Understeer reduced on cars with equal size tires front / back?
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Cadillac ATS Technical Discussion Forum Discussion, Understeer reduced on cars with equal size tires front / back? in Cadillac ATS Discussion Forums; The title says what I want to know. It's not something I can find out for myself by taking a ...
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    ajfr is offline Cadillac Owners Member
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    Understeer reduced on cars with equal size tires front / back?

    The title says what I want to know. It's not something I can find out for myself by taking a test drive, so I'm hoping there are some forum members who can report on the limit handling characteristics of these cars. The road tests I've seen all tested cars with larger rear tires.

    A little background. I have a daily driver and an '01 Z06 which I drive 2 - 3 weeks a year on trips to mountain twisties. I usually tow my sportbike and ride it half the time, so the 'Vette gets a lot less use than it should. As the daily driver is nearly worn out, I'm thinking of contracting to a single sport sedan, either a V6 ATS or a 350isF.

    Exiting corners under power makes the Vette pretty neutral, but the penalties for excessive speed are so severe in the areas I drive / ride that I tend not to use a lot of power on exiting corners. I get most of my fun with both the car and the bike out of diving into corners at a bit more than twice the posted advisory speed and trail braking part way down to the apex, then taking the rest of the corner at maintenance throttle. (I don't need to hear from any unskilled riders / drivers about how dangerous trail braking might be - I have a fair bit of motorcycle roadracing experience.) Unfortunately the 'Vette understeers enough to be a bit annoying under these conditions, and it appears that the ATS models with larger rear tires do the same, based on the road tests I've seen. I understand from the Z06 forums that larger front wheels fixes that issue on the 'Vette, but I never got around to trying it because I prefer to leave Active Handling on.

    I expect that the factory has tuned the springs, shocks and sway bars to ensure that ATS models with equal size tires understeer at the limit, but if they haven't those models would jump to the top of my shopping list.

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    investor74 is offline Cadillac Owners Enthusiast
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    Re: Understeer reduced on cars with equal size tires front / back?

    Certain models of the ATS do come with wider rear tires if that is what you want.

    You're going to have a lot of fun with the ATS. Very few people have driven it "to the limit", but when the ATS was first introduced, all the reviews praised its handling. Go to YouTube and watch the various test drives. The ATS has nearly a 50/50 front to back weight distribution which along with the advanced suspension components makes it the most fun to drive sedan out there.


    Any sedan made for the general public is going to have a little understeer built in because it's more natural for most people and considered safer for the average driver.

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    JavaGirl is offline Cadillac Owners Fanatic
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    Re: Understeer reduced on cars with equal size tires front / back?

    There is a red light not too far from my house where I need to turn left onto the other road. The two roads do not meet at exactly 90 degree angles; my left turn is a little sharper than 90. Both roads are four lanes with dividers (two lanes in each direction). I hate waiting on that light, and I will accelerate hard into it and break at the last instant if that will get me through on yellow.

    I can't believe how stable and fast the ATS is through that turn. I can easily do 35 and the tires never make a sound. It is not even near its limit there. I had never driven a car which handles like this (limited experience, but still...)

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    Re: Understeer reduced on cars with equal size tires front / back?

    I have logged a few hours on twisty tracks.
    Definitely recommend FE3 suspension package. I also have replaced stock run flat rubber
    With Michelin Pilot Super Sports.
    My ATS has been pushed to the edge and was very controllable under extreme cornering

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    ajfr is offline Cadillac Owners Member
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    Re: Understeer reduced on cars with equal size tires front / back?

    Agreed on the non-runflats. The only reason I bought the Z06 over the base model was the much softer steering response of the of the base model. Car and Driver later did some testing and concluded that most of the difference in steering crispness was caused by the runflats on the base model. Still, it's less of an issue than I expected. Running hard in the twisties I try to drive as smoothly as possible, so I seldom use the instantaneous response of the Z06 to abrupt steering inputs.

    I don't intentionally drift a car on the street, but I like to get a hint of tire slide now and then to confirm I'm running as fast as I aim at. It's a bit dispiriting that on the Z06 it's always the fronts that let go - having all four begin to slide at the same time is more challenging and more fun if you're careful about the corners where you push a bit harder.

    If all ATS models are tuned to understeer at the limit, one thought I've had is that I might get a second set of front wheels and mount sticky performance tires to use when I head for the mountains. Using stock sizes should keep all the electronic nannies happy, and leaving the standard all-season tires on the rear might eliminate the understeer, or it might go way beyond that to unacceptable oversteer. Anyone tried that?

