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Tire Width vs. Rim Width; Which Tires Fit Which Rims?

lennard@zinncycles.com (Lennard Zinn) — Mon, 30 Mar 2026 12:12:26 GMT

32 Inch wheels are here!

Which Width Tires Fit on Which Width Rims?

Tire and rim widths explained

By Lennard Zinn

Rim width should be directly tied to tire size. While an automotive tire store would not mount a tire on a car if it didn’t have the specific number code indicating its compatibility with the rim, cyclists often buy tires of the width they want without thinking about their rim width. And in the early days of wider road rims, one of their selling points was that you could mount a narrow tire on a wide rim and get the cornering performance of a wider tire without the weight of a wider tire. Some of those combinations riders were using back then, like a 700 × 23C tire on a rim of 21mm inner width when the Hed Ardennes appeared in 2008, are now understood to have insufficient retention for safety. The danger is exacerbated with hookless rims, tubeless tires, and carbon rims.

The ETRTO (European Tyre and Rim Technical Organization) created the guidelines for the below chart of approved nominal tire widths for various inner-width rims. Here it is:

Similar charts have been published by other tire and rim companies, especially makers of hookless rims. Those brands also specify maximum tire pressures on their hookless rims, because the absence of rim-wall hooks to grab the tire bead creates less tire-retaining friction than do hooked rims. Challenge says this reduction in rim-wall-to-tire-sidewall friction is 30%.

The below chart of tire width vs. inner rim width is one that I made combining charts I had received from Schwalbe and Mavic; the Mavic chart has both hookless (“straight-side type”) and hooked (“crotchet type”) rims. I added columns after each set of numbers of the minimum and maximum percentage of tire width that the rim inner width can be. I have the Mavic chart in the 6th edition of Zinn and the Art of Road Bike Maintenance and in the 7^thedition of Zinn and the Art of Mountain Bike Maintenance.

The Schwalbe-supplied chart is only for hooked rims and lacks four of the tire sizes that appear on the Mavic chart, namely 30, 55, 58, and 64mm. It also only has odd-number-width rims. Its numbers are identical to the hooked-rim specs on the Mavic chart, except even rim widths have been rounded down to the next smaller odd rim width.

As for mounting a narrow tire on a wide rim to make it wider without the heavier weight of a wider tire, you can see that a 23mm tire is not approved for use on a rim with an inner width greater than 16mm. And that the narrowest tire that can be used on a 21mm-inner-width rim is 35mm—not a 23mm or even a 25mm one!

The ISO chart, however, allows a much wider range of tire widths with each rim width. What’s odd is that the ISO chart appears to conflict with some of its own recommendations. Look at this Zipp Hookless Rim Tire Compatibility Chart, scrolling down and opening, for instance, the Zipp 353 NSW, a hookless rim with a 25mm inner width. Its “ISO-certified tires” width range is 29-40mm, although some 28mm tires also appear under “Dual Tested Tires” (tested by both Zipp and the tire brand). The 29mm minimum tire width agrees with the above ISO chart, but the 40mm maximum is far less than what the above ISO chart shows for a 25mm inner-width, which appears to be a 66-71mm tire width! Perhaps this has to do with the fact that the ISO chart does not specify hookless or hooked rims, and the Zipp 353 NSW is a hookless rim. But the Mavic chart for a 25mm-width hookless rim seems to allow tires in the 44-55mm width range! That’s at least closer to the max of 40mm on the Zipp chart.

Clear as mud, right?

Tire/Rim Calculations vs. The Real World

The ISO recommendations are based on the ISO 5775 bike tire-rim rule, which says that for a safe fit, the tire's BSD must exactly match the rim's bead seat diameter, and the internal rim width should ideally be 55%–65% of the tire width. Specifically, it says, “The inner width of the rim on which the tire is mounted should be about 65% of the tire's nominal section width for tires smaller than 30 mm and 55% for those larger.” The “nominal tire section width” is measured when the tire mounted on a “design rim” of the specific width at which a tire is engineered to measure “true to size.”

