CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[Racecomp Engineering]

Originally Posted by OkieSnuffBox

Less variables, but less accurate IMHO. I suspect the difference in OD in a tire at 28psi and 35psi would be hard to pick up with a tape measure. Since we aren't talking about touring tires or something.

@Racecomp Engineering do you have a hub to fender height starting place?


Thanks in advance!

Off the top of my head, 13.5 inches is a good starting place. I think that's just over an inch.

- Andrew

[Racecomp Engineering]

This is kind of a rant....

CHECK YOUR TIRE PRESSURES.

I know that most autocrossers and track day guys check them like every 20 minutes, but a lot of weekend warriors don't.

I had my oil changed the other day and of course they jacked up the tire pressure like they always do. For about 30 seconds though I'm driving down the road wondering if the mechanic took off my Bilsteins, revalved them with like 300 lbs more compression and rebound damping across the board, and then put them back on without saying anything. He's a good mechanic, but not that good. Then I pull over and take out 10-15 psi (!) at all 4 corners....and all is right with the world.

At the same time I do see people at autocrosses and track days that don't have a clue what they're tire pressures are and complain about sloppy turn in, too little grip, tires overheating, etc. Or weekend warriors complaining about an extremely harsh ride.

First question should be:
"What are your tire pressures?"
The answer is often:
"Oh. I don't know."

Sometimes the easiest solution is the most overlooked.

- Andrew

[gramicci101]

What is your target hot pressure and what do you set your cold pressure to in order to meet that target?

[Racecomp Engineering]

Originally Posted by gramicci101

What is your target hot pressure and what do you set your cold pressure to in order to meet that target?

It definitely depends on the tire and if it's auto-x or HPDEs or sprints/time attacks or race sessions. For my street daily driver on all seasons it's definitely not 48 psi though....

- Andrew

[gramicci101]

Originally Posted by Racecomp Engineering

It definitely depends on the tire and if it's auto-x or HPDEs or sprints/time attacks or race sessions. For my street daily driver on all seasons it's definitely not 48 psi though....

- Andrew

Maybe they thought you were one of those hyper-milers who crank up their pressure to minimize tire contact and lower rolling resistance? I mean, it could happen...

[Racecomp Engineering]

Originally Posted by gramicci101

Maybe they thought you were one of those hyper-milers who crank up their pressure to minimize tire contact and lower rolling resistance? I mean, it could happen...

I do think that's their goal for most people. I got an oil change and my mpgs went up!

- andy

[strat61caster]

I understand tire pressures are a secret sauce kind of deal (I drove a car with someone and we liked noticeably different pressures on same tires and setup and were within 1% on laptimes) and understand if I get somewhat vague feedback but here it goes.

I've been running OEM wheels (17x7) with Dunlop Direzza ZII Star Specs, 215/45/17 (OEM size) and I don't think I've ever gotten them truly hooked up. At first I was keeping them in the 35-40 range any time I checked (cold and hot, I think I was around 38 hot usually after 20 minute HPDE session @ Laguna Seca in January) based on past suggestions for standard road tires for newbies they didn't want debeading on track and the tires felt peaky to me, like a little after the first lap they'd start to grip then around lap 3-4 they'd fall off a cliff and I'd be sliding around the rest of the 5-10 minutes in the session. They were certainly a great improvement over the Primacy HP's that made me glad I bought them but I was never blown away by the grip. After doing some research I now believe I had them overinflated as some people are shooting for 32 hot with these tires.

Current car setup: OEM unless otherwise noted, crash bolts put me at -1.1 degrees camber up front, ~-2/-1.7 degrees camber rear, zero toe front, 1/16th toe in rear, Carbotech XP10 pads front and rear. (The pads are overkill for my driving right now, oodles of life left and they work great and should last me quite a bit as I step up my skills, thanks CSG! Well worth the $$$ as the stockers will get 40k miles out of them.)

