The VW MK4 Golf GTI/MK4 GTI understeer situation is well known. How each person describes their MK4 understeer problem might be a bit different so in this article I’m going to describe how I felt understeer before this mod and how the car feels with the mod.
The Car – MK4 GTI/Octavia RS
The Octavia RS used the MK4 Golf platform and this mod was done on an Octavia RS.
Mod List
This Octavia RS is not standard. It has:
H&R springs with Sachs stock replacement dampers at the front and Sachs sport dampers at the rear.
Michelin PS5 225/40-18
All bushes refreshed with stock replacement from Febi
Polyurethane front top mounts
Standard setting wheel alignment
Before the Understeer Delete Mod – How it felt
Honestly, I didn’t think it was too bad.
Braking
Understeer was most noticeable due to driver error, specifically braking into a corner. In this scenario, yes, front end cornering grip wasn’t great but to be fair, I think you could say the same for most/all cars.
Turn-In
The biggest problem, when the car was driven well, was initial turn in. There was a fraction of a second delay between turning the wheel and the car tracking into a corner. Like the car was waiting for the weight transfer to happen before it started doing something. Not a major issue but an issue that did dent the confidence a bit, especially in the high speed stuff.
General Grip
Generally I thought front end grip was decent during a corner but I wouldn’t say no to a bit more.
Why Change/Experiment
Why did I try this mod?
For the reasons listed above, I wanted more grip at the front and I wanted more positive turn-in
The Mod – What Did I Do?
Simple, I changed the front anti-roll bar bushes.
Why?
Because they looked tired. When I was jacking the car up to do maintenance I could see the bushes were deforming a decent amount at both ends of the anti-roll bar link, maybe 3mm on each bush. If this was happening during cornering we could have been looking at 10mm+ of total movement in the roll bar bushes before the anti-roll bar/sway bar started to do anything.
How
I have a 3D printer and TPU material so I had nothing to lose knocking up some replacement bushes.
The old bushes were pryed from the end links with a screwdriver. I measured up the size of the bush and printed some replacements. I used around 3mm thickness of TPU material for a bit of vibration absorption and the rest of the bush was made from solid nylon. The bushes were printed in two pieces so they could be installed in the end links without a press.
Jacking the car up with these new bushes, I could not see any deformation in the bushes at all, they are effectively solid.
The Result – What Was The Effect & How Did It Feel?
There was a bigger difference than what I was expecting
First Impressions
The thing that hit me first was how the amount of steering input had changed. With the uprated bushes I was steering too much into corners. To put it another way, I had to reduce the amount I turned the wheels to get the same about of turn. Literally, for the first 20kms on windy country roads I found myself having to wind off a bit of lock after corner entry. This has to be a good thing.
Second Impressions
Turn-in response. Turn the wheel are the car tracks into the corner immediately. That slight hesitation that was there before had gone. This gave me a ton more confidence, especially in the high speed stuff.
I’ve had the bushes on for a few thousand KMs now and I can say that I don’t have any doubts that the car is going to track into the corner immediately. The turn-in response on it’s own has been a mini transformation.
Third Impressions – The Biggest Surprise
With the new found confidence I could attack roads with more commitment and this is where the most surprising benefit revealed itself.
General consensus is, if you stiffen the roll resistance across an axle it looses grip. So if you put a thicker anti-roll bar at the front you increase rear grip at the expense of the front.
Not so in this case.
Front end grip has been increased significantly despite the fact that stiffer anti-roll bar bushes should be equivalent to an increase in the thickness of the sway bar.
Whereas before I drove the car more from the rear (because that had the most grip), now I feel like I can drive the car from the front. I can now stick the car into the apex and have the confidence to deal with whatever the rear might do. Personally I like that but it might depend on driving style.
Before the rear could be brought into action a little bit with a good lift off the throttle on corner entry, now the rear feels more mobile under normal steady state cornering. Nothing lairy but I know a lift will do more than before.
I wouldn’t go as far as to say the car feels like it is pivoting around my hips but there is a hint and it feels great.
How Has Grip Been Increased?
As I just mentioned, normally stiffening an axle moves grip to the other axle but the opposite has happened here. And I think this is because roll on the front has been reduced.
Less roll means the camber change (reduction on the outside tyre) through corners has been reduced and more camber generally means more grip.
The Downsides
So far I’ve made this VW MK4 understeer mod sound like it’s all puppies and rainbows but it isn’t. There has been some noticeable negative side effects.
Ride Comfort
Because the two sides of the axle are more tied together, a bump on one side affects the other side more. Basically it means the car is more uncomfortable on bad roads.
Traction
Again, because the two sides of the car are more tied together, they are less free to deal with road imperfections. Before, one wheel could sink into a hole to maintain traction, now the pressure it can exert is less because it is affected by what the other wheel is dealing with. For example, bumpy tarmac on an uphill, at a set of traffic lights. Pulling away gives more wheel spin than before.
Alternative Solutions – VW MK4 Understeer
There is a ton of advice available if you “Google VW MK4 GTI understeer”. The two main solutions are fit the front wishbones and hubs from an Audi TT and/or fit a stiffer rear anti-roll bar. Both these solutions costs hundreds of dollars/Euros/Pounds whereas a front anti-roll bar bush upgrade will probably cost less than 30.
VW MK4 Understeer Mod – Worth It?
You can probably guess by now that even with the downsides, I would definitely do this upgraded anti-roll bar bush mod again.
Transformation is a strong word but I think it can be used here.
This sway bar bush upgrade has given me more confidence in the car, it has significantly increased front end grip and has generally lifted the performance of the car and for minimal outlay.