How do you figure out where to make adjustments?

I picked up a few B class cars that I’m trying to tune. The two I’m focusing on are an S2K and BRZ. I feel like with both of these cars I’m sliding A LOT! My tire pressure and temperature is decent once warmed up (215f, 33psi). When I slide my tires chart doesn’t get hotter (it stays clear) so I don’t think it’s a matter of the tires being overwhelmed. I’m running them on the Indianapolis GP and I’m getting 1:40 for both cars. My fastest time on that track is with a R34 GTR (1:39, 4%) so I know the cars aren’t that slow but I’m really confused about all of the sliding that’s going on. I’m not sure what information I should include so please let me know if there is something I should be including.

BRZ:
380hp, 2813lbs

S2K:
368HP, 2916lbs

On both cars I have loosened up the suspension and sway bars a little (not far from stock), dampening is increased (~10.5) and stiffness is decreased (~3.5), differential is about 30%/15%. This is my standard baseline tune. I have tried to loosen up the rear suspension and sway bars a bit but I don’t notice much of a difference. I tried setting both tunes back to default and the problem still exists.

Both cars have all handling mods, aero, and max width tires. The BRZ has street tires while the S2K has Sport tires.

Most of my leaderboard times are below 5% so I’d like to think I’m a decent driver. I don’t really have these problems with other cars so I don’t think it’s a matter of needing the Driver Mod. I threw Race tires on the BRZ and ran a 1:38 (A class, ~630 ) but I still had some sliding so that sort of reinforces my theory of the tires not being overwhelmed. I realize my times are in the top 5% but I notice while I’m sliding just a little bit, other cars are passing me on the inside (online). My other light RWD cars feel predictable where as with my BRZ and S2K I feel like I need to walk on egg shells. I have a much slower BRZ and it is very stable but I get burnt on any type of straight line.

How should I begin troubleshooting this?

Side note: Can I pin/subscribe to this topic so I get email notifications?

Have you tried lowering the accel differential?

What camber are you using? Try -3.0 or even more negative camber.

Describe the sliding more. Are both ends sliding? On gas, off gas? Corner entry, mid or exit?

Sliding usually means something is too stiff. On those cars I would use Anti roll bars in the low to mid teens.

Might be worth showing the whole tune.

My differential is about 30%/15%. Do you think I should go lower?

I have tried the stock alignment as well as -3 camber. I will try giving it a little more negative camber. I was under the impression that if you go past -3 you will have stability issues but then again I already get that.

To describe the sliding a bit more, If I’m on a straight away and see a turn coming up I’ll start braking and the corner braking line will go away indicating I’m near an acceptable speed. Once I turn in it seems like both outside tires lose traction and I’m just sliding sideways. I don’t find myself spinning around and my tires never get hot. It’s just a controlled slide where it is pointing in the direction it needs to go but the car is still sliding sideways a little. It’s not as if I’m sliding in to the dirt but I slide enough that nearly 2 cars can be side by side and pass me on the inside. I never really lose control but it’s like “Oh great I’m sliding again and have to wait until the tires catch so I can get on the throttle”. It seems to primarily slide on corner entry when I’m off the gas. If it slides when I’m off the gas I don’t bother giving it any throttle because the tires are already past the point of grip.

My Anti Roll bars are set to 24/21 for my S2K and 23/19 for my BRZ.

If needed I can post the tune when I get home.

Put your diff down to 20% accel,18% decel and try your roll bars at 10.0/10.0… if you want more turn in/looser,lower front/raise rear arb’s. if you want less turn in/less oversteer raise the front arb’s. i also would recommend camber in the -3.0/-3.5 area,and try you rear toe from 0.0to-0.3. also try setting your tires to 32psi on the rear when warm,33psi will work fine on the front. other things worth trying are softer rear springs,very low bump 1.0-2.0,and rebound on the rear…try in the 7to11 area. I know from experience these 2 cars are not the easiest cars to tune to run without tcs. a roll cage will also help.

Thanks!

Just ran a 1:37 with my BRZ (no assists). Shaved 3 seconds off my original time. A second off my leaderboard time. Once I fine tune it a bit I’m sure I can go from top 5% to at least top 3%.

