Stan944

Following my yesterdays topic on 944 and autoX (and yes, I'll start with improving my driving skills):

The topic of 944 suspension upgrades surfaces up constantly, but I'd like to know the influence of these upgrades on autoX times. Although I probably won't be able to implement it immediately, I'd like to know the path for the future.

Let's say my stock 1983 944 needed 44.0 sec to complete the course. How many seconds (approximately) do I shave off by:
- putting a thicker front stabilizer bar (e.g. from 944S2)
- thicker front and rear stabilizer bars
- more agressive (but still street legal) tyres, currently all-year Bridgestone Potenza RE950, same size P215/60R15
- race tyres of the same size
- 16" rims instead of 15" rims (with street tyres). The aspect ratio would probably go down from 60 to 50?
- 17" rims (is it possible on this car?) instead of 15". The aspect ratio of 40?
- race shocks (currently using Billsteins)
- allignment changes, e.g. front camber from ~0 deg down to -1 deg or even -2deg?
- what else?

Please post even partial answers.
Stan

tifosiman

I'll give a partial answer and say that your N/A would do much better with lighter 16" wheels (like Fuchs) instead of 17" monsters.

Hope others can chime in with some other answers for ya.

Tifo

SoCal Driver

Box the A-arms too.

You are looking for a predictable suspension and tire combination.

Copy some one that is doing consistent fast times.

The rest is up to your ability to utilize it.

M758

You best time upgrades are 225/50 R 15 Race (R Compound) tire.

The smaller diamter improves gearing and the stick rubber adds grip. Beyond that everything else is very minor. To me 17" or even 16" wheels are too big and heavy for these cars. They are fine on the street, but are not as good as the 225/50 R15 because these cars don't have enough power to need more tire either in diameter or width.

Everything else might make the car fast or slower depending if it is done right or not. Suspension tuning takes time and sometimes good things actually make the car slower if they are not done in the right combinations.

Ag951

Definitely, but as a beginner, you might not want to go R yet. They're pricy, they won't last a week if you drive them on the street (so you have to tow or get an extra set of rims and change at the track), and they reinforce bad habits.

- putting a thicker front stabilizer bar (e.g. from 944S2)
Will induce understeer and hurt your times (also it will put you in SP, worsening your pax)
If you improve the front, you have to improve the rear proportionally, or you'll get understeer.

- thicker front and rear stabilizer bars
Will stiffen your suspension, improving tight cornering (but will worsen your pax, SP again, so might not improve overall)

- more agressive (but still street legal) tyres, currently all-year Bridgestone Potenza RE950, same size P215/60R15
Falken Azenis Sport or Kuhmo Ecsta MX or Yoko ES 100 (I think that's the good Yoko) will give you a good improvement for a decent price, and not change your class.

- 16" rims instead of 15" rims (with street tyres). The aspect ratio would probably go down from 60 to 50?
- 17" rims (is it possible on this car?) instead of 15". The aspect ratio of 40?
Will slow your acceleration and braking, hurting your times (and kill your pax as well)

- race shocks (currently using Billsteins)
I'm not sure how good Billsteins are. If they're not as good as Koni Yellows, get the Konis. They're allowed in stock classes, so they improve your cornering, but don't hurt your pax.

- allignment changes, e.g. front camber from ~0 deg down to -1 deg or even -2deg?
Camber helps. It improves cornering significantly, at a small cost to acceleration and braking.

M758

I guess the question is do you want to compete in class, just get faster for fun, or learn to drive better?

Competing in class requires skills and a car prepped to limit of the rules. Usally this means optimizing the car in particular areas since some big things are not legal to you.

Just for fun and fast times then the world open you and R tires are best time improvement possilble. AG951 is right however that you will not learn as much an have big tire bill.

If you want to learn then drive it as it and slowly upgrade where you feel it needs it over time. A good solid set of street tires 225/50 R 15 Yoko ES100's probably work well. Then you can do little things over time. Sway bar here and shock there. As you get better you will feel what the impact of each is. It may take 3 years to complete it since the first year is mostly driving practice and the last 2 are hardware upgrades.

Z-man

Here are my opinions on your possible upgrades:

- putting a thicker front stabilizer bar (e.g. from 944S2)
This upgrade will slow you down, due to increased understeer. (Did you read what I wrote in the other thread?!? )

- thicker front and rear stabilizer bars
Very little change: you will get less roll, but by increasing the stiffness on both sides of the car proportionately, you won't get better handling. (Hint: just get a thicker REAR sway bar!! )

- more agressive (but still street legal) tyres, currently all-year Bridgestone Potenza RE950, same size P215/60R15
IMHO, you'd be better off getting a wider tire, (Like a 225/55-15) while you are at it. I do think the Potenza tires are good performance street tires, BTW.

- race tyres of the same size
No need to go there yet! R-compounds usually shave 1-2 seconds off your time, but only if you know what you're doing!

- 16" rims instead of 15" rims (with street tyres). The aspect ratio would probably go down from 60 to 50?
Again, you may wind up slowing down a little! 16's are a little heavier than 15's, so you have more unsprung weight. Same is true for 17's. The smaller the diameter of the wheel + tire sidewall, the better acceleration you can have (as the cost of a lower top speed).

- 17" rims (is it possible on this car?) instead of 15". The aspect ratio of 40?
See above.

- race shocks (currently using Billsteins)
Again, be careful here: stiffen the front up too much, and you'll be plowing through the whole course! I have Koni Yellows all around, and the fronts are set to full soft (or medium: I forget).

- allignment changes, e.g. front camber from ~0 deg down to -1 deg or even -2deg?
Go with a -1.5 degrees. Some negative camber and performance street tires are you best bet at this point.

