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Wheel Rim and Tire Specifications Explained

What do those numbers on the side of a tire mean? Are your rims 15″, 16″, 17″, 18″ or bigger? What’s an offset and why does it matter? If you are questioning if those new rims you picked out will fit your ride then this guide is just for you. Let Pacific Motors take you on a refresher of the basics needed to choose the perfect replacement or upgrade wheels and tires for your special vehicle.

Tires Tire Size is expressed in a string of numbers and letters like: “255/50R19” 255 = width in millimeters 50 = A percentage ratio of the width divided by height of the sidewall. R = Radial, the type of tire construction (most common type on modern vehicles) 19 = Diameter measurement in inches, must match the diameter of the rim to be installed on

Tread depth is the measurement of remaining tread surface on a tire. A gauge measures the distance from the surface of the tire to the deepest part of the tread. Measurements of 4/32nd Inches or 3mm and greater are considered safe. Measurements below 2/32nd or 1.5mm must be replaced immediately.

Tread depth can be estimated without a guage as well. Insert the penny upright into a tread groove. If you can see all of Lincoln’s head above the rubber then tread is less than 2/3nd or 1.5mm and no longer safe to drive on.

Wheels Wheel Rims are the metal body that support tires and bolt on to the vehicle hub. Wheels are commonly made in two ways. One-piece rims are a solid forged metal construction. Advantages of the one-piece design are strength and performance. Disadvantages are fixed dimensions and difficulty repairing when bent. Two-piece wheels consist of a wheel face and inner barrel held together with bolts. Three-piece wheels work similarly, but with the addition of another barrel piece sandwiched in the middle. Advantages are cosmetic appearance and customizable offset and fitment using different barrel dimensions. Prices are often more than double that of forged rims. Wheels are commonly made from steel or an alloy of aluminum or magnesium. Steel is about 3 times heavier but also less likely to crack or bend. Alloys are lighter and dissipate heat better but are more fragile.

Wheel Measurements Specifications are usually stamped on the inside of OEM wheels. Alloy formula, part number, dimensions, load limit and offset are commonly included. Diameter is the measurement in inches between bead not including the rim flange. Width is the measurement from the inside of the bead on each side of the rim from front to back. It is difficult to measure with a tire installed but can be estimated by measuring the tire width and rounding down to the nearest 1.5-inch measure if dimensions are not stamped on the inside of the rim.

Bolt Pattern is the number and spacing of hub bolts. Bolts range from 3 to 12 or more and are arranged in a ring. Most passenger vehicles use 5 or more bolts. 5 bolts arranged in a ring with a 120mm diameter is expressed as 5x120, the standard bolt pattern for BMW vehicles. Measuring the diameter of the bolt ring by hand will only provide an estimated size. A special tool is used to get true measurements. The bolt pattern for most vehicles can be found by searching online. Lug Nuts come in three common varieties. The differences come from the seat surface which contacts the wheel. The designed used on the wheel will determine what type of nut must be used. Conical (tapered, acorn) lug nuts have a smooth cone on the inner mounting surface. Ball (radius, rounded) type have a bulging seat. Flat (washer, flange, mag) type have a straight 90-degree seat like any common bolt nut. Using the wrong type of lug nuts will prevent the wheel from torqueing to the hub properly and can be dangerous.

Offset is a measurement from the centerline (mid-point of width) to the mating surface where the rear of the rim touches the hub when bolted on. Maintaining an offset close to the original is important to prevent steering problems or wear on bearings. Offset measurements are noted as a number followed by the letters ‘ET’ such as - 37ET. To measure offset, place the wheel face down on a surface. Lay a straight edge across the rim on the bead flange. Measure from the bolt mating surface to the straight edge. This measurement is called backspace. Now take the rim width and divide by 2. The resulting number is the centerline. Subtract the centerline from backspace. A negative number indicates a negative offset. High positive offset improves stability while high negative offsets allow more design space for spoke effects. Offset will also affect the appearance of vehicle stance.

Centerbore is the opening machined in the center at the back of a wheel. This hole aligns the wheel on the hub and helps position it for torqueing the lug nuts. Measurement is taken as the opening diameter and stated in millimeters. OEM sizes should be maintained when possible. Aftermarket adapters are available to convert from a larger to smaller centerbore.

Are we forgetting anything?

If you have any unanswered questions about how to pick the right rims and tires please comment below and we will do our best to fill you in!

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What is an “Anti-Junkyard”?

Pacific Motors Anti-Junkyard Warehouse Retail Shelf

For Pacific Motors, this is an existential question.

Answering this amounts to defining ourselves and defining an industry. It involves addressing common perceptions and misperceptions that the average person simply does not have the time to consider – much like most of us don’t have the time to figure out whether or not George Washington actually cut down a cherry tree and refused to lie about it (Spoiler: He didn’t).

