A couple of the freeway roads around here have some fairly large bumps in them. For instance, on a section of freeway by my house it is a large sweeping left turn that goes up over another freeway and merges. Where two of the bridged sections come together there is a slight "hump" in the freeway that is maybe 4-6" in height, kind of like a really bad transitional patch job on the sections.

When I hit this going about 60Mph, it's just an up and down feeling, like going over a hump in the road (wow, great description), no big deal. However if I take it at about 80Mph, the car goes a bit sideways. The first time over this bump I was going about 80Mph and almost lost control of the car. :nono: Since I am already in a left hand sweeping turn, it really exaggerates the feeling of the backend of the car trying to slide out.

As I said earlier, there are a couple of spots on freeways around here that I have found that give me the same feeling, and I can tell you I don't like it one bit. What do I need to put on the car to help stiffen it up in situations like this? Strut tower brace? Sub frame connectors? New shocks or springs? I'm stupid when it comes to chassis modifications, so any help you can give would be appreciated.

And before anyone asks, no, it is not feasible to drive slower over these bumps. Speed limit is 75, and depending upon the time of the day, driving 80 will get you run over from behind.

Sean

 

Are you sure it is chassis stiffening? If so, you might want to look at:
http://www.bmrfabrication.com/2005Mustang.htm

On my '99 vert, I had a local fab shop do some custom stiffeneing and it worked well.

However, what you are talking about may be more than just chassis stiffening. Your springs may not be rebounding quickly enough to stay in contact with the road at those speeds. Hit the bump too hard and you may have momentary complete loss of traction. This may explain why it is fine when you are under a certain speed.

Of course, this is PURELY hypothesis, but something to think about.

The only cure I know of for that is stiffer springs/softer dampers which = harsher all around ride.

Now, if the chassis shudders (especially noticeable when going over rail road tracks), than that sounds like it needs to be stiffened. Usually you can feel when the chassis is flexing and requires stiffening, but this
sounds like something else entirely.

Not that stiffening the chassis wouldn't help it would allow the suspension to work better (it would reduce bound/rebound from the chassis that the springs/dampers would also have to deal with), but I don't know if that is the primary cause.

I am sure someone more knowledgable can help you better -- I am just throwing out thoughts.

 

moving this to the tech section since this really is not an exterior mod

 

This could also be a problem with the suspension, not the chassis. The car does have a live axle in back, and while it's an advanced design, live axles do still have a tendency to hop sideways in a fast turn on rough surfaces.

 

I'd say shocks at this point. If I hit a sudden transition in a curve the rear axle on my 05 really jumps / hops. This is a damping problem.

Like one of the guys said, rebound may be a tad slow, jounce may be a bit soft. Some higher end shocks with some rebound adjustability are required to cure this. On rebound adjustment, a lot of drivers get the false sense they are firming things up. What they are really doing is slowing rebound down too much. Where it hurts you is when encountering sucessive bumps quickly ... with too much rebound the the suspension slowly collapses because the tire can't get back up in time for the next bump. Then you bottom out whaich can really upset the balance, especially in a turn.

 

I think a lot of it has to to with the fact that this car has a live rear axle. This has happened to me before and it almost feels like the axle itself slides over. But then again I'm just guessin and really dont know much of what im talkikng about.

 

And people wonder why the SRA v. IRS debate is so heated......

 

I have notcied this a bit on one road I drive right here by my job - very bumpy right in the meat of the curve and notice the back will want to hop out - but also noticed it was because I had my foot in the gas - I tried taking my foot out of it (just lifting on the pedal a bit) as I hit that section and the problem dropped about 85%..... just a suggestion - not sure if it will help you.....

 

The disadvantage of the live axle vs IRS is its sprung mass no doubt. Likely there are many other opinions and lesser considerations. With the right (engineered) spring and shock set up, there is not much left to debate (I'll probably regret saying that here on this forum). The design beauty is in its simplicity and can be made to work. You need the right pieces parts. Not sure why Ford slipped up in this area.

 

Sorry about the placement of the topic, I was going to put it in Tech, but thought it was more appropriate in External Mods. I guess that's why you're the mod.

I've taken these bumps while off the throttle as well and still get the same feeling of the axle slipping out from under me. I'm glad to hear others chime in here, your experiences are exactly what I'm talking about.

Makes sense on the spring recovery rate. So would a combination of new shocks and springs work in conjunction to help reduce / eliminate this feeling? Not sure that the axle is truly slipping out from under the car, but would somehow enhancing the bracing on the axle help stiffen this up as well?

