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914World.com _ 914World Garage _ Handling issues - need adjustment advice
Posted by: Brian Fuerbach Jan 20 2022, 02:57 PM
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.
Posted by: brant Jan 20 2022, 03:29 PM
Does the rear come around or just a front push?
Any rear sway?
You did not mention a 4 wheel alignment after the components were installed?
You can usually dial push out. No matter the fuel level
Anything else??? Limited slip?
Posted by: Root_Werks Jan 20 2022, 03:34 PM
Somethings not right, a 914 shouldn't push or plow the front end like a Bug or early 911.
Could be the front is over sprung along with very off toe setting?
Drove a 996 months back the rear toe was in hard. Darn thing started hunting for grip at 30mph.
Posted by: Van B Jan 20 2022, 03:39 PM
Are your top mounts good? If so, increase front damping and see what changes.
If you’re getting a boat sort of feeling from the front, but no actual under steer, that’s generally a sign of being over sprung or under damped.
Van
Posted by: Freezin 914 Jan 20 2022, 03:42 PM
Is there ride height difference between front and rear? I notice a lot of these cars ride a bit high in the front compared to the rear. Are the front torsion bars adjusted to high? If you can get the front down a couple mm, should make the car more “darty”. Had this affect with my last driver.
Posted by: Superhawk996 Jan 20 2022, 03:47 PM
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.
What you've described is the very essence of understeer. 19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.
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Posted by: 914_teener Jan 20 2022, 03:57 PM
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.
What you've described is the very essence of understeer. 19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.
Stock bar is more than enough. Think also it is alignment and oversprung on the front end.
Posted by: Superhawk996 Jan 20 2022, 05:01 PM
Stock bar is more than enough. Think also it is alignment and oversprung on the front end.
I'm with you that there could be some alignment issue embedded in this but he's on stock torsion bars so not oversprung with big 21mm torsion bars or something like that.
These things are always hard to sort out based on words since handling is so subjective. Once man's balanced neutral handling is another's oversteeer or understeer.
The fact that it varies with fuel load is very typical of 914 handling with the inherent understeer improved at full tank or lugage loading. It could also be a symtom of what Freezin referenced, front end sitting too high and the fuel load brings the geometry back toward what it ought to be.
Keep in mind 914 track width is asymetric (narrower in front) with a design intent toward keeping a stock car biased toward understeer which is the "safe" design parameter. Further staggering tire widths toward wider rear & narrow front can further push this bias deeper into understeer. Not saying that is the case here since there was no mention of tire sizes (I'm assuming same widths front & rear at this point).
Posted by: Brian Fuerbach Jan 20 2022, 05:08 PM
Does the rear come around or just a front push?
Any rear sway?
You did not mention a 4 wheel alignment after the components were installed?
You can usually dial push out. No matter the fuel level
Anything else??? Limited slip?
Rear is planted and never feels loose. Front just feels like it is not biting the corner. After I installed the swaybar it did make the car much better all around.
Front had been aligned by previous po but I have no paperwork. An alignment at a shop that know what they are doing will be next.
No limited slip
Posted by: brant Jan 20 2022, 05:12 PM
Take a picture of the front sway adjustment
ie: how tight is the drop link on the bar end?
Can you loosen the front sway links to lessen the spring rate of the sway
I always disconnect both of my sway bars before alignment
Posted by: Brian Fuerbach Jan 20 2022, 05:14 PM
Are your top mounts good? If so, increase front damping and see what changes.
If you’re getting a boat sort of feeling from the front, but no actual under steer, that’s generally a sign of being over sprung or under damped.
Van
Top mounts have been replaced. I will try turning up the damping on the fronts. I have turned up the rear damping and found that it initiated corners much better. I have the fronts set at 1/2 turn and rears at 1.5 turns from full soft.
Posted by: Brian Fuerbach Jan 20 2022, 05:15 PM
Is there ride height difference between front and rear? I notice a lot of these cars ride a bit high in the front compared to the rear. Are the front torsion bars adjusted to high? If you can get the front down a couple mm, should make the car more “darty”. Had this affect with my last driver.
The car is pretty much level.
Posted by: Brian Fuerbach Jan 20 2022, 05:24 PM
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.
