Bicycle Mechanics - Tire Width/ Rim Width?

Hello,
Would it be dangerous to put a 40mm wide tire on a 14mm wide inner rim?
I asked at my local bike shop and they said "no"; however, according to Sheldon Brown's tire site, it isn't a recommended combination.
Can someone shed some light?
Many thanks.

I assume you're referring to this page? Seems like it's explained fairly well; better than I could do anyway. On a 14mm rim I don't think I'd go wider than 32; 28 would be better.

Width ConsiderationsAlthough you can use practically any tire/rim combination that shares the same bead seat diameter, it is unwise to use widely disparate sizes.If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of wide tires, and puts undue stress on the rim sidewalls.Georg Boeger (http://www.uni-stuttgart.de/tandem/Technik/reifentips.html) has kindly provided a chart showing recommended width combinations:


Which tire fits safely on which rim?
[all dimensions in millimeters]



Tire width


Rim width
(interior)
18
20
23
25
28
32
35
37
40
44
47
50
54
57


13
X
X
X
X












15


X
X
X
X










17



X
X
X
X
X








19




X
X
X
X
X
X






21






X
X
X
X
X
X




23








X
X
X
X




25









X
X
X
X
X


Note: This chart may err a bit on the side of caution. Many cyclists exceed the recommended widths with no problem.

Yep, that's the one.

I'm wondering why my LBS says that it won't be a problem and SB's site doesn't recommend it. I want to trust my LBS on this one, but I'm not at all sure I should.

I suppose I'm also wondering if it's time to change my LBS.

SB's site just recommends caution in going outside of the ISO/ETRTO guidelines which are represented in that chart.

SB's site just recommends caution in going outside of the ISO/ETRTO guidelines which are represented in that chart.

I know; I'm just trying to find out what's cautious and what's foolhardy. I commute on my bike every day in busy traffic. I need to know if the bike will be difficult to handle, if a tire will pop off, if I'll have issues turning, etc.

A 40mm tire on a 14mm inside width rim is quite far outside the chart on SB's site which has a has 32mm as the max for a 15mm irw.

Yeah. You'll probably be fine as long as you don't run too low of a pressure. I'd look for wider rims, though -- that would give more air volume for cushioning, and the tires wouldn't be as (potentially) floppy.

Just for fun, check out Georg's original chart: http://tandem-fahren.de/Technik/Reifentips/index.html#ETRTO ;)

Yeah. You'll probably be fine as long as you don't run too low of a pressure. I'd look for wider rims, though -- that would give more air volume for cushioning, and the tires wouldn't be as (potentially) floppy.

Just for fun, check out Georg's original chart: http://tandem-fahren.de/Technik/Reifentips/index.html#ETRTO ;)

Timebomb?! Eek!

Anyway, the whole story is that I asked the LBS to get me a new wheel because I kept breaking spokes on the generic rear wheel that came on my hybrid. They went ahead and ordered me "a strong wheel" but apparently the one that arrived was narrower than the one they had ordered.

They know I'm running 40mm studded tires at the moment. I expressed concern over the 14mm, but the mechanic said that I shouldn't have a problem. I don't know if the pairing will be genuinely okay or if the LBS just wanted me to take the 14mm because it would be less hassle than reordering 19mm rims.

If the latter, I think the LBS and I will be taking a break.

there's more leeway going the OTHER way with modern rims and tires, like a 23mm tire on a 23mm OD rim is actually a fairly common racing configuration as it leads to a ride more like tubulars.

a 14mm ID rim is probably 19mm OD ? I don't think I'd want to go over 35mm (about twice the OD of the rim). you'll likely find a really wide tire on a skinny rim will feel 'squirmy' on turns. if you picture whats happening with the inner tube and the tire bead, the sidewall of the tire would be bent quite sharply, and the inner tube will be bent into a 'keyhole' shape. since a tire as wide as a 40mm typically runs rather low pressure, I'm not sure there would be sufficient pressure to hold the bead snugly, especially if leaning over hard so the tire is pushed to the inside side...

They know I'm running 40mm studded tires at the moment. I expressed concern over the 14mm, but the mechanic said that I shouldn't have a problem. I don't know if the pairing will be genuinely okay or if the LBS just wanted me to take the 14mm because it would be less hassle than reordering 19mm rims.

