oh my!

Time to go back to basics.

Springs define how much deflection a wheel experiences from the neutral position when a given force is applied. A heavier spring makes the wheel move more slowly & a smaller distance when a force is applied, this will translate into less body roll & also less wheel travel when hitting a bump, aka a firmer ride assuming the damping is reasonably close to being right. However, a heavier spring will push the wheel back down faster when load is removed.

To compensate for this you need dampers to control the motion of the spring. These do need to be matched reasonably well to the springs. Damping is not hard or soft it’s fast & slow. Faster damping means the springs movement is quelled faster, so assuming the spring isn’t under damped this makes the ride firmer. If the damping is slowed down then the spring can move more freely, so assuming the spring isn’t under damped then this makes the ride softer.

An ARB joins the two wheels via a spring that is braced against the chassis so they can’t move completely independently. This means as you load one wheel up under cornering some of that load is pushed onto the other wheel, pushing it into the road! However, if you have an ARB that’s too stiff the ARB will unload a wheel when going over surface imperfections.

Go too far out of sync with the springs & dampers and you get odd behaviour. If you go too slow on the damping then the ARB starts acting like a spring damper by activating the opposite damper & spring to control wheel better. When people start talking about keeping the ARB matched on road applications it means either their damping is too slow or they're trying to apply top end motorsport suspension tuning to road applications which just confuses the issue. As you're not in high performance motorsport here for road application you only want to tune the amount of body roll you get.

So my upgrade path would be Springs/dampers -> LSD -> ARB
 
Interesting discussion. My 35is on 19" rims doesn't look to have a lot of negative camber at the rear but it does grip/handle a lot better than the apparent identical 35is I had previously. I had put this down to the RFTs having improved but it may just be a difference in camber.

The previous 35is would wag its tail quite happily if you got on the gas too early exiting corners or roundabouts even in completely dry conditions. At temperatures below about 7C you really did have to concentrate. At full chat in a straight line at any ambient temperature it would light up the dash and be skittish in the lower gears as well.

The current 35is is a lot, lot better even though it rides on the same RE050 RFTs as the previous one. By a lot, lot better I mean a whole heap better. Even at temperatures around 0C it has oodles more grip than the previous car but can still light up the dash on bumps in a straight line but always feels much more planted.

I have always thought the combination of a LSD and MPSS would transform the car in the grip/handling department.
 
Ever have your suspension geometry checked? My Z4 500 miles after delivery was out, but within, more critically not balanced left to right. Getting the suspension geometry centred improved things a lot.

MPSS imo are one of the most over-rated tyres out there. They had a stiff carcass so tend to skip more over small surface imperfections. They rely heavily on the very soft & sticky outside shoulder so tend to make the car snap away rather than progressively sliding. A lot of the RFT issues can be seen in the MPSS but in a much milder form. The big difference is they increase lateral grip compared to normal high performance tyres, RFT tyres use less grippy compounds.

MPSS improve handling? For me - track use, without significant surface imperfections until they start to let go, yeah. However, for road use, not so much.
 
MPSS overrated? I think not. I swapped the recommended Pirelli set up on my F355 to MPSS all round. The improvement over the Pirellis was astonishingly good and very, very noticeable on road. I am completely convinced by them. Fantastic tyre.
 
techathy said:
Thanks for confirming that it's an over-rated tyre ;)

You are right though, i cant compare non rft and rft and be surprised with how much better it is.

I am actually a little disappointed in the MPSS, which is why I want to reduce the camber to get ll the tread on the road! Apart from corners the rest of the experience isn't much better than rft (few thousand miles on them now)
 
stuartinzg said:
I am actually a little disappointed in the MPSS, which is why I want to reduce the camber to get ll the tread on the road! Apart from corners the rest of the experience isn't much better than rft (few thousand miles on them now)
I had to experiment with pressures with the MPSS to get an optimum set up. If you run the standard RFT pressures you may find them too high! Before adjusting suspension settings I would try adjusting tyre pressures first.
 
I also find the MPSS a good tyre. There are better tyres for pure grip but the MPSS performs well in the wet and my rears lasted 14k miles and fronts are still going over 18k which is a lot better than any previous performance tyres.

I can also put down all the power in 2nd in the dry in these warm winter temps which is impressive considering the boost I'm running.
 
Mpss fantastic tyres. Going to replace my rft's on my summer wheels soon. Fitted them to my last 3 cars & transformed all of them dramatically.
 
My problem with the MPSS is they act very poorly on the limit of grip or when you get weird road artefacts.

stuartinzg said:
I am actually a little disappointed in the MPSS, which is why I want to reduce the camber to get ll the tread on the road! Apart from corners the rest of the experience isn't much better than rft (few thousand miles on them now)
Are you getting flat tyre wear across the tyre? If you're not getting progressive wear across the tyre you'll need to adjust your cold tyre pressure.
 
Monitor and experiment. You need to work off changes.

I'll take tyre depth measurements every 500 miles. If I have a tyre that over 1000 70.1miles I get 0.2mm off the inside shoulder, 0.15mm off the middle & 0.1mm from the outside shoulder that's about right. However, if I was to get 0.2mm off the centre I'd know the tyre was over pressure & experiment with reducing the tyre pressure maybe 5kPa. Conversely if it was 0.05mm off the centre then I'd increase by about 5kPa.

On 245/40R18 I'm running 255kPa up front (a little high but with good reason) & 265/35R18 I'm running 260kPa
 
techathy said:
Monitor and experiment. You need to work off changes.

I'll take tyre depth measurements every 500 miles. If I have a tyre that over 1000 70.1miles I get 0.2mm off the inside shoulder, 0.15mm off the middle & 0.1mm from the outside shoulder that's about right. However, if I was to get 0.2mm off the centre I'd know the tyre was over pressure & experiment with reducing the tyre pressure maybe 5kPa. Conversely if it was 0.05mm off the centre then I'd increase by about 5kPa.

On 245/40R18 I'm running 255kPa up front (a little high but with good reason) & 265/35R18 I'm running 260kPa

What's that in psi ? :thumbsup: fitted my summers today set them at 34/36 psi
 
KERMIT1970 said:
techathy said:
Monitor and experiment. You need to work off changes.

I'll take tyre depth measurements every 500 miles. If I have a tyre that over 1000 70.1miles I get 0.2mm off the inside shoulder, 0.15mm off the middle & 0.1mm from the outside shoulder that's about right. However, if I was to get 0.2mm off the centre I'd know the tyre was over pressure & experiment with reducing the tyre pressure maybe 5kPa. Conversely if it was 0.05mm off the centre then I'd increase by about 5kPa.

On 245/40R18 I'm running 255kPa up front (a little high but with good reason) & 265/35R18 I'm running 260kPa

What's that in psi ? :thumbsup: fitted my summers today set them at 34/36 psi
http://tinyurl.com/yzgt66g
 
KERMIT1970 said:
Cheers :thumbsup: 36/38 psi
Er... you sure about that?
255/260 = 0.981
36/38 = 0.947

Also worth mentioning I've not got a good warm temp base line for my tyres. Certainly on my 1 series I was about 10kpa down on cold pressure when ambient was consistently in double figures overnight.
 
Why keep referring to kPa when most pump gauges are in psi and bar? Even the manufacturers normally quote tyre pressures in these values.
 
Back
Top Bottom