I cannot be trusted all the time...Chris is obvisouly correct when he writes that track changes will not affect ackerman. As I explained to Chris in a PM, I moved the ball joints and therefore control arms in sinc with track changes.

If Greg - Onasled - were walking with me at LRP and heard me say track changes cause ackerman changes, I think he would have hit me on the back of my head!

Apologies Chris!

 

On another note.. Why lower camber up front??

 

yr right, this is not ideal. however, not on purpose. i do not have adj rear arms on the car yet, so i'm stuck with 2.8 deg. i want to run 1.5 to 2.0 in the rear, will experiment a bit with that as soon as i get some arms.

i wish there was a way to measure exactly how much my car is leaning in the turns and then set the camber to exactly that angle up front, so the tire is as close to perpendicular to the road as possible. any ideas? maybe something with a gyroscope in it? i talk crazy.

yet.....hmmmmmm.... (gears turning...)

 

Unless I am wrong, the RSS clubsports have a very high front rate, more than double the rears, I think it is like 550 lbs/in front 250 lbs/in rear, I think I read that DMH did some testing with them. This would explain why his set up is working. Hope this helps.

-Addison

 

that would explain a lot actually. because even without the front bar i'm leaning less than my M7s with front bar. and i'm still thinking about more rear bar! my new DIY is going to be drilling a new hole in my stock rear bar and moving the link rod. it looks like i can get about an inch, it may be just enough.

i always try the free stuff first...

 

One easy, but less that absolutely accurate way is to jack up the car from the front jack point until just before thew rear tire leaves the ground. Then measure the camber angle on the opposite front tire. You can also build a step guage for one front wheel.

I beleive that the H&R kit that Don used have 469# spring up front and 350# in the rear. I do know his Leda kit is running 550# springs up front and 350# in the rear. FWIW

 

While you can measure lean in turns very, very accuratly, the lean is a function of car speed and turn radius. There is no one "lean" so like all things, you choose the best compramise for how you drive.

Matt

 

A step guage actually works pretty well - a piece of wood set up in either 1/2" or 1" incriments.

Remove one front spring and reinstall the shock. Place a steel billet or block of wood under the subframe at the inner control arm - on the side where the spring is missing. Make sure that the dimension of this billet or wood maintains ride height as with the spring. Then, run the step guage under the tire - front to back - and note the camber angle changes thru suspension stroke. You can also prepare channels along the length of each side of the guage. This will allow you to also install another board - perpendicular - to sit between the front of the tire and behind the front fender well - to check for toe changes.

1/2" incriments work best because it is easier to plot the values, and, easier to slide under the tire. The step guage will be about 3" long if enough room is left for contact patch.

Obviously, a very level place is necessary.

 

but that the amount of lean depends on the turn and the speed. So it's not possible to set the front wheels to a single camber and have it "match" what the car does in turns. In A turn, yes, in all turns, no.

Let's face it. With the camber curve of a Mac Strut, you'll NEVER have the camber control that you really want, like from a dual A-arm suspension. So with the Mac strut, you choose about where you want the front camber as a compramise, and live with deviations around that ideal because we have no choice...

Matt

 

While I am currently peicing together a coilover setup on a budget, 450lb/in up front 350lb/in rear, with 5mm spacers up front, and a big rear bar, I have always thought that a vendor would put together a trick double a-arm setup with real stiff rates up front, no front sway and a smaller rear bar. This with an lsd could prove to provide the traction the mini needs up front.

 

Agree completely.

 

RedOut,

What do you mean by a "double A arm" kit?

John Petrich in Seattle

 

Matt,

What you say about the camber control from a Mac Strut is true. And, that we have to live with what we get. Yes. That reality is not a bad one at all. With proper initial alignment, proper location of the roll center, and proper roll control the Mac Strut works like Buster's Gang. I look at all the successes that the larger BMW's have been having in the touring car championships as proof.

