Wheel Spacer FAQ: Everything You Wanted To Know About Spacers
This page consists of everything I have learned about wheel spacers for BMWs. I worked at what may have been the biggest BMW wheel spacer dealer in the world. That's no joke - we practically fostered the market. A lot of this info also applies to other cars as well. It's a very long and comprehensive collection of data, tips, and technical info. I hope it's useful to you but if you should have any further questions, please leave a comment or email.
|Contents (click to jump to page):|
|1. Why Use Wheel Spacers?||2. What Size Should I Use?||3. How To Measure Wheel Gap|
|4. Wheel Bolts||5. Wheel Studs||6. Secure Fitment
|7. Wheel Offset Issues||8. Hardcoating vs. Anodizing||9. Additional Info|
Why Use Wheel Spacers?
- Appearance. You want to push the wheels out for a better stance and more aggressive look. Most factory wheels have a "tucked under" look that can be improved by pushing them out.
- Clearance. You spent $2,000+ on coil overs or a big brake kit and your current wheels don't fit without rubbing. The inner rim may touch the coil over spring perch or the spoke of the wheel will scrape the brake caliper. The spacer will push the wheel away and give the proper clearance.
- Correction. You may have bought a set of wheels that don't have the correct offset for your car. The offset may be too high, resulting in the wheels sitting too far inward. This is both ugly and incorrect as the tire can now rub on the inside wheel well, or on suspension components, etc. A wheel spacer will push the wheel out and "correct" the offset.
- Handling. By spacing the wheels further apart, you can make the car more stable and corner better. You can gain a similar effect as adding a wider wheel without the added weight and expense.
What Size Should I Use?
This was one of the most commonly asked questions when I worked in sales. We didn't want to be jerks but this question has no obvious answer. There's too much risk that they will not be the right size, especially if the customer wants the spacers for looks. Most companies will not accept spacers back for a refund once they are mounted to the car. Would you be happy with spacers knowing they had been used and returned? And people buy spacers for different reasons and very few situations are exactly 100% alike. And it's so easy to check for the right spacer size yourself. The answer is right in front of you. If you can operate a ruler you can measure your wheel gap. This empty space will likely be your spacer size. You don't want to exceed the empty space because the tire will likely rub on the fender. And you don't want to get too thin of a spacer because that may not meet your needs.
When measuring, the outside edge of the tire is usually the widest point and the most likely to rub on the fender lip, The goal is to get the wheel as close to the fender lip without rubbing.
H&R has a great graphic showing the wheel gap that needs to be measured:
Old-Fashioned Tape Measure
With the car on the ground, hang a piece of masking tape from your fender. Stick a quarter or a nickel on the end so that it hangs straight down. Next measure in from the masking tape to the outside edge of your tire. This will tell you how much space you have until the tire would contact the lip of the fender. Pick a spacer that is slightly less than this measurement. This will ensure the tire does not rub on the fender lip.
Even More Old-Fashioned Rulers
Same as the method above but if you don't have masking tape to hang from the fender, you can use a straight-edge or ruler and another ruler or tape measure. Gently hold the straight-edge from the bottom of the fender lip. Measure in to the outiside of the tire. The gap between the straight-edge and the tire is your available clearance. Choose a spacer size slightly less than this dimension.
Wheel Studs and Washers
For this method, you would purchase at least two wheel studs to thread into the hub and corresponding nuts to lock the wheel down. You can buy generic wheel studs at any auto parts store (bring one of your stock wheel bolts for them to match up). Remove your wheel and bolts. Thread the studs into the hub. Place washers down the stud to the hub. Slide the wheel over the studs. If it makes contact with the caliper or suspension, add more washers. Once the clearances are set, lock the wheel down with the nuts. Lower the car to the ground and roll - don't drive! - the car back and forth so the suspension will settle. Check your clearances again and also for tire-fender contact. Adjust if necessary. The end thickness of your washers will be your minimum spacer size. If you have space left over before the tire hits the fender, consider going with an even bigger spacer for improved looks.
Remember to remove your studs or install them the proper way before driving!
Studs and washers installed in the hub. Pictured is a BBS 90mm stud and 5 washers (roughly 15mm).
Studs and washers installed with the wheel.
Remember that every wheel spacer needs a longer wheel bolt or stud. The correct length wheel bolt is your stock bolt + the thickness of your spacer. As a general rule, the stock BMW wheel bolt length is 25mm, as measured from the base of the cone seat to the tip, including all threads and shank. So a 10mm spacer will require a 35mm wheel bolt. However, there are some that are up to 28mm. An accurate measurement is crucial. A bolt that is too long will interfere with other parts inside the hub (ABS sensors, parking brake mechanism, etc). If it's too short the wheel will not be safely secured to the hub.