You can see that the 65% guideline for tires smaller than 30mm agrees with the combined Mavic/Schwalbe chart above except for the 18mm-wide tire on the 13mm-wide rim at the top. And notice that the 55% guideline for tires larger than 30mm agrees with the combined Mavic/Schwalbe chart up to a 54mm-wide tire, and after that, the percentages are lower.

Here is a more legible version of the ISO chart based on that ISO 5775 40% rule; this chart includes a column showing the design rim for the “true to size” measurement for each tire size. Again, this allows a very wide range of tire widths around those 55% and 65% guidelines.

The ISO calculation is intended to account for worst-case scenarios—the smallest possible tire bead on the widest possible rim tolerance—to ensure a safety buffer.

Beyond the math, there are several mechanical variables that a static chart cannot fully capture:

Rim Width Variation: Inner rim width can fluctuate slightly based on tire pressure or braking forces (on rim-brake models). Even spoke tension can marginally affect the diameter of the bead shelf.
Tire Construction: Variations in the molded shape of the bead and ability of the bead to stretch and by how much depend on how the beads are wound and what they are made out of.
Hooks vs. Hookless: The presence or absence of a rim hook (Crotchet Type vs. Straight Side, a.k.a. hookless) significantly changes the tire retention force (coefficient of friction) and hence the safety margin.

Tire and rim sizing

Bike tire size is not always obvious from the dimensions listed on the sidewall or packaging. Unlike traditional tire sizing, the international standard numbering system for bicycle tires and rims is clear and comprehensible. The first number in the “ISO” (International Organization for Standardization) code is the outer width of the tire or the inner width of the rim (“W” in the below Fig. 7.19 from the 6th edition of Zinn and the Art of Road Bike Maintenance). The second number is the tire or rim’s bead seat diameter (“BSD” in Fig. 7.19): the diameter of the ledge on which the tire bead seats.

While their ISO code usually appears somewhere on them, tires and rims are usually not sold by those codes, but rather by traditional sizing delineations with far-back roots resulting in bewildering coding in which different numbers often mean the same diameter. In late February I posted this blog explaining tire sizing and labeling.

Thanks for reading.

― Lennard

As a frame builder, Lennard Zinn has been designing and building custom bicycles for over 42 years; he founded Zinn Cycles in 1982 and co-founded Clydesdale Bicycles in 2017. His Tech Q&A column on Substack follows his 35-year stint as a technical writer for VeloNews (from 1987 through 2022). He is a former U.S. National Cycling Team member and author of many bicycle books including Zinn and the Art of Mountain Bike Maintenance, Zinn and the Art of Road Bike Maintenance, and The Haywire Heart. He holds a bachelor’s degree in physics from Colorado College.

Follow Lennard Zinn on Substack, Strava, X, Instagram, LinkedIn, or Facebook.

Bike Tire Size Explainer

lennard@zinncycles.com (Lennard Zinn) — Thu, 26 Feb 2026 00:51:36 GMT

32 Inch wheels are here!

Making Sense of Bicycle Tire Sizing

What does the “C” on a tire mean? (Or the “B”?)

By Lennard Zinn

Have you ever wondered what the “C” in “700C” or “700 × 28C” means (or the “B” in 650B)? You would not be alone in not knowing or in thinking it is an abbreviation of “cm” any other word at all. Rather, it is an arbitrary designation stemming from an arcane French sizing system.

ISO/ETRTO size designation

In bicycle tire sizes, the first number in the traditional French labeling tradition is the nominal tire diameter in millimeters, the second number is the nominal tire width in millimeters, and the letter is used to designate the width of the rim and the tire and the rim diameter. However, nowadays, the letter only specifies with accuracy the rim diameter.