My tune was similar to what you said minus the alignment and soft ARB’s. I tried to mess with the alignment but I didn’t like how the car felt coming out of the corners. I’ll probably put it in between where I had it and where you suggested. Thanks again!

Consider starting from very beginning. The very FIRST thing one needs to do for a good ride is to set “appropriate” spring rates. Without good spring rates, every other changes are bandages; you are just putting bandaids to a shotgun wound.

The car ALWAYS must be balanced FRONT-REAR first (acceleration-deceleration-ride over bumps). Then LEFT-RIGHT steady state (mid-corner). Then TRANSIENTS = POWER ON-OFF & CORNER IN-OUT.

If the car is sliding all over the place, difficult to get power down, and tricky in braking, chances are the FRONT-REAR spring is way to high. Even if you reduce it, going from very very hard to very hard will not show the change you are looking for. Try 50% of where you are currently. BRZ is a balanced car; rear spring rate should be about the same as the front.

THEN, to control the car roll mid corner use the ARB.

THEN, to control the car’s response characteristics use bump/rebound combo. For stiff springs use low bump high rebound combo. For soft springs use high bump low rebound combo. This allows the dampers to do its job (dissipate the energy going into the spring + energy stored in the spring).

THEN, use the differential to control the car’s attitude during power-off and power-on transients. I find higher diff easier to control (stable) where lower diff allows faster cornering.

BRZ tends to be slippery, I assume, because of it’s stiff modern chassis. Chassis acts as a spring. The car also has low profile tires. All pointing to slippery ride . . . therefore it would benefit from soft suspension.

Once you have figured this out, THEN you can add the AERO to settle the car down even more. If you try to do the above with high AERO settings, you will get very muted response because AERO will overpower the other settings.

Your target should be 1:35 or lower.

Those are my recommendations.

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Wow. This is such a great post and not even just for the BRZ. Thank you, I’m definitely saving this for future reference.

Very good post. I did get the end result I want but I went about it poorly. What you said will help me avoid making the same mistake. Thanks!

Also, 1:35 or lower? geeesh! I was pretty happy with my Top 4% time. Granted I’m sure that means there are 30,000 people better than me but to take about 3 seconds off of my time with 5 minutes of tuning, I’m happy! I agree though, always strive to be the best. I just wish there was some way I could race against the ghost of the #1 spot and then spin his ghost out in the first turn. That’s how you win a race, right?

Yep GRD 4 is pretty handy when it comes to explaining tuning processes. As a matter of fact I had saved an explanation from him of how to tune springs but I lost it. Not sure if it was posted on these forums or on another racing forum I just recognized his name. GRD 4 if you don’t mind can you repost the step by step for springs?

Im not sure if you had lowered the damping and arb to just focus on the springs or if you left them stock and added the damping/arb back once you had found the correct spring rate?

Well, I have learned some more last few months and just starting to get comfortable with the whole process myself with reasonable confidence & repeatability.

My process is designed to work with all aids turned off and NO downforce. The process that I follow is:

  1. Set Springs: Use the weight distribution as guideline but generally continue to lower the springs UNTIL the wheels don’t lock up easily, i.e. you have the control with trigger. If you reach this state, the throttle control will also be reasonably be in control too. Springs alone should be supple enough to absorb the bumps but ALSO stiff enough so the car does not wobble. It’s hard to tell whether the springs are correct or not but once you start playing around with different spring stiffness, you’ll start to see/feel the spring stiffness. Visually it is most noticeable in cockpit view. Use springs to control the straight line braking/acceleration/ride characteristics as springs are the MOST prominent tools.
  2. Set ARB: Use ARB to BALANCE the car in corners. Springs will support the car adequately when moving in straight line but in corner the car requires little extra support. For eg. if the car is stiffly spring at the front the car may need stiff rear ARB for the balance. Stiff = faster response but will also tend to slide more. Soft = slower response but will gripp better. This is true for both springs and ARB.
  3. Dampers: Dampers control how the spring energy will be dissipated; it helps “settle” the wobble. One must use BOTH bump & rebound strategically to match the stiffness of the springs being used. For a lot of slow curb riding, use soft bump + stiff rebound. For a lot of fast sweeping corners, use stiff bump + soft rebound (but rebound still higher than bump). Dampers are the most difficult part to understand and explain.
  4. Differential: usefulness of the differential cannot be overstated but it is also “hard” to feel the ideal zone. Try starting at 80% then reduce by 20% at a time until you CAN feel the difference. My differential settings are typically 30~70% accel and half that amount for the decel. IF you follow “change by 20%” method, you will be able to feel the difference. Generally, higher % will give you better “hook-up” where lower % will give you faster turning (sometimes too fast, resulting in spin). Once you have located the sweetpoints, then you can fine tune.

