NVR2L8 Posted March 21, 2009 Share Posted March 21, 2009 I am trying to get my '07 Shelby GT ready for the HPDE season. I am peparing to do the SS brake lines, pads, ducts, and re-tune next week. The following week I am taking the car to a local race car builder to do a rear seat delete and install a roll bar / chassis bar which will be rear only, not a full cage. The roll bar will be welded in place. As you all know, the lowered car body is off center from the frame. This became more visible when I installed a set of GT500 wheels. It looks like it is off by about .5" or so. My concern is that when I weld a roll bar in the car, will I then be unable to make further suspension and/or chassis upgrades because of the roll bar restricting adjustments, especially the body alignment correction? As mentioned by several responses to my previous threads, it seems that the most important suspension recommendations are the lower control arms and an adjustable panhard bar to correct the alignment. Is this correct? And what other upgrades do you recommend be done prior to welding in a roll bar? Thanks for all your help. Quote Link to comment Share on other sites More sharing options...
mcmmotorsports Posted March 22, 2009 Share Posted March 22, 2009 Before welding the bar in, make sure it adheres to the CCR. Once you put a roll bar in a car, regardless of the purpose of it, it must meet the guidelines set forth in the CCR. If not, your car will not pass tech. With that said, a Roll bar install should not have any effect on future suspension upgrades. Quote Link to comment Share on other sites More sharing options...
NVR2L8 Posted March 22, 2009 Author Share Posted March 22, 2009 Before welding the bar in, make sure it adheres to the CCR. Once you put a roll bar in a car, regardless of the purpose of it, it must meet the guidelines set forth in the CCR. If not, your car will not pass tech. With that said, a Roll bar install should not have any effect on future suspension upgrades. Thanks, Mike. We have reviewed the CCR specs, and will install the roll bar accordingly. Quote Link to comment Share on other sites More sharing options...
mcmmotorsports Posted March 22, 2009 Share Posted March 22, 2009 Thanks, Mike. We have reviewed the CCR specs, and will install the roll bar accordingly. Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 22, 2009 Share Posted March 22, 2009 As you all know, the lowered car body is off center from the frame. This became more visible when I installed a set of GT500 wheels. It looks like it is off by about .5" or so. Uh...with Mustangs, the body and frame are not separate, hence the term "unibody." You won't be adjusting much, other than the front fenders, doors, hood, and trunk. The Panhard bar isn't there for aesthetic alignment purposes, and I'm not sure if I would use it for centering the axle between the fenders while at rest. Has the car been hit and repaired? Bah..being off by 1/2" is pretty much "within spec" for Fords, so don't worry too much about that. You don't need to go nuts by upgrading too many suspension parts for HPDE at this point, but it's your budget. The stock parts are more than adequate for HPDE, and you can upgrade them as the driver improves. Mark Quote Link to comment Share on other sites More sharing options...
NVR2L8 Posted March 22, 2009 Author Share Posted March 22, 2009 As you all know, the lowered car body is off center from the frame. This became more visible when I installed a set of GT500 wheels. It looks like it is off by about .5" or so. Uh...with Mustangs, the body and frame are not separate, hence the term "unibody." You won't be adjusting much, other than the front fenders, doors, hood, and trunk. The Panhard bar isn't there for aesthetic alignment purposes, and I'm not sure if I would use it for centering the axle between the fenders while at rest. Has the car been hit and repaired? Bah..being off by 1/2" is pretty much "within spec" for Fords, so don't worry too much about that. You don't need to go nuts by upgrading too many suspension parts for HPDE at this point, but it's your budget. The stock parts are more than adequate for HPDE, and you can upgrade them as the driver improves. Mark Mark - Thanks for the input. No, the car has never had any type of damage. I am very new to the Mustang world, so I still have much to learn. I have heard that when a Mustang is lowered, like my Shelby GT with the FRPP suspension package, the geometry shifts the rear axle off center. It is this off center position which I am concerned about. With the GT500 wheels on the car, the driver's side rear tire sticks outside the fender by approximately .5", and the passenger side rear tire is flush with the rear fender. I am not looking to spend money unnecessarily, but I also want to fix any problems that will affect handling or performance. Quote Link to comment Share on other sites More sharing options...
