Help reading an alignment sheet.
12-08-2010, 07:15 PM
#16
Thanks for all the input. They did not in fact change anything on the car, just took the measurements. Apparently, as Makmov says, the numbers change on the rack. The final being the more accurate.
He did say there was not enough adjustment to get it back into spec, but I am not sure WHICH spec he was referring to. Standard US factory or ROW M030 , which must be different.
Also charged me two hours labor for the readings, lovely.
He did say there was not enough adjustment to get it back into spec, but I am not sure WHICH spec he was referring to. Standard US factory or ROW M030 , which must be different.
Also charged me two hours labor for the readings, lovely.
RoW M030 height is 30mm lower than any US 993 but other wise has the same stock suspension specs and for performance can profit form more neg camber at both ends and less toe, especially in front where 0 toe is often used
12-08-2010, 07:52 PM
#18
A bump steer kit is just a couple spacers and some longer bolts to mount the steering rack. No big deal. The idea is to put the steering rack geometry back into factory spec.
Rake, depends on how much rake. All the degree of rake goes into + or - specs of the alignment.
So you are actually reducing caster as you are increasing rake, as the caster is is reducing bump steer is increasing.
Rake, depends on how much rake. All the degree of rake goes into + or - specs of the alignment.
So you are actually reducing caster as you are increasing rake, as the caster is is reducing bump steer is increasing.
12-08-2010, 08:23 PM
#19
A bump steer kit is just a couple spacers and some longer bolts to mount the steering rack. No big deal. The idea is to put the steering rack geometry back into factory spec.
Rake, depends on how much rake. All the degree of rake goes into + or - specs of the alignment.
So you are actually reducing caster as you are increasing rake, as the caster is is reducing bump steer is increasing.
Rake, depends on how much rake. All the degree of rake goes into + or - specs of the alignment.
So you are actually reducing caster as you are increasing rake, as the caster is is reducing bump steer is increasing.
12-08-2010, 09:02 PM
#20
Racer
2 hours is excessive to just read the existing angles. Should be more like 1/2 hr. I could read and adjust both ends to reduce the toe in about an hour.
The rack on a 993 /964 can,t just be lowered with spacers. That procedure was possible with the torsion bar cars but the rack is mounted differently on the newer cars. The rack is mounted with saddle brackets which are oriented fore/aft. Spacers if added would not move the rack downward.
The rack on a 993 /964 can,t just be lowered with spacers. That procedure was possible with the torsion bar cars but the rack is mounted differently on the newer cars. The rack is mounted with saddle brackets which are oriented fore/aft. Spacers if added would not move the rack downward.
12-08-2010, 09:22 PM
#21
2 hours is excessive to just read the existing angles. Should be more like 1/2 hr. I could read and adjust both ends to reduce the toe in about an hour.
The rack on a 993 /964 can,t just be lowered with spacers. That procedure was possible with the torsion bar cars but the rack is mounted differently on the newer cars. The rack is mounted with saddle brackets which are oriented fore/aft. Spacers if added would not move the rack downward.
The rack on a 993 /964 can,t just be lowered with spacers. That procedure was possible with the torsion bar cars but the rack is mounted differently on the newer cars. The rack is mounted with saddle brackets which are oriented fore/aft. Spacers if added would not move the rack downward.
maybe he can explain how rake fits in here?
12-08-2010, 11:06 PM
#22
Then just use the tie rod end kit which drops the joint down on the knuckle end. Still not a big deal. Same principle idea, there are many ways to solve the same problem. If you want to spend the big money, get a set of dropped knuckles from an RS for about 2K.
Rake. Imagine the centerline upon which the wheel turns running up and down. This is your caster line. As you get further out from that centerline the greater the toe changes, correct? Therefore, as you rotate that axis the further or closer the contact patch of the tire to that centerline, correct? If you rake the back up you are in a sense reducing caster, correct.
Now if that centerline point has basically zero movement from bump, correct? Remember, bump steer is changing the amount of toe in and out as it wheel compresses and decompresses. So now if you were looking down from the top you would see, that you'll have virtually no movement at the center of the axis and more as you s you move towards the front of the tire and the greater the movement will be, correct?
Therefore, rake directly impacts bump, and the entire front geometry, in fact.
However, the likelihood that it been dropped so far down and used on the street that there would be a noticeable bump steer problem is probably negligible to a novice driver.
Here is bump steer.
http://www.youtube.com/watch?v=gKJAukSZRT0
Clearly the further you would stand it on it's nose, e.g. rake, the worse it would get. Yes?
Rake. Imagine the centerline upon which the wheel turns running up and down. This is your caster line. As you get further out from that centerline the greater the toe changes, correct? Therefore, as you rotate that axis the further or closer the contact patch of the tire to that centerline, correct? If you rake the back up you are in a sense reducing caster, correct.
Now if that centerline point has basically zero movement from bump, correct? Remember, bump steer is changing the amount of toe in and out as it wheel compresses and decompresses. So now if you were looking down from the top you would see, that you'll have virtually no movement at the center of the axis and more as you s you move towards the front of the tire and the greater the movement will be, correct?
Therefore, rake directly impacts bump, and the entire front geometry, in fact.
However, the likelihood that it been dropped so far down and used on the street that there would be a noticeable bump steer problem is probably negligible to a novice driver.
Here is bump steer.
http://www.youtube.com/watch?v=gKJAukSZRT0
Clearly the further you would stand it on it's nose, e.g. rake, the worse it would get. Yes?
