I GOT TWO QUESTIONS

[Tuck&Poke]

whats so bad about backfiring that everybody wants an exhaust that doesnt backfire and also what is wheel offset and how do they measure it.

[DSC]

well, backfireing is kind of embarrassing.  I dono exactly why else it would be bad except maybe a disruption in airflow is always bad for performance.

I don't remember what offset is for sure, but I think its the distance between the lugs...most likely measured in milimeters...

[240racer]

offset is where the wheel mounting plane is relative to the center of the wheel.  Search forum or check out tirerack.com for lots more talk on the matter.  

Backfiring is caused by unburned fuel in the exhaust.  It usaully happens at closed throttle and high rpms because the engine is getting more fuel then it is burning and the hot exhaust makes it finally burn or in other words explode.  Isn't really a bad thing unless it happens a lot and wears a hole in your exhaust.  However, it is a sign that you are running a little rich, which is caused by a lot of stuff.  You just might need tune up junk like plugs and oxygen sensor or somethinge else it's hard to tell.  But it pretty much is a sign that things aren't prefect, but they are definatly driveable.
Adam

[Tuck&Poke]

now wait if your wheel is offset wouldnt that mess up the lugs cause oh dammit is there like a joint or someting betweent the rim and the hub?  i just dont see how the wheel can not be parallel to the hub.  i always though backfiring was kinda cool i do it in my go kart all the time.

[LanceS13]

The wheel is parallel to the hub...I think you're somehow creating some weird conglomeration of offset and camber in your head.
Offset is how deep into the rim the hub attaches. Take the center line of the rim...3.5" into a 7" rim....that's 0 offset; the mounting surface is right in the center line of the rim. Adding offset would push the mounting surface closer to the outward face of the wheel. Negative offset, which is pretty rare, pulls the mounting surface in towards the car.
Click here (http://www.tirerack.com/wheels/tech/offset.htm) for a picture and more explanation.

(Edited by LanceS13 at 9:51 pm on Feb. 21, 2002)

[Tuck&Poke]

thanks lance i get it.  now how about camber...wanna explain that to me.  i know what it is but how does it...work?

[Jeff240sx]

Camber is more for agressive driving.  You'd want a large negative camber.
Think of a tire straight up and down.  That is zero camber.  When you lean the top of the tire into the car, that is negative camber.  My '96 240sx has -1.6* to -1.9* camber span, to be in factory specs.
If you have a high camber, the inside tire, rather than lean into a turn and loose part of the grip patch, will lean, and even out the tread to make a full contact patch.  
Whereas if you have no camber, and take a corner, your inside tire will roll onto the very outside of tread, loosing the grip patch.
This is really difficult to explain.  Mabey someone else can help me.  Or, mabey you understand??
-Jeff

[LanceS13]

Actually it's the outside tire it helps the most, since it does the most work due to the weight  transfer of taking the corner.
Negative camber is where the wheel tilts into the car at the top.
It is used to optimize contact patch when the tire begins to roll under cornering load. Too little camber and the inside edge of the tire will be lifted as the tire rolls to the outside, reducing the contact patch. Too much and you get premature wear on the inside edge...way too much and the outside edge doesn't tough the pavement even under hard cornering.
This isn't the best example, but it is a similar concept: stand straight up, legs directly under you (no camber). If somebody pushed you from the side (cornering load) you would likely fall over if you were pushed hard enough (spin out if take a corner too fast). Now stand with your legs spread a little to each side (negative camber). Now it would take alot more force to push you over because the angle of your legs is bracing you (you can handle more cornering load; go faster through the corner).

(Edited by LanceS13 at 10<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>6 pm on Feb. 21, 2002)

[transient]

What about some of these GT cars that i've seen that tend to backfire quite a bit?

[DSC]

Wow! I was way off! Just when I think I'm starting to know stuff (this is just one of many things) I realize there's a ton more. I think for every 1 thing i've learned in the past 6 month, I've found 10 things I know absoutely nothing about. Keeps things interesting tho...

Edit: this for example! &nbsp;<a href="http://www.tirerack.com/wheels/tech/torque.htm" target='_blank'>http://www.tirerack.com/wheels/tech/torque.htm</a>

(Edited by DSC at 10<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/wow.gif" border="0" valign="absmiddle" alt=':0'>6 pm on Feb. 21, 2002)

[Gismo R]

Basically, to understand what camber does is just imagine taking a turn that has a certain radius and is banked at a speed of 40mph. Now imagine taking the same turn, only it's not banked at all, at the same speed. The negative camber sort of pushes against the centrigal force thats created by the car taking the turn.

[wav399]

Yeah my car is backfarting quite a lot lately and I have new bosch platinum 4+ plugs and had a tune up from nissan. &nbsp;Does this mean that the exhaust is not the problem then? &nbsp;But it is something else?