Tire and rim weight

[Olorin]

Hi guys,

I've got standard rims and runflat tires (205/55 both front and rear) on my E90 320i. Just wanted to know how much weight I could save by changing rims and tires. 5 kg's/10 kg's ?

BMW tell me that if I want new tires and rims that I NEED to get them from them otherwise my motor plan is canceled. I asked them yesterday about color coding my handle bars and same story, I need to have them sprayed by a BMW approved company.

Just need opinions on the rims and tires. I've got 16's at the moment. I think I might want to go 17's with 225. If I go 225's all around, would that be doable or will this compromise performance ? There is also the space saver wheel that I'll need. I just want to make sure that I save weight vs what I've got currently. I need the lightest rims and tires I can get as everyone tells me that it will improve performance since I've only got a 4 cyl engine.

Suggestions would be appreciated. Thanks.

 

[moranor@axis]

you can get any tire that is approved by bmw you dont have to get it from them...

im not sure but wont 17" be heavier than 16" unless you go for a light weight rim(which probably wont be approved by bmw)...

you could save weight by changing to non run flats and as far as i know bmw do have them on the list

 

[Olorin]

See, the thing is that I definitely do NOT want run flats. I have to get normal tires. Everyone tells me that they are far more comfortable and I'll also have better grip plus they are lighter. Also cheaper.

 

[moranor@axis]

run flats are like CATs they have to go...

 

[Sankekur]

Just remember that really lightweight wheels will be really expensive, and you won't get any real gains from it unless it is part of a larger scheme of weight reduction ie cf panels etc.

 

[msm]

run flats are like CATs they have to go...

Agree. When I had the Mini, I compared the weight of a normal tyre to a runflat ... the runflat was almost twice as heavy :shocked:

 

[moranor@axis]

damn i did not think that would be that heavy...:dropjaw:

 

[whattingh]

source

Although Run-Flat tires may be 10~15% heavier than standard tires, eliminating the need for a spare tire reduces overall weight, and as a result, there is very little impact on either driving performance or fuel economy.

You might save weight in total by not have a spare but you have more unsprung weight.....

 

[moranor@axis]

its also rotational weight which is very bad...

the 10~15% is also claimed by people wanting to sell run flats so my guess is in most cases it will be 15% or more

 

[Rennzport]

some advice.. Get a different dealer, since they are telling you everything you touch will cancel your mplan.. Load of crap.
Just a question.. Is this your 1st bmw?

 

[Sankekur]

its also rotational weight which is very bad...

the 10~15% is also claimed by people wanting to sell run flats so my guess is in most cases it will be 15% or more

Yup, rotational inertia increases by the square of the distance that mass is from the point of rotation, so heavy tyres will have a pretty big effect on the rotational inertia of a wheel seeing as they are right on the outside.

And a increase in rotational inertia translates directly into a reduction of rotational acceleration for the same applied torque.

Moral of the story, get rid of run-flats

 

[applehero]

I have read that the runflats are 50% heavier. It seems like BMW have compensated for this by making lighter rims, fitted to runflats. Have a look on BMW Fans

Runflat
16 Inch Rims: 9 kgs
16 Inch

17 Inch Rims: 11 kgs
17 Inch

Normal Rims
16 inch Rims: 10.5 kgs
16 Inch

So rather keep the rims... :thumb: