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DerHase's 2019 GTI Rabbit Edition: HPDE shenanigans

DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Haven't done a whole lot lately, mostly driven it on the weekends and been working in the garage to add lighting and electrical for my tire machines to get back to doing tires on the side to fund track shenanigans.

Also just bent over and ordered a DO88 intercooler from EQT. Hopefully it gets here well before Fastivus on Oct 1st so I have time to install. Also waiting on brake pad info from @Mini7 for different rear pads. If we don't hear anything concrete from Ferodo/Essex soon, I'll be ordering some Raybestos ST43 to ensure I have something better on the rear next time out.
 

DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Decided I'd try something a little different on this car - on my last car (Mazda2) that I went full retard on suspension-wise... I ran tons of spring rate and no front sway bar at all. With $$ shocks they were tolerable but definitely STIFF on the street. Trying to avoid hating myself with this car so decided I'd buy some H&R front and rear 26mm sway bars. Went with them because they're solid (rather not worry about one snapping), priced decently, and according to many they use some special hotdog butter or something impregnated in their bushings and they just plain don't squeak or ever need lubed.

They sell the 28mm front and 26mm rear as a matched pair, and a 26mm front and 24mm rear as a matched pair. I ran numbers on all of them and in a nutshell the 28/26 SEEMS to be almost identical to stock as far as front/rear roll couple split goes. Since I'm not wanting to up the spring rate significantly, I DO want to get rid of some overall body roll via the front... but I want to add MORE roll stiffness to the rear to try and move the bias a bit towards oversteer to make it a little more lively. You can see the "total body roll" number in the spreadsheet snips below and how each set of bars affects it. Also the weight transfer from inside to outside tires as you change the front vs rear stiffness.

I'm running some VERY quick and dirty numbers through my spreadsheet which I used successfully in modeling the Mazda2 suspension and developing over about 6 years. It is VERY important to note that I have not verified any of these numbers myself. MANY dimensions are based on David's numbers alone. At SOME point I intend to get my car in the garage while it is still 100% stock geometry-wise and plot everything out with lasers and plumb bobs, etc. for higher accuracy.

As noted in the spreadsheet - when numbers go negative certain stuff needs to be taken with a grain of salt. Also something the spreadsheet does NOT take into account is fore-aft G-loading in a turn (braking/accel). So even if you have one setup with heavy springs, the other with heavy sway bars and soft springs, both can show identical dynamic corner loading... but the difference is that the softer springs car will squat a lot more on accel potentially picking up the inside front tire. I don't suspect that this is near as high a priority as it was for my Mazda2 which had an open diff.

Also I need to noodle on how to calculate the track width - on here I'm using center of contact patch to center of contact patch, but that isn't where the car technically pivots if it goes 2 wheels up. In the grand scheme of things it doesn't matter... the number changes are all relative to each other and just like a dyno should be treated as a tool to utilize, not an end all be all "this is exactly correct" type thing.

I will almost for sure install the rear first alone out of sheer laziness and lack of time. I'd like to try and get some data on rear only vs front + rear at VIR... but trips there are $$$. I may actually do an autocross in a couple weeks with the rear bar only, and try to do another after installing the front bar as well. Won't be scientific, but if I'm completely honest... on track it's moreso to keep the tires from rolling over as much to extend their life.

Stock suspension:
GTI rough calcs stock springs and bars.JPG


Stock front bar, 26mm rear bar:
GTI rough calcs stock springs and 26mm rear bar stock front bar.JPG



26mm front bar, 26mm rear bar (edit: this is what I purchased):
GTI rough calcs stock springs and 26mm front and rear bars.JPG



28mm front bar, 26mm rear bar:
GTI rough calcs stock springs and 28mm front and 26mm rear bars.JPG
 
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GTIfan99

Autocross Champion
Location
FL
Decided I'd try something a little different on this car - on my last car (Mazda2) that I went full retard on suspension-wise... I ran tons of spring rate and no front sway bar at all. With $$ shocks they were tolerable but definitely STIFF on the street. Trying to avoid hating myself with this car so decided I'd buy some H&R front and rear 26mm sway bars. Went with them because they're solid (rather not worry about one snapping), priced decently, and according to many they use some special hotdog butter or something impregnated in their bushings and they just plain don't squeak or ever need lubed.

They sell the 28mm front and 26mm rear as a matched pair, and a 26mm front and 24mm rear as a matched pair. I ran numbers on all of them and in a nutshell the 28/26 SEEMS to be almost identical to stock as far as front/rear roll couple split goes. Since I'm not wanting to up the spring rate significantly, I DO want to get rid of some overall body roll via the front... but I want to add MORE roll stiffness to the rear to try and move the bias a bit towards oversteer to make it a little more lively. You can see the "total body roll" number in the spreadsheet snips below and how each set of bars affects it. Also the weight transfer from inside to outside tires as you change the front vs rear stiffness.

I'm running some VERY quick and dirty numbers through my spreadsheet which I used successfully in modeling the Mazda2 suspension and developing over about 6 years. It is VERY important to note that I have not verified any of these numbers myself. MANY dimensions are based on David's numbers alone. At SOME point I intend to get my car in the garage while it is still 100% stock geometry-wise and plot everything out with lasers and plumb bobs, etc. for higher accuracy.

As noted in the spreadsheet - when numbers go negative certain stuff needs to be taken with a grain of salt. Also something the spreadsheet does NOT take into account is fore-aft G-loading in a turn (braking/accel). So even if you have one setup with heavy springs, the other with heavy sway bars and soft springs, both can show identical dynamic corner loading... but the difference is that the softer springs car will squat a lot more on accel potentially picking up the inside front tire. I don't suspect that this is near as high a priority as it was for my Mazda2 which had an open diff.

