Spring rates for Bilstein Cup coilovers with torsion bar delete?
11-05-2012, 12:49 PM
#61
Race Car
Join Date: Sep 2005
Location: TEXAS
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Tim, some of it is going to come down to your personal preferences and specific setup. Here are some rules of thumb to remember.
Softer settings for a particular end of the car provides more grip - e.g. more grip in the rear yields understeer; more grip in the front yields oversteer.
This applies to springs, damper settings, sway bars and tire pressures. But, softer settings have other draw backs - more chassis pitch, more chassis roll, bigger alignment changes under cornering, tires heating up more, etc.
Sway bars affect over/understeer balance mid-corner - e.g. at a steady-state point after the fore-aft weight transfer has happened.
Turn-in over/understeer is affected by the front shocks' bump or compression setting and rear shocks' rebound setting - e.g. as the weight is transferring forward and the spring are storing and releasing energy, which end of the car has more grip.
Track-out over/understeer is obviously the opposite because the weight transfers back under acceleration.
For the LSD, higher lockup allows for more controlled trailbraking and corner entry, because the back wheels are turning together; but, on corner exit, higher lockup keeps those rear wheels turning together and reduces steering (understeer).
For alignment, more negative camber can make a larger contact patch between the tire and the road under hard cornering, but creates a "triangular" contact patch on the straights that increases rolling resistance (and thus uses more energy).
Toe-in/toe-out also increases rolling resistance, but it can also reduce the slip angles needed to start turning the car - meaning the car turns in quicker/more aggressively. (If you want, think of it this way: if your front wheels have toe-in, when you're going straight, they both have a little bit of slip angle going on, but the slip angles are fighting each other. When you start turning, the inside tire will always have little slip angle fighting with the outside (loaded) tire. With toe-out, by the time the outside tire has some slip angle for turning, the inside tire has even more slip angle trying to turn in the same direction.)
Hope that helps.
Softer settings for a particular end of the car provides more grip - e.g. more grip in the rear yields understeer; more grip in the front yields oversteer.
This applies to springs, damper settings, sway bars and tire pressures. But, softer settings have other draw backs - more chassis pitch, more chassis roll, bigger alignment changes under cornering, tires heating up more, etc.
Sway bars affect over/understeer balance mid-corner - e.g. at a steady-state point after the fore-aft weight transfer has happened.
Turn-in over/understeer is affected by the front shocks' bump or compression setting and rear shocks' rebound setting - e.g. as the weight is transferring forward and the spring are storing and releasing energy, which end of the car has more grip.
Track-out over/understeer is obviously the opposite because the weight transfers back under acceleration.
For the LSD, higher lockup allows for more controlled trailbraking and corner entry, because the back wheels are turning together; but, on corner exit, higher lockup keeps those rear wheels turning together and reduces steering (understeer).
For alignment, more negative camber can make a larger contact patch between the tire and the road under hard cornering, but creates a "triangular" contact patch on the straights that increases rolling resistance (and thus uses more energy).
Toe-in/toe-out also increases rolling resistance, but it can also reduce the slip angles needed to start turning the car - meaning the car turns in quicker/more aggressively. (If you want, think of it this way: if your front wheels have toe-in, when you're going straight, they both have a little bit of slip angle going on, but the slip angles are fighting each other. When you start turning, the inside tire will always have little slip angle fighting with the outside (loaded) tire. With toe-out, by the time the outside tire has some slip angle for turning, the inside tire has even more slip angle trying to turn in the same direction.)
Hope that helps.
11-05-2012, 03:39 PM
#62
Three Wheelin'
The spindles are only US$170 each, cheaper than getting one CNC'd. And the steering arm/ball joint assembly is only US$80. Easy to adjust RC height with spacers...
I'll start a new thread when the parts arrive!
Cheers,
Mike
11-06-2012, 12:28 PM
#63
Rennlist Member
Van, thank you for comprehensive and logically structured explanation of the major set-up parameters - it's really helpful.
I'm wondering if my numbers look sensible so that at least I'm hopefully in the ball-park. The Tarrett swaybars are supposed to be the equivalent of a solid 28mm front & a 22 mm rear bar.
The tyres are R-compound Yokohama A048s - 225/40/18 front & 265/35/18 rear.
Thanks
Tim
I'm wondering if my numbers look sensible so that at least I'm hopefully in the ball-park. The Tarrett swaybars are supposed to be the equivalent of a solid 28mm front & a 22 mm rear bar.
The tyres are R-compound Yokohama A048s - 225/40/18 front & 265/35/18 rear.
Thanks
Tim
11-06-2012, 09:31 PM
#65
How about figuring it out for a PCA stock class car?
Stock weight
Stock Aero
Stock power
Stock brakes
Right height dropped approx 25mm
Sway bars are usually adjustable
Stock diameter wheels/tires
wheels allowed to be 1" wider, typically 255 section width
shocks and springs are free
Stock weight
Stock Aero
Stock power
Stock brakes
Right height dropped approx 25mm
Sway bars are usually adjustable
Stock diameter wheels/tires
wheels allowed to be 1" wider, typically 255 section width
shocks and springs are free
Don't forget the mods I mentioned.
11-06-2012, 10:24 PM
#66
Rennlist Member
Given that the price of spring sets is so low compared to some things we buy for these cars I am always surprised that people get so concerned about buying that 'one' correct set of springs first time. To me its like tires or brake pads, start with a sensible recommendation based on the wealth of real world experience out there, buy a few sets of different rates both softer and firmer and go try them out to see what works best for you.
11-11-2012, 01:31 PM
#67
Rennlist Member
Thread Starter
Got the Bilstein Escort Cup coilovers yesterday. I'm going to repack them and send them to Bilstein Motorsports to have them revalved and rebuilt.
What should I tell them to do to the rear mounting points? Will they put in spherical bearings for me?
What should I tell them to do to the rear mounting points? Will they put in spherical bearings for me?
11-11-2012, 02:47 PM
#69
Addict
Rennlist Member
Rennlist Member
11-11-2012, 06:14 PM
#70
Rennlist Junkie Forever
Just leave the regular rubber shock bushings. You won't notice a difference. You can use a regular style bolt which will never break.
Make sure when you revalve them put the car on the scales so you can give them the vehicle weight at each wheel.
And before you revalve them, you should know very close, what your final spring rate should be as they will need this information as well.
TonyG
11-12-2012, 05:35 PM
#71
Rennlist Member
Thread Starter
I just packed them up and got back from shipping them off to Bilstein. I told them to put in the spherical bearings.
You don't think the rubber bushings will deform or fall apart?
You don't think the rubber bushings will deform or fall apart?
11-12-2012, 05:46 PM
#72
Race Car
just installed my 750lb rear springs and they feel great for my street car. with the 400lb fronts, the car feels very stable taking hard, fast turns and people are checking me out as the wastegate dump opens
11-12-2012, 06:40 PM
#73
Instructor
I'm looking at buying the bilstein escort cup for my 86 951. I will use the car for my dd for the next year or so but also will do a few autocrosses and DE events. Any suggestions for spring rate? I'm thinking about doing the 750 rear and 400 front. Car is completely stock except for wheels.
11-12-2012, 08:02 PM
#74
Rennlist Member
11-12-2012, 09:45 PM
#75
Rennlist Junkie Forever
I use a washer on both sides of the shock eye to keep the rubber in BTW.
TonyG