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Old 12-05-2005, 11:32 AM   #1
javid
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Default Tuning: Neutral vs On throttle rotation

OK guru's learn me on what adjustments are going to change either of these or both and by how much. My current setup has great on-throttle rotation. It's a good bit of fun in 2nd and 3rd and gets a little less agressive in 4th but still rototes nicely. I would like to keep on-throttle rotation just about where its at. Neutral / mid-corner the car has great peak grip but ultimately pushes. The car is built for track events but I welcome imput from the autoX pros as I am sure you guys have played with this particualr issue before.

On enrty and in transistions I am pretty happy with the car's behavior;
we can get the car as loose / tight as we want with steering angle and a little brake.

Rather than spending hours trying different adjustments out I figured that some of you folks might have some experiance with this particualr tradeoff.

Right now the car runs 12k springs F/R. 24mm front bar with -2.5 and 1/8 toe out. 20mm rear bar with -1.3 ish and 1/8 toe out. Front dampers are at a higher rate than the rear.

Currently I can adjust
Front: Ride hieght, dampers, camber (0 to -4), toe.
Rear: Ride height, dampers, bar (20 to 24), camber (0 to -3), toe.

Anyone have experiance tuning mid corner with out changing exit?

Thanks
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Old 12-05-2005, 11:40 AM   #2
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What tires are you running? You should be able to add some more front grip, which should help the mid corner push. How are you shocks valved? The springs may be too stiff to compensate. Toe-out, (usually in much larger increments that you run) can cause the front end to wash out mod-corner.
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Old 12-05-2005, 11:59 AM   #3
javid
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I've always run 070s at the track and ran some 275 710s at an autoX this weekend. This was my first time on R-Compounds, so I still have some learning / tweeking to do to use them efficiently. Ultimately I am going to run a 275 street tire.

The shocks are the JIC -RS shocks. They quote "custom race valving" but I could never get the shop that ordered them to get the actual valving. They are the one part of the car/setup that I haven't paid much attention to. I have adjusted them for dry and wet use on track using the but-o-meter. Some local hot shoes have driven the car and never said "oh my god, your dampers are borked" so I guess they're OK...

I will adjust the Toe back to 0 all around before we hit the track. The small toe out was not by design. We have done a lot of work on the car in the past few months and I measured it this weekend and figured that it was good enough.
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Old 12-05-2005, 12:02 PM   #4
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I'll just call you with my stuff, it will be easier

-Tom
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Old 12-05-2005, 12:07 PM   #5
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Quote:
Originally Posted by trhoppe
I'll just call you with my stuff, it will be easier

-Tom
phone is at home, type biotch
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Old 12-05-2005, 12:57 PM   #6
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A touch more negative front camber should help with mid corner front end grip. Have you run tire temps? I was usually at -3 degrees or so when i ran the 070.

Hoppe is a *****

Chris H.
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Old 12-05-2005, 03:13 PM   #7
ratt_finkel
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What size wheels and what air pressures did you run with the 710's?
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Old 12-05-2005, 03:19 PM   #8
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17x9s and upper 30s lower 40s I believe. They were at the perfect pressures based on wear and rollover. I didn't have my temp gauge.

-Tom
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Old 12-05-2005, 04:07 PM   #9
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We pretty much threw the 710s on and ran the car; like the alignment, the temp's and pressures were the least of my concerns. We have been wrenching on the car for a while and we took it out to the autoX "to see what was going to blowup". Not much did so the event was a lot of fun, we spent most the day driving rather than fixing.

Coincidentally, the car exhibited a similar dry behavior (push mid corner and good on throttle rotation) and with 710s as it did with the street tires; so it motivated me to look into the balance a little more.

I' am not really looking for the silver bullet solution to my setup but rather more general solutions / ideas.

For instance, increasing the rear bar might give me more mid corner rotation but I think it may make entry too loose. Decreasing the rear camber would probably have a similar effect as well as reduce peak grip.

In any event, I will definetly bump the front camber back up to 3 or so next time out.
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Old 12-05-2005, 04:17 PM   #10
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Well I can tell you for a fact your air pressures were way too high. I would try something around 32 psi in the front next time.

You are very close to having a perfectly balanced car. Perfect balance in steady state corners is very hard to master. I was going to actually recommend reducing negative camber in the rear as well. My guess is, mid-corner the weight transfer front to rear has stabalized therefor, you are basically having too much grip in the rear.

Like you mentioned though, loosening it up for one thing is going to effect the other parts of the corner. I would defintely recommend trying it to see though, it may not be as loose as you think.

Also, leave the toe-out.
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Old 12-06-2005, 01:34 AM   #11
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Quote:
Originally Posted by ratt_finkel
Well I can tell you for a fact your air pressures were way too high. I would try something around 32 psi in the front next time.

You are very close to having a perfectly balanced car. Perfect balance in steady state corners is very hard to master. I was going to actually recommend reducing negative camber in the rear as well. My guess is, mid-corner the weight transfer front to rear has stabalized therefor, you are basically having too much grip in the rear.

