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Question for Alignment "experts" - corner balancing


QuaTTro
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I'm having an internal debate with my team over the value of corner balancing of our 1990 Audi 90 Quattro sedan.  As it sits now, the car is about 2700lbs with a 60/40 split due to the fact that Audi likes to mount the engine in front of the front axles.  Historically we've just done our best align the car ourselves for a good balance of removing understeer but preserving some tire wear so that we can last the race.

 

We have height adjustable coilovers (40 points!) and just kind of set the height of the car the same on all corners.  Had to DIY them a bit as you can see in the pics below since there aren't real Off the Shelf performance parts made for our car (who mods a 90's audi sedan???).

 

I've been wondering about having a local tuner shop help us with corner balancing the car, but my teammates don't think it will really help due to our 60/40 front weight bias. 

 

1.  What is everyone's thoughts about corner balancing a car like ours?

2.  What alignment settings would you recommend car a heavy awd car with poor front rear weight bias?  I think we have approximately -1.5 front and -1.25 rear camber currently.  

IMG_1766.jpg

installedcoilovers.jpg

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I'm sure Mr. Nabb will come in and tell me how i'm wrong on everything I say, but my impression of the value would be balancing your cross weights which have the effect of optimal and balanced left-hand compared to right-hand turning performance.

You won't be able to do much about that F/R bias. If you can do it yourself I'd have a go but I wouldn't spend a lot of money, unless something is severely off your lap time reduction will be small.

I'd get more negative camber on that thing all around!

Edited by Slugworks Paul
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I agree with Paul.  It's not about f/r bias.  It's about cross weights.

 

If you are guessing at alignment without knowing the impact, I would not worry that much about corner weights.

 

I Would worry about tire temps.  Align the car to have fairly balanced tire temps across your most heavily loaded tires (probably both fronts, with the possibility of both outside tires).

 

Get your temps to be pretty even and this should guide you on alignment and pressures.

 

Once you have that under wraps, then you can corner weight.  It will help eek out that last little bit.  

 

Then, go to wider tires and wheels to improve your wear characteristics.  Then, use the tire temps to reset your alignment and pressures.  Then re corner weight.....

 

I am guessing you will want to double your front camber....   

Edited by wvumtnbkr
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I have never corner balanced one of my Champcars. Not that it won't help, but it must not be too critical. I try and set my camber for "best tire wear" vs "best lap time", it works for me. For toe I'm sure you want to be close to 0, but maybe there are some tricks for AWD where you set it in a 1/16" here or out a 1/16" there. 

I agree that you might want to double your front camber and be like -3*. 

 

Last year I drove a car after it was involved in a major accident, and the car had like 10* camber on one tire and the toe got an eyeball job in the pits etc.....and it drove better than I expected.  


 

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Wedge is the term for "unbalanced" corner weights and is a useful tuning tool that can be used to bias the handling in favour of one direction over the other. 

I usually set mine within 10 lbs of optimum and leave it there, but I probably could play with that depending on the track. 

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Thanks for all the feedback everyone.  Keep it coming.  

 

We used to run more negative camber (-2.5 front), and I liked it....but we also found the tire wear pretty bad such that we could only get about 6 hours on our front tires.  It was super annoying and wasted time to swap tires during the last driver change.

 

Toe is set to 0 all around, and we really haven't played with that much.

 

We did switch from 205 to 225 width tires and that's definitely helped.  With our car, there are very limited wheel options (unless we change to a different bolt pattern and but more wheels).

 

Did I mention we are cheap bastards?  Seems like we end up doing things to save money even if it means we give up performance benefits.  

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We run a VW Fox.   Don't worry about the F/R bias.

We run about 3.5* negative camber and a touch of toe in.  We used to run 1/8 toe out but the car was just too darty down the straights although turn in was amazing.

The car does push a bit so we're probably going to add a front splitter for next year and see if that helps anything.

 

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4 minutes ago, QuaTTro said:

Thanks for all the feedback everyone.  Keep it coming.  

