I spent a good deal of time yesterday (2.5 hours) searching and disecting anything I could find on offset. to be honest, I didn't even know what it was. now that I have a better understanding of what it is, I'm having trouble understanding what it does and how its relation to wheel and tire size affect a car in certain applications. this more specific info I could not find enough of, or more pertinently, what I wanted to hear/read.

So, in what I believe is the first filter, I'm a 4th gen'er. Si, 5-speed. Secondly, I'm riding on a stock suspension at stock ride height. I've read that for a 4th gen, stock offset is 55mm for the stock 205/15x6.5/55. Half of my question is the noob standard, "if I buy a 16" rim with a 40mm offset, will that be ok?" But really, I want to know why or why not, and in which ways will it affect my car and its handling and traction.

So, if I buy the (mugen rip-offs for the budget-minded conscious) 16" rota C8's with a 40mm offset, and fit them with 215-225/45-50 tires, in which ways will this affect me, and why? (will I really notice the difference in traction by having 10-20mm more of tread on the ground? how much more violent would a 45-50 tire be than the stock 55? am I just wasting my time trying to appease the aesthetic?)

Nearly all of my driving is work commuting (not freeway, some stoplights, some twisties). I don't race, I could care less about the quarter mile big dick-a-thons, I don't auto-x (but someday I really want to), and I love revving the shxt out it. Ideally, as funds become very slowly available (I'm in the military, not an NCO, married, and have a mortgage), I would like to stiffen the suspension, reduce body roll, and not lower the car more than 2" at the most. so with the questions previously asked to the cars present situation, how will all those dimensions be affected 1.5" lower?

please don't flame the inquisitive mind. hopefully this sets a new standard for noob help questions (I did use the search and found it mostly useful) and hopefully I can get a good technical, informative discussion or response....

San Dimas High School Football Rules!

 

If you are looking to upgrade to 17 inch wheel you can get away with 45++ offset and tire size of 215 40 series rubber.

 

no, it's most definitely going to be a 16. I understand this may not be so popular, and maybe I am wrong, but I think a 16 is a good compromise between the performance of a 15 and the aesthetics of a 17. also, I have another 353 days until I am OUT of the army and back in socal where I belong. the roads in the fort campbell, kentucky/tennessee area are not that great and I would be worried about damaging the rims with a 40 the way I drive.

so, more specifically, for discussions sake, the difference between a 45 and 50 is what I am considering, as well as the difference between the stock 205 to a 215/225.

 

Ahh whats up soldier.. I would go with a 205 45 16 on that.. Oh kentucky huh? i remember those days.. Well I dont see anything wrong with a 16 inch rim and if you go with the rotas I think they will look good. Performance wise you wont lose anything.. But here is pic of my lude if you decided to go with 17 inches Hey soldier if you have any questions about ludes just send me a PM.

 

The shorter the sidewall the quicker the steering response and the less comfortable the ride.

I run 225/45/15 with near stock offset and 2 inch drop with no rub. I have friends that run 40 offset and can only run 215 due to rub. And yes the extra 10 or 20mm does make a difference.

I believe that staying as close as possibly to original offset as possible is best because Honda designed the suspension with that offset in mind.

On the other hand, I have a friend that has a 5th gen with stock height and runs RX7 rims with 245 tires. Going from 215 to 245 took 5% off his laps times.

 

i would run a 205/50-16 with a 16x7 40mm offset.......that will be a perfect fit

 

16x7 40 offset - https://honda-tech.com/zerothread?id=636077

not my car, but they are the rims you are looking at.

 

wow, I knew I had good taste.

holy phuckin hot shxt man. minus the lip, it's hard to believe I'll look like that in a month. thank you Daboi630, I won't be able to sleep for a week....

After 20,868 miles since March (when I got back from Iraq), I guess you could say this is my first "mod," other than audio.

::+4 points in pride and extreme satisfaction::

 

If you went with 18" wheels would a +50 offset fit? im looking at a set of racing heart c4's for my 5th gen..and i dont know if they will fit (in the rear) any one know?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by fenominal &raquo;</TD></TR><TR><TD CLASS="quote"> thank you Daboi630, I won't be able to sleep for a week....
</TD></TR></TABLE>

lol.... but to keep this on tech.

the lower your offset - the wider your track. i believe, don't quote me, that running a low offset will do harm to your wheel bearings. honda made the car to run a certain offset, but i do not know the side effects for running a low offset for an extended period of time.

 

Offset positioning which is the distance between the hub mount and the center of the tire, influences handling. Wheel offset should not be so severe that the tire extends beyond the body of the vechile.
Negative offset-moves the wheel away from the vechile. The advantage is increased vechile track and road handling. However the more negative the offset the greater the force on the hub, which can prematurely wear rolling parts and suspension. Too negative an offset puts the tire beyond the body.
Positive offset- Front wheels usually have positive offset. Front wheel drive vechiles have high positive offset wheels which allows for proper clearance of the hub assembly within the wheel well. On Front wheel drive or All wheel drive it is important to keep the front axle offset to factory designed specifications or very close to them.

