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post #1 of 30 (permalink) Old 10-18-2018, 03:24 PM Thread Starter
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Front End Grip Question

Sorry this will be a long and detailed post, because I'm really starting to like the way the car's handling but I'm dealing with a consistent tendency that I can't seem to tune out yet.

And what I mean by that is it still mostly verges on understeer. Now the way I'm driving it (focusing on apexing late and being on the power through the corner) amplifys that but that seems to be the proper way to drive the car.
Car does not oversteer really at all though unless I do something clearly wrong (It would take me jumping off the gas pretty suddenly mid corner to upset the car) but otherwise the rear end doesn't move.

And I'm dealing with mid corner understeer, and I feel like understeer is keeping me from getting on the gas earlier as getting on the gas makes understeer worse, so I'm waiting, waiting, waiting to get on the power, and the rear feels like it has plenty of grip to put down power earlier.

I spoke with Fred @fzust btw massive shout out to him for being the most pleasant individual to work with in this industry by a mile.
He spent about 20Mins with me on the phone and my alignment stats are as such.

Front Camber
-2.2
Rear Camber
-2.7
1/8" toe out in the front 1/16 toe in in the rear.

Standard BWR sway bar set to the loosest setting.
And Penskes set to the "Race / Competition" recommended settings from BWR.
Tires are 205 Front / 235 rear R888Rs on LSS wheels.

Fred recommended the toe settings and that helped what I would call initial turn-in or the front end changing directions suddenly but on tighter corners it feels like the rear end is dead stable (no where near it's limit) and the front is just fighting for grip.

And thats why I set the bar to it's loosest setting, to help front end grip.

Next thing we were thinknig was to get more front Camber. I already have the V2 arms and no shims, so whats the next step to getting closer to -3 degrees up front. I'm hoping this alone fixes it and we can start adding a bit more bar back in as Fred had suggested.
If not the only thing I can think to do is to go to a 15/17 setup with some 225 width tires up front, but I don't want to spend the money if I don't have to.


Also I'm only reporting about 1.1G of max sustained grip. That seems quite a bit off of what other cars are pulling, but these phone accelerometers are a bit wonky sometimes.
I'm running pretty good lap times, at the local track that I use as a test ground. Last year I was running 1:12s this past session I was down to 1:08 missing apexs and talking to my passenger the whole time (see video below)
Some of that is me, some of that is the changes made already, and like I said I feel like if we could get the car to turn in better, we could take those times down considerably, maybe knocking on the door of 1:05s which is seriously seriously quick, we're talking Ariel Atom quick. Shifter karts do it in 55-58 seconds for comparison. Anything under 1:10 is considered pretty quick.

BTW cold tire pressures are 23F/27R and I seem to be getting my best laps only 2-4 laps in and if you keep watching the video only 5-6 laps in the car starts sliding (4 wheel slide). I don't measure hot pressure/temp but maybe I'm starting at too high of a pressure which is why the car is starting to slide. It was only 60 degrees that day so they weren't getting greasy

Video provided for more detail, vid starts on the second lap out. After one good warm up lap I even comment "Tire's are gripping well" and I'm actually not feeling like I'm going that fast. By the 5th lap the car was sliding around, all of which you can see in just a small number of laps shown in the vid
https://youtu.be/9uxhNGQgDFw?t=61


Any help would be greatly appreciated, I'm really starting to enjoy the handling dynamics of this car and the rear end is dead stable. If I could make it more neutral I think I'd enjoy it a ton more, and drop considerable time off an already quick pace
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post #2 of 30 (permalink) Old 10-18-2018, 05:01 PM
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More camber. Lots more. And drive around it a bit. Lots of trail braking. When I run 205/245 re71r the car is super neutral, but that's with closer to 3.5 front camber.

Oh you asked how to get more front. Machine the upright. Take off 6? Shims worth so you have the ability to adjust a little. This will give you 3.7 max front I think.

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post #3 of 30 (permalink) Old 10-18-2018, 05:23 PM Thread Starter
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Originally Posted by kfennell View Post
More camber. Lots more. And drive around it a bit. Lots of trail braking. When I run 205/245 re71r the car is super neutral, but that's with closer to 3.5 front camber.

