'99 V70 Understear ?

  • Thread starter Thread starter Bob Sisson
  • Start date Start date
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Bob Sisson

Ok, I admit it I have a lead foot...

My new (to me) '99 V70 XC is fun to drive, but doesn't behave like I expect
in turns.

It plows (understears) if I go into corners hard. Ease off the gas and it
snaps in hard... WOW...

I just put on Dunlop SP 4000 A/S on... Got a front end alighnment when
they fixed the tie-rods...

What should I be looking at to reduce this... or where to start...

Yes, yes, I know this is not my eclipse.... but is hard when you want to
scurry into traffic from a corner and you are 1/2 a lane from where you want
to be....


Bob S.
 
Bob Sisson said:
Ok, I admit it I have a lead foot...

My new (to me) '99 V70 XC is fun to drive, but doesn't behave like I expect
in turns.

It plows (understears) if I go into corners hard. Ease off the gas and it
snaps in hard... WOW...

I just put on Dunlop SP 4000 A/S on... Got a front end alighnment when
they fixed the tie-rods...

What should I be looking at to reduce this... or where to start...

Yes, yes, I know this is not my eclipse.... but is hard when you want to
scurry into traffic from a corner and you are 1/2 a lane from where you want
to be....
Click to expand...

Check very carefully the viscous coupling / transfer box is healthy- it
sounds to me like the coupling is shot (i.e. locked solid) and too much
power is being sent rearwards..

Tim..
 
Bob said:
Ok, I admit it I have a lead foot...

My new (to me) '99 V70 XC is fun to drive, but doesn't behave like I expect
in turns.

It plows (understears) if I go into corners hard. Ease off the gas and it
snaps in hard... WOW...

I just put on Dunlop SP 4000 A/S on... Got a front end alighnment when
they fixed the tie-rods...

What should I be looking at to reduce this... or where to start...

Yes, yes, I know this is not my eclipse.... but is hard when you want to
scurry into traffic from a corner and you are 1/2 a lane from where you want
to be....

Bob S.
Click to expand...

I had the same annoyance with my 2WD V70 (98 T5). I put up with it for
6 years, before I finally fixed it last year. Before you try this, make
sure another car acts the same way, but what I did was put a rear sway
bar on that was from a sedan. The original wagon rear bar was 17 mm,
the sedan one, 21.5. I was worried that maybe this was going too far,
but to my taste the car was just perfect. Even in the snow, or on
gravel roads, the car seems perfectly balanced. I kick myself for
waiting 6 years.

The only trick for you is that Volvo doesn't list the bars by diameter.
You need to read the chassis code of the plate by the battery. On my
V70 the chassis code is 5F2PEVS, the 'V' refers to the rear sway bar.
On the S70, the rear bar is coded 'N'. You'll have to find an AWD S70,
compare bar size to yours, and hopefully it's bigger. Or you can try a
set of bars from ipd. I didn't want to use an ipd bar because they've
had problems with their rear bars breaking on the 2WD cars. The rear
bar is a different (normal) design on the AWD cars, so there shouldn't
be a problem.

Also, the XC is jacked up a bit and has tall tires, so it's never going
to be great.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Is there an EASY way to test the Viscous coupling ? Or is that a shop thing
?
 
Bob@Sisson said:
Ok, I admit it I have a lead foot...

My new (to me) '99 V70 XC is fun to drive, but doesn't behave like I expect
in turns.

It plows (understears) if I go into corners hard. Ease off the gas and it
snaps in hard... WOW...

I just put on Dunlop SP 4000 A/S on... Got a front end alighnment when
they fixed the tie-rods...

What should I be looking at to reduce this... or where to start...

Yes, yes, I know this is not my eclipse.... but is hard when you want to
scurry into traffic from a corner and you are 1/2 a lane from where you want
to be....


Bob S.
Click to expand...
Start with analyzing your technique regarding entry into the corner.
Understeer occurs when the slip angle of the tire contact patch is
exceeded and the tires just begin the sweet growly squeal sound that
lets you know the tires are working. The transistion from quiet tire
noise to the working sound should be smooth and gradual beginning just
after turn in at the entry of a corner to a constant pitch through the
apex and to the exit. Adjust your apex to see where the optimum entry
point should be for your chassis. Remember that a later apex will allow
a smoother transition into traffic, while an earlier apex will allow
higher exit speed and use more road. Anticipate. Although smooth is key
and exit speed is the name of the game you have to be constantly aware
of how much stick the car has. As soon as the tire pitch begins to rise
be prepared to correct the steering in anticipation of loss of rear
wheel grip. The tendency to overcorrect decreases with practice but is
almost always the result, so be prepared to correct in the opposite
direction to save the car from a spin. You will likely need to repeat
the correction two or three times to successfuly execute the save. If
when driving into a corner an abrupt lift on the throttle causes violent
trailing throttle oversteer then the chassis is horribly balanced and
will need extensive sorting to put it right.