Tires today not only carry the traditional French style of size labeling (like 700 × 25C) but also carry their more precise ETRTO (European Tyre and Rim Technical Organization) designation, which is shared by ISO (International Organization for Standardization, a non-governmental global organization developing voluntary international standards to ensure safety, quality, and efficiency of products, services, and systems). ISO/ETRTO specifies tire size in an XX-XXX format with only two numbers and no letters.

The first number (XX) is the nominal tire width in millimeters, and the second number (XXX) is the Bead Seat Diameter (BSD): the internal diameter of the rim that the tire bead sits on (see above illustration). So, 700 × 25C is 25-622 in ISO/ETRTO parlance.

Importantly, “nominal tire width” is the tire’s width when inflated on an ISO/ETRTO-specified “design rim”; see the below chart of design rim widths for tire widths. The actual tire width changes slightly, by around ±0.4mm per 1mm change in rim width, when mounted on rims with different internal widths.

The internal width of a hooked rim is measured between the faces of the hooks, as you can see in this illustration from Zinn and the Art of Road Bike Maintenance. It can vary a little for the same rim; internal width increases under tire inflation pressure and can also change under rim-brake forces and spoke tension.

ISO’s “nominal” tire width allows a tolerance range of width. ISO/ETRTO bases the tolerances on the section width of the tire as shown in the below table.

From the table, you can see that, for instance a tire with a 28mm section width would have a tolerance of +/-2mm, resulting in an acceptable width range from 26mm up to 30mm. So, a 700 × 28C tire can have a mounted width of anywhere between 26mm and 30mm and be considered in spec.

Rim internal width must fall within a narrow range for a given section width of tire; you can’t safely use any 700C rim with any 700C tire. I will discuss tire fitting based on rim and tire width in a future blog.

The “C”, “B”, “A”, etc. on a tire size label

Contrary to popular belief, the “C” on tire size was never an abbreviation of any kind, for instance of “centimeters” or “clincher” (or “crotchet”), as some think, referring to the type of rim; it was always an arbitrary designation as part of a letter series. Originally, the A, B, C, D designations in the old French sizing system referred to the tire and rim width, A being the narrowest and D being the widest. Now those letters have largely lost their tire width meaning and refer only to a diameter, namely the Bead Seat Diameter (BSD).

In the case of 700C tires, the “C” would have denoted a medium-width tire in the old French system (around 38-40mm historically) with a 700mm nominal outer diameter. 700C now refers to any tire, from very narrow to very wide, that fits on a rim with a 622mm BSD. In addition to these letter designations, tires can also be sized in decimal and fraction inch sizes, which carry different meaning.

In the old French sizing system, since the first number was a nominal tire diameter and the letter was a nominal tire width, the letter sizes of fatter tires resulted in smaller rim diameters to achieve the same nominal outside tire diameter, and vice versa. For example, 700A (narrow) tires fit on rims with a 642mm BSD, 700B (medium narrow) tires fit on 635mm BSD rims, 700C (medium wide) tires fit on 622mm BSD rims, and 700D (wide) tires fit on 583mm BSD rims. There’s no need to remember 700A, 700B, or 700D, since the A, B, and D have largely been abandoned in “700” sizes.

In contrast, in “650” sizes, only the 650B (584m BSD) designation remains on tire labels, although 650A (590mm BSD) and 650C (571mm BSD) tire sizes still very much exist. You won’t find 650A or 650C printed on tire labels; tires for those rim sizes are instead labeled in inch designations; 26 X 1-3/8” is 650A, and 26 X 1” is 650C. (Yes, tires labeled in fractional inch sizes fit different rims than those labeled with decimal inch sizes, even though the first number, denoting the diameter, is the same!)

As examples of road and MTB tires sharing the same 622mm bead seat diameter (BSD), a 700 × 28C road tire is ISO size 28–622, a 29 × 2.35” mountain bike tire is ISO size 61–622, and a 28 × 1” road tire is denoted by ISO as 25–622.

