One of the most important aspects of car setup is the static weight distribution and the cross-weight percentage. Why? Picture the following:
Your car is really fast in right-hand turns, but understeers in left turns. If you get the car neutral in left turns, it oversteers in right turns. The situation is frustrating. You've tried springs, shocks, different bars, neutralizing …
Thanks for posting this. I've read all the info before, in various places, but it's good to have a refresher. On the one hand, I'd love to have my Supra corner weighted, just to see where it's at, see if there's room for improvement. On the other hand, it drives really, REALLY good for being setup by this idiot behind the keyboard, and I really don't wanna spoil a good setup by chasing after a perfect setup... at least not yet.
Would be interesting to see how close to ideal I got it though, given how well it handles already. Basically so long as I don't completely overcook a corner entry, it does better than any car this heavy has any right to...
Good stuff. I've had my cars corner balanced a lot, but never really looked into the science of it. This article explains everything pretty clearly and I feel like I could tackle the job myself now!
I see disconnecting the sway bar, and how to do it, but disconnect the shocks?
Toebra said:I see disconnecting the sway bar, and how to do it, but disconnect the shocks?
I had the same question. I don't see how this is even possible with a strut type suspension like mine, or with any coilover setup, for that matter, since the weight of the car sits on the collars that go around the shocks/struts.
In reply to Toebra :
Unless you have some kind of stupid hyper-critically damped NASCAR type dampers this isn't really necessary. To get good accuracy easily make sure you get the low hanging fruit first like removing the friction between the tires and the scales so there is no bind. Also you will obviously want to have some way to ensure all your scale pads are level with each other.
I would imagine that disconnecting the shocks is only applicable to setups where the shock and spring are separate, like a lot of solid axle cars, or Mk2 Supras in my experience.
Funny. I dropped my integra off at edge to have this done today. looking forward to getting it back!
Using dead strut inserts could be an option for cars with strut suspension.
My big stumbling block on this subject is how to get accurate readings by removing all the friction/bind from the tires, sway bars, bushings, etc. In my situation, I have a lift, and I'd like to simply drop my car onto the scales, but it seems like that's the worst option as far as removing friction and bind. Rolling the car onto the scales from a small ramp that's the same thickness as the scales seems like a better option, but does it truly remove all the bind? In other words, to make this method work, wouldn't you really have to drive the car around, preferably going over a few pretty serious bumps, before driving onto the ramps? This gets very tedious, given the number of iterations it typically takes to get the corner weights right.
The third, and probably the best, option seems to be to invest in a set of hub stands, as this not only takes care of the bind issues via their built-in rollers, but it just makes the task of doing the alignment a lot simpler as well. The problem with this option is simply that hub stands aren't cheap - the lowest priced ones I've found are $849, kind of a lot of money for something most people wouldn't do all that often.
Maybe I'm over-thinking this, but I was amazed when I got my new scales, and let my car down on them for the first time. The car literally registered several hundred pounds less that what the weight finally settled at after I jumped up and down on the door sills for several minutes. Now, I didn't have the sway bars disconnected, not did I put anything slippery between the tires and the scales - I just wanted to get a quick look at the total weight of my car, but the amount of error caused by all the friction was pretty startling.
Interested in hearing peoples' opinions and (preferably) experiences.
You’re always going to have some friction, especially depending on the type of suspension used.
Struts and trailing arms generally aren’t great in this case as they have a lot of inherent bind. Using dead struts and lots of bearings will help.
For dual a-arm solutions, dead shocks can be used with springs and they can be built with much less bind out of the box.
Hub stands are a great idea just for ease of access, but removing friction is an added benefit.
Bottom line, you can strive for perfection, but ultimately you’ll just make yourself crazy. Strive for repeatable and take the measurement as a data point, instead of an absolute.
Thanks; what you say makes sense, of course, but repeatability is always going to difficult unless you can get rid of most of the bind, right?
You've mentioned "dead struts" a couple of
Cloud9...68 said:My big stumbling block on this subject is how to get accurate readings by removing all the friction/bind from the tires, sway bars, bushings, etc. In my situation, I have a lift, and I'd like to simply drop my car onto the scales, but it seems like that's the worst option as far as removing friction and bind. Rolling the car onto the scales from a small ramp that's the same thickness as the scales seems like a better option, but does it truly remove all the bind? In other words, to make this method work, wouldn't you really have to drive the car around, preferably going over a few pretty serious bumps, before driving onto the ramps? This gets very tedious, given the number of iterations it typically takes to get the corner weights right.
