Why a Car Lift Needs Big Wire Rope Sheaves

February 19th, 2018

When it comes to working under an elevated vehicle for hours, days and weeks at a time, it might be comforting to know just how precisely that lift was engineered and constructed. Like a well-oiled machine, there are literally dozens of parts and components that must work in perfect harmony to keep you and your vehicles safe.

BendPak upper lift column with cable sheaves

Cable sheaves in upper BendPak lift column

For this chapter of lift know-how, we’re going to talk about cables, sheaves and shafts, which are the most used, abused, fatigued and will-wear-over-time parts on any car lift, whether it’s a two-post or four post design. In varying roles, these critical parts are typically broken up into two categories: load-holding and equalization. Quite simply, that means that they, all by themselves, are either supporting that truck up in the air (load-holding components), or they’re being used to make sure that truck, as it rises and lowers, stays level, (equalizing components). The latter is not quite as weighty as the first.

First of all, cable or wire rope. Which is it?
In engineer-speak, “wire rope” typically refers to diameters larger than 3/8 inch (9.5 mm), while smaller diameters fall under the “cables” category. Wire rope has several strands of metal wire twisted together to form a spiral or helix shape. We call this the “rope.”

Wire cables showing corrosion

Wire cables showing corrosion

Rope strength design factor.
Rope strength design factor is the ratio of the actual strength of a wire rope divided by its max operating stress or load. Let’s say a rope has been tested by a nationally recognized test laboratory (NRTL) to have a strength of 50,000 lbs., and that same wire rope is being used to support 10,000 lbs. It would be shown to have a rope strength design factor of 5, as it is operating at one-fifth or 20% of its rated strength. Because car lifts involve elevated risk, high rope strength design factors must be maintained.

Types of Sheaves
There are two main types of sheaves that support wire cable, round grooves and V-grooves.

1) V-groove sheaves are not used in BendPak lifts. This sheave style is preferred in situations where traction is a high priority, so older and modern elevator styles often utilize these sheaves. As a consequence of a narrower channel for the cable, there’s more wear on both the cable and the sheave.

2) Round grooves are the preferred sheave for car lifts. These sheaves feature wider cable channels that reduce friction on both cable and sheave. BendPak uses over-sized sheaves—ones that are larger than necessary for the lifting application—because the larger the sheave, the longer the components will last.

Load holding wire rope.
If the wire rope is being used as a load holding component, the tensile strength should be tested and verified to safely support FIVE TIMES the load as per the North American ANSI/ALI ALCTV:2017 car lift standard, a standard that paraphrases many parts of the Federal Specification, Wire Rope and Strand RR·W-410E and ANSI/ASME 829.8, Leaf Chain Clevises and Sheaves standard. As you would have guessed, the 5x standard also applies to all connections and anchorages as well. See where we’re going here? Read more about certified lifts here.

Equalizing wire rope.
If a wire rope’s key responsibility is making sure that both cylinders on a two-post lift stay in relative unison, then it’s labeled as an equalizing component. The safety standards for an equalizing wire rope are a little more relaxed, not to say that they are not as important, but when a wire rope is used primarily for equalizing, fatigue on that wire rope is minimized. Tensile strength for an equalizing wire rope is THREE TIMES the load as per the ANSI/ALI ALCTV:2017 car lift standard, along with the connections and anchorages.

Earlier we referred to wire rope sheave as “the most used, abused, and fatigued and will-wear-over-time parts on any car lift.” Quite a mouthful! Yet most consumers are focused on other less-likely-to-fail features. At BendPak, we receive more inquiries from shoppers about ramp widths, lift arm heights, post size, lift color etc., but when we mention wire ropes, sheaves and axles, the importance of these critical components can get lost. Wire rope and their associated components when being used on a car lift are expendable items. In other words, they are items that will eventually need to be replaced. The question is, when will that time be? Will you remember to do so, and how much cash will it set you back? Remember, if you’re piloting a plane, be more critical of the wings and landing gear than the back-seat video monitors.

Single-Hub vs Dual-Hub Sheaves
Cable sheaves are specially designed to outperform your expectations on a daily basis. But not all sheaves are built the same. Some BendPak lifts feature cables that bend over single-hub sheaves and meet and exceed all contemporary lifting standards. However, we always put dual-hub sheaves at the necessary parts of our heavy-duty lifts. Dual-hub cables further reduce stress and fatigue, protecting the cable wire fibers. The more surface area on the sheave, and dual-hub sheaves significantly increase surface area, the less stress on the lift, and the longer the lift will go before requiring maintenance. The higher the weight capacity on a car lift, the bigger the sheaves. The difference between a 10.5″ and 12″ sheave might seem small, but to a mechanical engineer, it makes a world of difference. No matter which type of sheave you see on a BendPak, you’re getting the optimal choice for that design to meet and often exceed ALI standards. We never leave you questioning the integrity of any aspect of our lifts.

Dual-hub cable sheaves with wire cables inside car lift column

BendPak dual-hub cable sheaves

All About Sheaves
At BendPak, the importance of cable sheaves is no less important than any other part of the lift. This is because they protect your lifting and equalization cables, which require more attention than other lift components. (Your hydraulic lines and cylinders might be a close second.) While we know a good cable sheave will save you in maintenance expenses down the road, they remain somewhat forgotten elements of lifting. A well-made sheave should rarely require any serious inspection other a quick peak when you change the cables every few years. For your protection, BendPak’s sheaves are visibly more massive and sturdy than others in the industry. It’s no secret—just look at the image below!

BendPak cable sheaves next to a smaller sheave from another brand

BendPak cable sheave vs. other brand

It’s our goal to do our part to inform lift buyers who just see a “round steel thing” where we see a beautiful piece of engineering. Sheaves matter, and we hope you appreciate what needs to go into these vital components. Too often, other lift companies get away with putting smaller, weaker sheaves in their lifts’ columns. They use single-hub when they should use dual-hub, or they use smaller sheaves that increase cable wear, whereas BendPak spares no expense to ensure the longevity of your product. Wire cable replacements can and will make up the initial difference in savings with a cheap lift. Even worse, those cheap components compromise the efficiency and safety of your lift.

Love Your Lift
If you own a car lift, we have a quick challenge for you. The next time you do your inspections and maintenance, even if it’s just 30 seconds out of your day, take a moment to appreciate the little things that go into the making of this massive tool that’s lifting and protecting your cars. BendPak has built a name on being the best, and we’re glad you’re reading this article, because it means you want to know more about what’s really behind your investment. Until next time, wrench wisely and be safe out there.


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