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Kumho V700s, or How to Possibly Roll My Fiesta.

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Boulder Creek
#1
I am not sure if I should stick this in here, Suspension, or Wheels and Tires so I am going with here.

I have the possibility to get some new V700s for a good price and want to run them for their intended purpose of autocross. Since they have a treadwear of 50 that puts them into R compound territory. I know this will bump me from HS, but so will a few other mods I either intend to do, or already have done so that doesn't bother me. I was going to just buy them but then I remembered that this car can be put up two wheels at the autox course with stock tires and rims and 16s as well. What would be needed to stop this from happening, would simply putting a bigger swaybar up front like the non-st bar or any of the aftermarkets as well as the rear bar help to keep this from happening? I already have the TBP torsion and subframe bars so that is a start. Or would I need to lower the car as well or am I better off just not getting these tires at all?
 


jeffreylyon

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#3
Super sticky tires mean more weight transfer, more weight transfer means more lean. A lower CG will reduce weight transfer and lean. I haven't driven a FiST on R-compound tires, but I'm pretty happy with the stock sway bars and really happy with my lowered ride height. I tricycle plenty but don't have near enough stick to bicycle. Having said that, you can roll any car with the right amount of shitty input and a well placed bump.

I'd lower the car with decent coilovers or springs/shocks and tune from there. I'd be wary of running a larger front bar until you lower the ride height - sway bars are usually the last thing you mess around with (and you already have with the rear torsion bar).

Besides, a near-stock suspension with R-compounds tires in S/M is... weird. ;)
 


OP
Z
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Thread Starter #4
Yeah those were things I was considering as well, just figured I would ask because hey, its not hard to be wrong. Tricycling doesn't worry me much, that's a common FWD trait as the most important tires are in the front doing all the work. The only reason I was really looking at these tires is they are 400 bucks for the set and figured that is cheaper then a set of good summer tires. Maybe my best bet is just to pass them on to someone else and get something more appropriate to this car. It's kinda crazy that these are the OEM tires on the Mini GP.
 


M-Sport fan

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#5
Yeah those were things I was considering as well, just figured I would ask because hey, its not hard to be wrong. Tricycling doesn't worry me much, that's a common FWD trait as the most important tires are in the front doing all the work. The only reason I was really looking at these tires is they are 400 bucks for the set and figured that is cheaper then a set of good summer tires. Maybe my best bet is just to pass them on to someone else and get something more appropriate to this car. It's kinda crazy that these are the OEM tires on the Mini GP.
They reduced the price on those??

Tire Rack was getting $160.00 EACH for those in 215/40-17 last I looked. [dunno]
 


RAAMaudio

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#6
Lowering the car will help but do not go do low or all the weight will transfer to the outside tires due to the roll center geometry change, it can also introduce bump steer.
Wider wheels and wider track from outside to outside of the rims, side to side will also reduce the tendency to get up on two wheels but do not get to crazy with the offset as it will cause an issue with the scrub radius.

99.99% of cars lowered way down have very serious handling compromises, increased wear on bearings, bushings, and more.

SMOOTH inputs, not always easy to do in the rapid changes of direction in an autocross but always important for all types of driving.

Sometimes purposely tossing a car around hard can be faster but that is normally in poorly setup situations or purposely setup that way as i have done before but also knowing the car might not be safe in extreme situations when out on public roads.
 


OP
Z
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Boulder Creek
Thread Starter #7
They reduced the price on those??

Tire Rack was getting $160.00 EACH for those in 215/40-17 last I looked. [dunno]
I have a friend who is storing some for a guy that had a Mini GP and sold it the day before they got delivered. He just wants them gone, if you were in CA the offer would still stand since the owner just wants them gone. I was also 50 off on my price, but still 450 for 640 dollar set of tires is decent.


Lowering the car will help but do not go do low or all the weight will transfer to the outside tires due to the roll center geometry change, it can also introduce bump steer.
Wider wheels and wider track from outside to outside of the rims, side to side will also reduce the tendency to get up on two wheels but do not get to crazy with the offset as it will cause an issue with the scrub radius.

99.99% of cars lowered way down have very serious handling compromises, increased wear on bearings, bushings, and more.

SMOOTH inputs, not always easy to do in the rapid changes of direction in an autocross but always important for all types of driving.

Sometimes purposely tossing a car around hard can be faster but that is normally in poorly setup situations or purposely setup that way as i have done before but also knowing the car might not be safe in extreme situations when out on public roads.