In these arcane labeling traditions, tires bearing equivalent magnitude decimals and fractions do not denote the same tire size. For instance, 26 × 1.0” through 26 × 2.5” decimal sizes (with two ignorable exceptions) are tire sizes that fit on 26-inch mountain bike rims (559mm BSD). Fairly logically, the ISO designation of a 26 × 1.0” tire is ISO 25–559. However, 26 × 1” tires (no decimal or fraction), which you might logically assume would be the same size as a 26 × 1.0” tire, instead fit a 650C rim (571mm BSD; their ISO size is 25-571)! 26 × 1” was formerly popular in triathlon and called 26”. Adding yet more confusion, 26 × 1¼” and 26 × 1-3⁄8”(fractions) are both ISO 597 (597mm BSD), while 26 × 1½” (different fraction) tires are 650B (584mm BSD) and are also called 27.5”!! And 26 × 1¾” (different fraction yet) is an ISO 571 Schwinn cruiser size (yes, same BSD as a 26-inch triathlon tire that has no decimal or fraction)! Clear as mud?

Until the ISO/ETRTO tire and rim standards were finally approved by all ISO member countries in early 2023, some rim brands intentionally used a slightly increased BSD and lowered the height of the rim wall above the bead seat to change the fit and shape of the mounted tire. Some tire manufacturers tweaked the BSD of their tires accordingly, making tire fit a crapshoot dependent on brand. Now we should finally have confidence that bike tires and rims are made to the same standards, leading to more consistent tire fit, reduced mounting problems, and increased safety.

Since bigger wheels are becoming more popular, I want to mention two others. 32” is 686mm BSD. And 750D (660mm BSD) is a size between 700C and 32” that I like to call 30.5” when talking about MTB tires; it was introduced by WTB in 2023.

In the old French tradition, the “D” in 750D would have indicated a wide (~45mm) tire. However, WTB offers only 750x34D and 750x42D. 750D was chosen as the size reference mostly to add a letter to call attention to the bead seat diameter. As the tire cross sections WTB produces are more road than mountain, a metric number size rather than an inch size was chosen. The 38mm jump in bead seat dimension from 700C to 750D is the same as between 700C and 650B; 650B=584mm, 700C=622mm, and 750D=660mm. Also, 26” MTB tires are 559mm BSD, which also defines the 650D size; if you add 101 (almost 100!) to the 559mm BSD for 650D/26” MTB tires, you get the 660mm bead seat size for 750D.

Sheldon Brown has complete charts of tire sizing here. You won’t find 750D on them, as that size didn’t come along until 15 years after his death.

Thanks for reading.

― Lennard

Lennard Zinn has been designing and building custom bicycles for over 45 years; he founded Zinn Cycles in 1982 and co-founded Clydesdale Bicycles in 2017. His Tech Q&A column on Substack follows his 35-year stint as a technical writer for VeloNews (from 1987 through 2022). He is a former U.S. National Cycling Team member and author of many bicycle books including Zinn and the Art of Mountain Bike Maintenance, Zinn and the Art of Road Bike Maintenance, and The Haywire Heart. He holds a bachelor’s degree in physics from Colorado College.

Follow Lennard Zinn on Substack, Strava, X, Instagram, LinkedIn, or Facebook.

High-Speed Shimmy

lennard@zinncycles.com (Lennard Zinn) — Wed, 25 Feb 2026 20:44:29 GMT

32 Inch wheels are here!

Front-End Shimmy, a.k.a. Speed Wobble or Death Wobble

By Lennard Zinn

Has your bike ever started shaking when you got going fast on a descent or took your hands off the bars? Front-end shimmy has many nasty high-speed bike crashes and even more terrifying moments for riders that didn’t end up crashing. It’s the biggest reason I became a professional framebuilder—to cure the problem I had with my own bikes. It’s common on tall bikes, and I was 6’6” and racing on lightweight, thin-tubed steel frames in 1981 when it first happened to me.

