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I'm looking at making some changes for this upcoming track season.
initially, i was looking at camber shims and rear toe links. but then it was brought to my attention regarding some of the cons of shims, and bounced over to camber plates and rear toe links.
but then some friends suggest DSC box for the dampers. which isn't too far off the installed + part price of camber plates and rear toe links + alignment. a big pro of this is the quick reversion back to stock, should I sell the GT4 sometime this year, and the ability to reflash the DSC box for a 991.
which would you guys go with?
i'm continuing my driver mod, trying to up my skillset for progressing through PCA white group this season.
I'm looking at making some changes for this upcoming track season.
initially, i was looking at camber shims and rear toe links. but then it was brought to my attention regarding some of the cons of shims, and bounced over to camber plates and rear toe links.
but then some friends suggest DSC box for the dampers. which isn't too far off the installed + part price of camber plates and rear toe links + alignment. a big pro of this is the quick reversion back to stock, should I sell the GT4 sometime this year, and the ability to reflash the DSC box for a 991.
which would you guys go with?
i'm continuing my driver mod, trying to up my skillset for progressing through PCA white group this season.
thank you.
I recommend the DSC and TPC offset rear toe links. The combination of the two will reduce toe out on hard braking (which creates the rear end wiggle) and corner entry oversteer. I believe this will give you much more confidence driving the car and ultimately faster lap times. The DSC also makes the suspension softer and more comfortable on the street. Email Tom Chan at TPC and he will help you with set up and alignment specs. Tom is fantastic and you’re in good hands with him.
As for front negative camber, I went the shims/LCA inner/thrust arm bushings/tie rod route to widen the track of the car. My particular car was limited to -2.4 degrees of camber in the front. So as it turns out, anything more aggressive will require either longer LCA inners or add camber plates to my current set up. That being said, camber plates is cheaper overall and easier to reverse back to stock. I would go that route if you have any thoughts of selling the car soon. Camber plates alone should give you an extra 1.1 degree of negative camber so that should be plenty of adjustability for your needs.
I don't know much about the DSC controller but there are some threads on it. Seems you would still want some more static neg camber. I went with shims and rear toe arms and got -2.5 deg front camber and -2.0 rear. Caster is ok. Tire wear is fairly even on oem 20in size RE-71r. The other track mods I've done are AP J hook rotors in front and Ferodo DS 1.11 pads. Still a bit concerned about potentially cracking the ceramic discs on the caliper pistons which happened on my GT3.
If you guys don't mind I'd like to share my insight. While Suspension Geometry and Damping Control are both part of a car's suspension system functions, they each influence oversteer/understeer and can have crossover balance effect to each other to a certain extent, Suspension Geometry and Damping Control have completely different functions. To elaborate on each-
Suspension Geometry, in general the most basic form is static wheel alignment angles of camber, toe, and caster. These angle values are set on car at its neutral ride height in prediction for the amount of suspension travel and the rate(velocity) of suspension travel. For example, when the front suspension of a GT4 compresses during hard braking, the amount of negative front camber will increase and the amount of front toe will go outward dynamically to the amount/rate of travel. In particular with the toe going outward during front compression, if a driver trail brakes, this will decrease understeer(car will turn in better) because the toe is more outward(weight transfer to the front helps too but just isolating to geometry here), working as if its "pre-turning". So this is just one example of how geometry affects a car's balance. The car in question here is a GT4 so a few specifics on the GT4, adding alignment shims to the LCA's to increase neg camber also increases the car's track width and caster/wheel base. Using camber plates to offset the strut top inward have the opposite affect. Changing any of these values will affect the car's balance to a certain extent. Most track drivers read the tire wear pattern to make a decision on the adjusting alignment values, but an ideal wear pattern doesn't always directly translate to the quickest lap time on track. The front suspension geometry of the GT4 is very good, not much is needed for intermediate level HPDE use besides alignment shims for up to -2.5 deg front camber, for more than -2.5 deg front camber should have caster bushings. For more advanced level HPDE and time trials, a combination of camber plates, longer LCA inners, caster bushings, and alignment shims is the hot ticket. Having all of these items allows for a greater range of adjustment to achieve the best possible front grip via suspension geometry. Note on the front before moving on the rear- I have heard from reputable shops that on some GT4's they cannot increase beyond -2.0 to -2.2 deg of front camber with the max amount of LCA shims and with upper strut tower slots all the way inward. I have not seen on of these cars first hand so I don't know the reason. Moving on to the GT4 rear, first thing is absolutely must have adjustable(longer than stock length) rear toe links in order to achieve rear ideal range of rear camber for intermediate level and beyond track use. The reason is the stock rear toe link isn't long enough to support the ideal range of rear camber for track use. So for example here by adding front LCA shims and max inward on front strut tower slot to achieve -2.5 front camber and leaving the rear camber at -1.4 as rear camber is limited by the stock rear toe links, this would be a imbalanced car geometry-wise, meaning the front will have more geometry grip than the rear. Of course there are way to mask the imbalance via other system functions but we just talking about geometry right now. Moving on to rear toe, by design the GT4 rear suspension toe's outward during upward travel(during hard braking nose dive/rear lift). During hard braking not only does the weight transfers to the front the rear toe going outward will cause rear instability, with much instability depending the amount and velocity of the upward travel. There are different aftermarket adjustable rear toe links available, they all are longer length than stock allowing for the support of ideal range of track level rear camber, one particular brand was designed specifically to addressed the GT4's dynamic rear toe deviation, whereas with other brands more static "toe-in" is required to match the peak dynamic "toe-out" value.
