Any explanation for this odd tire wear? I know I overdrove them, but check this out - this is the same tire!
Any explanation for this odd tire wear? I know I overdrove them, but check this out - this is the same tire!
Given the amount of understeer that tire wear is not odd, or at least I don't find it odd.
hunter47 said:Any explanation for this odd tire wear? I know I overdrove them, but check this out - this is the same tire!
That's pretty much how they wear. Sticky tires stick. You know how a race track rubbers up with a dark section on the line and marbles outside the line? That's where the rubber comes from. It's essentially torn off the tires.
Also, seeing that tire confirms my suspicion that your pressures are too high. You should be getting those chewed edges on every grove across the tire. The wear pattern indicates that you could use more camber but I wouldn't add it on a street car and dropping the pressures will let the inside of the tire do more work. I'd start with 32 psi in the front and 34 in the rear and go from there.
Cool, glad that seems normal. Odd that it's not all the way around the tire and that it's only on one side, but considering what the track layout was like, it makes sense.
Are we talking about 32/34 hot? or 32/34 cold?
hunter47 said:Cool, glad that seems normal. Odd that it's not all the way around the tire and that it's only on one side, but considering what the track layout was like, it makes sense.
Are we talking about 32/34 hot? or 32/34 cold?
Hot.
In reply to APEowner :
Thank you sir. Most of the events I attend are about 100 miles out, almost all highway driving. Would you say that's enough to get the tires "hot" to where I can pump them to 32/34? Or is that still considered "cold" in terms of performance tires?
I ask so that my first lap out contains good information, rather than doing a tire pressure check dance every lap for the first 2 laps.
Hot like as measured immediately after finishing a run. And maybe not the first run of the day either, whatever it takes to get the tires fully hot. It'll take some experimenting but you should be able to figure out roughly what cold pressure that hot pressure correlates to for future reference. Probably 3-5psi lower.
Overinflation also aided in that wear.
hunter47 said:In reply to APEowner :
Thank you sir. Most of the events I attend are about 100 miles out, almost all highway driving. Would you say that's enough to get the tires "hot" to where I can pump them to 32/34? Or is that still considered "cold" in terms of performance tires?
I ask so that my first lap out contains good information, rather than doing a tire pressure check dance every lap for the first 2 laps.
You were at over 40/34 last time right? I'd try 34 all around first. I'd probably dot your sidewalls and check outside wear. If it looks good and still understeers, then try 32/34 or even 32/36. You have to balance tire wear and suspension with your driving style.
I drive my Subie RS on 34 all around on dirt and it understeers in slow corners (especially in throttle) and tail happy at higher speed and gets tail happy if you transfer weight forward with the brakes.m.
Honestly one thing is the AWD Subie platforms do not drive like RWD or FWD cars at all. People that ride with me leave in a state of awe. Drive it like you hate it.
In reply to AnthonyGS (Forum Supporter) :
I can't really parse "not like front or rear drive at all". All cars drive pretty much the same: understeer on throttle, some lift throttle oversteer, the degrees to which are as much down to chassis dynamics as drive type.
In reply to Pete. (l33t FS) :
I understood it as "all the bad of FWD and all the bad of RWD so you just have to deal with it".
In reply to Pete. (l33t FS) :
There is some merit to what AnthonyGS is saying: while the physics weight transfer doesn't magically change based on drive systems, AWD cars have the ability to exploit the advantages of FWD & RWD all in the same instant. It's not going to bend the space time continuum but it does allow for a somewhat unique driving style.
In reply to Tom1200 :
The main merit is that you can apply more power for a given cornering force because the torque is divided amongst all four tires.
Which exacerbates understeer, because you can unweight those front tires even more than a two wheel drive car can, with a side dish of asking the front tires to do two tasks.
hunter47 said:In reply to APEowner :
Thank you sir. Most of the events I attend are about 100 miles out, almost all highway driving. Would you say that's enough to get the tires "hot" to where I can pump them to 32/34? Or is that still considered "cold" in terms of performance tires?
I ask so that my first lap out contains good information, rather than doing a tire pressure check dance every lap for the first 2 laps.
I'm a road racer but everything I know about autocross I learned from the internet so I'm not sure what best practice is.
With that disclaimer out of the way here are my thoughts.
They will heat up from the drive but they won't be as hot as at the end of a run. I think I'd set em at whatever you're using as a target when you get there and then check em and bleed em after every run. I would guess that unless you're using tire warmers you're always going to see a pressure increase during a run but I don't know that for sure.
How much they change during a run is going to depend on ambient temperature, how much you slide them around (which paraxoically may dependent on starting pressure) and how much moisture is in the air in the tire.
In reply to APEowner :
Perfect, as long as I can get them heated-ish that means less time wasted playing with pressures. We don't get as much time at autox to play around with pressures like an open track day would!
