Hello all,

Looking for optimal to max width tires I can fit on a wheel.


My wheels have a 25mm outer width and a 21mm inner width. The bike can handle up to a 42mm


Thanks for the feedback

insert opinions here [____] measure the frame clearance next..

Tire Sizing Systems scroll down 90% of the way. The chart is merely a guide, I've run 47mm tires on 19mm inside width rims without a problem for many years.

Honestly, I'd expand the selection by 3, 4 or 5 squares to the right (and maybe one or two to the left) on each and every rim width. It would still be quite conservative. I regularly run 54mm tires on 17mm rims without issue. I'm using 35 to 37mm tires on my 14mm wide Velocity Deep V's for touring without issue as well.

You know guys, Bob's got this one. It doesn't really matter what "maximal" means in terms of rim width if the tire contacts the brake bridge! I have 25mm Bontragers on my roadie. I have it on good authority (Treks!) that no tire bigger than 28mm is ever going to fit this frame. Does it really matter what the tire size that is three places over on the rim fit table is??

There's no real limit in any sense of a clean line between OK and too much. It's more about sliding scales of benefits and drawbacks.

I won't go into the benefits, since you've already stated a preference for wider and I'll respect that. The drawbacks are reduced frame clearance, meaning less margin should the wheel break a spoke or get bent in a minor crash. My rule here, is that I want at least as much as I'd gain by releasing the brake, more if possible. While you're at it, be sure to note the vertical clearance under the brake caliper since this often becomes the first limiting factor.

The other drawback is much more subjective. It's the floppiness that wider tires on narrow rims have and how that effects handling, especially at lower pressures. To understand this effect imagine holding a water balloon between two fingers. The higher (closer to the diameter) you hold it, the more stable against side forces. A tire that's very wide compared to the rim is like holding that balloon with your fingers close together near the bottom and will feel squirrelly. But this is a question of degree and what I may feel is terribly unprecise handling, may be perfectly fine to someone else.

So go as wide as you want, subject to clearance issues, then if the handling isn't satisfactory, back down until you're OK with it.

Lastly, is the issue of hoop stress, or how hard the tire tugs outward on the rim flanges. This is proportional to the product of tire width and pressure. Rim makers design around expectations tire width and operating pressures with the assumption that wider tires will be run at lower pressure. However many wider tires have higher pressure ratings these days, and so can produce greater rim stress. This probably won't an issue on a new rim, but will determine the maximum wear limit before failure. Something to think about on a bike where rim wear is already an issue.

35MM? Better question, use? Dirt, pave, gravel? Touring? Need puncture protection?

Agree - don't underestimate how disturbing this feels. I put some 37mm tires on 13mm rims and everything was fine but it made cornering at speed feel like I was riding on jello.

I doubt this will be an issue with OP's fat rims though.

I agree with Scott. With 42mm as the upper limit dictated by frame clearance, the OP can barely reach the sweet spot on 21mm rims, much less go beyond it.

Also, which tire model and size, how much load, how much air pressure, etc.?

I don't know.

Many roadies ride 23 mm tires on 17 mm rims and 40 mm tires are frequently run on 24 mm rims for gravel.

That chart is definitely skewed. What is the source?

Mavic put out something like this stating that certain size tires should not be used on wide rims but that was before they actually produced any wide rims. My guess is that this is more of the same, bias toward a certain manufacturer's product line at whatever time it was produced.


-Tim-

Yup, there may be some handling issues with unusually wide tires, but you might not encounter that problem riding a bike with rims having a 21mm inner width. Most folks won't do hard, fast curves and cornering on a bike with 40-50mm wide tires.

I just went from 700x23 to 700x25 tires on my older road bikes 14mm inner width rims. Mostly I wanted to tame the chatter and vibration on rough chipseal. The bike was originally equipped with 700x18 tires, many years ago. It handled fine with 700x23, tracking like it was on rails on curves. But the past week it's felt a bit squirrely on curves with the slightly larger tires, which just barely clear the brakes. Even if it could squeeze in 28 tires the handling would probably be awful.

Handling may also be influenced by tread, especially pronounced tread on shoulders. Shouldn't be an issue with slicks or tires with very shallow tread/sipes.

The original lightweight MTB rims were narrow road rims rolled down to 26". Bontrager did it first using Mavic MA-40s, then Trek sold hundreds of thousands of upper end MTBs with their Matrix ISO aero rim. There is no real tire and rim fit issue with big tires on narrow rims.