So at the last AutoX I tried going out at 29 psi cold, came back at 33-34 hot and dropped a psi or two until it was consistent at 32 for the final few runs (6 total), but the tires still felt like they weren't biting. Now the conditions were very chilly, mid 60's at best, overcast, strong stiff ocean wind. My current thought is that I had two things going on:

1. It was just too damn cold, tires never got heat in them, I never observed them to be hot, only warm to the touch, sometimes very warm but never uncomfortable or overly tacky to rest your hand on them once back in the staging area, they never tacked up like they did during HPDE.
2. I am still high on my tire pressures, given how cold it was with the wind and surface leaching heat out as I leisurely roll back to the grid over a few minutes I'm skewing my tire temps and I'm actually much higher 'hot' than I think. I didn't feel like the tires were sloppy with too much sidewall flex, next time I'll chalk the wear bars.

My current plan (AutoX in 3 weeks) is to repeat going out on 29 psi cold (ambient, no sun) and drop pressures after each session to see if I hit a sweet spot or when I make it to the bottom limit of what's good and start making it worse. I'm expecting 34-35 psi hot after the first run based on the last day and expected warmer weather and I'll keep the tires chalked. Since I'm not competing for points or anything, every session is a test & tune. Unless I learn something radical I'll be trying the same at my next HPDE.



The tires currently have 8k miles, 3x AutoX, 2x Track days (100 minutes each) and they are my daily drivers. They look pretty good and I'll be keeping them through the year no doubt, at least 1x more track day and probably 4x AutoX, based on how they're holding up they may last me into next year, we'll see how much tread is left come September to handle the wet season (lol 'season' in CA is a joke, I really mean puddles). I expect they'll have 10k miles, 3x track days (300 mins total), and about 50 AutoX runs total by the end of the year. They (Z2 SS) seem to have a strong following and solid AutoX results, I'd like to at least understand them before I use them up, I'd like to try something different but that's a ways off and these may survive well into next year the way they look today at about 50% of what I expected their life to be. There are certainly counts of them being tolerable at ~200 runs but definitely not as quick, maybe they'll last me 1.5-2 years.

I'm really just looking to see if there's an idea or concept that will quicken the learning curve on these tires or a smack upside the head if I'm headed in the wrong direction.



Sidebar: When a course is biased to left/right handers and you end up with one side (left/right tires) taking more heat than the other, should you try to adjust it or leave the bias (say +1 psi on the right side) and adjust all four (or two, front or back to balance) equally? I'm still learning the ropes of road courses, in circle track racing every tire was treated differently and adjusting each tire had it's own effects within the car's current setup. While it's true with road courses as well setting all four tires differently to max out the important corners while compromising the less important corners is something even the pros struggle to do confidently and consistently.

Thanks for reading.


Aaand the thought just occurred to me to post this in a tire thread for cross reference...

Edit: For whatever reason I thought that this was the "Ask CSG Track/AutoX questions" not the suspension, oh well, tires are springs and people read this too Maybe I'll cross post tomorrow if I don't get a response.

[Shankenstein]

Originally Posted by strat61caster

I understand tire pressures are a secret sauce kind of deal (I drove a car with someone and we liked noticeably different pressures on same tires and setup and were within 1% on laptimes) and understand if I get somewhat vague feedback but here it goes.

I've been running OEM wheels (17x7) with Dunlop Direzza ZII Star Specs, 215/45/17 (OEM size) and I don't think I've ever gotten them truly hooked up.

Yeah. I've got the same tires, and they run pretty low pressure if you are targeting even temperatures/wear during autoX.

Generally, I start out at 32 psi front, 28 psi rear. That seems to *just* work them to the wear arrows. Depending on the course, I may go up or down 2 psi.

For smoother courses, you're not going to roll over the fronts as much... so I drop the front pressure to 30 or so. Cold days, I drop all 4 by a couple psi. Texas summer days, you can either raise pressures or spray them between runs.

