GNALUZU

Earlier this month I took the Turbo Cab on an overnight trip on some back roads. My wife and I did about 500 miles over the two days.

I have noticed that the handling at higher speeds was not as firm as I thought it would be. The front end felt extremely light and the car almost felt unstable at those higher speeds.

Now, for point of reference, I have had the majority of my high speed experiences in front engine cars. I am a HPDE instructor with Club Racing Arizona & BMW CCA, so I am pretty familiar with how front engine cars handle. Is it me? Am I just used to having all of the engine weight over the front of the car and that is resulting in the different feel?

I haven't had a ton of experience with rear engine cars. Do any of you feel that the front end gets a little loose at higher speeds? I have read posts about people using different alignment settings and that the factory settings, for lack of a better word, suck.

If that is the case, can someone post some settings that I can have the car adjusted to?

This car won't be used on the track, but I would like it to feel more stable (if that is possible).

Thanks,

Adam

SimonK

That's the way 911's are. You will get used to the light front. Top speed runs are always a bit floaty in 911's but just trust it, it is planted enough.

texas911

Sounds like typical 911 dynamics to me. You get used to it.

AAHTT

The TT does not and should not feel "extremely light" up front or unstable at speed especially on the street. I have taken mine to 180 mph several times on stock alignment and tires (TX mile) and although there was a very small hint of lightness up front around 140-150 mph, beyond that it became glued to the ground and I was actually amazed at the stability front and rear. There is no way I would call that extremely light.
That said, I have no clue how a cab would react at those speeds since mine is a coupe.
Eclou here has some good alignment settings for street and track which made a difference in handling, but not sure it will affect straight handling at speed.

insite

i 2nd a good alignment check.

the factory alignment specs will actually allow some toe out i believe; this will cause an uneasy, darty feel to the car at speed and also some braking instability. have them aim for around 1/8" toe in back and 1/16" toe in front. this should cure the instability issue.

TT Surgeon

Roger that ^ and keep it in sport mode, 100X more 'stable' feeling at speed, esp on the track.

funcars

Ditto on the alignment. When mine was delivered, I thought it felt a little weird on turn in to the right but not as much to the left. Got the dealership to do the alignment, and they found it well outside of specs. Once at the right specs, the weirdness was gone.

I haven't tracked it yet so I haven't yet moved to more toe-in. Planning on that this summer.

SimonK

He said he was driving front engine cars before. Yes 911’s might feel stable to some but comparing it to my 944 Turbo S or Ferrari I drove they are much lighter at speed. We discussed this at the 6speedonline forum. 911’s do not generate real downforce they have instead no lift management in place. I guess because of the rear engine layout there is no room for rear under-tray diffuser. So car does not firm up with increase in speed like Ferrari does for an example. Rear spoiler only generates 9kg of downforce which is nothing comparing to let’s say Ferraris with rear diffusers generating 200kg+ of downforce. Also, the rear under-tray car diffusers are really effective for downforce, much more than the spoilers. So, what you are feeling is normal. Nothing wrong with your alignment unless severe. But as you say you are the HPDE instructor you should be able to tell if something is really out of spec. 911 do feel a bit light once beyond 150mph comparing to other front engine cars where there is substantial weight over the front wheels and or downforce management is employed. As I said you will get used to it as the grip and stability is all there. However don’t forget you are quickly about 20% faster than in other cars. So a car might be considered more stable at 145mph but you are probably already doing 170mph in a 911TT.

Land Jet

Agree about alignment. The slope of the front hood provides plenty of downforce. Never heard of any 911 type car lifting and flipping.

GNALUZU

Thanks everybody for the replies. I am going to set up an appointment to have the alignment checked. I think that may be the issue.

To clarify a couple of points... The high speed where I felt the problem was between 100mph and 120mph. I haven't taken the car much faster than that because it just doesn't feel planted.

I agree with some of you that a little of this is just going to take time for me to get adjusted to a rear engine car. I'll let you all know the outcome of the alignment after I get it checked.

SimonK, you are right, I am definitely able to tell if there is a major problem with a car. However, with my lack of experience in a rear engine set up I was not 100% sure that this is a major problem. It just feels like something is slightly off.

As for my HPDE instructor experience... I instruct with the BMW CCA and a local club here in Phoenix, AZ. Since 95% of the cars that show up are front engine, I don't have much experience in the rear engine cars. When a student with a rear engine car does show up, we usually put an instructor who either races or has lengthy experience in rear engine cars, so that everybody is comfortable.

Thanks again for all the input. It is nice to have a resource like this board that is filled with such a wealth of knowledge.

Adam

1AS

Just to be clear, our cars can get the nose pushed a bit by the wind at speeds of 100, but I haven't been impressed by wander, or inability to get the car to go where the wheel is pointed. A BMW 850 is realtively impervious to cross wind. I can't really tell the difference between full and empty tank, but given the weight bias of the tt, that may create a discernable difference to some.
Finally, most of the cars that have been lowered are either dead level or have a stance that is slightly nose down. The standard springs do keep the nose of US cars a full inch higher than the engineers intended. If the allignment doesn't give you the feel you want, I'd lower the car. But then, you'll need another allignment. AS

funcars

I wasn't aware that the RoW 997TT ride height was different than the US. In the dealer info that I have, the tables indicate a single height for the RoW/USA 997TT. Was the dealer prep info in the "Product Information" booklet wrong?

Numbers are in mm, and are for RoW / USA:

997TT: 110/110
996TT: 90/110
996TT S: 90/110

1AS

You are right. I wasn't thinking clearly about your circumstance, and referenced the 996tt ride height. AS

funcars

Any idea why the RoW floated upwards to the USA ride height?

Haku

Thanks for your post. Also having my car aligned today as per your suggestion...1/8" toe in back and 1/16" toe in front. Will comment on change of handling.