Spare & M Mobility System...

[JT-KGY]

Just read Roundel... and discover that BMW is removing spares
from all new M Coupes and instead includes something called
M Mobility System... bascially a self tire repair kit...

I always wanted to remove the spare out of my car to save
some weight (E36 M3 97)... but heard from others that by doing
just that will compromise the safety from rear collisions...
But now BMW is doing that themselves (I know it's a different
model)... I start to question the validity of that statement
regarding safety...
Does anyone have document or some sort of statement from
BMW that removing the spare will really compromise collision
worthiness of our car??

Also, I hope that BMW could pass the savings to the customers..
one full size M wheel spare + tires... that should effectively lower
the vehicle price around $800???

Nah, dont think that will happen...

[Neil]

M Coupes have never been supplied with a spare. Because of the dual exhaust and the battery that resides between the mufflers, there is no room. For that reason, they came with the M Mobility System and lifetime roadside assistance.

[TechnoViolent]

The e46 M3 lacks a spare also, I think. However, the lesser e46's have a full spare. It is my undrstanding that although bmw designs its cars with the spare as a functional impact absorber of sorts, the spare is far from critical. One would think that bmw would warn owners to keep a spare in the trunk, or would structurally reinforce its "spareless" ///M models, if it were in any way vital to crash worthiness.

I replaced my spare with a can of fix-a-flat. It weighs about 50lb less. Coupled with my UUC exhaust, I've lost about 80lbs.

I also have "road side assistance" in affect.

[Stylin]

OK.. taking out ur spare tire does reduce wieght.. but losing 50lbs in the rear.. doesnt that mess up the whole 50/50 wieght distribution..?? Does losing that weight effect launching and wheel spin??

[TechnoViolent]

Originally posted by Stylin
OK.. taking out ur spare tire does reduce wieght.. but losing 50lbs in the rear.. doesnt that mess up the whole 50/50 wieght distribution..?? Does losing that weight effect launching and wheel spin??

I don't drag race, so I would not know about launch effects. I think it helps handling via increased mass centralization. You don't want mass hanging outside the axles. Toss a couple of 40 lb bags of dog food in the rear-most portion of your trunk and go for a spirited spin. I'll bet you like it better without the dog food

[Stylin]

But ur not increasing mass centralization.. ur removing precision measured 50/50 weight distribution. ur not adding anything to the center of the car. Less weight in the rear has to equal to breaking the rear wheel easier...: back to the original question. I'll probably like it more coz u are removing weight out of the car of course.. but does it have any handling or adverse effects?

[TechnoViolent]

Not only reduced weight, but reduced weight at the poles of the car. Generally, it is best to keep the weight within the axles (the whole idea behind mid-engine sports car design), reduces polar moment of inertia. and thereby allows the car to change direction quicker/easier. kinda like trying to spin a bar bell vs. a medicine ball.

[Zippy M3]

Originally posted by Stylin
But ur not increasing mass centralization.. ur removing precision measured 50/50 weight distribution. ur not adding anything to the center of the car. Less weight in the rear has to equal to breaking the rear wheel easier...: back to the original question. I'll probably like it more coz u are removing weight out of the car of course.. but does it have any handling or adverse effects?

I wouldn't really worry about the weight distribution. All the good/great M3 autocross guys remove the spare. Spoke to Bob Tunnell himself and he says there are all sorts of other variables to consider that can neutralize and alter the handling that you should be more worried about. (Tires size, tire pressure, sways, suspension, toe, camber....etc.)

[EuroKRN]

Well, I removed my spare because I put a system in.. so I lost the 40-50lbs from the spare, but added in about 100-150lbs for the system.. =( I guess my JL subs will act as impact absorbers in the case of a rear end collision (OUCH!) then again, 90% of all rear end impacts are the fault of the car in the back so I guess they can buy me a new system...

Don't all M3s come with lifetime roadside assistance? Or was it just the 99's?? cuz I'm pretty sure I got the lifetime roadside assistance (towing) without paying extra for it.

I'm gonna have to get some of that self-repair stuff. What's the best brand? And how exactly does it work?

[Stylin]

so how many of u guys run without the spare?

[gerry_miranda]

I dont have a spare and am thinking about getting the mobility system. It should be good unless you are running firestone and the tires come apart on you.

[tlp-96M3/2]

What exactly is included in the "M Mobility System"??? Can it be purchased directly from the dealer??? How much$$$$ I really like the idea of sheding an additional 50lbs!!!! I can totally feel the difference in my car between a full tank of gas and an empty one....not too mention between a passenger and no passenger. Perhaps it will eliminate a lot of the acceleration squat that I get from the stock springs also.

[Zippy M3]

Originally posted by tlp-96M3/2
What exactly is included in the "M Mobility System"??? Can it be purchased directly from the dealer??? How much$$$$ I really like the idea of sheding an additional 50lbs!!!! I can totally feel the difference in my car between a full tank of gas and an empty one....not too mention between a passenger and no passenger. Perhaps it will eliminate a lot of the acceleration squat that I get from the stock springs also.

There's a great write-up of the system in this month's issue of Roundel.

[tlp-96M3/2]

I just checked with my local dealer and the M mobility system kit is approx. $145.00. It's bascially and an air compressor with an integrated sealer that is refillable. I'm thinking of buying it and ditching my spare. I have a staggered wheel setup which is yet a another reason to leave the spare in the garage.

Does anyone know how much the M mobilty system weights???

[Josh///M3]

I bet pacific bmw has it for like $100.... 1-800-909-PARTS

Later,
Josh

[TechnoViolent]

The M Mobility system is a glorified can of "fix-a-flat". Don't waste your money. It is just an electric air pump w/ sealant dispensor in one. It is a temporary fix to get you back on the road to the nearest service station. "fix a flat" does the same thing, but uses an aerosol can filled with a compressed gas and sealant - costs 5.99.:p

[C///M3]

I want to remove my spare aswell; to offset the added weight of my system. But I keep hearing about the safety issue. If anyone finds out if it is part of the rear impact protection, PLEASE TELL US.

Also, has anyone ever actually used Fix-A-Flat? I have a can thats about 2-3 yrs old just sitting in my garage. Wonder if it actually works and if it expires. (gotta go read the can)

[leemoney]

My friend used a fix-a-flat spray can device (one of the cheap ones) and he said it worked perfectly. He had no damage to his 17in rims. He took his car to the shop immediately of course.