924Board.org

924RACR · Posted: Tue Jul 24, 2007 10:02 pm Post subject: How much wedge???

Can any experienced racers out there give advice as to just how much (%-wise) wedge I should try, like in what increments, to bias my handling a little? Likewise, refresh my memory which diagonal I want heavier for better turn-in/more oversteer for right-handers?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

!tom · Posted: Wed Jul 25, 2007 8:13 am Post subject:

Oops! I just wrote this reply thinking PORSCHEV wrote the post. This is a massive edit.

If you're loose one way and tight the other way, you want to add weight to the side that is tight.

So, if you turn better to the left than you do to the right, and you want to loosen the car up through right hand turns, you want to add weight to your left rear (right front) wheel.

I'd go in small increments -- this can be a very sensitive adjustment. I can't give you a starting point, since I've never raced a 924. I have done a lot of racing though.

As far as better turn-in goes, have you considered a bit less toe in the front? Maybe go a degree or two more toe-out than you have now. I don't know if you're running with toe in or toe out, but I often set up my race cars with a bit of toe out in the front for aggressive turn-in.
_________________
78 924 NA
5-lug

924RACR · Posted: Wed Jul 25, 2007 11:08 pm Post subject:

Thanks... yeah, I'm running a bit of toe-out; prefer to have more like 1/8 than 1/4", as the latter tends to drop off the diminishing returns slope... What I'm trying this weekend (actually Friday test day before this weekend at Waterford) is some slightly lighter/softer front springs - went from 660 to 600#, to try to get a little more bite up front. We'll see how that works to improve turn-in, and I may also try dropping the front a little - it's currently even in both weight and ride height, all around.

I'm looking to bias a little for right-handers; in addition to most of the turns at my home track (10 out of 13) being RH, an upcoming race is Mid-O, and I'm trying to bias for the two lower-speed (50mph) RH turns that lead onto the front and back straights; the other straight, between 1 and the Keyhole, is a LH turn, but it's an 80mph turn, so more stability and push/understeer is just fine there, to allow one to push the limits more securely.

So the goal is not to even out the car, but rather insert a bias in a car that is currently quite even.

Sounds like (both from your notes and talking to the circle track guys at work) that something between 2-5% heavy on the RF/LR will be the way to go, if anything.

Thanks!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

!tom · Posted: Thu Jul 26, 2007 3:47 am Post subject:

Remember that as you loosen the car to the right, you'll tighten the car to the left.

You may want to loosen the car overall as well as add a bit of tweak, which is what you're doing by softening the front.

I'm used to calling it "wedge" when talking about an oval car, and "tweak" when talking about a road-course car. Much like loose == oversteer, tight == understeer == push -- there's more than one term for the same thing, and different terms tend to be used for different forms of racing, when it's really the same thing.

How easy is it to adjust the toe in the rear?

Personally, I don't like having tweak on a road-course car, but I do know some people do exactly what you're trying to do. The fact that your car has an inline drivetrain screws up the handling a little bit too, and one way to try to compensate for that is with tweak, but you really can't do much about it. Maybe what you're trying to do here is counteracting a bit of torque steer.
_________________
78 924 NA
5-lug

924RACR · Posted: Thu Jul 26, 2007 4:22 am Post subject:

No torque steer on a RWD chassis. No, the car is symmetrically set up - it's the track that is not symmetric. Like I said, I understand that by tweaking the car a little to bias to the RH, I'll push a bit on the LH tuns, hence my comment about pushing more in Turn 1 being not a bad thing.

Toe rear adjustment isn't generally easy, and is maxed out on my car.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

!tom · Posted: Thu Jul 26, 2007 4:31 am Post subject:

As the drivetrain accelerates, the torque reaction will cause the chassis to roll in the opposite direction. This will bias the handling, one direction while accelerating, the other directon while decelerating, and not at all while at a constant speed.

It's not going to be as bad as a solid axle car due to the transaxle layout, but the effect will still be there.

This is what I was referring to as torque steer -- perhaps I used the wrong term.

It certainly sounds like you have no end of fun on your weekends!
_________________
78 924 NA
5-lug

924RACR · Posted: Thu Jul 26, 2007 5:15 am Post subject:

Right - but not enough torque in these cars to matter.

Torque steer is a term used to refer to a steering force reaction, in the steering linkage itself, from application of engine torque to the steering wheels (FWD).

Thanks!
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype