achilles heal. I think it will be interesting to see what happens.
     
  19. McRib 1s Back

    McRib 1s Back Well-Known Member

    You got me thinking about this, and I recall seeing at least one Neon and maybe a Civic or two do this.

    Hey, you're right, it might be good, let us know. For low speed auto-x, might have no apparent downsides. I wouldn't run that on a road course though.
     
  20. Cligedy

    Cligedy Active Member

    I wouldn't recommend this for a road course either. Lucky me though, another local club updated their schedule and will be hosting a test-n-tune. Hopefully that will give me a good chance to evaluate the setup. I'm stoked.
     
  21. RodMoe

    RodMoe Well-Known Member

    Looking forward to your feedback...
     

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