STX Rules and Setup Questions

[CoolHandMoss]

Originally Posted by steverife

Red car. 68/168 maybe?

Maybe...

Not sure how you figured that out but I am impressed lol

[sifl]

CoolHandMoss, your post from yesterday (#3707) really resonated with me.

I do have a different setup than you, but the mid-corner push, and the inability to trail brake, were the symptoms of my issue. I also went through the process of trying different driving styles and lines to make it work. However, I did end up correcting most of the issue in car setup.

For reference, here is an abbreviation of the setup I ended with at Nationals.

Racecomp Engineering Tarmac 3 Clubsport on 9k springs. Stock front sway bar on shortened Hotchkis endlink. Mann Engineering rear sway bar on medium with RacerX endlinks. I do have an LSD. I have no rake, -3.9 front camber and -2.9 rear camber. My tire temps are about 3 degrees F different from outside to inside (inside is hotter) on concrete with BFGs or Yokohamas, with the fronts being about 5 degrees warmer. I am using stock brakes, but with HP+ pads. I only use the button-press method to turn off traction control and stability control.

Prior setups this year included stiff front bar with soft rear bar, stiff rear bar with soft front bar (very, very tail happy with this). I had all kinds of settings for the dampers. I knew to soften the front, and stiffen the rear, but I didn't hit on the right settings for quite a while

In my testing, I ran at lots of types of events this year, and had many co-drivers to help with input. It wasn't until the final few events that I got close to a balanced setup, and the final test-n-tunes at Nationals by my co-drivers (STXL and STX) put it together.

As you can imagine with 9k springs, I'm running rather soft bars and settings for my dampers. Still, with the final issue of mid-corner push and lack of trail braking, we had to soften front low speed compression, and soften the rear rebound and high speed compression. My final settings were (all from soft): front 7 rebound, 3 high speed compression, and 2 low speed compression; rear 7 rebound, 4 high speed compression, and 5 low speed compression. For context, full hard would be 20, 14, 6. Yes, I run out of travel in the front. I will be replacing my front 9k springs with 7k, because I believe that will help the car get more mechanical grip.

In the end, the car handled great for initial turn-in, mid-corner felt good, and we could trail brake again. For context, me and my co-drivers were 87 STX (ProSolo Finale and Nationals), 187 STX (ProSolo Finale and Nationals), and 87 STXL (Nationals).

Your setup is different, but hopefully this will help you think through your specific scenario.

[CoolHandMoss]

Thanks for your response. I have to ask though, if you are already running out of travel in the front, why are you softening the front springs? Softer only helps grip until the travel stops and then you go backwards in my experience.

[sifl]

I still think I'm not getting the level of grip that the car is capable of achieving, especially when I look at my ProSolo data. Front to back weight transfer for launches and pin turns was too abrupt. Without being able to increase front rebound (which I tried, but it caused more pushing on corner entry), I'll always have more front end lift in the front in launches and sharp corner exits than the softly sprung cars. My rear tires couldn't hook up in launches, or I would get too much oversteer in tight corners rolling onto the throttle.

I have a lot of tuning capabilities with my dampers, so I'm taking the chance that I'll be able to get my damper tuning right to work with the softer springs.

[CoolHandMoss]

I would be curious to hear how that works out. Another option I have considered is less front spring, more front bar and to raise the front ride height 3-4mm to maintain travel with the increased front end dive. I hate making so many changes at once though.

[strat61caster]

You can still step through the changes and see how they feel, I think ride height as an adjustment seems under utilised in autox, understandable as it's not easy to do on a car with fenders. Problem is the number of events to test changes...
Cheers to the setup sharing sifl

[dvalue]

Anyone had a chance to play with the Yokos yet?

Also, I may have a bent tie rod. Are there any aftermarket options that or legal or is OEM good enough?

[Locust]

Originally Posted by dvalue

Anyone had a chance to play with the Yokos yet?

Also, I may have a bent tie rod. Are there any aftermarket options that or legal or is OEM good enough?

Pretty much everyone that ran at nats. Initial result is they don't tolerate heat well (are actually really good on their first run) and are closer in feel to the BFG than the Stones.

I personally don't like them very much because of the increased heat maintenance required but they are faster so if you're not running them you're at a disadvantage.

[steverife]

Originally Posted by CoolHandMoss

Maybe...

Not sure how you figured that out but I am impressed lol

Was hanging out in STX grid and watching relatively closely. Recall the VA tags. Also recall the car being visibly pushy where many cars were not.

[CoolHandMoss]

Originally Posted by steverife

Was hanging out in STX grid and watching relatively closely. Recall the VA tags. Also recall the car being visibly pushy where many cars were not.

Yeah it was frustrating. My co-driver did not really seem to have the problem but I certainly did.

I have been thinking about it and realized I may have lost some front compression travel when I changed out the camber plates not long ago. It may be a matter as simple as removing the bump stops. So that is the first thing I am going to check on now.

[Breadman]

so tire size for a 17+ with a final drive, still run 245 or move up to 255?

[Lincoln Logs]

Originally Posted by Breadman

so tire size for a 17+ with a final drive, still run 245 or move up to 255?

It will depend on the course, but I'd wager the 255 is going to be more advantageous than not. I've driven some 13-16 cars the same day as my 17 and there is a big advantage to less shifts.

