Sooooo I've gotten a couple of new suspension upgrades and am pretty much close to being finish on all that I want to do. My plans at some point are widebody kit or flared fenders. I've been reading that using WRX control arms and wrx lateral links that I can widen my track front and rear by 10mm on each side.Because I have coilovers I can pretty much use any size wheel and tire combo and not have it rub because I can adjust the height and stiffness. The real reason I really want to widen my track is because there are a lot of claims that a bigger footprint will increase handling. I plan to attend some Scott siegal classes and track days in the future. And I really want to get into autox and hpde events. What do all the track gurus think about a widened track? (I will also be going from a 215/45/17 to a 235/45/17 tire)
Might I suggest the 235/40/17 b/c the overall tire diameter is slightly smaller than stock increasing torque on the ground for better acceleration, perfect for auto X and Barrett Pkwy! As for track width , wider is better works for the pontiac grand prix, however many wide bodies accept larger off-set wheels for a wider track but handle worse do to horrible "scrub radius"(angle calculated by wheel vertical center-line and steering axis inclination) which,in a nut shell, means less grip. The steering geometry must be changed entirely! My opinion is that wide bodies are all show and no go, traction gained in track width is lost elsewhere w/out spending LOTS of money.
Well with the new control arms and lateral links I would have changed the suspension geometry right? I would now have a wrx setup. I'm not really trying to widen the track by using spacers or lower offsets. My goal is to gain superior handling.
SAI on your car is the line b/n the center of the upper strut mount and the lower ball joint to the ground. The longer control arms will increase this angle possibly requireing a different off-set wheel and more camber adjustability(shouldn't be a problem w/ your suspension) Do you know your stock wheel off-set and are the strut towers spaced the same as a WRX? If so that would be good b/c you would use a +42mm off-set and corner on rails!
My wheel offset is the same as a wrx. My strut towers I *think* are a lil bit closer together. We can measure them car to car. The offset of the wheels I have are +48
Handling is a lot nicer when upgrading the width. You probably will get bad gas mileage as now you have more frictional drag on the ground. You can definitely run a 235 with no issues, but be careful of the 245 if you change your rear camber to have less negative camber. It won't allow the tops of the wheel to tuck underneath the fender. I use a 245 R with a 48+ offset, but I had to take some material out of the inside of the fender. Flaring the fenders isnt too bad if you rent the special tool, but don't go with the widebody kit itsssh: .
Please explain how scrub radius will produce less grip. Also, what does steering geometry have to do with scrub radius, or rather how would you change it? ~ rockin 17x10s ET35 (it doesn't feel like I have less grip )
I think it is less grip because even though your going with a wider tire belive it or not only part of the tire is actually hitting the ground because of angle to the pavement. Steering geometry is done by tunning your suspension, change the tow in and out to change the scrub radius angle! Make sense yet? Have you ever noticed that lowered cars or widened cars, if you look at the inside of the tire that the inside tread is worn far further than the rest of the tire? This is due to scrub radius being off because suspension and steering geometry is off.
Only lowered cars get more negative camber and toe out, which is why the inside tread is destroyed unless you get a custom alignment with camber plates or bolts. I don't see how widining your tires will do anything to your suspension geometry, they aren't connected. Your contact patch can still be wider if you go with a wider tire. The front wheels should always have less contact (except when cornering) than the rear, because ideally you want more negative camber up front. Some of the contact patch also has to do with tire pressures. If you are running a good tire pressure, then "wider is better" regardless of suspension geometry. Of course the both together will work even better.
Nope. I think scrub radius really only effects NVH in the steering wheel and bearing wear. No matter what you do to your alignment or steering geometry the srub won't change, its a function of knuckle, bearing and wheel design and offsets. Scrub won't effect tire wear either, as clemsonscooby pointed out. To answer Wes' question, wider should be better but you want to balance your wheel/tire wieghts and radius with the power that you're making. Also, consider that if you run with a 16" wheel your wallet will be much happier with your autoX and HPDE habits than with a 17" wheel. Also, don't go wide body 'kit', go wide body 'stretch'. Doing a kit right takes alot of time and money and then if the flat bed truck driver at CMP is a moron he will rip your riced out front bumper from you fender.
You can definitely do an 8" wheel if you wanted to. The 225 tire, if you do the math is about a 8.5" wide and that will easily fit under your car as it does mine. The 235 should fit as well, which is 8.9" wide. That is all with a 48+ offset as well. Anything wider, then the geometry in the rear comes into play as well as your spring rates. For the math, just divide the tire width by 26.5 to convert to inches. I agree with javid as well about the 16" wheel being better for your wallet and autox, as thats what I do. The 17" definitely looks better for a street wheel, because you can go low on the aspect ratio without changing your speedometer.
Well widebody "stretch" was sort of my idea....lol I will be making a lot more power......but for right now I wish to kind of finish up my suspension/brakes/and transmission before i get working on my turbo setup. I want to learn to drive the hell out of this car without boost then as I get better to add that in later. Pricing on a 17'' tire isn't too much worse than a 16 from where I can get my tires. Oh and a lot of the complaints i've seen in all the motorsports and gc8 forums has been terrible front suspension geometry. That was one of the reasons why I wished to change it so it would react better.
Update. I've got JDM Ver7 aluminum control arms. I've also got the lateral link/trailing arm/front control arm bushings ready to go. All of this will be installed in a week or two. I'll let you guys know how it turns out.
There were several good articles in Sport Compact Car explaining car suspension and alignment. It'd be worth ordering the back issues for. Just ignore how he packs himself on the back with his "Dave Point" though...
The conversion from metric to imperical is 25.4. Unless you have a specific reason to divide by 26.5. Scrub radius will change with a change in rim offset. With the narrower strut tower distances you will actually make the angle of the strut farther from vertical. This will give you the opportunity to use a wider wheel and perhaps use the less offset. Moving the strut/coilover farther from vertical may require a change in spring rate but I don't think the angle will change enough to worry about that. Now the scrub radius will be an issue. The biggest problems you may see with an increased scrub radius is an increase in steering effort and a lack of return to center when the steering wheel is released after a turn. Handling can suffer increasing the scrub radius. Most experts agree that one should try to reduce the scrub radius as close to zero when optimum handling is a concern.