goin reverse stagger, maybe...

[strat61caster]

Originally Posted by ZDan

That would take away front grip and exacerbate the problem. Thing to do would be bigger *rear* sway bar, but then I'd have to add 41 lb. and possibly get into the realm of unloading the inside rear too much for the Torsen to deal with.

I said the same thing until I did it, the front rolls too much with the stock sway which reduces overall grip. Didn't decide to do a full suspension analysis just took the win and rolled with it.

Good luck.

[ZDan]

Originally Posted by M0nk3y

That's weird, I don't have bump stop issues at all...

Is your setup identical to mine? -1.25" lower so that's a lot of bump travel gone right there, plus another 3/4" or so taken away by the Raceseng camber plate roller bearing.

You're running a compromised setup trying to maintain point compliance.

Every setup is a compromise... But yeah, mine is particularly compromised because it's my daily street car as well, otherwise I'd get good coilovers with much stiffer springs.

IMO rear camber is too high especially if you're having mid-corner push. Shocks on entry can help you with aiding rotation, because that's really what you want in the end right?

Speaking of "throwing grip away"... If reducing rear camber *helped* the issue, it's only because it will have taken away lateral grip at the rear. No bueno...
Again, the problem isn't rotation on corner-entry, it's mid-corner push.

To each their own, but this is a very backwards way to deal with a setup issue.

IMO I think it's pretty spot-on. Reducing rear camber is the backwards way.

Outside front is for sure overloaded. Adding 10mm width up front should add a decent amount of front grip. Outside rear is underutilized. Taking away same 10mm of rear width will not take away as much rear grip as what I'm adding to the front, as the outside rear is in the more linear portion of the load/grip curve.

In the end I don't expect the change to be profoundly earth-shattering, but should help a bit.

[ZDan]

Originally Posted by strat61caster

I said the same thing until I did it, the front rolls too much with the stock sway which reduces overall grip. Didn't decide to do a full suspension analysis just took the win and rolled with it.

Good luck.

Thanks!

But note that front and rear roll *the same amount*. Unless you're getting a HUGE amount of twist in the chassis! I.e. you'll reduce roll at both the front and the rear with a stiffer front bar, or with a stiffer rear bar.

[M0nk3y]

Originally Posted by ZDan

Is your setup identical to mine? -1.25" lower so that's a lot of bump travel gone right there, plus another 3/4" or so taken away by the Raceseng camber plate roller bearing.

Every setup is a compromise... But yeah, mine is particularly compromised because it's my daily street car as well, otherwise I'd get good coilovers with much stiffer springs.


Speaking of "throwing grip away"... If reducing rear camber *helped* the issue, it's only because it will have taken away lateral grip at the rear. No bueno...
Again, the problem isn't rotation on corner-entry, it's mid-corner push.


IMO I think it's pretty spot-on. Reducing rear camber is the backwards way.

Outside front is for sure overloaded. Adding 10mm width up front should add a decent amount of front grip. Outside rear is underutilized. Taking away same 10mm of rear width will not take away as much rear grip as what I'm adding to the front, as the outside rear is in the more linear portion of the load/grip curve.

In the end I don't expect the change to be profoundly earth-shattering, but should help a bit.

Get rid of the roller bearing and go standard thrust sheets would help a ton. I personally hated their bearing design because of exactly that, it takes up bump travel.

As far as me, I'm fairly low as well...I don't run bump stops and never have had issues. I have MCS 2W so the canister is outside the shock which alleviates any and all travel concerns. Obviously I know you're point limited so a 2 way shock especially remote isn't the answer, but there ARE solutions to common issues on this chassis.



Regardless, I'm curious to see what the result is. Doing back to back testing same day?

[ZDan]

Originally Posted by TommyW

Also maybe look at your throttle input and see if maybe too early?

That's part of the problem, having to delay full throttle. I'd like to be foot-to-the floor *sooner* to improve exit speed, in addition to carrying more speed mid-corner. Need more front grip...

[ZDan]

Originally Posted by M0nk3y

Get rid of the roller bearing and go standard thrust sheets would help a ton. I personally hated their bearing design because of exactly that, it takes up bump travel.