Also I need to noodle on how to calculate the track width - on here I'm using center of contact patch to center of contact patch, but that isn't where the car technically pivots if it goes 2 wheels up. In the grand scheme of things it doesn't matter... the number changes are all relative to each other and just like a dyno should be treated as a tool to utilize, not an end all be all "this is exactly correct" type thing.

I will almost for sure install the rear first alone out of sheer laziness and lack of time. I'd like to try and get some data on rear only vs front + rear at VIR... but trips there are $$$. I may actually do an autocross in a couple weeks with the rear bar only, and try to do another after installing the front bar as well. Won't be scientific, but if I'm completely honest... on track it's moreso to keep the tires from rolling over as much to extend their life.

Stock suspension:
View attachment 257888


Stock front bar, 26mm rear bar:
View attachment 257887



26mm front bar, 26mm rear bar:
View attachment 257886



28mm front bar, 26mm rear bar:
View attachment 257884
So which fsb you going to go with?
 

DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
So in typical over-thinking fashion, I busted out the tape measure to try and get some approximate dimensions of the new sway bars since they're out of the car. On this chart I am ESTIMATING the stock GTI sway bar dimensions (based on the H&R stuff). Going to make it a spreadsheet on my drive since it'll probably be a continued work in progress. I have a much more in depth calculator offline, but it gets changed so often and copies made of every potential setup, plus it doesn't really display correctly in Sheets online. Attached are some snapshots of the overall roll calcs for the H&R 26mm front + 26mm rear bars on each of the two front settings (rear is not adjustable).

https://docs.google.com/spreadsheets/d/1BNEyQWiWCIOOsagJby22MS0jHr6J2nAlNEMRastNHw8/edit?usp=sharing


Here you can get an idea of relative roll stiffness increase vs stock. You can see how the rear sway bar is actually ridiculously stiff on it's own (it HAS to be due to the super low motion ratio)... those end links are being put through hell.

(spreadsheet redacted - info has been revised, see here: https://www.golfmk7.com/forums/inde...n-hpde-shenanigans.401435/page-3#post-7878553 Leaving the spreadsheet as an attachment just for reference though should no longer be used.

One thing I noticed about these bars is due to the goofy bends... in order to (more) accurately model them, you really need to measure them in their approximate rotation as-installed. See the rear sway bar standing up in the back? Used a plumb bob to drop the hole mounting points to mark the cardboard. Where it gets a bit iffy is where do you exactly call the "pivot" points where it transitions from arms to the torsion bar section? I'm estimating it to be just where the "long" middle section of the bar just starts to curl towards becoming the arms.

EDIT: disregard the above - now that I've actually spent some time under the car and dicking with lasers ignore the above. There is also a revised spreadsheet with good measurements at my latest post HERE: https://www.golfmk7.com/forums/inde...n-hpde-shenanigans.401435/page-3#post-7878553 Note that the rest of this post here is also going to be more wrong now that I have actual numbers but will leave it here for future reference.

mk7 sway bar modeling.jpg

The important thing to remember that all the measurements and modeling are to be treated as being relative to stock. So as long as I measure all the sway bars the same consistent inaccurate way it'll be alright :ROFLMAO:


H&R 26mm/26mm with front on stiff
H&R frt and rr 26mm softest front stock otherwise.JPG

H&R 26mm/26mm with front on soft
H&R frt and rr 26mm stiffest front stock otherwise.JPG
 

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AzteCypher

Ready to race!
Location
Austin, TX
Car(s)
Mk7 Golf R
I picked one up recently as well, just haven't made time to install it. I'd be interesting in seeing/hearing how the install goes.
 

GTIfan99

Autocross Champion
Location
FL
I picked one up recently as well, just haven't made time to install it. I'd be interesting in seeing/hearing how the install goes.
I know the feeling...
 

DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Ordered the special DS1.11 GTI rear pads today from Essex Parts. Big thanks to @Mini7 for initiating them to be manufactured by Ferodo! Hopefully this weekend I can get cracking on all the stuff that needs to be done to the car before Fastivus 🙃

Also picked up a new work/future tow vehicle. Doubtful I'll have a trailer in time for Fastivus, but hopefully at VIR in December I'll be set so I can bring my quick jacks and griddle for some good food in paddock. The new Blackstone has been my new favorite thing lately...

1662604054437.png 1662604118767.png 1662604142751.png
 

DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Been busy doing maths. When you have 2 weeks before an event this is probably not something you want to undertake, but I wanted some stuff to noodle on. Have to get final measurements once it’s back on the ground but with all the points plotted on X/Y/Z axis, all floor compensation values recorded for each point, plus floor grade compensation performed for where the quick jacks are mounted, I should be able to backwards calculate everything at a given ride height I think everything should be within +/-5mm accuracy for the entire thing when done. Fortunately all the measurement heights fell within 2mm of each other except for 3 spots, which are calculated to compensate for the -3/+4/-4mm dips where component heights were taken.
 

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DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
 

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DerHase

Drag Racing Champion
Location
Hampton Roads, VA
Car(s)
2019 GTI Rabbit
Also since I got the rear sway bar basically installed now - I was able to revise some measurements taken earlier, and also measure the OEM rear sway bar to get accurate numbers. Here is what I've got so far - Still debating whether I want to pull the sub frame with less than 2 weeks to an event or not... But I will get actual verified measurements on the OEM FSB when I do that.

1663554827578.png
 
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