UK-POLOS.NET - THE VW Polo Forum

iichel wrote: Wed Nov 29, 2017 12:10 pm I'd beg to differ, but OK.
I can just say it won't work, but as a teacher I think it's far more interesting to know why not and teach how to find the answer yourself.
I hope you don't mistake my tone, I'm not trying to lecture you, not at all, I'm just trying to help understand the reasoning behind it. It's with the friendliest of intentions.

First, let's have a look at the dampers. A damper (or more mistakenly called a shock absorber) slows down a movement. It tries to bring velocity to a minimum (so it accelerates or decelerates, hence the name a damper). The only thing to keep in mind is to keep a damper in its comfort zone. Otherwise, the only variable is the amount of deceleration it brings to the suspension system, regardless of weight and distance.

Now let's have a look at the springs. A spring typically deforms under force. Spring length (in meters) = force divided (in newtons or kgs) by the spring constant (meters per k or N). Spring rate is the stiffness, as you like. Higher spring rate, stiffer spring. So the only variable here is exerted force.

The largest force on the suspension is the weight of the car. It compresses the spring, brings it to the correct height and the weight of the car is accelerated up and down as you ride the bumps and holes on the road (remember, weight times acceleration is force).

So the 1.2 FSI 12V engined polo with manual transmission weighs in at around 965kg.
The Polo GTI 1.4 TSI with DSG gearbox is around 1265kg (4 doors, 2 doors is about 60kgs lighter). That's a massive 300kgs more.
The weight balance is about 65% at the front in a Polo GTI, making it around 825kgs up front and 440kgs at the boot.
The turbocharged and supercharged engine, intercooler, and DSG gearbox are insanely heavy.

The only difference at the rear is that the Polo GTI has a battery in the boot which makes it about 20-25kgs heavier.
Its minimal, I'd even save negligible. A bit of fuel or a spare wheel could make a larger difference.

So to make a bad looking table:
Engine - Front - Rear
1.4 TSI - 825kg - 440kg
1.2 FSI - 545kg - 415kg

So the rear springs will probably work fine between the cars, if both are 4-door cars.

But at the front, it's a completely different story. The spring rate of the GTI must be about 1,5 times that of the Polo FSI.
So you can imagine the front goes up quite a lot, the ride becomes very harsh and the handling characteristics (i.e. body roll) are not very good.

So in general, it is only recommended to fit springs with a weight range very close to what is on the intended vehicle.