What you've described is the very essence of understeer. 19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.
I guess it is possible that if I pushed it harder it could turn into noticeable oversteer but it just does not feel like understeer that I have experienced before.
Need find out what springs are in the rear now. Can you tell by diameter?
I used to drive this on the street, talk about oversteer.
(correction: "Understeer")
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Posted by: Brian Fuerbach Jan 20 2022, 05:26 PM
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.
What you've described is the very essence of understeer. 19mm is a lot of front bar that can lead to understeer. Especially so without a lot of rear spring or rear bar behind it to balance it.
Stock bar is more than enough. Think also it is alignment and oversprung on the front end.
Can larger rear springs be installed to balance?
Posted by: Brian Fuerbach Jan 20 2022, 05:30 PM
Stock bar is more than enough. Think also it is alignment and oversprung on the front end.
I'm with you that there could be some alignment issue embedded in this but he's on stock torsion bars so not oversprung with big 21mm torsion bars or something like that.
These things are always hard to sort out based on words since handling is so subjective. Once man's balanced neutral handling is another's oversteeer or understeer.
The fact that it varies with fuel load is very typical of 914 handling with the inherent understeer improved at full tank or lugage loading. It could also be a symtom of what Freezin referenced, front end sitting too high and the fuel load brings the geometry back toward what it ought to be.
Keep in mind 914 track width is asymetric (narrower in front) with a design intent toward keeping a stock car biased toward understeer which is the "safe" design parameter. Further staggering tire widths toward wider rear & narrow front can further push this bias deeper into understeer. Not saying that is the case here since there was no mention of tire sizes (I'm assuming same widths front & rear at this point).
Stock 2.0 Fuchs with 195/65r15’s
Posted by: Superhawk996 Jan 20 2022, 05:53 PM
I used to drive this on the street, talk about oversteer.
Please don't take this the wrong way. I'm trying to help. Honestly. I've done chassis tuning as my day job for a decent part of my professional career as a chassis engineer.
That buggy by definition will have steady state understeer. Beam front axle without camber gain, wide rear tires, narrow font tires, lack of weight on the front tires.
I don't think we aren't talking the same terms.
I do agree the buggy could have massive lift throttle oversteer at initial turn-in due to the inherent rear weight bias. Likewise, it could develop on-throttle oversteer with enough horsepower. Both of those are transient conditions.
As I understood your original post, we are talking steady state condition, after you've entered the corner, steady state throttle, and the front end isn't tracking. You're putting in more and more steering input to the point that you feel the tires are scrubbing but yet it's not turning or following your steering input.
Do I understand correctly?
Posted by: Brian Fuerbach Jan 20 2022, 08:22 PM
I used to drive this on the street, talk about oversteer.
Please don't take this the wrong way. I'm trying to help. Honestly. I've done chassis tuning as my day job for a decent part of my professional career as a chassis engineer.
That buggy by definition will have steady state understeer. Beam front axle without camber gain, wide rear tires, narrow font tires, lack of weight on the front tires.
I don't think we aren't talking the same terms.
I do agree the buggy could have massive lift throttle oversteer at initial turn-in due to the inherent rear weight bias. Likewise, it could develop on-throttle oversteer with enough horsepower. Both of those are transient conditions.
As I understood your original post, we are talking steady state condition, after you've entered the corner, steady state throttle, and the front end isn't tracking. You're putting in more and more steering input to the point that you feel the tires are scrubbing but yet it's not turning or following your steering input.
Do I understand correctly?
No worries, your not going to hurt my feelings and I appreciate your tuning knowledge. You are totally correct, I meant to write "understeer" and we are talking the same terms. Your assessment of the power on power off are spot on. The car was almost not drivable in the twisties until a sway bar was added.
Now back to a car I still drive. In my original post I described it like a scrubbing but not over steer as I dont feel the front is going to wash. I drove the car today on my 60 mile commute which has opportunities to create the condition on four onramps and interchanges. I filled the tank completely and the extra weight up front made the front feel more planted like it should. I have to note that the scrubbing seems to come with some roughness that when weighted with extra fuel seems to lessen. More damping needed?
