Handling issues - need adjustment advice |
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Handling issues - need adjustment advice |
Brian Fuerbach |
Jan 20 2022, 02:57 PM
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#1
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Member Group: Members Posts: 119 Joined: 1-July 19 From: Orange, Ca Member No.: 23,266 Region Association: Southern California |
When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking. Things get better with a full tank of fuel. Is that just the nature of the 914, full tank factored into weight bias, or can the suspension be tuned to emulate the weight.
Here is what Im working with; -19mm adjustable sway-bar set about 1” back from full soft. -Koni yellow adjustable shocks -Stock front torsions -Rear springs are aftermarket (reddish orange color) but I do not know the poundage. Any input would be appreciated. |
Superhawk996 |
Jan 24 2022, 07:42 AM
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#2
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914 Guru Group: Members Posts: 5,824 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
Here's the photo of 914Rubber 100 lb/in springs and measurement.
A bit thicker than 9.6mm but close accounting for coating thicknes. |
Brian Fuerbach |
Jan 24 2022, 11:11 AM
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#3
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Member Group: Members Posts: 119 Joined: 1-July 19 From: Orange, Ca Member No.: 23,266 Region Association: Southern California |
Here's the photo of 914Rubber 100 lb/in springs and measurement. A bit thicker than 9.6mm but close accounting for coating thicknes. My springs measure at 10.4mm in diameter so i am guessing 100lb? I found the attached chart that shows the stock spring specs. This weekend I loosened up the front swaybar all the way and took a drive through Santiago and Trabuco canyons. The bar is a GPR 19mm and at full soft is supposed to be close to the stock rate. This really loosened up the front end in general. Steering feels lighter and less controlled, but smoother for sure. Gonna hit the sweepers this afternoon on my way home and see what is does. How low does the car have to be to experience bump steer? Attached thumbnail(s) |
Superhawk996 |
Jan 24 2022, 12:52 PM
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#4
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914 Guru Group: Members Posts: 5,824 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
I found the attached chart that shows the stock spring specs. Can you post http link to that chart? It is interesting and I don't think I've ever seen that. I'm not fully sure I believe those rates. At 50 lb/in it would take 10 inches of spring pre-load to support the approximately 500lbs of corner weight that a 914 will have. Seems to me they would have to be very long springs to get the pre-load needed to support the vehicle. I was going to assemble my springs tonight but I'm thinking maybe I need to do a rate measurement just as a rationality check to this chart. |
slivel |
Jan 24 2022, 04:05 PM
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#5
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Old car....... older driver Group: Members Posts: 508 Joined: 10-July 04 From: San Diego Member No.: 2,332 Region Association: Southern California |
I found the attached chart that shows the stock spring specs. Can you post http link to that chart? It is interesting and I don't think I've ever seen that. I'm not fully sure I believe those rates. At 50 lb/in it would take 10 inches of spring pre-load to support the approximately 500lbs of corner weight that a 914 will have. Seems to me they would have to be very long springs to get the pre-load needed to support the vehicle. I was going to assemble my springs tonight but I'm thinking maybe I need to do a rate measurement just as a rationality check to this chart. It might be right, not sure. I'm not familiar with the stock springs on the 914/4 but if the chart is right and the free length of the spring is over 18 inches, that allows for a lot of preload. The motion ratio of the rear suspension (stock) is about 1.296 and is beyond the pivot point which gives a leverage advantage so the spring rate would be multiplied by 1.296 - I think. For most of my racing I had 350 lb/in linear springs on the rear. Now for the street I have stacked springs that give a progressive rate that starts at 150 and goes to 270 at full compression. Attached is the spreadsheet that I used when doing my development. Suspension_Worksheet.a.xls ( 33.5k ) Number of downloads: 48 |
Brian Fuerbach |
Jan 24 2022, 06:15 PM
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#6
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Member Group: Members Posts: 119 Joined: 1-July 19 From: Orange, Ca Member No.: 23,266 Region Association: Southern California |
I found the attached chart that shows the stock spring specs. Can you post http link to that chart? It is interesting and I don't think I've ever seen that. I'm not fully sure I believe those rates. At 50 lb/in it would take 10 inches of spring pre-load to support the approximately 500lbs of corner weight that a 914 will have. Seems to me they would have to be very long springs to get the pre-load needed to support the vehicle. I was going to assemble my springs tonight but I'm thinking maybe I need to do a rate measurement just as a rationality check to this chart. It might be right, not sure. I'm not familiar with the stock springs on the 914/4 but if the chart is right and the free length of the spring is over 18 inches, that allows for a lot of preload. The motion ratio of the rear suspension (stock) is about 1.296 and is beyond the pivot point which gives a leverage advantage so the spring rate would be multiplied by 1.296 - I think. For most of my racing I had 350 lb/in linear springs on the rear. Now for the street I have stacked springs that give a progressive rate that starts at 150 and goes to 270 at full compression. Attached is the spreadsheet that I used when doing my development. Suspension_Worksheet.a.xls ( 33.5k ) Number of downloads: 48 Impressive (IMG:style_emoticons/default/beerchug.gif) |
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