Of course I understand that it'll never be perfect as soon as I arrive but need to get a good idea of how not to waste time.
Using the data from TrackAddict I mapped the lap from the video and one of my fast "clean" laps.
Did a time vs. speed/throttle position of each one as well
27.204
29.301 (and here you can see where I realized I'm in 4th lol)
Pete. (l33t FS) said:In reply to AnthonyGS (Forum Supporter) :
I can't really parse "not like front or rear drive at all". All cars drive pretty much the same: understeer on throttle, some lift throttle oversteer, the degrees to which are as much down to chassis dynamics as drive type.
RWD cars tend to be unforgiving of stupid throttle inputs. FWD is better but asking the front tires to modulate power and steering isn't fun inducing.
AWD allows you to do really stupid idiotic driving and still be okay. AWD is far more tolerant of overdriving than RWD or FWD.
And yes you get the bad of RWD and FWD and it all depends on the corner coming up and how you approach it.
I need to get a camera so you can see the silliness of rallycross in grandmas Subaru. I'd rather smash it with a sledgehammer than autocross it on pavement though.
One thing to remember about over/under-inflation of tires...
A modern steel belted tire will bulge on the shoulders of a tire when over inflated. The steel belt keeps the tire from growing in the middle.
AnthonyGS (Forum Supporter) said:I need to get a camera so you can see the silliness of rallycross in grandmas Subaru. I'd rather smash it with a sledgehammer than autocross it on pavement though.
I've extensively rallycrossed rear wheel drive, front wheel drive, and all wheel drive of the Subaru mentality (clutch, viscous, and cam-and-pawl type center diffs), Audi mentality (locked center and rear diffs), and Haldex mentality.
I've autocrossed most of the above, although I can say for certainty that the Audi type AWD handled much, much better with the differentials open than locked. With locked diffs, your handling choices are snowmobile grade understeer or drifting.
Has anyone mentioned to this neophyte about shoe polish? I didn't totally read through this. But shoe polish helped me figure out pressures a lot. It also helped me see certain course designs effect on tires. The last ax I ran, all four re71 tires at 30psi cold. After two runs (75° Ambient) psi was 34 on all, despite the course showing that the passenger rear was not totally meeting the edge of the sidewall.
what I learned? Course took the least toll on the passenger rear, and the ambient temps and course heat cooked the psi up evenly.
In reply to Countingcrowbars :
What'd you call me??
Kidding, I think someone said tire chalk earlier which is a similar idea. Considering shoe polish is black and tires are (typically) black as well, how would that help? Just curious.
In reply to hunter47 :
As someone who wore snazzy white shoes in marching band in high school, I can tell you that shoe polish comes in white as well.
And you want something like this, liquid with a sponge applicator, much like the liquid chalk ones- https://www.amazon.com/Kiwi-Scuff-Cover-White-2-5/dp/B002S0YPME/ref=asc_df_B002S0YPME/?tag=hyprod-20&linkCode=df0&hvadid=366352759384&hvpos=&hvnetw=g&hvrand=4145017580030197408&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033316&hvtargid=pla-680111933949&psc=1&tag=&ref=&adgrpid=81880595728&hvpone=&hvptwo=&hvadid=366352759384&hvpos=&hvnetw=g&hvrand=4145017580030197408&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9033316&hvtargid=pla-680111933949
racerfink said:In reply to hunter47 :
As someone who wore snazzy white shoes in marching band in high school, I can tell you that shoe polish comes in white as well.
As could tell you anyone who has gone bracket racing.
Dial-In doesn't work so hot as tire marking compound.
https://www.youtube.com/playlist?list=PLhJbQ3YXFMgDBR2pfiZDdlRwyvCrQue6m
Put together a playlist of my time attack sessions last night.
I drove there on 38PSI square, I dropped it to 28PSI square. First lap out was warming them up and they hovered around 30PSI "hot". The track added a chicane after the start/finish line to prevent people from speeding into the barrier, but my times were actually better than my last time, which was without the chicane! They call that turn "little monza".
30PSI "hot" was the sweet spot for me! Plenty of grip, didn't feel any considerable understeer. Of course being AWD and me being a novice, still had some understeer. Did lots of trail-braking, heading into the chicane right before the back straight was all trail-braking, really helped stabilize the car. Still working on smooth and early steering inputs. The problem spots I notice right away are at the chicane before the main straight and the esses after "little monza".
Overall my PBs for the day were 48.71 for the first session and 48.70 for the second. The fastest times I've seen posted at the course are a 45.xx, and the average I've seen around 51-52 seconds. Not bad for a big (almost) stock AWD sedan!
I noticed you pushing ever so slightly wide coming to onto the front stretch. My thought is you could square up the corner with an ultra late apex to get a better drive down the front stretch.
Realistically you'd have to try it back to back and see what the times are.
You'll need to log in to post.