Like you mentioned though, loosening it up for one thing is going to effect the other parts of the corner. I would defintely recommend trying it to see though, it may not be as loose as you think.

Also, leave the toe-out.
Not sure what you found, but high 30s hot were the ticket for me on V710s. With an STi, you cannot reduce rear camber w/o seriously affecting the turn-out of the car. With every other Subaru I reducing the rear camber would apply. Not so in an STi IMHO.

-Tom
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Old 12-06-2005, 09:41 AM   #12
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Quote:
Originally Posted by trhoppe
Not sure what you found, but high 30s hot were the ticket for me on V710s. With an STi, you cannot reduce rear camber w/o seriously affecting the turn-out of the car. With every other Subaru I reducing the rear camber would apply. Not so in an STi IMHO.

-Tom
I found that 32psi all around for concrete and 30psi all around on asphault worked best on my car. With no roll-over. I think there is a lot of time to be had with lower air pressures in the 710's.
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Old 12-06-2005, 09:50 AM   #13
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are those cold or hot temps?
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Old 12-06-2005, 12:56 PM   #14
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Quote:
Originally Posted by ratt_finkel
I found that 32psi all around for concrete and 30psi all around on asphault worked best on my car. With no roll-over. I think there is a lot of time to be had with lower air pressures in the 710's.
Jeremy,

That is on your car and not an STi. You have driven mine and I think you would agree the corner exit is much different I think. I run a pretty big split in tire pressures (Azenis RT615) and I would think that would apply to 710s as well.

-Paul
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Old 12-06-2005, 02:23 PM   #15
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Quote:
Originally Posted by AtomicRacer
Jeremy,

That is on your car and not an STi. You have driven mine and I think you would agree the corner exit is much different I think. I run a pretty big split in tire pressures (Azenis RT615) and I would think that would apply to 710s as well.

-Paul
Most defintely Paul, I don't have to counter-steer in my car

But I did mention, "my car" previously.

Mako, how low did you go exactly to come up with those pressures. By the way, I am in now way refutting Andy's skills or anyone else here. Just stating what I've found to work best. And also, when comparing notes with other 710 drivers and recommending lower pressures, their results have been nothing but positive.
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Old 12-05-2005, 05:06 PM   #16
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I would go to -3.0 camber in front and swap to the Strano 32mm front bar. Damper settings and pressures obviously vary with environmental conditions to some extent, but they should be easy enough to suss out once you are happy with the hardware.
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Old 12-06-2005, 02:36 AM   #17
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38/35 with my 710's ... determined on a skid pad, using a pyrometer with Andy Hollis ...

What are your ride heights?

Instead of reducing rear camber ... could he do more to increase front grip ... add spacers? Have you thought of or tried increasing front Caster to help maintain camber in tight corners ...

Are you running your DCCD in Auto or ...
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Old 12-06-2005, 08:12 AM   #18
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mid-corner is definitely one of the more difficult corner phases to free the car up. especially when the car is a front heavy production sedan with a high cg, roll centers that are all over the map, and a camber curve that blows chunks.

adding more rear spring or bar will have a very minimal affect on mid-corner. it will mostly change the corner entry balance. raising the rear ride height will also mostly affect corner entry.

taking out rear camber will have minimal affect on entry and will free the car up mid-corner, but like tom said, it might make the car too loose on exit. the shocks you have don't have the adjustment range to dial down the exit rotation on their own so that probably won't work.

adding more front camber will increase front grip everywhere, but that means possibly too loose on entry and exit as well. basically, if you really want to free the car up mid-corner you are going to have to throw away your current entry and exit balance. once you've freed the car up mid-corner, then you can look into ways to tighten the entry and exit phases.

my suggestion based on the above would be to reduce both rear camber and spring at the same time. add in more front shock and a bit of rear toe in. the camber should free the car mid-corner, the toe, front shock and softer rear spring should stabilize it on entry and exit. it might not be the ultimate solution, but it's a shot.

nate
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Old 12-06-2005, 09:23 AM   #19
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Ride hieght: what ever the standard drop that everyone quotes on here, I forget.

DCCD: Auto

solo-x, thanks for the info. I know I am dealing with a compromise here and understand that I'm running fisher-price, my first motorsport shocks. But even for fisher price shocks the car is pretty fast. I am going to run some more front camber and see how it feels.
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Old 12-06-2005, 12:46 PM   #20
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Whatever the temperature is ... you start with that pressure and keep bleeding back to it ... at some point it will stabilize. If you start with (initial newly mounted tire fill) and keep using nitrogen your air pressure won't change as much ... because it doesn't contain moisture ... which is one of the main reason our air pressure changes so much as the tire heats up.

710's usually want lower tire pressures ... but Andy Hollis helped me determine my tire pressures using a skid pad ... and pyrometer ... really the best way ... and we ended up with 38/35 ... with my SM WRX using 12/10 springs.

One of our best drivers ... Karl Asseily auto crosses a jdm EVO7 with very sophisticated custom tuned differentials, anti-lag, etc. Although he uses the usual lower tire pressures in his other 710 shod rides ... he found that for his AWD Evo ... it wants higher pressures.

