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sventastic

Autocrossing an 850R

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Since the death of my poor S70 on the way to what was supposed to be my first autocross event, I've been wanting to autocross the 850R that I bought as its replacement. The date finally came where I had time to get to the track in and amongst all my tests and assignments at school. The 850R is stock aside from an IPD intake, so I got to experience first-hand the glorious understeer when pushing the car hard. Despite the never-ending tire squeal, I had a ton of fun and I can't wait to get the 25mm rear sway bar and lowering springs off of my S70 and see the difference they make!!

 

 

Edited by sventastic
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What kind (brand, size) of tires are you using? These cars love to plow but I bet you could get more traction. 

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On April 8, 2017 at 5:43 PM, adamdrives said:

What kind (brand, size) of tires are you using? These cars love to plow but I bet you could get more traction. 

The tires are Lexani LX-Seven in 215/45/R17. Heard of em before? Nah, neither have I... They're supposed to be a high performance all-season. They were installed by the previous owner and have only done about 5000km so far so they are basically brand-new and I can't justify swapping them out at this point. 

Despite their aggressive-looking tread they don't seem to be too great, but I did make several errors and could have taken a few lines much wider which would have meant less braking, and less accelerating (and wheelspin) needed. You can see there's a couple times I hit redline at 0:21 and 0:55 by quickly overwhelming their grip from turning+accelerating. I was getting better at left foot braking to help transfer weight to the front tires but this was still the best I managed

Not sure if I should consider different tire pressures, I was running 40psi front and 36psi rear. Maybe higher rear pressures would reduce rear grip and help the rear rotate more? After each run the fronts were hot, and the rears still just ambient haha

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Edited by sventastic

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12 hours ago, sventastic said:

Not sure if I should consider different tire pressures, I was running 40psi front and 36psi rear. Maybe higher rear pressures would reduce rear grip and help the rear rotate more? After each run the fronts were hot, and the rears still just ambient haha

Running that high is probably a good way to prevent the tires from melting, but I think you would have gotten more grip out of the front at 36psi instead. And you could probably drop the rear down to 32-34. Then keep an eye on them after each run to make sure they aren't showing signs of over heating. Isn't the factory spec 36 in the front and 32 in the rear?

I like a slightly higher pressure for highway driving but 40 seems uncomfortably high. Doesn't it right rough? Or did you choose those pressures specifically for the event?

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1 hour ago, Fudge_Brownie said:

Running that high is probably a good way to prevent the tires from melting, but I think you would have gotten more grip out of the front at 36psi instead. And you could probably drop the rear down to 32-34. Then keep an eye on them after each run to make sure they aren't showing signs of over heating. Isn't the factory spec 36 in the front and 32 in the rear?

I like a slightly higher pressure for highway driving but 40 seems uncomfortably high. Doesn't it right rough? Or did you choose those pressures specifically for the event?

I'm not so sure, I think I should have actually increased the pressure in the fronts and rears. There's a balance between the decrease in contact patch (from higher pressures), and loss of grip from tire deflection and rollover (at lower pressures). I did some research before the event and 40-45psi seems to be optimal for FWD cars. I think I will try something like 42 front 42 rear for my next event and put chalk around the sidewall to see exactly how much the tire is rolling over, and the decrease/increase to see the differences

I changed it specifically for the event, and actually forgot to decrease it for the drive home and yeah, it definitely rode a fair bit more harsh! Factory spec doesn't really apply for autocross since it's optimized for comfort and fuel economy rather than at the limit handling

You can see how the front tires end up loading basically onto the sidewall

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Edited by sventastic

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2 hours ago, sventastic said:

I'm not so sure, I think I should have actually increased the pressure in the fronts and rears. There's a balance between the decrease in contact patch (from higher pressures), and loss of grip from tire deflection and rollover (at lower pressures). I did some research before the event and 40-45psi seems to be optimal for FWD cars. I think I will try something like 42 front 42 rear for my next event and put chalk around the sidewall to see exactly how much the tire is rolling over, and the decrease/increase to see the differences

I changed it specifically for the event, and actually forgot to decrease it for the drive home and yeah, it definitely rode a fair bit more harsh! Factory spec doesn't really apply for autocross since it's optimized for comfort and fuel economy rather than at the limit handling

You can see how the front tires end up loading basically onto the sidewall

Hm. in my experience pressures that high or greater result in amazing feel, but the tire seems more prone to loosing grip. Granted, a lot of that is probably surface variation you hopefully aren't seeing on your track. Just using the OEM spec as a base point - and I'm not even sure it's optimized for fuel economy as higher should roll better. Combination of comfort, and long term tread wear which I assumed was through an evenly distributed contact patch.

The close-up, at first I thought you were looking at the cornering tread's wear pattern but I faintly see a second wear line half way down the ribbed area. And it looks more apparent in your distant picture. If that's the case, nevermind, I guess higher it is. Another consideration is if you're pushing the front too hard, or need to alter the set up. If you stuff the car in to a turn and yank the steering wheel, it's demanding a ton from the front tires. Especially in an under-steering car. The front tires just drag across the surface.

