front end slide out first

Mukilteo911 · 08-05-2003, 08:15 PM

I have a 70 911 with 6 and 7s on it. I had it aligned and it drives straight. but when I hit a bump in the road it seems to pull on the side of the bump both in front an back of car.

Also when cornering hard the front slides out real easy. This does not happen in my 77. any ideas ??

porcupine911 · porcupine911's Garage

what are the differences in the two cars?

is your '70 lowered?

the common term for "the front slides out" is "understeer". understeer can result from incorrect tire pressures, front shocks too stiff/rear too soft, front sway bar too stiff/rear too soft, not enough negative camber in the front, and more.

-chris

jluetjen · jluetjen's Garage

The way that Mukilteo911 describes the first issue, it also could be related to a bump-steer situation.

As far as the understeering, could you say some more about the situations when it happens: Are you on the gas, off the gass, on the brakes or using neutral throttle? Does it push on the way in, out or through the middle of the corner? Does it happen on 30 MPH corners, 70 MPH corners or both?

What are your tire pressures? What are the alignement settings? What is your ride height? What sway bars are you using? What T-Bars are you using? Does the car have a limited slip? What size tires are you using? What condition are your tires in? What can you tell us about your shocks?

Eric Mckenna · 08-06-2003, 05:36 AM

YOU MAY TRY TO EASE UP ON THE REAR SWAY BAR AS WELL.. SLID THE BOLTS BACK A NOTCH OR TWO THIS MAY HELP OUT WITH THE PUSH YER HAVIN...
ERIC mCKENNA

Mukilteo911 · 08-06-2003, 07:34 AM

cars is not lowered, I am on the gas comming out of corner about 40mph on your average 90 degree corner. I expect it to slide a little but it does so much more than the rear. New sport shock in frount, rears old but ok. No sway bar in rear, stock bar in front.

Early_S_Man · 08-06-2003, 07:58 AM

Put a rear anti-roll bar on the '70 ... I'm sure that will make it much more neutral. I seriously doubt that the '77 doesn't have a rear bar, and that would make a big difference in handling between the two cars!

tobluforu · tobluforu's Garage

Front is stiffer than rear, therefore you are inducing understeer. You say rears are old-how old? Stiffer shocks in back will help a tad, but you need a rear sway bar to even it out. Ex.When coming into a hard right hand turn, the right rear corner is going to lift like crazy causing more weight to be pushed to the left front tire causing mass understeer. You need to stop this from happening. Lowering helps, torsion bars help, but since you have a front swaybar, I would get a rear to start. My 2 cents.

masraum · 08-06-2003, 08:11 AM

If you have new sports in the front and old rears then the front is likely stiffer than the rear which could be exaggerating the problem.

How about the tire brand/make, age, and inflation. If the fronts are older than the rears then they won't stick as well. If they are a different brand or even the same brand, but a different model there can be a huge difference. What are the front and rear inflated to?

Is there a rear sway bar, and is it connected?

Mukilteo911 · 08-06-2003, 09:37 AM

great stuff guys, thanks.

My 70 is running 38 psi in front and 40 in rear on AVS tires. My 77 has had the rear sway bar removed due to an idiot that owned it before me. Thanks another story.

I think I will look into the shocks and start looking for a rear sway bar.

masraum · 08-06-2003, 10:00 AM

Those pressures sound pretty high if they are cold pressures. The norm is more like 32-34 front and 34-36 rear with the rear being a tad more than the front.

stlrj · 08-06-2003, 10:05 AM

Meanwhile, you might try lowering your pressures up front. 38 psi sounds a bit high to me. I have mine at 29 psi which seems to help.

Joe

steveW · steveW's Garage

My 71 T had a stock rear anti-roll (sway) bar, but nothing on the front. The result was lots of oversteer. Now I have got 22mm Weltmeister all round and with the front on full soft and rear on hard, I have understeer..............I hate understeer!!!!!

Also, I've got 205/60 15 on the 7" rears and 205/55 15 on 6" fronts.

Another thing is that I have taken everything out the front, while very little weight has been taken off the back. This has also resulted in a tenency to lock the front brakes quite easily!

Playing with tyre pressures also makes quite a difference

However, I suspect you are either running too much camber on the rear and not enough on the front.

Hope this helps.......otherwise put 3 bags of potatoes in the front and keep your tank full!!!

masraum · 08-06-2003, 11:56 AM

Why the taller tires in the rear??

masraum · 08-06-2003, 12:01 PM

Steve W

Many tires will put more tread on the ground with a lower profile.

