I don't understand coilover spring rates.

[Lincoln Logs]

Originally Posted by Spacemane969

So would you still recommend a stiffer rate in the rear? What happens to this platform when they are both equal?

I've tested a variety of spring rates and prefer the platform with square spring rates. With higher rear spring rates you start shifting the balance to oversteer. I've found the car to be faster with square spring rates.

My current set up is 8kg front and rear, and with the amount of camber I run I still find the car a touch too loose. I have a 20mm sway bar I am going to toss on and see how I like it before investing in the Karcepts sway bar.

You also need to keep in mind an autocross specific set up is not going to be ideal for a track day and vice versa.

[Goingnowherefast]

Originally Posted by Lincoln Logs

You also need to keep in mind an autocross specific set up is not going to be ideal for a track day and vice versa.

This is a big factor people need to consider. A great autocross setup (generally set up to be very loose/willing to rotate) isn't necessarily an optimum track setup (and vice-versa).

Like others mentioned, modern day tire and aero tech require a massive increase in roll stiffness, thus you see 2/3x increase in spring rates vs. OEM. Keep in mind there's WAY more to the equation, but that's the crux of it. Suspension is there to help the tires work the best they can.

[Clutch Dog]

Gonna hit up the autox set up vs track thing


the difference between a good autox set up vs a "higher speed" track set up is about how the car feels into corners.

We had literally this between myself and a friend at buttonwillow. I had "tamed" my alignement down for track ( true 0 toe front and rear, mediocre camber up front and back, and dialed back caster a tad) and set my shocks to relatively neutral with soft sway bar set up

vs my friend in his ND1 on "racing slicks" with his autox alignment.

My car would lap after lap be comfortable and tractable and readable meanwhile he was "working" his hard, dealing with fidgetiness on braking and mid corner traction.

The biggest influence on this would be sway bar setting and toe out he had. Makes for good turny turny at low speed. Raise the speed and it becomes a handful

This became severely evident towards the middle of the day in our sessions when my set up with 200 tw kumho's was outrunning his set up on 80 tw slicks

it took him 23 more laps to beat my time and only by 2/10ths of a second.

again my set up is a compromise of something someone can run both at the track and autox and also street ( im a full factory interior car)

your dedicated set up's are going to bend rules and ultimately undo what Subaru/toyota had initially designed.

[steverife]

It seems like a well set up/well driven SSC or STX autocross car is good to go on the track with minimal changes.

[strat61caster]

Originally Posted by steverife

It seems like a well set up/well driven SSC or STX autocross car is good to go on the track with minimal changes.

Many people who comment on autox setups haven't setup many successful autox cars. (Hell I'll include myself in that category)

Extreme toe is the only thing I see in autox that doesn't carry over to track, but extreme toe isn't necessary on this chassis.

[wparsons]

Originally Posted by strat61caster

Many people who comment on autox setups haven't setup many successful autox cars. (Hell I'll include myself in that category)

Extreme toe is the only thing I see in autox that doesn't carry over to track, but extreme toe isn't necessary on this chassis.

Depends on what type of course the car is dialed in for too. Most auto x courses favour setups that transition faster vs a setup that holds a bit more G in a long steady state corner, you'll typically see a lot more front roll stiffness for that reason.

[strat61caster]

Originally Posted by wparsons

Depends on what type of course the car is dialed in for too. Most auto x courses favour setups that transition faster vs a setup that holds a bit more G in a long steady state corner, you'll typically see a lot more front roll stiffness for that reason.

Most national level competitive style courses are fairly balanced between transitional and sweeping elements.

Edit: here's this year's STX champ

[steverife]

I think most good FRS autocross setups are reasonable front bars, stockish rear bar, and reasonable rates (400/400 or softer, or something like a 280/504 or 300/450 built around an OS Giken) and minimal toe.

[Lincoln Logs]

Originally Posted by steverife

It seems like a well set up/well driven SSC or STX autocross car is good to go on the track with minimal changes.

It will be good, just not optimal.

Originally Posted by strat61caster

Many people who comment on autox setups haven't setup many successful autox cars. (Hell I'll include myself in that category)

Extreme toe is the only thing I see in autox that doesn't carry over to track, but extreme toe isn't necessary on this chassis.

I've had both, and successfully set up both. I worked in a shop for 5 years doing this. A vast majority of autocross set ups can work at the track but the reality is a track focused car is going to have a different set up. Alignment is a big one. Another element that is often overlooked is the rules for some autocross classes cause you end up with less ideal modifications. Stock class comes to mind for this. STX is an outlier for the crossover and why it is one of my favorite classes, STR has a lot of crossover too.

Originally Posted by wparsons

Depends on what type of course the car is dialed in for too. Most auto x courses favour setups that transition faster vs a setup that holds a bit more G in a long steady state corner, you'll typically see a lot more front roll stiffness for that reason.

Bingo.