Yeah, I was strongly considering machining down the Raceseng upper mount (stock-diameter spring size) and eliminating the radial bearing and letting the spherical rotate. Bad idea some peeps assured me! Throwing in some kind of low-profile rotational thrust bearings w/ needles, or thrust sheets(?), maybe even Igus bearings, and getting back that bump travel would be a good idea!

As far as me, I'm fairly low as well...I don't run bump stops and never have had issues. I have MCS 2W so the canister is outside the shock which alleviates any and all travel concerns. Obviously I know you're point limited so a 2 way shock especially remote isn't the answer, but there ARE solutions to common issues on this chassis.

Yeah, I think one big part of it is I'm set up a bit soft for the track at 4.4F/5.3R... Bumping that up to 8/10ish and getting stiffer front and/or rear sways would be a lot better for track.

Regardless, I'm curious to see what the result is. Doing back to back testing same day?

Yeah, I'm going to put the A052s 255F/235R on for 1st session on June 19th then go back to 245/40-17 square CR-1s for my other 3 sessions of day1.
For day2 I'll put the A052s back on for practice 1, if they seem like their def. gonna be faster than CR-1s I'll just leave them on for practice 2 and then run them in the time trial.

So yeah, testing A052 vs CR-1 at the same time as 255/235 vs. 245/245

[M0nk3y]

Originally Posted by ZDan

Yeah, I was strongly considering machining down the Raceseng upper mount (stock-diameter spring size) and eliminating the radial bearing and letting the spherical rotate. Bad idea some peeps assured me! Throwing in some kind of low-profile rotational thrust bearings w/ needles, or thrust sheets(?), maybe even Igus bearings, and getting back that bump travel would be a good idea!

Yeah, I think one big part of it is I'm set up a bit soft for the track at 4.4F/5.3R... Bumping that up to 8/10ish and getting stiffer front and/or rear sways would be a lot better for track.


Yeah, I'm going to put the A052s 255F/235R on for 1st session on June 19th then go back to 245/40-17 square CR-1s for my other 3 sessions of day1.
For day2 I'll put the A052s back on for practice 1, if they seem like their def. gonna be faster than CR-1s I'll just leave them on for practice 2 and then run them in the time trial.

So yeah, testing A052 vs CR-1 at the same time as 255/235 vs. 245/245

Depending on your shaft size, MCS sold a set of SCCA Compliant stock spring perch set. Might be worth taking some measurements and getting away from Raceseng's perch (or fabbing up your own).

I have a small spacer I made that's probably 3/8" in total height on top of my normal spring perch with these guys on the top and bottom, FWIW:

https://www.swiftsprings.com/products/misc/

[steverife]

Personally, I think that adding a front bar is worth an additional 41 lbs. In lieu of that, I'd go stiffer on front springs if possible.

If front grip issues are related to roll stiffness, adding front grip without stiffness is only going to exacerbate that by getting you to that unhappy place earlier in the turn. And possibly more frequently. And you've added a gearing and rake change to the equation.

[ZDan]

Originally Posted by steverife

Personally, I think that adding a front bar is worth an additional 41 lbs. In lieu of that, I'd go stiffer on front springs if possible.

If front grip issues are related to roll stiffness, adding front grip without stiffness is only going to exacerbate that by getting you to that unhappy place earlier in the turn. And possibly more frequently. And you've added a gearing and rake change to the equation.

If mid-corner front grip issue is related to roll stiffness (whether due to front camber loss or outside front on the bump stop), better to add roll stiffness to the *rear* of the car, not the front. Fronts are palpably overloaded during steady-state cornering, and front tires are wearing a lot quicker than rears. Adding roll stiffness to the front is a backwards idea, it might alleviate camber loss and being on bump stop by a bit but that would be offset to some degree by the increased front roll stiffness acting to load the outside front. I'd sooner add rear roll stiffness to achieve the same end of reducing mid-corner roll, while redistributing some of the cornering load off of the outside front and onto the outside rear.

With the same roll stiffness (which is what it's going to be as I'm not going to trouble with sways or springs at the moment), going to wider fronts should increase the load at which the grip/load starts to nose over, so grip should be improved at the same load. We'll see!