But unlike George Washington’s childhood, this question has immediate consequences. For us, of course. But also for anyone who might at one point or another need to repair a car.

So, let’s hold off on answering that question for a moment, and we’ll answer one of the underlying questions first.

What is a junkyard?
Obviously, we have to define a “Junkyard” before we can define an “Anti-Junkyard.” And we’ll indulge the rest of the world and just treat perception as reality (because, truthfully, it’s close enough):

A junkyard is a disorganized and chaotic heap of broken down cars,
with an inaccurate inventory,
of items which often don’t work,
and aren’t returnable,
run by people who don’t much care about the quality of the items they’re selling,
(and who definitely don’t care about customer service).

In our experience, that is approximately correct (…or correct enough of the time to where the perception is understandable). Call up a run of the mill junkyard looking for something as straight-forward as an alternator and you’ll have an obstacle course to run through before you can get the item because they’re not actually sure that they have the item that they say they do. And then, assuming they have it and you purchase it, once you receive the item (probably about 8 days later), you’re in the precarious position of trusting that the company you purchased it from correctly cataloged the item. And even if they did, they’re probably just playing the odds and guessing as to whether it is functional or not (because testing items is time-consuming). And then, if it happens to not function, they’re probably going to reject your return, or in the best case make it extremely difficult by throwing around “restocking” fees in excess of 20%. And then, even if you send it back, you’ll probably have to follow up 2 or 3 times to get them to process the refund.

That’s a nightmare. And it is a direct result of an industry that doesn’t take itself seriously. On top of that, it’s a legacy thing. It’s in their blood. And changing is hard. Who wants to adapt to new technology and consumer demands if you don’t absolutely have to?

Below is a chart provided by Google Ngrams showing the frequency of words used in English-language books between 1885 and 2008. It’s a solid enough way for us to track how junkyards came to prominence. You’ll note we combined “automobile” and “car,” and we had to multiply the use of “junkyard” by 300 times to make it visible on the chart (not elegant, but it still serves our purpose). Anyhow, the point is, you can gauge that junkyards really started to emerge in the 40s and 50s and took on more prominence through the 80s. Today, most people understand the concept of a junkyard and expect that there are plenty of them near most metropolitan areas, even if they don’t frequent them. This industry came into its own in a very different time and place.

The Anti-Junkyard

Our approach is different than the one we mentioned above. Let’s try to compare definitions…

An Anti-Junkyard is an organized collection of automotive parts removed from insurance vehicles,
with an impeccably accurate inventory (rivaling most retail stores),
of items which have been tested or inspected,
and are returnable,
run by people who care both about the quality of the items they’re selling
and good customer service.

Our return policy has more in common with Target’s than with other salvage yards’ policies. Our customer service is closer to IKEA than to Bob’s Pick-a-Part. Every item we have listed for sale has passed through at least four people’s hands before it is sold. Every thing which could have been tested, was tested. Each and every item we have for sale has multiple high-resolution images attached. We’re entirely invested in every part and understand the seriousness of needing to repair your vehicle.

Pacific Motors puts ourselves in our customers’ position anytime we make a decision and our customers have come to expect this type of approach from us. We’ll continue to do what we’re doing, which is to say improving daily while making purchasing reliable OEM automotive parts as easy as possible.

Pacific Motors Anti-Junkyard Warehouse Retail ShelfAnd we’d invite any “junkyards” still shoveling questionable items out the door as quickly as possible to begin to take themselves seriously.

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Here’s What Else Happens When a Cement Truck Falls on a BMW i8…

BMW i8 Wreck Crash Total Cement Truck

At 8:40 am, in the course of an altogether innocent morning commute, amidst the wintry, February hell of Southern California, one oblivious Cement Mixer and an unwitting BMW i8 had an unexpected interaction at the Newport Coast Drive off-ramp on California State Route 73. Unbeknownst to the participants, and 2,300 miles away in Detroit, Pacific Motors was carrying on as if nothing on earth of consequence was about to occur. Instead, this proverbial butterfly of an auto wreck flapped its wings, and Pacific Motors would never be quite the same.

BMW i8 + Cement Truck
Photograph from The Orange County Register

The wonderful people over at Jalopnik decided to report on the aforementioned incident and what happens when a cement truck falls on a BMW i8. While Andrew P Collins did a bang-up job of detailing the immediate aftermath of such an incident, largely relying on the Orange County Register’s account of the crash, there was one trailing question at the end left unanswered,

And to anybody building up a BMW in the SoCal area; keep your eyes on the junkyards for a set of i8 seats? (Too soon?)”

Andrew, it wasn’t too soon, then. And it certainly isn’t too soon now. And though we managed to drag the car all the way to Detroit, we can still help out folks in SoCal.