Use this chart if you're not sure if your bolts are correct for your spacer size and application. BMW bolts are 12x1.5, 14x1.25, or 14x1.5. You can tell if you have enough of the bolt installed in the hub by counting the number of turns or checking the threads for their engaged length (the threads will be discolored or coated in grease).
|Wheel Bolt Type||Safe Engagement Length||Number of Turns|
Wheel Spacers With Wheel Studs
Wheel studs protrude from the hub and help to locate the wheel to the hub. A wheel nut (lugnut) would then be used to fasten the wheel to the hub. The issue with using them with spacers is that it can actually push the wheel out too far, leaving you without enough threads to securely fasten the wheel nut. Here are some things to keep in mind when choosing studs and spacers -
- length of available stud sticking out from the hub
- brake rotor hat thickness (varies)
- wheel bolt bore depth (the depth of the hole in the wheel) (varies)
- spacer size
- number of turns on your wheel nut (see above for the correct number of turns)
For instance, a full-threaded wheel stud usually has enough threads left over to use a 10mm spacer. However, a big brake kit may have a thicker rotor hat than stock which would reduce your available space on the stud. As well, the thickness inside the wheel bolt hole can vary a lot as well. A thicker wheel will reduce your available threads. A longer wheel stud may be needed to safely secure the wheel.
Turner Wheel Spacer and Stud Design in SolidWorks
(click the image below for a super-sized version)
This image was created by Turner engineers in SolidWorks - a CAD program. All components are scaled correctly in relation to one another. Here you can see the relationship between wheel spacers, wheels, and the hub (wheel bearing). You can also see how brake rotor hats and wheels also play into spacer fitment. This particular drawing is of a E36 M3 with a Turner 12.5mm spacer, a stock BMW brake rotor, a Turner 75mm wheel stud and Turner wheel nut, and a generic wheel design. There's a lot to look at on this drawing but things to pay particular attention to are -
- the fitment of the spacer (green) to the hub (red),
- the fitment of the wheel (grey) to the spacer (green),
- the thickness of the wheel bolt bore where the nut is fastened. A deeper bore will result in less threads for the nut to engage -OR- will require a longer than normal wheel bolt.
How often should wheel studs be replaced?
All fasteners are considered consumables at some point. The point when to replace them depends on their use. Endurance racing team replaces their studs every six months or after any crash. That's excellent life considering the number of times the tires are changed during a typical endurance race weekend. For the 'typical' track car a two-year replacement schedule to be adequate. Most of the lifespan is determined by how the nuts are tightened onto the stud - by 'feel', torque wrench, impact gun, etc. Over-torqueing, as well as under-torqueing, will shorten the life and decrease the strength of a wheel stud. Make sure your shop agrees with you on this and practices responsible torquing. Also, avoid using anti-seize on the threads. It will skew the torque rating into a higher value (over-torqueing).
A spacer is another piece in the wheel-hub puzzle - the pieces have to fit together precisely. BMW spacers use of the same stock hub lip that the wheel rests on. The spacer has to fit snugly over this lip and fit square against the brake rotor hat. A number of factors can influence how well the pieces fit together. A millimeter of clearance can result in a total failure so precise checking of the pieces is critical.
Small Flat Spacers Without A Hub Extender
All BMWs were engineered so that the wheel sits on the hub. A lip protrudes from the hub and the wheel slides onto the lip. This is known as a hubcentric fitment. And all BMW spacers should be "hubcentric". Since spacers also slide over the hub, a small flat spacer (3mm, 5mm, 7.5mm, and some 10mm) will use up the available space on the lip. There will be less space for the wheel to securely rest on.
