Flagg

Hi,

I reciently had new autocross tires put on a second set of wheels. Those wheels are now on the car, with the street wheels against my garage wall.

I often change my wheels (autocrossing vs street use). I don't remember if this was in the manuel or what - but I am always very careful to put the wheel lock on the wheel stem with the hint of red on it. That is the stem OPPOSITE the tire valve. For some reason I thought that was important.

When I got my car back home yesterday, I realized that all 4 wheels were mounted different (only with regard to the location of the wheel lock, vs the valve stem).

Should I jack the car up this weekend, and fix it - or does it really not matter at all?

Anyone know???

Flagg

Colin 90 C2

It matters only if you have the 17" wheels.

Tom W

I read the valve stem opposite the stem in the manual (and lock opposite the stem) and have always been puzzled. The wheel is balanced with the stem in place - what possible effect could the mounting have on any aspect of the car's mechanics? It's a moot point for me as my bolts have all been replaced (no red indicator is present anymore) and I use steel lugs (no lock).

Flagg

Colin 90 C2,

I do have the 17" wheels.........can you explain why it matters? Just out of curiousity? I guess I will be fixing it this weekend..........

Flagg

Christer

John Boggiano

I believe the only reason it matters is consistency...

If you always mount the wheels the same way in relation to the hub then, if you develop a problem with balance, etc., you will eliminate the variables introduced by refitting the wheels differently once removed.

Did that actually make any sense?

springer3

John nailed it. The red mark is simply to preserve the wheel placement relative to the hub. My previous 911 balanced better after the shop experimented with rotating one rim relative to the studs. Something was evidently slightly off center, or possibly the wheel and the hub were danaged. The early cars did not have the red mark, but the shop put one on just to make sure the wheel got put back on the same way. It probably makes no difference most of the time, but staying consistent with something known to work is a great idea.

JasonAndreas

Did the factory balance the tires with the wheels on the car?

Flagg

I don't know the answer to that question.

Actually I guess I don't know much about ballancing tires. I thought the wheels were ALWAYS ballanced off the car with a machine that rotated the wheel......then when the wheel was perfect off the car the car it could be mounted on the car......

My red dot on the wheel stems, by the way, are almost faded away. I have to hit it with some more paint one of these times I change wheels.......or else this will all be a moot point!

Flagg

Flagg

Can anyone explain the process of ballancing a tire and whether it is done on or off the car???

Thank, Flagg

Tom W

It's done off the car.

It can be put on a fancy machine and spun, with the machine measuring the forces and basically telling the operator where to add weight (and how much) to balance the wheel. I believe this is (or used to) referred to as a dynamic balance and is by far the most common method. The wheel can also simply be put onto a stand with a bubble level and balanced that way (a static balance).

DarrylH

OK, so I'm confused - not uncommon.

Regarding the red-marked stud, the manual for my 90 C2 Coupe says:

When fitting complete wheels, make sure that the color-coded wheel bolt is nearest the wheel valve. Always install the lock-up wheel nut on the color-coded wheel bolt. Before removing a wheel, always mark its direction of rotation (sic), e.g., FR, FL, RR and RL. This precaution will ensure that the wheels can be refitted in their original positions, avoiding imbalance.

But surely a balanced wheel & tire doesn't know where it is relative to the bolts, and presumably it couldn't care less. It seems a complete crapshoot whether whatever this is trying to accomplish would work out correctly just by virtue of having the valve stem and red bolt in any kind of relationship. If there's some rotational irregularity in the system other than that of the wheel and tire (in the rotor, or hub, or half-shaft or...) then it can't matter how the wheel/tire is fitted, assuming it's correctly balanced. I think the red stud thing is just to drive us crazy, and make us even more **** than we already are.

As you guys say, just my $0.02!

Darryl

Flagg

I swear that my manual says the opposite about where to locate the red wheel bolt............I will have to check. Maybe it is just to drive us crazy

I still think I am going to fix mine to the way I have always done it........I guess I am crazy!

Flagg

springer3

The reason it is important to get the wheel back on the same way it was balanced is that manufacturing tolerances are such that the wheel is not bolted on with exactly the same center of rotation at every stud position. If you change the center of rotation even slightly, it can cause imbalance. The wheels leave the factory centered and balanced, and they just want to make sure you don't cause a problem by changing the wheel position. I agree in most cases it makes no noticeable difference, but there are certainly cases where it makes a big difference.