Regretfully, the seats could not be preserved complete and intact… However, being an automotive recycler, we did our best to save all that could be saved.

But, we’d like to provide everyone with a more complete view of what happens when a Cement Truck falls on a BMW i8. So here is what happened next:


Prior to stripping the chassis clean of its flesh like a vulture does carrion, we almost miraculously we skillfully managed to resupply power to the limping beast before we put him out of his misery.


Anyhow, to put a nice, little bow around this whole ordeal and give it the happiest ending possible, we checked the back of the BMW i8’s title and it turned out that this unfortunate guy was an organ donor. This was wonderful news for us, but even better news for each and every i8 in the world (especially for those without health insurance). Upon hearing the glorious news, our dismantling & inventory staff meticulously tested, reviewed, photographed, tagged, categorized, and listed each and every one of the salvageable parts, which are generously available in our Parts Store.

So, to celebrate the gift of life, all of our remaining i8 parts can be had at a 10% discount by using the Coupon Code “Jalopnik”.

And to the rest of you, let this be a lesson – Share what you have when you no longer need it!

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How to know which type of Used Replacement Engine you should buy for your Vehicle

Maybe you purchased a car with a bad engine for a great deal… Maybe someone hit the front of your car and cracked your engine block… Maybe you finally decided to change the oil all by yourself and then forgot to put the drain plug back in… Doesn’t matter. You like your car, and now you need an engine.

So you find yourself shopping for an Engine. You begin to come across terms you’ve never heard before. You start to notice a significant level of complexity, don’t have the time to do a ton of research, and can’t make heads or tails of what exactly various companies are trying to sell. On top of that, you’re dealing with a garage and a mechanic and only partially understand what they’re telling you. You’re about to drop a nice chunk of change between parts and labor. So now, you’re ready to grab the first engine you see for a price you can tolerate.

Slow down. This is a very big decision.

At this moment, our job is to make you a more informed consumer, so that you can make the best decision possible. We’re going to first explain what you need to know about different types of engines. And to close, we’ll give you a few quick pointers on how to determine whether the engine is in good shape and whether the seller of the engine is reputable. (And we’ve decided to frame this as analogous to a fairy tale, so it should make for some light reading).

(TL;DR: You should probably buy a Longblock, but confer with your mechanic and take their advice, armed with some new knowledge).

Goldilocks and the Three Bears

You’re Goldilocks, and your Engine is one of the three bears…

We’re going to cover 3 basic types of “engines” you may be considering for your vehicle: a Complete Dropout, a Longblock Assembly, and a Shortblock Assembly. Any engine could become any one of these types before it is removed from a vehicle and sold. But once out of the vehicle and prepped for sale, for all intents and purposes, it will fall into one of these three categories. We’ll discuss them from most inclusive to least inclusive.

The Complete Dropout Engine (Papa Bear)

This is about as close to a plug-and-play engine as you can find. All of the engine’s accessories (starter, alternator, power steering pump, manifolds, wiring harness, etc…) are left on the engine. This is great from a convenience aspect and should allow for a relatively quick and easy installation.

If your engine is trashed from a fire or a pretty catastrophic situation, this may be your best option.

However, if the problem with your engine is isolated to a particular area (e.g. bent rod, spun bearing, cracked block, bad head gasket), you’re probably getting way more than you need if you buy a Dropout Engine. To put that another way, you’re probably paying way more than you need if you choose to pick up a Dropout Engine.

Once you understand the differences in these types of engines, and have consulted with your mechanic, you should be pretty well-equipped to determine whether you need all of these items with your engine. (And be advised, when consulting with your mechanic, be very clear about whether your mechanic wants a particular type of engine for the job, or actually needs a particular type of engine for the job. Labor costs will be affected, but you’ll have to determine if the price difference of the engine can offset this).

Pacific Motors generally keeps about 10-20% of our engines as Dropout Assemblies. Usually, we’ll keep performance-oriented engines as dropouts for engine swaps into different vehicles, and occasionally, if we have a few longblocks available, we may keep some Dropouts so as to present our customers with multiple options.

Summary: A Complete Dropout Engine might be the right choice for you, but in most cases, you will find this chair to be too big…

The Longblock Engine Assembly (Mama Bear)

The Longblock Engine Assembly is essentially the core powerplant of your vehicle. You should expect to have everything from the Oil Pan up to the Cylinder Heads included, with the accessories having been removed. All components internal to the Engine (Crankshaft, Pistons, Rods, Camshafts, Timing Components, etc…) are included with a Longblock.

Call it the happy medium. This is Pacific Motors’ preferred way of selling engines because it allows the customer to purchase a replacement engine without a ton of unnecessary components added on which unnecessarily raise the price.

