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  1. #1

    Default Street Car Rear Suspension -- Less is More

    I wanted to share that last year I did a lot of reading about spring rates and sway bar rates on foxbody Mustangs. I've mentioned some of those facts in other threads several times.

    Basically the rear springs on the GT cars and TRX cars are so stiff that very similar if not lighter rates were used on the 1993 Cobra R. Meanwhile the front springs are softer than the R but the front sway bar is nearly the same. On a race car!

    Now let's look at the 1993 Cobra which is respected as a better riding car with good street car handling. It had less sway bar -- front and rear combined -- than the GT cars have only counting what's in front. The front springs are the same as our GTs, the rear springs are the same rate as a 4 cyl LX foxbody car.

    Meanwhile the 93 Cobras have 17x8 rims with 245/45/17 rubber under them and we are rolling on TRX or 15x7 rims from the factory with somewhere around a 225/60/15 with very stiff sidewalls.

    Conclusion? No wonder out cars ride so rough and still don't handle well on street, especially in inclimate weather.

    What is a proper spring vs swaybar suspension tuning balance? IMO basically the sway rate applied to the front is more than adequate for total swaybar front and rear. Further in a front heavy car a strong front and no rear will cause some diagonal load transfer -- inside out and rear to front. On the street this helps balance out the massive oversteer condition

    How should we get there *cheaply*?? If it's a street car, how does free sound? Just remove the four bolts on the rear swaybar and remove the swaybar. Take your car for a drive and see what I mean. Far better ride. Way stronger rear bite, far less oversteer tendency. The inside wheel in back no longer so easily comes unglued and causes the limited slip to blow the outside tire off too. Now it might even turn a corner under hard acceleration instead of going in a circle!

    Other things that I've found also help include:
    - softer 4 cyl LX rear springs
    -softer sidewall rear tires. Get an S or T or TR rated tire if you aren't going to drive mach 2.
    - wider rear tires. A 235/60/15 or 235/55/15 or there-abouts gives quite a bit more rear tire width on the ground
    - narrower front tires. A 215/65/15 is the same height as the 235/60 and adds a little ground clearance. It will just barely rub at steering lock due to height but it's not bad. You do not want a taller tire in rear than front as it transfers weight forward - keep this in mind.

    Why is it important? Because the stock setup causes massive suspension bind and leads to a horribly dangerous snap-steer condition in the rear.

    What basically cures the suspension bind problems and should allow some reintroduction of rear sway-bar or movement of sway from front to rear? A watts link or panhard bar

    I had a strut tower brace and subframe connectors for years. I removed the rear swaybar and added 4 cyl LX rear springs and went to a 1995 rearend and converted to 5 lug with ranger rotors up front and swapped to 17" rims with 245/45 tires all at once on my 1986GT. It was a huge difference but impossible to know why.

    I did one change at a time on my son's 1986 GT convertible. We started 100% stock and 100K miles. We added new shocks and struts. We put 235/60 S rated rear tires on factory 10 hole rims and 215/65/15 S rated in front. We added a strut tower brace and subframe connectors. The car still rode like a lumber wagon -- very hard in the tail -- but was better handling than before we started. It still didn't handle worth anything on the street in even the slightest hint of rain. Come winter or snow or ice -- this was even with 225/60/15 studded mud and snows and weight in the rear during winter last year.

    So enough! This past Sunday was time to settle this and put the theory into practice while (in theory) making the car ride better, handle better, and be much safer

    Our test - ease out on the clutch and floor it while turning left around a median.

    Before- the car violently slid entirely sideways. Once the inside tire spun at all the outside tire blew off also and massive oversteer was experienced.

    After - it went around the median at full throttle while staying in the inside lane

    It's a totally new car in terms of both ride and handling. This upgrade achieved simply by removing the rear sway bar!

    Today it was raining and the theoretical vastly improved predictable handling and traction are there as hoped. The car drove FAR better than before. Night and day better really.

    Will it make much difference on a track? It might depend upon dampeners, tires, etc, but in general I suspect it will. I may test it with my car. It is also lowered around 1.5" via X2's and caster/camber plates and LX springs in back so it is an extreme of less swaybar needed which may exaggerate the findings.

    It would be great if others would also test the rear swaybar removal improvement and post their results.

    Personally I'm sold and won't consider a rear swaybar again until my panhard is in place and my front swaybar is closer to a sane size.
    -- James

    86 Mustang GT - Black with red interior. 5.0 T5 built as Z. Original motor ~1/2 million miles. 18 yr daily, 7 a toy
    85 Mustang Saleen 1985-0006? (Lol) Planning Medium Canyon Red / Grey interior. Mystery. Current project roller, tons of Saleen pedigree

    Also in the stable - 1986 Mustang GT Convertible. Black/Black/Black conversion. 93 leather. VM1 ECU. T5Z
    past foxes - 1989 Mustang LX Sport 5.0 AOD white/tan black top

    I'm a four eyed pride supporter, are you? Become one today!

  2. #2
    FEP Senior Member waggin's Avatar
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    Default

    Going to have to read and re-read this to fully appreciate the results from what seems like a counter-intuitive approach. I love "less is more" solutions!
    '78 Fairmont Box Top w/Straight 6/3-spd Manual Everything
    '81 Zephyr Wagon 4/4-spd
    '84 Mustang SVO 5.0 Swapped semi-junker (I didn't do it!)
    MAF, GT-40, BBK Shorties

  3. #3

    Default

    I'm curious as to what Jack Hidley or Dave Zimmerman would say.

    subscribing
    84 Cougar, 88 HO with 700DP, Edelbrock RPM intake, 1.7 RRs, shorty's and SS exh, T-5, KC clutch, Hurst pro billet, line loc, 8.8, 4.10s, suspension mods....blah, blah,blah.

    71 Comet, 289, Liberty TL, 9", 6.00s, 11.9x @ 112.... blah, blah, blah.

  4. #4

    Default

    I am curious what anyone with knowledge has to say. And look forward to enjoying the comments.

  5. #5

    Default

    I am curious what anyone with knowledge has to say. And look forward to enjoying the comments.

  6. #6

    Default

    Quote Originally Posted by erratic50 View Post
    I am curious what anyone with knowledge has to say. And look forward to enjoying the comments.
    .....ECHO....echo.....LOL
    84 Cougar, 88 HO with 700DP, Edelbrock RPM intake, 1.7 RRs, shorty's and SS exh, T-5, KC clutch, Hurst pro billet, line loc, 8.8, 4.10s, suspension mods....blah, blah,blah.

    71 Comet, 289, Liberty TL, 9", 6.00s, 11.9x @ 112.... blah, blah, blah.

  7. #7

    Default

    If you can get it to quit rubbing, or just straight don't care about tire rub in front, is there any benefit to running taller tires in front than rear? You had said that running taller tires in back than front shifts even more weight forward and causes problems. Would taller tires in front shift weight back, and net a positive result?

  8. #8

    Default

    Shorter tires in back net slightly lower gear ratio.

    Should add effective Ackerman. Will change bump behavior mildly due shock and strut angle.

    toe is relative to where the tire makes contact so that could also be change there.

  9. #9

    Default

    RIP thread...... it didn't turn into what I had hoped, but hopefully it helped someone else
    Last edited by erratic50; 10-19-2017 at 04:11 AM.

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