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No.

The front pressure should be high enough that you aren't rolling the tire in corners.  On high performance tires there are small arrows (typically triangles) that indicate the wear limit on the sides.  The Lexani tires don't have them from what I see, but also you could have lowered your pressure in the front for better traction.

Since you most likely don't have adjustable suspension, air pressure is the only thing you can change.  I would run the rear tires at 40 and the fronts at 38 next time.  Use a piece of chalk and mark a few lines on the side of the tire to use as indicators.  The higher air pressure will help with the heat, but you lose traction doing that.  Buy a $10 garden sprayer and just fill it with water to spray the tires when they get too hot.  You want them warm for maximum traction, but too hot and they will become greasy and you lose traction.
Higher pressure in the rear will help the car rotate better.  The rears will never get hot on the 850.

Remember to set your pressure back to normal for the street.

That tire is probably great in the rain, but performance driving in the dry, not so much.  I am guessing a 340 treadwear on it. 

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8 hours ago, Fudge_Brownie said:

Hm. in my experience pressures that high or greater result in amazing feel, but the tire seems more prone to loosing grip. Granted, a lot of that is probably surface variation you hopefully aren't seeing on your track. Just using the OEM spec as a base point - and I'm not even sure it's optimized for fuel economy as higher should roll better. Combination of comfort, and long term tread wear which I assumed was through an evenly distributed contact patch.

The close-up, at first I thought you were looking at the cornering tread's wear pattern but I faintly see a second wear line half way down the ribbed area. And it looks more apparent in your distant picture. If that's the case, nevermind, I guess higher it is. Another consideration is if you're pushing the front too hard, or need to alter the set up. If you stuff the car in to a turn and yank the steering wheel, it's demanding a ton from the front tires. Especially in an under-steering car. The front tires just drag across the surface.

The surface of the track I was on is known for being pretty crap, it's actually quite rough so there's even less grip because of it. That would make sense about the factory pressures!

I think that second worn area you are looking at is actually from rubbing a curb, not wear from tire roll! I'd be pretty surprised if it was, anyways. You can see it's only about half the tire that has that mark.

I think my driving left quite a bit to be desired haha. I had to get used to the handling since I really haven't pushed it (or my S70) on the street, I've put my efforts into getting the car mechanically sound first - PCV, timing belt/WP/idler/tensioner, ABS module, vacuum lines - it still needs inner tie rods, control arms, and boost leaks sorted out. The only other car I have tracked is my school team's FSAE car, which is a completely different handling experience and has massive grip. 

 

3 hours ago, Zappo said:

No.

The front pressure should be high enough that you aren't rolling the tire in corners.  On high performance tires there are small arrows (typically triangles) that indicate the wear limit on the sides.  The Lexani tires don't have them from what I see, but also you could have lowered your pressure in the front for better traction.

Since you most likely don't have adjustable suspension, air pressure is the only thing you can change.  I would run the rear tires at 40 and the fronts at 38 next time.  Use a piece of chalk and mark a few lines on the side of the tire to use as indicators.  The higher air pressure will help with the heat, but you lose traction doing that.  Buy a $10 garden sprayer and just fill it with water to spray the tires when they get too hot.  You want them warm for maximum traction, but too hot and they will become greasy and you lose traction.
Higher pressure in the rear will help the car rotate better.  The rears will never get hot on the 850.

Remember to set your pressure back to normal for the street.

That tire is probably great in the rain, but performance driving in the dry, not so much.  I am guessing a 340 treadwear on it. 

I was hoping you'd chime in Zappo! Any tips on the actual driving?

'No' to increasing the pressure further? I should've been more clear - I actually started them at 38, and they were 40 when hot when I checked them. Might it be worth trying out 36 or so?

Nope, no adjustable suspension, the car is all stock. Definitely will consider putting my lowering springs on for upcoming events... Rear sway bar too, of course. I'll have to bring some chalk next time, I considered it last week but didn't actually do it. Good to know about high tire temps losing traction, I'll definitely keep that in mind.

Maybe I'll get a wet event to try them out on, that'd certainly be interesting! You're right though, they look like they lack a lot of contact batch which has been given up for those big sipes. I checked and they have a treadwear of 420

Edited by sventastic

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if you started at 38, then lower them back to 38 as they heat up.  You want things to be consistent.  If you let the pressure change, your traction changes and the car handles differently every run.  You don't want that unless it is to make improvements.
You should see other drivers in the grid checking and adjusting pressure in their tires after runs.  When the events are warm or hot,  you will see the sprayers come out to cool down the tires.

You want your front tire pressure as low as you can go without rolling the tires.  The lower the pressure, the bigger the contact patch and the more traction.  Traction is everything in autocross, and with FWD, the front tires are doing almost everything.

