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Wise Folks,

There's a bit of debate on another forum regarding whether lifting the inside rear tire on corner entry is:

a. avoidable

b. indication of a setup opportunity - not desirable!

c. normal, not an issue

d. overdriving 

My STX MCS does not do this but I'm running coil overs so I'm not surprised.

Should this behavior be tuned out with shock settings?  Does it matter?

Thanks very much for your opinions on the matter.

Sincerely,

Charlie

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

Perfectly normal
 

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The Brown Sean

1988 Honda CRX Si (STS2 #48)

Not DFL at DC!

thanks!  not wishing to sound skeptical, but if you had DA shocks would there be any point in adding compression up front and a bit of rebound out back to try and dampen the pitch/roll on corner entry?  it just seems intuitive to me that four wheels are better then three...

in addition, would you think it odd if the car three-wheeled through the middle of the corner - after the brakes are released?

cheers,

charlie

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

On my yellow CRX with the Koni DAs at full stiff on the rear the car would three wheel through the entire corner. 

 

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The Brown Sean

1988 Honda CRX Si (STS2 #48)

Not DFL at DC!

thanks again - there's a picture worth at least a thousand words...

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

cmt52663:

thanks!  not wishing to sound skeptical, but if you had DA shocks would there be any point in adding compression up front and a bit of rebound out back to try and dampen the pitch/roll on corner entry?  it just seems intuitive to me that four wheels are better then three...

in addition, would you think it odd if the car three-wheeled through the middle of the corner - after the brakes are released?

more front roll stiffness is required if the inside rear is coming up i.e. a larger front sway bar and/or the shock changes you mentioned (front bump first, then rear rebound).  what's more, sometimes the inside rear lifts because there isn't enough droop travel.

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Doug #81 STS2
1990 Mazda Miata
STU 2000 Audi S4 (retired)
STU 2005 Mazda RX-8 (retired)

shinronin:

cmt52663:

thanks!  not wishing to sound skeptical, but if you had DA shocks would there be any point in adding compression up front and a bit of rebound out back to try and dampen the pitch/roll on corner entry?  it just seems intuitive to me that four wheels are better then three...

in addition, would you think it odd if the car three-wheeled through the middle of the corner - after the brakes are released?

more front roll stiffness is required if the inside rear is coming up i.e. a larger front sway bar and/or the shock changes you mentioned (front bump first, then rear rebound).  what's more, sometimes the inside rear lifts because there isn't enough droop travel.

thanks.  i can see the tradeoffs get tricky right away - for the MCS stiffening the front roll bar would seem likely to increase the native understeer.  if the stock bar permits enough chassis roll to exhaust rear droop in a steady state situation (those are rare though aren't they?) then there you are.

that lovely picture of the CRX seems to me to illustrate that situation very well - the chassis has quite a bit of roll, although it looks settled and quick.

i wonder though if the MCS has the same steady state characteristics, and wonder if any of our darned fast MCS folks are willing to comment?

 

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

cmt52663:

shinronin:

cmt52663:

thanks!  not wishing to sound skeptical, but if you had DA shocks would there be any point in adding compression up front and a bit of rebound out back to try and dampen the pitch/roll on corner entry?  it just seems intuitive to me that four wheels are better then three...

in addition, would you think it odd if the car three-wheeled through the middle of the corner - after the brakes are released?

more front roll stiffness is required if the inside rear is coming up i.e. a larger front sway bar and/or the shock changes you mentioned (front bump first, then rear rebound).  what's more, sometimes the inside rear lifts because there isn't enough droop travel.

thanks.  i can see the tradeoffs get tricky right away - for the MCS stiffening the front roll bar would seem likely to increase the native understeer.  if the stock bar permits enough chassis roll to exhaust rear droop in a steady state situation (those are rare though aren't they?) then there you are.

that lovely picture of the CRX seems to me to illustrate that situation very well - the chassis has quite a bit of roll, although it looks settled and quick.

i wonder though if the MCS has the same steady state characteristics, and wonder if any of our darned fast MCS folks are willing to comment?

yes, in the case of FWD a larger FSB won't help (iirc most if not all STS2 CRXs run with no FSB), but the pic is deceiving because setting the rear to full stiff with DAs isn't tuning out the inside rear lifting.  in that pic imagine if the front wasn't rolling so much such that the car is not pivoting from front left to rear right.  most ST* FWD suspension setups rely on a much higher rear spring rate compared to the front to induce more neutral handling.

but, in the case of GS suspension limitations, some inside rear lift is probably inevitable but you can limit it with shock tuning.

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Doug #81 STS2
1990 Mazda Miata
STU 2000 Audi S4 (retired)
STU 2005 Mazda RX-8 (retired)

The yellow CRX was in GS trim, not sure if that changes the perspective. 

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The Brown Sean

1988 Honda CRX Si (STS2 #48)

Not DFL at DC!

yep, gotcha.  my last post was done in a hurry and wasn't crystal clear but i was trying to describe both the MCS in STX and GS trim to address charlie's original post.  i was trying to describe what charlie correctly identified as the tricky tradeoffs in grip vs. roll stiffness on a FWD car in stock trim.  in GS, tire pressures, alignment, shock tuning are key.  i was just pointing out that addressing three-wheel motion by tuning the rear won't help.

there's an article in the latest GRM addressing FWD setup on a MCS.  check it out. 

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Doug #81 STS2
1990 Mazda Miata
STU 2000 Audi S4 (retired)
STU 2005 Mazda RX-8 (retired)

Just saw your post for the 1st time.  The wheel up attitude of the Mini is completely normal and common among all the top cars.  (see pic to your left) The R56 gets a bunch more air under there due to it's soft spring package.  Since I'm trying to dial more rotation into the car most of the time... maybe 3 is actually better than 4 after all.
 

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Tony Savini
2005 Mini Cooper S

racnmni:

Just saw your post for the 1st time.  The wheel up attitude of the Mini is completely normal and common among all the top cars.  (see pic to your left) The R56 gets a bunch more air under there due to it's soft spring package.  Since I'm trying to dial more rotation into the car most of the time... maybe 3 is actually better than 4 after all.
 

 

and that settles that!  Thanks very much Tony.

Cheers,

Charlie

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Charlie Thompson
'04 JCW Cooper [STX]
NER Cannon Fodder

I'm trying to think of any point in vehicle dynamics where dynamically raising the CG is a good thing. Aside from drag racing, I can't think of any. If you want to talk more about it Charlie, find me at the next Devens event.

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Nate Whipple
NER
188/88 DSP ITR

As far as I know the only two examples where low CGs are not beneficial for handling machines = karts and dirt track racecars.  On dirt a highish CG will help the tires dig into the dirt surface which increases total grip so the cornering speeds rise.  For karts...since there is no differential and a huge F/R tire bias favoring the rear they want to understeer.  So with a highish CG inside rear tire lift allows the thing to turn much more effectively.  I think that is because basic kart design = Engineering nightmares where you have to fix one problem by creating others.

Stan:

As far as I know the only two examples where low CGs are not beneficial for handling machines = karts and dirt track racecars. On dirt a highish CG will help the tires dig into the dirt surface which increases total grip so the cornering speeds rise. For karts...since there is no differential and a huge F/R tire bias favoring the rear they want to understeer. So with a highish CG inside rear tire lift allows the thing to turn much more effectively. I think that is because basic kart design = Engineering nightmares where you have to fix one problem by creating others.

Ah, didn't think of dirt, and karts I class under "anomalous".  

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Nate Whipple
NER
188/88 DSP ITR