12-09-2010, 12:49 AM
#23
Racer
But remember caster is a measurement in degrees from vertical. caster is not measured perpendicular to the floor of the car. A caster angle of 6 deg set with the car level and then measured again after the car is raked will perhaps change to 5 deg but that means the car now has a wrong caster setting.. This is why an alignment is required after a change in height to restore the caster to specification in this case 6 deg.with the car raked.
I am only casually familiar with the knuckle end kit. I am unsure if it is applicable to a 993. I haven,t seen it used on the 993/964
I am only casually familiar with the knuckle end kit. I am unsure if it is applicable to a 993. I haven,t seen it used on the 993/964
12-09-2010, 02:12 AM
#24
Rennlist Member
I see the question was asked and answered re: bump steer spacer kits for post-torsion bar cars. Even those don't really work on torsion bar cars. God knows, we started messing around with pretty much every conceivable ride height when I had my shop and a spiffy brand new Hunter alignment rack/machine circa 1985. Bump steer gets goofy, not to mention annoying, really quickly once you're slammed past a certain point.
Carrying it forward to this generation of car, some of the worst cars I've driven came out of the "name" shops around here in the early-mid '90s when there still wasn't even a 993. Looked cool being so low like the 964 Cups. But then I got my hands on a customer car and persuaded him to not fall to the temptation. When he ponied up for Hoosiers, we were consistently 1 and 2 of the non trailered cars in time trialing with a more-or-less stock RSA.
So, bump steer is real. The faux RS doesn't have at its slammed height because it's got all the right parts. The RSA is a good 1+" higher to drive at all similarly.
Carrying it forward to this generation of car, some of the worst cars I've driven came out of the "name" shops around here in the early-mid '90s when there still wasn't even a 993. Looked cool being so low like the 964 Cups. But then I got my hands on a customer car and persuaded him to not fall to the temptation. When he ponied up for Hoosiers, we were consistently 1 and 2 of the non trailered cars in time trialing with a more-or-less stock RSA.
So, bump steer is real. The faux RS doesn't have at its slammed height because it's got all the right parts. The RSA is a good 1+" higher to drive at all similarly.
12-09-2010, 02:34 AM
#25
But remember caster is a measurement in degrees from vertical. caster is not measured perpendicular to the floor of the car. A caster angle of 6 deg set with the car level and then measured again after the car is raked will perhaps change to 5 deg but that means the car now has a wrong caster setting.. This is why an alignment is required after a change in height to restore the caster to specification in this case 6 deg.with the car raked.
12-09-2010, 09:41 AM
#26
Then just use the tie rod end kit which drops the joint down on the knuckle end. Still not a big deal. Same principle idea, there are many ways to solve the same problem. If you want to spend the big money, get a set of dropped knuckles from an RS for about 2K.
Rake. Imagine the centerline upon which the wheel turns running up and down. This is your caster line. As you get further out from that centerline the greater the toe changes, correct? Therefore, as you rotate that axis the further or closer the contact patch of the tire to that centerline, correct? If you rake the back up you are in a sense reducing caster, correct.
Now if that centerline point has basically zero movement from bump, correct? Remember, bump steer is changing the amount of toe in and out as it wheel compresses and decompresses. So now if you were looking down from the top you would see, that you'll have virtually no movement at the center of the axis and more as you s you move towards the front of the tire and the greater the movement will be, correct?
Therefore, rake directly impacts bump, and the entire front geometry, in fact.
However, the likelihood that it been dropped so far down and used on the street that there would be a noticeable bump steer problem is probably negligible to a novice driver.
Here is bump steer.
http://www.youtube.com/watch?v=gKJAukSZRT0
Clearly the further you would stand it on it's nose, e.g. rake, the worse it would get. Yes?
Rake. Imagine the centerline upon which the wheel turns running up and down. This is your caster line. As you get further out from that centerline the greater the toe changes, correct? Therefore, as you rotate that axis the further or closer the contact patch of the tire to that centerline, correct? If you rake the back up you are in a sense reducing caster, correct.
Now if that centerline point has basically zero movement from bump, correct? Remember, bump steer is changing the amount of toe in and out as it wheel compresses and decompresses. So now if you were looking down from the top you would see, that you'll have virtually no movement at the center of the axis and more as you s you move towards the front of the tire and the greater the movement will be, correct?
Therefore, rake directly impacts bump, and the entire front geometry, in fact.
However, the likelihood that it been dropped so far down and used on the street that there would be a noticeable bump steer problem is probably negligible to a novice driver.
Here is bump steer.
http://www.youtube.com/watch?v=gKJAukSZRT0
Clearly the further you would stand it on it's nose, e.g. rake, the worse it would get. Yes?
http://www.youtube.com/watch?v=Stp9k...layer_embedded
yes, the o/s kits work well, but as w/ the steering rack lowering kits I have never seen one for stock 993 tie rods.
they do exist for the RS tie rods that are designed to work w/ the RS wheel carriers w/ short steering arms.
RS and stock tie rods are not interchangeable, they only work w/ their designed wheel carriers
as to the rake issue a small amount of rake is usually desirable for aero reasons, the suspension is set up after the ride height is determined so caster, camber etc are all set after any rake is introduced to the car and are compensated for by the subsequent alignment, there is a small effect on the anti dive properties of the suspension as well as on the camber and toe patterns but these are minimal especially when the reduced wheel travel of a lowered & track prepped car are taken into consideration.
I agree that for normal street ride height bump steer isn't going to be an issue for most people.
The factory felt that the RS uprights and tierods are desireable at 124mm front height and they become necessary at the Cup car height of ~100mm. But most people won't be running their street cars at that height.
