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Handling: Camber Attainable with Struts. Your Experiences?
I'm not worried about the power and torque. 197 BHP and 151 lb-ft should be plenty, depending on gearing. The high rev limit should be a boon to autocrossing, again, depending on gearing.
Speaking of autocross, I'm more concerned with handling than power. The weight is lower than any other 4-seat RWD car that I know of, which is the main reason I'm considering this for my family car. The low center of mass is very exciting. The only concern I have with the car is the front McPherson struts. All my Miatas have had double wishbones up front, and those cars would give over 2 degrees of negative camber without camber links, camber plates, or any other nonsense. Plus, they give camber gain under compression. I know that some strut-equipped cars, BMWs in particular, are camber-challenged; they have limited static camber and poor camber curves. Stuts often give camber loss, rather than camber gain, as the suspension compresses. The drivers I know who autocross Bimmers in Stock classes or in Street Touring classes frequently complain about not being able to get enough camber. Fortunately, I don't seem to hear this complaint as much from the folks racing WRXs and STIs, though the grip offered by AWD may be mitigating the problem in their cases. So, can anyone comment on how much negative camber one can achieve in the front of other Subarus? Also, what are the camber curves like? Do you see much camber loss? How about with aftermarket dampers and springs that lower the car dramatically? |
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I looked into it some and you can get around 3 degrees of camber with a plate on the front suspension. Have to wait for the Subaru/BMW guys to chime in for any facts. :iono:
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Skeeler: Unfortunately, I've been double wishbone all around for years, so I need to relearn mac strut junk myself so I'm no help on this one currently. |
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Anyways, how much actual space we can get depends on the car. I think the old RX7 race car I used to crew on got around 5 degrees with plates, 3 degrees was around the middle of the plate... so it's going to depend on how much space there is to move the top of the strut inboard. |
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Mac struts have little camber gain or loss, assuming the control arm is reasonably long, total stroke is short, and the control arm angle isn't excessive.
If you plan on doing stock-class Auto-x, then you'll have to hope the strut towers are slotted, or the knuckles have an eccentric connecting it to the strut. That would be the only built-in adjustment apart from an eccentric control arm bushing set or adjustable strut top. Another solution is to add stiffer sway bars and/or springs, to keep the car flatter in corners. This will improve contact patch, however it may adversely affect wheel rate [unless the car is too soft out of the box]. Long story short, there are solutions and none of them are ideal. |
With plates and/or aftermarket bolts on an Impreza, you'll be able to get more camber than you really need (well over -3.5).
2008+ Impreza can get -1.5 to -1.8 if you're lucky up front with the stock adjustment (eccentric bolt). Pretty good for a fun street car but not enough for track/auto-x with sticky tires. I'd expect the same from this car but we'll see. Maybe okay for stock class auto-x on such a light car if the standard springs are decently firm. The Impreza is OKAY up front....it gets worse when the car is dramatically lowered though. - Andrew |
Ryphile,
Thanks for your reply. Unfortunately, springs can't be replaced in Stock, and only one swaybar can be. Fortunately, I'd probably run this car in Street Touring. Looking at the numbers, it might be nearly competive with the two fastest cars in the Street Touring R class: The NC Miata and the AP1/AP2 S2000. The weight, torque, and power posted for the FR-S all land between those of the NC and S2k. Springs, dampers, and ARBs can be replaced in ST. So, tf the front suspension can be given enough camber in a Street-Touring-legal way (eg, with camber plates or "crash bolts"), and if the car can be made to fit 9-inch wheels and 255 tires, it might not do too badly. My NC fits those wheels and tires, so I'm hopeful the 275-lb-heavier FR-S can, too. (Too bad I won't be able to use my existing wheels, thanks to the 5x100 lug pattern.) The lengthy wheelbase won't help it, though. Thanks again. |
For what it's worth, STU class Imprezas don't have any problems getting enough static camber.
- Andrew |
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Do you know much about the Street Touring category? There's a lot more that can be done to fix factory problems in suspension. That's one reason I run my NC there: The NC's stock suspension is ridiculously high and soft, but the design of the suspension arms and the rest of the platform is excellent, so the car is really transformed with dampers, wheels springs, and roll springs. The STIs certainly do well in Street Touring U, but I don't know if AWD grip hides an underlying problem with the strut suspension. Obviously, that grip will be lacking in FR-S and BRZ. I guess I need to pay more attention to what the STU Subie drivers have to say. Lightness is relative. My last five cars have been Miata, Miata, Miata, CRX, and first-gen Prelude. The FR-S and BRZ are big cars to me. |
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As a Subaru guy who has done pretty much everything with his car suspension wise (bushigns, coilovers, whatever, even lifting the car for off-road purposes) I'll chime in...