I have been working with the adjustments that I have to improve this. The two things that made the most improvement was adding the swaybar and then tightening the rear shock rebound.
Posted by: roblav1 Jan 20 2022, 10:00 PM
Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.
Posted by: yeahmag Jan 20 2022, 11:18 PM
I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.
Posted by: Superhawk996 Jan 21 2022, 06:37 AM
Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.
I think you've got to much stiffness on the front between the dampers and the Anti-roll Bar (ARB).
As Brant suggested. Move the ARB links toward the absolute end of the adjustable bar. I.e. increase the length of the arm - decreasing stiffness of the front ARB.
As Roblav1 suggested. Dial out dampers (softer). Adjustable dampers are only adjusting rebound damping. Lots of front rebound damping ends up fighting the ARB on the inside wheel. In additon, the net effect of too much front damping only further stiffens the front end in addition to the what the ARB has already added.
What we're working on here is to soften the front end relative to the rear.
My impression is that you like the extra body roll control that the front ARB added but that it's been over done with the 19mm front bar. I don't think you have mentioned yet if there is a rear bar. The OEM set up added a bar on both front (15mm) and rear (16mm). The dual bars provides a more balanced split of body roll control. If you don't have a rear bar, you're trying to do all roll control off the front end which stiffens the front end, inducing steady state understeer.
When you added some damping to the rear, you stiffened it - which has the same net effect as softening the front end relative to the rear. Hope this makes sense the way I've written it.
All tuning is done on a relative basis. You can soften the front or stiffen the rear for the same net effect. Sometimes you will have to do both to achive a desired result. But for right now, no need to get into additional rear spring or damper changes. Just work on one end of the car at a time with the overall direction of softening the front relative to the rear. Ideally, you work on the end you want to affect. I.e. if you want to soften the front; do the work in the front. When you run out of front "knobs" to turn then you can start stiffening the rear further.
I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.
Take Yeahmag up on this. It is always way easier to tune when you can see and feel what is happening vs. trying to do it by words on a forum like this.
Posted by: Brian Fuerbach Jan 21 2022, 10:25 AM
I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.
Thanks for the offer. will pm you after an alignment.
Posted by: Brian Fuerbach Jan 21 2022, 10:44 AM
Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.
I think you've got to much stiffness on the front between the dampers and the Anti-roll Bar (ARB).
As Brant suggested. Move the ARB links toward the absolute end of the adjustable bar. I.e. increase the length of the arm - decreasing stiffness of the front ARB.
As Roblav1 suggested. Dial out dampers (softer). Adjustable dampers are only adjusting rebound damping. Lots of front rebound damping ends up fighting the ARB on the inside wheel. In additon, the net effect of too much front damping only further stiffens the front end in addition to the what the ARB has already added.
What we're working on here is to soften the front end relative to the rear.
My impression is that you like the extra body roll control that the front ARB added but that it's been over done with the 19mm front bar. I don't think you have mentioned yet if there is a rear bar. The OEM set up added a bar on both front (15mm) and rear (16mm). The dual bars provides a more balanced split of body roll control. If you don't have a rear bar, you're trying to do all roll control off the front end which stiffens the front end, inducing steady state understeer.
When you added some damping to the rear, you stiffened it - which has the same net effect as softening the front end relative to the rear. Hope this makes sense the way I've written it.
All tuning is done on a relative basis. You can soften the front or stiffen the rear for the same net effect. Sometimes you will have to do both to achive a desired result. But for right now, no need to get into additional rear spring or damper changes. Just work on one end of the car at a time with the overall direction of softening the front relative to the rear. Ideally, you work on the end you want to affect. I.e. if you want to soften the front; do the work in the front. When you run out of front "knobs" to turn then you can start stiffening the rear further.
I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.
Take Yeahmag up on this. It is always way easier to tune when you can see and feel what is happening vs. trying to do it by words on a forum like this.
Your explanations are very understandable and appreciated. I do not have a rear bar but will soften the front damping and arb to full soft and see how it goes.
I plan on getting a real alignment and make the suggested changes before visiting Yeahmag.
I have often read here on the forum that a rear bar is not desired by most. What is you opinion?