Oh you asked how to get more front. Machine the upright. Take off 6? Shims worth so you have the ability to adjust a little. This will give you 3.7 max front I think.
Ok, how do you like the RE71's? I'm looking for a replacement for the R888Rs and I find them a bit muted in terms of response/feedback.
I figured it was just a matter of more camber, the wear on the front tires despite 6,000 street miles and a few events on them is pretty even up front.
They'll be heat cycled out next year so I'm wondering if I can find a fix with the LSS wheels (ideal) or if I should make the swap to 15/17s

I was also going to ask about braking balance, as I am planning to mount the front twin pistons radially out back. I'm assuming this shift in balance will help the car rotate if I do any sort of trail braking (maybe a bit too much)
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post #4 of 30 (permalink) Old 10-18-2018, 06:10 PM
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What are your ride heights? Increasing the rake may help pin the front end more, or the addition of a front splitter if you don't already have one.

I'd also recommend playing around with your suspension a bit more if you haven't already - deviate from the recommended settings with changes that add grip to the front or take it away from the rear and see what happens.

I mention this last but I think it should be the first thing you evaluate based on your stated settings - go to a nasa event, or some type of event that has some competition level type drivers, and have them either right seat you or have a go in your car and get their impressions. You need to evaluate if what you are observing is a result of your driving technique. I say this because most people I know with penske's observe that front end grip is greatly increased.

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post #5 of 30 (permalink) Old 10-18-2018, 06:22 PM
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As I mentioned on the phone and as Kfennell suggests, lots more negative front camber. More rear compression can also help.


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post #6 of 30 (permalink) Old 10-18-2018, 06:39 PM
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Originally Posted by Ls1Rx7 View Post
Ok, how do you like the RE71's? I'm looking for a replacement for the R888Rs and I find them a bit muted in terms of response/feedback.
I figured it was just a matter of more camber, the wear on the front tires despite 6,000 street miles and a few events on them is pretty even up front.
They'll be heat cycled out next year so I'm wondering if I can find a fix with the LSS wheels (ideal) or if I should make the swap to 15/17s

I was also going to ask about braking balance, as I am planning to mount the front twin pistons radially out back. I'm assuming this shift in balance will help the car rotate if I do any sort of trail braking (maybe a bit too much)
AFAIK the re-71R are the single best non slick tire, including all the 40TW tires excluding hoosiers. On my car with the very stiff suspension and low ride height they feel great and the car is very easy to drive at and over the limit.

IMO don't put the twin pots on the rear till you are 100% comfortable catching the car when the rear gets loose. Or you are going to install the rear bias bar. If you do it without installing the bias bar put at least 1-2 less compound in the rear.

If going to change wheels I like changing to 15 square with 15x8 and 15x9 and miata wheels with spacers. Nice short tires in the rear really help.

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post #7 of 30 (permalink) Old 10-19-2018, 08:29 AM
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Driving style will greatly impact the car wanting to "turn in" at the start of a corner. An obvious one is turning the wheel "too quickly" which will induce an understeer condition. A less obvious impact is trail braking. A misconception is that trail braking is used to make the rear of the car "loose" so it will rotate easier. In actuality, what you are doing is keeping weight transferred to the front of the car so the steer tires have more weight so more grip. Early release of the brake on corner entry will actually unload the front tires creating a turn in problem. Since our cars are mid-engine and carry about 60% of the weight on the rear tires, you have to do everything possible to transfer the weight to the front and hold it there.

If you want to be able to pick up the throttle early in the corner, you need a car that will transfer weight to the outside rear tire. This will need to be done with spring and shock settings. Increasing the front sway bar will actually stop the needed weight transfer. So, if you have basically no front bar in the car, the rear is not helping the car rotate.

Later,
Eldon
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post #8 of 30 (permalink) Old 10-19-2018, 09:21 AM
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I say driver mod. I'm running 1.5deg camber up front on R888R and my car rotates extremely willingly on entry/mid corner. Yes of course it will understeer on the throttle; it has no weight up front. This is not a car to square off corners and late apex. You need to dive in hot trailing brakes until the car is pointed at the exit. Then you get on the gas hard - our cars have excellent traction. This will lighten the nose and the car will push wide; that's why you have to get the car rotated before getting on the gas.

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post #9 of 30 (permalink) Old 10-19-2018, 12:11 PM Thread Starter
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Originally Posted by eldonz View Post
Driving style will greatly impact the car wanting to "turn in" at the start of a corner. An obvious one is turning the wheel "too quickly" which will induce an understeer condition. A less obvious impact is trail braking. A misconception is that trail braking is used to make the rear of the car "loose" so it will rotate easier. In actuality, what you are doing is keeping weight transferred to the front of the car so the steer tires have more weight so more grip. Early release of the brake on corner entry will actually unload the front tires creating a turn in problem. Since our cars are mid-engine and carry about 60% of the weight on the rear tires, you have to do everything possible to transfer the weight to the front and hold it there.

