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Discussion Starter #1
Are any of you guys running your MM control arms in the upper holes on the MM kmember?

Ive got the car torn down for a little winter tune up and I'm wondering if I should do this while I'm in there. I'm going a little stiffer on the front coil overs so it's not much more of a step to raise the control arms to the upper bolt holes.

My car is not terribly lowered but it's on coil overs all around so it's easily adjustable.

*When is it advantageous to use the upper holes Vs. the lower holes?*
 

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Once your A-arms go beyond level and start to angle upwards towards the wheels then it's time to use the upper holes. Of course that's in a static position. There is probably something to be said about how a-arm angle will change as the suspension is cycled. Someone with more trustworthy information than I should comment on that. I use the lower holes right now with my A-arms dead level.
 

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Discussion Starter #3
Perhaps as I'm moving up from a 400lb spring to a 500lb spring and MM valves race bilstein there will be much less A-arm "roll" and it would be more advantageous to use the upper holes?
 

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I use the upper holes for a better camber curve, as they're closer to level in that position, but Jack at MM once pointed out some downsides and I'm damned if I can find the communication. I've considered moving back to the lower holes but I don't want to add another inch to an already long bumpsteer stack.
 

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I've considered moving back to the lower holes but I don't want to add another inch to an already long bumpsteer stack.
Wouldn't lowering the inboard side of the LCAs reduce the length of bumpsteer stacks here?


Norm
 

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Discussion Starter #6
Yes, if you lower the control arm to the bottom bolt, you would have to REMOVE approximately 1" of your bumpsteer stack.

So you would be better off as far as your bumpsteer stack of spacers go MFE. If this is something you decide to do PLEASE report back and let me/us know what kind of difference it made 😊 If you happen to find the communication between you and Jack on this subject I would be interested in that too!
 

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Ive been using the upper holes since day one. I figured this would allow me to keep the car lower and still keep the arms level.
 

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I have mine in the lower holes with the A-arms level. I've considered going to the upper holes but due to tire to fender clearances I wouldn't be able to have the arms level. They would angle down from the kmember toward the wheel/tire. Are there any downsides to the arms angling in this fashion?
 

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back later
 

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back later
How much later? I have my MM K-member install going as I type. I'm going with the lower holes. My car is low, but I see lower ones regularly.
I still have a couple fingers of room in the non-modified fenders.
 

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I made the switch a couple weeks ago but I won't be back on track for a couple weeks more.
 

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Discussion Starter #12
So what made you decide to switch? What are the advantages and when is it advantageous to do it?

Or, is this more of a test to just see the difference? Very very curious about your "testing" results one you get it on track. Possibly notice anything on the street with it? Did you have to remove or add an inch of bumpsteer shims to correct bumpsteer?

PLEASE PLEASE PLEASE report back after you have a chance to put it on track.
 

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So what made you decide to switch? What are the advantages and when is it advantageous to do it?

Or, is this more of a test to just see the difference? Very very curious about your "testing" results one you get it on track. Possibly notice anything on the street with it? Did you have to remove or add an inch of bumpsteer shims to correct bumpsteer?

PLEASE PLEASE PLEASE report back after you have a chance to put it on track.
I removed about an inch of spacer stack. I say "about" an inch because I forgot to record exactly how high my rack was mounted before I took it down, so I re-measured and re-adjusted the bumpsteer for the location its in now. Assuming nothing changes, you can remove exactly an inch of spacer stack. Interestingly, the resulting stack is shorter than the shortest tapered spacer MM provides.

As for why I changed it, I've been chasing a rather persistent understeer condition for a long time. I have the rear where I want it with 500-lb springs and an Eibach bar. Meanwhile I've also been chasing uneven tire wear in the front. No matter what, I wear out the edges of the tires long before the rest of the tire is gone.

Jack Hidley once had this to say about the location of the arms:
Lowering the FCA in the k-member increases the distance from the roll center to the CG. This results in less roll stiffness at the front. Less roll stiffness means less load transfer, AT THAT END OF THE CAR (FRONT). This means each of the front tires is more equally loaded and therefore can provide more total grip.
This is pretty basic, and it's always made me wonder if I was sacrificing grip for a better camber curve. Meanwhile:

Another advantage is this. The higher the roll center, the greater the jacking forces created from cornering forces. The jacking force actually causes the sprung mass to lift. Tire scrub tends to hold it up. Higher sprung mass cg, increases the total weight transfer of the car, which reduces total cornering grip. This is why fairly low roll centers are important.
Hmmm...jacking forces, tire scrub, reduced grip...it's been getting me thinking. Furthermore:

One of the local guys that runs AI with our parts dropped his FCAs in the k-member, added 30% more spring rate to increase the roll stiffness and dropped his lap times about 1.5 seconds due to the decreased understeer.
Sold. Except I'm not increasing the front spring rate beyond the 425's I'm already running, so this should be educational. Unfortunately I'm not a consistent enough driver to nail it down to lap times (I took 3 seconds off my best lap time on Arizona Motorports Park last time I was there, with NO changes to the car), and I'll be running different tires next time anyway. So my report back will likely come down to how it feels and how tire wear nets out.
 

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Been running in the lower mount for three years. Rack is as high as it will go. Bump-steer stack is very short. At my ride height, arms are level. But I'm in the process of measuring the mounts and running an analysis to see what this thing is doing in dive and roll; caster and camber gain, roll-center migration, etc. I know the MM front strategy is low travel/high roll. I'm interested how this compares to other strategies and if advantageous, whether the others can be accomplished on the Fox chassis.
 

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To add to Fraser's comments in post #14.

The closer the roll center is to the cg, the faster the weight transfer occurs. The higher roll center does increase the roll stiffness some, but this is a smaller affect than the transient change.

With the higher front roll center, the car will turn in faster, but understeer more due to the slightly greater weight transfer.

Virtually all of the differences between a high and low roll center can be tuned in or out with different swaybars and infinitely adjustable dampers.

This works essentially the same as IC does in side view for the rear tires. More AS% allows the weight to transfer faster to the rear tires, but it does not affect the total weight transfer. This is still super important to have high AS% for maximum forward acceleration because if the engine and clutch deliver power to the rear tires faster than the weight transfers there from acceleration, then the tires will start spinning and all is lost, without lifting and waiting.

RC height in the front or rear affects how quickly weight transfers at that end of the car. This affects the transient handling balance. With a high rear RC and/or a low front RC, the lateral weight transfer is going to occur faster across the rear tires, so the car is going yaw faster. This will not affect its steady state cornering power.

In Fraser's case, I'm pretty sure that he still needs a larger rear swaybar.
 

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Amazing the difference that a couple hundred or so milliseconds can make.


Norm
 

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Discussion Starter #18
This is very interesting. Looking forward to your experiences with it...
 

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As I suspected, my only data is mostly anecdotal. The one session I timed put me in similar times to what I've run before, but I did catch myself saying "feck me" like an Aussie several times, as the car wanted to turn in RIGHT NOW, it seemed significantly looser, and I had to dial way back on my usual trail-braking. I anticipate further disappointment in the tire-wear department ad the left front seemed to be wearing its outside edge pretty hard at 40 psi hot. I haven't taken the wheels off to look at the inside edges yet. Seems looser in turning left and tighter turning right which is obviously a tuning issue but I don't know what yet. Bumpsteer is perfect, and while it's not corner-weighted, both perches on each end of the car are within 1/4 inch of each other. Bottom line is the car seems like it wants to rotate a lot easier than before and is more lively to drive, but not sure of ultimate lap time change.

 

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Discussion Starter #20
So you like it better overall?

You went from the top holes to the lower holes, correct?
 
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