If you use downforce WHILE tuning, it is much more difficult to “feel” these changes. Once the car feels good to you then add the downforce to gain more confidence.

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If you don’t mind me asking how does alignment fit into all of this? I’m trying to make tis RUF CTR2 just right, and with no alignment changes and just finishing with dampers I’m already 3 seconds up at mazda laguna seca, I’d like to squeeze another 2 seconds out if all possible and I feel like maybe alignment could be the thing to tip iit right over the edge to perfection.

Thank you. This is so very helpful. A lot of what you posted I already knew, but giving me the ability to read it, they way you said it, that gives me confidence and a better understanding of why I do things the way I do when I tune the car. I always say you learn best by learning, and it’s one thing to know how to do something but to understand why or how it works brings a whole new level to your abilities.

Thank you.

I thoroughly agree, PPiDrive. Why or how it works takes long time to learn if you are on your own.

I think “why/how” questions are very important as they reveal the nature of the tuning components. One starts to see the relationships between each components and really start to pay attention to how the car behaves in each situation.

For those of you that have not seen this…it’s a thread started by GRD (thanks!) suggesting the Test Track to debug your tunes… Thought it might help some of you as well. Goes well with this particular thread.

http://forums.forza.net/turn10_postst13698_Test-Track-Air-Field---Is-Actually-Very-Good-For-Quick-Tune-Build-Testing.aspx

Check it out! And, again, thanks to GRD!

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PERFECT!!! Thanks for bringing this to light…I’d never seen this & I’ve never thought about using the Test Track for, well, for “testing” my tunes! It seems as kind of a no brainer now that I’ve seen the thread. Again, thanks for sharing it & thanks to GRD for sharing the knowledge!!!

By the way, there are some very good threads with responses from OGR Moss (and others) on ARBs, as well as, a couple of other threads on alignment. Just search in the Tuner’s Lounge. I’ll try to get some additional ones that I have also liked over time. I’ll try to dig out a list of threads that I pulled together on tuning from this lounge, some great stuff posted throughout time.

Tuning Reference Threads and Information

Check these threads out…

Sorry: Links not working…, will try again…
Sorry about that…trying again…

http://forums.forza.net/turn10_postst221_Tuning-Guide.aspx

http://forums.forza.net/turn10_postst6455_Universal-Tuning-System.aspx

http://forums.forza.net/turn10_postst7220_Drows--Guide--For-Beginner-Tuner.aspx

http://forums.forza.net/turn10_postst13959_Camber-Tuning-Techniques.aspx

http://forums.forza.net/turn10_postst13698_Test-Track-Air-Field---Is-Actually-Very-Good-For-Quick-Tune-Build-Testing.aspx

http://forums.forza.net/turn10_postst5760_ONR-RoadRunner---Damping-Formula.aspx

http://forums.forza.net/turn10_postst13277_True-or-False---Tuning-Statements.aspx

http://forums.forza.net/turn10_postst14462_Three-Minute-Tune.aspx

There was also a “tuning guide” posted by K Steinwand, and another by JezNasty that you might want to check out.

Looks like you have upgraded power before reducing the weight, on the RW drive cars I tend to reduce weight as much as possible and increase the rear tire width, you can get loads of tuning tips but the build has to be right also, in the s2k make sure you reduce the weight as much as possible add handling, I think my stats on my B class s2k is:
6.1
5.5
8.0
on the top 3 not sure about launch or breaking, mine feels pretty good too, doesn’t slide etc, the only thing is I don’t really use B class cars and haven’t played around with it much