interesting steering rack ratio Numbers.

[BMWZ4MC]

...you've got a point there although I'm not convinced its anything to do with power but just that the CSL is so well ballanced - a hard trick on the Z4. Anyone corner weighed our cars? On the subject of "celebrated" steering its also to do with feel which rubber type, tyre pressure and geometry all affect greatly. From experience there is ample room to improve our Z4's steering feel. It was my primary goal and I'm thrilled with the results. The compromise of 15-20% harder ride, tramlining and overall "livelyness" is well worth it for my use of the car.

For what it's worth, I had mine corner weighted when I fitted Clubsports and stiffer front and rear ARBs. The handling is phenomenal now - no understeer at all, easily provoked and controlled oversteer with huge amounts of feedback. My cornering speeds are much faster so my braking points are much later. Heel and toeing down through the gears under heavy braking and turning in is a great pleasure with the uprated engine mounts too. Driving mine back to back on track with my Westfield on semi-slicks makes me want slick tyres and perhaps an even faster steering rack.

[carl]

Out of all of them the CSL was the most celebrated by far yet it has a slower ration then with roadster or coupe, I'm guessing the quickness of the steering is more due to such power in a short wheel base car.

I think the ratios are the wrong way round but I wonder if it's to do with the physical size of the wheel somehow?

[exdos]

For what it's worth, I had mine corner weighted when I fitted Clubsports and stiffer front and rear ARBs. The handling is phenomenal now - no understeer at all, easily provoked and controlled oversteer with huge amounts of feedback. My cornering speeds are much faster so my braking points are much later. Heel and toeing down through the gears under heavy braking and turning in is a great pleasure with the uprated engine mounts too. Driving mine back to back on track with my Westfield on semi-slicks makes me want slick tyres and perhaps an even faster steering rack.

I'm a sceptic on the value of corner weighting on a car like the Z4MC, because there are a few variables that can alter the weight distribution after the car has been corner weighted, such as carrying a passenger, fuel load fluid in windscreen washer bottle etc. Do you notice the difference in handling when the fuel tank is full and when it's empty? What are the ride heights at the highest points at each of the wheel arches?

Now that you've got your car at this level, what do you think of the OEM suspension?

[Beedub]

...you've got a point there although I'm not convinced its anything to do with power but just that the CSL is so well ballanced - a hard trick on the Z4. Anyone corner weighed our cars? On the subject of "celebrated" steering its also to do with feel which rubber type, tyre pressure and geometry all affect greatly. From experience there is ample room to improve our Z4's steering feel. It was my primary goal and I'm thrilled with the results. The compromise of 15-20% harder ride, tramlining and overall "livelyness" is well worth it for my use of the car.

For what it's worth, I had mine corner weighted when I fitted Clubsports and stiffer front and rear ARBs. The handling is phenomenal now - no understeer at all, easily provoked and controlled oversteer with huge amounts of feedback. My cornering speeds are much faster so my braking points are much later. Heel and toeing down through the gears under heavy braking and turning in is a great pleasure with the uprated engine mounts too. Driving mine back to back on track with my Westfield on semi-slicks makes me want slick tyres and perhaps an even faster steering rack.

get some slicks on and you will be blown away at how good the car can feel with the right work.

[inkey$]

This just reminded me I need to source a Z3 1.9 rack at some point for my MC as the stock M ratio is extreme!

[TomK]

Out of all of them the CSL was the most celebrated by far yet it has a slower ration then with roadster or coupe, I'm guessing the quickness of the steering is more due to such power in a short wheel base car.

I think the ratios are the wrong way round but I wonder if it's to do with the physical size of the wheel somehow?

The CSL wheel is some 370mm as apposed to ours which are our IIRC 352mm. It's a major part of the gearing system if I understand it correctly.

[Beedub]

Not to sure to be honest tom

[exdos]

The CSL wheel is some 370mm as apposed to ours which are our IIRC 352mm. It's a major part of the gearing system if I understand it correctly.

The OEM 224 ///M wheels are 490mm diameter so I'm confused as to what you are describing as the "wheel" from the sizes you've given?

The specs are as below:
M3 CSL
wheelbase 107.4 inches
track/tread (front) 59.8 inches
track/tread (rear) 60 inches

Z4M
wheelbase 98.3 inches
track/tread (front) 58.5 inches
track/tread (rear) 59.7 inches

The Z4M has a wheelbase which is more than 9% shorter than the CSL which means that it will rorate more readily. You can fine tune the steering response by adjusting the toe angles as well as by driving technique.