The reason that I am responding in such a way is that all of the scientists and would be scientists among us (myself included) have a tendency to split hairs and sometimes get caught up thinking about performance details reminescent of long dead discussions about how many angels the head of a pin can accommodate. The facts on the ground suggest that the Mac Strut suspension compromises are to the greatest measure academic and that those with real talent can work the Mac Strut work marvelously.

I know you and don't think you go too far. But someone like you, with a large public profile should be careful that you don't accidentally send the wrong message. Yes, the Mac Strut has limits, but not so that the likes of people like me will ever suffer from them.

John Petrich in Sammamish

 

HOW? an inquiring mind wants to know...

absolutely. but what i want to do is set up the camber for maximum grip in the turns. so basically i want my outside front tire to be perpendicular to the road when the traction is maxed out. any other turn would not max out the traction, so the tire does not have to be cambered properly. so i want to measure how far my car leans over during a maximum lateral G turn.

 

I guess this means that we'll be seeing the Mac Strut in F1!

But John, as usual, you raise good points.

Now, Sonichris, how much money do you want to spend?

The cheapest way I know to do this is to set up a video camera and watch yourself in turns. The most expensive way has no limit. There are accelerometers to measure local acceleration, you can use items that look at travel (linear encoders) to measure how far a suspension component is compressed or extended. You can use thingies like park distance control sensors to measure the distance from the bottom of the car to the ground....

Anyway, there are lots of data loggers for cars, and the types of stuff you're looking for is "race team" budget. The video camera will get you close. Put a friend at a turn and have at it! It won't be perfect, but you'll get the idea.

And if you're meticulous, you can do a series of the same turn at different speeds and make a lean vs speed curve for that curve. Do that for a few more curves and you'll really have the nature of the suspension nailed! All it takes is a tape and some time.....

Matt

 

If you plot the camber curve, that's all that is needed. And, it can be done as I described above thru the entire suspension stroke.

Augment the above with another rather crude but effective method that establishes how much stroke is used during certain kinds of manuvers - springs rates affect the portion of the camber curve the car spends most of time. Place a zip tie on the damper's piston and drive a defined route. If you have a G meter you can tether the distance the zip tie moves to the camber for a given spring and damping rate. Obviously one needs to balance large static neg camber values with what is required for different types of turns. As long as the Mac strut doesn't does 'go positive' at full compression, you've not made things worse.

Other than that, a kinimatics program is quite helpful.

 

i see what you are getting at, but that won't work. plotting a camber curve (wheel camber vs displacement), while informative to the CURRENT workings of your suspension setup, will not tell you what to set the camber TO.

example:

take the stock mini front suspension. about -0.5 camber up front. plot the curve. what would the max be? -1.0 degree, tops? make it -1.5, just to give the benefit of the doubt. so you've learned that at the bottom of the travel, the tire is leaned at -1.5 deg. now drive the car. i doubt you will bottom out the outside front strut. say it went down 70% of the way and that's -1.2. what does that tell me? it says that my outside front tire is leaned in at -1.2 degrees to the body, but is it perpendicular to the road? nope. any video with a stock mini shows that outside front leaned over way positive on fast turns. so, given that information, what should i set it to?


i think the best and easiest way is what that dr. obnoxious wrote, film it!

 

I was reading about chassis set up in a book from the 80s. Fancy data acquisition for this stuff was in nosebleed territory. So they did the video stuff. The photo of the "portable" video camera looked like what professional news crews use now! The idea stuck with me as a real easy and cheap data system, with lots of post acquisition beer drinking opportunities! What a feature!

Matt

 

The common way for optimizing camber setting (and tire pressure) is to use a tire pyrometer.

Just do your autocross run, or whatever, then immeadiately measure the temperature of the tire on the outside edge, middle, and inside edge.

If the outside edge is hotter than the inside edge, then you need more camber. If the inside edge is hotter than the outside, you need less camber.

