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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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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.