Matching T-bar sizes??
 

I've got 22/30 t-bars in my cab with Bilstein Sports and Tarrett adjustable sways. I have been working hard to dial out the loosness or push in the car, but I'm getting a lot of wheel lift. This past weekend at Mid Ohio I got tons of comments about the huge lift in turns #8 and #11. Is the 30 too soft for use with this car and the 22? How high can you go reasonably with t-bars? I need to stay with the t-bars set-up for the TT class I run with Nasa. Any input is greatly appreciated.


John

If you are pushing and lifting too much, soften your front sway bar.

Yeah, you didn't say what your SB size was. The Ragamuffin ran 21/27 with 7 inch wheels all around. I used 19mm SB's on stock thru the body arms (reinforced). The front never lifted that I know of and the steering was nuetral during entry and as expected in the middle and on exit. Meaning perfect as long as the go pedal was down.

You need bigger TB's with wider wheels, we know that. But, if you have 7's in front and you car weighs 2300-2500, I think your 22's are good. (I think, I'm not a F1 engineer). But, you've got to let the front work.

I'll mention that I had Koni adjustable Sports all around, but Steve Weiner points out that shocks have nothing to do with it, they just manage spring movement.

Could the wheel lift be a function of the car being a cab? Chassis flex? I don't think the source of your issue is the torsion bars. I have 22/29s and I think that combo is very balanced.

Mike

Ah, good point. And again, maybe the SB's are too much. I'd put some clay wads in the door jambs and see how much the body moves.

22/30 T-bars
Tarrett 22mm F/R Sways
Bilstein Sports
Door frame re-enforcing
Roll Bar
7.5 & 8.5/17 wheels
I would think the cab flex would make it less likely to lift not more.

John

Charlie told me that wheel lift on your car is a good thing!! ;)

The notion that wheel lift is a problem always puzzles me.

Should we also worry that there's gasoline sloshing from side to side in the tank? ;)

http://forums.pelicanparts.com/uploa...1138778944.jpg

That's the TPC car Randy Pobst (and others) drove to the GT class victory at the last 24 Hours of Daytona.

22/30 is a fine spring combination, but it's only one small part of your suspension package. Other than lifting a front wheel, is the car handling well or poorly? I don't understand what you mean by 'dialing out looseness or push.' Is the car loose, or is it pushing?

Not really. It isn't like the back end is trying to bring up the front and the front is resisting. The front is coming up on its own. And, the point about some lift is valid, but it sounded like your car was way off the ground. Now maybe the observers are not used to seeing this and think it's bad.

Jack's qusetion is a good one regarding the use of terms. I take it that the car pushes, or "loses" some grip in the turn, either on entry or on exit (which can be a real problem). But many racers and especially the roundy-round racers call loose a condition opposite of yours. IOW, the tail won't stick.

Come back and give the forum a walk thru of how the car handles from off-the-gas into the corner to completely straightened out and headed for the next corner. You can differentiate between high speed sweepers and slow tight corners. With that info, you will get some spot on advice from the members here.

Not me, I'm only generalizing.

Ok,
I added the adjustable sway as well as switched to Pilot Sport Cups this year so I've been working at adjusting the suspension. The car pushed very badly everywhere, until I removed the triangulated strut brace. Unfortunately I made several changes at once and have been chasing the handling ever since. The strut bar went out last week before Mid Ohio so I was basically starting over. With the strut bar out the car was very loose at turn in and pushed at exit. I opted to drive several sessins like this to make sure of the symptoms. I then started making sway adjustments. It got a little better, but still not where I want it to be. I'm just concerned my t-bars are mis-sized and I am trying to put a bandaid on a bigger problem. I dialed out the sways some more and will be on track this weekend at Autobahn CC.

John

I really like the 22/30 combo on my '87 coupe. The cars balance is pretty neutral, with a slight tendency to oversteer which I enjoy much more than understeer. I tracked the car last year with 22/28 combo and I constantly fought understeer. I also still have the stock Carrera sway bars and running RA1's for tires.

Don't know if this information helps much, but just wanted to say that the 22/30 is working really well for me.

Okay. The quickest way to solve your problem would be to spend a day at the track with a suspension guy to work on your setup. Shy of that, I don't think you should be attempting to tune any aspect of your suspension with the strut brace. If the brace is making a noticeable difference in the car's handling, you might have some chassis issues that are more significant than just typical Cab flex.

If you're experiencing push, then 22/30 bars are definitely not your problem. If anything, that combo should make the car oversteer.

As a first step, we should try to get a handle on exactly what you've got in your suspension. By that, I mean everything from wheel widths, shocks (age, whether they've been revalved), bushings, swaybar sizes (and settings, if adjustable), even any mods like a cage or other rigidity reinforcements.

Next up, It'd be helpful to define our terms on the handling. What one person perceives push might be something different to another driver. Also, there are ways a driver's particular driving style -- from corner entry speeds to braking style -- can create oversteer or understeer. Someone might describe a car as oversteering when it's really the driver, not the car, that's creating the problem.

On top of that, it's important to note how the car behaves going into, through, and then out of a turn. Like Milt points out, it's important to pinpoint where it's doing what. All 911's push at low speeds, for example.

I run 22/30's on my car also. Seems to work well in that the car is fairly predictable in its oversteering.