I have done the lowered thing and learned my lesson there. Just a little lower would be all I am willing to go anyways, suspension geometry aside, due to this being CA and roads being war zones half the time. Just spit balling here but how about some 8" rims since the tires are 215/40/r17s with some Bilstein B8s and slightly lower springs? That might be a bit more then I want to spend to run a 200 dollar savings tire but for future reference. It's also sounding like a good mod is the driver mod, I am OK and undersand the basics but need that seat time.
 


Last edited:

RAAMaudio

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#8
I would go for 15 or 16x8, 4x100 conversion, a great deal more options, better ride, less wear on the chassis, lower costs by far over time as well.
 


AZST

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Tucson
#9
Lowering the car will help but do not go do low or all the weight will transfer to the outside tires due to the roll center geometry change, it can also introduce bump steer.
Wider wheels and wider track from outside to outside of the rims, side to side will also reduce the tendency to get up on two wheels but do not get to crazy with the offset as it will cause an issue with the scrub radius.

99.99% of cars lowered way down have very serious handling compromises, increased wear on bearings, bushings, and more.

SMOOTH inputs, not always easy to do in the rapid changes of direction in an autocross but always important for all types of driving.

Sometimes purposely tossing a car around hard can be faster but that is normally in poorly setup situations or purposely setup that way as i have done before but also knowing the car might not be safe in extreme situations when out on public roads.
May be a noob question, but can you elaborate a bit on the scrub radius issue please?
 


RAAMaudio

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#10
This link helps, wiki, sometimes best to do more research as somethings there are not always correct but this seems to be right on.

Basically using a lower offset wheel will induce more torque steer which is more profoundly "entertaining" the more power and stickier the tires. My car had considerable amounts of it with the RA1 or Rival S in 225 width and boost really kicked in, enough it was hard to drive fast in the mountains without a bit of danger of going off road! Filling the drivers and passenger side mounts with urethane helped a bit and it would of been worse if I did not have urethane suspension bushings.

http://https://en.wikipedia.org/wiki/Scrub_radius

I need to dig up my suspension books or find it online, there is a reason why adjusting camber is better at the knuckle than the strut top according to my recollection but the wiki seems to say otherwise. I had to adjust mine at the top due to the 9" wide +35mm wheels being to close to the coilovers. I have mine wedged at the bottom to full positive in the bit of movement allowed by the stock bolts.

I am a little foggy this morning, been a trying few days without much rest, coffee just kicking in now....(of course it is fine coffee, organic, fair trade, single bean Guatamalan, filtered well water, fresh ground, gas stove percolated, a dab of fresh organic cream, when you drink coffee like this Starbucks will make you gag if you try it:)
 


M-Sport fan

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#11
I am a little foggy this morning, been a trying few days without much rest, coffee just kicking in now....(of course it is fine coffee, organic, fair trade, single bean Guatamalan, filtered well water, fresh ground, gas stove percolated, a dab of fresh organic cream, when you drink coffee like this Starbucks will make you gag if you try it:)

[thumb] LOL

Starbucks will make me gag (and give me SEVERE reflux on top of that) if I taste it after drinking Dunkin Donuts medium roast, pre-ground, made in a Black & Decker coffee maker with filtered tap water, and with Giant store branded half and half mixed in!!!!
 


RAAMaudio

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#12
Haha:)
Most gas station coffee tastes like some kind of solvent but I have had some that was much better than the last Starbucks I had when in Scottsdale last summer.

-------

There is more to scrub radius than torque steer issues, I forgot to cover that but looking for a place I can quote or paste a link to, easier and less chance of making an error, etc.....fine tuning a suspension is far more involved than just camber, toe and castor, it can get very complicated as most of it interacts with each other significantly.

The basics of making a car work better can achieve a great deal if you do not get to far away from stock.
1) moderate lowering
2) perhaps a bit of castor change
3) toe set properly
4) not to stiff a spring rate
5) not to stiff sway bar changes
6) stay as close as you can to stock wheel offsets though a bit more change can be tolerated to allow wider wheels and tires
 


OP
Z
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Thread Starter #13
I would go for 15 or 16x8, 4x100 conversion, a great deal more options, better ride, less wear on the chassis, lower costs by far over time as well.
That was kind of what I was originally looking at, minus the 4x100, to lower the overall unsprung weight as my main goal. I already passed on these since its likely not going to be the best setup for the money and comes with potentially bad side effects.
 


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