944 tire problems

[Josh Y]

i have 1" deep set fuchs on the front and 2.5" deep set fuchs on the back with RA1s on an 85.5 944

ive heard and experienced that the 944 is known to push

would putting the deeper set tire on the front, widening the front track, remove the "push" problem and maybe make the front stick a little better?

and would this be bad for the car and/or tires?

any input is greatly appreciated

[ttweed]

would putting the deeper set tire on the front, widening the front track, remove the "push" problem and maybe make the front stick a little better?

The short answer would be "Yes". A wider track and/or larger front tire will make the car understeer less. That said, it may not be the ideal solution to just switch front and rear, although it may be the cheapest. 944s seem to like the same size tire and wheel all around. By putting the narrower tire on the rear, you may find you transition all the way to oversteer. I would try to find a pair to match the rears and sell your fronts.

If money is a problem, and you have Fuchs on it now, you could go to a cheaper set of wheels, like the phone dials or cookie cutters, and sell the Fuchs for twice as much and come out with a net profit.

YMMV,
TT

[Josh Y]

is there an alternate solution to the understeer/push problem? maybe an innexspensive fix or just some tuning advice

[ttweed]

is there an alternate solution to the understeer/push problem? maybe an inexpensive fix or just some tuning advice

I am not a 944 guy, and I don't know enough about your situation to really comment effectively, but I would have to start with paraphrasing the old quote: "What part of this racing thang did you think would be easy and cheap?"

You haven't mentioned the rest of your car's setup, or in what part of the corner you are experiencing the understeer (entry? mid-corner? exit?) Have you done the basics to prepare the car--had the suspension components, alignment settings and corner balance checked? Your understeer problem could be something as simple as not having enough camber in the front to make the tires work well.

If you are just taking your street car and trying to go fast with it, without spending any money, there are only a few things you can do. One is to alter your driving style. If you are pushing on corner entry, you are entering the corner too fast for your car's setup--you need to brake sooner and harder, and slow down enough that you can get the car to turn. The time you lose by braking earlier may be made up on the next straight by the fact that you can get on the throttle earlier once you get the car turned.

You can also try trail braking to put more weight shift on the front end during turn in, but this is a tricky technique, as your front tires will be using some of their grip for braking, still, and have less available for turning. It will allow you to brake later, though, and possibly reduce your lap times, while helping the front tires to bite better on turn in, if you can find the optimal point on the friction circle for the front tires.

Mechanically, there are only a couple of things to try that are simple and cheap. In general, to correct understeer, you want to soften the front end to get more grip. Do you have a front anti-roll (sway) bar? If it is adjustable, go to a softer setting. If not, you might try disconnecting it and see if that helps. The only other adjustment you can make without spending any money is with tire pressures, which is also a stop-gap measure, IMHO. Essentially, you would have to set the fronts to their optimal pressure (to maximize grip) and set the rears at a sub-optimal pressure (probably extremely high) in order to reduce grip at the rear enough to balance the car. This results in less overall grip, however, so it would be a better solution to increase the grip in the front to match the rear rather than just decrease the rear to match the front.

Hope I haven't totally confused you, now.
TT

[Josh Y]

the only modifications that have been made are koni adjustable shocks in front and back, 400 pound springs in the front and camber is maxed out with the stock setup, i think its at negative two degrees all the way around

no sway bars no strut braces, it still weighs 3000 pounds, but im sure the semi sticky RA1s have to help a little bit

all my previous instructors have said my driving style is excellent, i dont enter to hot and i get on the throttle at the right time

oh yeah, and i feel the understeer in the middle of the corner, right after or right at the apex most of the time

thanks for all the help tom
i appreciate it

[ttweed]

the only modifications that have been made are koni adjustable shocks in front and back, 400 pound springs in the front

Are you saying that the front springs were uprated without any corresponding change to the rear spring rates? That sounds like a recipe for a push to me. I've always heard that the 944s are well-balanced in stock form, so it seems to me that spring rates should be upped front and rear at the same time, proportionally, no???

i feel the understeer in the middle of the corner, right after or right at the apex most of the time.

