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Spring change

Suspension Tuning & Optimization

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I’m prepping for a time attack event in a couple weeks. I have a 98 DSM, running 12K front springs and 10K rear springs. The car obviously has some understeer set up in it with those rates and placement. I’m looking to try and get more yaw in the car. Now, I was thinking of simply flip flopping the springs front to rear, but the car does have a decent front splitter, and I don’t want to bottom it out. So my next step was to step up to a 14K rear spring. Unfortunately, I don’t have many options as far as ARBs. I run a stock bar up front and a non adjustable one in the rear. I have an upgraded front bar in my shop that I never installed, so I was thinking about bringing it with me to the track just incase this spring change requires a little stiffness put back in the front. My question is, is my logic sound? I do run a big rear wing as well, so a stiffer rear spring will keep it in the air more. What do you think? Thanks

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By "yaw" you mean a more rapid initial response, or something else?

When are you finding the understeer to be most noticable - high speed, low speed, entry, exit, mid-corner, under braking, under acc'n, or some mix of those?

As a general rule, the end with greater roll stiffness, whether by spring, ARB, or geometry, will be the end that slips more. However, once an inner tyre lifts from the track surface the vehicle's roll resistance is all on the other axle, it's at 100%. Any increase/decrease there will just affect the camber gain in roll - with some vehicles, this camber gain in roll can be so bad that a stiffer front ARB is used to reduce understeer because the reduced +ve camber is of greater benefit than the load/weight transfer being a -ve.

Yes. So I’m looking for for rotation in the car. Usually my push is on corner exit. When I pick up the throttle after the apex, so my thought is load transfer to the rear when exiting is creating the push. I’ve worked on shock adjustments to try and dial it out, but I’m not on a super high quality coilover. KSport RR. They were fine for a little while, but as I’ve learned and gotten faster, I clearly need a more proper coilover. The car is AWD, so I made sure that the droop travel was correct to keep all four tires on the track. The car has upper and lower control arms front and rear, and I’ve raised the roll centers a bit to stay more in line with the COG.

Usually the load/weight transfer will increase tyre slip angle, so it may not be that.

There are some very smart people who can better advise you, but dropping the rear will lowering the CoG with the attendant benefits, and slightly improve the castor angle and gain a little negative camber in turning. Tyre pressures will also affect the tyre's slip angles so may be worth trying a couple of PSI change either way (check the minimum recommended first, though).

That said, a very common reason for running wide is not placing the apex far enough round the corner - making it too early will always cause one to run wide and it will seem like a car rather than driver problem. It may help if you use a later, wider turn in, if it is part of the problem.

I’ll try adjusting my line, But I’m confident I’m ok in that area. I’ll also try adjusting thing like tire pressure and shock settings before taking any big spring or ARB changes. My alignment is pretty tame. 0 toe front and back, bumpsteer is set to .007” (.178mm) toe out under full compression. Camber is -3.7 in front and -3.5 in the rear. I’ll try some base changes before swinging for the fences with a Spring change. It’s easy enough to swap springs in the back of the car.

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