This is an extreme example using a 10mm spacer but it clearly shows the hub disappearing with a flat spacer -
Here are more examples of the lip disappearing with a flat spacer -
click for larger
click for larger
This is not an issue on spacers over 10mm because they are usually thick enough to cover the existing hub and include their own hubcentric lip for the wheel. However, on smaller (flat) spacers it's physically impossible to include a lip because it would have to be larger to fit over the stock lip. However, Turner Motorsport has a great solution:
Turner Hub Extenders
The Hub Extenders press into the front hub and add another 10mm of lip surface area. The Hub Extenders take the place of the stock wheel bearing dust cap and simply tap into place. They are the best solution for getting back the lost hub lip with flat spacers. These work on the front hubs of nearly all 5-lug BMWs from 1982-2006 and 2012+. They will not work on the rear, or most front hubs after 2005, because the hub has an inner taper preventing these from pressing in. Hub Extenders work with 3mm, 5mm, 7.5mm, and flat 10mm spacers as long as the center bore of your wheel can accommodate the extra lip. And one of the best things about them is you can swap those spacers in/out for different needs and keep the Hub Extenders installed.
click for larger
F80 M3/F82 M4 Hubcentric Spacers
Shortly after the F8X M3/M4 came out, there was a surprise for spacer manufacturers on the front and rear hubs. Instead of a full steel ring for the lip, the hub had tabs. BMW did it for weight savings but it leaves even less surface area than before. But Turner quickly realized an opportunity. With the gaps in between each tab they could build a small spacer with "teeth" to lock into the hub. And the Turner Interlocking Technology Spacers were born. These are 5mm, 7.5mm, and 10mm Spacers with an integrated Hub Extender. The Turner Interlocking Spacers have a new 12mm hub for the wheel to rest on. Genius! With this spacer design you no longer have to worry about the wheel not resting securely on the hub. And it fits the front and rear M3/M4 hubs.
click for larger
The spacer must sit flush against the brake hat and must not bottom out against the lip as that leaves a gap between the spacer and brake hat. The spacer will then flex over the lip and eventually crack to pieces. Unfortunately, there is no common or standardized lip depth. Most BMWs have a depth of less than 10mm. But there are a few where the lip sticks out further - E46 M3 rear, E90 325xi, F30 3-series, and maybe more. Production tolerances, and even choice of brake rotor and/or hub, can also play a factor in how the spacer fits. For instance, a rotor with an aluminum hat may be thinner than a cast iron part and the thinner hat will allow more lip to protrude. Many BMW owners have run into this problem, especially with 10mm spacers. The 10mm spacers are more susceptible to this because it physically will not fit over a lip larger than itself. Most spacer manufacturers consider 10mm to be a "tuner" fitment where the shop would make the necessary changes to ensure a correct fit. If any spacer bottoms out on the lip instead of against the rotor, there are two options: buy a larger spacer, or shave/grind down the lip until it clears. Using a larger spacer is better as moving up in size is usually a small jump (the difference between 10 and 12mm is the thickness of a nickel!).
Wheels With Incorrect Beveled Edge
Some wheels (Kosei in particular) have a beveled mounting surface that is at a different angle than on the spacer. The spacer may use a 45* bevel but the wheel could be 60*. Since the parts are not snug together the wheel will vibrate. This situation is not very common but does come up once in a while. The solution is to use a larger spacer that may not have any bevel at all. Or, depending on the spacer size and location, you could use our Turner Hub Extenders and Flat Spacers.
2012+ F30 3-series Fitment Notes
The F30 3-series models have a deeper hub lip than most other recent BMW models. This will limit the available spacer options. As this is a new model and not yet through brake/chassis revisions, it will be best to check the available lip depth before ordering or installing spacers. A deep lip will bottom out inside the spacer and not allow the spacer to fully engage the lip and sit tight against the brake hat. This is a very dangerous issue as cornering forces will lead to stress cracks on the spacer and eventually the total failure of the spacer itself.
We advise people to measure the lip first and then call to check spacer fitment. Keep in mind that the front and rear lips are different depths and must be measured separately. No returns will be available on any spacers that have been opened or installed on a vehicle.
Wheel Pad Size
The back face of the wheel (the backside that mounts to the hub) is called the pad. Over the years the wheel pad on factory BMW wheels has varied in size - 150-156mm. However, spacer size has remained constant at 150mm (5.91"). There have been no issues with using a larger wheel pad with a smaller spacer as long as the spacer is fully seated to the hub. The difference is only a few millimeters. Most of the major wheel manufacturers, for street as well as top-level Prototype and GT race cars, said they prefer the smaller wheel pad for less unsprung weight. For aftermarket wheels you will most likely be using the smaller spacer but on factory wheels you can choose between the small pad and big pad spacers.
A smaller spacer is better for a few reasons: lower weight, lower cost, and less wasted material during manufacturing. But for aesthetic reasons it may be better to have a "large pad" spacer so that the spacer is uniform with the back of the wheel. The big pad spacers have some advantages too - the larger surface area spreads the load better across the hub (could be important on bigger, heavier cars) and there is more friction between the spacer and the hub so it doesn't shift or move around as easily. But those are relatively minor advantages with no data to back them up. Without supporting data our opinion is that this is an aesthetic issue only.
