Spring, suspension and tire pressures

Hope spring is making you get out to the garage to check what the winter has done to your cars and how they can slowly get just that much more fun on the track! 

When switching over Deb’s snow tires the other day, I got a nasty surprise - a crack in the wheel rim on the inside. That explains the slow leak. 

With the potholes slowly being filled (and then opened up again with rain), its also a great time to get your alignment looked at. I just had mine done at Roger’s (~$80 - great deal!) and nothing was too awry. But I had Dave tweak mine a bit for autocross by adding additional negative camber (top of wheel/tire pushes in toward car and bottom pushes away ever so slightly) to improve handling in the twisty corners of the autocross. 

I learned a little more about suspension setup by trying to edumacate myself before visiting Roger’s and watching them tweak my undercarriage (gently). I learned that most cars are set up to push (understeer or lose traction on the front wheels - and steering) when driven hard. This is for safety in theory as it’s a bit more catchable than having the back end break loose and swing around. When a car is described as “neutral” both ends break loose at about the same time - which is why mid-engined cars have general advantage with the weight of the engine well-centered in the chassis. I wanted my car to be a bit more neutral, but in retrospect I probably headed toward the opposite due to limits with the stock adjustability. 

Tire pressure also plays an important role in handling. Low pressures in the front, while often recommended by manufacturers, also tend to make the car push/understeer (for safety of course). So bumping up the front pressures before autocross and track work may provide a bit more front grip and less push. Dave at Roger’s has been very accommodating in helping my understanding of how this all works together. He is also willing to do things that are beyond the “manufacturers recommended settings” - something that scares most dealers and other big auto shops. 

Through reading, I also learned that you don’t want the difference in camber between your fronts and rears to be more than 0.5 degrees or things start to get very unpredictable. And if you dial in lots of negative camber, you start to risk a few things - straight line stability (you are riding on less tire in a straight line), straight line braking (since the tire is less “flat” to the ground in a straight line so smaller contact patch), and tire wear (since it will now ride on the inner shoulder when traveling straight you get uneven wear rate across the surface of the tire). There are some trade offs to consider especially if the car is being used for multiple purposes. And then there is caster and toe-in - subjects for another day.

With new folks (welcome Matt!) jumping into the ACF, it was finally time to make the move to a platform that would allow all these emails to pull together into one place so we can catch folks up on where we’ve been and where we are headed. So I’ve dumped a bunch of our old communication (carefully with considerations for public/private, anonymity of SergioC/Attilio..., etc) to a blog platform that can be the content hub for us. The new home is : http://acf.posthaven.com/

Its not flashy or fancy but is supposedly guaranteed to stick around for a while.

And A was kind enough to send along some new autocross events that will be at Thompson and in Hartford through CART - the CT Autocross and Rally Team. They are now on the schedule at http://clientextranet.us/acf/

Dave S. and I are off to Austin TX this weekend to watch the MotoGP races at the Circuit of the Americas (bucket list item) - but we’ve got some fun coming up 4/27 with ADSI down at Quonset, autocross 4/12 in Hartford if you’re up for it, and still looking for a co-driver for the endurance kart race opener at F1 Boston on 4/28 (Monday 6:30pm - hard with kids for sure).

