v6 cup loose rear - LotusTalk - The Lotus Cars Community
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post #1 of 25 (permalink) Old 09-19-2017, 08:19 AM Thread Starter
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v6 cup loose rear

Interesting problem witht he v6 cup. Had a pro driver in it nad he reported somethign I have felt. the rear end is "loose" its oversteering going into and exiting a corner.

Rear negative camber is only -2.4 yet we see that the inner two thirds of the tire are being used and the other 1/3 is not doing serious work.

Softer shock settings has the car hooking up comming out of bends but then the rear feels like its falling down and the tail is wagging aorund at speed.

Somehtings not right and we need to ge the rear to work, is it ride height, not enough rear toe, or ar the nitorns justy plain wrong ie initial response too hard and then too soft, in other words not progressive.
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post #2 of 25 (permalink) Old 09-19-2017, 09:23 AM
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sounds like you have some rear toe-out, or not enough toe-in in the rear. Toe-out would be easily noticeable! The rear would come around really easy! You might have a worn suspension component causing a different toe setting on one side compared to the other.

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post #3 of 25 (permalink) Old 09-19-2017, 09:25 AM
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if you have too much rebound damping, then the suspension can weight jack down and get too firm, not able to respond to the ground and maintain tire contact with the ground over bumps. Use the minimum amount of rebound damping.

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post #4 of 25 (permalink) Old 09-25-2017, 12:21 PM Thread Starter
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Originally Posted by Vulcan Grey View Post
if you have too much rebound damping, then the suspension can weight jack down and get too firm, not able to respond to the ground and maintain tire contact with the ground over bumps. Use the minimum amount of rebound damping.
As car is new, and I know there is adequate toe in rebound makes sense. Ill try one click less it next time out.
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post #5 of 25 (permalink) Old 09-25-2017, 12:35 PM
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Some owners have found their alignment settings are not correct when the car is new. I would hope your V6 Cup was correctly set up by motorsport, but... Worth checking. if you have changed your ride height or anything like that, it would change the Toe setting.

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post #6 of 25 (permalink) Old 09-25-2017, 12:36 PM
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I'd start with minimal rebound damping and work up, IMO, unless you know someone with the correct setting for the same car/suspension to copy settings from.

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post #7 of 25 (permalink) Old 09-25-2017, 01:49 PM
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@boxerman ...1 click change on rebound will not be noticeable -- you will need to do more to see if you can feel a difference. Can't speak as to how good (or bad) the Nitron 2-way valving is for your application. I'm sure the shock valving was not optimized for slicks, as it was used on their street Cup cars and set up for R-comp tires.

I'm assuming the car was aligned, ride-height adjusted and corner balanced post delivery, no?

If not, that's your first thing to do.

Are you running with any stage of the DPM on?

I'm running more negative camber than you in the rear and tires show good/full wear across the tire. I'm also running the 3mm total toe-in for the rear. FWIW, I believe that the specs for the Cup car was ~ .6 degrees of total toe-in for the rear, which would be more like 4.6mm of total toe-in.

Also, I do not suffer from corner entry or exit oversteer. Obviously, we can't compare the two cars, as I'm running different shocks, different spring rates, a plate-type LSD, etc.

Sorry, I can't be of more help.

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post #8 of 25 (permalink) Old 09-25-2017, 02:29 PM
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With the way you are describing the car, it sounds as if there is little to no correct weight transfer. A car that is typically loose on corner entry is because the weight is transferring too quickly to the front tires. This can be a multitude of different problems but if we make the assumption that the springs are close then I would start by putting compression in the fronts and taking rebound out of the rears. Loose on exit is exactly the opposite problem; take rebound out of the fronts and put some compression in the rears. Now, all of these adjustments are controlling the dynamics of the car. This all occurs at the beginning of brake and throttle application.

As Jack said, you are going to have to make big swings at the shock settings to see if this is the right direction. Once you find both sides then you can find a setting that is in between. Now that being said, a shocking setting that you like may not be the same shock setting a Pro likes. As I said, shocks control the dynamic weight change. A smooth driver will not require the same settings as an aggressive driver.

As far as not wearing out the third of the tire, if you are not getting weight transfer you will not load the tire to make use of the camber. If this weight transfer is not occurring because the car is loose in and out then I can see this happening.

Something to try which I have a hard time to get drivers to do, approach a corner at the speed you know the car will go through the corner without using the brakes at entry or lifting on the throttle. Drive through the corner and off. How does the car feel? Did it push or get loose? Slowly increase the speed through the corner until the car no longer tracks the arc of the corner. Which corner gave up first; front, rear or both? Then work on that end of the car.

