I am trying to sort out my 1983 Porsche 944 race car. The challenge is understeer. My thought is to install linear potentiometers to determine suspension movement from corner turn-in, apex, and corner exit. My challenge is the car has understeer from apex to track exit in turn 5 at WGI. In all other "slow" corners, the car rotates is is essentially neutral.

 

I encourage you to watch the Suspension Analysis webinar by Roger Caddell for AIM Sports Thursday at 1 PM EDT. It will be available on demand after, but you can ask questions live.

Linear sensors are powerful tools that take substantial calculation and preparation to set up the platform analysis correctly, but it may be worth it for you.

Will post the link, but it’s on the bottom of the AIM-Sportline.com page.

 

Also bear in mind that 4 linear travel sensors are like $1100+ and that assumes that you have the available channels to accommodate, otherwise you'll also need a channel expansion model which is like another $250 I think. That money could also be used to pay for coaching, track time, springs and swaybars to test with, etc. Just food for thought.

-Mark

 

Linear sensors typically need logging rates in excess of the limit of Channel Expansions (100 Hz is their limit).

The best architecture would be to connect the linear sensors to logger channels 1-4 and plug sensors that don’t need to be refreshed as often into the Channel Expansion.

I agree there are probably simpler ways to resolve this specific challenge.

 

Thank you for your thoughts. I am thinking to use a rotary potentiometer mount on the chassis with a cable linked to the suspension lower control arm or trailing arm. I am looking for homemade setups with photos and/or sketches.

I have tested with a 26.8 mm and a 25.5. mm front sway bar and switched front spring rates from 500 to 450 #/". The 25.5 front sway bar and the 450 springs have greatly reduced understeer in the slow corners.

My thought is that the rear torsion bar diameter needs to be increased, currently 31mm to 33mm to improve car rotation. The 33mm is a better match with the 19mm rear sway bar with 3 adjustable positions. I was at 50/50, did not try full hard.

At WGI, turn 1, should be apex to exit quick and in carousel after the bus stop, is where there is the most apex to exit understeer.

I adjusted tire pressures, with fronts 2# less than rears. Perfect for high speed corners, but no effect on slow corner s

 

The shock pots will certainly get you data to help, but you know your basic problem. 50 lbs of spring isn't a huge change. You probably have an on throttle push. Some cars without enough power to break the rear loose can unload the front enough to make it push on exit. Try less from bar / more rear bar / spring change / etc.With more detail about how it's doing it, you might want a bit more rear bump in the shocks too. Are you doing the setup or do you have shop do it?

I don't know your ride heights, but I've also see things like this when the car is on the bump stops (much higher spring rates).

For cheaper than motorsport linear sensors, check out something like http://www.autobahnparts.com/part/te...1nRVKbS1OKuGJ8 or or
Noted below, but you could get satisfactory data for your needs from the channel expansion provided you have an MXL2, MXS, MXP, etc. The Pista was limited to 100 Hz.

I've never used any of those. I usually find the labor and materials fiddling and setting up a cheaper sensors eats up any costs savings.

You have a very known chassis. I would expect you can figure out what is going on without needing the shock pots, but I am always for more data. #DATADriven




On an MXx device, channel expansions run 200 Hz. The 100 Hz was a Pista / Evo4 limitation.

 

[QUOTE=Matt Romanowski;16881788]
You probably have an on throttle push. Some cars without enough power to break the rear loose can unload the front enough to make it push on exit. Try less from bar / more rear bar / spring change / etc.With more detail about how it's doing it, you might want a bit more rear bump in the shocks too. Are you doing the setup or do you have shop do it?

I don't know your ride heights, but I've also see things like this when the car is on the bump stops (much higher spring rates).
You have a very known chassis. I would expect you can figure out what is going on without needing the shock pots.

Matt. Thank you for your response. I believe I can figure it without the shock pots.
1 Most 944's 2.5L NA run front 450#/in spring rates. The front sway bar is. M030 25.5 mm sway bar and the rear has hollow torsion bar 31 mm with an adjustable 19 mm reat sway bar. The bar was set 50/50. The tires were Toyo R888R 2. Was at WGI where he track surface was cool. Air temp wax 70F with totally overcast sky.
3. The car stuck in the carousel,, the line was very close to the curbing, tried to apex a little early at full throttle but could not totally unwind the steering wheel until the end of the curbing at exit.

4. I could go to full stiff on rear sway bar but do not believe it is enough to significantly reduce the exit understeer.
so either smaller diameter front sway bar or larger diameter rear torsion bars.

5. Ride height and take is good

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