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    Re: Understeer reduced on cars with equal size tires front / back?

    ok here's the setup you want, go v6, unless you plan to tune then go turbo, you also need to go premium so you get magnetic ride and the competitive mode setting in the traction controll lastly ask your dealer to swap the wheels for the same wheels from a performance trim. your dealer won't mind you "upgrading" their car, and you won't mind losing the staggered wheels for less under steer , win , win

  8. #7
    SLA
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    Re: Understeer reduced on cars with equal size tires front / back?

    Every car with staggered wheel widths from the factory understeers (before adding power-on oversteer). It's just a matter of physics...the wider rear tires have more grip, so the fronts will give up first. I've been fighting understeer in my M3 all season. With the staggered setup, there's not a whole lot I can do on it before going to the aftermarket (which is very limited for my class).

    You want the Performance model not only for the MRC shocks, but also for the LSD. The Performance Model ATS (or any 2.0 with a 6MT) has a torque vectoring rear diff. Couple that with a good alignment, better tires, and you'll have a stellar handling ATS that retains its warranty. I think one guy had his ATS aligned but he never reported back with the range of factory adjustment. Even if the camber adjustments are limited, you can still decrease rear toe in, which will help the car rotate. I run about 1/8th total in on the rear of my M3. It helped significantly to get the car to rotate. I could go less, but it's a street driven car so I just drive around the understeer.

    Don't waste your time trying to balance understeer with different tire types. You'll have a drifter, not a corner carver. Plus you can't rotate the tires.

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    marktanner is offline Cadillac Owners Enthusiast
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    Re: Understeer reduced on cars with equal size tires front / back?

    Only the Premium ATS has the MRC (FE3) suspension, and only on the RWD models. The run-flats are summer only, and pretty sticky. As set up from the factory, understeer is fairly minimal, even with the stagger. All other models have FE2 with 225s all around, but understeer is minimal with that set up too. Increasing the front tire size (or reducing rear tire size) will reduce understeer further, Though finding a tire with the same circumference without going all the way to a 255 may be tricky. Pilot Super Sports will certainly be stickier, but the stock tires aren't bad, and have been tested to corner in the low to mid .9s.

    All Premium RWD ATS, as well as all 2.0 MT ATSs, have the limited slip. Even with the traction control on, it is easy to throttle steer the car, and it's even easier in Comp mode or with the TC off. Try it first; it's more neutral than you might think.

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    Re: Understeer reduced on cars with equal size tires front / back?

    Quote Originally Posted by SLA View Post
    Every car with staggered wheel widths from the factory understeers (before adding power-on oversteer). It's just a matter of physics...the wider rear tires have more grip, so the fronts will give up first. I've been fighting understeer in my M3 all season. With the staggered setup, there's not a whole lot I can do on it before going to the aftermarket (which is very limited for my class).

    You want the Performance model not only for the MRC shocks, but also for the LSD. The Performance Model ATS (or any 2.0 with a 6MT) has a torque vectoring rear diff. Couple that with a good alignment, better tires, and you'll have a stellar handling ATS that retains its warranty. I think one guy had his ATS aligned but he never reported back with the range of factory adjustment. Even if the camber adjustments are limited, you can still decrease rear toe in, which will help the car rotate. I run about 1/8th total in on the rear of my M3. It helped significantly to get the car to rotate. I could go less, but it's a street driven car so I just drive around the understeer.

    Don't waste your time trying to balance understeer with different tire types. You'll have a drifter, not a corner carver. Plus you can't rotate the tires.
    no MRC on performance like I said buy premium for MRC, dealer swap to downgrade premium staggered wheels on premium to their non staggered equivalents and you have the ultimate setup, the best suspension of the premium and the slightly more balanced (less under steer) handling of the performance

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    ajfr is offline Cadillac Owners Member
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    Re: Understeer reduced on cars with equal size tires front / back?

    Quote Originally Posted by pissedoffwookiee View Post
    no MRC on performance like I said buy premium for MRC, dealer swap to downgrade premium staggered wheels on premium to their non staggered equivalents and you have the ultimate setup, the best suspension of the premium and the slightly more balanced (less under steer) handling of the performance
    This sounds like a great idea. The staggered setup uses rear tires that are effectively the same diameter as the fronts. Looking at the tire specs I had guessed that the electronic safety systems would have to be programmed differently, but doing the calculations shows the rears should be only 1.5 mm smaller, so there should be no issues with swapping wheels. If there's still a bit of understeer left, I could probably minimize it with alignment changes, as suggested by SLA.

