## How Wide a Tire Can I Run?

Many cyclists want to ride on wider tires, but are limited by the clearances of their bikes. So they want to use the widest tires their bike can fit. How do you determine your bike’s maximum tire width?

You need a set of calipers (below). If you don’t have any, bike shops have them. Please leave a generous tip if you ask a shop mechanic to help you with this!

Measure the width of your current tires. Be careful not to pinch the tire. Instead, increase the opening of the calipers by 0.5 mm increments, and check whether the opening has play when it is slipped over the tire. (The calipers “rattle” when you move them.) When this happens, the calipers are set just a tad larger than the actual width of your tires. Use this measurement as your current tire width.

If you pinch the tire with the calipers, you may get a measurement that is up to 2 mm narrower. Also don’t us the width that is printed on the side of the tire. More likely than not, it’s inaccurate.

Then check all around how much clearance you have. Most important are:

• fork crown
• brake calipers (front and rear): squeeze your brakes to get the clearance when braking
• chainstays
• seatstays can limit the clearances on some bikes.
• fenders: often, you can adjust the fenders to get rid of a tight spot.

I recommend a minimum of 3 mm clearance between your tires and the closest part of your bike. Any less, and you run the risk of having your tire rub, under hard acceleration or if the wheel develops a slight wobble.

Then deduct the minimum clearance, 3 mm, to get the existing available clearance for your wider tire. Multiply this by 2 (you have that much room on both sides of the tire), add the current tire width, and you get the maximum tire width.

Example: Your current tires are 29 mm wide. You have 5 mm clearance at the tightest spot. That leaves 2 mm available clearance. You can run 4 mm wider tires than your current ones. You maximum tire width is 33 mm.

This assumes that your new tires have a similar height-to-width ratio as your existing ones. Some inexpensive tires can be much taller than they are wide, but high-end tires usually are relatively round, and this formula works well.

If you find yourself between two available tire sizes, I suggest you use the narrower tire. High-end tires tend to expand over time as the casing “relaxes,” and you don’t want your tire to rub every time you rise out of the saddle and flex your wheel. If you find that you still have extra clearance, you can go up one more size when the new tires wear out.

By the way, the bike in the photos does not appear to have extra clearance, so if your bike looks like that, you probably should stick with the tire width you have. You still can improve the ride and performance of your bike by using more supple tires with higher-quality casings.

Photo credit: Ernie Fong.

## About Jan Heine, Editor, Bicycle Quarterly

I love cycling and bicycles, especially those that take us off the beaten path. I edit Bicycle Quarterly magazine, and occasionally write for other publications. One of our companies, Bicycle Quarterly Press publishes cycling books, while Compass Bicycles Ltd. makes and distributes hard-to-find bicycle components.
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### 27 Responses to How Wide a Tire Can I Run?

1. Will Morris says:

I’ve noticed my frame is most limited by the vertical clearances, especially the seatstay bridge. Is there a good way to estimate how tall a particular tire is going to be based on its width and the rim you are using?

Thanks.

• That depends so much on the tires. Inexpensive tires often are incredibly tall. High-end tires usually are much more round. Generally, you can assume that a high-end tire isn’t going to be taller than the ones you have, with rare exceptions. So I’d use the same way of figuring your maximum tire width.

2. cbratina says:

Jan,

I measure the height of the various inflated tires above the edge of the rim with the caliper as well on a Mavic Open Pro rim. Since the brake caliper is generally the limitation on tire height, this gives me the maximum tire size I can use. The other issue with wider tires is how far a brake caliper will open. With a Dura Ace or Ultegra brake and even the Shimano BR-600 long reach brake caliper, they do not open enough to fit an inflated Grand Bois Cypress 30c tire when set up for an Open Pro rim. I would have had to go to a wider rim to adjust the cable enough to accept the tire. This is actually a very important reason to use cantilever or short linear pull brakes (Paul Minimoto) on a bike as they do not limit the tire width.

