SCCA Solo C Street Discussion

[Simmons]

Originally Posted by Rexpelagi

Ask and you shall receive. :-)

2014 DC Pro Solo - 57 CS - John L.:

I left some time on the left just by not improving on day 2, and I can see a few tenths here and there. However I think I would have needed some exceptional runs to catch Mark. The car probably had it, but it would have been tough.

Unlike John, I actually think the RX-8 had a bit of an advantage on these courses. With the extra 30hp the RX-8 is what I would choose to climb the hill, and with almost no transitional elements the RX-8 probably had the advantage with the wider tires/wheels and better suspension in the sweepers. Having driven both I think the BRZ has the advantage in quick transitions (slaloms) which weren't present here.

It was a fun weekend though and it was awesome meeting more of the CS crowd that I hadn't met before!

I like how early you turned in for everything,....just need to find a way to get rid of the understeer now.


Simmons

[vroom4]

Im fighting the same animal. Im turning in early, which leads to a slightly early apex, which leads to push on corner exit.

Just need to pound it in my brain to carry a little deeper into the corner before braking I guess.

[Rexpelagi]

To those running the 245/40R17 size - do the tires clear the suspension with +48 wheels or do you need +42?

[7thgear]

Originally Posted by vroom4

Im fighting the same animal. Im turning in early, which leads to a slightly early apex, which leads to push on corner exit.

Just need to pound it in my brain to carry a little deeper into the corner before braking I guess.

consider the verbal approach

talk to yourself when coming up to the key turns "wait for it, wait for it, wait for it",

[MTCRX]

Originally Posted by vroom4

Im fighting the same animal. Im turning in early, which leads to a slightly early apex, which leads to push on corner exit.

Just need to pound it in my brain to carry a little deeper into the corner before braking I guess.

In most cases- late apex, late apex, late apex.

[7thgear]

Originally Posted by dwx

With my MCS CS shocks I ran them with no bump stops initially, which was technically not legal. They have no dust boots, and I used the tie wrap around the shaft trick to find out my shock travel was.

Originally Posted by dwx

I would have been on the bump stops on a couple courses, but for the most part I wouldn't have hit them even with the MCS shocks.

Originally Posted by AustinTX

Funny how you almost always believe that everyone else is either wrong or they don't understand. You are posting in a thread full of people who have been there and done that many times, so don't discount their opinions for your own so easily. Either way, you are free to trim them. I don't plan on it, though.

To DWX: Are the MCS dampers monotube? Did they come with their own bumpstops or you had to re-use yours? Do they have internal bumpstops?

To AustinTX, you say “opinions”, this is not a matter of opinion, this is a matter of simple math. There is only one answer.


I decided to take a step back from the discussion because, admittedly, I did not have my own empirical evidence, but a few weeks ago, as a prerequisite for a side project, I took apart the rear OEM coilover and re-installed the damper sans spring and dust boot and then leveling the car to its OEM height (reference measurements of which were taken before)

My measurements indicate roughly 3/8” of free travel before bumpstop engagement.

Drawing from the available info on spring rates and motion ratios, we’re dealing with around 240lb/in of spring resistance to movement

That means that the rear corner can only handle roughly 90lb of weight transfer before the progressive bumpstop becomes an integral part of the spring rate calculation.

Merely getting on the gas really hard is enough to do this, and is also why the car with a suitcase in the trunk and a person or two in the back handles noticeably different than when you’re alone... and why the SCCA rules would prohib them being longer.


I've yet to do the front of the car but from my personal experiences with MacStruts (VW's and Imprezas) i'm not expecting to be surprised by inches worht of free travel. I predict around 3/4 at the very most.

If my measurements are incorrect then please point to a possible error in my procedure. But at this time i'll revert back to my statements that you are in fact engaging your bumpstops to some degree quite often, even during a daily drive.

[renfield90]

Originally Posted by 7thgear

To DWX: Are the MCS dampers monotube? Did they come with their own bumpstops or you had to re-use yours? Do they have internal bumpstops?

To AustinTX, you say “opinions”, this is not a matter of opinion, this is a matter of simple math. There is only one answer.