Under most circumstances, the accessories or attachment parts (again, like the alternator, starter, AC compressor, etc…) from your old engine are perfectly fine. These items rarely fail in tandem with an engine. It is conceivable that having your mechanic reuse your accessories could save you upwards of 40% (or more) on the cost of your engine.

We strongly advise you to consult with your mechanic and discuss the feasibility of using a Longblock Assembly for your replacement. With hundreds and hundreds of engines sold in the recent past, we have discovered that people usually find the Longblock the most cost-effective solution (and we keep about 75-85% of our engines as Longblocks). However, if your mechanic strongly advises you in a different direction, please do listen to them. We just want you to be armed with the best possible information for your particular situation so you can confidently and knowledgeably question the decisions being made.

Summary: A Longblock Engine is often the best choice for an engine replacement. With that said, listen to your mechanic! Sometimes, it may be too little engine, and sometimes, it may be too much engine, but we’re guessing that you’ll think this porridge tastes just right.

The Shortblock Engine Assembly (Baby Bear)

Shortblock Engine | Pacific Motors

What makes an Engine a “Shortblock”? Take a Longblock and remove the Cylinder Heads.

This is even more basic than a Longblock, composed of at least the Engine Block and the integral internal components (Crankshaft, Pistons, Rods).

This type of engine is relatively uncommon. If we have any in stock, they would typically make up about 5% of our Engine inventory, at most.

While this type of Engine will probably be the most affordable, you need to keep in mind the amount of labor necessary to install a Shortblock. This is where a conversation with your mechanic will again be strongly advised. Further, you’ll need to be able to determine whether or not this item includes the less critical components often left on a Longblock, such as sensors or timing-related items. The Oil Pan is rarely included, but you should inquire about that from the seller, as well.

Short of a bare Engine Block, this is as basic as it gets.

Summary: A Shortblock Engine can be a great value, but is often not the ideal solution for your engine replacement. Before purchasing a Shortblock Engine, please consult at length with your mechanic. While the bare minimum might serve your purposes perfectly in some cases in the most cost-effective way, we think that you will likely find this bed just a little too soft.

Other things to consider:

  • Measure twice, cut once: Talk to whomever is selling you an engine and be 100% sure that the engine will fit your exact application. Usually, if you provide the seller with your VIN, they should be able to guarantee compatibility with your vehicle. Also understand that the types of engines above will fit more and more vehicles as you take more parts off (e.g. A Dropout may fit 5 year+model+submodel combinations, where the same Longblock will fit 10, and then the Shortblock will fit 13). Regardless, you do not want to buy an Engine just to get it shipped, have your mechanic get everything set to swap, and then be told that it doesn’t fit.
  • Is there a core charge?: Often, sellers will charge a “core charge” when selling a component like an engine. This means you will effectively put down an additional deposit on top of the retail price of the item which would be refunded upon your return of the old/faulty item. Be sure to ask your seller about the core charge; especially on an Engine, because this can result in an additional 10-20% cost at the time of purchase. (Pacific Motors opts for a more hassle-free process and does not bother with core charges – we prefer that your sale go as smoothly and easily as possible. You can read more about core charges here).
  • Does the seller have nice, clear, high-resolution photos?: No reputable seller of engines would ever think to not display or provide photos of the exact Engine which you are buying. This is a significant purchase, and the item being purchased is complex. If there are no photographs available, demand them. It would be advisable to share the photographs with your mechanic while you are assessing which engine to purchase. If a seller has problems getting you clear, detailed photographs – go elsewhere.
  • How will the Engine be shipped?: Make sure that the Engine will be shipped in a responsible manner (preferably strapped securely to a pallet and shrink-wrapped or protected in some way). Make sure the seller uses reputable carriers to deliver the item (and note, Greyhound is not a reputable carrier – they are the definition of a budget carrier, and you usually get what you pay for). And absolutely make sure that the seller is up-front about shipping charges. Pacific Motors sells all of our items with Free Shipping so that you never have to worry about surprise costs.
  • Demand details from the seller about the Engine: Ask the seller exactly which vehicle the engine is coming from. Ask for the mileage of the donor vehicle. Ask for video of the Engine running, or ask for results from a compression test. Ask for the reason the donor vehicle was totaled in the first place. Demand transparency and ask for proof. Any seller who dodges or provides unsatisfactory answers to these questions is probably not trustworthy. You’re making a big purchase here and you have a right to get this information. Don’t settle. (Pacific Motors will happily provide videos, data, pictures, reports – whatever you need when deciding to purchase an engine. We think you’re entitled to this information, so don’t be hesitant to ask).

If you’ve read this and still have questions about your looming engine purchase, contact us or leave a comment on this post. Even if we don’t have the Engine you need, we probably do have some good advice which we’ll share with you for free.