You may have handling issues, but that really isn't the basis for the chart that Diabloscot that comes from the ETRTO and is designed for industry standardization.

I have 40 mm tires on 35 mm rims, still works. OP, answer? 35 -40 mm tires will work just fine.

That ETRTO/ISO chart has always bugged me a little. It's one thing to debate whether 2.2x or 2.4x the inner rim width is too wide for a tire, but they are inconsistent at applying any formula I can think of. If 57mm is okay on a 25mm rim, and 50mm on a 21mm rim, why not a 54mm tire on a 23mm rim? If they approved an 18mm tire on a 13mm rim, why not a 32mm tire on a 21mm rim?

We understand that these are guidelines and that we can go outside of them if we're aware of the side-effects, but guidelines themselves ought to be internally consistent!

Perhaps you are more sensitive to the ride than I am but I've never felt any kind of tire problem even when running my 54mm tires on 17mm rims. Certainly not like I'm "riding on jello". These are full on knobbies with aggressive off-road knobs and I'm not shy about cornering. I corner at the similar speeds on my road bike or mountain bike. I also have 37mm tires on 14mm wide Deep Vs and I'm not shy about hurtling down hills on a loaded touring bike either.

If the tire is going flat, I can feel the bike get a bit flaky but "flat" in this case means down around 20 to 25psi or lower. My normal pressure on knobs is around 45psi with a 200+(+)lb load. My pressure on the touring bike is a more normal 100 psi with a 200+(++) load.

The chart isn't about any absolute limits. It's just a guide, highlighting the range for optimal all around performance. The narrower end may offer more precision in steering feel, though may ride more harshly. Conversely, the wider end may offer more comfort, at the expense of sloppier steering (depending on pressure).

In any case, the chart reflects a general consensus among tire manufacturers (not rim makers) about maintaining the ideal Omega profile that's proven itself over a century or more.

So, use the chart as a guideline to find a starting place, then let your actual experience guide you toward wider or narrower section tires, and of course to find the best pressure for the specific tire based on your weight, preferences and road conditions.

FWIW - many tire makers offer tire/rim width charts, and you'll find them to be similar across the board.

If the chart is a guide then it is guiding people away from perfectly good solutions.

If the chart is the consensus of tire manufacturers then their consensus does not reflect the reality of what is done on the street and trails by many, if not the majority of cyclists today.


-Tim-

Some great information already!

As always as the OP I have left some key information out.

Currently I am running GranD Prix 4 Seasons... I have been happy with the tire, but I am looking to lean more toward a gravel bike set up. Urban exploration is the term to best sum it up. I go from pavement to hard pack to curbs grass and trash covered streets all with in the first few miles of some rides. I want to expand my options a bit further with terrain yet still be road capable.

Thats my biggest concern with the wider tire making the bike feel too loose.

We know what the chart is for and who made it, so we don't have to pretend that it is either of those things.

Live free - take the risk.

That may be, but I'll venture that most, if not all OEM pairings reflect the charts. As I said, they reflect what the manufacturers consider optimal. That many (I strongly doubt most) riders feel differently isn't a surprise.

Keep in mind, that unlike the auto industry where both the tare and gross weight of any vehicle fall within a fairly narrow band, the bike tire world has to deal with the reality that the "normal" GVW can range by something close to 2:1, and the wider range can easily exceed 3:1. So, there's no simple formula or guide that can be right for every tire width, pressure, rim width, person and road conditions.

If there's anything where the disclaimer YMMV applies it's bike tires.

If you read my earlier posts, I don't speak to what's best, but to the overall balance of ride precision and comfort. Once folks understand how these vary, they can slide along the range to what they feel is the best balance ----- for them.

The link from Sheldon's site directs to a german language site below, which is really quite informative.

Reifen und Felgen für Fahrräder

Which translated will show the source as DIN 7800;
Tyres for bicycles

The ETRTO/ISO standard is still being actively updated. 5775-1 (tires) was last updated in 2014, 5775-2 (rims) is up to 2015.

Fwiw on my 29er the giant s-xc2 rims internally are 19mm, and I run 2.2"(56cm) tires. I've found pressure to be more important then tire size. I'll inflate my xkings to near max pressure of 65psi and hammer around on pavement. It rolls well but it's noisy.

So to the OP, get the widest tire in your preferred tread that's economical and well stocked. You can always bump up pressures for a quicker ride on wide tires. Get one with a sticky compound and be done.