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Discussion Starter #1 (Edited)
The BMR bars are installed and ready to go.. I was working on calculating the % increase of the rear bar over the stock GXP bar and came up with some interesting numbers.


GT rear bar diameter is 18mm
GXP rear bar diameter is 20mm
Given that the two bars are both solid and of the same design the GXP rear bar would be 52% stiffer than the GT bar.

That along with BMR's published increases of their bar over the GT rear bar I got the following
hole 1 - 26% stiffer than GXP rear bar
hole 2 - 74% stiffer than GXP rear bar
hole 3 - 154% stiffer than GXP rear bar

Given the front bars are the same for both cars at
hole 1 - 87% stiffer
hole 2 - 137% stiffer

Then the fact that I would like decreased body roll with just a little more rear bar bias then my current stock setup leads me to think that full stiff on both bars might be the best bet F137% / R154% (17% stiffer bias to the rear than stock GXP). This would seem to be the only choice to get close to what I am looking for.

All the other choices stiffen the front bar more than the rear bar increasing bias to the front (increasing under-steer). If this ends up being too stiff a set-up, the only choice would be to go back to the stock front bar with the BMR rear set to hole 1 for a 26% increase to the rear but that will not do much to decrease body roll.. We will see how it goes on the course this Sunday.
 

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Definitely let us know how the sway bars perform for you once you get them installed, I am really interested in hearing some feedback from you.
 

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Definitely let us know how the sway bars perform for you once you get them installed, I am really interested in hearing some feedback from you.
I thought you guys were the experts and would be able to provide input to the guy......any testing done bu you guys??? :driving:
 

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Go full soft front, full stiff rear.
Balance is excellent on stock springs w/fe3 gxp
This is how I have mine set up as well...
I do have some of the rear supporting BMR components, but honestly the car handles Soooooo much better than stock.
 

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I'll be installing the BMR sways soon. I'm a GT but will have FE3's and Eibach lowering springs. Will this be a good starting point? Full soft(hole 1)/Full stiff(hole 2)?
 

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Discussion Starter #7 (Edited)
Go full soft front, full stiff rear.
Balance is excellent on stock springs w/fe3 gxp
I am running Bilstein and King HD springs on the car. I like the balance of the car front to rear and if anything would like just a little more bias toward the rear. 87% F / 154% R seems a bit too far (an increase of 67% bias toward the rear). I am also looking to control body roll more than the stock bars and King springs were doing.

I agree that 137% stiffer in front isn't ideal for keeping good loading on the outside front tire, and if the rear bar had a 100% stiffer option, I would be picking the 87% front setting.

Who knows, after this Sunday's race I might pick the soft front setting and the medium rear to see if that increases grip without inducing to much additional oversteer. I actually had that setting on the car yesterday and swapped to the stiffer settings today after a little soul searching and street driving.
 

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Discussion Starter #8 (Edited)
Today I setup a low speed skid pan in an unused parking lot and went to work testing the different settings I was considering.

I used Harry's Laptimer on an iTouch with a 5Hz external GPS to record lateral acceleration and speed data to help quantify the different settings.

My plan for testing was for the following combinations. Test 1 and 4 were the same to help find any errors with the test over time(tire temp, track cleaning and the like)
test 1; F-hard/R-hard
test 2; F-soft/R-hard
test 3: F-soft/R-medium
test 4; F-hard/R-hard

I then downloaded the CSV file from the data logger for all the runs and played with the results in excel - the highest peak speeds and accelerations were found on tests 1 and 4 with test 2 following very close behind (really close), test 3 was a bit farther down.

So it looks like full hard is the way to go on the rear bar and it is up to your driving style and comfort as to how you set the front. I think what is happening in the front is on the hard setting the bar is reducing the body roll enough that the outside tire is retaining more negative camber and that is working to get you around the turn quickly, on soft more weight is transferring to that outside tire giving it more traction.

I am going to go with the front on full hard. Everything being equal - keeping that outside tire's negative camber by reducing body role will hopefully save a little wear on those outside shoulders, and might allow me to lower my tire pressures on the track for even more traction.

I am looking forward to seeing how it does on the autocross track tomorrow.
 

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Great test data!
Probably close enough that it will depend on tires, shocks, springs, camber and track conditions.
I never went full hard on the front, but I did like full hard rear better than medium.
I am putting a set of eibachs and new fe3's on soon... May try full hard at some point down the road after the Michelin SS's are broken in.
My camber is at -1 front and back an the wear is more on the inside edge, so I can't go much more without tearing up my new $$ rubber.

Let us know how you do at the autoX!
 