You're sorta making the argument I once heard regarding a tire test where lower-profile tires on +1" diameter wheels tested at less lateral grip vs. same make/model same-width tire with a taller profile on smaller diameter wheels (similar tire OD). Tire representative said: The +1 is making more grip, which gives more roll, which causes LESS grip. So yeah, arguing that having MORE grip gives LESS grip, hmmm...

Gearing:
My fellow BRZ class competitor and I compared data between his '13 and my '17 (both at the limit of class-legal points, equalized on power/weight) at Palmer. 4.1 diff vs. 4.3 diff. We turned similar lap times and our acceleration plots down the straights fell right on top of each other. Going from 245/40-17 to 235/45-17 rear tires is same as going from 4.3 gearing to 4.17 gearing. I'm not worried about losing time from that, at this track. "Better" gearing isn't always faster at the track anyway...

Rake:
Going from flat rake with square tire setup, to 25.2" OD 255/40-17 fronts and 25.5" OD 235/45-17 rears gives 0.15" more rear ride height, sin-1(.15"/101") = less than a tenth of a degree change in rake. That might make a difference on an F1 car, not so much on a softly-sprung, "heavy", near-zero lift/downforce BRZ.

In the end, this is an experiment, if dry weather is forecast I'll take both sets of tires, 245/40 square and 255/40 front 235/45 rear. If there's time and I feel like it, I'll also try "normal" stagger with 235F/255R.

Thing is, the 245s are Nankang CR-1 and 255/235 are A052s, so that's a big joker card right there!

In fact the main reason I'm doing this is because I was beaten by a tenth at NHMS and I want to see if A052s will give me an advantage. But 245/40-17 A052s aren't available until after Palmer event! While 255s, 235s and 225s are. Reverse stagger had been a goofy notion I've thought about doing with this car for a while, given how much it abuses the outside front. This situation kind of gives me the excuse to try it

[steverife]

Okay.

[Pat]

Recently I experienced something similar. Maybe you can learn from my mistakes. Recently my front right height was lowered by an alignment shop. Suddenly the car would understeer in high lateral g turns. I raised the car back up to where I had it before (a little more than one inch lower than stock), and the understeer went away. I raised it a little bit at at time, and each time it got better.
If you really want to address the root cause, I doubt wider tires on the front will do it. It may even make it worse if you are getting into the bumpstops.

[ZDan]

Originally Posted by Pat

Recently I experienced something similar. Maybe you can learn from my mistakes. Recently my front right height was lowered by an alignment shop. Suddenly the car would understeer in high lateral g turns. I raised the car back up to where I had it before (a little more than one inch lower than stock), and the understeer went away. I raised it a little bit at at time, and each time it got better.

Yeah, again my suspicion is I'm on the outside front bump stop, loading up the outside front.

Ultimately might go to RCE Tarmac springs to raise ride height about 1/2".

If you really want to address the root cause, I doubt wider tires on the front will do it. It may even make it worse if you are getting into the bumpstops.

In that sense, the way to make it "better" is to go slower. Hell, going to 205 all-seasons all around might make it "better" in the sense of not having nearly as much roll and not being as hard into the outside front bumpstop, But ultimately I'm looking for tenths of a second in lap times, so I'd rather carry more speed and be a bit further into the bumpstop. If I end up with the same mid-corner push but at a higher speed, that's progress.

Anyway, hopefully time allows and I will be able to isolate the differences between A052 and CR-1, as well as the differences between front- and rear-stagger.

[Wally86]

I have nothing productive to add but just a reference point for reverse staggered. I have a buddy with an RS3 and it seems they run reverse staggered from the factory which is certainly interesting. 255/30r19 & 235/35r19 which sounds awfully similar.

[Pat]

Originally Posted by ZDan

In that sense, the way to make it "better" is to go slower. Hell, going to 205 all-seasons all around might make it "better" in the sense of not having nearly as much roll and not being as hard into the outside front bumpstop.

No, that would not address the root cause. The root cause of your understeer isn't too much grip, although it is a factor. If my theory and personal experience hold true in your case as well, the root cause is ride height and/or spring rate which determine how much you get into the bumpstops.