A Practical Guide to Shimming: How to Correct Saddle Fit for Asymmetrical or Changing Horses
Does your saddle seem to have a mind of its own, consistently slipping to one side? Or perhaps you’ve noticed your horse feels slightly unbalanced in the canter, but you can’t quite put your finger on why. You’re not alone.
In our experience at Iberosattel, over 60% of horses have some form of shoulder or back asymmetry. This isn’t a flaw—it’s a reality of equine biology. Just as humans are right- or left-handed, horses have dominant sides that can lead to uneven muscle development. Factors like training, age, or recovery from injury also mean a horse’s back is a dynamic landscape, constantly changing.
So, what can you do when a perfectly fitted saddle suddenly doesn’t seem so perfect anymore? The answer often isn’t a new saddle, but a small, powerful tool: the shim. This guide will walk you through the why and how of shimming, turning what can be a confusing concept into a practical solution for harmony and comfort.
Why Shimming Isn’t a ‘Band-Aid’—It’s Biomechanics
First, let’s clear up a common misconception: shimming isn’t about forcing a bad saddle to fit. It’s about creating a level, stable surface for a well-fitting saddle to rest on when the horse’s back itself isn’t symmetrical. Think of it as a custom insole for your horse’s back.
The need for this kind of support is backed by science. Research has long shown that most horses have a degree of natural asymmetry, often stemming from a stronger, more dominant forelimb (Clayton, 2015). This can result in one shoulder being more developed or one side of the withers being slightly lower than the other.
When a symmetrical saddle is placed on an asymmetrical back, it can create a cascade of problems. A 2018 study published in the Journal of Equine Veterinary Science found a direct link between high-pressure points from ill-fitting saddles and atrophy of the epaxial muscles—the crucial muscles running along the spine. This creates a vicious cycle:
- The saddle puts pressure on the more developed side of the back.
- This pressure restricts blood flow and inhibits muscle function, causing the muscle to wither or atrophy.
- The muscle loss makes the horse even more asymmetrical.
- The saddle fit worsens, and the cycle continues.
Shimming interrupts this cycle. By filling in the ‘hollow’ areas, you can redistribute pressure evenly, improve your saddle fit, and give your horse’s muscles the space and freedom they need to develop correctly.
Image: A horse with visible muscle atrophy behind the shoulder, highlighting the hollow spots.
Caption: The tell-tale sign of pressure-induced muscle atrophy: a hollow behind the scapula, an area where a well-fitting saddle should encourage muscle growth.
The Shimming Toolkit: What You’ll Need
Your main tool for the job is a corrective saddle pad. Unlike standard pads, corrective saddle pads have built-in pockets that allow you to insert shims in specific locations.
Shims are typically made from two materials:
- Felt: Provides firm, dense support and is excellent for making structural corrections, like leveling the saddle on an asymmetrical wither.
- Foam: Offers softer, more forgiving cushioning. It can be useful for sensitive horses or for filling in less defined hollows.
The goal is to use the thinnest shim possible to achieve balance—in shimming, more is not better.
A Step-by-Step Guide to Placing Your Shims
Before you begin, remember that shimming often takes a bit of trial and error; the right placement for your horse may require a few adjustments. The following steps outline a basic approach for the most common issues.
Image: A diagram showing the four quadrants of a corrective saddle pad (front-left, front-right, back-left, back-right). Simple line art style.
Step 1: Identify the ‘Hollow’ or ‘Lower’ Area
First, you need to know what you’re trying to correct. With your horse standing square on level ground, run your hands over their back behind the shoulder blades.
For Muscle Atrophy: You’ll feel a distinct ‘hollow’ or dip behind one shoulder. This is the area you need to fill.
For Asymmetrical Shoulders: One shoulder blade may appear larger or sit farther back. From the front, you might notice one side of the withers is lower. Your saddle will consistently slip towards the lower side. Your goal is to lift that lower side.
Step 2: Choose Your Shimming Strategy
Based on your assessment, you’ll place the shims in the corresponding pocket of your corrective pad. Always shim the ’empty space’ or the ‘lower side.’
Scenario A: The Horse with a Hollow Left Shoulder
Problem: Muscle atrophy has created a dip behind the left scapula. The saddle panel doesn’t make even contact here.
Solution: Insert a shim into the front-left pocket of your corrective pad. This will fill the void and allow the saddle panel to make even contact.
Scenario B: The Horse with a Lower Left Shoulder
Problem: The horse is naturally lower on the left side, causing the saddle to slip to the left.
Solution: Insert a shim into the front-left pocket. This will lift the left side of the saddle, helping it sit level on the horse’s back and preventing it from slipping.
Image: Close-up photo of someone inserting a felt shim into the pocket of a high-quality corrective pad. Focus on the hands and the material.
Step 3: Test and Assess
After placing the shims, tack up your horse as usual.
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Check the Balance: With the girth snug, stand behind your horse. Is the cantle level? Now look from the side. Is the deepest part of the seat parallel to the ground?
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Ride and Observe: Ride your horse in a walk, trot, and canter on both reins, paying attention to whether the saddle feels more stable and if your horse seems more balanced underneath you.
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Check the Sweat Marks: After your ride, look at the sweat pattern on your horse’s back and the underside of the pad. You’re looking for even, symmetrical patches of moisture, which indicate even pressure. Dry spots can signal pressure points or areas with no contact.
This method is proven to work. A study in the Journal of Equine Veterinary Science (Belock et al., 2012) demonstrated that corrective pads with shims can significantly improve the symmetry of saddle pressure, validating their use as a therapeutic tool.
Common Shimming Mistakes to Avoid
Shimming is a powerful tool, but incorrect use can create new problems. Be sure to avoid these common pitfalls:
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Over-shimming: Using a shim that is too thick can lift the saddle too much, creating a new pressure point. Start thin and only add more if necessary.
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Shimming the Wrong Side: A common mistake is to shim the side the saddle slips away from instead of the side it slips towards. Remember: lift the low side, fill the hollow side.
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Ignoring the Root Cause: Shimming is a management strategy, not a permanent cure for a poorly fitting saddle. It’s most effective when used with a saddle that is fundamentally a good fit, simply adapting it to the horse’s changing body.
Frequently Asked Questions About Shimming
How do I know if I need to shim my saddle?
Look for signs of imbalance: a saddle that consistently slips to one side, uneven sweat or dirt marks on the pad, white hairs appearing under the saddle area, or visible hollows behind the shoulders. Your horse may also feel less willing to bend in one direction.
Can shimming fix a saddle that is too wide?
It can help. Placing shims in the front pockets on both sides can fill the extra space and improve the stability of a saddle that is slightly too wide. However, it cannot correct a saddle with a tree angle that is fundamentally wrong for your horse.
How long should I use shims?
This depends entirely on the horse. For a young horse developing muscle or a horse recovering from injury, shimming may be a temporary solution that you can reduce over time. For a horse with permanent conformational asymmetry, shimming may be a long-term part of your tack setup.
Should I use foam or felt shims?
For structural issues like lifting a low shoulder, firm felt shims are generally preferred as they provide stable support without compressing too much. Softer foam can be useful for cushioning sensitive areas or for very minor adjustments.
The Goal: A Bridge to Better Balance
Think of shimming as a conversation with your horse’s back. It’s a dynamic, responsive way to provide support where it’s needed most, allowing for comfort, freedom of movement, and correct muscle development.
By understanding the principles behind it, you’re not just putting a pad on your horse—you’re actively contributing to their well-being and strengthening the harmony you share. Your journey to understanding equine comfort is a continuous one, and every small adjustment is another step toward a better partnership.
