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Suspension adjustments/tuning help

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#1
mazdaspd

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I have read the Jim Daniels setup guide in the downloads section but still have a few questions that I would like cleared up...

 

To fix handling issues such as loose everywhere, tight everywhere I understand that you can either raise or lower the rear coilovers and/or soften or tighten the rear sway bar to get the car dialed in. 

 

Lets say at a certain track you want the car to handle better (loose or tight) in a certain direction, what adjustments should be made to fix this? 

 

Assuming these are track side adjustments, without access to scales or alignment equipment, what adjustment should be made first? Rake, sway bar, tire pressures? And which adjustment will give a greater change, do they all have the same effects? Are there any downsides to doing certain types of adjustments to fix handling issues?

 

Thanks!



#2
Steve Scheifler

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Everyone is too distracted I guess, but I'll start with a couple very general thoughts.

By design this class has very few "knobs to turn" so it is a good place to learn a lot about just a few adjustments. You've already mentioned things which impact handling in b oth directions, now read up on cross-weight changes. Remember to do half of your change on each side (one up and one down) to minimize changes to ride height unless you intend that as well. You mentioned tire pressures and that is another thing to tune for a given direction or for a particularly important corner if the trade-offs don't cost more than it helps. then of course there is camber which need not be the same from side to side. Here again, you may gain enough by exiting onto a long striaght to justify being slightly slower somewhere else. Look for where you can improve I cases like that or through very long corners. If you start playing with asymmetric tire pressures and camber it might be helpful to watch tire temps if you aren't already.

As for which you try first, that will depend on what you are feeling and other factors such as where in the corner you need help, turn-in, mid-corner, track-out. Try various things and make notes of what changes.

I think what I wish for most is access to more affordable track time to work on exactly this kind of thing. A busy race weekend with just a couple sessions makes it very difficult and risky. I wonder how often people in other regions get together and rent a track for the day just to test & tune?
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#3
RussMcB

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When I searched on the internet to get a better understanding of the benefits and effects of wedge (especially with regards to SM), I did not find any great explanations (I'm sure it's there, just didn't find it).

 

After reading and thinking, below is what I came up with.  Experts, feel free to correct anything that is wrong.

 

If you had a road course with equal right and left turns, you would want 0% wedge (and symmetrical suspension settings).

 

However, let's say your car is understeering in a right hand corner and you've determined it is hurting performance and/or lap times and you want to address it.  What is happening in that corner is the rear has better grip than the front, so you want to "help" the front end of the car.  You do this by transferring some of the weight from the (overworked) LF to the RF.  By doing that, you are making the RF do a slightly higher percentage of work than it was before.  On the whole, the front end will turn right better.

 

Of course, when you help one area you hurt something else (but hopefully it is a good compromise).

 

Positive wedge (defined as the RF and LR corners supporting more than 50% of the car's weight) will:

 - Help the front grip better in right hand corners 

 - Reduce the rear grip in right hand corners 
 - Reduce the front grip in left hand corners 
 - Help the rear grip better in left hand corners 
 
Normally to change wedge you raise (and lower) spring perches, but similar effects can be made by pre-loading the anti-roll bars (such as, making the RF link longer), or adjusting tire pressures (i.e., adding to the RF and/or LF).
 
Hope that makes sense.

Racer Russ
'99 SM
Marietta, GA
Joined SM class in '13

 

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