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11-20-2017, 05:29 PM #1
suspension setup for a mostly street with strip usage
I just purchased a steeda K-member and want to change up my set up a little. I do most of my driving on the street but want to start drag racing more often. I am not look at getting serious so i will be keeping a 6 speed and the IRS.
Here is my setup as it is:
Front: oem struts H&R race springs
Rear: Viking DA shocks H&R race springs.
With it still being primarily a street car in mind what would be the best setup to run?
I am thinking a different spring in the rear to match the vikings and then one of the following.
- Option A: viking DA front coilover
- Option B: MM front coilover
- Option B1:MM street series coilover with 225# springs
- Option B2: MM sport series coilover with a 350# springs
- Option C: keep it spring in perch in the front and get a Single adjustable strut and call it a day?
- Option D: ?
What do you think?
Last edited by SVT_Troy; 11-20-2017 at 06:49 PM.
11-20-2017, 07:08 PM #2
With a drag racing rear suspension you are fundamentally trying to put as much of the engine's power onto the track through the rear tire's contact patch and without wheel hop and with minimum chases twist as possible. The front suspension provides the way to either place more or less of the car's total weight onto the rear tires.
The first thing you want to do is build your rear suspension to not squat and also not rise. It will look for all intents and purposes as if the rear end were solid mounted. Here is a YouTube video of WV_Snake (Harold Horton) leaving the line at WCF 2016. Watch from about the 1:10 point. Harold's rear suspension has very little movement and what movement it has pushes the tire int the track w/o a perceptible rise in the rear of the car.
Harold Vid <= Click. Watch the top of the slick and the top of the rear wheel well arch. While you are looking at stuff watch how and how long Harold's front suspension keeps the front tires off the ground.
The vid of how the rear suspension works is essentially how you want your rear suspension to work. Suspension setup is engine power level dependent. There are a number of good websites that deal with four link suspension setup. A mustang with a IRS will not benefit from the knowledge at those sites but a stick axle car will because the OEM setup on a non-IRS car is basically a four link.
When you get to the IRS setups you will end up building them much the same as a Funny Car rear suspension, which is to say solid mounted. Any suspension you get in the rear of the car will be attributable to the tire being mashed into the track surface. That type of set up typically uses stiff springs, shocks and a very robust rear ARB to essentially simulate a Funny Car style solid mounted rear end. The front suspension is used to control how much weight you transfer to the rear. What you want to avoid is carrying the front tires more than 4 to 6 inches high and more than two car lengths. You do that by using adjustable shocks and controlling how fast and how high they allow the front end to come up. Remember you are only looking for 4 to six inches of daylight under the tires and only for a car length or so.
Important to keep in the back of your mind is do not turn the steering wheel while the tires are off the ground. If you do it will become unnecessarily exciting when they touch down again. I know it sounds stupid but only steer when the tires are on the ground.
If you decide to go the straight axle route then sites like this => Tuning 4 Link Suspensions will become increasingly valuable to you in the setup of the rear suspension so as to launch hard while controlling the car's predisposition to wheelstand.
Robust adjustable shocks and a strong ARB will provide you with the lions share of your chassis tuning capabilities. If you go straight axle you will find some additional benefits from the chassis location of the anchoring points for what amounts to the OEM four link equivalent suspension arms.
11-21-2017, 09:29 AM #3
I can't imagine that the H&R race springs would do you any favors at the drag strip, but that doesn't mean you can't have a good time there. You just need to use a sticky tire. A street radial is not really going to get the job done at the track, unfortunately. Get yourself a set of dedicated wheels/tires for drag strip use. A sticky tire on an IRS does a pretty dang good job.
Since you are "mostly street", then I would recommend you tailor your suspension to that. It looks like you're wanting to go with a coil-over suspension, and that is fine. I just recommend you go through a manufacturer that you can discuss your plans with and let them help you make a decision. Chatting with Maximum Motorsports is quite a pleasant experience, and they will give you some things to think about. Remember, those guys do this stuff for a living. They are your only option, but definitely a good one.
11-21-2017, 11:46 AM #4
11-21-2017, 03:42 PM #5
Thanks guys, I believe I have a general understanding with what works on paper to make suspension work at the track. With that said I do not have experience with brands and what has worked “in the field” for those before me. I’m not looking to build the most optimal drag racing setup but something that would be better than what I have now since I’m refreshing my front suspension. If that means rebuild my OEM struts and stick with my H&R springs that’s fine with me.