If you want to be able to pick up the throttle early in the corner, you need a car that will transfer weight to the outside rear tire. This will need to be done with spring and shock settings. Increasing the front sway bar will actually stop the needed weight transfer. So, if you have basically no front bar in the car, the rear is not helping the car rotate.

Later,
Eldon
Quote:
Originally Posted by SeniorDingDong View Post
I say driver mod. I'm running 1.5deg camber up front on R888R and my car rotates extremely willingly on entry/mid corner. Yes of course it will understeer on the throttle; it has no weight up front. This is not a car to square off corners and late apex. You need to dive in hot trailing brakes until the car is pointed at the exit. Then you get on the gas hard - our cars have excellent traction. This will lighten the nose and the car will push wide; that's why you have to get the car rotated before getting on the gas.


So you guys are suggesting to essentially drive this car more like a FWD car.
I'm not very good at leftfoot or trailbraking (not in my skill set yet) but I understand the concept, yet it goes against my preconceived notion of how to drive this car which has been mainly focused on being smooth and not mixing inputs. I feel like the majority of my spins on corner entry when i was learning the car were because I was still braking while initiating turn in.

Also keep in mind I have a Rev400 and a Quaife Diff, don't think those change much in terms of this discussion though.
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post #10 of 30 (permalink) Old 10-19-2018, 12:29 PM
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Quote:
Originally Posted by Ls1Rx7 View Post
So you guys are suggesting to essentially drive this car more like a FWD car.
I'm not very good at leftfoot or trailbraking (not in my skill set yet) but I understand the concept, yet it goes against my preconceived notion of how to drive this car which has been mainly focused on being smooth and not mixing inputs. I feel like the majority of my spins on corner entry when i was learning the car were because I was still braking while initiating turn in.

Also keep in mind I have a Rev400 and a Quaife Diff, don't think those change much in terms of this discussion though.
That Canaan track is mostly late apex designed on most corners...at least that's how I've been doing it. Only way I seem to carry any speed through it.

But I have been trail braking on occasion for turn 1 and turn 7. Seems to work pretty well. But yea, have to balance brake pressure and turn in.

I actually found it easier to do with the stock brake setup before switching to the 2-pot calipers all around. Even with a different compound in the rear, it seems to be more sensitive to braking and turn in. Even in some straight line braking, my rear seems to get loose at times. Maybe a brake bias cage in the future.

2007 Chrome Orange Lotus Elise
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post #11 of 30 (permalink) Old 10-19-2018, 12:35 PM
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Quote:
Originally Posted by Ls1Rx7 View Post
So you guys are suggesting to essentially drive this car more like a FWD car.
I'm not very good at leftfoot or trailbraking (not in my skill set yet) but I understand the concept, yet it goes against my preconceived notion of how to drive this car which has been mainly focused on being smooth and not mixing inputs. I feel like the majority of my spins on corner entry when i was learning the car were because I was still braking while initiating turn in.

Also keep in mind I have a Rev400 and a Quaife Diff, don't think those change much in terms of this discussion though.
You have to drive with the respect that it is a mid-engine car. You have a rear weight biased car. A FWD car is an extremely front weight biased car. Two totally different driving styles.

If you are loose on turn in during corner entry, you are unloading the rear weight too quickly. Adding some sway bar will help this or adjusting the shocks to control the weight to match how you brake.

You need to learn to trail braking and it does not require left foot braking. My guess is that you are over slowing the car which is why you are picking the throttle up so early. If you are on the throttle before the apex of the corner, this is a good sign that you are over slowing the car.

Later,
Eldon
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post #12 of 30 (permalink) Old 10-19-2018, 12:46 PM Thread Starter
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That Canaan track is mostly late apex designed on most corners...at least that's how I've been doing it. Only way I seem to carry any speed through it.

But I have been trail braking on occasion for turn 1 and turn 7. Seems to work pretty well. But yea, have to balance brake pressure and turn in.

I actually found it easier to do with the stock brake setup before switching to the 2-pot calipers all around. Even with a different compound in the rear, it seems to be more sensitive to braking and turn in. Even in some straight line braking, my rear seems to get loose at times. Maybe a brake bias cage in the future.
Interesting... getting more rear bias is on my to-do list. I do feel like the fronts are doing way too much work right now but remind me what pads your running again front/rear?
What tire pressures are you using BTW? I seem to be getting a few good laps and then the car starts losing grip and sliding more not necessarily like they're getting greasy but maybe as if pressure is getting too high

Last edited by Ls1Rx7; 10-19-2018 at 01:02 PM.
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post #13 of 30 (permalink) Old 10-19-2018, 02:20 PM
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Originally Posted by Ls1Rx7 View Post
Interesting... getting more rear bias is on my to-do list. I do feel like the fronts are doing way too much work right now but remind me what pads your running again front/rear?
What tire pressures are you using BTW? I seem to be getting a few good laps and then the car starts losing grip and sliding more not necessarily like they're getting greasy but maybe as if pressure is getting too high
Per BOE's advice, I went with RC8 front, RC6 rear. They also suggested Cobalt XP3 front, XP4 rear. I think I'm still getting a little too much bite in the rear with the RC6...or maybe I just need to be smoother with the brake...still working on it.