Make sure you do this with a corner that has plenty of runoff. This is trying to learn the feel of the car and not trying to set a fast lap. If you are taking data, I will almost guarantee that you will go through the corner faster than you did braking for the corner. It is hard to do on a road race track if there are many cars on the track.

Later,
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post #9 of 25 (permalink) Old 09-25-2017, 02:36 PM Thread Starter
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yep everything was redone and reset by alex a krugspeed. Stock setup from factory was a total mess.
However we have only 1.5 mm toe in rear.
In nay vent were not using the tire correctly. For exit this implies the rear is too stiff, ie too much compression, and on entry too much rebound. Ill play around and see.
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post #10 of 25 (permalink) Old 09-25-2017, 02:58 PM
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Quote:
Originally Posted by boxerman View Post
yep everything was redone and reset by alex a krugspeed. Stock setup from factory was a total mess.
However we have only 1.5 mm toe in rear.
In nay vent were not using the tire correctly. For exit this implies the rear is too stiff, ie too much compression, and on entry too much rebound. Ill play around and see.
This is why I made the statement about a smooth vs. aggressive driver needing different setups. An aggressive driver, on corner exit, needs compression because he wants the dynamic weight transfer to go to the tire contact patch very quickly. If not, the tire does not have the weight required to take the traction request. A smooth driver applies the throttle in a longer period of time thus the car has more time to transfer the weight to correspond with the requirement of the needed traction.

More toe-in in the rear will make a big difference on how the car handles on corner exit.

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post #11 of 25 (permalink) Old 09-26-2017, 07:03 AM
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Quote:
Originally Posted by boxerman View Post
yep everything was redone and reset by alex a krugspeed. Stock setup from factory was a total mess.
However we have only 1.5 mm toe in rear.
In nay vent were not using the tire correctly. For exit this implies the rear is too stiff, ie too much compression, and on entry too much rebound. Ill play around and see.
If you have total toe-in for the rear set at 1.5mm .. that is way too low.

I'm sure Alex got the recommended alignment track specs for the V6 Exige from Allen at VSA and he would have recommended 1.5mm per side.

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post #12 of 25 (permalink) Old 09-26-2017, 07:35 PM Thread Starter
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If you have total toe-in for the rear set at 1.5mm ….. that is way too low.

I'm sure Alex got the recommended alignment track specs for the V6 Exige from Allen at VSA and he would have recommended 1.5mm per side.
That may be an issue, esp on liftof. But power on oversteer, not using he outer third seesm like shocks to me. If the rear roll bar was adjustable thats where I would start, but its not. adjustable.

Will be back at track next thu with fresh tires(the old ones have corded on the inner part) and will fiddle with shocks to see how even we get tire wear.

Allen also wants a pic of the old rear tire.

Persoanly I think the Nitrons on this car suck, they are not progressive so you risk making hem too hard intialy in order to not have them fall off too far under load.

I could attribute a lot of this to my lack of skill, but Elivan is the fastest man in the east and he was impressed i could drive the car as well as I did given how it is.

Yeah after the shock fiddle this winter well look at tire wear and adjust accordingly. I also want more negative toe in front to enable turn in.

Seems like the right setup is -1.5 per toe per side front and +1.5 per side rear. With -2.4 camber up front the tires indicate we could use a bit more negative camber. At the rear with -2,4 we are not using the outer 1/3, so the theory is were not getting enough roll at the rear, ie try softer compression and or less rebound.

Once these tires are used up in about 2-3 days its our winter and well adjust accordingly, Alex thinks the rear can use a little more ride height too. Its all a work in progress.

Meanwhile in imporved braking alone I gained 2 secs per lap at Monticello. Dont know how that would translate at the Glen but as I was running a 2.11 on 8 heat cylced tires before seems like breaking 2.10 should be doable now as is. Get the rear workign properly and the driver(me) improved and who knows, once 2'10 falls then its 2.07 and then 2.05.

So yeah sort the suspension for next year, then year after gearing. All fun.

Meanwhile I am absolutely loving the car, its just plain fun to drive and even with things subotimal its not mean. Plus I can feel so much raw potetial in it, its very much growth for me to recalibrate my brain and ability up to the cars.

My Elise which i drove on track for 6 years i think i knew pretty well. At the Glen it was a 2.19 car and at MMc 2.46 so same driver 7 secs per lap faster in the exige and there is clearly much more to go.

