Tw557

I have an 05 GT that I am looking to be a bit more composed on the back roads here in Pa. The roads are twisty, and have plenty of choppy spots. I also have a Mustang ecoboost that handles perfectly over these same areas with Ford racing shocks and springs. And of course the IRS. The 05 has ford 1.5 lowered springs, roush shocks and a panhard brace. When hitting a decent dip the rear hits hard on the lightly cut bump stops which only have about 1.5 inches of clearance. I also have a fair amount of swagging from side to side, not leaning. And also in general the tires seem to chatter around.
I have gotten a bit of advice to do upper and lower control arms first. But I have read about very ridged control arms are great for the strip but not for the road. I'm not concerned about wheel hop and I don't do hard launches. I kept thinking I should get better shocks first but now think maybe the control arms first but don't want to go too ridged to the point they would sort of bind up under road uneven loads. So I am looking for any advice from the guys that know about handling more so then drag racing.

Norm Peterson

Can you describe what you mean by "swagging from side to side" and provide some information on wheel and tire sizes?

I'm afraid that I don't know enough about Roush shocks to comment directly. But I used to lap a Roush Mustang inside of 20 minute sessions down at NJMP (haven't seen that car recently).

Just to get things started, I'll use my car - which hasn't been all that heavily modified - as something that works well enough on the track without giving up enough to notice from stock in terms of street manners. Here's what it looked like (plus a video from the inside on one of my better outings, overlaid with speed, lap time, and g-data). The car was still on its OE springs at that point, but the shocks, struts, sta-bars, wheels, tires, and rear lower arms had been changed, and the OE PHB had gotten its OE bushings stiffened a bit. I've since lowered it, but only by a little more than 0.6".









Rear control arms for a corner-carving car do have slightly different requirements from drag racing, but that doesn't mean you have to stick with rubber-bushed OE-style arms either. With NA 4.6L power in a corner-carving environment there really isn't much need to bother with the upper arm at all. I'd changed the LCAs on my '08 GT mostly because of some cracking due to age, but I still haven't touched the UCA.

I've never been into drag racing, but the corner-carving mindset goes back at least as far as the mid-1960's.


Norm

ohskigod

Id change the LCA's first (as I recently learned my changing them last plan was stupid). I have a feeling you will notice the biggest improvement for the least money on that to start.

1.5" seems to be that weird spot where people have weird issues. Some say that you should get relocation brackets with your lower control arms when you install them. I'd research that at least(I'm lowered less than an inch)

Also, that chatter over the bumps is something I dialed in with a Watts Link....NOT an economical solution so I'd save it for last rather than first.

Tw557

Norm, Thanks for the reply. I have seen many of your post on the various forums and have always felt they were some of the most insightful comments.
I have 2011 GT500 9.5" rims. I have 255-40-19 front tires and 275-40-19 rear. They are Bridgestone re970as. They seemed to get very good reviews for an all season but I am now concerned I should have went for a summer only tire. I don't drive in bad weather and hardly any rain even, but I do get it out at low temps at times if the roads are good. The swagging I'm talking about is the rear feeling like it is swapping from side to side if I transition from left to right quickly. Or going down the highway quickly steer left and right the rear will feel pretty "soft" like the rear wants to come around but the front is very solid and sharp. The rear doesn't lean much just "swags" back and forth. It feels like very soft tire sidewalls but I felt pretty much the same when it still had the factory GT500 285-35-19 F! tires. I tried pressures from 32 to 50 and didn't feel a big difference. The bushings in the panhard bar and LCA's don't seem too bad as I pry on the ends with a crowbar and the mounts. The shocks don't wallow over the road heaves as much as my stock ecoboost did but not as firm and the Ford racing suspension. But over the rough bumps in a series I get that feeling of my old 82 GT I first had.
I have always been into the corner carving too. 15 years of asphalt Go kart racing and 10 years of Roadbike racing. I respect what it takes to be fast on the drag strip but just not my thing also. So now I'm making this car a bit of a project to see what I can do to get it to work pretty good for a "bang for the buck" plan. Here is a picture to show the stance. As you can see the painted needed some help too from all the swirls. But that's another story.

Tw557

BTW Norm, That is a very nice run on the track you have a video of. The car seemed very well mannered and composed but not discounting some pretty nice driving though too.

