944 Cup Car rear ride height question/problem
#16
Drifting
Join Date: Jan 2008
Location: Suburban DC
Posts: 2,641
Likes: 0
Received 0 Likes
on
0 Posts
I just did the t-bar delete and went with 6" 600# springs on Escort Cup coilovers. To be honest, I think 7" springs would have been better. With the 6"ers I'm right up to the top of the threads, and that's with the "slinky" helper springs taking up at least 1/2".
#17
Rennlist Member
Thread Starter
Join Date: Dec 2005
Location: Beaufort, SC
Posts: 1,124
Likes: 0
Received 0 Likes
on
0 Posts
Van, I thought the factor was .65, which I used in my table. I think that's supposed give you the differential between the front and rear. am I missing something here?
Greg, good information. what ride height are you running and what's the diameter of your tires?
Greg, good information. what ride height are you running and what's the diameter of your tires?
#18
Drifting
Join Date: Jan 2008
Location: Suburban DC
Posts: 2,641
Likes: 0
Received 0 Likes
on
0 Posts
I use 15" phone dials with 225/50/15 tires.
#19
Drifting
Join Date: Jan 2008
Location: Suburban DC
Posts: 2,641
Likes: 0
Received 0 Likes
on
0 Posts
I use 15" phone dials with 225/50/15 tires.
#20
Rennlist Member
There's no guarantee that the 2 fenders are manufactured/spot welded on in the same place. An accurate ride height measurement is taken from the ground to the axis the torsion bars pivot around.
Johntorg, for the rear spring/wheel rates, the formula is as follows:
-The "motion ratio" is about 63% - that means, if the wheel moves up 1", the shock compresses 0.63".
-The formula to calculate wheel rate is "motion ratio squared, times spring rate".
-That would be, (0.63)^2 * 550 lbs/in
-Which equals 218.3 lbs/in
Johntorg, for the rear spring/wheel rates, the formula is as follows:
-The "motion ratio" is about 63% - that means, if the wheel moves up 1", the shock compresses 0.63".
-The formula to calculate wheel rate is "motion ratio squared, times spring rate".
-That would be, (0.63)^2 * 550 lbs/in
-Which equals 218.3 lbs/in
#21
Rennlist Member
Thread Starter
Join Date: Dec 2005
Location: Beaufort, SC
Posts: 1,124
Likes: 0
Received 0 Likes
on
0 Posts
Van, OK I guess we were looking at two different thngs. Anyway, I found out that my front springs are 500 lb/in so I will go with 750 lb/in in the rear as a starting point. The better 944s I looked at, running 15 Inch wheels, were all around 23.5 to 24 inches measured from the ground to bottom of the wheel arch at the wheel centerline. I will use that as a starting point.
Greg, I have some 225X50X15s I can measure and subtract the radius from my ground up measurement. The reason I would like to know is that I am afraid that I will run out of adjustment on the 6 inch shocks if yours are very near the top at a ride height (measured from the ground of 23.5 to 24 inches. If you ride height is higher, I should be Ok with the 6 inch springs.
Greg, I have some 225X50X15s I can measure and subtract the radius from my ground up measurement. The reason I would like to know is that I am afraid that I will run out of adjustment on the 6 inch shocks if yours are very near the top at a ride height (measured from the ground of 23.5 to 24 inches. If you ride height is higher, I should be Ok with the 6 inch springs.
#22
Drifting
Join Date: Jan 2008
Location: Suburban DC
Posts: 2,641
Likes: 0
Received 0 Likes
on
0 Posts
The reason I would like to know is that I am afraid that I will run out of adjustment on the 6 inch shocks if yours are very near the top at a ride height (measured from the ground of 23.5 to 24 inches. If you ride height is higher, I should be Ok with the 6 inch springs.
#23
Rennlist Member
Thread Starter
Join Date: Dec 2005
Location: Beaufort, SC
Posts: 1,124
Likes: 0
Received 0 Likes
on
0 Posts
Greg, Thanks, I have the same shocks and so I guess I should go with 7 inch springs. I wasn't planning on using helper springs. Any thought on that? BTW do the Escorts use 2.25 or 2.5 inch springs. i haven't removed mine yet to check.
#24
Addict
Rennlist Member
Rennlist Member
Join Date: Mar 2009
Location: Montreal
Posts: 2,193
Likes: 0
Received 0 Likes
on
0 Posts
If I can add my 2 cents, most of the guys I know usually keep a max of 200 lbs difference between front and rear. I currently have 400 and 600. I was suffering high speed oversteering, so I will reduce to 550 at the back. I even tried 450 at the back and it was fine, but a bit too soft.
C.
C.
#25
Rennlist
Basic Site Sponsor
Basic Site Sponsor
Johntorg, for the rear spring/wheel rates, the formula is as follows:
-The "motion ratio" is about 63% - that means, if the wheel moves up 1", the shock compresses 0.63".
-The formula to calculate wheel rate is "motion ratio squared, times spring rate".
-That would be, (0.63)^2 * 550 lbs/in
-Which equals 218.3 lbs/in
-The "motion ratio" is about 63% - that means, if the wheel moves up 1", the shock compresses 0.63".
-The formula to calculate wheel rate is "motion ratio squared, times spring rate".
-That would be, (0.63)^2 * 550 lbs/in
-Which equals 218.3 lbs/in
Plus, in your formula you forgot the sin of the spring angle. http://www.miracerros.com/mustang/t_wheel_rate.htm
__________________
Larry Herman
2016 Ford Transit Connect Titanium LWB
2018 Tesla Model 3 - Electricity can be fun!
Retired Club Racer & National PCA Instructor
Past Flames:
1994 RS America Club Racer
2004 GT3 Track Car
1984 911 Carrera Club Racer
1974 914/4 2.0 Track Car
CLICK HERE to see some of my ancient racing videos.
Larry Herman
2016 Ford Transit Connect Titanium LWB
2018 Tesla Model 3 - Electricity can be fun!
Retired Club Racer & National PCA Instructor
Past Flames:
1994 RS America Club Racer
2004 GT3 Track Car
1984 911 Carrera Club Racer
1974 914/4 2.0 Track Car
CLICK HERE to see some of my ancient racing videos.
#26
Addict
Rennlist Member
Rennlist Member
Join Date: Mar 2009
Location: Montreal
Posts: 2,193
Likes: 0
Received 0 Likes
on
0 Posts
#27
Rennlist Member
Plus, in your formula you forgot the sin of the spring angle. http://www.miracerros.com/mustang/t_wheel_rate.htm
The front motion ratio is 0.91.
Also, remember, it's not motion ratio times spring rate, it's motion ratio squared times spring rate. 0.91 squared is 0.83 (not much different) - but 0.63 squared is 0.397.
#29
Rennlist
Basic Site Sponsor
Basic Site Sponsor
No, I didn't forget the sin of the spring angle. I got that 0.63 number from very careful measurements in a controlled environment with dial indicators and calipers. I'm telling you, for exactly 1.000" of wheel travel, the rear shock compresses 0.630". That is the motion ratio - the difference between wheel movement and shock displacement.
The front motion ratio is 0.91.
Also, remember, it's not motion ratio times spring rate, it's motion ratio squared times spring rate. 0.91 squared is 0.83 (not much different) - but 0.63 squared is 0.397.
Also, remember, it's not motion ratio times spring rate, it's motion ratio squared times spring rate. 0.91 squared is 0.83 (not much different) - but 0.63 squared is 0.397.
Motion ratio X spring rate = effective spring rate. Maybe not as informative for suspension engineers as wheel rate, but good enough comparison for us common folk.