Lots of good pointas and thank you all for the help. Here's a more detailed breakdown of the car.
'84 Cab - 2960lbs w/diver
Bilstein Sports
22/30 t-bars
Tarrett Adjustable sways - 22mm fairly neutral at this point
7.5 F 225/45-17 Pilot Sport Cups
8.5 R 245/40-17 Pilot Sport Cups
No strut brace
Lowered
ERP Bump Steer ends
Poly Graphite Bushings
Elephant rear monoballs
Approx -1.1d F and 2.0d R negative camber
Fairly agressive alignment
1x2 door bar welded re-enforcement
DAS bolt-in roll bar

So, the car is very loose at turn in, fairly settled at mid-turn and understeering a fair amount at exit. I have driven MO three times this year, once for a day in another car, so I have a good feel for everything. I am able to rotate well at mid-turn for this tight corners, but the faster corners make me sweat as I drop speed to keep the wheels on track and fight the oversteer.
Unfortunately I don't have the ability of giving the car to a pro team to set up on track for a day so it's up to me to solve these issues one at a time.
Back to my original question, are my t-bars miss-matched and making me try and compensate for the differences through other adjustments.

TIA, John

I was at MO in May with Potomac and one thing I noticed was the difference in the track surface. My Toyo R1's were screaming like car tires and never really hooked up.

You can listen to them here on the video. Check out the wheel position needed also to keep the car near the apex and the consistent mid-turn corrections needed to keep the back-end from coming around. I've been running the same setup on my car for the past 2 years and it has been pretty predictable except for here with the new surface. Maybe, I'll try Hoosiers next time.

http://video.google.com/videoplay?docid=-8691430556285024777&q=track+day+fun

You have a nice suspension setup, just need to tune it a little. I don't think your t-bars are mismatched. You could go to a 23 in front if you wanted.

So your car oversteers at turn-in and understeers at corner exit? Your swaybar settings, camber, toe and/or tire pressures need to be adjusted. It would be very worthwhile to let another experienced 911 driver take your car out on the track. Ride as a passenger and ask them what they think.

What sort of toe settings do you have?

I tune my car by getting the tire temps dialed in through alignment settings and pressures and then adjusting the swaybars.

Put your strut brace back in. They do wonders for our cars. You should tighen it up a bit to get another 1/2 deg negative camber or so. Get all the negative camber in front that you can. After that get your car aligned to set the camber and toe. Everyone is a little different, but I would seek about 1/2 deg more neg camber in back. Use the resulting alignment settings as your baseline and then proceed as follows.

Get your camber settings dialed in so that you have a flat gradient in tire temps across the tires. Use a pyrometer to check your tire temps (immediately) after your next track session. No majors gradients? -> good, you are maximizing your tire usage. Now adjust car balance with swaybars and/or tire pressures. Gradient? -> adjust the camber settings and then reassess. Once you have flat temp gradients use the sways (preferably) and/or tire pressures to adjust car balance.

Try not to add too much front swaybar as you tune (take away rear swaybar instead) since it will exacerbate your front wheel lift. As Jack said though - a little front wheel lift is not a terrible thing.

What is your ride height? It's hard to tell from your pic how much uptravel you're using. The amount of rear uptravel from the static ride height determines some of the front wheel lift.

I would say that with a 3.2, it being a cab, and overall weight as you listed that you would want a 31mm or greater rear t-bar.

Thanks for the input.
The car is on stands right now, but I think the height from the gound up is like 24.25Fand 24.75R I can't put the strut brace in if I want to stay in the same Nasa TT class so for now it's staying out. 89911 I hear what you're saying about MO, but I had similar issues at Beaver Run so I'm confident about my interpretations. I guess I will work the rear sway bar first and see how it effects turn-in and exist and then fine tune the front. I'll wait until the winter to potentially change the rear t-bar if that looks like a better long-term option. I've done temps a few times and they have been pretty even. For the record I'm using 25lbs cold and into the 32-34 range hot. First few laps of the day are tough, but once I get some heat in them things are good.
I will be at Autobahn CC this weekend so maybe I can get some advice from our resident Pelican racer expert, Chris Streit. I will be carrying extra adult beverages as a form of pursuation.

John

To make sure we are all on the same page, explain what you mean by "loose, settled, and understeer". Too often these terms are mis-used and the problem becomes impossible to diagnose.

Also what are doing with the brake and throttle while this is happening; corner entry, mid, exit?

You said you have sport shocks. Both front and rear or the popular HD front, sport rear?

Corner Entry - trail braking into turn-in. Rear end wants to come around a lot

Mid turn - transitioning to throttle, able to get to apex on fast turns, car rotates quickly in slow turns as the rear still wants to come around

Exit - back on throttle hard, car understeers and pushes to track out.

Bilstein Sports all around

I'll say my driving is not perfect, but I've been experimented with various entry speeds and driving changes and these symptoms are prevalent throughout. Similarily classed cars are killing me by carrying much more speed into the turns.

John

Having the car balanced mid-turn in a high speed turn indicates your tbars/sways are balanced about right.

You should expect oversteer while trail braking. It's a matter of degree, try trail braking less or not at all.

Understeer with hard throttle = normal. The front end gets light. Again a matter of degree. If you have a limited slip that goes double.

It would be helpful if you list your alignment settings.

John - everything except the understeer is standard for a 911 on track. Add some rear swaybar to help with corner exit understeer.

You don't seem to have much front camber - not the best way to go after a corner exit understeer problem but might help to get it up around -1.5 to -2.

Trail braking a 911 into many corners is the fastest way through the corner. You just need to get comfortable with that feeling of the rear end coming around a little. Let it rotate as you trail brake on the slower corners. Once you get on the throttle the rear will hunker down and all will be well.

Cheers,

Jeff