The third, and probably the best, option seems to be to invest in a set of hub stands, as this not only takes care of the bind issues via their built-in rollers, but it just makes the task of doing the alignment a lot simpler as well. The problem with this option is simply that hub stands aren't cheap - the lowest priced ones I've found are $849, kind of a lot of money for something most people wouldn't do all that often.
Maybe I'm over-thinking this, but I was amazed when I got my new scales, and let my car down on them for the first time. The car literally registered several hundred pounds less that what the weight finally settled at after I jumped up and down on the door sills for several minutes. Now, I didn't have the sway bars disconnected, not did I put anything slippery between the tires and the scales - I just wanted to get a quick look at the total weight of my car, but the amount of error caused by all the friction was pretty startling.
Interested in hearing peoples' opinions and (preferably) experiences.
I don’t get this. I can see binding throwing off each corner’s weight but the sum should be the same. Or maybe I read the post wrong. Did you mean it was off several hundred pounds per corner? That seem like a lot.
Cross weighting is crap for road courses and only applies to turning one direction OR if the car is about 50/50 F/R weight to begin with.
Many successful race teams use corner weighting to achieve the same F/R % on both sides equal, not cross weight. Andy Hollis does this.
So LF/LR = RF/RR is what you shoot for. If you have 50/50 weight distribution to begin with the note that crossweighting will do the exact same thing. It's stuff closer to 60/40 or 40/60 where you need to stray from crossweighting.
Then there is what I do for FWD stuff... That is forget the rear weights entirely, and just balance the fronts to be equal. My left rear is something like 150lbs heavier than the right rear, with both fronts even at ~740lbs each on a 2425lb FWD car.
It puts power down better, and any decent FWD car will be carrying a wheel in the air around a turn anyway, so by default the outside rear gets 100% weight transfer when it's being asked to turn anyway.
There are many ways to corner balance a car. Don't just blindly cross weight it thinking it's the "right" way. Then if it's for a particular road course, you will find several seconds optimizing for select turns and throwing any of the above methods out the window... A friend's Chump Car found 2 sec at VIR making it turn right better than left.
Go out and experiment with it.
Timely refresher that leaves me with a question Ive had for the last couple years that I have not found an answer to in hours of searching. I have a 96 civic with a d16/manual. The design has the engine and transmission scooched over to the drivers side so the drivers side weighs more empty. At the time Honda was still favoring their home market I reckon. I weigh 220. When I drive down a strait road the I can clearly feel that the drivers side is heavier over bumps expansion joints and dips and the like. Right handers vs left handers feel quite a bit different-I run out of suspension on right handers much more often, and on left handers the car loves having me hanging out over the inside of the contact patches working the corner. Right now I have (IIRC) 350 lb front and 200 lb rear springs (koni sport, eibach pro line, ST anti sway bars) . Besides the eventual move to an adjustable ride height set up, I feel like I need 100 lbs or so more spring in the left front. So 2.5" springs and experimenting is the way to go- I think I know that much.. . Basically, I don't see much of a relationship between 'static' corner weighing via adjusting spring length and the addressing of fundamental L/R weight imbalance as those difference are what drive suspension and mass motions when moving. Or am I missing something?
Yeah, I'm a little puzzled by my result when I let me car down on my new scales as well. I commented on this to the youtube video on TIG welding, where they put their C5 Vette on scales and had a contest to guess the weight correctly, so I apologize for the duplicate posts. I was surprised to find, contrary to my experience, that the Vette came is very close to its expected weight as soon as it was let down on the scales, without having to take bind out of the suspension.
Thinking about this a little, the weight measured by the scales is the sum of the force of gravity acting on the car's mass, and the force of the springs pressing downward. Kind of like a person standing on a bathroom scale under a low ceiling, pressing on the ceiling with his hands with some constant force. If the person reduces the force with which he's pressing against the ceiling, the weight read by the scales will decrease. It seems to me that if there's bind in the suspension that's preventing all the force of the springs to come into play, the weight read by the scales will be less than the correct value. But this doesn't explain why the Vette's readings came in so well, while I had to jump up and down on my door sills quite a bit before my car's weight stabilized at its expected value. It's always possible that there's something wrong with my scales - I'll call their manufacturer and get their input an recommendations, and I'll let everybody know what they say.