Sean

 

I would start with the Steeda springs. They should be stiffer than stock (react quicker) and don't give too much drop to keep suspension travel high. See if that helps.

If you problem really is over-damped springs, I wouldn't get any new shocks/struts yet as it may only worsen the problem.

 

Not too much you can do with the much higher sprung weight of an SRA without sacrificing ride quality. And even then, you can never get around the mid-corner bump on one tire effecting the other simultaneously (reducing overall traction).

Both conditions are apparent in this situation which is a very good illustration of the benefits of IRS on a steet car driving over rough surfaces (important distinction).

As with everything there are pros and cons. It is just about which outweighs the other. That is why both sides of the argument have strong points and why it will continue to rage along like superchargers v. turbochargers; Coke v. Pepsi; Taste Great v. Less Filling........

 

Sean

If you were outside of the car looking at it go by, i think what you might observe is the wheel grabbing air just after it hits the bump. The axle housing might move around slightly, but it does not need more bracing. You can go with harder suspension bushes, but then you will pick up more road noise and harshess. You will not be happy. This is a spring / shock issue.

There are a number of spring kits out there. Getting spec's on them is difficult but i did get info out of Steeda (200F / 175R vs 165F / 142 R stock).

A higher performance shock would be better than just stiffer springs alone ... and to do the fronts either way you end up with everything all apart ... so do the whole job one time. And you need to do both ends of the car at the same time in the interest of maintaining balance.

I have been a Koni and Bilstein regular for many years, but neither have a product out yet for the 05/06 Mustang. I have a strong recommendation from one of the Mustang part retailers (StangSuspension) for the 5 point rebound adjustable Tokico strut / shocks. I am hearing that the Saleen / Steeda / Roush are just rebranded / spec'ed Monroes (that is what one of my sources indicated to me ... so do not know that for fact ... so accept that with a grain of salt)

I am planning an upgrade on my suspension ... how immediate is hard to say. Looking at the stat's on some of the other reader cars, many have upgraded spring / shock kits. maybe one or more of them will chime in?

In the meantime, anticipate the axle bounce ... usually only requires minor correction to compensate. And think about a spring / shock / strut 'package'. The effort will be more rewarding.

 

Paul,
This is from an article in MM&FF called "Layin' it Low" where the guys from Toyo tires went to Eibach's headquarters to have the springs put on. This part was in the middle of the article.

Here's a link to the article online: Layin' it Low

I hope that's the numbers you were looking for.

 

f1-cobra

Nice bit of info ... thanks. I linke that there is some tunability in the front sway bar. The progressive rate of the front and rear springs is a nice touch too.

 

I am going to try some Tokico D Spec shocks and Eibach's Pro Kit very soon. Hopefully, this will decrease the bump steer that's apparent in this vehicle. I am also going to add a sway bar kit as well. That should really change the dynamics of this vehicle. Lastly, the best mod you can do is wider, low profile tires. Grassroots Motorsports has a good article on Max Performance street tires vs R compouns. Any good Max performance tire will great improve the grip and response of the car. A 235/55 series tire isn't great for handling; too much sidewall.

 

I am leaning the same route, including the Eibach sway bars. Too bad I do not live in Corona any more. That MM article is very informative about the kit and the installation.

Hate to break the news to you but lowering the car will not necessarily correct for bump steer ... I suppose the geometry change could all go in a favorable direction, but that is about as likely as hitting the Mega Lotto. There are probably more than one kit out there, but each is usually developed around that manufacturers 'whole' package (Steeda for instance) I am not sure if Sallen or Roush have gone that far ... I have not come across an article yet professing that.

The main cause of bump steer is the steering linkage geometry relationship to the rest of the front suspension (strut, lower TCA, et al). It's usually optimized by moving the vertical position of the steering tie rod end to the front hub. Steeda has moved the position of the lower TCA, and that adds another dimension to the solution, and may be part of it, but what I think they are primarily doing there is raising the roll center of the front of the car.

Unless you can take the time to actually check the change in bump steer by adding a kit, its a mod you might not want to try. Why, because you are taking it on faith these guys did their homework right and the rest of your front suspension is exactly just like theirs (including ride height).

Now I may have read you completely wrong and you are referring to the car jumping when it hits a bump in a turn ... which is the original point of this thread. That is not bump steer ... though it may sound like it.