Top 10 Best shims in 2026

Last Updated - 6/7/2026

🏆Best Choice

TRIWONDER

TRIWONDER Bike Seatpost Adapter Shim 25.4mm 27.2mm 28.6mm 30.4mm 30.9mm 31.6mm 33.9mm 34.9mm Aluminum Alloy Bicycle Seat Post Tube Adapter for Mountain Bike, Road Bike (27.2mm to 31.6mm)

9.8

ChoiceComparer.com Score

9.8

/ 10

Outstanding

Main highlights

•✅ DURABLE & LIGHTWEIGHT - Made of high-quality 6061 aluminum alloy with CNC machining anodizing process surface, which offers high strength and corrosion resistance, ensuring long-lasting use
•✅ VARIOUS SIZES AVAILABLE - Length: 100mm. Diameter: 25.4mm to 27.2mm/ 28.6mm, 27.2mm to 28.6mm / 30.4mm / 30.9mm / 31.6mm / 33.9mm, 28.6mm to 31.8mm, 31.8mm to 34.9mm
•✅ EASY TO INSTALL - Just open the seatpost clamp, insert the appropriately sized shim and seatpost, adjust to your desired height, and then lock the seatpost clamp
•✅ UNIVERSAL FIT - Suitable for most road bike, fixed gear bicycle, mountain bikes, downhill bike, track bike, BMX, DH, etc. Solves the problem of mismatched frame and seatpost sizes
•✅ ATTENTION - Please measure the correct outside diameter of your seatpost (or check the size marks on the seat post) and your bike frame seat tube inside diameter before buying

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$6.99

$7.99

-13%

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COGSTER

Cogster Alloy Bike Seatpost Reducer Shim, 100mm Length Aluminum Bicycle Reducing Sleeve Seat Post Tube Adapter for MTB,Mountain,City Bike,Road Bike, Adapting 30.9mm seatposts to 31.6mm seat Tubes

9.7

ChoiceComparer.com Score

9.7

/ 10

Outstanding

Main highlights

•Cogster Bike Seatpost Adapter Shim serves as a crucial part that adapts smaller seatposts to larger tubes, ensuring a proper fit.
•Comes in various sizes to accommodate different bicycle seatpost diameters and seat tube diameters.
•CNC'd from 6061 aerospace alloy, this bike seatpost shim balances superior strength, light weight, and corrosion resistance for long-term use.
•Featuring tool-free installation, this bicycle seat post tube adapter is designed to avoid damage to the bike frame or seatpost, ensuring ease and safety.
•By enabling the use of a different size seatpost, you can adjust the height or tilt of your saddle more accurately, thus improving your overall cycling comfort and performance.

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$9.99

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GANOPPER

GANOPPER Mountain Bike Seatpost Shim 27.2 to 31.6 Suspension Seat Post Adapter Reducing Sleeve Shims for XC,Trail, MTB, FR

9.5

ChoiceComparer.com Score

9.5

/ 10

Outstanding

Main highlights

•Material: bike Seatpost shim is made of high quality 6061 aluminum alloy, CNC machining CD texture surface ,anti-rust and durable
•Feature:Use this bike post shim, 27.2 ID Seat Post shim can be converted to 31.6 mountain bike seat post, bike seatpost adapter shim can help you change the bicycle seat tube outer diameter to meet your needs
•Size: 31.6 to 27.2 seat post shims. Length: 100mm.
•Tips: Please check your bike frame seat tube outside diameter. Measure the inside diameter of your old clamp. Or measure the outside diameter of your seat tube (on your bike frame). Then make a right choice. - - -Because of hollow design，In the process of transportation are squeezed may be out of shape，Please kindly exchange one
•Application: Bicycle Seatpost reducing sleeve shim matches well with most bicycles, such as MTB ,BMX ,Fixed Gear bike,mountain bike, road bike, city bike and more, you can easily adjust the diameter of the bicycle seat post, eliminating the trouble of repurchasing the bike seatpost.

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$9.95

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Xmomx

Xmomx Set of 7 Sizes Bike Seat Post Adapter Shim Seat Post Adapter Bicycle Seat Tube Conversion Sleeve 27.2mm to 28.6/30/30.4/30.8/30.9/31.6/33.9mm 60mm Aluminum Alloy for Road Mountain Bike MTB

9.4

ChoiceComparer.com Score

9.4

/ 10

Excellent

Main highlights

•There are more sizes for your choice with 25.4/27.2mm to 27.2/28.6/30/30.4/30.8/30.9/31.6/33.9mm
•They are made in high quality material of Aluminum Alloy to support the high strengh
•You can use this product to adjust your bike seatpost to different sizes ones
•Instructions：1, Measure the size of your bike seat post, 2, Measure the size of your bike seat post clamp, 3, Find a suitable seat post adapter shim and put it between the seat post and seat post clamp, 4,Lock your seat post well.
•Note: Please be sure that check your bike seatpost before placing order

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$16.99

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Xmomx

Xmomx Set of 4 Sizes Bike Seat Post Adapter Shim Seat Post Adapter Bicycle Seat Tube Conversion Sleeve 25.4mm to 27.2/28.6/30.9/31.6mm 60mm Length Aluminum Alloy for Road Mountain Bike MTB

9.2

ChoiceComparer.com Score

9.2

/ 10

Excellent

Main highlights

•It's widely used for not only Road bike, but also for Mountain bike MTB
•They are made in high quality material of Aluminum Alloy to support the high strength
•You can use this product to adjust your bike seat post to different sizes ones
•This set of Bike Seat Post Adapters is included 4 sizes with 25.4 mm to 27.2/28.6/30.9/31.6 mm
•Note: Please be sure that check your bike seat post before placing order

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$12.99

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Cane Creek

Cane Creek .ST27316 Seatpost Shim, 27.2 I.D. to 31.6 O.D.

