Suspension and spring rates

[JERMzSS]

It's technically autocross but it reminds me more of a time attack style course.

I have a very big aid with the A7s keeping me under wraps alot. When I added more negative camber it helped plant the rear alot more for me even with my street tires.

 

[ccannx]

On the rear the wheel rate is about 89% of spring rate. I use 50% when guessing front wheel rate.
If you use a 500# spring your rear spring will hanging loose on the inside wheel of a turn.

Brad

On the skid pad rear inside was in the air with the 175lb springs ! 500 was way to much !

 

[Desert Sasqwatch]

Are you running the rear swaybar? The SS came with a 23mms - way too stiff - but the base models came with a 18mm, which has possibilities. It would allow running softer springs but still keep the inside rear wheel on the ground. In my thinking, getting the rear to keep both wheels in contact with the pavement using as soft springs as possible, then tune the front to match as it has much more adjustability.

 

[ccannx]

Are you running the rear swaybar? The SS came with a 23mms - way too stiff - but the base models came with a 18mm, which has possibilities. It would allow running softer springs but still keep the inside rear wheel on the ground. In my thinking, getting the rear to keep both wheels in contact with the pavement using as soft springs as possible, then tune the front to match as it has much more adjustability.

Now running a 36” 6” arms front swaybar with 300lb springs. The rear I have variable rate 140/250 springs and no swaybar a 275 equivalent front rcomp and a 295rcomp in the rear. 1/4 toe in front 1/4 toe in rear.

lost the ability to settle the rear with throttle when I changed from 150per inch to the variable spring. The variable ramps up to 250 and then more when the bump stop makes contact. Which seems kinda like what a swaybar would do but without the effect of pulling the inside tire away from the pavement.

 

[ccannx]

Took akerman out of the front and put front toe back to zero car feels much better during high speed maneuvers.

 

[George]

Have yoy removed bump steer.

Brad

 

[ccannx]

Have yoy removed bump steer.

Brad

Should be less wish I had a guage to measure it. Would like to get the bumpsteer out of the rear, thinking about cutting the toe bar and moving both inner ball joints out about an inch to help.. My biggest issue is the instant yaw moment from the akerman when I crank the wheel.

 

[George]

Before I bought one this can be done. Remove wheel Attach a laser beam to the rotor for the rear pointing back. Use a white board or plywood as a target. Remove spring set suspension to ride height then when you raise and lower the suspension the lase will plot your bump steer curve very exaggerated.

Brad

 

[ccannx]

Before I bought one this can be done. Remove wheel Attach a laser beam to the rotor for the rear pointing back. Use a white board or plywood as a target. Remove spring set suspension to ride height then when you raise and lower the suspension the lase will plot your bump steer curve very exaggerated.

Brad

Was your bumpsteer coming from the length, angle position or both ? I had to put the stock link ends back on for more length eventually I plan to go the heim joints.

 

[George]

To adjust rear bump steer just shorten or raise the inter tie rod mount first. If you go with heims as I did you can use washer under the heim to control arm also. My heims are mounted under the steering arm.

Brad

 

[Fozda]

What is the advantage of switching to heims for the tie rods?

 

[George]

I did for adjustability and free movement of suspension. They are not required although they make the bront bump steering much easier to adjust.

Brad

 

[Fozda]

That's good to know! Do you remember which heims you used for that?

 

[George]

There is a picture in my build log post #223

Brad

 

[ccannx]

I used a buble level laser with a nice 90 angle to project towards the rear and put an old peice of Styrofoam to mark. 72" from the hub getting 1.75" of movement. Looks like under compression the wheel toes out but not sure how to calculate how much. 1.75 is 2.43 percent of 72. So would that be .0243 of an inch at the hub ?

 

[George]

Do not worry about calculating just make a change and see if you can improve. With that multiplication it will show up real quick.

Brad

 

[ccannx]

Do not worry about calculating just make a change and see if you can improve. With that multiplication it will show up real quick.

Brad

OK its starting to make more sense. Moved the ball joint down 1/2 now there's only .5 of bumpsteer over 72", getting closer !

 

[George]

.5" at 72" is very small. You now hAve the picture. Be sure to map the full travel.
It can do funny things.

Brad