Suspension travel?

Hi All,
Can someone tell me how much travel they have with the spring and shock removed, what is the distance from the lowest to the highest point for the front and rear? What is the ideal height from the floorpan to the gound, assuming the floorpan is the lowest point?

Thanks Steve
 
This is a bit hard to generalize about. For the street "speed waves" is setting the limit or a grage entry. The ride height selected then will govern the spring ratio possible to use. And the A-arm geometry has a great influence on how much we can let the car roll in corners. I guess GT-40 owners sometimes use different suspension systems.
For track use, as low as possible groud setting is prefered
for lower CGH. But again, A-arm angle may be to steep and monting ears may need to be adjusted. What ultimatley sets the springrate then is the tire of choice since this governs the G-force that loads the springs and roll bars.
Myself I have 3 inches of ground setting for street and track use. Wheelrate is 3Hz or say 10kg/mm without the bars included.
Regards
Goran Malmberg

Regards
Goran Malmberg
 

Tim Kay

Lifetime Supporter
Goran,
Your knowledge is light years ahead of me and I find myself reading your post several times to let your information soak in /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/laugh.gif

If you wouldn't mind, could you give me a description of "wheelrate" in the context above. Just learning and I follow your information up to the wheelrate term, then I went "huh?" /ubbthreads/images/graemlins/cool.gif
 
[ QUOTE ]
hi
according to this post:
http://www.gt40s.com/ubbthreads/showflat.php/Cat/0/Number/52087/an/0/page/0#52087
The original suspension travel seems to be 3,5" at front and 3" at rear. Ride height original is 4,5" as i recall but that can vary depending on road conditions
Hope tis helps
ingvar

[/ QUOTE ]

Those figures are for damper travel to contact with the bump stop, <u>not</u> suspension travel. Konis typically have very long bumpers which allow considerable progressive compression. In addition, the angle of the damper multiplies the base travel. I suspect that the <u>useable</u> wheel travel on the original car is almost 5", front and back. That allowed the street car to have 5" ground clearance while the comp cars ran 4" or less while still allowing adequate wheel travel.

The ERA has 6+" useable wheel travel front and back.
 
Tim. Of course, I be glad to help every fellow Gt.40 owners.
Just one problem right now. I am leaving for a few weeks of wacation today, so Ill be back to you when I am back.
Cheers!
Goran Malmberg
 
Tim

I too enjoy reading Gorans comments, although some of them I find unfathomable e.g what does he mean by……. “For the street “speed waves” is setting the limit or a grage entry.”??? I assume it looses something in the translation but since my Swedish is non existent I am definitely not the one to critize Gorans English…. Hang on, I have just reread that again after putting this Posting aside for a couple of hours and I think he is talking about how speed bumps or a garage entry set a lower limit to the ride height

In his absence perhaps I could add a few observations of my own to his comments. I will look forward to seeing what he (or anyone else) thinks of them when he gets back from his vacation.

He says he runs with a wheel rate of 3Hz or say 10 Kg/mm. I assume what he means by this is that his suspension frequency (N) is 3Hz =180 cycles/min (that is getting into the bone jarringly high area for a street car) and secondly the wheel rate is 10Kg/mm or 559lb/in.

Using these figures in the formula (187.8/N) squared x wheel rate gives a Sprung weight of 608lb. This figure can then be used to calculate the Static Deflection of the suspension which comes out as 1.2in.

Finally Goran hasn’t given a figure for his suspension leverage ratio. I assume that the values given are for his Hemipanter so if I assume a figure of 1.6, this gives a Spring Rate of 1431 lb/in. If that is correct it is very high but as can be seen from the above calculations it follows naturally from him running a ride height of only 3in.

Steve

In answer your question about the ideal ride height. Ideally we want the car as low as possible to get the lowest possible C of G but, as you can see from the above calculations, the lower the ride height the higher the suspension frequency will need to be and the stiffer the Spring Rates. For street use a compromise has to be made to give the best handling but without the car bottoming out or becoming too uncomforable to drive.

For my GT40 I chose a frequency of 1.75Hz which, when the calculations are done, gave a ride height of 4.5 inches.

Regards

Tom
 
Thank You all,
I just measured the travel of the rear suspension without the springs or shocks and was worried there wasnt enough travel. It has about 70-80ml in travel which seems to be just enough.

Steve
 
Hi Steve,

The questions in you post are totally important. I have followed them with interest. Here is some more fuel for the fire which I would give the cheesy title: The Mother of All Brackets.