Size Height Width
Challenge Triathalon 23c 24
Michelin Pro Race 2 23c 22 24
Grand Bois Cerf Blue Label 26c 25
Continental Gator skin kevlar 23c 22.5 23
Continental Grand Prix 4 Season 25c 25
Grand Bois Cerf Green Label 28c 27 29
Continental Gator skin kevlar 25c 23.5 24.5
Continental Grand Prix 4 Season 28c 26 27.5
Michelin Pro Race 2 25c 25.5
Grand Bois Cypres Green 30c 29.5 32
Continental Gator skin steel 28c 26 26
Clement LAS Cyclocross 32c 33 32
Panaracer Pasela 35c 34.5

3. doug says:

Well, I think it’s about time I became that type of bicycle nerd: the kind who measures things with calipers.

• If your bike is properly designed for the tires you want to run, then you don’t need calipers. My new René Herse is designed with clearances optimized for 41 mm tires. If I wanted to run 38s, it would be fine. If I put on 43s, it wouldn’t be a problem. However, I don’t plan to run anything but the tires for which it was designed, because 41 mm tires are about perfect for my riding.

My Alex Singer was designed for 25-28 mm tires, so running 32s required some measuring (with calipers), and replacing the fenders with a wider model…

Many of us have bikes that aren’t the designed for the tires we want to run. And that is when we bring out the calipers to optimize them in ways their makers never intended.

• Fortunately, my new bike is optimized for 32mm tires. But I still want to measure tires with calipers!

4. Paul Ahart says:

This topic is important for bike shop employees to understand. I’ve often had customers blithely pick out fat tires for their road bikes, and had employees waste time just slapping them on the customer’s wheels….only to find…”Gee! It rubs…Guess you can’t use that wide a tire.” Measuring existing tires ON THE BIKE, and the clearances available is critical, before mounting the new ones. Thanks for this good article. I’ll make sure my guys READ it!

5. Bubba says:

Calipers are super useful for countless things on your bike. Super primative ones at the hardware store for \$5 or so will get you to ~0.2mm resolution, which is good enough for most everything. Getting hub dimensions for spoke calculations. Figuring out chainring spacing and chainline. Checking seatpost diameter and handlebar clamp diameters. Everybody who works on their own bike could get some value out of a very inexpensive caliper.

• I totally agree, except you might consider buying a good set while you are at it. I resisted way too long until I put a set of good calipers on my birthday wishlist about 20 years ago. I still use them today – they are shown in the blog photo.

• Greg says:

I would second the recommendation to get good ones that can last you a lifetime. For measuring things like seatpost size and hub/freewheel thread diameters, you need to be pretty accurate. A high-quality set of calipers is a joy to use. The Chinese-made Park ones are OK (I have one), but I much prefer my Mitutoyo Digimatic that I finally splurged on, perhaps a decade ago. I’d rather have one \$125 set than five \$25 ones….

• Digital calipers are nice, as long as you never drop them. (There isn’t an easy way of checking whether they still are accurate!)

Mine are vernier calipers, simple and strong, and don’t require batteries. They are accurate to 1/128″, which is plenty for bicycle work. The digital ones are easier to read for beginners, though.

• Greg says:

Um, ouch…. I don’t recall changing the battery in my Mitutoyo (but I have certainly replaced the cheapo batteries in the cheapo calipers), so that’s a non-issue. I’ve probably dropped my Mitu at some point (although I can’t say for sure) and I’m not sure why that would be any more of a problem than with a mechanical one. When closed, it must read zero. Put a known part or parts into it to verify accuracy if need be, but that’s never, ever been an issue for me….
I used to use slide rules exclusively in school, too, but over the years I moved on from that as well! No need for historical re-enactment.

• Matthew J says:

eBay and other auction sites from time to time offer quality German, Japanese and even older U.S. models.

At work currently so cannot verify the name but I have very precise German calipers I got for a good price on eBay. These are machine shop precise. Overkill for bikes but fun nonetheless.

At a garage sale I picked up a less deluxe but still nice Craftsman calipers. Sears sourced these from high end Japanese shops in the 50s through the 60s. Amazingly well made considering the humble source.

• Shu-Siin says:

My Mitotoyo digital calipers come with a set of metal strips with varying thicknesses (thickness of each is engraved on the metal piece). This is used for calibrating or verifying accuracy. They are now an essential part of my toolbox.
Replacing batteries on them is a pain though, and not cheap either. We need a dynopowered digital caliper!

