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Cross Weight Adjustment Question

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#1
bmarshall1

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OK - so I am going through my suspension and had everything completed (Caster, Camber, Toe etc...), but my Cross Weight was 48.40.  Using scale stands and tightening the suspension in compression.  The rake was neutral to abut 1/8 down in the rear.  Bilstein shocks,  I generally run about 3/4 - 5/8 gap between the shock body and bump stop.

 

 

So....doing what I thought was the right way, I turned the collars UP on the RF and LR (to increase the weight) and DOWN on the LF and RR.  First 1/2 turn, then a full turn; now 3 1/2 turns later the X Weight is EXACTLY the same, but the rear is too low and the front (especially RF) is too high.  I seem to be transferring weight to the rear with no impact on the X Weight

 

Should I have just adjusted one corner or did I use the proper procedure.  Lastly I can't share before and after numbers as my car seemed to have gained 25 lbs overnight and my 2402 weight is now 2427on Longacre scales. 

 

 

 I suppose I will reverse all my adjustments and this time only adjust one corner at a time?  My pinch welds are pretty fubar so pinch weld measurements are tough, my home track is Sebring which is bumpy.  Maybe run about 4 1/2 inches to the pinch welds, is more or less better?  I am a definite mid to 3/4 back of the pack.



#2
TylerQuance

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Check that your scales are plugged into the correct positions
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#3
bmarshall1

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Check that your scales are plugged into the correct positions

Been there and done that once!  I'll double check, thanks.



#4
Alberto

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Personally, I do one corner at a time.  Usually in increments - meaning if I think I might need more than 1 turn on that corner, I would do 1 or 1.5 turns and re-check.  

 

I'm not super experienced though so it's more reliable for me to get to where I want the weight to go incrementally rather than make multiple changes that will be harder to get back to where I was if I make a mistake.


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#5
bmarshall1

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Tyler - You Da Man.  Other than I am an idiot, I'm not sure how I did it but I had the pass side F and R reversed.  I even have the stands color coded.. I owe you one free bump draft, but seeing as I'm slow, I'll block the guy behind you for your next pass. :optimist:

 

 

Alberto - Normally I don't make 'wholesale' changes but I wanted to keep all other settings fairly similar and was under the impression up on one cross and down on the other as I was looking for 2% change (vs. less than 1/2%).

 

Putting everything back 3.5 turns I am at 49.17, one turn on the LR brings it to 49.9, so about .7%.

 

I am about 1/4 rake in the rear and think it may be slightly much?? Anyone care to comment.  I will likely go up 1 turn on the LR and 1/2 on the RR and see if that fixes the Cross weight then check all the numbers again, what fun!


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#6
Steve Scheifler

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What you describe is not possible unless something is binding or otherwise causing scales to read wrong. (Edit: I see now you had cables mixed but that doesn’t explain why things didn’t change a LOT).

Your approach was fine. If you were shooting for 50% (not necessarily correct for Sebring, ask those who are fast there), then from 48.4 initial cross you would have raised RF & LR 1/2 turn, and LF & RR down the same amount. That would get you close but probably still a tenth or two low. However, equal/opposite adjustments all around may not always be your best choice. Look at things like L/R weight on the front tires, and likewise in the back. Depending on where it would leave your bump-stop gap you might (for example) want to do more change on one end vs the other to reduce brake lockup issues on one corner.

After making adjustments, re-check everything else because camber and front toe change with ride height.
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#7
Steve Scheifler

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Personally, I do one corner at a time. Usually in increments - meaning if I think I might need more than 1 turn on that corner, I would do 1 or 1.5 turns and re-check.

I'm not super experienced though so it's more reliable for me to get to where I want the weight to go incrementally rather than make multiple changes that will be harder to get back to where I was if I make a mistake.

Honestly, really bad idea. You can chase numbers that way and end up with a mess unless we’re talking about very small amounts (which 1 turn is not). Generally, if you are starting from “level” and want to change cross, adjust at least two opposing corners at a time in equal amounts, and usually all four by smaller amounts. That gives you the shift in cross weight with the least impact on camber, toe and bumpstop gap on any given corner. Once you become familiar with the adjustments and know where you currently are relative to a good baseline it’s often worth breaking the general rule for a specific reason and knowing the outcome even without measuring again, but that comes with experience.
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#8
Steve Scheifler

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Tyler - You Da Man. Other than I am an idiot, I'm not sure how I did it but I had the pass side F and R reversed. I even have the stands color coded.. I owe you one free bump draft, but seeing as I'm slow, I'll block the guy behind you for your next pass. :optimist:


Alberto - Normally I don't make 'wholesale' changes but I wanted to keep all other settings fairly similar and was under the impression up on one cross and down on the other as I was looking for 2% change (vs. less than 1/2%).

Putting everything back 3.5 turns I am at 49.17, one turn on the LR brings it to 49.9, so about .7%.

I am about 1/4 rake in the rear and think it may be slightly much?? Anyone care to comment. I will likely go up 1 turn on the LR and 1/2 on the RR and see if that fixes the Cross weight then check all the numbers again, what fun!


We always measured rake in degrees but 1/4” either way is small. (What’s your reference if pinch welds are bad?)

In any case, more rake (higher in rear) will tend to make the car rotate more particularly from turn-in as weight is transferring. If it starts feeling too loose early in the corner, come down a turn or two on both sides, both reducing rake and adding camber. If it doesn’t want to rotate after turn-in and you can’t get it headed for the apex without fighting it, go up in the back. (Note: this assumes you already have enough toe-out in front to get the nose to start turning but the rest isn’t following, and not so much that it’s pushes hard on exit. All this stuff works together to create “balance”, you know, like ugly shoes with a smokin’ hat. :) )
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#9
bmarshall1

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We always measured rake in degrees but 1/4” either way is small. (What’s your reference if pinch welds are bad?)