[TomK]

I was referring to the size of the steering wheel itself not the wheels.
Got the numbers a bit wrong, just checked, 375mm for an m3/CSL wheel and 356 for z4m wheel.
Surely the size of the wheel itself affects the gearing of the rack?

[exdos]

I was referring to the size of the steering wheel itself not the wheels.
Got the numbers a bit wrong, just checked, 375mm for an m3/CSL wheel and 356 for z4m wheel.
Surely the size of the wheel itself affects the gearing of the rack?

I refer you back to my earlier link: http://en.wikipedia.org/wiki/Steering_ratio The ratio is related to the angle of the steering wheel not it's diameter.

[TomK]

I was just reading that

It doesn't quite add yup for me as whilst I understand the rotation of the wheel will be the same regardless, that actual distance traveled by the wheel will be different.

There's some 'interetsing' reading to be had on the subject also on this
http://www.g-w.com/pdf/sampchap/9781605252230_ch09.pdf
page 178

[exdos]

I've just had a "speed read" through that reference and on Page 169 it says: "The steering wheel size has an effect on the effort expended by the driver to turn the vehicle. The larger the wheel, the less effort needed to turn it. This is due to the leverage exerted by the larger wheel."

This is true, but with PAS does it really make that much difference? Then again, as the diameter of the steering wheel gets smaller there is less movement of your hands for the same angular rotation of the steering wheel gives less steering feel. For me, there's an optimum steering wheel size, especially for use on bad public roads, where the road surface gives a lot of input to the steering, whereas on a go-kart on a smooth track a small steering wheel is much better, although it requires more physical effort to turn it. I think the size of the Z4M steering wheel is just about perfect for the car. My Z3MC has an OEM steering wheel which feels like it's come off a bus and it's 375mm: it's far too big.

[TomK]

Agreed, much prefer the size of the z wheel to the m3 wheel (also 375mm) and as you say it is a combination of factors that influence the steering system designs.

This seems to put it quite well... "Steering ratio, as well as overall handling and ease of steering, is determined by many factors. The size of the steering wheel was already mentioned. The relative size of the gears in the steering gear, the size and shape of the steering arms, and the angles formed by the linkage all affect the steering action. The percentage of vehicle weight placed on the front wheels and whether the vehicle has front- or rear-wheel drive are also factors."

[tertius]

For what it's worth, I had mine corner weighted when I fitted Clubsports and stiffer front and rear ARBs. The handling is phenomenal now - no understeer at all, easily provoked and controlled oversteer with huge amounts of feedback. My cornering speeds are much faster so my braking points are much later. Heel and toeing down through the gears under heavy braking and turning in is a great pleasure with the uprated engine mounts too. Driving mine back to back on track with my Westfield on semi-slicks makes me want slick tyres and perhaps an even faster steering rack.

I'm a sceptic on the value of corner weighting on a car like the Z4MC, because there are a few variables that can alter the weight distribution after the car has been corner weighted, such as carrying a passenger, fuel load fluid in windscreen washer bottle etc. Do you notice the difference in handling when the fuel tank is full and when it's empty? What are the ride heights at the highest points at each of the wheel arches?

Now that you've got your car at this level, what do you think of the OEM suspension?

That's true of all cars though - you have to compromise somewhere and so you corner weight for your chosen scenario - e.g. mine was done for: driver (me), no passenger, and a full tank of fuel. Don't think the screen wash will change enough to really matter in a 1500kg car ...

[exdos]

That's true of all cars though - you have to compromise somewhere and so you corner weight for your chosen scenario - e.g. mine was done for: driver (me), no passenger, and a full tank of fuel. Don't think the screen wash will change enough to really matter in a 1500kg car ...

I agree about it all being a compromise for the best handling/performance in the dynamic situation. Likewise, I can see in your case, where you've replaced the OEM seats with lightweight seats, and possibly done other weight reduction mods such as exhausts and battery, where weight is mostly removed from the rear, that the car may need to be rebalanced and corner weighting is possibly the solution. My scepticism largely relates to a car where corner weighting dictates that the positive rake angle is lost, which would increase aerodynamic lift, which would then completely bugger up all that corner weighting.

Do you notice a difference in handling with your corner weighted car, between a full and nearly empty tank of fuel? Would you mind giving me the heights from floor to the top of the wheel arch at each corner of your car and what is the total weight?