Kind of depends on temp, but I've been starting at like 23-24 front, 25-26 rear and then trying to maintain 26-28 after I get off the track hot. Sometimes I've seen that 26 balloon up to 32ish. So I'll try to check after each session as I usually get faster and the track gets hotter as the day wears on. I'm 205 front, 235 rear. Thinking of also stepping up to 245 rear which might help with my rear brake bias issues.

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post #14 of 30 (permalink) Old 10-19-2018, 02:57 PM
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Originally Posted by Ls1Rx7 View Post
Interesting... getting more rear bias is on my to-do list. I do feel like the fronts are doing way too much work right now but remind me what pads your running again front/rear?
What tire pressures are you using BTW? I seem to be getting a few good laps and then the car starts losing grip and sliding more not necessarily like they're getting greasy but maybe as if pressure is getting too high
Without seeing data and matching video I could be wrong. But from what you are saying here I suggest NOT going to rear 2pots for you unless you are also getting a bias bar. It makes the car HARD to drive.

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post #15 of 30 (permalink) Old 10-19-2018, 03:13 PM Thread Starter
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Without seeing data and matching video I could be wrong. But from what you are saying here I suggest NOT going to rear 2pots for you unless you are also getting a bias bar. It makes the car HARD to drive.
How about just running a more agressive pad compound out back with stock brakes.
For example the Rc5+ has a lower average coefficient of friction than the RC6. I was thinking of using the Rc6s in the back on stock rear brakes to artificially shift the bias rearwards a bit. It's much less extreme of a change
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post #16 of 30 (permalink) Old 10-19-2018, 03:36 PM
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I ran RC8 rear and 6 front. I have some new RC8 here I can sell, and will include all the used pads that I have if you want to try some combos.

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post #17 of 30 (permalink) Old 10-20-2018, 08:40 AM
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Sorry for my different approach, I know it will be a big discussion by my question and comment!

What type of diff you have?

I am using a open diff, with 390 whp, 550 lbs fr and 700 lbs rear and helper spring (very important), traction control set at 10% slip, stock sway bar on std position, and the car handle nicely with aero, on Track with curve between 50 to 110 mph. Very nice handling. But for sure, the car with an open diff do not have traction for auto-cross on small track, but the open diff help to limit, based on my personal experience, the understeer on throttle.

Please, donít **** on me, I can remove my comment if it is too much **** for my comment.

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post #18 of 30 (permalink) Old 10-20-2018, 10:29 AM Thread Starter
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Originally Posted by elise/europa View Post
Sorry for my different approach, I know it will be a big discussion by my question and comment!

What type of diff you have?

I am using a open diff, with 390 whp, 550 lbs fr and 700 lbs rear and helper spring (very important), traction control set at 10% slip, stock sway bar on std position, and the car handle nicely with aero, on Track with curve between 50 to 110 mph. Very nice handling. But for sure, the car with an open diff do not have traction for auto-cross on small track, but the open diff help to limit, based on my personal experience, the understeer on throttle.

Please, donít **** on me, I can remove my comment if it is too much **** for my comment.
I actually have the Quaife diff. I don't know how much they lockup
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post #19 of 30 (permalink) Old 10-20-2018, 01:01 PM
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re: handling, diff, sway bars, etc..

Quote:
Originally Posted by Ls1Rx7 View Post
I actually have the Quaife diff. I don't know how much they lockup




quaife may make a few different ATB's for a given transaxle, if it is used as fwd, mid-engine or drag.

Usual lock-up is 2.5. Although,m this number does not really apply to ATB's or torsen diffs.

The combination of all of the above and springs and shocks and driving style will determine
what equipment you should use. There are a few long discussions on this subject in this forum from
waaay back.

My preference (I started with high-powered front-engined Corvettes at Mosport) is Torsen/ATB/Quaife, front
and rear sway bars. Neutral to mild under-steer. I trail brake to rotate the car. Understeer can be corrected in any corner with
application of power!

Anton

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post #20 of 30 (permalink) Old 10-20-2018, 04:33 PM
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I would suggest trying a little more tire pressure up front, sometimes its the simple things.
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