Last edited by boxerman; 09-26-2017 at 07:40 PM.
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post #13 of 25 (permalink) Old 10-09-2017, 02:08 PM Thread Starter
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The old tires it was the passenger side that corded on the inner third, indicating were not rolling the rear enough to really use the tire, and or too much negative camber.On track you can feel betetr grip on rh turns from the rear which is ridiculous as thats where the weigh sits and there are fewer lh turs which meas the righ rear shoudl alst better.

Reducing rebound made a big difference. Reducing compression made the car squirrely and while rear grip improved somewhat it was no longer accurate or consistent.
We're still not using the rear tire all across consistently and I am nowhere near the limit of the front when the rear gives up.

I am going to dial out a little rear camber to use the tire better.

So much poetntial to this car, I just have to keep working at dialing it in.

this winter we will also revalve the nitrons, it seems their way is to be stiff and then let go/fall off like a knee.
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post #14 of 25 (permalink) Old 10-10-2017, 12:52 PM
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Bring it to Palmer next week with SCDA and I'll go out and watch you drive. It s been a while since we were together on track. Will let me see what the car is doing. With that assortment of corners, we should be able to provoke it!

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post #15 of 25 (permalink) Old 10-10-2017, 12:55 PM
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post #16 of 25 (permalink) Old 10-16-2017, 06:19 PM Thread Starter
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yes 1.5 per side
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post #17 of 25 (permalink) Old 10-16-2017, 06:26 PM Thread Starter
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Ok I puuled two clicks rebound out the rear, each click improved things somewhat on turn in, power out was a little better, more compression on the rear seems to make the power oversteer worse. maybe I have to pull some compression and rebount out the front.

I also tried removing one click compression and the car had better traction out but was falling on its ass.

Persponally i think it could use a little ride height at the rear so it works better.

Meantime I am going to pull half a degree of negative camber out the rear and reset the rear toe, Ill see what the tire says then.


Maybe thats working around a larger issue. I'll see how it goes, and in nay event reset ride height corner balance align etc again this winter.
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post #18 of 25 (permalink) Old 10-25-2017, 06:59 PM Thread Starter
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Put the car on the alignment rack. the fronts were toed in and the rears toed out, which explains a lot.

So we put 3mm total toe in rear and 1.5 total toe out front, and left the rear camber as is, ie -2.6. As others have said large front toe out affects braking and the front end wants to go one way or the other but run in is great, Ill probbaly half the toe out for next year. The rears with toe in are now wearing more evenly, however the rear still has that pendulum effect. This I partialy attribute to a 36% front 64% rear weight boias, but also and the rake on my car being wrong.
The rear is sitting at 125 mm and the front 122 should be 136/125. So perhaps the roll centres are off too.

meanwhile the front discs look to be toast with cracks running off the drilled holes. Anybody have experience with Giro disc on track. I ran those on my elsie with RS14 blacks, but the exige with ap calipers and carbotechs brakes in another league so wondering what choices there are.
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post #19 of 25 (permalink) Old 10-25-2017, 07:51 PM
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The toe-out in the rear would explain why the increase in rear shock compression made the car respond extremely. Once you get the toe corrected and back on track, play with the rear compression again, it should help in a more positive way.

Later,
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post #20 of 25 (permalink) Old 10-29-2017, 01:41 PM Thread Starter
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The toe-out in the rear would explain why the increase in rear shock compression made the car respond extremely. Once you get the toe corrected and back on track, play with the rear compression again, it should help in a more positive way.

Later,
Eldon

Sadly down for the winter now so it'l be next spring.
But makes sense that toe out in the rear and more compression would upset things. Even still last outing with correct toe in still had lurid power oversteer, maybe compression would help this. The rear of the car still is nowehere near what the front can do, I mean like 30-40% away.

Even though the mtor is crying for pipes and atune, I am seriously thinkign of biting the bullet and buying the Cup R ohlins setup, I fear the nitron setup that comes with the V6 cup is still a "streetable" setup springwise, and I will be forever trying to work around it on track.

One other issue can be the lack of LSD given the TQ of the V6, but still there are issues on fast sweeping bends where the lack of lsd should have little effect.

I do think though that the current lack of rake is messing with things a lot, roll centres rear weigh bias etc. Its really a fiunction of wehehr I setup the car properly as is(nitrons and springs), or set it up properly with the Cup r ohlins, and I am leaning that way because I know ultimately in year or two I'll end up there anyway.

So do I spend $ this winter on header and a tune, or shocks and springs. The V6 has pre cats in the manifold but no 3rd cat downstream as evoras do the stock setup is doing the motor no favors. Yeah do both, but budget intervenes, not least because the front drilled rotors are cracking and I need some slotted ones.
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