- what else?
- A harness system (5 point or 6 point) will help you greatly: you won't be using the steering wheel to hold on: you'll use it more to steer.
- Better brake pads would help too. (Most people forget about the fact they need to stop well!)


-Z.

Ag951

Z-man's what else points are good advice. I have a harness in my Acura, and it really helps.
I thought I put the brake pad (and fluid!) upgrade in this thread, but it must have been the other autoX thread. Definitely an important upgrade (and it doesn't hurt your classing).

hacker-pschorr

Ok, I agree about the wheel weight. What if someone were to buy a set of 16" or 17" wheels that were the same weight or lighter than the 15" 944 wheels? Something like a Fikse wheel. A friend of mine has 18" Fikse wheels on his 928 running 385/30 tires. They felt light to me considering the size. I'll admit I have no idea what the 15" 944 wheels weigh. Anybody have data for an exact comparison?

Ag951

Technically wheel weight isn't any more of an issue than the weight of a battery or something. It's the wheel's moment of inertia that matters. The moment is the sum of the mass of every point of the wheel times that point's distance from the axis of rotation (i.e. the farther out from the axle the mass is, the worse it is. Spin in a chair and extend and retract your arms to see an example).
So even if you get 17" rims that weigh a pound less than your 15" rims, you'll probably have more weight toward the outside (the bigger the diameter, the bigger the circumference, so the more weight you have on the edge).
The best way to compare them, would be put the wheel on something where it can rotate easily (a free spinning hub on a jacked up car is a decent choice), rotate the car with a constant push (such as by putting the speedo up to 10mph each time, then putting in the clutch), and time how long it takes the wheel to stop. The longer the wheel can go from that push, the lower its moment of inertia, and the better it is for acceleration and braking.

bart1

What weighs more, aluminum or rubber? If you have a given width tire, say 225, and a lower profile version of this tire on a larger rim, which will have more inertia? I would say that a 225/45/16 would be better than a 225/55/15 (that should put them close to the same height). Also, you have more sidewall flex on the 15.

-Bart

M758

Guys for autocross the answer is quite simple really.
Smallest diamter wheels and lowest profile. Don't think that you need to maintain stock tire diameter. Infact if you get a smaller tire diamter you effectively increase you final drive ratio. This means more RPM for the same speed. This typically means more power at that same speed. Who cares about top speed in autocross? Remember also a smaller overall tire diameter means even less interia. What is ligheter rubber or air? The onyl reason you want larger wheels to fit larger brakes under it.

The ideal race wheel just fits over the brakes and has the lowest profile tire that fits on that wheel.

Stan944

Thanks guys for your opinions,
Some of the answers surprised me a bit, e.g.:

I thought 16" rims would allow installing 50 (instead of 60) aspect tyres, and allow for faster cornering speed. I though the cornering speed was more important in autoX than straight line acceleration. I didn't see much comments on this...

Similarily, I though stiffer stabilizer bars (front and matched rear) would also let me corner at higher speed. But if it compromizes handling (I wonder in what way?) too much, than it's not good.

I have yet no racing experience (except for 1 autoX), and naively thought I could gain a lot with simple upgrades. Looks like it's not the case.

Making the front camber might help as Z-man mentioned. I'll probably do it one day. Unfortunately, this is my daily driver, and -1.5 deg would probably make it unstable on the highway. I may simply adjust it at the lower strut mount (will it let me make -1.5 deg?), or get the adjustable top strut mounts. The hard part is that I probably need to adjust the front toe after every camber change. It would be annoying to take the car to a shop before and after each race. I can do it myself with elastic strings mounted to the tyres and a ruler, but it's very tedious (I did it once, but it took me many hours...) Also, would alignment changes or adjustable camber plates take me out of a stock car class?

Once again, thanks a lot guys. For now, I'll stay stock, and try improving my driving. But next year I might do some mods!

Z-man

Stan,
-1.5 may cause a little inside tire wear, but not too bad. IT would help balance the outer-edge tire wear from autocrossing!

But if you are concerned, just go with a -1.0 camber: it shouldn't really effect your highway cruisin at all.

Sway bars help handling, but if you go too stiff in the front, you'll get too much understeer. The trick is to get the rear end to be a little more stiff, and that should help with your handling.

-Z.

Ag951

Bart, the problem is that on the border between tire and rim, the tire is empy, while the rim is a solid cylinder of metal. The larger the diameter of the rim the bigger (and therefore heavier) and farther out from the axis that cylinder is. Those are the two factors that increase your moment of inertia, and the two you want to reduce.
M758 has a good point about running lower diameter tires. Unfortunately, my tire profile is about the same as my ride height, so if go with low profile tires, I won't be able to drive over the cord for the timing lights without bottoming out.
Also lower profile tires lower your ride height, which lowers your center of mass, and improves your cornering, always a plus!

Definitely. If you can exit a corner at 45, while a power monster like a vette has to take it at 30, you'll get to the next corner quicker, just because he has to make up all that speed. Keep the small rims, and get small tires for them. Make your wheels look like a 914.

The part that needs the most work is the one between the steering wheel and the seat.
Practice, practice, practice. When you're an expert in a few years, borrow some newbie's stock 944 and take it for a spin, you'll be amazed by how well these cars can perform when the driver knows what he's doing.

Camber plates will change your class. You can do 1.5 on the street without noticible effect.
I have -3 on mine, and when the tires wear out, screw it, I'll buy new tires (or switch left vs. right the first time).

Smart plan. But do the best you can get away with in stock: koni yellows, a good alignment, smaller tires (on a set of track only rims), and a racing harness.