As for driving tips, your line looks good, but you need to be smoother on the steering inputs.  The entry into the first slalom was good and you were back siding the cones the whole way, but your steering was becoming snappy at the end.  That is part of the reason the tires were talking to you because they are losing traction because of snap steering inputs.  Tires talking to you on a sweeping turn is good as you are near the limit of traction.  Steering angles were more than you needed for that slalom as well, but that is because you need to be closer to the cones.  The tighter you are to them, the less steering you need to do to get around them.

This is mostly because you are new at it.  Like almost anything, the more you practice, the better you become.  If you haven't done a rain event, that will help you as it will force you to be smoother.  Don't be afraid to hit cones either.  Yeah, it is 2 second penalty, but you need to know just how close you can get to them.  You are out there to have fun, so have fun.  Don't worry too much about your time starting out.  If you are smashing cones with the front bumper or tires, too close.  If you are tapping them with the rear tires, the force is flowing through you.

Here are 2 videos of me driving.  The side camera view is so I know how close I am getting to the cones.  First is my car, second is in an Evo 9.  Both are clean runs.  I had only been racing autocross a few years at this point and probably less than 30 events total.  You WILL get faster fairly quickly, you just need the seat time.

 

Be on the cones to be fast!

 

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@Zappo All great tips, thank you! I'll keep a closer eye on my tire pressures next time around, and chalk the wheels to see how much the tires are rolling over.

Yeah, my steering was too aggressive in the slalom, and it looks like I left 2-3 feet of space by the cones. I checked the videos of my previous 6 runs and they were all much smoother, I think for my last run I pushed too hard and that resulted in all that understeer. Time through the slalom was just as quick, if not quicker in some of the other runs even though they looked much slower, the tires were quiet. I will definitely focus on getting closer to the cones! Looking forward to improvements at my next event...:biggrin:

Edited by sventastic

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Good luck and have fun.  If you have any questions, feel free to ask.

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Autocross #2 after a slew of new parts and upgrades. Since April, the car has gotten 302mm brakes with stainless brake hoses and StopTech Sport pads and new calipers, IPD lowering springs, IPD 25mm rear sway bar, new control arms, tie rods, plugs, wires, and trans torque mount. Overall, it added up to a much tighter and more responsive car that was way more enjoyable to drive. There was way less body roll and brake dive, and it was much easier to rotate with trail braking. That said, it still understeers, but to a much more manageable degree

I had a senior driver with me for the first few laps which was incredibly helpful, as I went from a 65.8s lap on my second run, down to a 59.6s lap on my 7th and final run. He said if I were on some R-compound tires (like everyone else), I'd be down another 3 seconds, which would actually put me mid-pack for PAX times. 

Got the tires hot enough to get into melted rubber territory. Even the rear tires were a bit melty which tells me the rear end was coming around a decent amount. Brakes were hot enough that the front wheels were almost too hot to touch and the rotors got a blue tinge, but I never felt any fade. Really happy with these Stoptech pads... The heat cycling on the tires even seemed to bake off the last of the tire shine from a month ago, as the tires were still completely black before the autocross

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Edited by sventastic

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Tires are one of the most important changes you can make.  They are also a big investment.  You should pick up a cheap garden sprayer to cool off your tires between runs.  I am sure you saw others there with them.  Once the tire overheats your traction starts to drop.  It is a balance of keeping the tires warm enough to stick well without getting them too hot.

Are you running wheel spacers?  If so, don't race with them.  They widen the track which increases turning radius.  On the rear, they will keep the car from rotating in the corners.  They are fine on track days, but autocross they are slowing you down.

Your lines look good and I see you are much closer to the cones.  The more seat time the better.  It sucks it is a police training course so you have those painted lines distracting you, but at least you have a place to race.

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1 hour ago, Zappo said:

Tires are one of the most important changes you can make.  They are also a big investment.  You should pick up a cheap garden sprayer to cool off your tires between runs.  I am sure you saw others there with them.  Once the tire overheats your traction starts to drop.  It is a balance of keeping the tires warm enough to stick well without getting them too hot.

Are you running wheel spacers?  If so, don't race with them.  They widen the track which increases turning radius.  On the rear, they will keep the car from rotating in the corners.  They are fine on track days, but autocross they are slowing you down.

Your lines look good and I see you are much closer to the cones.  The more seat time the better.  It sucks it is a police training course so you have those painted lines distracting you, but at least you have a place to race.

For sure, it would be really cool to see how much faster I'd be with some R-compounds, but that's just not in the budget. I'm sure it will be more beneficial to improve my driving first anyways though. Yup, lots of tire sprayers out! Would be interesting to try them out. I had my fastest lap on my third and final run of the afternoon session, and I did a few more "fun laps" after the official event was over but couldn't best my time, I'm thinking the tires were definitely overheated at that point. 

Nope, no wheel spacers

I actually hit a few cones this time :P The lines actually weren't distracting at all, when I was driving I was so focused on the next set of cones that I didn't even notice the lines. This venue is so much better than where I did my first autocross, it's huge, flat and smooth with no curbs to worry about, and way more course design options.

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