Once this is achieved start adjusting tire pressures until the maximum
speed can be attained through the same radius turn with reliable
precision. Find an empty parking lot at a factory where you can drive in
circles of various diameters and spin without running into things. At
this point adjusting the sway bars is in order. Stiffening the front,
going to a larger diameter bar, and going to a stiffer rear bar will
keep the car flatter through a turn. Although too stiff a rear bar will
induce understeer. This puts more load on the outside front tire on turn
in so that in a street car it's prudent to raise the tire pressure
enough to keep the tire on the rim while turning. Since street tires
don't develop all that much grip anyway a pressure somewhere in the mid
to high 40's psi should be adequate.

Sorry for the rant. Driving techniques need to be learned and practiced.
Bravery is no substitute for skill at high speed.

Bob
 
Bob Sisson said:
Is there an EASY way to test the Viscous coupling ? Or is that a shop thing
?


and
Click to expand...

Jack up the front of the car and place it on stands, *just clear of the
ground*.

*VERY* carefully engage top gear or Drive if auto and gently apply a very
small amount power, handbrake off.

If the front wheels spin and the car stays still the Viscous is ok.- tho
there will be some bind.

If the front wheels dont turn and it tries to push off the stands, the
viscous is shot.- i.e. locked solid.

Tim..
 
Not to worry about the rant.... I enjoyed reading it.

My elcipse was where I practiced just what you said...

I would go into the same corner harder and harder until the tires
screemed...

And they I would listen to see how hard they screemed. I learned that I
liked it when the scremed a bit, but if they were screeming a lot it was not
a good thing because they could let go at any time.

I also learned that different tires behave, well, differently. The Dunlop
AS 4000's screemed LOTS, and were very predictable. The next set of tires I
got I never found they edge of because they were to sharp... They stuck like
rain raicing tires in the straights, but barely screemed at all before
loosing it... GREAT drag tires, lousy street or rally tires.

My Volvo 850 doen't have the musscle to be pushed the way I like to drive,
which is a good thing, but it is extreemly neutral in driving.

The '99 V70 is fun, not as much fun as my old eclispe, but it weighs twice
as much and has half the HP. Needless to say the first time I went into a
corner expecting 850 results and I was half a lane from where I was supposed
to be, plowing ahead, I got off the gas, and was quickly re-united with the
line I desired. I have been "pushing" to find that edge ever since...

Bob S.
 
"Robert Dietz
Start with analyzing your technique regarding entry into the corner.
Understeer occurs when the slip angle of the tire contact patch is
exceeded and the tires just begin the sweet growly squeal sound that
lets you know the tires are working. The transistion from quiet tire
noise to the working sound should be smooth and gradual beginning just
after turn in at the entry of a corner to a constant pitch through the
apex and to the exit. Adjust your apex to see where the optimum entry
point should be for your chassis. Remember that a later apex will allow
a smoother transition into traffic, while an earlier apex will allow
higher exit speed and use more road. Anticipate. Although smooth is key
and exit speed is the name of the game you have to be constantly aware
of how much stick the car has. As soon as the tire pitch begins to rise
be prepared to correct the steering in anticipation of loss of rear
wheel grip. The tendency to overcorrect decreases with practice but is
almost always the result, so be prepared to correct in the opposite
direction to save the car from a spin. You will likely need to repeat
the correction two or three times to successfuly execute the save. If
when driving into a corner an abrupt lift on the throttle causes violent
trailing throttle oversteer then the chassis is horribly balanced and
will need extensive sorting to put it right.

Once this is achieved start adjusting tire pressures until the maximum
speed can be attained through the same radius turn with reliable
precision. Find an empty parking lot at a factory where you can drive in
circles of various diameters and spin without running into things. At
this point adjusting the sway bars is in order. Stiffening the front,
going to a larger diameter bar, and going to a stiffer rear bar will
keep the car flatter through a turn. Although too stiff a rear bar will
induce understeer. This puts more load on the outside front tire on turn
in so that in a street car it's prudent to raise the tire pressure
enough to keep the tire on the rim while turning. Since street tires
don't develop all that much grip anyway a pressure somewhere in the mid
to high 40's psi should be adequate.

Sorry for the rant. Driving techniques need to be learned and practiced.
Bravery is no substitute for skill at high speed.

Bob
Click to expand...

And of course, for multiple reasons, practising this should not be done
on public roads, but you should know where the limits are - both yours
and your car's.

One other point: A stiffer rear sway bar will induce oversteer or
reduce understeer. Increasing roll stiffness at one end of the car
increases the amount of the force that counteracts the car's lean at
that end. This allows the tires at the other end to remain more evenly
loaded (i.e. less weight on the outside tire), giving that opposite end
more grip.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)
 
Turned out to be a broken component.

turning (slowly) the other day my Left front Axel folded back. Apparently a
bolt holding the axel to the strut snapped and had been doing strange
things.

Glad it didn't happen at speed....
 
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