Foxbody Analysis Paralysis: Spring Choice

After checking the suspension on my new found toy I discovered the springs are mismatched

The rear springs are BBK 2501 (250lb)

The fronts are H&R Super Sports (500lb)

The issue with the fronts is the Super Sports are meant more for looks than performance. The car is an inch lower in the front.

The easy fix is just pop in different springs but well analysis paralysis is in full swing.

I called helpful folks Maximum Motorsports for some help. They have a service whereby I can send them my specs and they will make recommendations..........all good except analysis paralysis.

I know the right thing to do is wait and get the recommendations BUT there is an autocross in two weeks and a track day in a month.

Call me Varuca because I want to drive it now. I could have the springs here and changed next weekend

I could also drive the car as is......the handling is decent but may be a bit understeery.

What say ye O wise and noble hive???

I'd probably drive as is unless you are chasing a target. They aren't great handing cars to begin with, and you may be chasing marginal improvements in any use outside of just driving. 
 

FWIW also a fox guy who wishes he was driving his, so that may be skewing my view on things 

Patience grasshoppa. Having the calculated specs is usually my first move.

How does it handle now? If you run it with the current set up you MAY find it feels good on the butt-dyno.

May I humbly suggest we don't generally get cars with the idea of looking at them on this board.

My 2 cents, drive it on course, see what it does that you like or don't, will be less analysis paralysis at that point, to boot.

In reply to Cooper_Tired :

The guy at Maximum was a bit taken aback when I told him I bought because they aren't great handling cars.........I love that it's a bit crude.

In reply to Tom1200 :

Don't they make a good chunk of business out of re-engineering the suspension because they aren't great handling cars? 

Spring rates will look "weird" because the front and rear springs work against a lever arm.  I know when Ford made the Cobra R they made the rear springs softer, and by softer I think around 160lb vs. 200lb for standard GT/Cobra rear springs.  Something like that.

Another kind of weird thing on first glance is that the 4 cylinder cars had stiffer suspension bushings than the V8 cars.  

I agree with the others.  Get it out and try it first.  

That being said if you look at spring kits originally offered by Ford Motorsport (which are progressive rates), both the fronts and rears have an average rate around where yours are at each end.   Motorsport M5300-B and M5300-C springs are very well known in the Fox community and are my reference point.  Translation:  your setup might seem strange but in fact it may be that way very intentionally and the result may please you more than you expect.

In reply to Tom1200 :

I'd love to know what else got done to to the suspension to make a Foxbody "understeery"?  My vivid memory from the day is the potential for ridiculous oversteer.  To the point where most of them found in scrapyards had damage to the rear of the car from over rotating and leaving the road going backwards.

In reply to 11GTCS :

The rear suspension had a weird tendency to bind and snap spin, complicated by the front suspension's fairly low roll center.  The roll axis had a good amount of slope to it.

Plus, Mustangs gonna Mustang.  The front end did all sorts of things to hurt grip with respect to scrub radius and poor Ackerman, the steering feel suuucked (the SN95 rack had a lot of attention paid to it to improve driver feedback), the back end had to deal with V8 torque and a sometimes recalcitrant Trak-Lok that, because it had C clip axles and the clutches were direct acting on the side gears (and relied on tooth pressure from the spider gears to force the clutches under load) wear on the clutches did weird things to axle float, which was sort of OK with drum brakes but unpleasant things could happen with disks...

11GTCS said:

In reply to Tom1200 :

I'd love to know what else got done to to the suspension to make a Foxbody "understeery"?  My vivid memory from the day is the potential for ridiculous oversteer.  To the point where most of them found in scrapyards had damage to the rear of the car from over rotating and leaving the road going backwards.

To be fair, if you're hamfisted with the throttle you can make nearly any RWD vehicle oversteer. 

11GTCS said:

In reply to Tom1200 :

 ridiculous oversteer.  

There is no such thing.........my experience with cars that suffered from suspension bind may have colored my opinion.

My experience with flexi flyer motorcycles may also be skewing my opinion........I love my Yama-swaper MX bikes......you can never have to much rebound damping.

Are you trying to fix the rake, or address negative handling characteristic you aren't yet sure the car presents?

Drive the car as-is. Decide how much of your money you want MM to spend correcting the behaviors you find unappealing; because they can, and will, do both.

If you want to adjust the rake, start by letting us know how many isolators are currently installed and in what locations.

OTOH, one of the Fox body tricks used to be to drill new control arm mounting points in the front crossmember.  Usually the front one a little higher and the rear one a lot higher, which will raise the roll center and increase brake antidive.  Antidive being the primary goal.  Doing this will also raise the ride height for a given spring.

11GTCS said:

In reply to Tom1200 :

I'd love to know what else got done to to the suspension to make a Foxbody "understeery"?  My vivid memory from the day is the potential for ridiculous oversteer.  To the point where most of them found in scrapyards had damage to the rear of the car from over rotating and leaving the road going backwards.

If the front springs have a low ride height but are not stiff enough, he may be sitting on the front bumpstops while cornering. They have a very high spring rate and very little compliance, which would lead to understeeryness.

I'm extrapolating from general vehicle dynamics, I know nothing of the Fox chassis in particular.

Thanks all for the input.  My ride at the time was an '86 Jetta GLI which had it's own quirks but it was a pretty decent handling car for that time.  Jumping from that into my BIL's '86 Mustang GT was always unnerving, it was quite quick by the standards of the day and had those massive (at the time ) Goodyear Gatorback tires but it always felt like it wanted to rotate.   I also remember the brakes sucked for all the go power.  (Tom's has the 5 lug / 4 wheel disc conversion so I'm sure it's way better than stock.)   I haven't driven my BIL's in years, might have to do a back to back between my 2011 and that some day and see how my memory compares to an actual drive.

In reply to gumby :

I don't want the car cornering on the bump stops; which definitely is a possibility.

In reply to Keith Tanner :

You pretty much summed it up.

In reply to 11GTCS :

I've driven most generations of Mustang; I seem to enjoy the Foxbody the most. I like that it's still rough around the edges.

I have nothing substantive to add. First time I drove one was my friend's 86 GT. I got it sideways going left at a 4 way stop and nearly ended up in his lap in the passenger seat. "Oh shoot, the floorboard is shot so the seat isn't bolted to anything!"

Fun cars :)

Tom1200 said:

In reply to gumby :

I don't want the car cornering on the bump stops; which definitely is a possibility.

How much strut shaft is visible at the current ride height?

In reply to P3PPY :

Pulled that exact maneuver many times in my BIL's 86.  The rear just wanted to kick out.   His was new (still looks new now!) so no worries on the seat thing.