Gewow
Gewow
7/19/21 7:42 a.m.

Hey guys. I was wondering if you lower the car the exact same amount on all corners, will it change the corner balance?

My mind says no, but my mind is not always correct. 

 

Thanks :)

Pete Gossett (Forum Supporter)
Pete Gossett (Forum Supporter) GRM+ Memberand MegaDork
7/19/21 9:14 a.m.

In reply to Gewow :

I'd say it depends on the suspension type, geometry, and how great of a change you're making. Generally though, if you're changing the height on all-4 corners the same, and it's a minimal change, I wouldn't think it would throw off the corner weights. 

The only way I can imagine it impacting overall balance might be F/R, but even then it would require something specific about the geometry that would cause weight transfer when raised or lowered beyond a specific point. Honestly though, I can't think of anything real-world offhand. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/19/21 9:28 a.m.

As long as you make the same change at each side of an axle, you should be okay. And yes, you can adjust just one end.

You cannot shift weight F:R using corner adjustments. You can only shift it diagonally. Until you get to really extreme amounts and the CG starts moving around :)

Your static alignment will change with a ride height change, though.

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
7/19/21 9:57 a.m.

How are you measuring "the same amount"?  If you're talking about measuring distance from a fixed point on the body to the ground on all four corners and changing that value by the same amount then I agree that the corner balance shouldn't change.  If you're talking about measuring by counting turns on the adjust spring perch collars, then it's more complicated.

The biggest factor is that the motion ratio between the spring perch and the wheel movement is often different between the front and rear (different suspension geometry), so "the same amount" needs to be calculated.  For example a Miata is .69 front and .75 rear, so 4 turns on the front is equivalent to 4.3 turns on the rear.

Another factor is that since the wheels generally move up and down in an arc rather than straight vertically, you're changing camber.  That camber change is pushing one sidewall into the ground harder than the other, and depending on things like tire pressure and sidewall stiffness that may add or subtract a little bit from the effective ride height.  Again the front and rear geometries are usually different, that extra bit will likely be different too.  I don't have any numbers, but I suspect that as long as you're changing ride heights by small amounts within normal working ranges then this effect is going to be very small and can be ignored.

 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/19/21 10:14 a.m.

Doesn't really matter if the front and rear adjust by different amounts from each other. What's important is the adjustment across the diagonals be equal. So dropping the rear by 2 turns will have no effect on the cornerweighting. Same with dropping the front by 4 turns. Or dropping the left side by 4 turns. Where you get in trouble is adjusting a single corner. Motion ratio is not relevant to the corner weight in this case as it will be symmetrical - if not, we have a whole lot of other things to talk about :) Motion ratio will determine the ride height change for a given number of turns.

I would use turns of the perches as the most reliable way to ensure the drop is even.

I am not just talking theory, I have confirmed this behavior by experiment :)

frenchyd
frenchyd UltimaDork
7/19/21 10:25 a.m.

In reply to Gewow :

Just remember to put spring adjusters in and you'll be fine.  Torsion bars have their own adjusters but you'll need to make spring adjusters for coil springs.  Stock car racers have been doing it since the 1960's but for some reason I never see them on road racers( except by chassis builders with stock car backgrounds).  
 

In case you're wondering how to make them get a large circular plate,  a biggish bolt and Nut for each spring.  In the spring pocket weld the plate to the bolt and the nut to  the hole at the top of spring pocket. Once you have a set in your car you can adjust  corner weights to suit the track, your driving style,  or tires.  
  Major improvement in handling. 

codrus (Forum Supporter)
codrus (Forum Supporter) GRM+ Memberand PowerDork
7/19/21 10:29 a.m.
Keith Tanner said:

Doesn't really matter if the front and rear adjust by different amounts from each other.

OK, I agree it doesn't affect the diagonal corner weights.  And I agree that trying to measure ride height changes relative to the body is a very inaccurate way of doing it, I mentioned it more as a way of mentally modelling the concept rather than a practical measurement technique.