Why have spacer manufacturers stuck with 150mm spacers? Because bare aluminum rod stock comes in inch sizes and 150mm = 5.91" - perfect for a 6" aluminum rod. The next size up is 6.25" / 159mm. That can be machined down to 156mm because that's the largest BMW wheel pad and the machining will remove excess material and weight even if it adds cost and time.
Here's an illustration of where the large wheel pad spacers fit in relation to a small pad spacer -
click for larger
Using the normal pad spacers on a "big pad" wheel will result in a small step down between the wheel pad and the brake rotor. The strength and durability of the spacer is not in question. It is just an aesthetic preference.
click for larger
Which pad size should I use? There is no hard and fast rule. The pad size has increased over the years so your factory wheel is probably already in the middle of the range. If you have factory BMW wheels and a few extra ounces of unsprung weight is not important to you, then use the Big Pad spacers. They will match up better with the wheel. If you have aftermarket wheels then it's probably best to use the Normal Pad spacers.
F10 M5, F12 M6 Carbon Ceramic Brakes
The brake rotor hat on the M5/M6 Carbon Ceramic Brakes includes a machined recessed area where the wheel is mounted. The factory BMW wheels that come with the CCB option are designed to sit within this recess. But some factory and aftermarket wheels have a larger mounting surface that will prevent the wheel from sitting down inside this 'pocket' (they actually sit over it). This could be a very dangerous scenario as the wheel will not be sitting flush with the rotor hat. And the wheel bolts may not reach a safe depth inside the hub. Our Turner Big Pad spacers solve this problem! Our 3mm or 5mm Big Pad spacers fit perfectly in the pocket of the brake rotor. The pocket problem is eliminated, opening up many more new wheel possibilities (including more winter wheel options)!
Carbon Ceramic brakes with special machined area highlighted
Turner 5mm Big Pad spacer installed with Carbon Ceramic brakes
Measuring Hub Lip
A lot of times I make a reference to measuring your stock hub lip. This is very important for a number of reasons -
a) to ensure the spacer fully seats on the lip and against the brake disc hat. If the lip sticks out too far, the spacer will not be fully seated and will bottom out on the lip instead of against the rotor (see Bottoming Out above)
b) with a flat spacer you want to ensure there is enough lip left over for the wheel to rest on. With nearly all flat spacers (all under 10mm) the spacer will take up valuable space on the hub. For example - a 5mm spacer will occupy 5mm of depth on a 9mm hub, leaving only 4mm of space for the wheel to rest on. And if the wheel has a bevel on the back that can mean the wheel is never fully seated to the hub. It's not an ideal situation and will most likely leave you with a vibration or worse, the hub and/or wheel bolts can fail.
The hub depth varies, even on the same model line. The biggest variance comes from different brake rotor hats. A thicker hat will also eat into the lip. Manufacturing tolerances and designs (OEM vs aftermarket) can also have an affect.
Here are some examples of measuring the stock hub lip, with and without a spacer -
checking hub depth of the stock E9X M3
hub and brake rotor
checking hub depth with no spacer
on MINI R56 GP
checking hub depth with 5mm spacer
on F30 hub
Spacers for Wheel Offset Issues
A lot of calls are to correct a wheel offset when using a wheel not intended for the chassis. Examples - E36 M3 wheels on an E30 M3 or E46 wheels on an E34. The 3-series cars generally have a higher offset than the 5-series. This results in the wheel being tucked in too far and making contact with brakes, suspension components, or the inner wheel well. The differences in offset are usually around 15-20mm but that's not the whole story...
Not only is the offset different but the width of the wheel is usually different as well. An E30 M3 had a 7.0" stock wheel. Most E36 wheels are 7.5" or 8.0" and a higher offset. So not only are you fighting the higher offset but the wheel is physically wider. If the wheels were the same width, your spacer would simply be the differences in the offsets. But add the extra width and you now have another dimension to figure out. The mathematical formula is very intricate but you can find offset calculators online. Call us if you need further assistance.
E39 owners need to be careful because their wheels use a different center bore than most other BMWs. This limits their wheel choices. The E39 center bore is 74.0mm. Just about all other BMWs use a 72.5mm center bore. Depending on what the wheel was originally designed for (E36, E46, etc) there may be an offset difference to deal with as well. In the case of fitting one of these wheels to an E39, a wheel spacer adapter is required that is 72.5CB on the wheel side and 74.0CB on the hub side. These adapters come in 15mm and 20mm sizes to take up the offset difference. See these adapters on our website here - 15mm adatpers, 20mm adapters.
