Toe in/out is different to camber. To describe simply it is front/rear angle as opposed to top/bottom angle which is camber.
Spring height should not change toe - this is done by packing shims behind the rear radius arm brackets.
A new strong spring may however give positive camber (where the bottom of the wheel tucks in more than the top) with the vehicle sitting high. A lowering block will help this, as the vehicle gets lower the camber moves in the negative direction.
I've had this on the Herald rally car and cured it by exactly that. Now the new spring has settled a bit I'm looking to fir a slimmer block to raise the car back up a bit.
Marked drop of wheel due to the new spring would rotate the "radius arm" down and this would change toe in/out by moving the hub horizontally. Whether or not to a significant degree I don't know. Depends on how things were sitting originally. I think this is what Bainzy was wondering about.
The way I look at it, the lowering block simply adjusts the body height relative to the rear axle. Positioned between the spring and diff it has no effect on the suspension setup, as everyth with regarding to toe in/out...
Bainzy: Lowering has less effect on the handling than things like polybushes, stiffer springs, better dampers, etc. My spit handles like the proverbial go-kart! (negative camber at the back also helps!)
Brainzy, if you have positive camber then get a lowering block. I got one that is 1" and wow what a difference. Will really sort out your handling. I did a thread on this, its well worth it mate. Just make sure if you get the 1" block you get longer diff studs and then go for a 4 wheel alignment check after. Anything that doesnt sit right will be picked up on this and your car will be much better.
Thanks guys, just realised I made a typo, should've read "is correcting it much of a faff". junkuser is correct in describing what I was trying to say!
If you've ever tried to reattach a radius arm onto a vertical link you'll know they move in an arc; the position of it in this arc will bring the hub/vl assembly closer or further away to the front of the car, and change the angle slightly.
The book has 2 quoted figures for laden and unladen toe-in/out, because the toe changes depending on how low the car is sat. I'm a bit concerned that lowering the car will make this incorrect, though to be fair I've no idea whether it's 'right' at the moment either. Probably not if the camber is wrong as well.
My car is polybushed in most suspension bushes, though I haven't got a poly spring pad - not sure what the best type to go for there would be. Will do that one when adding the lowering block.
Cheers for the link Chris, I'd forgotten about that thread - very informative. Your car had a lot more positive camber than mine does now, so I should get away with 1/2" or 3/4". Think the alignment check is a good call.
Will adding a 1/2" lowering block change the toe-in/out of the rear wheels? If so, is that much of a faff?
Experienced some 'interesting' handling on the limit in the Spitfire today, made me a bit keener to get suspension where I want it. Rear end under braking seemed uncannily similar to that of a fish!
The car currently appears to have no negative camber at all and sits too high (imo) at the back, due to having a brand new leaf spring.
Lowering the rear with a lowering block (shim in between the diff housing and the transverse leaf spring) will change rear toe, but only a tiny bit (sorry, I don't have the quantification of "tiny" in this instance). Rear bump steer is much much less than front bump steer on small chassis Triumphs. I agree with Chris--measure and adjust rear toe yourself, or take it to an alignment shop and have them do it when you are done.
BTW, each 1/4 inch of lowering block thickness results in a just under 1 degree of net negative camber change, so a 1/2 inch block will yield 1.5 to 2 degrees of additional negative camber from wherever you are now. For more info on this subject, including a drawing of a lowering block if you'd rather machine your own vs. purchasing one, check this out:
BTW, I use a 1/2 inch block on my '78 Spitfire to set my total unladen rear camber at negative 4 degrees, and I really like the resulting handling (virtually no jacking and no feeling of lightness in the rear end when cornering hard or braking and cornering). Simply going from 2 degrees negative to 4 degrees negative made a significant difference for the better. I drive this car to and from work on precipitation-free days/anywhere from 5000 to 8000 miles a year, and autocross it a few times a year.
Thanks Paul, that's extremely helpful. I've read your site to death over the years and learnt loads, and the front & rear ride heights of your 1500 are bang on what I'd like to achieve with my own car.