In the broader context here though, presumably the goal is to raise or lower the car without changing the way that it drives very much.  Raising or lowering one end relative to the other will change the handling balance, even after accounting for camber/etc changes, because of the line between the roll centers.

APEowner
APEowner GRM+ Memberand SuperDork
7/19/21 11:30 a.m.

As Keith and Pete are indicating it is possible to change ride hight without messing up the corner weight.  As codrus is indicating suspension changes are never really totally independent and changing ride hight is likely to have some effect on how the car handles and it might not be a good one.  Personally, I'll make a ride height adjustment at the track (usually on just one end) without rechecking cross weights but I double check cross weights when I'm back at the shop.

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/19/21 11:52 a.m.

In reply to codrus (Forum Supporter) :

Agreed that you might get other handling changes on purpose or by accident, but the question was specifically about the effect on corner weights so kept the answer constrained to that :)

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/19/21 12:02 p.m.
frenchyd said:

In reply to Gewow :

Just remember to put spring adjusters in and you'll be fine.  Torsion bars have their own adjusters but you'll need to make spring adjusters for coil springs.  Stock car racers have been doing it since the 1960's but for some reason I never see them on road racers( except by chassis builders with stock car backgrounds).  
 

In case you're wondering how to make them get a large circular plate,  a biggish bolt and Nut for each spring.  In the spring pocket weld the plate to the bolt and the nut to  the hole at the top of spring pocket. Once you have a set in your car you can adjust  corner weights to suit the track, your driving style,  or tires.  
  Major improvement in handling. 

I think you're overlooking the fact that it's often done at the lower spring seat. Pretty much every road race car has the ability to adjust the spring perches. Heck, I can do it on a number of my street cars.

Barb_Dwyer
Barb_Dwyer New Reader
7/21/21 8:17 p.m.

In reply to Gewow :

How much will change depends on the suspension type, geometry, and extent of the change. If you change the heights equally on all corners, I would think changing the corner weights wouldn't affect them. 

If the geometry was such that weight transfers occurred when it was raised or lowered above a certain point, balance could be affected. The only real-world example I can think of right now is fictional. 

Tom1200
Tom1200 SuperDork
7/21/21 8:57 p.m.

I have a fixed spot on the floor for the race cars. I measure from a fixed point on the chassis.

I hadn't had the Datsun corner weighted in 5 years; when I had it done this past year I was only off by about 30lbs on a 1652lb car. That was after I had the suspension apart multiple times.

Mark the floor and place the car in the same spot then simply mark the car. 

Gewow
Gewow New Reader
7/24/21 9:50 a.m.

Wow guys the level and quality of answers is exceptional. Truly appreciate the wisdom. I think we all have a common goal of just going faster :)

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
7/24/21 2:03 p.m.
Tom1200 said:

I have a fixed spot on the floor for the race cars. I measure from a fixed point on the chassis.

I hadn't had the Datsun corner weighted in 5 years; when I had it done this past year I was only off by about 30lbs on a 1652lb car. That was after I had the suspension apart multiple times.

Mark the floor and place the car in the same spot then simply mark the car. 

If you're careful, you can get away with that. But you can have a level car with bad cornerweighting. Lower two opposite corners by 1" and then raise the opposite corners by the same and you'll still meet all your measurements...but your diagonal weights will be all messed up. It's when you decide to "fix" one corner that you get into trouble. Adjusting both sides the same will keep you in the ballpark.

Tom1200
Tom1200 SuperDork
7/24/21 4:58 p.m.

In reply to Keith Tanner :

Agreed, it is possible to be off and that's why I had it checked. 

In discussing changes on the F500, Jay Novak (Novakar builder) told me they use a similar method. I figured if it's good enough for a multiple RunOffs winner it's good enough for me. 

 

wspohn
wspohn SuperDork
7/25/21 11:02 a.m.

Affect corner balance, no.

As Keith pointed out, toe setting definitely yes and I'd add possibly anything up to a crapload of bump steer.

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