Chassis Dynamics 101... - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

Reply
 
 
 
Thread Tools Search this Thread
Old 06-01-2007, 01:26 AM   #11
Senior Member
True Car Nut
 
Join Date: Jun 2004
Location: Glendale, AZ
Posts: 3,459
Thanks: 0
Thanked 1 Time in 1 Post
big_news_1 is on a distinguished road
Default

Great stuff, Curt. I have already used some of this information in a conversation with a friend, and I think I understand the factors affecting suspension performance a little better now
big_news_1 is offline   Reply With Quote
Old 06-01-2007, 02:00 AM   #12
Junior Member
Thread Starter
 
Join Date: May 2006
Location: BonnevilleHell
Posts: 0
Thanks: 0
Thanked 0 Times in 0 Posts
clm2112 is on a distinguished road
Default

Next thought: Understeer, Oversteer, and the "First United Bank of Traction"

These are a little beyond the basics...they are more some of the nastier side effects of messing with the suspension geometry (and your personal driving style..or lack thereof)

First, the "Bank" of traction. I'll credit Motorcycle Roadracing Guru Keith Code for planting this philosophy in my noggin (along with the Bank of Concentration..which is more of a racing strategy.)

All right, what is "Traction" ?...it is the amount of force available by the interaction between the tire and pavement. In Physics terms, it'* the normal force and the three coeeficients of friction (static, rolling, and sliding.)

That seems a little dry...so back to the "First United Bank of Traction" analogy...we each have an account at the bank. The money in that account is the sum of the traction from each tire at any given moment. How much money we have changes based on the road surface, the tire temp and compound, and how we choose to spend that traction at any given moment.

So, we go tooling down the road at a steady speed, in a straight line, on a warm sunny day with good tires. Cool, we are fat happy cats with a ton of traction in our bank accounts to spend.

Rain comes along, pavement gets wet, temps go down. We are not the fat cats anymore, as our back account of traction is a little light..better be carefull how we spend it.

Rain turns to ice and snow...Ok, we are screwed and about to be overdrawn at the bank of traction just going in a straight line...we had better be really carefull how we spend our traction funds.

Now, How DO we spend from the bank of traction?

Well, anything we do to make the car deviate from travelling in a straight line at a constant speed is spending money from the bank of traction.

First, stomping on the gas spends traction bucks. Pretty obvious to anyone drag racing...hammer the gas too hard and you are suddenly overdrawn at the bank of traction as wheel spin takes place and clouds of tire smoke errupt from the contact patches. (Don't answer the phone...it'* either the bill collectors or the EPA looking for you.) In physics terms, you transitioned from the rolling coeficient of friction to the sliding coefficient of friction...ok, you really didn't need to know that...suffice to say your wrote a check your tires can't cash

Next, standing on the brakes can also cause problems at the bank of traction...when you hit them too hard the tires are overdrawn and you hopefully slide to a stop without hitting anything solid or expensive to fix.

Last, making the car change directions with the steering wheel spends money from the bank of traction. This is the sneeky one, because we are so fixated on acceleration and braking that we often forget that turning left or right spends traction bucks too...often a lot more than we think.

So, You should be getting the drift of this by now...You spend traction through acceleration, braking, and turning or some combination of them. You just have to know how much cash you have at any given moment in the bank of traction before you spend it.

Now, we talked about weight transfers in the suspension of the car...that'* like the car shuffling around the money in our bank of traction..some in savings, some in checking, a little in the Christmas fund. The car'* suspension reacts to how we drive by moving traction around from wheel to wheel. If the car'* suspension is pretty good at this money manegment, no wheel has less traction available than it really needs when we go and spend it.

Oversteer is one condition where the money manager at the bank of traction is not on the job. It happens when the car becomes unbalanced in a turn and the rear wheels start to slide to the outside of a turn in a skid. The weight transfer got messed up and not enough force is pressing on the rear tires to hold the side loads they need to generate. Worst case, the car swaps ends as the rear wheels break free (Overdrawn at the bank of traction again.) Can be fun if you dig doing doughnuts in the parking lot for kicks...not so fun is it happens in a turn when you are not expecting it.

Understeer is the exact opposite...the FRONT wheels are now overdrawn at the bank of traction and the car doesn't want to make the turn you just told it to do! This is pretty hard to do, and it takes a really bad suspension setup to induce understeer. As the driver, it is more likely to wrote this bad check yourself...usually by trying to accelerate or brake the car in a hard turn.

In terms of driving style, the first rule of roadracing is never ask the car to do more than one thing at a time! (Ok, it'* the second rule..the first rule is Don't Panic!) You brake before you enter a turn, execute the turn with enough throttle to maintain the car'* cornering speed without unbalancing the suspension, then you can accelerate out of the turn as the turning forces lighten up. The tires are generating traction into the bank account and you are spending it on one thing at a time. Try to spend on more than one thing at a time and you are going for a little excursion off into the haybales.

