I was reading back over an old evo magazine report on their long-term 3.0i Z4 that they ran on their long-term fleet for almost a year, and came across this:
"the Z4 seemed to wander from bump-to-bump, sending confusing messages to the driver as to what was really going on. It felt like an advanced form of tramlining and became christened the 'Thrill of Writhing' in the office. At first I thought it had to be the fault of the standard run-flat tyres, so after the Z4's disappointing performance at last year's eCOTY (063), we swapped the Bridgestones (having covered 11,000 miles, they were around 60 per cent worn) for a set of Vredestein Ultracs. The initial ride coarseness certainly improved on the Ultracs, while wet grip was transformed. But even so, the Z4 never felt really relaxed unless the road was glassy smooth.
The real culprit was finally revealed on the Mercedes SLK launch last month. Mercedes brought in a Z4 for evaluation during the SLK's development and had noticed the same strange chassis behaviour that we'd experienced. After putting the car on a chassis rig, the explanation seemed to be a noticeable change in rear toe angle when the Z4's rear suspension moved up and down, meaning it would start to 'steer' from the rear on undulations. Now, increased toe-in on compression is great on track as it tucks the car into the apex, killing understeer in the process, but pretty useless on our lumpy roads as the change in toe angle can cause the constant wandering we'd experienced as the rear wheels steered their own independent course to the fronts."
I've highlighted the intersting bit (to me!) in bold. It sounds like it's the geometry setup of the Z4's suspension/chassis that causes the Z4 to be sensitive to bumps. I'd describe it as "lively" handling if you're tanking along lumpy A/B-roads, and find it somewhat limits your speed even at lower-than-the-speed-limit speeds.
Now, I'm wondering if there's any parts of the suspension that could be changed to give a change in the suspension behaviour, and remove or reduce this change in rear toe angle under load? Possibly a question for folks of the likes of Curtis perhaps but does anyone know about this?
Cheers
Ally
"the Z4 seemed to wander from bump-to-bump, sending confusing messages to the driver as to what was really going on. It felt like an advanced form of tramlining and became christened the 'Thrill of Writhing' in the office. At first I thought it had to be the fault of the standard run-flat tyres, so after the Z4's disappointing performance at last year's eCOTY (063), we swapped the Bridgestones (having covered 11,000 miles, they were around 60 per cent worn) for a set of Vredestein Ultracs. The initial ride coarseness certainly improved on the Ultracs, while wet grip was transformed. But even so, the Z4 never felt really relaxed unless the road was glassy smooth.
The real culprit was finally revealed on the Mercedes SLK launch last month. Mercedes brought in a Z4 for evaluation during the SLK's development and had noticed the same strange chassis behaviour that we'd experienced. After putting the car on a chassis rig, the explanation seemed to be a noticeable change in rear toe angle when the Z4's rear suspension moved up and down, meaning it would start to 'steer' from the rear on undulations. Now, increased toe-in on compression is great on track as it tucks the car into the apex, killing understeer in the process, but pretty useless on our lumpy roads as the change in toe angle can cause the constant wandering we'd experienced as the rear wheels steered their own independent course to the fronts."
I've highlighted the intersting bit (to me!) in bold. It sounds like it's the geometry setup of the Z4's suspension/chassis that causes the Z4 to be sensitive to bumps. I'd describe it as "lively" handling if you're tanking along lumpy A/B-roads, and find it somewhat limits your speed even at lower-than-the-speed-limit speeds.
Now, I'm wondering if there's any parts of the suspension that could be changed to give a change in the suspension behaviour, and remove or reduce this change in rear toe angle under load? Possibly a question for folks of the likes of Curtis perhaps but does anyone know about this?
Cheers
Ally