[949 Racing]

Xidas were mentioned here so I though I'd chime in.

Everything else being equal, spring rates need to be tailored to roll moment. Roll moment is basically how much force is trying to roll the suspension over. Bigger, stickier tires generate more roll moment.

The other factor is CG (Center of Gravity) vs RC (Roll Center). Cars are designed with RC below CG. Imagine the RC is a virtual pivot down the centerline of the car. The CG is above that so when you turn, the CG generates a moment (leverage) over the RC. The farther the CG is from the RC, the more leverage it has.

With pretty much any car suspension, the RC drops when you lower the car. Because control arms can not be infinitely long, the RC will drop faster than the CG. Meaning that when you lower your car 2", your CG drops exactly 2". Your RC however, might drop 3 or 4 ", depending on suspension geometry. Why does this matter? Because, as we noticed earlier the further the CG is above the RC, the more leverage it has. This effectively lowers rolls stiffness. Lowering your 86 2" is the exact same effect as putting smaller sway bars on.

Combine this reduction in roll stiffness with a greater roll moment from bigger tires, then reducing total bump travel because it's lowered, and you have the recipe for lotsa bottoming. This is why such high spring rates are required to keep a lowered car with sticky tires off the stops.

So think about the roll moment you plan to tune in (how much grip from wheels/tires) and how low you will run it when choosing spring rates.

The 86, in our opinion actually has quite a bit of roll stiffness relative to other cars in this segment. Also has very high bounce frequency OEM, meaning fairly stiff springs. This is why our Street spring pack (175/150) for the Xidas is so soft. We actually had to regress from OEM a bit to get the ride quality we were after. Those soft rates still work on track but only with medium grip tires and with the damping adjustment cranked up. Not a great track set up but still fun if you don't have a full track wheel/tire setup and are focused on comfort.

The Race spring pack (500/500) was balanced for 255/40/17 Super200 tires on 17x9 and about stock weight. Just enough spring to just kiss the stops here and there on the bumpiest tracks. They're pretty busy on the street but liveable if you are after max grip with your race wheelset.

As someone else mentioned, valving, shock length, bumpstop shape/durometer/length all play a role in compliance, ride height and grip. I'm still not sure how so many 86 owners run 3-4" below stock. Out 255's smash into the chassis when we got that low unless we ran springs so hard that the suspension stopped working. Compliance = grip. The stuff Blub will soak up with impunity still amazes us.

[norcalpb]

Originally Posted by Lincoln Logs

I'm not saying it is ideal, the Xidas are just going to behave BETTER than the competition in that scenario. Shock behavior while bottomed out IS important. You can adjust that with bumpstop rate, length, shock valving, etc.



Take any modern Super-200TW tire, install a 245 or 255 on a 17x9 and pair it with soft suspension (ex. Flex-A). Enjoy cornering on bump stops. These cars need way more spring rate to support a sticky tire, it's not rocket science. I've tested a bunch of spring rates from 4k-9k and anything less than 8k you are into the bump stops a lot more than you realize.

I have really soft springs and now I’m worried I’m hitting the bump stops on turns. What is the negative part of hitting the bump stops mid corner? If I’m not mistaken this car is designed to hit the bump stops as the bump stop has its own “spring rate” built in. When a car is mid turn and fully resting on its bump stop, will this cause stability issues on the track compared to not hitting the bump stops at all?

I have STi springs that lower the car 10mm with shorter bump stops paired with 245 200tw tires. Significantly more body roll than my old RCE tarmac springs but dramatically more comfortable driving to work. I added a 19mm front bar and body roll is similar but still more than my RCE setup. I plan on getting stiffer coilovers if my STi springs are “not ideal” or “weird” when it comes to tracking.

[strat61caster]

A bump stop is just another spring, one that progressively gets stiffer and stiffer as it's compressed, it is not inherently evil. What will happen when loaded up and a bump is hit is that the effective spring rates gets much stiffer to prevent the car bottoming out, even 949s setup has bump stops. Many people do their best to reduce the spike in stiffness because as above grip comes from compliance. You'll be ok on the springs and factory bump stops, they're compliant and reasonably designed to handle abuse. NorCal tracks are pretty newbie friendly, don't try and launch the car over the curbs and you'll be fine.

[wparsons]

People get all worried about riding bump stops because 30 years ago they were very hard and not meant to be used as part of the active spring rate. They weren't really compressible at all, and were basically an infinite spring rate when you hit one. That's why they were bad for handling.



Current suspension designs are very different, and it's not a problem like it used to be. As bump stop active as these cars are, I'll bet very few people have ever truly bottomed them out mid corner.

[steverife]

Depending how you set your shocks and bars, the SSC autocross package can be really bad about hitting the bumpstops and suddenly coming off of them when aggressive on throttle on corner exit. And it makes for an insanely snappy car.

It is largely a non-issue in other facets of the turn.