OK, so this really got me thinking (not always a good thing). My MA sent me a MINI technical bulletin regarding the new (to the US anyways) JCW sport suspension.

Here they make a big song-and-dance about how you, the customer, can select the optimal set of springs (to complement their customized shock absorbers) based on the actual weight of your particular MINI to optimize the suspension performance. So, how much of a difference does this make?

I'm not so much interested in the JCW kit per se, but I was wondering how much of a compromise the stock suspension set-up is on the MCS. For example, if you order the sport package with the 17" S-Lites and, for arguement's sake, the run-flat all seasons, you're looking at a wheel/tyre weight of around 55 lbs If you stick with the standard 16" X-lites + runflats, the wheel/tyre weight is around 40 lbs.....a 60 lbs difference just from the wheels/tyres. So, do they change the stock springs and/or shocks depending on whether you go for the X-Lites or the (much) heavier S-Lites....I have no idea, but I doubt it.

Also, what if you run a very heavy wheel/tyre package for the winter (say S-Lites + All-season RFs @ ~55 lbs per corner) and then change to a very lightweight package for the summer (say 16" SSR comps + non-runflats @ ~33 lbs per corner). How would the optimized JCW set up (or even the stock suspension) cope with such a weight difference? Would it be better to optimize the springs/shocks for the heavier or lighter wheel package or would it end up being be a trade-off with neither performing optimally......or is this kind of weight difference inconsequential to suspension performance ?

What do you guys think ?

 

I think you are looking at 2 different issues. ... I think I understand what you are asking...

Since the actual weight of the wheel and tires are already transferred to the ground, the tire/wheel weight changes you talk about only alter unsprung weight for acceleration and braking and does not have much to do with
which springs/struts you choose.

 

I think tuning the springs and the shocks for the sprung weight (as
opposed to the wheels and tires and part of the moving suspension parts)
is more important in terms of selecting those items.

On the other hand, a lighter wheel/tire combo will perform better than a
heavier one, both in the power needed to get it rolling and transient
response on less than smooth roads, but you probably don't need a
different shock or spring to reap the benifits of a lighter wheel.

 

Thanks guys..........so JCW are probably talking about whether or not you have a sunroof fitted (or roofrack ); can't think of much else which would affect the "sprung" weight in a big way ?

 

Of course the weight of the wheel will affect how the suspension works and how it rides. But how can anyone really answer this without testing different setups?

I run a light wheel/tire setup during the summer and stock wheels and RF's for the winter. Big difference in weight, tires, and ride! Huge, in fact.

Summer: Kosei K1, 215/40x17 with Kumho MX tires
Winter: S-lites, Pirelli RF in 205/45x17

I run high pressure in the MX's due to the low profile, and with the suspension changes on my car, it is stiff and rides pretty damn hard. I just installed the stock wheels yesterday, running 32lbs, and it feels like a different car. Ride is MUCH better.

While the car works really well in summer garb, what am I giving up with the winter setup? I give up the hard ride and then who cares? I just won't drive it as hard with the winter gear.

 

To get everything out of it you'll need the actual weight of your vehivle. Here's how I do this on my Focus:

I take off 1 wheel, and weigh it. multiply by 4, and add 30%. This is your apprimate unsprung weight.

Now, take the car to your local dump/transfer station or truck complaince center, and ask them nicely if they will weigh your car. Most places like a transfer station will do it for free if its a light day, because it takes them 10 seconds. They will give you a weight (should be around 2600).

Then, go home and weigh yourself.

Now, complete the arithmetic:
(TOTAL VEHICLE WEIGHT - your weight - unsprung weight) + 10%

This is the 'sprung weight' of your car in 'ready to go' form. Choose springs based on this weight.

 

What about the calipers and rotors?

 

Right there, silly! :smile:

 

>Of course the weight of the wheel will affect how the suspension works and how it rides. I run a light wheel/tire setup during the summer and stock wheels and RF's for the winter. Big difference in weight, tires, and ride! Huge, in fact.


Ok, now I know for sure we are talking about 2 different issues.

1)You say: The weight of the wheel will affect how the suspension works.

For changes in dive due to changes in braking characteristics? For changes in squat due to changes in acceleration dynamics? ok,
possibly.....I've never heard of people changing suspension setups to 'match (?)' the weight of the wheels, nor have I ever done that myself.


2)You say: The weight of the wheel will affect how it rides.

Really....?!? I thought ride was measured by how stiff or how soft the
suspension and tire, etc setup is... I've yet to hear the WEIGHT of
the wheel actually altering vehicle ride.


3) You say: You run a light wheel/tire setup during the summer and stock wheels and RF's for the winter. Big difference in weight, tires, and ride! Huge, in fact.


But you don't change spring/strut setup when you change wheel setup do you? Isn't that wat gr8britwjh is asking?

 

Man, I'm not sure if we're talking about the same thing.

I didn't mean to imply the weight changes the mechanical action of the suspension. But weight does affect the motion of the wheels, ie. how much energy it takes to move a tire, up, down, acceleration, and brake energy to slow down the rotation, etc.

A heavier wheel may require a different compression and rebound damping rate, maybe even different springs, especially if we looking for tenths of a second (maybe even seconds) in lap times. The need for such changes on a street car is probably a moot point in most cases unless you're trying to refine how the car rides, not so much how well it sticks in corners, etc.. A lighter wheel will be more compliant to the road surface, all else being equal.

A heavier wheel requires more energy to move (and to stop movement). Of course that could affect the quality of the ride - but, a matter of degree and subjective opinion. If a wheel is too heavy or too light, it might even affect how well the care handles overall. A heavier wheel could also affect geometry, since bushings, struts, et al are deflected to a greater degree.

No, I don't change anything else because when running the winter setup, I don't care if it does not handle as well. My car is set up to work best with the summer wheels/tires, and by "work best" I mean to handle better, and ride quality is not so important. The ride quality is better with the 205/45s with 32lbs of air compared to the 215/40s with 40lbs - for sure! LOL. The 215/40s turn fast and hard, but they rattle your teeth. The winter setup is a much more comfy in that regard. The higher weight of the winter setup probably helps in comfort a bit, too. How much? I have no way of knowing at this point without experimenting .

 

>Man, I'm not sure if we're talking about the same thing.



hehehe. I think that I don't think we are talking about the same thing.

 

My brain hurts (he mutters using a Pythonesque voice ).........