As for tire size the lower the aspect ratio or sidewall height the harsh your ride will be but your steering response will be quicker due to the added stiffness in the side wall.

As for figuring out an acceptable size tire and wheel use this formula
take your tread width i.e. 225/205/ etc. i used 205/55r15 for this example , then divide by 25.4(always standard) = 8.07 take this number and take the aspect ratio percentage of the tire your thinking about which for me is 55%, so 55% of 8.07 is 4.43 than multiply this number by 2 and add the wheel diameter which is 15 so you get 23.87 which is the overall original diameter of tire and wheel on a stock 4th gen lude si. So whatever combo size tire wheel you choose first do out this process and compare it to the stock diameter, a change of 5% is acceptable either up or down.

Hope this helps

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BlissSkr &raquo;</TD></TR><TR><TD CLASS="quote"> Offset positioning which is the distance between the hub mount and the center of the tire, influences handling. Wheel offset should not be so severe that the tire extends beyond the body of the vechile.
Negative offset-moves the wheel away from the vechile. The advantage is increased vechile track and road handling. However the more negative the offset the greater the force on the hub, which can prematurely wear rolling parts and suspension. Too negative an offset puts the tire beyond the body.
Positive offset- Front wheels usually have positive offset. Front wheel drive vechiles have high positive offset wheels which allows for proper clearance of the hub assembly within the wheel well. On Front wheel drive or All wheel drive it is important to keep the front axle offset to factory designed specifications or very close to them.

As for tire size the lower the aspect ratio or sidewall height the harsh your ride will be but your steering response will be quicker due to the added stiffness in the side wall.

As for figuring out an acceptable size tire and wheel use this formula
take your tread width i.e. 225/205/ etc. i used 205/55r15 for this example , then divide by 25.4(always standard) = 8.07 take this number and take the aspect ratio percentage of the tire your thinking about which for me is 55%, so 55% of 8.07 is 4.43 than multiply this number by 2 and add the wheel diameter which is 15 so you get 23.87 which is the overall original diameter of tire and wheel on a stock 4th gen lude si. So whatever combo size tire wheel you choose first do out this process and compare it to the stock diameter, a change of 5% is acceptable either up or down.

Hope this helps </TD></TR></TABLE>

all i can say is...wow
very nice, i just only wish i had at least an i.q of 30 so i could understand it.

 

BlissSkr, I followed your example, but in your computation with your numbers, I got 18.63 instead of 23.87. With the measurements I calculated at 205/50/16, I got 20 even. Multiply 18.63 times 5 and subtract that number from 100 (20 even times 5) and I get roughly 7% for the measurements I chose. Think this could matter for the worse?

 

205/25.4=8.07(50%) =4.03x2=8.07+16=24.07
orig 23.87 + 5% =25.06 your in the clear with 205/50r16

 

http://www.whalentire.com/

go to the tire sizes, plug in the numbers and viola

 

very impressive I love numbers and worked mine up I run 205/40/17s was thinking about switching to 215s now I believe I will since this formula yields a ration which is within .01 of the original diameter numbers I appreciate it a lot

 

the finest n00b post ever.

impeccable grammar, clearly stated question, kudos, sir.

bliss explained what offset is, and a rough formula for tire sizing (my preferred calculator is found at http://www.miata.net/garage/tirecalc.html) but the offsets constraints are generally these two factors:

fender rub and suspension/inner wheelwell rub.

if you don't have enough offset, the tire will be flush or protruding from the wheel well, under suspension compression, the tire will rub the fender. Enough of this, and either the tire or the fender will become damaged. Most people address this by "rolling the fender" which is a technique that creates extra clearance by physically altering the metal in the fender. The more expensive route that race teams and people with lots of money use is to use a whole new "widebody" fender that will not rub the tire.

If you've got too much offset, you'll find that the tire rubs against the trailing arm which is the arm that connects the upper and lower control arms, or will rub the inside of the wheel well when you turn the wheel. in this case, the tire bears the brunt of the damage.

so when considering a wheel, it's important to consider all 3: tire size+wheel diameter, offset, wheel width. +55 offset on a 6.5" wide wheel does not = +55 offset on a 8" wheel in terms of compatibility with our cars.

Lowering one's car also usually cuts down on the available clearance, so rim/tire selection becomes that much more constrained, but there's a database over at preludeonline.com that has it pretty well documented on what will and what will not fit.

General rule for 16"x7" wheels is 215/45/16 tires with an offset between 43 and 48. Of course there are exceptions, or freak cases where strange things like 16x7 +38 rims with 215/55/16's have never rubbed.

For reference, i've run 15x7 +45mm 205/50/15; 17x7 +42 215/45/17, and 17x8 +48 215/40/17 and they've all fit. Though when i get wider tires for my current set of 17x8's (probably a 235/40/17 or a 225/40/17 if they ever make a decent set in that size) i may or may not have clearance issues (too much offset/width).