BACK TO BASICS: WHEEL OFFSET? (Pictorial Explanation for Offset Novices)
 

Not sure if this has ever been covered here PICTORIALLY. But if not, well, this might help some with the concept of WHEEL OFFSET.

Note/Warning: Most of you on this forum can probably skip this as WHEEL OFFSET is something that most know and understand. But I had these NEW wheels to use as a whiteboard so thought I might give it a shot to help anyone not quite clear on the concept.

For the benefit of anyone who DOESN'T understand wheel offset, this pictorial might help you get a better understanding for when you go to choose a set of wheels for your Z. This pertains mostly to aftermarket wheels but applies equally to getting OEM wheels - as is the example here - to fit the way you might want them.

First thing is the explanation of what wheel offset is:

Offset is the distance that the MOUNTING FACE of the wheel is away from the center line of the wheel.

https://cimg3.ibsrv.net/gimg/my350z....072059c978.jpg

Offset is engineered into the overall suspension design by the manufacturer to account for the different type and physical geometry of the suspension. It is designed in for purposes of steering response (how quickly and how smoothly the car reacts to steering input) as well as for comfort and, most importantly, how the car handles and "feels" when delivered to the end user/customer.

Factory Z wheels are "mostly" +30mm which means the mounting face sits 30mm outboard of the centerline. This amount of offset is engineered into the wheel to provide smooth running as well as giving your Z moderately crisp steering response - given the Z's stock suspension.

Deviating too far from this "could" ultimately cause problems with clearance, bearings, and sluggish steering response but for the most part, a modest deviation (+/- 15mm) will be fine and actually can improve your Z's handling - up to a point of diminishing returns.

That won't be covered here. Suffice to say that you CAN go too far positive OR negative and any gains in performance you got by going for a modest deviation from stock will start to fall off drastically, hence "diminishing returns".

So let's say you bought a car with a set of aftermarket wheels on it or you want to pick up a set from someone on craigslist or the classified section here.

How can you be sure of what you're getting and/or will they fit and if so, how WELL do they fit? Best way is to actually take a physical measurement (barring casting marks indicating offset on the inside of the wheel - which is actually pretty rare).

Start with a bare wheel, off the car. Get a ruler or tape measure (ruler is better as it's stiffer and will give a more accurate measurement). And find the centerline of the wheel. Mark it with a Sharpie.

https://cimg8.ibsrv.net/gimg/my350z....88eea17a7b.jpg

In this pic, while the wheel is advertised as a 9" wide wheel, the actual width - including the inner and outer lips - is 10" - give or take a few mm as this isn't necessarily a precision measurement and actual measurements will be within a few mm, nothing to worry about.

Note that I marked the center line. (I'll get to the second line in a second.) Note that there's a popular misconception that the center of gravity and the rotational line is or should be at the wheel center line. Nope, pretty easy to see that the center of gravity is going to be somewhere near or in the spoke line of direction, outboard of the center line (and sometimes inboard). Don't concern yourself with this for simple application.

Next, drop a stiff straight edge down along the mounting face and mark the wheel with a second line where the mounting face theoretically intersects the barrel of the wheel.

https://cimg4.ibsrv.net/gimg/my350z....dc1c38179e.jpg

The distance between the two lines is the wheel offset.
https://cimg6.ibsrv.net/gimg/my350z....5fb6b8786c.jpg

You'll note that in this example, the offset measures about 50mm - which is pretty close to accurate as this is a 370Z specific wheel whose claimed offset is 47mm. Close enough for general work.

Note: if you are bothered by this 6.4% difference, you shouldn't be. In practical application, it's negligible. But if you are, you can take the claimed measurement and start the center line measurement from the point inside the wheel rim on each side or by the difference between the claimed width and actual width/2 and start from that distance inwards from the outer and inner lips.

Confused? Yup, meant to be. For general application, just measure outside to outside. ;)

Now take note here as this is why this whole thing came about in the first place. The +47mm offset of this wheel is unsuitable for the Z33 platform (including G35) despite this being a Nissan OEM product - built by Rays, as are all of the Z "sport wheels" - as the mounting face sits too far outwards of the wheel center line (too much positive offset) and because of this, steering response will be sluggish and take away from the driving experience that is the Z33. (It works fine on the Z34 because it was engineered to work that way with different suspension geometry, sizing, etc.)

To make it work for the Z33, a spacer is "required". Let me clarify that... The wheel clears the brakes and suspension without it but again, steering response suffers unless you "restore" the offset to closer to stock or below. (This is due to an alteration in the scrub radius, which I won't cover here either; suffice that a large positive offset is just as detrimental as a "too negative" offset without some pretty serious suspension modifications).