Looking as some random Firestone tire

205 60 15 tread width 6.7"
205 55 15 tread width 7.0"

You may have more tread width in the front than the back.

steveW · steveW's Garage

Uh.... I was using it as a daily driver and doing a lot of highway mileage so I figured I'd save a bit of fuel...........but I did get more oversteer - I think you might have given me a clue here...thanks

stlrj · 08-06-2003, 02:44 PM

Quote:

I had it aligned

Do you have the printout? Often 911's are aligned to be equal from side to side and not necessarily to spec since the adjustments are very limted particularly if the car has been lowered as most have been.

Joe

jluetjen · jluetjen's Garage

As you can tell from the wide range of suggestions, the answer could be any/all/none of the above. Your best bet will be to work away at it methodically.

1st) Make sure that what you have is set-up correctly. With a street driven 911, there are few if any secret settings that the factory didn't supply. So I'd go around and do the following:

1) First and foremost: Make sure that your tires are set to spec. They are the only contact that your car has with the road (hopefully!). Cold pressures should be 26 psi in the front and 29 psi in the back. Use 32 psi in the front and 35 psi in the back if you're driving the car over 125 MPH.

2) Confirm the ride height. For now you can use the easy method and confirm that the highest point on the lip of the front fendor is about 1/2 inch higher then the highest point on the lip of the rear fender.

3) Confirm the alignment settings.
Front: 0 toe when pressed, 0 camber, equal caster on both sides.
Rear: About -3/4 of a degree of camber and 0 toe to slightly toed in.

It sounds like the lack of a rear sway bar could be your problem (among other things). Be sure that if you get a rear bar, that it will work well with the front bar. What is the size of your front bar? Is it in the stock location just below the trunk? It's not the under the car type is it?

masraum · 08-07-2003, 08:38 AM

The stock alignment specs are designed to give understeer, tire life, mileage, etc... they are a trade off of many things and not really very sporty. With the stock alignment settings (above) you'll have plenty of understeer.

jluetjen · jluetjen's Garage

I'm not disagreeing Steve, although I'm not sure that I'd say that the understeer is excessive, especially for street use. I'm just trying to get back to baseline before we start stirring the pot up even more.

Personnally I like more negative camber on both ends and a touch of toe-out in the front, but then I'm not Mukilteo911 and he may not like the resulting wonder at speed and edginess (dartyness on turn-in), not to mention tire wear.

The other thing is that at least intially the stock settings are safe. In the few years that I've been driving my car (warm months only) I've had two situations were I almost threw the car off the road.

1) Fast sweeping exit ramp which I routinely drive on. One time I took it at 65 rather then 50 as I normally do. The slight swell in the ramp became a fairly serious issue since the car in front of me suddenly slowed up. Big time TTO!

I'm thankful for having had about 8 years of racing experience and Skip Barber because otherwise the car would have been toast.

2) A different time. About a mile up the same road, 2 lane exit ramp where two interstates cross. My 3 year old daughter in a car seat next to me. I'm following a car in the right hand lane which slows up to take the first ramp after the exit. I'm going on across the overpass onto the second ramp so I pull into the left hand lane of the exit ramp and accelerate slightly to about 55 MPH. Lo and behold another car down the road changes their mind about taking the exit and pulls from the right hand lane across my lane (at a 60 degree angle and blocking my lane) and STOPS next to the beginning of the guard rail waiting for an opening on the main highway. This is within about 150 yards of the front of my car and I'm doing 55 MPH!

No time to think -- press the breaks to buy time, check the mirror for anyone behind/next to me and execute sudden lane change while first on the brakes and then on the gas to avoid getting rear ended and to keep the rear end planted. That was very close to being the end of me AND my daughter.

My point -- Dialing out push on a 911 is a great idea, until you need a car that is not too loose in emergency situations. I prefer to err on the side of safety.

HarryD · 08-07-2003, 10:38 AM

I must be slow, but I do not understand which way to slide my Sway Bars to loosen (create oversteer) the car.

I attached this sketch to show the configuration of my Weltmeister front and rear bars:

To loosen the front, I move the drop link from "B" to "A".

To loosen the rear, I move the Drop link from "D" to "C".

I would think to "loosen" the car, I would first adjust the front and then, if more is needed, I would adjust the back.

Do I have it right?