 

We used to run more negative camber (-2.5 front), and I liked it....but we also found the tire wear pretty bad such that we could only get about 6 hours on our front tires.  It was super annoying and wasted time to swap tires during the last driver change.

 

Toe is set to 0 all around, and we really haven't played with that much.

 

We did switch from 205 to 225 width tires and that's definitely helped.  With our car, there are very limited wheel options (unless we change to a different bolt pattern and but more wheels).

 

Did I mention we are cheap bastards?  Seems like we end up doing things to save money even if it means we give up performance benefits.  

What part of the tire wore out?

 

If it was the inside, that can be from toe issues as well.  It can also, to a lesser degree, be pressure related.

 

Tire temps will tell you what camber and pressure to run to make the tire happiest.

 

I am amazed you aren't destroying the outsides of the tires on a front heavy, probably understanding car, with that little camber.

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You guys have given some good advice. I think we are on the same page. A couple of quick notes I had from my own experience 

 

  • You cannot change noseweight, Right side weight or total weight via "setup" changes, unless that setup involved moving the wheel locations in a meaningful way. Or you cut things off while setting up the car
  • Doing the math on what it takes to change noseweight in a large way is soul crushing, and may resulting in cutting your car in half to move the axle locations....:)
  • If you have stiff enough springs you can end up with pretty large changes in crossweight when using the "eyecrometer" to set ride heights. I checked one of my cars with heavily cut reasonable stiff springs and it was 7% crossweight out. That made a measurable difference in balance, when turning left vs right. All depends on how terrible you set the car up the first time
  • The optimal camber will depend on tire load and air pressure. At 205 and a heavy car if you run high pressures your wear may not indicate needing more camber (at 60 psi the ideal camber may be 1 deg at your wheel loading). If you get the tire size right and the hot tire pressures close I would guess you will end up with 2.5 to 3.5 deg of front camber. This would be at 225 or 245 width tire on a 8+" wide rim and mid 30's for hot pressure. Some of us push the pressure lower and camber higher, but you can work your way up to this. 
  • You can have a "neutral" setup without oversteer or understeer at may different grip levels, and a understeering car with more overall grip can beat a car with poor grip that is balanced. In our terms you can have a balanced car with 185 tires running 80 psi at zero camber or a 245 at 35 psi running 4 deg camber....... I think we know which one will win. Not achieving ideal camber is a pretty fundamental grip adder, most vehicle dynamics guys would attack other things to get the balance right before taking camber out. 
  • If you think of the tire as a heat transfer device (to the ground), at your weight a 205 is going to be on the hot side and a small width increase might get the temp low enough to really change the wear (this is not linear, often a step you either are below or now)
     
Edited by Black Magic
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We have found that the biggest improvement with adjustable perches is simply to get the car as low as possible reasonable in the front and adjust the rake angle the car has.

 

We have corner weighed our car in the past, have not in over a year but probably will once we make a few modifications this winter just to see where it stacks up again. Plus its kind of fun to fart around with.

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You can get into trouble when lowering a strut suspension too far, that will result in a positive camber curve once the strut and lower control arm go past a 90 degree angle to each other. Best way to avoid that is to make sure your lower control arms are very close to horizontal at ride height.

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Thanks for continued good advice!  Seems like the best next step for me is to run some hot laps and collect data on tire temps.  We've never done that....we just look at tire wear during the race.

 

Additional notes about our car:

 

We are running 350 lb springs all 4 corners.  This was recommended by the person that supplied the coilover kit because we primarily run on bumpy Texas tracks (harris hill and COTA).  I wonder if we should run different springs front and rear?

 

We have factory sway bars front and rear.  I forget the sizes but something between 20-22mm.

 

Tires are 225 on 7 inch wide rims.  That's all we have available for now.  😞

 

Our front shocks are adjustable dampening, but rears are not.