Speed wobble or shimmy is the increasing-amplitude oscillation of the bicycle’s front end described mathematically by a Hopf Bifurcation. Front-end shimmy can be treated more simply by thinking of it as a resonance phenomenon. If the resonant frequency of the bike and rider is close to the frequency of things encountered on the road, like bumps, cracks, chip seal, and wind, then the oscillation of the frame whipping back and forth can be continually reinforced and magnified in amplitude by those factors.

Things reducing the torsional stiffness of the frame are:

Tall frame
Small-diameter tubes
Large open spaces between tubes in its front and rear triangles
A lower Young’s modulus of the material in its tubing

With low torsional stiffness, it will deflect further under a twisting force and won’t snap back as quickly as a stiffer frame would. The length of time it takes for one back and forth twist of the frame (the “period” of one oscillation) will be longer and hence the resonant frequency of oscillation will be lower. Add the rider to it and the resonant frequency drops further (the period will increase)—the heavier the rider, the greater the drop in resonant frequency.

Stiffer wheels will help somewhat. Simply tightening spokes has fixed shimmy problems for some riders. Increased tire pressure may, too. So will ensuring that there is no play in your hubs or headset and that your tires are properly seated so there are no hops in them as they spin.

In addition to not being stiff enough, tall frames are often set up for shimmy by having overly steep head-tube angles as a means to reduce the length of the wheelbase. The steeper the head angle of the frame, though, the less the fork can absorb bumps and mitigate jolts coming into the frame.

A cracked or misaligned fork can be the culprit. In the days of steel forks, a misaligned fork could induce shimmy, but today’s carbon forks come straight out of a precision mold, so that’s rarely an issue. Back in the day (1980s), I cured the shimmy in some bikes by increasing the offset (rake) of the fork, which required bending the fork. That’s not possible with a carbon fork.

We build a lot of titanium bikes for tall, heavy guys, and I make sure the bikes don’t shimmy. To prevent shimmy on tall bikes, I design the frame with large-diameter, straight-gauge titanium or steel tubing. I slope the top tube to shorten the actual lengths of the seat tube, top tube and seat stays while maintaining the same effective lengths and thus the same positioning of hands, butt and feet.

I also make the cranks proportional to the rider’s leg length and design the bike with a correspondingly higher bottom bracket. This results in a shorter seat tube (since more of the seat height is taken up in the longer crank length) and down tube from the bottom up. And then I use a shallow (often 72-degree, sometimes less) head angle to let the fork take up more of the shock. And I make the wheels very stiff.

Some of my customers coming to me for a shimmy-free bike do so because they have essential tremor. Their hands continually shake the handlebar as if they were shivering, which can induce high-speed shimmy in bikes that otherwise would not shimmy under a rider of that height and weight. In such a case, in addition to taking the above measures in the design and building of their bike, I also install a headset steering damper (I used to employ Hopey Steering Dampers for this, but that company is no longer in business). For mountain bikes, Pademelon’s CS.1 Steering Damper takes the place of the Hopey damper.Simply installing a Cane Creek Hellbender 70 Visco steering stabilizer headset may cure a bike that shakes at speed.

Wheel balance can make a difference. Put the bike in a bike stand and turn the crank rapidly while in high gear until the rear wheel is spinning very fast. Let go. The bike will likely bounce up and down wildly because of the out of balance rear wheel. You can reduce this by balancing your wheel(s) like this:

Let each of your wheels spin down to a stop (the brake must not be rubbing, and on a rear wheel, the chain must be off). If the hub bearings are smooth and properly adjusted, the wheel will rotate back and forth a bit each direction before coming to a complete stop. If it’s got an aluminum rim, it will likely always stop with the valve at the top. Screw multiple valve collars onto the valve stem until the wheel spins down to a stop with the valve in random positions rather than always at the top (if it instead stops with the valve at the bottom, the fix will be to use stick-on wheel weights at the opposite side). Once balanced, when you crank the wheel up to high speed again, the bike’s bouncing will be much less. That could make the difference on a bike that shimmies.