You adjust tire pressure until the outside, middle, and inside are all the same temperature.

I don't think you can just figure out how much the car leans and set the camber to that much. This is because the lateral force on the tire deflects the sidewall, so you really need more camber than the car is leaning.

 

you bring up a good point with your last paragraph, and i did have this in mind. about the pyrometer, i know about that method. i used to have an indy 500 computer game on my amiga 500 (any remember those?) that you could adjust every part of the suspension (swaybars, camber, ride height, shocks, tire pressure, etc.) and you would use a pyrometer, trying to, as you mentioned, equalize the temps inside, middle, and outer. once you got the temps equal all across, your car was as fast in the turns as it could go.

i think the real world may be a little different. in the straights, or accelerating out of turns (especially), the insides would get hotter, from the extra camber and from spinning the inside tire. on the turns, the outside of the outside wheel would, but so would the INSIDE of the inside front wheel... so the temps also become a factor of how the course or track is set up.

i think a pyrometer is still a very important tool, because regardless you can't have the tire temps go too high or your traction will drop. but as long as you are in your "safety window" you'll be ok. that being said, i think a combination of visual observation, tire chalk (to check for sidewall "rolling" in turns) and a pyrometer would be a very thorough way to do it.

how about using a Gtech and measuring lateral Gs, plotted against front camber settings?



ya know, i sure do like to talk a lot. i think i need to stop talking and start testing...

 

sonichris,

Camber is actually a very complicated measurement since its operation is determined by the front roll center/instant center. Folks are typically concerned with a static camber values when the camber curve really depicts how camber changes affect a car in a dynamic situation.

You are obviously comfortable with geometry, so try this somewhat complicated task. Plot the front end geometry and locate the instant centers. The IC is the fulcrum ( also called the swing arm) from which the control arm pivots. In other words, the IC determines the arc of the wheel as it moves from full droop to full compression. Lowering your car will move the IC location and it is not a static location; it moves around as does the roll center since the left and right IC determine RC location and migration.

I bring this up only because dynamic camber influences the amount of work your tire can perform. If you've installed 1,000# springs, you might want to adjust your camber to be strongest in the first 1/2" of travel. If you've installed 100# springs - really soft - you may need to adjust static camber so that the outside tire is not positive at full compression - more static neg camber is necessary when using lighter springs.

From 85K miles of experience in a mostly daily commuter and track car, 2 deg neg is about all you need on the road, and near 3 deg neg will work very well on a track only - 3/4" drop front rates in the 350# range.

 

My gut says that the pyrometer method would actually give the best lap times, since you're basically looking at average tire usage over the length of course.

Plotting lateral G's against static camber angle is a really cool idea. This would place much more "weight" on pure cornering G's, though, and could lead to being over-cambered, such that braking and accelarating would suffer. This is actually why the pyrometer (and I guess stopwatch) seem like a more balanced solution. Not sure though.

In the end, this is why I like being a stock class autocrosser All I have to know about camber is that I don't have nearly enough

 

One very funny reconciliation Kind of like, "oh well". Sometimes oh well is a lot more fun Roger...

 

Sorry, but I didn't take the time to read the entire thread....

But I just wanted to add:

Shocks affect the transistional response (initial turn-in and corner exit)
Springs and sway bars affect steady state cornering (mid-turn for a sweeper)

With this in mind, I'm hoping to use the shocks set to high compression rates to control the transisional response. Then remove (or use the 16mm bar) to get the car more neutral mid-corner. Less front sway bar helps with traction exiting the turns as well.

(sorry if this is off topic, I was responding to the original post)

 

Mitchman, I'll be curious to see how that works. I think such a small (or non existent) front swaybar with stock springs and camber will probably make mid-corner understeer worse and cause you extra tire (or should I say "sidewall") wear. You should get mad traction on corner exit though.


Michael- ya, I think so, too It's also usually "slower", though