How to design a sway bar w/ 3link + watts linkage

[funcars]

There are books that have formulas for calculating sway bar rates based on diameter and shape. Then you can calculate wheel rate based on the combination of the springs, locations, angles and sway bar rates. You can start with wheel rates that have an equal percentage of rate front to rear of what you had before you started changing things and go from there. Some of the Steve Smith books have lots of explanation and formulas to help. They are older books but so are most of the cars we are messing with.

An interesting approach to get a good starting point for your combined wheel rate (vs throwing a dart) is to look at the moment-moment method as explained by the articles at circle track. It is based on using combined wheel rates and calculating the overturning moments at front and rear and attempting to get them approximately equal to get a neutral handling starting point. It is a slightly different approach than looking at roll couple lines and easier to calculate - take a look if you are interested.

[JRouche]

Originally Posted by funcars

There are books that have formulas for calculating sway bar rates based on diameter and shape. Then you can calculate wheel rate based on the combination of the springs, locations, angles and sway bar rates. You can start with wheel rates that have an equal percentage of rate front to rear of what you had before you started changing things and go from there. Some of the Steve Smith books have lots of explanation and formulas to help. They are older books but so are most of the cars we are messing with.

An interesting approach to get a good starting point for your combined wheel rate (vs throwing a dart) is to look at the moment-moment method as explained by the articles at circle track. It is based on using combined wheel rates and calculating the overturning moments at front and rear and attempting to get them approximately equal to get a neutral handling starting point. It is a slightly different approach than looking at roll couple lines and easier to calculate - take a look if you are interested.

You are correct. But... When you are talking about formulas, calculations, wheel rates, locations, angles, diameter and SHAPE, moment-moment, overturning moments, roll couple, and the other settings they all translate into numbers.

Numbers some guys might not be able to get, or do and just really dont need that type of detail. There are some numbers through measurements that some guys just cant get, meaning they would have to do some major fact checking to get the raw numbers. More work than its worth.

I have read all the books. And feel like I have a grasp on the relationship between the numbers (measurements). But to understand it doesnt translate into how to pull the numbers out of the geometry of the suspension.

And some folks will get a kinda glazed over look in their eyes when you start talking about ALL the variables.

What I have found is the dart thrown into the board will get you very close if its just a nice street car or even a track car. And unless you are putting in a completely custom bar the extra number gathering is extra.

Weight of the car with a rough estimate and mimicking other cars that are similar.

I dont think there are many engineers looking at this thread. More likely a guy like myself that just wants to get a bar rate as close to usable as possible.

Many car guys that arent hard core racers are on this site. They just want a bar that is well within the range for their car.

Yes, there are some that want to dial it in as close as possible. But Im thinking thats 1%. The other 99% just want to get it pretty darn close..

But great info!!! JR

[funcars]

Yep - I think you are right. These threads seem to be more beneficial to folks who use primarily bolt-on parts that are already designed and analyzed. I'm an engineer myself and designed and fabricated a complete new front end with cup car parts so I had to know enough to get close with all of the changed geometry. That said, the math for sway bars is not that complex and there is a large benefit from having a good feel for how the numbers relate to the change in feel of the car. Almost any car will improve from some chassis tuning to match the driver technique.

Another very helpful tool is to get pictures of your car at the track so you can see obvious issues like an inside rear wheel lifting off, excess body roll, etc.

[JRouche]

Originally Posted by funcars

Another very helpful tool is to get pictures of your car at the track so you can see obvious issues like an inside rear wheel lifting off, excess body roll, etc.

Yes, I agree, pics or a vid. Inside tire lift would be a nice thing to see. And if all the other tires are working hard you may not know what the looseness in the rear is till someone showed you a pic of yer car with it lifting its back leg. Now thats an animal of a car, trying to take a leak while on the run LOL Ever see a dog do that, I have, kinda funny. But really kinda sad. Usually with runners with their dogs. Like dude?? Give yer dog a chance to take a leak or pinch a loaf. Good point.

I dont ever plan to take my car to the track, would love to but money would be the deal breaker. I cant afford it.

But if I did I would love to have a video of the car going around. Vids of any sport, including car racing can show the driver where he might be upsetting the car. See a lil uneasiness in the late braking, maybe a lil smoke from the tires (not good) or a lil wiggle. Or a lil hard on the go pedal on the exit, rear moves out too much, some more smoke from the tires. Smoke from the tires is loss of speed. It wont stop faster with them dragging and it wont accelerate faster with them spinning. Traction is speed. A video might be the only way the driver sees that.

Turning, braking and accelerations should be completely fluid motions. Not jerky and twitchy. Aggressive YES, jerky and snap type driving feels like fast driving on the seat of yer pants. But its slower than controlled driving.

And Im not trying to make any brownie points with the ladies but maybe thats why some of them that want to be involved in the sport are really fast drivers. More control and less aggressiveness. They are great drivers.

A video of yer driving might show some flaws in the driving habits also, besides the unapparent car actions. I like the idea. I SOOO wish I could afford to take a few laps on a track, I think I would be hooked. Thats the cost I cant afford, I would need to go as often as possible. And since time isnt an issue it becomes money. Errrr JR

[funcars]

At least in CA isn't not that bad to get some laps in at a track for a day. A few hundred bucks is worth it to be able to actually use some more of the capability of the car than you ever can on the street and learn a ton about driving too.

You could always autocross your car. Less expense and risk and teaches you tons too.

[JRouche]

Originally Posted by funcars

At least in CA isn't not that bad to get some laps in at a track for a day. A few hundred bucks is worth it to be able to actually use some more of the capability of the car than you ever can on the street and learn a ton about driving too.

You could always autocross your car. Less expense and risk and teaches you tons too.

Yeah, but even a few hundred bucks is more than I have. Its just NOT in the budget. Keeping the house and paying the taxes and ALL of the other expenses is on the top burner right now. Taking my car to the track for fun is a few hundred bucks out of line for me right now, way back burner, on a super slow simmer.

As it is prolly the same for alot of folks these days.

I need to make the extra bucks that are available to treat the entire fam, not just myself. They could care less about me tracking the car. But they would love to take a weekend to San Diego and visit Sea World, still just a few hundred bucks.

Thats the cost of having a family with a limited budget. You need to consider the other peeps.

When you dont you are headed to a single life again and scraping and scrounging cause all the extra money is going to child support and God forbid alimony.

Nope, I have my ducks in a row. I get to play with the car as much as I can. And Im happy. But the family comes FIRST!! Has to, otherwise there is no family and just you. JR

[JRouche]

Originally Posted by funcars

At least in CA isn't not that bad to get some laps in at a track for a day. A few hundred bucks is worth it to be able to actually use some more of the capability of the car than you ever can on the street and learn a ton about driving too.

You could always autocross your car. Less expense and risk and teaches you tons too.

Yeah, but even a few hundred bucks is more than I have. Its just NOT in the budget. Keeping the house and paying the taxes and ALL of the other expenses is on the top burner right now. Taking my car to the track for fun is a few hundred bucks out of line for me right now, way back burner, on a super slow simmer.

As it is prolly the same for alot of folks these days.

I need to make the extra bucks that are available to treat the entire fam, not just myself. They could care less about me tracking the car. But they would love to take a weekend to San Diego and visit Sea World, still just a few hundred bucks.

Thats the cost of having a family with a limited budget. You need to consider the other peeps.

When you dont you are headed to a single life again and scraping and scrounging cause all the extra money is going to child support and God forbid alimony.

Nope, I have my ducks in a row. I get to play with the car as much as I can. And Im happy. But the family comes FIRST!! Has to, otherwise there is no family and just yerself. JR