SCCA Solo C Street Discussion

[AFRichZC6]

Originally Posted by AustinTX

You can simply look at spring rates and ride heights of STX cars to determine whether the new package will help...

CS and STX cars can't be looked at the same.

Competitive STX cars have much more static camber than CS cars (>2 degrees) and much higher spring rates (7k+) that compensate for lower ride height and possibly compromised front strut suspension geometry. I doubt the US-spec TRD lowering springs, based on how they are marketed, are going to be very high in rate. They would probably be similar to Eibach lowering springs that lower height by at least an inch and front spring rates are probably in the 3.5k range.

[Briankbot]

Originally Posted by AustinTX

You can simply look at spring rates and ride heights of STX cars to determine whether the new package will help...

True but STX cars can have camber correction devices to make their ride heights and spring rates work.

Originally Posted by AFRichZC6

I would wait until the TRD-packaged FRS show that they are consistently and significantly faster than a standard CS-prepped FRS/BRZ before jumping ship or grabbing a pitchfork.

My prediction (and hope - mostly hope) is that the lowering springs actually hurt performance. I think that they will reduce ride height enough to compromise suspension geometry while not having enough camber (static, camber gained through compression, and camber gained through caster), spring rate, and bar rate to make up for it.

This is my first Japanese car, but coming from a European car background US spec cars almost always have a higher ride height than ROW (rest of world) cars. This has to do with our bumper height requirements. The idea that the ride height of our USDM cars is better than JDM or ROW maybe incorrect.

Another thought I have coming from Mac-Strut cars is the angle of the control arm under static load and body roll induced compression. The general guideline I am familiar with is that under static load the wheel end of the control arm shouldn't point upward very much or you will loose negative camber under body roll. With stock springs the control arm appears to be pointed down a bit. After installing the TRD springs the arms will probably point up slightly but the reduced body roll will probably keep them within the same camber range under compression. Overall I'm hoping this is enough to increase the contact patch of the outside front tire which I think would be beneficial.

If I was a BRZ owner I would be writing letters trying to get the springs and bars approved for cross platform use. The BRZ will not gain an unfair advantage with them and if anything CS turnout numbers will benefit which will be good for the class and the SCCA in general. Alienating drivers and reducing class numbers isn't good for anyone...Hell I may write a letter myself.

[Briankbot]

^^^ Took too long to type that...

[renfield90]

You are fooling yourself if you think the springs will be a net loss to performance. Full stop.

Sincerely,
Someone who's already run the car with them

[7thgear]

so....


I was planning on buying some bilstein dampers (B6, for OEM height), but this got me thinking if the B8 for "sport" would be a better match for the TRD springs.

any thoughts?

[renfield90]

Originally Posted by AustinTX

I will probably have my car there, but I don't plan on running it after the revelation of the TRD package. The BRZ is now my DD and perhaps occasional autocrosser. For this season, at least. Hoping for a move to ES for next. Otherwise, the car's national competition career is over.

What were your times at nats compared to ES? I think the move makes more sense now. Write a letter!

[renfield90]

Originally Posted by 7thgear

so....


I was planning on buying some bilstein dampers (B6, for OEM height), but this got me thinking if the B8 for "sport" would be a better match for the TRD springs.

any thoughts?

I think the B8 have a shortened shock shaft - not street class legal since the spring upgrade does not change the OEM damper. Double check the rules.

[7thgear]

Originally Posted by renfield90

I think the B8 have a shortened shock shaft - not street class legal since the spring upgrade does not change the OEM damper. Double check the rules.

I thought the only thing they care about with shocks is spring perch mounting location (and stuff like electronic adjustment and levels of adjustability)

checking rulebook now.

EDIT: interesting..


The fully extended length must be within ±1" (±25.4 mm) of the dimension of the standard part


rats

[chucky12012]

Originally Posted by 7thgear

I thought the only thing they care about with shocks is spring perch mounting location (and stuff like electronic adjustment and levels of adjustability)

checking rulebook now.