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From a mysterious participant: A note about alignment changes, their effects will vary enormously with everything else in a car, suspension geometry and settings, tire type/size, roll center and weight distribution and vehicle design. What goes for one car does not go for another. For example the recommended track & autocross alignment for a Subaru Impreza is lots and lots of negative camber (wheels tilting towards each other at the top like a tripod or tent) up front. The rear, they actually recommend less or even lowring the camber and having the tires more vertical due to the rear's different suspension geometry that actually adds camber when you turn. In other words the double wishbone design of the rear makes the wheels tend to roll in the direction you want them to when braking or cornering, so adding camber to the rear, even with the most aggressive handling characteristics in mind is counterproductive. Regarding different uses, effects and tire wear, it will vary by driving style. For example if you are an aggressive driver, or if the car has a McPherson strut type suspension (as opposed to double wishbone) more negative camber will actually wear the outer edges of the tire less and you will get more even tire wear, to a point. But yes, while braking and bad weather traction will suffer with more aggressive camber settings, it is physically impossible to dial in much more than -1 degree, maybe -1.5 degrees of negative camber at the most on any production vehicle without specialized aftermarket suspension parts. That will be plenty aggressive for any street driven car likely to see autocross. The problem is here: most street driven cars have screwed up alignment from the factory and you the owner don't even know it. The car may pull to one side or just not quite handle as you'd like, and you never know why. The factory has certain tolerances, and while your car is most likely within them, if the tolerances of the different wheels are such to constructively interfere with each other, you can still get problems. Think of it like a dating website where you plug in your zip code (as I did w/ my wife on Match.com) and "maximum distance". Well if you are on the very edge of the zip code, and the person you want to date lives on the opposite edge of another zip code opposite you, the computer doesn't measure that. It measures the minimum distance from the 2 closest points of the 2 zip codes, so if you plug in "25 mile" max distance to the match.com, you can actually wind up searching for people who live over 50 miles away. Well, I am glad that this error found my wife, but to have two rear tires both toeing in the same direction (one in, one out) at 0.2, the maximum allowable by the factory for toe, was a "normal" finding for the dealer despite having some problems handling my car. However, that made the car pull to the left, and be overly unstable when braking. This tendency was fixed with a simple 80 dollar alignment @ Roger's Tires. Therefore, for all beginners, I would suggest telling your alignment shop: "I want perfect, 100% symmetric alignment on both axles left to right (but not front to rear) with the following specs: -maximum dealer/factory recommended camber where adjustable and the same on each axle (front 2 should have the same amount, rear 2 should have the same amount if adjustable) -maximum dealer/factory recommended caster if adjustable, otherwise same on both front wheels. Caster angle is just for the fronts as it has to do with steering angle, but this should be checked and made symmetrical if not already. -zero toe all around for all 4 tires down to the 2nd decimal place (0.00)." This will be a fairly reasonable, not too aggressive alignment that is within factory tolerances, won't get anyone's panties in a bunch, void your suspension warranty or make the car difficult to control. Don't play with toe, if anything that makes the car start to be very twitchy, especially toe in the rear. Even a small change, like from zero toe to 0.01 can cause a striking difference in the handling balance, and unless you are trying to accomplish something very specific, like gaining an advantage in a competitive class where modifications that would likely just be better overall would push you in a more expensive, difficult class (like racing against Porsches instead of staying with other factory stock, unmodified Mazda Miata's), don't bother. That said small tweaks, like 0.01 toe in for the rear for stability or 0.01 or 0.02 toe out for the front for more brisk steering response can be helpful, but beyond this toe more than camber can cause bad tire wear or dangerous handling and leave it to the pros. Caster angle is good to increase. A simple example of caster is like a chopper bike with the front angle exagerrated. When you turn the wheel, the inward tilt of the tires will be exaggerated; this is good because what that means is the wheels are more upright when straight so you brake and get better traction, but when turning the wheel you get added negative camber as the wheel kind of tilts inwards. So you get the "type" of desirable camber you want when you want it and not when it's less advantageous. Also it makes the car more stable and want to go in the direction that the wheel is already set instead of wandering in its path. However, most street cars have little to no caster adjustability so don't play with it. It's not as dangerous as toe, but until you understand caster, leave it alone. That said camber plates are a great way to get another degree or two of added caster but that's another story! Yes Sterling, I noticed your Porsche was more tail happy than I expected. Mine still ploughed up to a point. Once I learned how to compensate my driving style, the car became joyously tail happy and easy to control, so much so it gave me confidence so I spun it out a bunch of times to settle my ego! But that was mostly my error and thanks to ADSI I learned by the end of the day I had stopped spinning out my car. I can't make it to CART @ Thompson on 4-12, but I will do the day thing at ADSI on 4-27. I recommend the whole day, you will get waaay more out of the autocross and enjoy it much more if you do the AM lessons, trust me on this one. I started out driving terribly, basically getting lost in the course and missing cones. Then I started to go fast enough to spin the car out. I finished off only 3.5 seconds behind Sterling, not great, but a decent overall time for anyone's ADSI, even better considering it was a rainy, slippery day. Do keep my real name out of any posts, please! [ed: your wish is our command, Attilio!] If anyone has any questions about changing stuff, I have quite a bit of experience with this and as time goes by I will getmore. Sterling has more experience with these events than I do, but I want to see if I can get faster times than he once my experience level gets up there. I am nowhere near his ability though, that's for sure! In order to do that, I will need to wear a black firesuit (at an autocross!!!), a helmet with a silver/reflective shield, driving gloves, register at the event dressed in full combat gear that way, and then proceed to try to knock down as many cones as possible.
— A posthaven user
A: interesting point about suspension types. I did a little digging for additional info and came up with: http://www.team-integra.net/forum/blogs/michael...
— A posthaven user
Another good comparison: http://mechanicalmania.blogspot.com/2011/08/com...
— A posthaven user
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