I think that is the term for what I experienced this morning. While traveling on a freeway interchange transition road there was a slower car in front of me in the fast lane. I passed him on the outside and then pulled back in front of him. The road has a positive incline (slightly banked attitude). My 997 seemed to want to stay in the outside lane rather than make a smooth transition into the fast lane. Please excuse my description.

I recently had the car lowered and aligned, but retained the alignment specs of a stock car. The alignment shop could have aligned the car to GT3 specs at the expense of more frequent tire changes. The GT3 specs would have given me more toe. Would that have helped me with this situation. I travel this transition road almost daily.
I hope this makes some sense to someone.

Doc

 

I refer to what you experienced as "tramlining." There was most likely some type of groove/line that your tires were in.

 

cjv,
That may have been part of the problem. My steering wheel seemed to want to take small bites towards the high side (banked side) of the road, climbing until the curve lessened towards a straight-a-way. I was going about 78-80 mph at the time. Car does not follow rain grooves at all.

 

Yes, that's called tramlining. Crabbing is when your car is traveling straight down the road with it's nose deviated from dead center. Think of it like this. You are sitting in a car that has 4 wheel steering. Turn the wheel slightly to the right or left and all 4 wheels point in whatever direction you turned to. Now imagine that you are traveling straight down the street in this slightly turned configuration. You are crabbing, your rear tires are not directly behind your front tires. This usually happens when your rear end alignment is off or if you have severe frame damage.

 

Thanks Robert. What is the possible genesis of the tramlining problem. Although this isn't a huge problem I want the car potentiated.

Doc

 

CJV or others will obviously have better knowledge of this but I can only draw from my own experience from setting up suspensions. Tramlining usually occurs because of wide stiff sidewalled tires. Even certain tires of the same size are more susceptible to tramlining than others. Since you didn't change wheels or tires, you can rule that out but even with stock alignment specs, installing lowering springs does more than just lower the ride height. I would probably look at 2 possibilities that are causing your problems. You have to think of it this way. The stock suspension has a certain amount of travel up and down. When you lower your car with shorter springs, you are essentially using up some of that suspension travel to make the car sit lower. Although you have normal alignment settings, your control arms etc are not sitting at the same angles anymore. You have essentially slightly modified your suspension geometry. Once aligned, it won't effect camber or toe-in but you may have changes in caster which will induce changes in your car's steering. (Kind of like taking a stretched chopper and adding 2" of preload to the front forks to make the chopper sit lower. The length of the forks will change the way the bike handles. A longer more stretched fork is harder to steer and not as responsive as a shorter fork.) This slight change in suspension configuration could make your car tramline more.

The other possibility is. When you install lowering springs, you are installing springs that are a little stiffer than stock to compensate for the shorter travel. Even a progressive rate spring will be stiffer than stock. Without a stiffer spring, you would experience the same effects that people get when they cut their springs. The possibility of bottoming out and general instability from soft springs with short travel. The stiffer springs will increase the tramlining effect.

I guess the last possibility is that your alignment is off. Maybe the guys did not do it right. I would think the only place that could make sure it was done right is the dealership. The 997 is a new car and some shops may not have experience aligning it.

I may be wrong on all accounts but those are the only possibilities that I can think of. If you went to Arling to get the springs installed and the car aligned then I will just shut up because Arling knows what he is doing. My response in that case would be "**** happens".

 

In addition to Robert's astute analysis, I'd add that whenever you drive a vehicle with wide tires on imperfect terrain, the larger contact patch width tends to kick back leverage against the rotational axes at the wheels and "fights" against running straight intermittently as surface irregularities are traversed. I've experienced this when switching up to GT2 format wheels/tires on my car with no other suspension changes. As Robert mentioned, the sidewall stiffness in a lower profile tire is also key, as any irregularities are transmitted more directly through a stiffer sidewall and resistance to shear forces is greater. With a combination of more compliant sidewall and narrower wheel/tire pkg, I believe "normal" street driving is much easier; it's when you're in the mtns and track where that compliance becomes less valuable in favor of a more responsive setup with higher lateral grip limits. If you got to see some of the Ford GT test mules in testing versus the F360, you'd have seen the test team solve a very disconcerting instability issue in the 360 with a simple tire change. All things being equal, tire changes and pressures can make significant recognizable handling differences.

Certainly, before making any changes, have your alignment checked. And adding toe in or out will generally not solve your problem IMO. What's more, at higher speeds your car will tend to create more outward toe under accelerative forces, so it'd be smart to align for neutrality in general driving (such as commuting) and then get aggressive for track only...unless of course, you don't mind a car that likes to hunt and wear tires often. Hey, it's a hassle to deal with it, but fun on cloverleafs, right?

I'm no expert, just commenting from my own experiences with street and track cars. A good shop that preps street and track cars will be a valuable ally for you in tuning your suspension and optimizing suspension and tire setup.

Have fun. Great car from what I've heard.

 

Dr. Super I concur....