In reply to Cloud9...68 :
The total weight will ALWAYS be correct unless you can find some way to suspend gravity, if you can let me know. It has to, it's just the laws of physics. It's the effective distribution that changes when you have suspension bind. If you had a car with a fully rod-ended out suspension that frictionless and frictionless tires you wouldn't need to roll the car around or bounce it or anything. It would just automatically settle.
When I weigh my cars I try not too overthink all this binding stuff. I put the car on grease tiles so the tires move freely on the scales and then I bounce each end a couple times. Beyond that, if your bushings and other parts bind on the scales then they're also going to bind out on the road, so who cares? Same goes for for swaybar endlinks. Are they adjustable? Disconnect and adjust later. Are they non-adjustable? Then just leave them attached. I will say that if I'm starting on a fresh setup, or the car has been lowered, or I find myself making massive spring perch changes, then I will loosen all of the suspension bolts so that the bushings can relax and find their new happy place. I retighten them after I've made all my adjustments. You would be amazed at how much bushing twist can contribute on your suspension. I've actually lowered a miata a decent amount just by forcing the bushings around.
In reply to freetors :
What you're saying makes sense, but I can't explain why it took so long for my car to settle into its final weight reading. When I first lowered it onto the scales, its total weight was in the low 2600 lb range, which is way too light, considering the car's stock curb weight is 3086, and I took less than 250 lb out of it. Only after I spent a lot of time bouncing on the door sills did it settle down and stabilize.
Maybe there's some sort of bind in the scales. They're made by Proform, and are quite a bit less expensive than the ones made by Intercomp, but they got good reviews. I'm anxious to see what Proform says about my experience.
Cloud9...68 said:In reply to freetors :
What you're saying makes sense, but I can't explain why it took so long for my car to settle into its final weight reading. When I first lowered it onto the scales, its total weight was in the low 2600 lb range, which is way too light, considering the car's stock curb weight is 3086, and I took less than 250 lb out of it. Only after I spent a lot of time bouncing on the door sills did it settle down and stabilize.
Maybe there's some sort of bind in the scales. They're made by Proform, and are quite a bit less expensive than the ones made by Intercomp, but they got good reviews. I'm anxious to see what Proform says about my experience.
Proforms are cheap scales. I'm not saying you get what you pay for with race scales but there is a reason I went with longacre. I don't like the lower weight ratings and plastic scale pads of proform. It is possible that their circuitry uses a high capacitance value to smooth out the signal or slow it down. Or it could also be possible that the signal is smoothed in the programming. That's all total speculation though.
In reply to flatlander937 :
This was a very interesting post to me. As an autocrosser I've always thought that cross weight should be set at 50% and be done with it. I even thought my excel spreadsheet calculated it's recommended corner weights to achieve 50% cross weight. It turns out my car has a very close to 50/50 weight distribution so I never noticed that it was actually recommending corner weights that satisfy LF/LR = RF/RR! I plugged in a bunch of numbers into my calculator and it all checks out. Now that's pretty cool! I have now added the ratios so I can visually see what's happening. Here is a screenshot with some random-ass corner weights.
Cloud9...68 said:Thanks; what you say makes sense, of course, but repeatability is always going to difficult unless you can get rid of most of the bind, right?
You've mentioned "dead struts" a couple of times - what do you mean by that? A strut with its innards removed? How would you make something like that? Or do you just mean an old, worn-out strut? And what do you mean by "lots of bearings"? Thanks.
Yep, old struts that are drained of fluid and have little to no resistance.
Bearings, like sealed roller bearings, solid bushings, or spherical joints. Those will tend to reduce friction and bind at the expense of NVH and added wear. For pure race cars this isn’t a consideration. For street cars it certainly can be.
In reply to Stefan :
Ah, OK, thanks for the clarification. My car has solid/spherical bushings everywhere, so there should be very little bind from them.
Since this article still gets a bunch of traffic, just bumping it up.
Thanks and enjoy.
Do these percentages apply for front wheel drive cars? My car is a 1987 Honda CRX, set up according to ITC class rules. Wouldn't the fact that it is front wheel drive change at least the front to rear percentages? Do you have recommendations for such corner weight percentages?
Equal weight on each front wheel, same on the rear. The front will show close to 60%. It varies with weight removal, added.
Cross weight will come close to 50%
So if you have 60% on the front , you should have 30% on each front wheel.
Get the numbers right and the percentages will follow.
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