Wheel Offset Examples:
E36 M3 wheels on an E30 M3. The stock wheel is a 15x7.0 ET20. The new wheel will be a 17x8.0 ET40. If we just installed the wheel with no spacers, it would be 33mm futher inward than stock and still 7mm narrower overall than stock. The stock E30 M3 has a lot of wheel clearance before the stock wheel will hit the fender (20mm using the measuring methods above). So right away we know that a big spacer can be used without worrying about it rubbing on the outside fender. Let's say we put just a 7mm spacer on - it will bring the new wheel to the same position as the stock wheel on the outside, but will still be 26mm tucked in towards the strut (and rub on the strut). But we know that we can safely go another 20mm more and still not touch the fender. If we put a 25mm spacer on the new wheel, it will rest 18mm further out than stock and only 8mm further in. We now have a wheel that is spaced out enough to sit flush with the fender and not rub on the inside!
Winter Wheel Package for E92 335 coupe. Many people are finding themselves without a true winter wheel package on the E9X models. These cars come with a stock wheel with an offset quite a bit lower than the E36 and E46 predecessors. When trying to fit these E36/E46 wheels to the 335, they sit too far inward because of their higher offsets and narrower width. The best solution would be to buy wheels with the correct offset. Aside from that, spacers can be used to make up the difference.
First measure your stock wheel clearance as outlined above. We'll use a 17x8.0 ET40 as the winter wheel. The stock 335 wheel is a 18x8.0 ET34. In this case, you only need a 6mm spacer to get it back to the original stance. However, the back wheel is a 18x8.5 ET37 and to use the winter wheel you will need a 9mm spacer to get it back to stock stance. Because you measured beforehand, you know how much more room you have to space the stock wheels out. This is critical because 6mm and 9mm spacers don't exist; you will need something larger and you need to make sure there is adequate clearance for it.
Another common scenario:
E46 M3 19" ZCP wheels on an E92 335 coupe. The stock sport package wheel is a 18x8.0 ET34 and 18x8.5 ET37. The E46 M3 uses a 19x8.0 ET47 in front and a 19x9.5 ET27 in the rear. Using our calculations, the front will sit further in by 13mm. A 15mm spacer will bring it back to the factory wheel stance. Measuring the stock wheel beforehand we know that it will take a 12mm spacer before the stock wheel contacts the fender. Therefore, adding 15 and 12 gets us to 27mm. So the E46 M3 front wheel will take a 20-25mm spacer in order to sit flush with the E92 fender. The M3 rear wheel will sit only 3mm in but an additional 23mm further out. Measuring beforehand, we found that the stock wheel only has 15mm of clearance before it hits the fender. The M3 wheel will most likely rub on the fender, requiring the fender to be rolled or negative camber added for more clearance.
Because of their location and proximity to the air, wheel spacers should use a military-spec hardcoat instead of a "simple" anodize. Terms like "military" or "aerospace-grade" are thrown around in this industry like "artisan" and "gourmet" are used for fast food. But in this case it really does matter. Where anodize is fine for making parts look pretty, it's not tough enough for year-round spacer duty. Trust me, and my experience in tuning as well as New England seasons - aluminum spacers are very susceptible to the salt used on our roads during the winter months. Type III hardcoatings can be found in firearms, ordnance, high-speed machine parts, aviation/aerospace, and even domestic uses like cookware. Hardcoating is stronger and more durable than anodize, is more resistant to color change from heat, and is chemically resistant. One other note about hardcoatings: all mil-spec hardcoats are inherently dark in color. Anodizing can be done in any color, including black, which makes it easy for an inferior product to appear equal to our own on paper. All forms of anodizing will vary in color so it's not unusual to get spacers that are slightly different shades from each other.
Additional Info, Notes, and Details on Spacers
|How do I know if I've gone too far?
Enlarge the photo on the left. This car has had too large of a spacer on the front wheels. The wheel is rubbing on the fender lip. This car is tracked and the extra thick spacers are probably there to keep the wheels from rubbing on the brake cooling hose when the wheels are turned to full lock. Instead of rubbing occasionally on $80 hose, the fender is cutting two $150 tires. A better solution would be smaller spacers and our own steering rack stops that limit inside steering travel.
* Note that H&R and Turner Motorsport each make a 10mm hubcentric spacer but due to interferences between the spacer and lip, it's best to leave this to specialized applications. See below for more detail.