    I haven't been able to get a '14 brochure to see whether the tire options have changed. I need the V6 because the fours aren't approved for towing. (Otherwise I'd choose the turbo manual.) A driving supplement in the local newspaper reported that the '14 V6 would get the same 8-speed auto as the V model as an option when the V model debuts later next year. Since that might fix one of the reported negatives of the car (compared to the Lexus that has won all the comparison tests), I'll likely wind up waiting for it. The problems with CUE probably don't matter to me since I never use the audio system in any car, and I have a GPS that I know how to use and really like so I won't bother with CUE for that either. I expect that even a computer nitwit like me can eventually learn to operate the HVAC.

    My only remaining concern is finding some way to shut off OnStar completely. I don't like the invasion of privacy it entails, and if it can't be removed it would be a deal breaker. I might start a separate thread for that question when I get closer to a final decision.

    Thanks for the suggestions, everyone!

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    SLA
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    Re: Understeer reduced on cars with equal size tires front / back?

    I can't believe you can't get the MRC on the Performance model.

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    Re: Understeer reduced on cars with equal size tires front / back?

    Quote Originally Posted by SLA View Post
    I can't believe you can't get the MRC on the Performance model.
    it's true, MRC is premium only, I totally understand why, premium sales would fall off a cliff in favor of the performance model if they did that

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    ajfr is offline Cadillac Owners Member
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    Re: Understeer reduced on cars with equal size tires front / back?

    Quote Originally Posted by pissedoffwookiee View Post
    it's true, MRC is premium only, I totally understand why, premium sales would fall off a cliff in favor of the performance model if they did that
    It's bizarre that if you want a V6, many of the things I would call performance options (MRC, limited slip differential, "performance cooling system", "track performance package") are not available with the Performance Collection. You need to get the Premium Collection, according to my '13 Canadian brochure. Since the Premium Collection contains a lot of expensive crap that I don't need, I'm hoping the '14 models will have a more rational options list.

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    Re: Understeer reduced on cars with equal size tires front / back?

    Quote Originally Posted by ajfr View Post
    This sounds like a great idea. The staggered setup uses rear tires that are effectively the same diameter as the fronts. Looking at the tire specs I had guessed that the electronic safety systems would have to be programmed differently, but doing the calculations shows the rears should be only 1.5 mm smaller, so there should be no issues with swapping wheels. If there's still a bit of understeer left, I could probably minimize it with alignment changes, as suggested by SLA.

    I haven't been able to get a '14 brochure to see whether the tire options have changed. I need the V6 because the fours aren't approved for towing. (Otherwise I'd choose the turbo manual.) A driving supplement in the local newspaper reported that the '14 V6 would get the same 8-speed auto as the V model as an option when the V model debuts later next year. Since that might fix one of the reported negatives of the car (compared to the Lexus that has won all the comparison tests), I'll likely wind up waiting for it. The problems with CUE probably don't matter to me since I never use the audio system in any car, and I have a GPS that I know how to use and really like so I won't bother with CUE for that either. I expect that even a computer nitwit like me can eventually learn to operate the HVAC.

    My only remaining concern is finding some way to shut off OnStar completely. I don't like the invasion of privacy it entails, and if it can't be removed it would be a deal breaker. I might start a separate thread for that question when I get closer to a final decision.

    Thanks for the suggestions, everyone!
    I understand the desire for privacy, but i wouldn't worry about onstar unless your into a Tony Soprano like lifestyle. If you have a smartphone you've already given up way more privacy than the car would. a couple of years ago GM decided they wanted the same data smart phones were sending (crowdsourcing) and wanted to leverage this capability built into their cars for years to use for traffic information. they ended up walking away from this initiative because of a big backlash they received, i believed it centered around GM's ability to light up onstar cars whose owners opted not to subscribe, and send gps data back to the mother ship. which is exactly what every google maps/bing maps/apple maps equipped smart phone does already.

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    ajfr is offline Cadillac Owners Member
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    Re: Understeer reduced on cars with equal size tires front / back?

    No smartphone. iPad 3G with location services turned off. I have a SPOT with tracking and emergency road service, which I use when driving / flying / motorcycling in remote areas without cell service. Then, the safety enhancements outweigh the privacy issues. The advantage is that I can turn the iPad and SPOT OFF most of the time. So no need for OnStar, and GM / big brother doesn't know my location continuously. I find that just, well, creepy.

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