In any case, more rake (higher in rear) will tend to make the car rotate more particularly from turn-in as weight is transferring. If it starts feeling too loose early in the corner, come down a turn or two on both sides, both reducing rake and adding camber. If it doesn’t want to rotate after turn-in and you can’t get it headed for the apex without fighting it, go up in the back. (Note: this assumes you already have enough toe-out in front to get the nose to start turning but the rest isn’t following, and not so much that it’s pushes hard on exit. All this stuff works together to create “balance”, you know, like ugly shoes with a smokin’ hat. :) )

I have straightened them the best I can and use the lowest, straight part on each one, I *think it's a good reference as it seems to agree with a level on the door sill and bump stop gap.  I use bump-stop gap, but since I'm not certain the front and rear gap is/should be the same I always double check with a level.  I could easily place a inclinometer to see the degrees. So in other words I use one to check the other.

 

I have about 1/8 total toe out in the front, 1/16 toe in rear, 3.2 degrees all around, and forget the exact caster but equal per side around 6 or 7 degrees? (I may be really off on the camber).

 

My issue is I lack the finesse to use the rotation a little less rake may offer,  so I err on the side of safety to prevent a spin.  I seem to either push or spin.



#10
Steve Scheifler

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More rake (high rear) = more initial rotation. But some of the fastest guys actually run a bit of negative rake (low in back) at least on NBs, which I confess surprises me a little, but again it’s a multi-part system and no one setting alone means much. But even as I say that, 1/8 total out in front is on the low side. That’s OK for a super speedway where you want minimum scrub (which I believe requires a bit of toe out given suspension geometry). You might find the car more responsive at turn-in with double that (measured with toe plates but even at the rim it’s fine). On tight tracks you may benefit from even more but definitely try 1/4 or a smidge more and see what you think.
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#11
bmarshall1

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thanks Steve, I'll get a little more toe-in on the front and see how I Like it.  Should the front feel more planted, or what exactly are the effects of more toe in.  Better turn in and front end sticking?



#12
Steve Scheifler

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thanks Steve, I'll get a little more toe-in on the front and see how I Like it. Should the front feel more planted, or what exactly are the effects of more toe in. Better turn in and front end sticking?


Mostly just crisper turn-in, easier to get it to rotate towards the apex with less input. It may also feel more stable straight ahead though not as much so as toe-in used for street cars. If you take it too far the car will start pushing noticeably at corner exit but that’s generally above 3/8” measured at the rim.
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#13
Jamz14

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People think I'm nuts here in the west. Only partially because of the amount of front toe I run .

Totally concur with Steve on front toe and rake.
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#14
bmarshall1

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I'll post some more numbers later, but I added toe as suggested, the rake is .2 degrees lower in the rear (about 1/4 at the pinch welds).

 

I am a mid to back packer and currently the camber is F 3.2 and R 2.9.  Should I add a few 10ths?

 

Once I get on the track again perhaps raise the rear 1/2 to 1 turn to help get it to rotate?  It's currently pretty stable and the rear does not rotate (I have felt it rotate most likely by accident, but I see how it helps quite a bit).



#15
bmarshall1

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What is the the recommended way of determining proper ride height. Measuring bump stop clearance, pinch weld, or free threads on the shock collar?

 

The right rear shock free-thread measurement has me a bit perplexed as it seems to be low as compared to the others, I could raise it but then I would be lowering the LF, which is already lower than the RF

 

Per my bump stops I am at:

 

    L      R

F 7/8    1"

R 3/4   5/8

 

Per the pinch weld  ON RAIN TIRES, I need to install my Toyos tomorrow:

 

5-1/4    5-1/16

5-1/8    4-15/16

 

Looking at shock threads below the collars:

 

2"         1-15/16

2-1/16  1-5/8



#16
Steve Scheifler

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There are various “recommended” ways but only pinch welds or other fixed chassis references (like center of eccentrics) give you absolute numbers for actual height. Of those only the pinch welds (at the correct locations) are comparable front to rear. Bump stop clearance is not the same when level even side to side much less front-rear because actual weight distribution is not even. Similarly, spring perch heights will all be different because different amounts of weight compress them different amounts. That’s why the RR perch is the lowest, it has the least actual weight compressing the spring so the collar must be lower because the spring is holding the car up higher. It is all a bit counterintuitive until you think about how it’s all connected and riding atop four springs.

Once you get truly level fully ballasted (not yet corner balanced), you can record the spring perch threads, bump stop gaps, whatever, as a baseline reference so you can easily get back there if needed to start over. Then do the fine adjustments for 50% cross and again record your reference measurements. Now you have two sets of baselines and “sanity check” references from which to work.
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#17
bmarshall1

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 Steve - thanks for the information and guidance.  Assuming I have correct pinch weld numbers (and I will double check them (I also have an unmolested 99 for reference points)). Ignoring the other numbers, it would appear to me that raising the right side about 3/16 *should get me to pretty darn level while maintaining my X weight or close to it, 

 

 

I believe the shock threads are 3mm peak to peak.  Therefore about 1 - 1.5 turns should raise the right side 1/8 - 3/16  One turn should get the rear-to-front level (no rake).

 

In theory, like all great ideas :optimist:  how does this sound?  or... as my old boss would say 'you're separating fly shit from pepper, go out and race".

 

But I like your idea of establishing a repeatable base line.



#18
Steve Scheifler

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Yes, the collars are 8 turns per inch and as I think you noted above each full turn (combined or on a given corner), shifts cross by about 0.7%. That’s always a useful number not just for quick changes but a sanity check while on the scales to confirm that you actually moved things the right direction and that nothing is bound up or distorting the numbers.
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