If these fixes don’t do it, try some Rolf Prima paired-spoke wheels. I explained why paired spoking can reduce the tendency for shimmy in this column: https://lennardzinn.substack.com/p/investigating-chain-skipping-and.

― Lennard

Follow Lennard Zinn on Substack, Strava, X, Instagram, LinkedIn, or Facebook.

Zinn Gravel Fondo - 2026

lennard@zinncycles.com (Lennard Zinn) — Fri, 13 Feb 2026 19:44:01 GMT

We are super excited to host our first big ride from our new shop in Louisville, Colorado. Lennard has been hosting Gran Fondo's from his house for ages, but after he developed his heart arrhythmia, riding over 200 miles in a day became a non-starter. Now that he's been training on his gravel e-bike for years, he's ready to bring back the Fondo, this time, a gravel version.

Seatpost Slippage

lennard@zinncycles.com (Lennard Zinn) — Thu, 15 Jan 2026 00:31:32 GMT

32 Inch wheels are here!

Preventing Seatpost slippage

By Lennard Zinn

Do you notice that your seatpost slips down while riding? Sometimes your seatpost can creep down so slowly that you don’t notice, like not noticing the increasing height of your kids. You may not even notice the height reduction at all until somebody else says, “Wow, your saddle is really low!”

Just tightening the binder bolt more may not cut it. There are limits to how tightly you can cinch the binder clamp; the bolt is small and you can either break it or round out the hex hole in the bolt head if you apply too much force on the hex key. And by overtightening the clamp, you can either damage a carbon seatpost or bind a dropper post from snapping back up.

Since for over four decades we at Zinn Cycles have specialized in building bikes for big and tall riders and have consequently made lots of Zinn-brand custom bikes and Clydesdale brand bikes for heavy riders, we know how seatposts can slide down while riding. It’s not easy to prevent seatpost slippage on a bike with a rider sitting on it who weighs over 350 pounds! We deploy various measures to keep the seatpost from slipping when we sell a bike to a heavy person.

There are ways that you can stop seatpost slippage while out on a ride. And there are better, permanent fixes that you can do at home with more time, tools, and materials. Although this specifically addresses standard round-cross-section seatposts, seat tubes, and seatpost clamps, some of the principles apply to non-round seatposts and clamps, too.

Causes of seatpost slippage

The most likely causes of seatpost slippage are high rider weight, an insufficiently tightened seatpost clamp, or a seatpost with a smaller diameter than ideal for the frame. Riding surface is also important; bumpy roads and trails can inspire a seatpost to slip down.

The tolerance of the inside diameter of the frame’s seat tube and the outside diameter of the seatpost are critical. So is the seatpost material: chromed steel seatposts are harder, smoother, and more likely to slip than anodized aluminum ones, and the outer layer of many carbon seatposts can squish in and allow slippage.

The key to it all is the seatpost clamp. You may have noticed that the bolts in seatpost clamps and even the clamp bands themselves have become wimpier than they were a decade or two ago. While an M6 binder bolt that takes a 5mm hex key (right photo, below) used to be standard to adjust saddle height, now seatpost clamps almost always come with a skinnier, M5 binder bolt that takes a 4mm hex key (left photo, below).

I believe that the shrinkage in binder bolt size is due to the advent of dropper posts and superlight carbon fiber seatposts. Overtightening the clamp around a dropper post can bind the post from snapping back up when you push the button and stand up after having dropped it down.

Carbon seatposts can get dangerously point loaded when clamped too tightly, and if the post breaks, the consumer tends to blame the seatpost manufacturer and the bike company.

The response by bike companies to issues with both seatpost types is to use a tiny bolt and a thin clamp band that can’t be tightened very tightly. They also may etch a low torque number into the clamp.