EDIT: interesting..


The fully extended length must be within ±1" (±25.4 mm) of the dimension of the standard part


rats

Well, we'll see how this weekend at the national tour goes, might give some idea. Although if it's really rainy, not sure how helpful the results will be. I'm running the B6's, but revalved, and I just installed the TRD springs. From what I could find from Bilstein, the B6 should be good for up to a 30mm drop and the B8 should be used for a drop in the 30-40mm range. I think the TRD spring drop is 30mm or less, although I will admit that I haven't measured (hindsight...).

[AFRichZC6]

Originally Posted by Briankbot

This is my first Japanese car, but coming from a European car background US spec cars almost always have a higher ride height than ROW (rest of world) cars. This has to do with our bumper height requirements. The idea that the ride height of our USDM cars is better than JDM or ROW maybe incorrect.

Another thought I have coming from Mac-Strut cars is the angle of the control arm under static load and body roll induced compression. The general guideline I am familiar with is that under static load the wheel end of the control arm shouldn't point upward very much or you will loose negative camber under body roll. With stock springs the control arm appears to be pointed down a bit. After installing the TRD springs the arms will probably point up slightly but the reduced body roll will probably keep them within the same camber range under compression. Overall I'm hoping this is enough to increase the contact patch of the outside front tire which I think would be beneficial.

If I was a BRZ owner I would be writing letters trying to get the springs and bars approved for cross platform use. The BRZ will not gain an unfair advantage with them and if anything CS turnout numbers will benefit which will be good for the class and the SCCA in general. Alienating drivers and reducing class numbers isn't good for anyone...Hell I may write a letter myself.

You have the right idea. There's more to it.

When you lower a car with strut suspension, the roll center is lowered, and the roll couple (distance between center of gravity vs roll center) is increased. When this happens (considering spring rate is unchanged), you actually get more roll (fun fact: if roll center and CoG are at the same point, there would theoretically be zero roll). So when lowering a strut susp. car, you'll want to reduce that increased roll with firmer springs, and lowering springs are almost always firmer than stock. Usually when strut susp. cars are lowered, they need either a lot more spring rate or static camber to keep the suspension working in the camber curve's "happy zone"

Most stock cars with strut susp. have control arms parallel with the ground or slightly pointed down. As the control arm swings up under roll compression, some camber is gained until it reaches a certain point when it starts to lose negative camber. The only way we would know for sure at what point our cars start to lose camber is to plot and measure everything to draw the camber curve. My prediction comes from knowing that many strut suspensions don't need a whole lot of compression to begin losing camber, ie. VW Mk4/Audi TT chassis from my experience.

But who knows. Maybe our geometry is still totally fine with being lowered more than an inch while having only slightly firmer springs in front. Our cars also have a very low center of gravity, so that helps keep the roll couple relatively small. I guess I'd start by asking to see if the drivers who have switched to the TRD setup have seen more outside tire wear, with all other factors being the same (OE camber bolts installed), and if they're running consistently faster times than the other drivers they are benchmarking against.

Too long of a post to type on my phone. (RIP my thumbs and eyes)

[AustinTX]

Originally Posted by renfield90

What were your times at nats compared to ES? I think the move makes more sense now. Write a letter!

I would have finished 2nd in ES, 0.2 back.

[AustinTX]

Changing the rear bar alone will improve everything, because it'll allow a larger front bar.

[Biggins]

Originally Posted by AustinTX

Changing the rear bar alone will improve everything, because it'll allow a larger front bar.

I think this is the bigger difference as well. I'm keeping my frs in my 2014 setup form for now, but I'll convert to the TRD stuff later this year if I decide to drive this car at Lincoln again.

[AFRichZC6]

Originally Posted by AustinTX

Changing the rear bar alone will improve everything, because it'll allow a larger front bar.

Didn't think about that. Good point.

I guess I don't have too much to worry about since I'm just trying to be fast regionally. I have no aspiration to go to nationals.