Note in the following pic, I have installed a 20mm spacer on the wheel (for illustration only as this mounts to the hub then the wheel attaches to the spacer). Yeah yeah, some might think, "Mic, that's pretty obvious!" Uhhh, no..... it's not. Trust me, best to write to a lowest common denominator and take the ridicule for sounding so "obvious." :icon17:

https://cimg1.ibsrv.net/gimg/my350z....1fa269e77e.jpg

Note: I do NOT like spacers. So much so that even though my rears could use them and I have a brand new set of 15mm spacers on hand, I chose to NOT use them since the rear wheels already have a "stockish" 30mm offset.

BUT, to use the fronts, it almost isn't an option due to the "huge" 47mm offset and I had to use them to restore something closer to stock wheel geometry.

Now I take a mounting face measurement from the back of the new spacers and transfer that to the barrel of the wheel as I did the original back plane of the wheel. Note the NEW offset is 20mm smaller than the original. The new ~30mm offset from the spacer is what's called "effective offset". Artificial, yes, optimum for performance, no. BUT.... it's pretty close and more neutral vis a vis the stock offset wheels.

https://cimg3.ibsrv.net/gimg/my350z....e656ceac27.jpg

And that's how and why spacers do have a place in the modder's tool chest. It might not be the best solution (buying the proper offset and hub centric diameters is the best) but they work as long as you get quality spacers and install them with as much diligence as you do your own wheels.

So, with that all said, can you see how offset affects the placement of the tire and wheel in the wheelwell and in relation to the suspension?

Here's a before and after set of pics:

Without spacer

https://cimg3.ibsrv.net/gimg/my350z....2b58e162c5.jpg
Note how "sunken into the fenderwell" the wheel sits. This not only looks funky, it hurts performance as mentioned above.


With spacer

https://cimg1.ibsrv.net/gimg/my350z....e0fd7e01f4.jpg

https://cimg2.ibsrv.net/gimg/my350z....d87545710c.jpg

Subtle difference to the naked eye, I know, but if you were standing directly in back (or front in this case) looking down the center line of the tire, you'd see that the "subtle difference" relative to the fender lip is not so subtle. 20mm is fairly substantial when it comes to tire placement.

Anyhow, hope this helps take some of the confusion out of wheel offset. This just touches on the subject but should answer the most basic questions about what and how it helps you set up your tire/wheel combo the way you want it.

Bottom line: the most popular offsets for performance application range from about +15 to +25 or so. There are obviously exceptions to this for those seeking the "flush" or "cambered" look but my advice for best all around performance, one should keep the offset in this range unless you're tracking, stancing, drifting, etc. - in which case, best to consult with others who have or use wheels that deviate from this for "the hot tip". Again, this is just for general knowledge, not recommendation.

https://cimg5.ibsrv.net/gimg/my350z....43b5f9ca65.jpg


Cheers,

Mic

:thumbup: Mic… Great post! Even those like me learn benefit from a good explanation of offset.

_______________________________________
I think a very good wheel-setup for the 350z is…

Front: 9.5” width with a 15mm offset
Rear: 10.5” width with a 15mm offset.

There are many examples of this on the Enkei wheel thread.

Nice write up. So does the whole scenario change when you add a wider rim? Or will a 10mm offset be flush regardless of width?

Ok probably not...

A 8 inch wheel with 10mm offset will be flush... 10 inch wheel with 10mm offset will stick out a little. 12 inch wheel 10mm offset and you need some bushwacker fender flares... Correct?

I purchased aftermarket 18s for my rsx 11 years ago.. I put them on and they looked super cool, but I lost so much performance from the weight I gave them away and never thought about aftermarket wheels ever again.

My touring edition car came with 18s and I can't help but think the car would be so much more happy with some light weight 17s.... Like 17x10s with some 275s back their. But I am kinda a dreamer.

^^ Good information...

Yup... wheel and tire weight can make a HUGE difference. A lower diameter wheel often provides setup that weighs less and provides superior handling and performance.

Thanks Spike, long time no hear from! And yes, those sizes are probably the optimum (and most popular set up for wider stance and performance)! Before I did anything to my cars, I looked at the thread endlessly and figured out what I wanted/needed. Great source of info and pics for anyone selecting wheels, definitely.