Posted by: gereed75 Jan 21 2022, 10:53 AM
Softening the front roll bar won't hurt but a 19mm is not in itself out of line assuming rear springs are reasonably stiff (110 -140)
There has been no mention here that I saw about front tire pressures or did I miss it? High tire pressures could certainly cause the symptoms you describe
Posted by: rhodyguy Jan 21 2022, 11:30 AM
IIRC the Koni instructions stated neither full soft or full hard on the settings.
Posted by: Superhawk996 Jan 21 2022, 11:33 AM
I have often read here on the forum that a rear bar is not desired by most. What is you opinion?
My opinion is that I want a front AND a rear bar. I want to be able to manage roll couple distribution between front and rear as independently as possible.
Roll couple distribution is affected primarily by spring rates and ARB rates. If I don't have a rear ARB, then the only other knob I can change is rear spring rate.
The problem with changing spring rate is that cascades to other things like ride quality degrading as the spring rate goes up. Likewise as spring rate goes up, a fixed rate damper tends to become underdamped or needs to be retuned for the new spring. Aftermarket springs also have a terrible tendency to affect ride height as spring rates go up.
The whole idea of ARB's when they were "invented" was an effort to decouple roll rate from spring rate to get better roll control without the ride degradation.
If you look under most cars, you'll find both a front and a rear - they are typically standard equipment for safety/handing reasons. Contrast that to the 70's when roll bars were often optional equipment.
Posted by: Brian Fuerbach Jan 21 2022, 01:35 PM
Softening the front roll bar won't hurt but a 19mm is not in itself out of line assuming rear springs are reasonably stiff (110 -140)
There has been no mention here that I saw about front tire pressures or did I miss it? High tire pressures could certainly cause the symptoms you describe
The bar is a hollow 19mm if that makes a difference. The rear springs are an unknown. Can the diameter give an indication? What is the diameter of a stock coil?
Tire pressure 26 front 29 rear on Pirelli P6000 195/65R15
Posted by: dr914@autoatlanta.com Jan 21 2022, 03:33 PM
you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference
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.
Posted by: Brian Fuerbach Jan 21 2022, 05:01 PM
you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference
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.
I would have to disagree. The addition of the front bar transformed my cars handling for the better. But with that said, maybe a rear bar would be twice as good.
Posted by: JamesM Jan 21 2022, 06:53 PM
you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference
Sure you can, just beef up the rear springs and get the weight distribution/ride height setup properly.
I run a 21mm front bar with no rear bar and 180lb springs on my autocross car. Absolutely love how it handles. Its setup to where I can adjust my angle mid corner with the throttle.
The one 914 i have setup with stock front and rear bars gets far to lively in the rear end for my liking.
Posted by: Brian Fuerbach Jan 21 2022, 07:34 PM
you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference
Sure you can, just beef up the rear springs and get the weight distribution/ride height setup properly.
I run a 21mm front bar with no rear bar and 180lb springs on my autocross car. Absolutely love how it handles. Its setup to where I can adjust my angle mid corner with the throttle.
The one 914 i have setup with stock front and rear bars gets far to lively in the rear end for my liking.
I like the way the rear feels just the way it is, but unless I have a full bag of gas the front does not inspire confidence.
Posted by: Brian Fuerbach Jan 22 2022, 09:02 PM
So I talked with the PO today and he thinks that the rear springs are in the 70 to 80#range. Not sure of the brand though. Would a higher pound spring be added to help balance the the 19mm swaybar? Thinking 100# as long as the ride does not suffer too much.
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Posted by: Shivers Jan 23 2022, 06:49 AM
Well, looks like it is still a hot topic. Years ago all that Weltsmiester stuff came through here, got mine from George. To get a rear bar or not to, 19mm is too big for the front ...I got the front and rear, 19mm for the front, 140 lb springs for the rear and I think the front TB's were 21mm. Now I was no expert suspension doctor so I had it set up by Steve Floyd at european auto, he was. He says to me "Now all you have to do is drive" and he was right. At this time I'm adding Bilsteins front and rear and better brakes. I had KYB's and I'm really looking forward to the Bil's
Posted by: Superhawk996 Jan 23 2022, 09:18 AM
So I talked with the PO today and he thinks that the rear springs are in the 70 to 80#range.