Does this correspond to when you are trying to get back on the throttle? If the rear is too soft, then the chassis will squat at that point and weight will be shifted off the front tires, increasing the tendency to push. If the shocks are adjustable, I would try going full soft on the fronts and full hard on the rears and see if that helps. It sounds to me like increasing the rear spring rates would be the best option, though.

Keep in mind that I am not a race engineer--I only play one on the Internet.

TT

[harnishclan]

Tom is right, you have unbalanced the car a lot with 400# springs in the front. Why so stiff? 250# in the front with 27/28mm bars in the back is a great combination AX/street spring rate. 400 is something you would find on (a smooth) track. To come closer to balancing your setup, you would need to add no less than a 30MM rear torsion bar and place the rear shocks on the stiffest compression setting. The other thing you can do is take 1/2" height from the front of the car if the spring perches are adjustable. I would also check alignment. try to get closer to -3 in front and -2.5 in the back. Old bushings in rear go with at least 1/16 static toe in and 0 with new delrin or metal bushings. Because the suspension will toe out under braking. Of course you may want this with your present understeer condition. With Toyo RA-1 get as much pos caster as you can stand.

[Jad]

Tom gave you excellent advice for a 911 guy

You didn't mention what size RA-1's you were running? Even with your different rims, you should try to run 225's all around.

And even if your driving is right, it may not be right for the car, so go in slower and out faster to compensate for the push or spend money to fix it right. At this point your cheapest fix is probably to put 200-250 lbs springs in the front with 225's all around. That is a decent setup capable of winning the class.

[Josh Y]

well i do have 225 all the way around, just the rears are more deepset than the fronts

but front and rear are 225/45/15

sorry if that caused confusion

at the last autocross i tried going in slow enough to were it wouldnt push at all and it just felt awkwardly slow, ive tried messing with tire pressures, lowering the front and raising the rear and riasing the front and lowering the rear, but i just cant seem to find a good medium

thanks everyone for the help
this goes to show that i am not a car wizz
but thanks i really appreciate it
now if only the chargers would loose so i can do some testing

[ttweed]

well i do have 225 all the way around, just the rears are more deepset than the fronts

Are you running 6" front and 7" rear rims? Or 7" and 8"? Your description of how "deepset" they are isn't the best for determining the size. Look on the back side of the spokes and you should see the size stamped there. It will be in the format "6J X 15" or "7J x 15". You may have to clean off the brake dust and road grime to see the numbers.

If you are running a 225 on a 6" rim in the front, that could be part of the problem--the rim is not wide enough to offer proper sidewall support for the tire, and the contact patch is distorting under load and reducing your front grip in cornering. A 7" (or even 8") rim would help, but if your spring rates are as you say (400lb./in. front and stock in the rear), I don't think that will solve your handling problem. Swapping the front and rear tires, as you first proposed, may help, but it certainly won't be optimal, by any means, and won't let you catch the fast cars in your class.

Now that the 944 experts have chimed in, I think the only real solution (if you don't want to continue "driving around" the problem) is to change the front springs for softer ones, or go up on the rear rates to match, as Jad and Brian have suggested. The only thing a 944 has going for it is its handling (I'm ducking for cover here ), so if you can't keep up momentum in the corners, you are not going to be competitive.

The only other thing to try is using your shocks to "mask" the imbalance in spring rates somewhat. This is also a "sub-optimal" solution, but it's all you have left, without breaking out your wallet. You didn't say if they were single or double adjustable, but I assume they are single? By increasing the compression damping of the rear shocks as much as possible, and reducing the front compression, you will offset some of the impact of your spring rates, but probably not enough to balance the car. A single adjustable shock changes both compression and rebound damping with one knob, so this is not ideal by any means, but the adjustment range for compression is usually much greater than for rebound, and it is all you can do at this point.

now if only the chargers would loose so i can do some testing

Good thing you put in that winkie-smilie thing. There are a lot of people in this town who have been waiting 13 years for the Chargers to finally win a playoff game again!

