suspension? spring rates n stuff

[dieselnutjob]

I am finding the suspension on the 607 a bit hard. I'm even thinking about getting some custom softer springs made up.

For example the company car park is block paving and I think I can feel every brick.

The front shock absorbers have been leaking oil for a few years, so I have a new pair ready to go on. They are Bilstein B4s as I have been advised that they are the most comfort oriented shock absorber available for the 607.

When I fit them is there an accurate way to measure the spring rates that are on there now? I spoke to the guy at http://www.coilsprings.co.uk/ but he has no data on the 607.

[dieselnutjob]

I had a go at this www.reliablespring.co.uk/calculator.htm

 

I got about 130 lb/in or 22500N/m but it's not a very accurate way to measure them, and I have no idea whether that's a particularly hard spring

[garethj]

The trouble with a spring calculator like that is you don't know the material that the spring is made from.

 

I'd load it up with a known weight and see how much it compresses. That's your spring rate right there.

 

Whether the rate is high or not is also difficult to say in absolute terms; if the spring is close to the hub like a McPherson strut the spring rate might be ok, but if the coil spring is inboard so you get less favourable leverage the same spring might be too soft. Comparing one car's spring with another doesn't really make sense because of this.

 

You could always pop over to RetroRides and gather up all their bits of offcut coil springs, then weld them on to yours

[M'coli]

I'd pop the new strut inserts in and see what it's like; it will probably be much better, just from them alone. Peugeot were not known for making an arse of their spring/damper rates on big cars, so the lack of damping in worn-out shocks will probably be the main contributor to the shonky ride.

[dieselnutjob]

I'd load it up with a known weight and see how much it compresses. That's your spring rate right there.

 

I never understood this. If you double the weight on a spring it doesn't compress twice as far does it?

[Junkman]

I'd load it up with a known weight and see how much it compresses. That's your spring rate right there.

 

I never understood this. If you double the weight on a spring it doesn't compress twice as far does it?

 

That depends on the spring rate. It's mm per N. Assuming the spring rate is linear.

[dieselnutjob]

I'll put it another way

if you put 100kg on a spring and it moves say 2cm

does that mean if the spring already has 1000kg on it and you make it 110kg that it will still move 2cm?

I think not

[Junkman]

I'll put it another way

if you put 100kg on a spring and it moves say 2cm

does that mean if the spring already has 1000kg on it and you make it 110kg that it will still move 2cm?

I think not

 

If it's 2cm for every 100kg, then if you make it 110kg it would be 2.2cm. If you make it 200kg 4cm, if you make it 300kg 6cm...

This is completely irrespective of the pre-load.

[M'coli]

If a spring's rate is linear, say, 100kg/cm and it has 1000kg on it, it will have compressed 10cm. Add 100kg to make 1100kg, it'll move 1cm and be compressed by 11cm. Front springs on FWD cars are usually linear, whereas rear springs on FWDs are usually multi-rate to deal with different loads - as the load is increased the lower rated parts of the spring become "coilbound", i.e. all the travel of that part is taken up, allowing the higher rated parts to continue to provide the suspension at the right rate for the load. Springs like this are usually denoted by regions of differing distance between the coils for soft, medium and hard rates.

[dieselnutjob]

ok I stand corrected

I'm sure I can rig up something

I think Peugeot lost the plot when they went from 505 onwards

the 607 handles like it's on rails, but that isn't what I want

[M'coli]

The other thing to remember if you do go for softer springs is that a softer spring needs to start off longer to have the same ride-height - if you get a company to make you some softer springs, the compressed height of the springs when the car is at rest may be required to allow them to work out what length they need to make them (on the other hand, they may not and have enough experience to suss this out for themselves!)

[dieselnutjob]

I am told that Coil Springs Ltd will sort all that out. I probably won't do this any time soon but I just wanted to collect some data whilst the springs are in bits just in case I decide to in the future.

 

I did a very quick and dirty comparison of the 604 vs 607. When I sit on the front wing of the 604 that corner drops 25mm. When I sit on the front wing of the 607 it only drops 11mm. That seems a huge difference. At the back the difference was less marked.

 

I heard that early 607s had handling issues, which was that they tended to swap ends (just like a 205 GTI). I suspect that they hardened up the front to reduce lift off oversteer.