Not likely. 70 or 80lb/in would be very light springs.
OEM springs are claimed to be around 100 lb/in. Without going into a spring dissertation, there is way more to a spring than simple rate but
that is the way the aftermarket handles spring marketing. Here are the OEM spring parameters:
Wire diameter 9.6mm
Number of coils 11.5
Effective coils 10.
Visually those springs on your car look like they have thicker wire diameter than stock springs. Really the only way to know would be to put them in a spring tester that that compresses a given distance them while simultaneously measuring the load force changed.
I just purchased a set of 100 lb/in springs from 914Rubber. I'll post a photo later today for visual comparison
Posted by: slivel Jan 23 2022, 11:27 AM
Suspension dynamics were interesting to me as a club racer who spent lots of time and money developing my car over 23 years. When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes. This includes things like springs, shocks, sway bars, corner weight, unsprung weight, wheels tires, alignment settings and probably a few more. I recommend a web search using the search term "suspension frequency". Things like wheel rate and motion ratio and the natural frequency of the suspension will be presented.
This is a cut and paste form a quick search:
Common suspension frequencies:
1.0 Hz - passenger cars
1.25 to 1.75 Hz - sports cars
2.0 to 2.5 Hz - autocross and racecars with low downforce
2.5+ Hz - high downforce racecars
1.45 Hz - Subaru BRZ (front and rear)
Higher frequency suspensions get jiggly and are obnoxious and street cars and they tend to bounce over rough surfaces. Race tracks that are rough require suspension tuning (lower frequency) to get max performance vice smooth tracks.
Auto manufacturers have compromise settings that you can move away from in either direction depending on the result you are seeking - Cadillac ride or McLaren ride.
The wisdom and experiences here on this forum can help get you where you want to be, but some research will also help a lot. It's a process. On my car with no wing and little downforce and racing on a wide variety of tracks/surfaces I used less than 2.0 Hz.
Posted by: Superhawk996 Jan 23 2022, 12:55 PM
When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes.
Truth! Posted by: Shivers Jan 23 2022, 01:57 PM
Suspension dynamics were interesting to me as a club racer who spent lots of time and money developing my car over 23 years. When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes. This includes things like springs, shocks, sway bars, corner weight, unsprung weight, wheels tires, alignment settings and probably a few more. I recommend a web search using the search term "suspension frequency". Things like wheel rate and motion ratio and the natural frequency of the suspension will be presented.
Oh Holy Physics Batman!
Posted by: Superhawk996 Jan 24 2022, 07:42 AM
Here's the photo of 914Rubber 100 lb/in springs and measurement.
A bit thicker than 9.6mm but close accounting for coating thicknes.
Posted by: Brian Fuerbach Jan 24 2022, 11:11 AM
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?
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Posted by: Superhawk996 Jan 24 2022, 12:52 PM
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.
Posted by: Brian Fuerbach Jan 24 2022, 01:08 PM
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 neeed.
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.
I did a google image search and the chart came up which led me back to 914world. I took a pic with my phone so I dont have the link. PM me your number and I will text the image to you.
Please share your finding on the 914rubber springs. I was thinking of ordering a set.
Posted by: slivel Jan 24 2022, 04:05 PM
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: 47Posted by: slivel Jan 24 2022, 04:12 PM
Here is another spreadsheet just in case anyone is interested in progressive springs.
Spring_rates.xls ( 35k )
Number of downloads: 46
Posted by: Shivers Jan 24 2022, 04:48 PM
Thank you
Posted by: Brian Fuerbach Jan 24 2022, 06:15 PM
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: 47Impressive
Posted by: Superhawk996 Jan 24 2022, 06:40 PM
So I did a quick rationality check tonight using the highly scientific bathroom scale and tape measure.