6. Seth says:

On one of my bikes, a wider rim lets me run wider tires (switching from 19mm wide Open Pro’s, to 23mm wide Velocity A23 rims). The tire profile is shorter and wider, with the wider rims. Also, I’ve had tires stretch enough, during the first day or two they are inflated, that they could seem to barely-fit when first installed when they really don’t quite fit.

• High-end tires tend to grow a bit as the casing relaxes over time. At Compass Bicycles, we list the actual sizes of the tires we sell, rather than the “nominal” sizes. But even there, it depends on the rim you use. Trying to nail down something made from rubber to a millimeter borders on futile.

7. John Duval says:

If only you could tell how wide a tire was by the label. I just bought a set of 35mm tires that net smaller than the 32mm Cypres they replaced. Unfortunately under sizing is an ongoing problem in the industry.

Broken glass is a big issue on my commute. I really miss my Grand Bois!

• Have you tried tire wipers (also called tire savers) to prevent flats on your Grand Bois?

Regarding tire sizing, making tires still is very much a black art. The amazing truth is that when tire makers make molds, they don’t know exactly how big the tire will be that comes out of the mold. Simply going from the stiffer “white label” casing that Grand Bois initially used on their Cyprès to the more supple “green label” casing increased the width of the tires by 2 mm!

It should be possible to factor this into the mold design, but tire makers don’t seem to do this. As a result, their high-end tires tend to run wider than the nominal size, and their low-end tires tend to run narrower.

• Kevan says:

Perhaps this issue could be avoided if tire makers stopped molding the nominal tire size into the sidewall. This, along with inflation pressures, could be included in a printed label on the sidewall instead.

• John Duval says:

Wipers were almost standard items when i started road riding in the 70s, but I got flats every other ride anyway. I researched wipers when I first ordered the Grand Bois, and again after you published your own test. I found nobody who advocated them, and many who said they did nothing. My bet is up to half my flats could have been prevented with them, leaving me with 1 flat a month on average. Still too much for commuting to work.

I was thinking more along the lines of Stan’s Notubes. It should make Grand Bois even more supple, light and fast. Have you considered testing tubeless in one of your famous tests?

• We have considered testing tubeless. It’s on our to-do list.

Regarding tire wipers, few people know what they are these days, and many people have strong opinions online without having done any real testing. You might be a great test case for testing them, if you get that many flats. Put one on the back, none on the front, and see what your flat frequency is for each wheel. Usually, most riders have slightly more flats on the rear, so if the wipers work, you should have fewer flats on the rear than the front.

8. I have that same caliper in my electronics box! “Hecho en Mexico”

9. Garth says:

Jan, I’ve always admired your writing skills, which include your use of grammar. But shouldn’t you include the proposition “of” in your title? “How Wide OF a Tire Can I Run?” : )

• I put this question to our proofreader (who proofs Bicycle Quarterly, but not this personal blog), and here is his response:

“In phrases like the one mentioned, the “of” is considered redundant, if common in spoken American vernacular. Here’s what Dictionary.com–not the last word in grammar usage, I’ll admit–says:

Of is sometimes added to phrases beginning with the adverb how or too followed by a descriptive adjective: How long of a drive will it be? It’s too hot of a day for tennis. This construction is probably modeled on that in which how or too is followed by much, an unquestionably standard use in all varieties of speech and writing: How much of a problem will that cause the government? There was too much of an uproar for the speaker to be heard. The use of of with descriptive adjectives after how or too is largely restricted to informal speech.”

So while the “of” now is acceptable, it is largely restricted to informal speech. Does that make me “formal”?

10. Carlos says:

How wide are the Hetre Extra Leger tires when mounted? I’ve read in this blog that the EL tires came out wider, but they are still listed as 42mm on Compass Cycle. I just want to be sure I have enough clearance before buying.

• Measuring a Hetre with standard casing and an Extra Léger, both measure 41 mm wide on 23 mm-wide Velocity Synergy rims.

• Carlos says:

Thanks Jan,

My 650b wheels are on their way. Looking forward to trying these tires with the conversion.