Hey DBA, varying widths of wheels will obviously have a different look and stance. What happens though, is if you keep the offset the same - 10mm as in your example - but vary the width, yes, there's going to be a significant difference in how it sits on the car.

But keep in mind that when you vary the width, there will be added width on the INSIDE of the wheel as well.

That's why it's important to know what offset does to both inside and outside edges of the wheel. That's where the Tire Calculator comes in really handy. (Under the Tools drop down at the top of every my350Z page or here: https://my350z.com/forum/tire_rim_calculator.php ). This is the best tool on this site. Any combination tire/wheel can be input and this gives a really good "visual" (in numerics of course) of what your desired combination will do once on the car.

On the subject of wheel weight, well, that's a WHOLE 'NOTHER TOPIC! :o

But yes, big mistake a lot of people make is to NOT take that into account when shopping, sadly. That extra unsprung weight KILLS performance. (Which is why I'm constantly changing up my wheel sets....) :o My 18" Track V.1s at 17.x lbs a piece were/are the liviliest set of wheels I own. None of the sets (5 or 6 sets... lost track! :p) since could compete in giving me the best feel and control of any since, including my Nismo V3s (nor the identically spec'd GT/Track 2s).

That is, until now.... my S-Tunes are 20.x# a piece and that's super light for 19s - especially being an inch and 2 inches wider than my Tracks. This is my go-to now. With the suspension to back up the uptick in tire size, and allowing them to still heat up to a good running temperature, they're a righteous alternative to my Track V.1s. Tested this morning and all I can say is "Thank you Jenny Craig!"

Every wheel set I own now are forged and because of the incredible high strength:weight ratio, I'll NEVER run anything else. Track V.1s are the best bang for the upgrade dollar, wheel wise, IMO.

Nice right up mic! But on the subject of wheel weight, yes your weights 20# a wheels, but since its 19s, the performance will be less than a 20# 18s will it not?

Farther away from the rotating center the bigger effect weight has. Myself, i prefer 18s due to the fact that its a perfect balance of both looks and performance. But like you said, weight is another subject.

As far as handling goes, offset plays a role, but i consider it as the BOTTOM of the list. The tires themself is alot more important. I rather have ill offset and good tires, than proper offset with bad tires.

Imo, my listing, other than suspension compnents. I would rate, of importance, tires, wheel weight, tire pressure, THEN offset. In terms of what effects handling more. But that is just MY own personal opinion on it. Would love to here your thoughts.

You're absolutely correct on all counts and your preferences make sense.

Of course, the tires are the most important aspect of good chassis tune as they are the link to the road and all suspension tuning/modifications, wheel selection are (or should be) based around the tires, NOT wheels alone. (And if anyone wants to argue that point with me, I'll gladly not shy away from that discussion. Heh heh.)

As far as which of the two sizes handles better, well, that's a really big can of worms to open here. There's the weight argument that you bring up but then that can be countered with the whole argument about the lower aspect ratio of a 35 versus a 40 series tire having quicker response due to a stiffer sidewall. And of course, contact patch dimensions and symmetry are a BIG factor which can be argued both pro and con for each size wheel.

But in all truth, I think that's splitting hairs.

Back when I was running around in an S30, lower profile tires were still in their relative infancy and back then, a Phoenix Stahlflex 3011 60-series tire was the one to beat in AX and to some degree on a road course (for cars requiring DOT-legal rubber). But today, even some of the cheapies available can outhandle those old gumballs so it's not even an argument any more. I am NOT advocating going out and buying a set of "Ling Long Crosswind" tires. Not by any stretch of the imagination. Just that while they are cheapie tires, TODAY's el cheapos are a LOT better than el cheapies from back in the day! :icon8:

And no, that's not racist for two reasons: consider who's saying it :icon17: and that they actually exist....

https://cimg5.ibsrv.net/gimg/my350z....9be6012885.jpg
:icon17::icon17::icon17::icon18: Which I had a set of on my Z32 just cuz they were cheap placeholders while I was figuring out if I wanted to do anything to that car.

Back on topic, I say that if you can FEEL the difference between running on a good set of 18s versus 19s, well, you're way ahead of 90% of the people out there.

My preference for strong, light weight wheels has little to do with overall grip as based on the argument just above, they're all pretty good in terms of that. No, my pref comes from the need for extremely sharp tactile response and predictability.

I want to know that the tire will react *RIGHT NOW* and that I can know what it's going to do at any minute. I can feel breakaway before it happens so want to know that I can counter steer or lift before something ugly happens. So, running a 35 series tire versus a 40 *might* just give me that a tiny bit more. (But I doubt it.)

