There are no dead coils on the front of the E30. The springs will be stiffer after being cut and heat affects can change their characteristics.
Even on the E30 H&R Race springs? Most of the ones I've seen do have several dead coils at the bottom of the spring.
A spring is simply a torsion bar in a coil; when the spring compresses, the wire actually twists. There are two things that affect spring rate - length of the torsion bar and diameter of the wire.
Most of the stock-location aftermarket "race" springs use a thinner wire and a bunch of dead coils to effectively shorten the active part of the spring (as once the dead coils are in coilbind, they no longer twist). This winds up with 2-4 coils of usable spring(torsion bar), thereby allowing for a thinner wire.
The heat certainly will affect the characteristics of the wire. That said, if there are dead coils (anyone have a picture of an H&R e30 race spring?), it won't matter - a dead coil is just taking up space. If there are no dead coils, ehhh, I don't think it'll hurt a thing - I've cut several sets of springs over the years (Audi 100 {old Audi 100} rear springs make great VW Rabbit rear autocross springs for those on a budget), I've had zero issues. Add that personal experience to the (literally) thousands of people who have cut their own springs, well, I don't think the heat-issue is truly an issue.
Is the "right" spring the right answer? Sure. Does the car know the difference? Nope. Not as long as the spring does not break.
In addition, the suspension is getting into excessive negative camber (for the road) territory.
Two things - negative camber does not kill tires, toe does. I've run as much as 3.5 degrees on the street; my inside edges _absolutely_ wore faster than the outside edges, but by the time the insides were done, the rest of the tire was close behind. Secondly, MacPherson Strut suspensions _lose_ negative camber (gain positive camber) as soon as the control arm goes beyond parallel to the ground - if the control arm is pointed "up" to the wheel from the body, it has less negative camber than if it were parallel.
The rear is another story - the rear does go far more negative, but he's not talking about lowering the rear more.
But he has the wrong circumfrance tyres on in the first place...
So? Stock size is 195/60-14, right? He's got a 205/40-16?
195/60-14 23.21" diameter
205/40-16 22.45" diameter
So, the difference is .76" shorter. Not bad. .38" difference in wheel gap (divide difference by two to figure out how much the car was lowered by the wheels).
That's not bad. Using a shorter diameter wheel can be _very_ good for handling - it reduces gear ratio, center of gravity, etc.
Don't forget that BMW spec'd a tire for the car's intended purpose - once you start narrowing it's intended purpose, things can change. Changing wheel and tire dimensions does wonders for performance - I'm currently running 275/35-15s on a 15x10.5" wheel on my autocross 2002 (which is street legal, fwiw), the enginerds at BMW certainly did not _intend_ for that much tire, and if the car does start tearing itself apart because of that much tire, I'll not complain - but the results are certainly worthwhile.
Dunno. I don't think there's any problem with cutting the springs. Are there better answers? Sure! Are there cheaper answers? Nope. Is it _bad_? No - not at all. As long as the car does not run out of shock travel, things will be OK. Would it be better to get shortened struts (cutting and welding or threading the strut tube), coilover sleeves and doing it right? Yup - but if he's happy with the ride quality & has the means to chop of a small chunk of spring, he should just cut the spring - he just needs to ensure that he's not cutting too much off.
It is not rocket science. Cutting springs is a bit crude, but it works - and in this particular case, I think it has merit - I think he could achieve all of his goals with a Sawzall without making any sacrifices.
Iain