Just keep in mind, that your chassis setup dictates what you can spend and when you can spend it. Do it right and you'll have a lot of traction to spend. Screw it up..well..you get the point.
clm2112 is offline   Reply With Quote
Old 06-01-2007, 02:19 AM   #13
Senior Member
Posts like a Turbo
 
bigerik's Avatar
 
Join Date: Jul 2006
Location: Toronto
Posts: 442
Thanks: 0
Thanked 0 Times in 0 Posts
bigerik is on a distinguished road
Default

Yet another amazing post. You should publish this stuff, my friend!
bigerik is offline   Reply With Quote
Old 06-01-2007, 04:39 AM   #14
Senior Member
Certified Car Nut
 
Join Date: Jun 2003
Posts: 15,928
Thanks: 0
Thanked 0 Times in 0 Posts
BonneMeMN is on a distinguished road
Default

I subscribe to the circle of traction myself.. There are a few points I would like to discuss. To me independent suspension can include a sway bar.

I do agree that overdoing the brake parts can be a waste of money, but all FWD bonnevilles 87-99 have been "underbraked" from the factory. I think the disc/drum setup also further complicates it due to the adjustment in the rear, and how that affects the front brake modulation, overall power, and effectiveness.

I believe that maintaining suspension part groups (FE1, FE2) is necessary in spring rates and damping, but mixing and matching sway bars is a great way to get the balance of a car to where each individual driver wants it. This is why most "modifiable cars" have rear sway bars with a few settings for stiffness on them, to dial in the strength of the rear bar, proportionate to the front. If anything, the std 92-99 chassis needs more rear bar added, and perhaps more front IMO. Personal preferences for car balance come into play obviously...

I don't know if you covered it but if you added more rear bar, the car will tend to turn easier/oversteer more then factory settings. More front means the car may be harder to turn. When I did front only, I could feel the back end of the car puling up higher when turning compared to the front, almost like it was trying to tripod the rear-inside wheel off the ground.

Swapping around OE sway bars isn't too much of an adjustment for most 87-99 cars IMO, it'* certainly not as drastic as many aftermarket bars for other cars, some that are well beyond 300% stiffer then OE.

But good reading for sure. A lot of good info in there for those who may not have seen this stuff before.
BonneMeMN is offline   Reply With Quote
Old 06-28-2007, 03:01 PM   #15
Senior Member
Posts like a 4 Banger
 
Join Date: Jun 2006
Location: Chicago, IL
Posts: 113
Thanks: 0
Thanked 0 Times in 0 Posts
67Goat is on a distinguished road
Default

Quote:
Originally Posted by BonneMeMN
I subscribe to the circle of traction myself.. There are a few points I would like to discuss. To me independent suspension can include a sway bar.

I do agree that overdoing the brake parts can be a waste of money, but all FWD bonnevilles 87-99 have been "underbraked" from the factory. I think the disc/drum setup also further complicates it due to the adjustment in the rear, and how that affects the front brake modulation, overall power, and effectiveness.

I believe that maintaining suspension part groups (FE1, FE2) is necessary in spring rates and damping, but mixing and matching sway bars is a great way to get the balance of a car to where each individual driver wants it. This is why most "modifiable cars" have rear sway bars with a few settings for stiffness on them, to dial in the strength of the rear bar, proportionate to the front. If anything, the std 92-99 chassis needs more rear bar added, and perhaps more front IMO. Personal preferences for car balance come into play obviously...

I don't know if you covered it but if you added more rear bar, the car will tend to turn easier/oversteer more then factory settings. More front means the car may be harder to turn. When I did front only, I could feel the back end of the car puling up higher when turning compared to the front, almost like it was trying to tripod the rear-inside wheel off the ground.

Swapping around OE sway bars isn't too much of an adjustment for most 87-99 cars IMO, it'* certainly not as drastic as many aftermarket bars for other cars, some that are well beyond 300% stiffer then OE.

But good reading for sure. A lot of good info in there for those who may not have seen this stuff before.
I agree that the front brakes from the factory were cheap trash. I switched to all metal front rotors and it made of world of difference compared to the cheapie composites. The rear drums did a fine job as long as they were adjusted, but for some reason, GM failed to design my old '95 with an adjustment slot - I had to take the whole wheel and drum off whenever they needed adjustment, no wonder my fronts always wore quickly. I think that was just a tricky way to give the dealers more business to do more brake jobs.
67Goat is offline   Reply With Quote
Old 06-29-2007, 11:56 AM   #16
Senior Member
Posts like a Supercharger
 