Especially with a carbon seatpost, you should avoid stacking up the slots in the seat tube and the seatpost clamp (many seatpost clamps come with an angled or offset slot for this reason). Rotate the seatpost clamp so that its slot and the seat tube slot do not line up. This avoids driving the top corners of the seat tube slot into a carbon seatpost and breaking some of its fibers.

Curing seatpost slippage

Tighten the binder bolt. Obvious first step. Don’t exceed the recommended torque for the frame, the binder, or the seatpost. Another option is a two-bolt binder (below) for more friction without going to higher clamp torque. We sell these as well.

If the binder alone can't stop your saddle from getting lower as you ride, you will need to remove the seatpost. If your seatpost has a Shimano Di2 battery inside, take care when removing it to not unplug any of the wires. Take similar care when removing a dropper post. You will need to push the cable housing or hydraulic hose into the frame as you pull the post out to not damage the housing or hose. You may need to remove the trigger lever from the handlebar to get enough slack in the housing or hose to get the post all the way out.

Create more friction between the seatpost and seat tube. If you are out on a ride, you can pull the seatpost out, rub sand into the grease that’s on it, reinsert it, and retighten the clamp. This is cheap and easy and may solve the problem.

A less messy and likely more effective option for creating more friction is to apply carbon assembly paste or spray to the seatpost shaft. This stuff is sticky or has small, gritty silica or plastic beads in the solution that press back against the clamp to increase the pressure uniformly and avoid point-loading while also protecting (like grease) against corrosion. You can also get small packets of it that you could carry in your seat bag.

Shim the seatpost. If the seat-binder lug or binder clamp slot is pinched closed, and you still can’t get the post to not slip down, even with assembly (friction) paste, your seatpost and seat tube diameters don’t match closely enough. A large mismatch is of course addressed by getting the proper size seatpost; try the next size up and see if it fits into your frame.

Another possibility is that your seat tube has been adapted to fit your seatpost by means of a slotted cylindrical shim sleeve and that the shim sleeve is too thin. Seatpost shim sleeves are available in different diameters and thicknesses. They sometimes have the outer diameter of the seatpost and seat tube inner diameter they’re made for etched into them. If your seatpost’s diameter or your frame’s seat tube inner diameter don’t match the corresponding number etched into the shim sleeve, you’ve identified the problem. Get the correct shim.

The size discrepancy between inner and outer diameters may be too small to resolve with a larger seatpost or a thicker seatpost shim. In that case, you can cut a 1 × 3–inch piece of aluminum from a pop can as a shim. Pull the seatpost out, grease it and the pop-can shim, and insert both back into your frame. Bend the top lip of the shim over to prevent it from disappearing inside the frame. You may need to experiment with various dimensions of your beer-can shim until you find a piece small enough to go in with the seatpost and big enough to still prevent slippage.

Add a second seatpost clamp. Stacking up a second binder clamp atop the one on the frame adds enough friction to keep the seatpost from sliding down even under a very heavy rider without over-torquing either clamp. Depending on what kind of secondary clamp you use, this will either be an elegant solution or an ugly one. The ugly solution is to tighten a hose clamp around the seatpost right above the seatpost clamp on the frame.

We offer a more elegant solution at Zinn Cycles (and at Clydesdale Bikes). On bikes for heavy riders, we install a secondary seatpost clamp machined to fit the seatpost rather than the outer diameter of the frame’s seat tube. It clamps around the seatpost above the frame’s seatpost clamp as you can see in the photos. This is a more aesthetically pleasing version—without a hose clamp’s sharp edges to hang up on your clothing or cut your skin.

Any of these options except the machined secondary seatpost clamp can work with non-round seatposts.