Tw557

Yeah, the lower control arms are probably the cheapest and possibly easiest change I can make first. Any recommendation of brand name?

Norm Peterson

When I first got my '08 I already had plans for the 18x9.5 GT500 wheels for that year, along with 255/45-18 max performance tires (I ended up with the original Goodyear Eagle F1 Asymmetrics). An upper-level summer tire is likely to be at least as good in the wet as an all-season tire, generally at some expense in tread life and perhaps ride quality. Some summer tires are better at cooler temperatures - I'm talking down to low 20's F here, not subzero, where what you really need is a dedicated winter tire. I actually tracked the car on the Asymmetrics half a dozen times or so before all the DD wear plus the track day wear was down as far as I was going to tolerate (don't remember how much tread was left).

That was the point where I got more serious, with 285/35-18 Michelin Pilot Super Sport tires on 18x11 wheels, which was what I was on in the earlier video, as well as this next one in the pouring rain.



I've been working at smoothness for almost all of my driving life, and that's been of great benefit in the wet. There's also a generally unrecognized advantage in that the smoother you drive, the less likely it'll be that your passengers will mind if you do pick up the pace in the twisty bits.


Just a guess at this point, but this could be an axle roll-steer issue. Typically when you lower these cars without relocating the axle-side LCA attachment points, you end up with more understeer. At some point, the rear axle's steering starts getting out of step, and this would probably be exaggerated if the control arm bushings and/or the rear shocks are getting a bit tired. Increased tire pressure can't crutch those things very well.


Norm

Tw557

That was a pretty good pace you were running in the rain. rain will certainly require smooth transitions and straightening out the line as much as possible. I did a few Go Kart street races in the rain that were sketchy but fun but never liked roadbike racing in the race. I can so relate to you about driving a smooth line. It actually bothers my wife. Her SUV has that damn lane detection and if it sees a white or yellow line it beeps. Well I use all the lane and some extra if its available. Just that little bit of enjoyment of driving efficiently. Plus I usually always had somewhat underpowered equipment when racing so I always wanted to be the first to the throttle with late apex and smooth exit. Especially when racing the good Ol Briggs and Statten. I can tell already because of this handling issues I have adapted a smoother and slower steering input which then feels decent.
I think first I will swap the front tires to the back and see if that helps the feel. Also I tried a little test. I turned my mirror all the way down to see a little of the rim just flush with fender. I then weaved back and forth. I could see a little tire deflection but I was looking at the top. It did seem like I was seeing more or less of the actual rim. I also hit a series of bumps and wheel really did look all jittery and almost looked like it was moving forward, backward, up down, in and out. I should hook up my sons cheap go pro knock off and a take a little video of the rear suspension. That would be interesting. I'm also a mechanical engineer so all this interaction is interesting as to how it all works. Plus the challenge to make something handle that doesn't have a reputation to being able to very well. It was always very rewarding to race with an older motorcycle but cross the line first. Such tracks like Daytona if you were underpowered it didn't matter how good you drove though. Oh well, fun to reminisce.
The axle roll issue you talk about is interesting too. I'll need to do a little research on that topic also. I have the stock springs that came with the car. I could pop them in pretty quick to see the difference. Plus it sure seems like some good LCA's are on my short list.

Norm Peterson

Lane-detection would drive me nuts. Driving on the street with the same philosophy as you would on the track (just at a slower pace) also seems to pay dividends on the track, at least once you've got your timing for the faster pace back, and I'd really hate to have the practice I'm getting constantly interrupted like that. Can you turn it off? Or at least temporarily blind it?

After the 'Vette made that mistake, I was finally able to get down the main straight at more the pace I was expecting (mid one-teens). But for HPDE it simply wasn't worth the additional risk of trying to drive in the worst of all that spray, and he didn't seem at all inclined to point a lowly Mustang by.

I know that Millikens' Race Car Vehicle Dynamics has good explanations of suspension geometry, and as far as I know it's still available through the SAE bookstore. It's a college-level text, so it's a bit pricy. But worth it as you start seriously trying to understand what's going on.


Norm

ohskigod

you're not going to go to wrong either way, but the BMR piece I put on really seemed like the significant bang for buck after really researching it. It being red and matching many of my other aftermarket suspension bits was merely a bonus..lol

There are also matching relocation brackets that you might want to consider as your car is lowered 1.5" Mine isnt lowered as much so I opted against them