Hoosier says to use high pressure up to and around 50 psi with their S-05's ... and say "resist the temptation to reduce tire pressure" even though lower tire pressures will feel better ... more control ... higher pressures will result in faster times. Of course with more control one might be able to drive faster. :-)

Our fastest Vette racers use air pressures over a 10 psi range with their 710's ... so it really is a personal preference based specifically on the car's set-up.
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Old 12-06-2005, 12:55 PM   #21
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To me that would be a hot pressure. Since the car is used mostly on track; it gets up to temp and stays there for a while so simple hot pressures work fine for me. It needs about 2 minutes to bring the tires, brakes, and -driver- up to opperating temps.
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Old 12-06-2005, 02:40 PM   #22
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Get a heavier trunk monkey and teach him to jump to the outside mid-corner.

I emailed you this morning before I saw your thread. CN: Don't go down on rear camber as you won't be able to put down any power on exit (which is the car's greatest strength). Try a bit more rake. If it gets loose in transition then there are cures for that too.

Also, I run 35 psi all around in the dry (285/30/18 V710s). I was running 33 on Sunday because it was still damp and grip was less than 100%
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Old 12-07-2005, 06:22 PM   #23
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During an EVO Dial-In course ... we did timed runs on a Skid Pad. I tried my single adjustable Tein Flex's with 550/550 springs at Full Stiff all around, Full Soft all around, Full Stiff in front, soft in back, Full Soft in front, stiff in back ... to see those effects. Then narrowed the settings down so that I got my fastest times.

I then tried different air pressures using a pyrometer to get tire temperatures that were about 10 degrees warmer on the inside. Adding more air caused the center of the tire to heat up, less created more temperature on the outsides. It was very cut and dry. The problem with using a pyro after the car comes in off of a regular course ... is that the inside of the inside front tire gets dragged across the corners, if you have a decent amount of camber ... artificially giving one an elevated inside edge tire temperature.

I'm very consistent in these type of tests ... doing three lap runs within a tenth of a second of each other. Also got that type of consistency in the EVO 1 "run-off." Timing gear broke during Evo 2. :-(

Ideally it would have been good to have gone back to playing with the struts on the skid pad ... but there wasn't time for that.

The "ideal" strut settings on the skid pad resulted in wild oversteer on the transitional handling course. I had to soften the rear end rebound to control that. Also soften the rear sway bar one notch.

But optimal set-up is very course dependent. If we have a course with few transitional elements I need to loosen the car up, ... lots of slaloms and I soften the rear end ... using rebound, sway bar, rear camber, toe and/or tire pressure.
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Old 12-07-2005, 10:18 PM   #24
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Thanks for the info and suggestions guys. This has given a lot to think over and try..... baby steps.
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Old 12-08-2005, 10:46 AM   #25
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Quote:
Originally Posted by makofoto
During an EVO Dial-In course ... we did timed runs on a Skid Pad. I tried my single adjustable Tein Flex's with 550/550 springs at Full Stiff all around, Full Soft all around, Full Stiff in front, soft in back, Full Soft in front, stiff in back ... to see those effects. Then narrowed the settings down so that I got my fastest times.

I then tried different air pressures using a pyrometer to get tire temperatures that were about 10 degrees warmer on the inside. Adding more air caused the center of the tire to heat up, less created more temperature on the outsides. It was very cut and dry. The problem with using a pyro after the car comes in off of a regular course ... is that the inside of the inside front tire gets dragged across the corners, if you have a decent amount of camber ... artificially giving one an elevated inside edge tire temperature.

I'm very consistent in these type of tests ... doing three lap runs within a tenth of a second of each other. Also got that type of consistency in the EVO 1 "run-off." Timing gear broke during Evo 2. :-(

Ideally it would have been good to have gone back to playing with the struts on the skid pad ... but there wasn't time for that.

The "ideal" strut settings on the skid pad resulted in wild oversteer on the transitional handling course. I had to soften the rear end rebound to control that. Also soften the rear sway bar one notch.

But optimal set-up is very course dependent. If we have a course with few transitional elements I need to loosen the car up, ... lots of slaloms and I soften the rear end ... using rebound, sway bar, rear camber, toe and/or tire pressure.
Mako - A couple of things that I noted from your post that seem odd. I also did the Evo dial-in school in Atlanta with Andy Hollis. The goal of measuring tire temps on the skidpad should be to have even temperatures across the face of the tire. If you are measuring tire temps coming off course, you would expect to have higher temps on the inside of the tire due to braking and acceleration, but the skidpad is just one big turn. Therefore, the ideal camber and tire pressure settings would give even temps on the skidpad rather than higher on the inside.

More importantly, we setup our shocks ("bracketed" them, as Andy called it) on the slalom. Basically slaloms are a series of turn-in and turn-out events, which is what you tune shocks for. The procedure was to turn rebound all the way down and work on compression settings until the tire started to skate slightly. Then we turned compression down a tad and worked on the rebound. I don't know how you would benefit from shock tuning in a steady-state situation such as a skidpad. The shocks will have much less effect there.
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