The most technical responders always seem to answer these questions with spring rates and frequency. I am sure their answers are absolutely correct. However, I believe that, BEFORE a spring rate is selected, the suspension can (and probably should) be set so that all the components are centered in their most optimal position. Some setup details we just pick because it looks cool, like ride height and how low the body sits over the wheels to fill the wheel wells. Some setup is entirely restricted by clearance dimensions under the car. And, other things are just a seat of the pants guess. For example........

The range of suspension travel should not allow the tire to rise up so high that it can bump into the underside of the wheel well. The importance of this seem obvious and is entirely a function of dimensions under the car.

Ground clearance should never be allowed to go to less than a certain minimal distance. Who wants the bottom of their car to get beat up by dips and rises in the road. I think most of us just guess at a safe number. After all, most of us (but not all) probably think zero ground clearance is not enough.

When the suspension is at full drop, the rear trailing arms should not touch or bang into the chassis. My trailing arms just got a fresh coat of powder paint and I do not want them skinned up or bent (not to mention the unhelpful rear end steering that might result).

The adjustment nuts on the coil over shocks should be in the middle of their adjustment range when the car is at static ride height. I paid for adjustability and it just seems like good sense to preserve adjustability.

Shock absorbers should have at least 50% of stroke available for compression. I never want my rubber bump stops to be an active part of my daily suspension.

All of this comes down to positioning the upper shock mounts which I am starting to believe are The Mother of All Brackets. Here are the dimensions that I wish I knew in advance. Over the next month as I finish my upgrades, I will post actual measurements. I think a comparison of this basic information from other GT40 owners would be very interesting.

REAR SUSPENSION---------------Full Rise-----Static Ride Height------Full Drop

Ride Height------------------------------?----------------4.5"----------------?

Wheel Well Clearance------------------?-----------------?------------------?
(Top of Tire to Underside of Wheel Well)

Shock Absorber Compression---------?---------------1" 33%-------------?
(Inches & %)

Suspension Movement at Wheel Hub-?---------------+/- 0.0--------------?
 

Peter Delaney

GT40s Supporter
Bob - good point about simple practicality. I found 2 problems with my rear suspension :

a) On extreme compression (only found after hitting serious bump onto a bridge at speed), the rhs bottom trailing arm whacked up into the edge of the sheet steel panel thru which it protrudes. It put a nice little curve in the edge of the panel, but amazingly, just a minor scratch in the Jet-Hot coated trailing arm. A bit of die-grinding of the panel & all is now ok.

b) With the car fully jacked up & the suspension dropped, I had a little binding of the inner UJ's - just enough to take the paint off. Again, some die grinding (on each side to maintain balance) & the problem was solved.

Problem (a) would be hard to check statically unless you could hold the chassis down whilst jacking up the suspension to see where the coil-over bump stop kicks in.

Problem (b) is easy to check - just jack the car up, let it all drop & rotate the wheels !

Its all good fun (sort-of) !

Kind Regards,

Peter D.
 

Lynn Larsen

Lynn Larsen
Bob,

How right you are! I had my ride height set at the obligatory 4.5", BUT with the shape of my driveway entrance, the nose dragged. My new ride height of 5.25" allows me to enter and exit my driveway with two people and full gas without dragging the nose. Its amazing how quickly theory can be tossed out the window when presented with practical issues. :)

Regards,
Lynn
 

Howard Jones

Supporter
Here's an easy way to see what's going on. Put plastic tie wraps on the shock rods. The little 3/16th inch wide ones work best for me. Jack the car up so the wheel is in full droop. Then push the tie wrap all the way to the bottom of the rod against the shock body. Repeat of other 3 corners. The idea is to have them remain in place until the shock travel slides them up to the limit of the travel they are experiencing. If you measure the rod length in full droop and again when you set the car down you will have a static load at rest baseline point of reference.

Drive the car as you would to get the data you are looking for. In my case I was interested how much travel I was getting if I curbed the LF on a particular corner at my local track. I wanted to know how close I was to the bump stop. Now see how far the tie wrap is moved upward from you baseline spot. This is shock travel. Total suspension travel at that corner is affected by the geometry of the suspension but you do have a good idea what's happening at the shock which is more useful anyway.

Anyway when you are done with the test, you can cut them off or redo the test with them if you vary the ride height, shock settings, roll bar setting (you can even check roll this way if you think about whats going on here), or spring rating.

I run right at 4 inches at the front and 4.5 at the rear. 400Lb front, 475lb rear springs, and get about 2 inches of shock travel on track if I stay off the curbs. The curb in question added about .8 inches of travel on that corner by the way.
 
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