Damping Control, with however the car's geometry grip is, Damper Control manages weight distribution to each corner of the car affecting the balance of the car(sway bars shares this function as well). Damping control does this by providing damping force(resistance to force) during the suspension's compression(aka bump) and extension(aka rebound). On a completely stock GT4, by adding damping force to reduce the suspension's travel velocity(at appropriates moments) the car's grip will increases taking the balance limit to a higher threshold. The reason is the damping force "smooths down" the rate of weight distribution and thus reduces the toe-out to time rate. Better damping control over stock can be had through electronics(DSC) or mechanical(stiffer springs, stiffer/adjustable damper) or combination of. Here's one example of feedbacks I get, this one from a friend who's a world class championship wiining race team crew chief-
To sum things up, if you are looking for quicker track lap times, either improving Suspension Geometry or Damping Control will do it for you. If you looking to improve tire wear on track then Suspension Geometry is a lot better at achieving that although Damper Control have some crossover affect to help by managing rate of toe deviation. If you are looking to improve the car's stability over bumps and over apex curbing and during hard braking then Damper Control does that. I don't discount on the merits of either system functions, ideally an advanced level track car should have both, plus sway bar settings and differential to match, The Full Setup . Sorry I am of no help suggesting which one of the two you should do. If anything I may have confused you more but hopefully you get the merits of each system function and how they can intertwine to made a decision for yourself.
I'm an analog type and don't sell parts. You do need aftermarket rear toe links to get sufficient rear camber. I use Tarett and I'm sure TPC would work. Whether TPC really helps the toe curve is debatable. Regardless of the toe link, I and many others agree that you need about 3 mm of rear toe per side to settle the rear of the car under braking. If you shim the front LCA to get desired camber you end up with excessive caster. I just completed the mod I listed in the Wiki setup page. I added camber plates and removed some shims. My caster went from 10.66 when shimmed to 9.02 with camber plates. I'm running Hoosiers and wanted a little more negative camber. I went from -2.8 to -3.1 F camber
the set up on my Gt4 evolved from stock to camber plates, TPC rear links and DSC module. -3 F and -2.5 R. castor 9.1. even tire wear, settled under hard braking, neutral set up - very happy.
Whether TPC really helps the toe curve is debatable.
TPC provided hard data on toe curve that any person using a bump steer gauge or alignment machine can reproduce. One unaffiliated rennlist member even did a computer modeling to come up with consistent results to our data.
Originally Posted by Bill Lehman
Regardless of the toe link, I and many others agree that you need about 3 mm of rear toe per side to settle the rear of the car under braking.
Agreed that 3.0mm per side is necessary for non-offset rear toe links to calm the rear.
We run 1.0mm to 1.8mm per side with our offset toe links. Less static toe-in for less expected deviation. The reason we prefer less static toe-in is from our racing experience less toe-in produces less tire scrub, less forward friction. In competition we do everything possible to have an advantage. We understand that this may not matter at all for HPDE drivers, but we still offer to the public the best that we have to offer and something that we are truly proud of.
I installed the TPC rear links and DSC. Front camber at -2.5 and rear at -2.0 with 1mm toe per side. This setup works great for me on a combination street/track car.
I installed the TPC rear links and DSC. Front camber at -2.5 and rear at -2.0 with 1mm toe per side. This setup works great for me on a combination street/track car.
You were able to achieve -2.5 with stock alignment?
I installed the TPC rear links and DSC. Front camber at -2.5 and rear at -2.0 with 1mm toe per side. This setup works great for me on a combination street/track car.
Basically my exact setup...I do have 7 mm spacers up front too. Most GT4s I have seen were able to achieve -2.4-2.5 on the front just with shims and pushing the top of the struts completely in. At -2.5 you are getting close to need the caster pucks for correcting the caster.
Biggest lap time improvement for me came with 19's and Pirelli DH slicks on a track alignment setup. It will be tough to go back to street tires after feeling that grip. Easily gained 3 seconds or more on my familiar tracks.
You were able to achieve -2.5 with stock alignment?
Yes. I achieved -2.5F with shims alone and stock wheels. -2.0R with rear links. When I went to -2.7F and 20" HRE wheels at offset 55 required caster pucks due to very slight fender liner rub.
Buy my car was delivered with -1.9 all around, which seems to indicate I was fortunate for what I have read others report.
You were able to achieve -2.5 with stock alignment?
I forgot to mention that my car is dropped 1/2" and that helps a bit with camber. Also the DSC does make the car a bit more civil on the street. Much appreciated for the long drives.
I am close to needing camber pucks. No rub yet.
Biggest lap time improvement for me came with 19's and Pirelli DH slicks on a track alignment setup. It will be tough to go back to street tires after feeling that grip. Easily gained 3 seconds or more on my familiar tracks.
I have been debating this setup but with Hoosiers.....the thing is I really like driving to the track doing the whole day and later drive back home. Our events are just one day so it means I have to carry more stuff in a separate vehicle to the track just for a day.
But if I do jump into 19" wheels I think I might as well go with slicks....even that PAG warns against using them.
02-11-2018, 09:13 AM
GT4 track upgrades....what to do.
