Holding It All Together: The Frame and Suspension

In This Chapter

^ Understanding how your frame is built ^ Knowing what to look for in a frame ^ Inspecting a frame for problems ^ Identifying the different types of suspension ^ Adjusting and maintaining your suspension

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or all the focus given to other parts of the bike when it comes to

improving comfort and bike handling, the frame is given surprisingly little attention, especially considering how important it is to your bike. The frame dramatically impacts the personality of your bike — its stability, how it handles corners, whether it can carry loads, and how aerodynamic it is. It also determines your position on the bike in relation to the pedals, the seat, and the handlebars. Slight changes in this position can greatly impact the way a bike rides.

In this chapter, we take a closer look at the frame and how it impacts the biking experience. We discuss how frames are designed and constructed and what qualities you should look for when shopping for a new frame. We also provide advice for inspecting and maintaining your frame.

We also discuss bike suspension in this chapter. The suspension acts as an extension of the frame by being an intermediary between the road and the bike to absorb the bumps and jars so your frame and body won’t have to. Suspension is found on more and more bikes these days, so understanding how suspension works and the steps to adjust and care for it is a good idea — if your current bike doesn’t have suspension, your next one just might.

I’ve Been Framed: Your Bike’s Frame

Although there are a number of different frame designs, some more strange than others, the diamond shape is most popular. In this design, there is a main triangle that includes the following:

✓ Head tube: The head tube is where the fork connects with the frame and where the headset sits to enable steering.

✓ Top tube: The top tube connects the seat tube with the head tube and can be horizontal or angled up or down, depending on the style of the bike. Cables are frequently run along the top tube.

✓ Down tube: The down tube connects the head tube with the bottom bracket. This is where your water-bottle cage usually goes. On older bikes, this was the location for the friction shifters.

✓ Seat tube: The seat tube is what supports your butt by holding the seat post and saddle in place. It’s often used for attaching water-bottle cages and bike pumps.

✓ Bottom-bracket shell: This is a short, fat tube that holds the bottom bracket. It runs sideways across the bottom of the bike and is usually threaded.

There also is a rear triangle, which consists of the seat tube, along with the following:

✓ Chain stays: Chain stays run parallel to the bike chain and connect the bottom bracket to the rear dropouts. On some bikes, cables are routed along the chain stays.

✓ Seat stays: The seat stays connect the seat tube with the rear dropouts. They’re often used for mounting brakes, fenders, or bike racks.

The final section of the frame is the fork and steerer tube. The fork is how the front wheel connects to the bike. It consists of two legs with a dropout each for the wheel and a steerer tube, which inserts into the head tube.

A number of factors in the geometry of a frame affect how the bike handles:

✓ Seat-tube angle: The seat-tube angle is based on the angle of the seat tube in relation to the ground. This angle determines how your weight is distributed between the saddle and the handlebars. A steeper seat tube creates a more aerodynamic position with more of your weight shifted forward to the handlebars. With a shallower seat tube, the saddle

is positioned farther behind the bottom bracket and your weight is directed toward the back of the bike.

The angle of the seat tube also impacts how you pedal, because it changes your position in relation to the bottom bracket, where all the pedaling takes place. A steeper seat-tube position provides a more direct transfer of power from your legs and is better for higher-cadence pedaling. A shallower seat tube is better for slower pedaling, such as climbing while seated.

✓ Head-tube angle: The head-tube angle impacts your bike’s handling.

A steeper head tube will provide more responsive steering, whereas a more shallow tube will give you more relaxed steering. If you use your bike on mountain trails and need quick, responsive turning to avoid hit­ting objects, a steeper head tube is for you. On the other hand, if your riding consists of taking two-week tours where you’re on long stretches of road for hours at a time, a more shallow seat tube is probably the way to go.

✓ Chain-stay length: Chain-stay length also impacts a bike’s handling. A shorter chain stay brings the wheel closer to the bottom bracket and makes the bike’s handling more responsive. For racing and perfor­mance, a shorter chain stay won’t allow the frame to flex as much, so more of your pedaling energy is transferred to the rear wheel. In addi­tion, because more of your body is above the rear wheel, traction is improved, which is useful on mountain bikes.

A longer chain stay flexes more and provides a larger wheel base, which improves stability and comfort. Longer chain stays are found on many touring bike frames, where stability for a loaded bike is important. Having the wheel farther back also helps keep your foot from hitting the pannier bags.

✓ Bottom-bracket drop: The bottom-bracket drop is how far the bottom bracket sits below an imaginary horizontal line drawn between the front and rear dropouts. Most mountain bikes have less of a bottom-bracket drop because they need the extra clearance to avoid the obstacles found on trails. Racing bikes also are designed with less of a bottom-bracket drop to prevent the pedals from hitting the road in tight corners. An increased bottom-bracket drop extends the wheelbase and lowers the bike’s center of gravity, both of which improve stability. As you may expect, a lower bottom-bracket drop is found on touring bikes where stability is valued.

So how do all these frame options come together to form the bike that’s perfect for you? For the average rider, bike frames designed with comfort and stability in mind are probably going to be the best choice. Frames with slightly longer chain stays, lower bottom-bracket drops, and more relaxed seat-tube and head-tube angles provide this. For mountain bikes and more expensive road bikes, the tendency will be for more responsive and stiffer rides with frames that have shorter chain stays, higher bottom-bracket drops, and steeper seat-tube and head-tube angles.

Figure 12-1 illustrates a mountain bike frame and Figure 12-2 shows a road — bike frame. See if you can notice some of the differences between the two frames: The mountain bike has a shorter chain stay, a higher bottom bracket, and steeper seat tube and head tubes than the road bike.

Holding It All Together: The Frame and Suspension

Holding It All Together: The Frame and Suspension