05

Project Mustang 5.0 (White)- Reducing Understeer  with Ford Racing

by Mike Kojima

The McPherson strut suspension found in our Mustang has some good and bad points.  The good points are that it is simple, lightweight, inexpensive to produce and takes up minimal space in the car. This in turn allows room for more narrow shock towers so the wider DOHC Coyote engine can fit. The bad points are few but perhaps the worse is that strut type suspension has some compromises when it comes to geometry, particularly when lowered.

Strut type suspensions tend to have the roll center (Geometric point in space that the car rolls about in cornering) drop rapidly as the car is lowered.  A lower roll center can mean that the roll couple gets longer which increases the cars tendency to roll while cornering, all other things being equal. (The roll couple, in a very general and simplified explanation, is the distance from the roll center to the center of gravity, the longer the roll couple the more of a lever arm centrifugal force has to make the car roll over in a turn). 

Strut suspensions also tend to lose negative camber under roll when the angle of the strut axis to the lower control arm gets greater than 90 degrees, common in a lowered strut car.  This causes the camber to become more positive as the car leans over in a turn, exactly the opposite of what you want to maintain a good tire contact patch and maximize front grip.

So the benefits of lowering a car can be nullified in a strut car if the car is lowered by more than just a little.  Often lowering a strut equipped car makes the car handle worse, particularity in the front of a strut equipped car where over lowering manifests itself as increased understeer.  To fix this, some lucky owners of cars where there is a nice aftermarket have off the shelf aftermarket solutions to fix the front suspension geometry.  If you are a Mustang owner you are in luck as Ford Racing has a well engineered geometry correction solution for you right off the shelf.

Read more about project Mustang!

To fix our roll center and camber curve we got all the right parts right out of Ford Racing competition parts catalog.  The Ford system is the most well engineered set up we have seen and is straight off of the Boss 302R Grand Am Continental race car.  The system starts with new lower control arms that have a special ball joint with a longer shank.  This effectively lowers the lower control arm pivot to around where it was at stock ride height restoring the roll center to around the stock location.  This also reduces the overall roll couple and fixes the camber curve. The control arm also includes special hard urethane bushings getting rid of the large, highly compliant lower control arm bushings.
You can see that the longer shank drops the pivot point by about 1.5".  The ball joint mounting boss angle has also been changed to reflect the longer shank and to prevent binding.
The control arms have a zerk fitting so the bushings can be fed with grease without disassembling the front suspension.
The rear of the control arm has a pivot.  The pivot on the arm remains stock but the frame side is very different than stock.
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Comments
ginsu
ginsulink
Monday, July 06, 2015 2:54 PM
Sooo....-3 and toe-out on the front? That sounds somewhat unstable, twitchy and prone to oversteer. Is this a drift car?
Mike Kojima
Mike Kojimalink
Monday, July 06, 2015 3:32 PM
No it isn't a drift car and yes it will be awesome.
spdracerut
spdracerutlink
Monday, July 06, 2015 9:33 PM
I run -2.8 on Project S2000 and 0 toe, granted multi-link geometry. On my old 2005 Evo with front struts, I ran -3.0 on the street and it dramatically improved turn-in and reduced understeer compared to -1.0. I prefer zero toe from a tire wear point of view and willing to sacrifice a bit of turn-in.
Mike Kojima
Mike Kojimalink
Monday, July 06, 2015 10:30 PM
When you run higher negative camber toe out actually reduces rolling resistance.
Supercharged111
Supercharged111link
Tuesday, July 07, 2015 8:26 AM
How much camber is enough for this? My Camaro seems to like -2.3 camber and 1/8" toe out.
Mike Kojima
Mike Kojimalink
Tuesday, July 07, 2015 9:49 AM
If you were racing for instance, more like 4 or more degrees negative.
Scott Helmer
Scott Helmerlink
Tuesday, July 07, 2015 7:46 PM
Great stuff, guys! I'm not much of a Ford guy, but I'll admit that adjustable ball joint is pretty sweet.

Interestingly, that special bar for measuring toe is still standard operating equipment for doing allignments on heavy duty diesel trucks, such as semi's.
Supercharged111
Supercharged111link
Wednesday, July 08, 2015 7:54 AM
Well dang, I'll never get there. Tire temps have about a 5-7 degree spread across the face where it sits now.
Mike Kojima
Mike Kojimalink
Wednesday, July 08, 2015 9:53 AM
Typically for a DOT type tire, you want to see 10-15 degrees higher on the inside when your tire pressures are around 28-35 psi hot.
Supercharged111
Supercharged111link
Wednesday, July 15, 2015 9:50 PM
Ohh, so I still need more camber. I've got more adjustment left so I'm going to mess with this now.
Mike Kojima
Mike Kojimalink
Wednesday, July 15, 2015 11:07 PM
Makes a huge difference on a strut car.
BillyJ
BillyJlink
Sunday, July 19, 2015 7:34 PM
I've always shot for 20-30* spread (inside hotter) -which obviously dictate the ideal camber based on the Cg and roll resistance of the car. Depending on the setup and tires; -3* of camber is sometimes too much for the front of a Mustang.

For heavier cars that run slicks like an R6 or R1; 38-40psi hot is sometimes needed although those are rare cases with under-tired cars. I typically dont' like to see above 36psi hot on most street tires.
Mike Kojima
Mike Kojimalink
Sunday, July 19, 2015 8:51 PM
20-30 degrees difference across the tread is often too much variance for many situations. Temperature variation as measured across the tread is highly dependent on how and where the tire temps are measured so unless you have a lot of experience in interpreting that information, caution should be used in making setup generalizations from it and it is just one data set to consider when deciding on what works best.

-3 of camber is usually not enough for racing on most strut equipped cars and the only reason why we didn't run more negative camber on this car is that it is street driven and we sort of have to think of tread wear when driven at less than track speed. What is the best amount of negative camber is also influenced by the geometry particularly the relationship of Caster and KPA if these are extreme as they are in some cars (but not the Mustang). My opinion on camber is derived from the tire manufacturer's data when provided such as camber thrust curves and slip angle curves as well as actual measured data from cars when doing development.

I can only think of two particular brands of DOT race tires that often like 3 degrees or less on a heavy strut car, most like 3.5-5 degrees of negative camber. Of course my rules of thumb don't apply every single time but most strut suspension car/tire combos fall within this window.
BillyJ
BillyJlink
Monday, July 20, 2015 7:12 AM
A 20-30* spreads is a common target for a lot of professional racing (when used with a probe type pyrometer) and a general rule of thumb that have served me well from street cars, track day toys, to pro racing; although as you said there are a lot of compromises especially for a street driven car.

For the S197 Mustang, I have found that they typically don't require as much camber as other cars with struts. Depending on the tire/setup (which dictates how the tire is loaded) -3* is probably close to the upper limit unless the car does not have enough roll resistance in the font.

FWIW the East Coast NASA TT3 Champion runs -2* on a 275-square Hoosier R6 on his BOSS 302 Laguna Seca.
priapism
priapismlink
Thursday, August 06, 2015 8:38 AM
Pardon my ignorance, but are these control arms only beneficial if you're lowering the car? I have a Boss, and I'm not interested in lowering it (won't get in my driveway, plus it causes other issues), but I'm definitely interested in reducing understeer. Thanks
Mike Kojima
Mike Kojimalink
Thursday, August 06, 2015 10:15 AM
Mostly it helps only if you are lowering the car.
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