You can easily get -2.5-3 front camber with camber plates and the stock camber bolts. The stock bolts are good for just over -1.5 as Racecomp mentioned (great guys BTW, they know far more than I do, LOL!). If this is indeed just a take-off suspension from an Impreza, then STI aluminum control arms are an option up front as well, and I'm not 100% on this but they might also modify the suspension angles a bit (more caster too). There are also kits out there for adjusting suspension angles when the car is lowered, at least in terms of the control arm location and tie rods. There are also LOTS of bushing upgrades and other such bits available that you can use in Street Touring classes, and those work wonders. Working with the front suspension is VERY easy on these cars. I can have the front struts off and back on in under an hour with hand tools. Although I haven't worked with the rear multi-link yet... |
Camber loss on struts is always the problem. It's a dichotomy; run lots of static camber to achieve good contact patch at peak cornering, or zero static camber to get peak grip and stability at WOT and full-brake. You can't have both. This is why some tires are especially designed for strut cars; their carcasses are flexible to stay reasonably stable in a straight line with high static camber.
However, if the car has good roll stiffness, the amount of camber loss up front won't be a big deal, or perhaps even a real problem. With enough roll-stiffness, even -1.5° static will be an acceptable compromise between straightline stability and using maximum tire shoulder in corners. |
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- Andrew |
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- Andrew |
Wow. Thanks so much for sharing guys! I thought the number I found was fishy but it sounds like it's normal for Macpherson struts.
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Wasn't that hard to do either, just get some weight off suspension and pull it back into place. 15 minute job at most. |
I had macphersons in my 323, while they are challenged in the 'camber curve' I could run ~2degrees all around (macphersons all around) with the camber plate on neutral and 6 degrees (was just for test never actually drove like that) with camber adjusted to max. I did have coilovers that have a WIDER lower bolt arc slot so it allowed for a very good setup.
By maximum I mean maximum on the bottom and maximum on top combined. The top swing was 4 degrees from start to finish and the bottom swing was 2degrees from top to bottom. But what you really want with a macpherson for auto cross (for my 323 anyway) is decent static camber and as much caster as you can get to increase your dynamic camber ;) in autocross dynamic camber is more important than static |
^^Excellent point! Dynamic camber is what's relevant.
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Ooh whoops there wasn't meant to be a dislike thumb there.. Was supposed to be a :)
I never got more than 4deg positive caster, but some ppl run up to 8 I also only did a few autocross, never really had time... |
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Dynamic camber as in anything happening under compression/extension/steering
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Exactly.
It's not a perfect system, as dynamic camber is maximum with tight-radii corners. Those that run HPDE/track-days would likely have to run more static camber, as steering angles are less on a track vs. auto-x. At this point however, we're kind of nitpicking a perceived problem that may not exist. We're not familiar with the cars' balance at the limit in various situations [street tire auto-x vs. Hoosier track-days]. The problem may end up being the rear-end camber curve, a roll-center axis issue, or a bump steer problem front or rear. Of what I've seen so far of the suspension, I may hazard a guess that the rear toe-control link might result in too much bump steer with the rear wheels. ...or the car could indeed be close to perfect; who knows at this point. Remember that Porsche's are all strut and they manage to make it work very well. |
The 323 is all strut and porche designed it (apparently)
Iv never had issues apart from snap oversteer but that was due to the rediculously stiff swaybars+tower braces+springs I had on payload, the car would squat about 5mm.. Overly stiff for street but SO fun in corners My 8 is different. Double a-arm front and multylink rear, has a very soft ride but very low body roll. Planing on getting some thick swaybars and stiffer bracers very soon (and some chasis bracing as well) |
maybe its just me but i think i would rather keep the miata to auto x. i would have to imagine that the miatas suspension is going to give you a more useable camber curve while still needing less - camber simply because of the design. all that suspension talk aside, you have a car with a huge aftermarket and a car that has already been dialed in by many people. then there is the factor of tire which has gotta be the second biggest issue for auto x behind driver. the miata can fit some significant amounts of tire in the wheel wells. that combined with the fact that you already have the miata make it seem like you should hold on to it and see what people start doing with these cars.
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Hopefully, Toyota and Subaru has design the front Macpherson strut to the newer super strut design like the Ford Focus RS in Europe. The inclination angle is not inline of the pivot points. which gives a different scrub radius than typical Macpherson. I believe the Porsche Cayman design their Macpherson stut this way, the reason the Cayman handles very well.
The FR-S will not fit in the "ST" class because of the limited slip. It should fit the "STX" class well. I also want to try it in the stock class. More likely to be classed in D-stock. http://www.autolinedetroit.tv/journal-wp-content//uploads/2009/02/revo-knuckle.pdf Even though Ford design this for a front wheel drive to cure torque steer, it still can advance the steering feel for macpherson strut. Cliff 369 st civic |
As mentioned before the problem is not static camber on a strut car, but dynamic camber. The problem comes from the SAI built into struts. This is something I knew from experience autoxing bmw e30s but didn't understand. I used to run 9.8 deg of caster and only 2-2.5 deg of camber.
The reasoning behind this is involved and the best description I have seen of it is by stretch on iwst.com, go search it. But what it boils down to is you want to run as much caster as possible (there is an upper limit of what works, but is different for every car) and as little added camber At the TOP of the strut as possible. If you need to add static camber do it at the bottom with slots on strut or camber bolts. In the STi I am running 6.8 deg caster, all I could get, and only 1.5 deg of camber. With a 245 stretched on a 9.5" wheel I am getting very even tire wear and wonderful front grip. Also, I think it was mentioned but this car will Not be eligible for STR due to the back seat. It should fit in wonderfully in STX however. And is hopefully dominate ;) |
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