I'm with you on tire temps. On cold days, I'm intentionally driving like a hooligan to warm the tires up. First run is a throw-away, but given my driving skill, that's to be expected.

[strat61caster]

Originally Posted by Shankenstein

Yeah. I've got the same tires, and they run pretty low pressure if you are targeting even temperatures/wear during autoX.

Generally, I start out at 32 psi front, 28 psi rear. That seems to *just* work them to the wear arrows. Depending on the course, I may go up or down 2 psi.

For smoother courses, you're not going to roll over the fronts as much... so I drop the front pressure to 30 or so. Cold days, I drop all 4 by a couple psi. Texas summer days, you can either raise pressures or spray them between runs.

Thanks, are you setting when hot/cold/right before going out etc?

Interesting that you go up when hot, I would have thought the opposite. Down when cold makes sense to me as you want the rubber moving around searching for grip but I would have figured on hot days allowing the tires to expand unchecked would result in a loss of traction.

I definitely noticed having the rear lower by 2+ psi hooks it up and increases the natural understeer, that should have been my first clue that I was overall setting my pressures up too high, at this point I like the on-throttle rotation I get with even pressures front/rear. When I had lower rear pressures every once in awhile I would get in over my head and just have to give up a corner to terminal understeer of my own design, it's probably faster as you can get on the throttle earlier with more confidence but I'm not yet consistent enough in my driving to lean on it for improved times.

Definitely have some work to do on the nut behind the wheel before I can truly start blaming the car/tires/lack of camber.

[Shankenstein]

Originally Posted by strat61caster

Thanks, are you setting when hot/cold/right before going out etc?

In the parking lot at the start of the day. As I go through runs, I'll check temps and wear.

If things aren't warming up or wearing evenly, I'll drop the pressures.

After the course walk, if it looks like a tough day on the tires, I'll start at 34/30.

As you said earlier... there's enough wrong with the driver that fine-tuning tire pressure is probably a waste of my time. It makes me feel faster

Per your question. Warm weather = warm tires. Since warm tires will grip better than cold tires, I assume that they will roll onto the sidewalls more. Boosting the pressure prevents this (both from the portion of tread engaged and the tire's stiffness). I could be 100% wrong though.

[cdrazic93]

Originally Posted by Shankenstein

I could be 100% wrong though.

Pretty doubtful.

[Jcl]

Quick question. Putting stock lcas back on do I need to get an alignment?


Sent from my iPhone using Tapatalk

[cjd]

Originally Posted by Jcl

Quick question. Putting stock lcas back on do I need to get an alignment?


Sent from my iPhone using Tapatalk

Given the change I had from carefully matched LCA'S from stock, of not be surprised if toe were all out of whack after you swap back.

[DeaconRoc]

Originally Posted by Racecomp Engineering

This is kind of a rant....

CHECK YOUR TIRE PRESSURES.

I know that most autocrossers and track day guys check them like every 20 minutes, but a lot of weekend warriors don't.

I had my oil changed the other day and of course they jacked up the tire pressure like they always do. For about 30 seconds though I'm driving down the road wondering if the mechanic took off my Bilsteins, revalved them with like 300 lbs more compression and rebound damping across the board, and then put them back on without saying anything. He's a good mechanic, but not that good. Then I pull over and take out 10-15 psi (!) at all 4 corners....and all is right with the world.

At the same time I do see people at autocrosses and track days that don't have a clue what they're tire pressures are and complain about sloppy turn in, too little grip, tires overheating, etc. Or weekend warriors complaining about an extremely harsh ride.

First question should be:
"What are your tire pressures?"
The answer is often:
"Oh. I don't know."

Sometimes the easiest solution is the most overlooked.

- Andrew

If you change to a different brand and type of tyre but in stock sizes should you just stick with stock pressures or should they change? If they should change how's the best way to work out what to change them too (without the use of a racetrack, tyre thermometer, etc!)