168 lbs at 1.75" travel = 96 lbs/in for the 914Rubber 100lb/in spring. Pretty close.
quick design comparison using an online spring calculator
https://www.thespringstore.com/spring-calculator.html
Design #1 close to 914Rubber
9.6mm wire diameter
105.5mm OD
380 mm free length (15 inches)
6 effective coils
Result 90.795 lb/in (sorry for mixed units -- Imperial units for ease of comparision)
Design #2 close to published stock data and the chart data above
9.6mm wire diameter
105.5 mm OD
470mm free length (18.5 inches)
10 effective coils
Result 54.477 lb/in
Design #3 published data from factory manual
9.6mm wire diameter
95mm mean OD -- this works out about the same 105.5 mm OD I measured directly
460 mm free length (18.1 inches)
10 effective coils
Result 54.477 lb/in
So I was wrong assuming that the chart data seemed low at 50's ish lbs/in rate.
That is super interesting since I've always been lead to believe that stock springs were in the 90-100 lb range. I guess I'm guilty of propagating mythology.
Anyone have an OEM stock spring to confirm free length? Super interesting information that I should have verified for myself long ago!
Posted by: mepstein Jan 24 2022, 07:05 PM
I always heard stock was 60-70 and 100 was an upgrade for performance.
Posted by: Brian Fuerbach Jan 24 2022, 07:56 PM
So I did a quick rationality check tonight using the highly scientific bathroom scale and tape measure.
168 lbs at 1.75" travel = 96 lbs/in for the 914Rubber 100lb/in spring. Pretty close.
quick design comparison using an online spring calculator
https://www.thespringstore.com/spring-calculator.html
Design #1 close to 914Rubber
9.6mm wire diameter
105.5mm OD
380 mm free length (15 inches)
6 effective coils
Result 90.795 lb/in (sorry for mixed units -- Imperial units for ease of comparision)
Design #2 close to published stock data and the chart data above
9.6mm wire diameter
105.5 mm OD
470mm free length (18.5 inches)
10 effective coils
Result 54.477 lb/in
Design #3 published data from factory manual
9.6mm wire diameter
95mm mean OD -- this works out about the same 105.5 mm OD I measured directly
460 mm free length (18.1 inches)
10 effective coils
Result 54.477 lb/in
So I was wrong assuming that the chart data seemed low at 50's ish lbs/in rate. That is super interesting since I've always been lead to believe that stock springs were in the 90-100 lb range. I guess I'm guilty of propagating mythology.
Anyone have an OEM stock spring to confirm free length? Super interesting information that I should have verified for myself long ago!
Thanks for sharing your measurements. I am really interested to know what my springs are but not enough to to pull one out.
So if the 914rubber springs are 9.6mm wire and 96lb and my springs are 10.4mm diameter, would the larger wire automatically translate to a higher pound rating?
Posted by: Superhawk996 Jan 24 2022, 08:30 PM
So if the 914rubber springs are 9.6mm wire and 96lb and my springs are 10.4mm diameter, would the larger wire automatically translate to a higher pound rating?
Yes larger wire = higher rate but don't forget that you have coating thickness on the wire. I'd assume the powder coat on springs is at least 0.5 - 1.0 mm thick.
If you can see the coils, count them and them if you're around 8 coils, I'd say you're probably running 100 lb/in springs
Assuming you're around 100 lb/in spring rate, to take us back to your original understeer behavior that you don't like, your choices are add rear bar or increase rear spring rate to decrease steady state understeer assuming you stay with the 19mm front bar.
I ran 140's back in the day but I also gave up a good bit of ride quality and back then my car was biased toward oversteer when running stock torsion bars in the front and no anti-roll bars, 185 tires.
Posted by: slivel Jan 25 2022, 10:58 AM
This thread may have played out but I just love to explore the complexities of chassis and suspension. I think suspension and chassis engineers must be some of the most gifted in the auto world. In a previous career in telecom we said the same thing about antenna designers.
Here's a thought experiment: Many do not realize that tires have a spring rate. If you change out your stock wheels and tires, say 15" wheels and 60 ratio sidewalls for 16" wheels with 50 ratio sidewalls you have effectively increased the overall spring rate of the suspension. When the tire encounters a bump, the suspension takes up some of the shock but not all. The tire deforms and the sidewall absorbs some of the shock too. Low profile tires with short sidewalls typically have a higher spring rate. So the higher performance of low profile tires is due in part to increased spring rate, though tread design, compound, and carcass are also a big part.
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