Frank Corkran Posted March 22, 2009 Share Posted March 22, 2009 You're talking about an adjustable Panhard bar to compensate for the slight lateral axle movement when lowered that comes from the fact that the bar isn't necessarily horizontal from the factory. Guess what, the axle will move relative to the body on track as the car rolls left/right and moves up/down on the springs. That's inherent to a certain degree in a Panhard. Don't worry about it. You should see how far the axle moves with the old Fox 4-link suspension. The Shelby GT is an very good handling car. In fact, it completely dominates some autox classes. Don't mess with it (except safety items to protect you should the worst happen), just drive it. If you're just starting in HPDE, work on the driver and not the car. That's what HPDE is all about anyway, it's just that most cars will need some improvements to survive track duty as you get faster. As you move up in HPDE you'll have plenty of time and opportunity to educate yourself about suspension and other mods that work (and those that don't) before deciding. Throwing parts at any car without knowing exactly what each will do is not the way to build a fast, safe, reliable track vehicle. Or to maximize your return on investment. In other words - what Mark said. Quote Link to comment Share on other sites More sharing options...
NVR2L8 Posted March 22, 2009 Author Share Posted March 22, 2009 You're talking about an adjustable Panhard bar to compensate for the slight lateral axle movement when lowered that comes from the fact that the bar isn't necessarily horizontal from the factory. Guess what, the axle will move relative to the body on track as the car rolls left/right and moves up/down on the springs. That's inherent to a certain degree in a Panhard. Don't worry about it. You should see how far the axle moves with the old Fox 4-link suspension. The Shelby GT is an very good handling car. In fact, it completely dominates some autox classes. Don't mess with it (except safety items to protect you should the worst happen), just drive it. If you're just starting in HPDE, work on the driver and not the car. That's what HPDE is all about anyway, it's just that most cars will need some improvements to survive track duty as you get faster. As you move up in HPDE you'll have plenty of time and opportunity to educate yourself about suspension and other mods that work (and those that don't) before deciding. Throwing parts at any car without knowing exactly what each will do is not the way to build a fast, safe, reliable track vehicle. Or to maximize your return on investment. In other words - what Mark said. Frank - Thanks, this is just the type of sound advice that helps with my "comfort level" to make the correct decisions. Tom Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 22, 2009 Share Posted March 22, 2009 I have heard that when a Mustang is lowered, like my Shelby GT with the FRPP suspension package, the geometry shifts the rear axle off center. It is this off center position which I am concerned about. With the GT500 wheels on the car, the driver's side rear tire sticks outside the fender by approximately .5", and the passenger side rear tire is flush with the rear fender. A common set of lowering springs (1.5" to 2") won't change the axle offset by 1/2" if the Panhard bar was already reasonably horizontal. By doing some quick geometry, you will find that a 36" long Panhard (not stock length; just an example) would have to be raised or lowered 6" at one end in order to make a 1/2" offset. So, there probably isn't even a total of 1/2" of sideways axle travel in the entire range of motion of the axle, from full droop to full compression. Figuring it backwards, with a 36" long horizontal Panhard, lowering the car 2" will only result in 0.055" lateral axle movement. That's not even 1/16", which is less than negligible. A longer Panhard will cause even less lateral axle movement. If anything, you might want to consider adjusting the mounting height of the Panhard so that it is horizontal at the new ride height (the more horizontal it is at ride height, the less lateral motion of the axle as it travels up and down on track), something that might not be possible with a stock Mustang but should not make a difference in early levels of HPDE. At this point, there could be billions of discussions about Panhard height affecting roll center, blah blah blah...not necessary here, though. Unfortunately, you might be getting too much information elsewhere from people with more keyboard experience than garage or middle-school geometry experience! Mark Quote Link to comment Share on other sites More sharing options...