[CoolHandMoss]

Originally Posted by CoolHandMoss

I'm getting a little frustrated with my setup development so maybe the community here has some helpful advice. Throughout the last two years of running a twin in STX I have tried a variety of setups in terms of spring rates and sway bars and I have consistently had issues with mid-turn push. The current setup is 350F/400R, stock rear bar, Karcepts front bar. Caster is 7*, 4.1* camber in the front and 2.5* in the rear. I have about 3mm of positive rake. I currently run rivals and I run the fronts at 27 PSI and I get just a little roll over on the edge but not a lot. I've tried down to 26 PSI and that was definitely not an improvement. I've checked tire temperatures and I find about 15* warmer on the inside edge with the middle measuring closer to the outside edge than the inside which has led me to experiment again with higher front pressures which has yielded mixed results. I like the turn in but it doesn't help my mid turn grip problem. Turn in feels very good as is and the car transitions pretty well. Once I shed enough speed to get the front end planted the car exits very well with good balance on throttle. Generally adding throttle to rotate out of the push will just cause more push unless the speed is just right to have the power to really break the rears loose. The car also will not trail brake at all. Holding a little brake in to a turn just causes the car to push on entry rather than turn in nicely before pushing. Almost every single sweeper or 90* at nats was a nightmare. I was slowing more than I wanted to before turn in, getting a decent entry and then once the car was set the front end just pushed until I shed enough speed to be able to get on the gas so I was always on the gas late.

I've ended up adjusting the front bar down to the third softest setting of 7 which is still rather stiff at 346 lbs. In order to keep turn in crisp when changing to softer sway bar settings I have bumped front compression damping up to about 7 clicks on MCS.

The obvious course of action I think would be to continue softening the front or to stiffen the rear but the problem I am running in to is that the front is already getting to the point where it's soft enough to be close to running out of travel. I made sure that I'm maximizing travel in the front when installing this suspension system. I use a bump stop that contacts the damper body within a few mm of when the tire contacts the fender liner. I am not currently running out of front travel but pictures of the car on course show that it's not too far from doing so. I've tried the front bar all the way up to almost full stiff and that really made the problem worse. I've tried a stiffer rear bar but that made the rear end really snappy under throttle and I had trouble putting power down. I believe the next thing I am going to try is stiffer rear springs (450 lbs as I can't find any 425s in the right length) and if the car gets too loose I can balance that out with more front sway. I'm not really a fan of this solution though because I already am not using all of my rear travel. I took a video of the rear suspension motion at the damper on a rough road through some hard turns and found that the suspension is really only traveling through 60% of the available range and as such stiffer springs will really only act to sacrifice rear grip rather than to improve front grip.

Another solution I have considered is to use some rear toe out. I have usually kept rear toe at 0 but currently I have just a hair of rear toe in, about 2mm total.

Understandably, many will say that this problem is more a result of driving style than of setup. I have been trying to drive around this by reducing entry speeds and keeping steering inputs smooth but in order to avoid this mid-turn push I end up sacrificing entry speed so much that I'm just slow. Not to mention, using some rear compression damping has the car so balanced on initial turn in that it's even harder to give up that entry speed.

I would appreciate any constructive input on this. I'm just stumped as to whether the front end is pushing because it's too stiff, is it a matter of tire pressure and/or camber, is it that there is not enough front roll stiffness and the body is rolling too much, or are the weight distribution and other inherent characteristics of this car just such that I need to accept limiting rear travel and grip by going too stiff on the rear springs in order to get the car balanced out mid turn so I can get on the throttle earlier.

Any other suggestions on this matter? I have gone through and evaluated my suspension travel measurements and found that I was not limited on front compression travel. I did make an adjustment to allow 6mm more front compression travel but I doubt it will make a difference as there were indications that I had not ever reached max compression up there. I spaced the rear shafts down a few mm because I had more rear compression travel than I could use but not a lot of droop. But that won't help the pushing issue. I also lowered the front ride height 2mm.

So, going forward, my plan of action is to experiment again with front tire pressures, start significantly higher and work down. Then I'll try softening the bar as soft as it will go. I'll play with lower and higher front compression settings. I'll try increasing rear rebound and decreasing front rebound. If I'm still not there I'll put my 450 lb springs in the rear and I'm sure that will give up all kinds of rear grip but likely solve the front grip problem.

[steverife]

Originally Posted by CoolHandMoss

Any other suggestions on this matter? I have gone through and evaluated my suspension travel measurements and found that I was not limited on front compression travel. I did make an adjustment to allow 6mm more front compression travel but I doubt it will make a difference as there were indications that I had not ever reached max compression up there. I spaced the rear shafts down a few mm because I had more rear compression travel than I could use but not a lot of droop. But that won't help the pushing issue. I also lowered the front ride height 2mm.

So, going forward, my plan of action is to experiment again with front tire pressures, start significantly higher and work down. Then I'll try softening the bar as soft as it will go. I'll play with lower and higher front compression settings. I'll try increasing rear rebound and decreasing front rebound. If I'm still not there I'll put my 450 lb springs in the rear and I'm sure that will give up all kinds of rear grip but likely solve the front grip problem.

I haven't started with STX suspension yet, so this is just general....

Where is your front toe? I feel like toe out causes mid-corner push.

Also, what happens when you stiffen the front bar or spring?

Also, is this solely inspired by Lincoln? Or does the car generally handle that way?