stiffening the front will create more understeer won't it?
Yes and no.
Its been a while since I read up on my suspension tech; but my understanding from both tech articles and a variety of different setups on MKV Golfs is that the rear can be stiffened up to a degree to aid turn-in and change the chassis dynamic from under steer to neutral. In the case of adding a rear sway bar that is very stiff and keeping the stock front bar a mismatch occurs in the following way:
Take for example your GTI is making a spirited right turn.
The chassis leans to the left side, this causes the stiff rear bar to transfer the load laterally across itself to the right unloaded inside rear wheel, helping push the inside unloaded right wheel down onto the ground and create some yaw slip. This is great for initial turn pre-apex. Once apex is very near, the stiff rear sway bar does not allow any body roll in the rear part of the vehicle. The dynamic energy of the weight transfer has to find another outlet, the path of least resistance. The dynamic energy is tranferred diagonally across the GTI to the outer front loaded wheel (front left in this example as we are turning right ... remember). The energy on the front wheel causes it to roll into positive camber, so much so that the tyre & wheel on the outside loaded front left rolls on it outer edge, with the inner part of the tyre lifting off the ground. The effective tyre grip is reduced from a 225mm tyre to someting like a 175mm tyre. In addition, the positive induced camber of the outside left loaded wheel also causing the inside right unloaded wheel to roll into negative camber, also failing to ultise the full width of the 225 tyre. In extreme cases, the whole inner front right wheel could lift off the ground. In this case you would only have 1/2 a tyre of grip (outside loaded tyre with positive camber) as available grip near the apex of the turn. In other words, the rear is stiff and doesn't roll; the front end rocks like a boat, onto the most outer edge of the outside front loaded tyre. Problem is: when you get on the power at the apex of the turn to hammer out of a corner, all you get is understeer as front tyres are not utilising their full tread (remember the outside goes into positive camber rolling the tyre outwards; inside tyre falls into negative camber, rolling inwards). The front end slips away from you under power from apex and beyond. Add a stiffer front anti-roll bar, so when the dynamic force is transferred from the rear diagonally across the GTI to the outer front wheel, the stiffer front bar keeps both the outside tyre from falling into positive camber, and the innder unloaded tyre from falling into negative camber - in other words, both tyres are kept flat on the ground, increasing grip levels when powering out of the turn from apex and beyond. That is why Eibach & H&R have big front bars and smaller rear bars (both adjustable). On sharp hairpin turns, every Golf I have seen with a rear sway bar only has always run wide on corner exit. Similar thing with Mario's R32 if pushed beyond 7/10ths. A very heavy rear bar also has the propensity to get the rear end very light, as the lateral forces side to side, can cause both rear wheels to get light, causing a spin out (aka Peugot 205GTI). So its not as simple as beefing up the rear bar to the biggest size you can find. Clear as mud?
In the last 3 days, I've been fortunate enough to either drive or ride in 3 differnt type of R32:
Ray's R32: OEM suspension + f&r H&R sway bars (soft/hard) + Haldex.
Jester_Fu's R32: HPA KW SHS + OEM sway bars + Haldex.
Mario's R32: OEM suspension + neuspeed rear sway bar only.
All 3 handle & ride differently.
Cheers
WJ