Join Date: Dec 2005
Location: montreal,canada
Posts: 195
Thanks: 0
Thanked 0 Times in 0 Posts
94BonnieSE is on a distinguished road
Default

thanks for all the info Curt, loooots of info in there,
and easy to read, follow and understand, I learned a whole lot as im sure most of the
club will too!
i have a way better idea on choosing the suspension "upgrade" pieces.

cant thank you enough!!!
94BonnieSE is offline   Reply With Quote
Old 11-22-2007, 08:40 PM   #17
Junior Member
Posts like a Ricer Type-R
 
Join Date: Nov 2007
Location: Marlborough, MA
Posts: 15
Thanks: 0
Thanked 0 Times in 0 Posts
SuperchargedLSS is on a distinguished road
Default

[quote="bigerik"]
Quote:
Originally Posted by willwren
I agree with Willwren, but that does not mean that higher profiles work better either. Like all things, its all about balance. I think the 60'* used in our cars strike a nice balance between a .............. compared to a low profile which gives no warning and loses traction RIGHT NOW!

what if i put 19'* on my car, with a little 40series sidewall? say, a 19x8.5? does the difference from a 16x7 to a 19x8.5 make any difference in what size sidewall i should use, or am i only using what i can fit.. i wouldn't expet a 60series sidewall on a 19in rim to clear the fender wells, ahh..
so.. the question is, would i be suffering or benefitting from putting (relatively) lightweight, taller, wider wheels with a 40series sidewall
SuperchargedLSS is offline   Reply With Quote
Old 01-30-2008, 11:14 PM   #18
Junior Member
Thread Starter
 
Join Date: May 2006
Location: BonnevilleHell
Posts: 0
Thanks: 0
Thanked 0 Times in 0 Posts
clm2112 is on a distinguished road
Default

Quote:
Originally Posted by SuperchargedLSS
the question is, would i be suffering or benefitting from putting (relatively) lightweight, taller, wider wheels with a 40series sidewall
Sorry to be so late in offering comment...I've been busy with other projects.

My thoughs are this:

1.) Is the new wheel & tire combination going to be larger in diameter than the stock tires? This is a issue the folk doing "donks" are generating with the unwitting use of larger than stock wheel/tire combinations: The caster on the front wheels gets bigger too! By increasing tire diameter, the spindle gets further away from the ground, and the contact patch moves further away from the imaginary line through the ball joints. Bigger caster numbers mean more stability at the expense of steering response. Get them big enough, and you better grab hold of the wheel with both hands and heave hard to make the barge turn the corner. Keeping the tires diameter about the same as what the engineers designed the suspension around is sound advice.

2.) Ok, lets say you kept the same diameter, but now you are replacing rubber with aluminum by making the rim bigger and the sidewall of the tire smaller. Basic geometry will be more or less OK, except for a harsher ride quality and the amount of camber in turns. The harsher ride comes from having less cushion in the sidewalls. The camber comes from the loss of flexability in the tire across the tread. You will likely need to make the dampening rates in the springs and shocks lower to suck up what the tires themselves no longer can. You will also have to be more agressive in the sway bars, you have to work harder at keeping the car level in turns so the contact patches don't end up on the sidewalls. This may seem counter-intuitive advice ("Make the shocks softer and the swaybars harder?? WTF??") But in terms of engineering, your choice of rims and rubber is different than what GM'* engineers picked for the suspension they designed. So if you want a smooth ride and take advantage of the cornering forces, you got to give the car what it wants. You can actually create a situation where you have LESS cornering traction available because the steering geometry is tipping the tires too far into the direction of the turn and thus lifting the center of the tread off the road.

Now, if you don't mind the harsh ride (I kinda dig feeling every ripple in the road and don't mind the extra wear and tear that comes with it) The go the opposite way on the shocks and springs..or just leave them alone and work at getting the car to corner as level as possible and keep the contact patches near the center of the treads.

Same thing happens when you increase rim width. Wider rubber will not quite match up with the designed in camber of the car'* suspension in turns and needs to be kept as level as possible to get the most traction out of them. (You are effectively trying to limit the vertical motion of the suspension to keep the tires perpendicular to the road in a hard corner.)

You also have some adjustment available in the shock towers. Not a lot, but if you can strike a reasonable average camber setting that keeps the contact patches roughly centered, then by all means make use of it.
clm2112 is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Engine related fluid dynamics question corvettecrazy Lounge 3 09-25-2007 03:57 PM
[b]Chassis upgrades[/b] JimmyP70 Performance, Brainstorming & Tuning 16 10-28-2005 04:16 PM
Chassis dyno search BonEvilSSEi General GM Chat 0 10-22-2004 02:02 AM
Chassis Lube Schedule Damemorder 1992-1999 13 12-31-2003 01:46 AM
'95 SSEi chassis lube Brad_Olson 1992-1999 1 12-31-1969 08:00 PM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 08:50 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.