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We have been scaling our car from day one, My brother been running Modified for 30 years and helped use and trained me with a lot of brotherly fighting .

  • Your are running to soft on spring rate  should be in 600 LB range 
  • No sway bars
  • if you wish the rear to be loose up spring rate or tire pressure
  • all the camber you can get in it
  • fix the roll center
  • fix the bump steering 

full of fuel 20GAL driver in car  grid ready last year with the 18.L turbo 6 speed AWD

At NH coming in to turn 1 just under 90 MPH as  you can see its flat and planted 

 

kLCUeMr.jpg

 

PFSSNUQ.jpg

paAVOm3.jpg

 

 

Aztcbge.jpg

Edited by DRVOLKS
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5 hours ago, QuaTTro said:

Thanks for continued good advice!  Seems like the best next step for me is to run some hot laps and collect data on tire temps.  We've never done that....we just look at tire wear during the race.

 

Additional notes about our car:

 

We are running 350 lb springs all 4 corners.  This was recommended by the person that supplied the coilover kit because we primarily run on bumpy Texas tracks (harris hill and COTA).  I wonder if we should run different springs front and rear?

 

We have factory sway bars front and rear.  I forget the sizes but something between 20-22mm.

 

Tires are 225 on 7 inch wide rims.  That's all we have available for now.  😞

 

Our front shocks are adjustable dampening, but rears are not.

 

I'm no set up expert, but 225 on a 7 inch rim is pretty pinched.  I'd expect to see that on autocross cars, but for the track, 205 would be more appropriate on a 7 inch.  But as others have said, a tire that small is going to get hot faster and wear faster too.  If money were only a small issue, 245 on a 9+ inch would make a huge difference.

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Spring rate will really depend on motion ratios and what your drivers are comfy with. It can be a bit unnerving getting into a really stiff car when you're used to more of a boat as the feedback feels different, and there is some truth to softer spring for rougher track in my (limited) experience.

 

Camber wise, follow the tire temps as long as you have very little toe and aren't spinning the inside front coming out of corners. Static camber doesnt mean nearly as much as dynamic camber. Going into the corner the weight is on the outside front and compresses that corner. Tire moves up in relationship to the body, the camber angle most likely changes in relationship to the chassis, and the chassis angle to the ground also changes. A higher spring rate will reduce all of those motions for a given load, which tends to help as the dynamic camber change tends to be non-linear. Most suspensions have a sweet spot, a higher rate can help you stay in that sweet spot longer. If you're using aero, an added benefit of higher rates is that it keeps the aero components in a narrower (and hopefully more effective) height range. A splitter for example gains downforce rapidly as it gets closer to the ground, right up till it hits. Then it goes to zero.... 

 

My long winded point is this- get the tire temps happy for one driver. Then send the others out and see if they stay happy. Then add a bit more camber and see what happens. If tire temps are still happy and lap times improve, go until they get worse again, then back it off to where you're happy with the balance of wear and grip. Try to tune to your middle drivers, the fast one can adapt, and the slow one will improve faster than if you tune to the fast guy's wants.

 

Static numbers anywhere from 0 to 4ish are fine for most, it's that dynamic situation that really matters. It's just a ton easier to measure static and since most folks are running similar spring rates for the same or similar cars, we all talk in static. The big series guys use sensors that measure the shock travel so they can go back and model the real time of all the angles. With a smooth track and entrance/exit you can get an idea of the maximum compression with zip ties on the shock shaft. I've had better luck scaling off pictures using known features on the car....

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Here is some old bump steering test and adjustments on the Audi or VW beetle ? we only care on the left of the scale compresses 2 inch down. Stock  audi and VW the line from the center to the left form 0 to 100 th  line B of tow in on one wheel that 1/4 +inch of tow out on corner entry. the center line A is fixed 0 to 10 th of and inch just some thing to think on.  so stock is line B it has over .400 th of tow in and out  per wheel for 4 inch of up and down

image1.jpeg

Edited by DRVOLKS
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