I did not lay out my suspension setup as I am just trying to see what others have had success with and recommend for my purpose. I have a full FTBR rear, Ford racing cover, Wavetrac diff, Mark Williams caps with ARP studs, Gforce halfshafts, PST driveshaft with the pionion angle set, 26 spline in my T56, and an RXT.
I have a pair of Weld RTS’s in 15x10’s and Hoosier slicks. If I don’t like the slicks I’m thinking about trying the QTP’s next. Either way there will be a pair of bias plys out back for the track. I’m looking for a deal on a second pair of Welds that I want to run MT street SS’s only for the street.
Last edited by SVT_Troy; 11-21-2017 at 04:04 PM.
11-21-2017, 07:55 PM #6
- Join Date
- Aug 2004
- Horsham, PA
I just did a 1.36 on IRS full weight plus, stock k member, 28" Hoosier slick with 650rwhp with viking DA/stock springs rear (3c 7r), and viking da/stock springs front (10c7r). I'd get the Viking DA fronts with coilover springs, and eventually add to them the da rear coilovers for IRS that will be coming out soon.
Then the IRS housing broke.
- - - Updated - - -
11-22-2017, 01:37 AM #7
Whenever the rear of the car squats you are unloading the rear tire. The easiest way to identify squat is to watch the to of the rear tire and the top of the rear fender well arch. When the rear of the car does not 'squat' but rather stays the same or rises the tire is being loaded rather than unloaded.
The easiest way to tell if the car is level or rising is to watch the distance from the top of the tire to the bottom of the rear fender well arch. If it decreases the car squatted and unloaded the tire. If it doesn't change the car loaded the tire. If it increases the car loaded the tire even more.
If you can control the front end rise to last approximately 2 car lengths down the track and no more than 4 - 6 inches of air between the bottom of the tire and the ground you will launch with a minimum of all the car's weight on both rear tires. If the rear fender rises so as to increase the distance between the top of the rear tire and the top center of the wheel well you can actually apply more down force to the tire than the entire weight of the car. If the rear of the car does not rise at all but the car mashes the tire into the ground you will again carry more than the entire weight of the car on the tire.
The condition where you cause the distance from the top of the rear tire to the peak of the fender well arch to increase is only possible on a straight rear axle car — it is not possible to duplicate on an IRS car. That said the higher the engine power level the more the car will like the equivalent of a solid mounted rear axle.
A IRS vehicle suspension can very nicely duplicate the solid mounted rear axle phenomena by literally strengthening and stiffening up everything back there. You will want the stickiest tire you can fit in the rear wheel well and when the car launches it will literally rotate on the centerline of the rear axle as it leaves the line. With this type of rear setup you need to pay particular attention to the front suspension. Front suspension is how you control wheelstands.
Loosening up the shocks lets the front end rise easily and quickly. With a high powered modmotor this can be a formula for disaster because you will get the front end real high, real fast. Suddenly the bottom of the car becomes a sail and the wind drag from the car's forward acceleration adds to the pinion's attempt to climb the ring gear and the next thing you know the wind drag tries to blow you over onto your rear bumper.
Tightening up the shocks on the other hand causes the pinion gear to have to lift the entire weight of the car and the front suspension from the hit. This usually puts a significant damper on dangerous wheelstands.
Last edited by eschaider; 11-22-2017 at 01:55 AM. Reason: Spelling and Grammar
11-22-2017, 06:50 AM #8
- Join Date
- Aug 2004
- Horsham, PA
I was always under the impression that rear suspension is almost more important than front suspension for an IRS car as well (do to wanting it to squat, which I believe goes against what you are stating, again, I'm talking about IRS car as OP has). I guess there are just different trains of thought when it comes to IRS. I completely agree with what you are stating otherwise, it just doesn't seem to work that way with IRS. Or perhaps it's a function of not being able to work that way.
either way, 1.36 60's on IRS at full weight an minimal power seems to be getting it done while squatting, but I'm going sra anyway.
Last edited by ITSTOCK; 11-23-2017 at 09:18 AM.
11-22-2017, 11:21 AM #9
While everyone is entitled to their own perspectives and opinions you might want to try an experiment to help visualize the forces in action as a squatting event occurs.