But that's the problem with improper offset - in MY opinion only - scrub radius is a big issue with me where a low offset will push the scrub radius more positive resulting in an approach to zero scrub which takes out steering sensation and response, possibly leading to squirm. I'm not big on anything that takes away feel.

Stock Z33 has a really good, responsive, and most importantly, predictable feel to me so I have little inclination to "flush my wheels" with the fenders for the sake of appearance. I always say that if a modification or component doesn't INCREASE performance, it doesn't go on my car. (Yet, here I am with spacers.... heh heh.... :icon17:)

But all said and done, I used to say I'd never go with 19's but here I am, hypocritically (but I prefer to think of it as "accepting the status quo", laff....) with nearly every set a 19 (all my Volks) or 18/19 combination (Nismo, Track 2). I'm OK with it and don't make a big deal about it if it does what I want it to do (above).

There's a lot of subjectivity in this discussion since not everybody has the same expectation or need for ________________ (name your pref, whatever it is).

But again, purpose of my threading this topic is only for information and not necessarily stating what's "best" cuz MY best is someone else's "I don't give a da*n." And vice versa... :rolleyes:

Mic

Not gonna quote because that was extremely long.

2 things i have to say, first of all, linglong tires, theyre extra jdm. :thumbup:

Secondly, i alwat tell everyone i know, the difference between a good driver and an average driver is that the good driver can tell that his car is about to break lose and can correct it before anything happens.

Everyone think theyre good driver until their skills are actually put to the test. By no means do i consider myself a good driver, but i can tell you 90% of the time when my tires are about to break lose before it actually breaks loses. Whether its in a turn or in the straight line. Its just something you have to experience to know.(not directed towards you as im sure youve experience it many time if not on a daily occurrance.) Its that split second before it happens, and how you react will determine whether youre in full control or youre about to lose all control.

But like everything with cars, its all debatle, even the proven methods that works can be argue against. 3+3=6 but so is 2×3. There is never just one way to do things.

Mic must use an actual computer for his my350z posts. El cheapo over here doesnt have the world wide web at his house so my semi short posts are always from the smart phone... My eyes were burning by the end of that last one.

Heh heh.

O.R.G.*











*Olde Retahred Guy...

...who gets paid to evaluate sh*t and write recommendations to makes them bettuh. But OK, I get the hint. No more longishness. Oooops, just went over my allocation of keystrokes. Bye now, gotta run to the Walgreens... :(

https://cimg9.ibsrv.net/gimg/my350z....31b71a0c4f.jpg:icon39:

This is solid

Well thought out and explained Mic :thumbup: Vote for sticky.

OH MAN. I've watched and watched videos on offset but you using an actual wheel to mark the offset worked so well. I could never understand the skeleton wheel diagrams. lol.

I have taught myself a LOT about wheel offsets, because I am a wheel whore, and the other very common misconception about offsets, is when people think because they have the correct offsets the wheel will automatically fit. While this is true probably majority of the time it is not always. The design of the spoke makes a huge difference! This is why you see Volk selling High disk, Medium disk, and low disk. These are for brake caliper clearance. This is the amount of material they leave on the mounting surface. High disk will have a lot more material whereas low disk there is very little. If you have huge calipers, the offset of the wheel can be correct but if you have a very concave spoke design the spoke will hit the caliper before you can even get the wheel to the hub mounting surface. Then the offset becomes irrelevant because it doesn't fit regardless. Every car is different and every wheel is different. So the old question of "Will this wheel fit?" It all depends. Best way is to find someone who has been there done that with the same car same wheel same widths and same offsets. The reputable aftermarket wheel makers are probably one of the best sources as well. They know what their wheels fit on, at least most of the popular cars that aftermarket wheels are being put on.

Wheel offset info
 

Look for new wheel for the 03 z with brembo brakes. Would 20mm or 40 mm offset work? I think the factory is 30mm offset and from my reading + or - 15mm is ok but what way would I want to go more? Here is the wheels i'm looking at.

TSW WHEELS

JARAMA 18x9.5 for the rear 18x8 for the front.

Not sure how heavy they are.

20mm the wheel will stick out more. the 40mm will have the wheel sink in more. 20mm is better

do 18x9.5 +20 on all corners...... trust me

^^ Agreed. I did 18x9.5 +15 and it looks and handles just great.

ok to let me get this strait. generally a +20 offset and under works best for a new wheel. If you have an offset of say+50 you have to use a spacer to get back to the original +30mm oem offset?