I decided to take a step back from the discussion because, admittedly, I did not have my own empirical evidence, but a few weeks ago, as a prerequisite for a side project, I took apart the rear OEM coilover and re-installed the damper sans spring and dust boot and then leveling the car to its OEM height (reference measurements of which were taken before)

My measurements indicate roughly 3/8” of free travel before bumpstop engagement.

Drawing from the available info on spring rates and motion ratios, we’re dealing with around 240lb/in of spring resistance to movement

That means that the rear corner can only handle roughly 90lb of weight transfer before the progressive bumpstop becomes an integral part of the spring rate calculation.

Merely getting on the gas really hard is enough to do this, and is also why the car with a suitcase in the trunk and a person or two in the back handles noticeably different than when you’re alone... and why the SCCA rules would prohib them being longer.


If my measurements are incorrect then please point to a possible error in my procedure. But at this time i'll revert back to my statements that you are in fact engaging your bumpstops to some degree quite often, even during a daily drive.

Solid data. Thanks for sharing.

My first reaction was "hey, we actually get more spring rate out of the car than we thought!"

But really, do you think we should be cutting the bump stops and by how much? I'm personally happy with how the car drives, I'm hesitant to go try and fix it 'til it's broken.

[jprice130]

Originally Posted by Rexpelagi

To those running the 245/40R17 size - do the tires clear the suspension with +48 wheels or do you need +42?

I haven't tried any of the street tire offerings in 245/40, but back in 2012 I ran 245/40 Hoosier A6s on the stock wheels and did not have an issue with inbound clearance. It was close up front, but it still cleared the spring perch just fine (this was with the OEM crash bolts too). Might not hurt to keep some 3mm slip-on spacers handy for the front just in case.

[7thgear]

Originally Posted by renfield90

But really, do you think we should be cutting the bump stops and by how much? I'm personally happy with how the car drives, I'm hesitant to go try and fix it 'til it's broken.

at the OEM level there is no problem (well, maybe too much rebound dampening and not enough compression)

bumpstops are often cut to facilitate lowering springs, whose spring rate would be overriden entirely by compressed bumpstop approeaching infinity.

but i was merely showing support that bumpstops in general are an integral part of most modern suspension systems. A lot of people still seem to think as "bumpstops" as the hard stop that prevents damper bottoming and that the only time they hit the bumpstops is when they "BANG"... when the fact is that when they BANG is when both the spring and the bumpstop are overloaded into infinity at a super rapid rate and the shock is transfered directly into the chassis of the car.

for all practical purposes, the FRS comes stock with a "progressive roll resistance" mechanism that comes in the form of the 2.5" bumpstop (in the rear anyway.. i haven't gotten the front)

[G_Ride]

Originally Posted by Rexpelagi

To those running the 245/40R17 size - do the tires clear the suspension with +48 wheels or do you need +42?

@cactus?

[gramicci101]

How does ECU tuning play into the CS class rules? For instance, an OFT stage 1 flash.

Also, I saw that suspension bushings are not allowed; what about drivetrain bushings such as the shifter, transmission insert, rear subframe, and diff lock collar bushings?

I'm not concerned with what class I end up with, because I'll be there to learn and have fun, not beat everyone else. But I should probably know what to tell them when I get there, so I don't look completely clueless.

[7thgear]

Originally Posted by gramicci101

How does ECU tuning play into the CS class rules? For instance, an OFT stage 1 flash.

Also, I saw that suspension bushings are not allowed; what about drivetrain bushings such as the shifter, transmission insert, rear subframe, and diff lock collar bushings?

I'm not concerned with what class I end up with, because I'll be there to learn and have fun, not beat everyone else. But I should probably know what to tell them when I get there, so I don't look completely clueless.

on the first page of this thread you will find a comprehensive outline of what you CAN do in C-Stock

if a mod is not on there, that means you can't do it and even a single non authorized mod will bump you up.

[itzmik3]

Originally Posted by Rexpelagi

To those running the 245/40R17 size - do the tires clear the suspension with +48 wheels or do you need +42?

no problems at all.
even on full lock and a big tire such as the yokohama

[Rexpelagi]

Awesome thanks!

I know it has been discussed before but what are people's thoughts on the 245/40R17 Rival vs. The 235/40R17 ZII? I'm a big fan of the ZII, but the potential for free tires vs. nothing has an appeal...