9.1

ChoiceComparer.com Score

9.1

/ 10

Excellent

Main highlights

•Versatile fit: Compatible with various seat tube sizes
•Material: 3-7/8 inch machined aluminum, black anodized, with laser-etched sizing details

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$13.41

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SM SunniMix

SM SunniMix Ultralight Aluminum Alloy Bicycle Seatpost Shim Adapter Mountain Road Bike Seat Post Conversion Tube, 27.2 to 31.8

8.9

ChoiceComparer.com Score

8.9

/ 10

Great

Main highlights

•【Premium Material】Bicycle Seatpost Shim Adapter is made of premium high quality aluminium alloy material,high strength, lightweight and solid enoug. Full CNC precision machining with smooth edges 't hurt your finger.
•【Application】Bicycle Seatpost Shim Adapter is suitable for mountain Bike, old school, Road Bike etc. Let you build your own unique bicycle.
•【NOTE】Please bike frame seat tube outside diameter. Measure the inside diameter of your old clamp. Or measure the outside diameter of tube (on your bike frame)
•【Different Size】27.2 to 31.8, 31.8 to 34.9. 2 size specification conversions can solve the problem of inappropriate size of your frame and seat tube. To change post size easily with this bushing without changing seatpost.
•【Easy to Install and Remove】No other tools needed, just a few seconds to install,convenient for you to use. And you can change the size of the bike seat tube as you want.

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$9.99

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Cane Creek

Cane Creek Seatpost Shim, 31.6 to 34.9mm - AAE0008

8.8

ChoiceComparer.com Score

8.8

/ 10

Great

Main highlights

•Seatpost Diameter: 31.6mm
•Clamp Diameter: 34.9mm

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$16.95

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RLECS

RLECS Aluminum Alloy Bicycle Reducing Sleeve Seat Post Tube Adapter Shim for MTB,Mountain,City Bike,Road Bike, Bike SeatPost Adapter 27.2mm to 30.4mm

8.6

ChoiceComparer.com Score

8.6

/ 10

Good

Main highlights

•What's Included: 1pc x Bike Seatpost Adapter.
•Material: Aluminum alloy material, strong, rust-proof, durable, CNC machined surface anodized.
•EASY INSTALLATION: Easy to install and remove without additional tools, it only takes a few seconds to install and it is convenient for you to use.
•Colour: Black. What's Included: 1pc x Bike Seatpost Adapter.
•Scope of use: suitable for mountain bikes, off-road bikes, off-road bikes, folding bikes, road bikes, etc.

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$6.66

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OUKENS

OUKENS CNC Aluminum MTB/EBike Seat Post Adapter Shim Kit (27.2 to 28.6/30/30.4/30.8/31.6/33.9mm) - Bicycle Seatpost Size Adapter for Mountain Bike, Road, BMX, Dropper Posts

8.5

ChoiceComparer.com Score

8.5

/ 10

Good

Main highlights

•[PREMIUM CNC ALUMINUM MTB SEAT POST SHIM] This bike seat post adapter features aerospace-grade aluminum alloy construction with CNC precision machining. The anodized finish provides corrosion resistance while textured inner walls ensure no-slip grip - supporting riders up to 300lbs without deformation. Ultra-lightweight (13-54g) maintains your bicycle's optimal balance.
•[TOOL-FREE 60-SECOND INSTALLATION] Engineered for tool-free installation, this seat post shim converts diameters in 3 steps: Insert → Align → Tighten! Includes 6 critical sizes (27.2→28.6/30/30.4/30.8/31.6/33.9mm) - no specialized knowledge required for perfect bicycle seat post compatibility.
•[UNIVERSAL BIKE SEAT POST ADAPTER] Solve compatibility issues instantly! This universal diameter converter creates secure interfaces between mismatched components. Works as reducer (30.8→27.2mm) or up-sizer - ideal for upgrading vintage road bikes or modernizing MTB seat setups without new purchases.
•[ALL-TERRAIN COMPATIBILITY GUARANTEE] Fits 98% of bicycle seat posts including MTB, gravel, BMX, Fixie & hybrid bikes. Precision-toleranced for Giant/Trek/Specialized systems. Weatherproof construction withstands trail mud, road salt, and year-round commuting - the ultimate gravel/road bike shim solution!
•[PRO SIZING GUIDE FOR PERFECT FIT]① Measure seat tube outer diameter ② Verify old clamp inner diameter ③ Match to our 6 conversion options. Note: All seat post shims are 60mm (2.36") long with knurled anti-rotation grooves. Still unsure? Contact our cycling experts 24/7!

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$7.59

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