harveyf

Great explanation and picture Van!

My N/A track car with an open diff will exhibit some wheelspin of the unloaded rear tire but it is rare. The most common place is on the VIR North course, the turn just past the bridge, which is a right hand turn that leads strongly uphill. I'm personally sort of thrilled that there is one place on the track where I can spin the damn tires Oh, make that tire.

I have the Paragon 944Spec suspension which has a pretty hefty rear bar but my suspension spreadsheet shows pretty good front to rear balance. I would be disinclined to soften up the rear for just this one place on the track. As Van says, it is always a compromise for the total course configuration you are running on.

Here's on of my favorite pics! Road Atlanta Turn 5.

Player0

Thanks for the great explanation on softening the rear. That makes a lot of sense. I really like the balance of the car in most other corners and as someone else mentioned, I'm wondering if I'm going to notice any oversteer elsewhere.

Picking the right line does certainly help quite a bit

The LSD might very well be in the cards as well. My thought was to get the right tires on the car, and then add the LSD perhaps in the summer.

BikePilot

FWIW my 968 has 255s on 9" rears (17") and they seem to fit that rim quite nicely.

V2Rocket

Would be worth a try then to remove the bolts that hook the rear swaybar to the dogbones and swing the bones out of the way, two bolts and its all disconnected...

Van

Yes, that's the easy way - just disconnect the droplink from one side. Then the suspension movement is decoupled.

Player0

Yeah it's pretty easy to disconnect the sway bar under there. I have to replace an axle anyway when it warms up so I'll be under there already.

BTW, I run DE with PCA NER region. I could have sworn there was a rule about R compound tires not being allowed in the beginner run groups, but darned if I can find it now.

So disconnecting the sway might buy me the hill. Is there any reason increasing tire size won't help in general as well?

My other major problem is braking with no ABS. I have the S4s and I replaced the bias valve to give more rear and this has helped a lot, especially with lengthening pedal travel. But the wheels still lock up so early. I can't stop anything like a modern car can.

So back to tires: 225s on 7s and 245s on 8s in the rear sound pretty good and I won't have rubbing issues? I'll probably burn through the existing tires before I change them out. I may want to focus that money on the LSD.

crooster

What brake pads are you running?

Dougs951S

In regards to brakes, I'm pretty against computer aided anything but I too have an issue with no ABS as my car has gotten faster and my available grip has increased. I just don't feel like my stock turbo brakes match my car's speed potential anymore. It isn't like they don't bite hard enough, they just lock up so easily. Would more rubber up front help? My tires are michelin super sports, 10" rears but I'm only running a 225 tire up front on the 7.5. Since my fronts are almost shot anyway, when I get new tires would cramming a 245 up front help with delaying lockup?

9turbo51

'87 951, Hawk Blue, m030 front brakes, 255/40-17 on 9" rims all around, no ABS. No unbalanced or early lock up.
Prior to LSD...one tire fire!

harveyf

If you are truly a beginner, I would advise running a stock setup with modestly priced tires. Those modestly priced tires will start to squeal as you get near the limit, which is an excellent teaching tool. That is why they don't want you running with R-Comps in the beginner groups, which is wise on their part. Instructors don't like a trip into the tire wall any more than you do

It is exciting to think about all the things you can do to improve the performance of the car but until you get a lot of track time under your belt, it won't be the car that is holding you back, it will be your brain. Save your money and spend it on seat time. And a roll bar. And a 6 point harness. And a fire suit. And a good seat. The one performance upgrade I would consider right away is some good track pads, like the KFP Golds that Paragon sells. You'll get tired of running through a set of regular pads in a single DE weekend and the track pads do represent a "bite" or "feel" that you might as well get used to.

morghen

Forgive me if i'm wrong...and if i am...explain why.

The 924NA have way softer sway bars and the early cars have no sway bars on the rears.
Are they faster around a bend than a 951S or a 951S with M030 option? or any 944...?

Softer sway bars means that the unloaded wheel will have more chances to stay on the ground but it ALSO means that the loaded wheel WILL dive deeper into the arch and you'll get more weight transfer and body roll....so even if the unloaded wheel will stay on the ground it will have very little weight on it.

The sway bar connects the two springs and when one is compressed it also compresses the other one..that means that at high compression the force one spring can hold will be aided by the other spring which is also loaded trough the sway bar.

If you have a stiff sway bar and turn into a bend, one spring will be compressed and because of the sway bar the other one will also be compressed. If all four corners are balanced the result is that the unloaded side will not raise and keep both wheels on the ground.
I think that if you do raise the front tire that much it means you chassis is not stiff enough and/or the rear sway bars and springs are too weak and they compress too much.

ANYWAY why are you getting wheel spin in a corner? you should not be near full pedal in a corner....or?

Van

Your understanding is correct, but bear in mind that softest sway bars don't necessarily mean the fastest... Because body roll (due to weight transfer and one side's suspension compressing and the other side's extending) changes *how* the tire is held to the road. E.g. primarily camber, which affects your contact patch , which is your only connection with the pavement.

Suspension setup is really a balance of dealing with surface irregularities in the road, managing weight transfer, and keeping the tires as perpendicular to the road as possible.

In my picture with the right front wheel off the ground, there are a few things going on here - obviously, I have the left side fully loaded, but I'm also on full throttle here (being post apex) so weight is transferred to the rear, taking weight off the front, and, I even bumped the apex curbing, which helped give that wheel an upward thrust.

In a corner, the "apex" is typically the tightest arc or the most steering angle input. From this point, as you go to track-out, your steering angle decreases. Because of the limited power of a 944, as soon as this steering angle opens up, you should be at full throttle.

To the OP, you mentioned you're having this problem uphill on right hand turns - you don't mean the Uphill at Lime Rock, do you? As you crest the hill? It's normal to get wheel spin there, even in a 944.

You'll hear my RPMs spike as I crest the hill... because of the unloading of the car I spin the wheels with an LSD.

harveyf

Van is doing a great job of explaining this, as far as we can go in limited forum environment. It is of course a complicated subject, if it weren't all race teams would set lap records in the first 1/2 hour of practice

If you want to spend some time getting a very good in-depth introduction to suspension analysis, I would recommend the series posted at Far North Racing. Best discussion I've seen on the web, for free.

http://farnorthracing.com/autocross_secrets.html

One interesting thing you should come away with after you do your reading: Springs and sway bars have no effect on ultimate total weight transfer in a corner ie steady state weight transferred to the outside set of tires in a turn. Total weight transfer is only a function of car weight, center of gravity height, and track width.

Van

Yes, this is spot on.

We can use shock tuning (especially with adjustable shocks) to change how quickly or slowly the weight transfer happens - but it's still going to happen

Player0

I run HP Hawk Pro track pads. I know they're not the most aggressive pad out there, but I find they warm up pretty quick and work fine for street use with only occasional squealing when cold.

I couldn't agree more that I don't need this for learning how to drive on the track. But I'm also an engineer so I've been bitten by the technology bug as well. I have fun seeing how much better my driving can get and I have fun tuning the car. Hopefully those aren't mutually exclusive things. But I have heard that non-R tires are better for the inexperienced.

Thanks for the input. I do have new seats that will allow for a harness but I still need to locate and install a roll cage. I wonder if they make a firesuit in size fat

The trouble turn is NHMS turn 4. I'm just about straight going up the hill and I have an instructor yelling for power in my ear but I really have to feather it. Other 944 owners tell me they don't have to do this and are at full pedal going up. I hope to be at limerock at least this year tho! I've been watching that Skip Barber video taken there quite a bit. I feel like I know it already.