86 Rims

[ke70dave]

if you keep the same rolling diameter (difficult to do on larger wheels, need to get crazy low profile tyres) then im pretty sure the ability to spin them doesnt change, and may even be "easier" to spin.

the arguement being that on larger wheels there is more weight towards the outside of the wheel (moment of inertia is changed)

however if you use light weight 16/17" wheels (NOT rotor grids) but SSR's or *insert light weight wheel*

and since you would need such a low profile tyre, thus less weight towards outside of wheel, then there is a chance that using the larger wheel/tyre combo may have a less moment of inertia, and thus be "easier" to spin.

i cannot confirm this, but it would be an interesting experiment to do.

[sundee]

Brave 2nd post. lol

i like what your saying dave, but wont an increased rolling diameter require a larger initial force to gain the same movement?
also keeping in mind that unless u spend big $$ on wheels your gaining weight aswell

[ke70dave]

it all depends on the the Polar moment of inertia.

(Polar moment of inertia is a quantity used to predict an object's ability to resist torsion, in objects (or segments of objects) with an invariant circular cross section and no significant warping or out-of-plane deformation) stolen from wiki.

which is a quantitative measurment of the "ease" of turning an item with a torque applied.

this value is difficult to calculate for a complex cross section of a mag wheel, with spokes etc. easily done with a 3d model though.

it is all about the placement of the mass within the object in relation to its position relative to the centre of the rotation. this is important for what you said sundee as if the wheel is "light" and thus there is less mass on the "larger diameter" then it may be the same as having a larget mass with a "smaller diameter" may have the same effect, thus the change to polar moment of inertia (ease of spinning) is negligable.

a common example we are all aware of, take a broom for example. grab hold if the end with the stick and try and spin it around with your wrist (like a fire twirler) now grab hold of the end with the bristles on it, and try and spin it around with your wrist. you know that this is going to be "easier" since the mass is closer to the centre of rotation.

a small mass further away from the centre of rotation can have the same effect as a larger mass closer the the centre of rotation.

now this is a little of track, but what im trying to say is that simply saying "bigger wheels are harder to turn" is wrong. but like you said bigger light wheels are going to be expensive....

edite with more info:

been chatting with a guy from the office here, and he tells me there there is hardly any material in the sideall of a tyre. the bead of the tyre makes up a fair percent of the weight with alot of wire and rubber, and of course the tread contains alot of high tensile wire with alot of rubber.

so by moving from a 14" to a 16" wheel, the bead and of course the outer "rim" of the wheel is moved further away from the centre of rotation by 1"

so it would seem that my initial thoughts are wrong, mainly due to the fact i overestimated the amount of material in the sidewall that would be lost by using a lower profile tyre.

so it would seem that that changing to a larger wheel/tyre combo is detromental to the polar moment of inertia (and its "ease" to turn. but larger wheels do allow bigger brakes and with a reduced sidewall come with reduced sidewall flex.

so like most things its a trade off.

[Sam-Q]

A 205/40/16 is within 1.3% of the diameter so virtually the same and should be readily available.

[sundee]

GO dave! good read fella

[Ham86]

cheers guys.
it also dosn't have a AC can i get one installed or is that to hard and wont fit or somecrap

[squish_m8]

I'd go for the somecrap option.

you can do just about anything you just need to spend the $$$

[Sam-Q]

did you do a search on that?