The experiment involves standing on a bathroom scale with your legs fully extended and then squatting while both feet remain on the scale. If you watch the scale's weight indicator window you will see your weight decrease as you squat. The slower the squat the less the decrease and the faster the squat the greater the decrease.
Now perform the same experiment but start from the squatting position. As you rise (stand up) the scale will show an increasing weight. If you go up quickly the increase will be greater if you go up slowly the increase will be less but still more than your static weight on the scale.
The process is described in detail in first year Physics texts where they speak to motion, force and free body diagrams. The internet has some very good plain language Physics sites that can add considerable depth to the explanation. One of the well written ones that does a good job in the explanation department is the PhysicsClassroom.com.
Most of the time the straightforward scale experiment illustrates the phenomena with surprising clarity.
11-23-2017, 09:11 AM #10
The "squatting" that is seen is the chassis/suspension trying to lift the tires off the ground. But since the tires can't really be lifted off the ground the rear of the car gets closer to the tires instead. When the tires are trying to be lifted off the ground there is less contact pressure between the tires and concrete as Ed is explaining.
Imagine laying in the trunk of the car and grabbing a hold of the rear axle and pulling up on the axle. When this happens the rear of the body goes down simulating the squatting affect. If you were to put a scale under the rear tires and pull up on the axle housing real quick/hard the scales will read less, ie unloading the rear tires.
If you see the rear of the car raise up and the tires being planted into the ground there is a LOT of pressure on the tires/concrete. Since this is true the complete opposite (rear of the car going down) can't be true...you can't have both be true since they are complete opposite actions/reactions.
11-23-2017, 11:48 AM #11
I love you guys!
So im going to keep my current rear setup and see how it works. I am going to add the upper isolator as it currently sits too low. The H&R race springs are slightly stiffer than OEM as they are a lowering spring but i will see if i can just adjust (loosen) compression on the viking DA shocks to make up for stiffness.
As far as the front im not going to get too crazy. I am leaning towards just running MM's sport struts with 350# springs. This will be geared more towards my primary use, street. MM's sport series struts recommend a spring range from 350-400#. Most people that i've read using the sports prefer to go towards the heavier/firmer spring.
With that said I am torn between the sport/350# coilover setup and a street/325# setup. My thoughts are I have a aluminator block (-65lbs) plus a steeda K-member (-19lbs), MM A arms (13.4lbs) and the battery relocated to the rear (35+/-lbs). will this 132lbs be enough weight saved to allow me to run MM's street series strut with 325# springs. With the street struts i can go all the way down to a soft 150# spring which should be optimum for drag racing so i ever choose to go more that route. I just don't want to have crappy/floaty street manners associated with running to light a sprint/strut setup on the street. What to do, what to do.... A good street car makes a less than optimal drag car and vice versa.... that middle ground is what I seek.
If you celebrate, Happy Thanksgiving to all!
11-23-2017, 12:19 PM #12
I should have made my explanation more complete, guys — apologies. Your commentary and my commentary while correct Kevin, are correct with the following caveat.
A SRA car has two lever arms that simultaneously push and pull on the back of the car. The uppers pull and the amount of force they apply longitudinally to the chassis is diminished by the angle they are offset from being co-linear with the car. The lower arm is co-linear with the car and there is no reduction for angular offset in terms of the lift applied to the chassis or conversely the push applied to the tire.
In the SRA example both your explanation and my explanation are spot on, Kevin. The IRS however, is a different if not more complex rear suspension in some important ways.
On an IRS rear suspension we have no upper or lower lever arms that act on the chassis in the same way as a SRA car. The IRS upper and lower A-Arms instead only provide support for vehicle weight. The IRS suspension design essentially isolates the vehicle chassis from the torque loadings that an SRA equipped car experiences. In the IRS model the rear suspension simply provides springing to support the weight of the car. All torque applied to the car is done by the IRS center section through the cradle it is bolted to. Those forces applied to the IRS equipped car appear identical to a solid mounted rear axle in a Funny Car
When we launch an IRS equipped car, the weight transfer from front to back will cause the rear suspension to compress as Steve was observing. There will be no attendant lift (or tire planting) that the suspension can provide through the rear axle mounting geometry. Instead what is occurring is the springs, shocks and ARB components of the car's rear suspension act like a shock absorber softening the rate of application of that weight transfer.