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Discussion Starter #10 (Edited)
Well after a great day on a good fun course, I am happy with both bars on full stiff. The car is really neutral. At the end of the video (link below) you can hear the announcer commenting on a slide during my downshift (kept a pretty neutral throttle), you notice no slide within the car or any counter steering input required. The slide was a very controlled four wheel slide, felt good.

On the run after this one I pushed past the limits of adhesion in a few different spots to see what would happen - during braking I got under-steer, on the power I got over-steer, and on a neutral throttle the handling was neutral. Couldn't ask for much more.

Link to post with video of best run
 

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Discussion Starter #11 (Edited)
I also found an error in my first post's calculations.. The rear bar sizes are 18mm and 20mm - that changes the rest of the numbers since that increase is a 52% stiffer bar. I will work it out and make the corrections shortly.

Done - The info has been corrected.
 

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Thanks for the video and the detailed feedback! I want to do the sways soon. Sounds like full stiff is the way to go.
 

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Great info!!! I run the bars at full stiff and agree with you completely. The car feels balanced/controllable in the corners.
 

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I thought you guys were the experts and would be able to provide input to the guy......any testing done bu you guys??? :driving:
We have actually done a good bit of testing with our sway bars but what many people fail to realize is that there isn't one magical setting that is the perfect setting. There are many variable that contribute to what sway bar settings will work best like power level, tire being used, driver prefernence, etc,etc. Some people say full soft in the front and full stiff in the rear but I personally prefer to have the sway bars set at full stiff front and rear. There is no right and wrong settings when it come to the sway bars. Generally I like for people to find the settings that work best for them.
 

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Well after a great day on a good fun course, I am happy with both bars on full stiff. The car is really neutral. At the end of the video (link below) you can hear the announcer commenting on a slide during my downshift (kept a pretty neutral throttle), you notice no slide within the car or any counter steering input required. The slide was a very controlled four wheel slide, felt good.

On the run after this one I pushed past the limits of adhesion in a few different spots to see what would happen - during braking I got under-steer, on the power I got over-steer, and on a neutral throttle the handling was neutral. Couldn't ask for much more.

Link to post with video of best run
I also found an error in my first post's calculations.. The rear bar sizes are 18mm and 20mm - that changes the rest of the numbers since that increase is a 52% stiffer bar. I will work it out and make the corrections shortly.

Done - The info has been corrected.
Thanks for posting up the video and giving us some very thorough feedback! :)
 

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what is happening in the front is on the hard setting the bar is reducing the body roll enough that the outside tire is retaining more negative camber and that is working to get you around the turn quickly, on soft less weight is transferring to that outside tire giving more traction across the pair.
Fixed that for you ;)

To paraphrase late great Carroll Smith in Tune to Win, "any increase in lateral load transfer between two tires decreases the total traction of the pair". That's because traction increases with tire load, but not linearly. For example if you have 1000 lbs of load on a tire and you add 500 more, you don't get 1500 lbs of traction, you get 1250 (strictly for example's sake). So if you have two tires each with 1000 lbs of load, you have 2000 lbs of available traction at that end of the car. If you take 500 off one tire and put it on the other, now you have 1500 and 500 lbs of load, but only 1250 and 500 lbs of traction, for a total of 1750 lbs at that end of the car, which is 250 lbs less than you started with.

And that's why, assuming a properly set up car in the first place, you lose traction at the end of the car you stiffen. Or, in your case, you keep traction at the end of the car you don't stiffen.

What complicates all of it is camber control, among other things, which you already know. If you're losing camber on the outside tire due to body roll, then reducing body roll by adding stiffness nets you more traction than you lose to the increased load transfer.
 

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Discussion Starter #20
MFE, I see what you are getting at and its a good point..

But I stand by my first statement, if you assume the rear bar fixed at full stiff and the two choices are stiff and less stiff for the front bar it is more total traction across the pair on soft due to larger lateral weight shift with more weight to the outside tire and the increased weight caused by that load transfer will give the outside tire more traction when compared to the stiffer setup (you pointed it out you loose traction as you stiffen that bar). The outside tire is doing the lion's share of the turning work - Here is where your quote comes in.. if you transfer weight off the outside tire to the tire not doing as much work with a stiffer bar you loose total traction at that end.

And like we both pointed out camber control issues then rise up and make the whole issue into something else because both set ups end up with the same total traction and you end up making the decision based on tire wear patterns and car feel at the limit.

This stuff is complicated, hard to get your mind around and even the experts have differing opinions on why things work and others don't. And why after all the thinking is done you go out and test and decided what feels good for the car and your driving style.
 
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