soundguydave Posted March 22, 2009 Share Posted March 22, 2009 Mark, I both agree and disagree (respectfully) with you on the rear suspension issue... On one hand, I completely agree that the offset caused by lowering is usually nowhere near enough to "require" an adjustable Panhard bar to correct, and that the change induced is usually well under 1/8", lowering distance dependant. That said, however, the offset error is cumulative, and if you're starting with a vehicle that was at the outer edges of "spec" right from the factory, and then lower it, you can wind up with a pretty decent amount of offset. Here, you can wind up with a large net offset, and if it bothers the owner, for whatever reason, I see no issue with throwing an adjustable unit at the car to correct it. If he's measuring 1/2" of offset, he sounds like the victim of a cumulative error, and that is enough offset to warrant correction. It kind of comes down to noticing an issue and correcting it. It may not be a huge issue, but if it's there, and he has the desire to fix it, why not? I do, however, STRONGLY agree with the premise that "seat time" will pay far larger dividends than any piece of suspension kit at this level. Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 22, 2009 Share Posted March 22, 2009 You can disrespectfully disagree..."Jane, you ignorant 5lut!" lol While I agree that it's an unfortunate situation that the body isn't centered on the axle (and cannot be fixed by any body-chassis adjustments as first stated above), I suppose that it's fine to use an adjustable panhard bar to center the body on the axle. However, I would also be cautious that the rear arms are no longer parallel (or at least mirror images of each other relative to the centerline of the car) after making the adjustments, which can put the stock bushings into slight bind (not that they will fight much) while the car is sitting still. The upper arm should be parallel to the centerline of the car. But, if everything is cockeyed back there as it sits and cranking it sideways lines everything up, then cool. Mark Quote Link to comment Share on other sites More sharing options...
soundguydave Posted March 23, 2009 Share Posted March 23, 2009 "Jane, you ignorant 5lut?!!!" Dude, you just dated both of us... When I re-did my rear suspension, I replaced EVERYTHING with adjustables, and while it was a time-consuming effort without an alignment rack, I can categorically state that with the axle centered to within 1/16" (static), pinion angle at -2.0*, and the thrust angle dead on, the three "trailing links" (I just can't let that one go...) are all but parallel to the rest of the chassis. Of course, that all changes when you load the suspension, but as you mentioned, the arc is really very shallow given the length of the bar. I think we can all agree that the axle will offset some amount when the car is lowered, and given that the Panhard bar is the same one that came on the GT, with a higher ride height, there is by definition an offset present with EVERY Shelby GT that left the plant. If we were to assume that the tolerances for frame-side mount, axle-side mount and bar length were to stack up just the right way, then I could see that kind of offset when lowered... Simple fix: throw parts at it!! One question: how do you bind a piece of wet spaghetti? Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 23, 2009 Share Posted March 23, 2009 the three "trailing links" (I just can't let that one go...) LOL! Notice how I only referred to everything back there as "arms." Mark Quote Link to comment Share on other sites More sharing options...
TurboShortBus Posted March 23, 2009 Share Posted March 23, 2009 "Jane, you ignorant 5lut?!!!" Dude, you just dated both of us... Well, I saw that one in reruns! lol Mark Quote Link to comment Share on other sites More sharing options...
NVR2L8 Posted March 23, 2009 Author Share Posted March 23, 2009 "Jane, you ignorant 5lut?!!!" Dude, you just dated both of us... One question: how do you bind a piece of wet spaghetti? OK, then I'm busted too! Dan Akroyd, Jane Curtain, Saturday Night Live, early 70s. Back to the issue at hand. You guys are talking way over my pay grade, but at least I have learned enough to understand the basics of the geometry and the suspension parts that are at play. For now, I will run a few track days with no suspension mods, and then reassess. As I mentioned earlier, "Perfection is the enemy of good". BTW, I would be interested in learning about a good book or manual that gives a thorough explanation of the chassis and suspension. I may be getting old, but I can still learn pretty well, maybe just not as fast. Thanks, guys for all the help. Tom Quote Link to comment Share on other sites More sharing options...
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