― Lennard

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Zinn B.I.G. 32 inch wheel mountain bike

nick@zinncycles.com (Nick Wigston) — Wed, 27 Aug 2025 18:40:39 GMT

32 Inch wheels are here!

Zinn Cycles has the first production 32er full suspension bike for big and tall riders

By Nick Wigston

We've been building gravel bikes, e-bikes, and hybrids with 32 inch wheels for about 10 years now, and they are very popular for big and tall guys. The larger diameter makes a tall bike look more proportional, and the wheels provide a feeling of confidence and stability. We have been limited in making 32ers more mainstream due to the lack of availability of forks, rims, tires, and spokes. This has been changing recently, and has enabled us to confidently produce a 32 inch wheel full suspension mountain bike. We do hardtail as well, but this full sus 32er is a unique bike and puts performance cross country trail riding on the table for a tall guy who wants 32 inch wheels. Shop 32er mountain bikes.

We are producing our super popular B.I.G. Full Suspension mountain bike in a new model with 32 inch wheels and tires. This bike comes in a 2XL/3XL size as well as 4XL/5XL. The "smaller" size is great for riders from 6'4" to about 6'8" and the bigger size is great for those taller than 6'8". There is plenty of standover clearance, so there is room to size up or down depending on riding style.

Making a bike proportional to the rider is one of the core concepts at Zinn Cycles in all of our designs. We strive for proportionality whenever possible. When 29 inch wheels started being introduced in the early 2000s, we were an early adopter because it was so much more proportional for our Megabike and Gigabike, which were the first real full suspension bikes made for tall riders. Now that there are more rim and tire options for 32ers, it felt like time to bring this bike to market. Shop 32er mountain bikes.

While there are still no suspension forks that are designed for a 32 inch wheels, we have found one that works really well. Wren Sports has been making inverted suspension forks for some time now, and we learned that it's possible to reduce the travel on this fork without shortening the overall fork length. A longer fork is important for two reasons on this bike. One is to have clearance for the taller wheel, and another is to get the head tube high enough so we can have an appropriate handlebar height for a 7 foot tall rider. One thing big guys are tire of is getting a bike with the seat super high and the bars super low, so we are very careful to build our bikes with good seat and bar heights.

Another super important part that needs to be proportional is the crank length. There are numerous reasons for this. One being the improved pedal stroke. A very tall rider has much longer legs than an average sized person, so they need to proportionally increase the crank length to achieve a proportional pedal circle and be able to use their full range of motion. The other factor is seat height. If you increase crank length the seat height can be lower relative to the bottom bracket, which makes it much easier to get the handlebars closer in height to the seat. The proportional crank also brings the foot further forward when in the front horizontal crank position giving the rider more power and allowing for a steeper seat angle and not requiring set back seat posts. We are well aware of the trend in mountain biking to ride on "short" cranks, and we are not against this concept. We have always gone shorter on mountain bikes than we do on road bikes for tall guys. However, it's important to know what you are comparing to. Just because a tall guy was riding 175mm cranks doesn't mean that was the right length for them previously. If a tall guy wants to go with "shorter" cranks, we advise a lower proportion to the leg length. Instead of 21% of leg length which was previously considered a good proportion, we suggest 20% or even 1.95%. This will still come out longer than 175mm for most tall guys. Click here for more info on how to compare for shorter cranks.

Another reason for proportional cranks is to increase the width of your stance when descending. This adds stability to your ride when going fast downhill and helps keep your center of gravity a little lower. Think of a snowboard, it would feel wobbly and unstable for a 6'8" guy to have his feet in the same position as a 5'10" rider. Same thing applies to mountain biking. Shop 32er mountain bikes.

Compare 29er vs. 32er

These two bikes show the same bike. the first one has 32 inch wheels and the 2nd one has 29 inch wheels.

The 29er will have a shorter wheelbase, more tire options, more fork options, and a shorter chain stay. The 32er will be more proportional overall and roll faster with a little more high speed stability. The 32er still lacks in tire and fork options, but that is changing.

Shop 32er mountain bikes.

Lightweight Sporty Flat Bar Ebike for 5'0" rider

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