Good luck, and if you do have 6" fronts and want to see what difference a 7" rim might make, I have a set of 7x15" phone dials with 225 RA1s on them you are welcome to try at the next autox.

TT

[Josh Y]

i like brians idea of adding a 30 mm torsion bar in the rear, ive been meaning to get one, but i didnt know the benefits....
what exactly does the torsion bar do?
and does anyone know were i can get one without spending a fortune with performance products?
and im sorry my tires are 6" and 7"
thanks all

[Jad]

The torsion bar is the rear suspension. A giant bar that twists to control movement. It is not a quick or easy, or cheap, change. I also do not feel it is generally needed. My old turbo 944 had the stock torsion bar and had numerous top times of day. You are getting the car too stiff for AX, where you need body movement for tight corners.

A big adjustable sway bar along with adjusting the shocks should be able to help with the problems, but really you need to lose the 400lbs springs and get bigger rims all around. You can probably find 16 or 17" Boxster take off for almost nothing and buy two sets, just using the rears for all four corners, or look for other equal rims of about 8" width. Get the car back near factory balance, take weight out and enjoy learning to drive for a couple of years without messing with the car.

[Dan Chambers]

i like brians idea of adding a 30 mm torsion bar in the rear, ive been meaning to get one, but i didnt know the benefits....
what exactly does the torsion bar do?
and does anyone know were i can get one without spending a fortune with performance products?
and im sorry my tires are 6" and 7"
thanks all

There are several ways you can balance your set-up; one of the least expensive would be to lose the rear Koni's or see if they can be re-valved to be much stiffer on the compression side of the travel. Or, replace the Koni's with Bilstein's and have them custom re-valved for your set-up. I did this with my '87 944 and was amazed at how much improvement was gained. I was running 200# front springs with adjustable Koni's in front: and Bilstein's in rear. I did not need new torsion bars (an expensive re-fit), the shock re-valving worked and only cost $130.00 for the entire job. (Bilstein is located in Poway.) The re-valved shocks stopped the rear from squatting on excelleration, and the understeer on exiting stopped.

I would have to agree with Jad, though. Before spending any more money, work with the set-up you already have, and focus on slow (smooth) in and fast (smooth) out. It may seem too slow, but check the times at the end of the run. Smoother often feels "slower," but in fact is faster.

One other suggestion: many of the understeering cars are excellerating too hard before the apex, causing the rear to compress/front to lift too fast ... and understeer. Try feeding the throttle just a tad slower/smoother on the exit of a turn. You might experience less understeer.

Just my personal experiences here....

Good Luck!

[pdy]

One thing not mentioned is alignment.

I ran a 924 Turbo for many years, using 225/50-15
Front & Rear. I found that even slight adjustments
to Toe - both front and rear - can make a HUGE
difference in the way a car handles. My 924 Turbo
understeered a lot, but after setting the toe to
near 0° front and rear, it was sweet! It was very
neutral, and I could use the throttle to change
the car's attitude easily in a corner. Keep in mind
that this is for a car that didn't get driven on
the street much. Having no toe-in (or having some
toe out) will tend to make the car wander a bit
on the freeway, and might wear the tires' inside
edges if you drive a lot on the street.

Sure, you ought to have the spring rates set up
right, and shocks will make a little difference,
but the toe setting can change it a lot.

[ttweed]

You can probably find 16 or 17" Boxster take off for almost nothing....

Jad-
If he has an '85.5 944, wouldn't he use the early offset wheels that are the same as the early 911? I think he would need big spacers or adapters to fit the late offset Boxster wheels, no? It was only in '87 that 944s changed to the bigger (late) offsets, IIRC. Once you add the cost of 1"-1.5" spacers or adapters, the cheap late-offset takeoffs are not as great a deal.

For an 8" rim, I think you would want an offset of about 11mm to fit the early cars. The later model rims have offsets in the 40-65mm range, I think.

TT