The visible evidence of this softening effect is the amount and the rate at which the car squats as it leaves the line. The IRS equipped cars behave very much like the solid mounted rear axles in the Alcohol and Nitro Funny Cars and Dragsters. The difference is the suspension. IRS suspension is essentially a damper that will soften how hard the car can hit the rear tires. By progressively increasing spring, shock and ARB stiffness you can cause the car to hit the tires progressively harder and harder.
In a race car with a solid mounted rear axle the launching traction is controlled by the tire pressure (and size). By lowering the pressure you increase the launch footprint and by raising the pressure you decrease the launch foot print. Additionally the increased tire pressure will cause the car to hit the tire harder with a smaller footprint. To a point (car dependent) this can improve performance.
By lowering the tire pressure you can create a larger launch footprint but down track the car will not accelerate as well because you are in effect driving on a "flat" tire. The happy medium that we look for is the footprint adequate to provide the best combination of 60 foot time and down track acceleration. That combination while initially somewhat elusive can usually be found in the first three or four passes down the track, especially if your tire sizes are rules limited.
When an IRS equipped car allows the rear springs and shocks to participate in the launch process by allowing suspension movement, the number of permutations of tire size, pressure, spring rate, shock rate and ARB stiffness take a relatively simple puzzle to optimize and turn it into an impossible puzzle to optimize.
A number of years ago a nameless ProMod driver frustrated with his 60 ft times, took a look at his rear suspension and decided to get it as close to the solid mounted rear suspension of his old Alcohol Funny Car as he could. Even with the stiffest springs he still found movement at launch. In a final effort to simulate the solid mounted rear axle he remanufactured his shocks. By taking out all the insides and running a single piece of a large diameter bar stock with heim ends through the now empty shock tubing he was able to both give the appearance of suspension and solidly locate the rear axle.
In time he was discovered and the procedure was disallowed in the rules. Until that time however, his short times improved significantly. Today with the newer technology in the aftermarket ECU's the ProMod cars can leave with significantly reduced ignition timing in first gear so as not to blow the tires off and then ramp in timing as the car goes down track.
An IRS (or SRA) Cobra with an aftermarket ECU can do similar things today. However, the underlying free body diagrams that describe the resolution of forces at launch will always argue for what amounts to a solid mounted rear for an IRS car. Although you can minimize/eliminate low gear wheel spin by pulling timing at the launch, the car will not move as hard or as fast as it would have with the additional timing. The optimum solution is (essentially) a solid mounted rear axle and a properly sized and inflated tire.
As luck would have it and as surprising as it may sound, our IRS equipped Cobra's essentially boil down to miniature Funny Cars.
Last edited by eschaider; 11-23-2017 at 12:26 PM. Reason: Spelling & Grammar
11-23-2017, 04:59 PM #13
I sure hope you didn't type all that on my behalf. I completely understand the IRS vs the SRA differences and why the chassis reacts the way they do.. But it was a great read that others should also understand and I have to admit I'm glad I wasn't the one that wrote it all out..
I was simply making sure that people understand that when a car is squatting (the rearend being pulled up) the rear tires are actually trying to be lifted off the ground. I get a lot of people thinking that b/c the rear of the car is dropping towards the ground (squatting) then the rear tires must be getting loaded harder which is not true.
11-23-2017, 07:12 PM #14
- Join Date
- Apr 2017
On a decent horsepower street car with irs what would be your ideal setup for shock and springs, If you were looking to help plant some power? my car gets driven a lot in the summer, makes 800whp, it is a turbo car. The r888r's helped out a lot with traction, front has stock bilstiens with mm coilovers 12/250 spring rate upr tubular kmember. The rear at the moment just has stock rear shocks with steeda lowering springs. Its also a vert.
11-23-2017, 07:17 PM #15
When I read your explanation, I knew you already understood Kevin.
I took the effort to expand upon my original commentary for those who follow us that might want to understand more of the difference between the IRS style and the SRA style chassis, along with a bit more of what happens and why it happens.
When the realization first hit me a number of years ago I was just dumbfounded. Here we have a street car that wants the same rear suspension treatment that high end drag cars want for unbelievably (or maybe not so unbelievably) the same reasons.
These 03/04 Cobras never cease to amaze me.
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