I suspect this. They should have given you a wheel that's appropriate for the tires you want to run.

there's more leeway going the OTHER way with modern rims and tires, like a 23mm tire on a 23mm OD rim is actually a fairly common racing configuration as it leads to a ride more like tubulars.

a 14mm ID rim is probably 16-17mm OD ? I don't think I'd want to go over 35mm (about twice the OD of the rim). you'll likely find a really wide tire on a skinny rim will feel 'squirmy' on turns. if you picture whats happening with the inner tube and the tire bead, the sidewall of the tire would be bent quite sharply, and the inner tube will be bent into a 'keyhole' shape. since a tire as wide as a 40mm typically runs rather low pressure, I'm not sure there would be sufficient pressure to hold the bead snugly, especially if leaning over hard so the tire is pushed to the inside side...

Thanks for this. the 14/40 combo didn't sit well with me.

I'll get them to reorder the 19mm and give back the 14mm. I'm a little disappointed they treated me like this. Luckily there are plenty of LBSs here. They've lost my upgrade business over this.

I suspect this. They should have given you a wheel that's appropriate for the tires you want to run.

It looks that way. ****e.

If it's the rear wheel then I would think about it less because if the tire slipped in the front, then you could potentially lose your ability to handle the bike. In the rear, I don't find it so crucial.

If it's the rear wheel then I would think about it less because if the tire slipped in the front, then you could potentially lose your ability to handle the bike. In the rear, I don't find it so crucial.

Yep, it is the rear. It isn't what I wanted, so I'll just take it back and get the 19mm. I was really looking forward to my new wheel!

Now Wholly owned Trek name, Keith Bontrager rolled down 40 hole road rims into smaller Mountain bike rims, home garage frame shop..
to make them Uber light, but the use was on loose soil mountain bikes so the tire slipped on the dirt sideways
as much as it was deformed by the side forces cornering.


My studded tire wheels are the opposite.. Wide Rims, 45mm and A 26x2 tire , or 50mm


The D shaped cross section increases the contact patch to let more of the tire studs down,
to grip better..

.. I need to know if the bike will be difficult to handle, if a tire will pop off, if I'll have issues turning, etc

I used a 17 mm internal width rim on my MTB several years back, together with 2.1" tires. Handling was a non-issue. At the pressures I had to run to avoid snakebite, the bike tracked and steered entirely predictably. If I reduced pressure to get better "buoyancy" on soft surfaces I could possibly sense some vagueness when I hit a hard patch, but that'd usually be moments away from snake bite anyhow, a much bigger problem.
I've only had two tires pop off, ever. One was a clear case of overinflation(borrowed shop compressor), another was a bead failure for unknown reasons. Then of course I've had a couple of folding tires coming off as a result of a flat, but I think of that as another thing.

Biggest thing I can say about the combo I used is that it seemed to be extra harsh on the tire sidewalls, right where the bead merges into the sidewall. Had to retire several tires of different brands early b/c of fraying right there. But even that happened at an acceptable mileage.

In short: I think you should have what you originally ordered anyhow, if not for the actual benefit, so for your rights as a customer. Even if the narrower rim is unlikely to cause much of a problem(if any), it's still not the most suitable option.

I used a 17 mm internal width rim on my MTB several years back, together with 2.1" tires. Handling was a non-issue. At the pressures I had to run to avoid snakebite, the bike tracked and steered entirely predictably. If I reduced pressure to get better "buoyancy" on soft surfaces I could possibly sense some vagueness when I hit a hard patch, but that'd usually be moments away from snake bite anyhow, a much bigger problem.
I've only had two tires pop off, ever. One was a clear case of overinflation(borrowed shop compressor), another was a bead failure for unknown reasons. Then of course I've had a couple of folding tires coming off as a result of a flat, but I think of that as another thing.

Biggest thing I can say about the combo I used is that it seemed to be extra harsh on the tire sidewalls, right where the bead merges into the sidewall. Had to retire several tires of different brands early b/c of fraying right there. But even that happened at an acceptable mileage.

In short: I think you should have what you originally ordered anyhow, if not for the actual benefit, so for your rights as a customer. Even if the narrower rim is unlikely to cause much of a problem(if any), it's still not the most suitable option.

Thanks for this. Much appreciated. I'll be taking the wheel back and ordering the 19mm.

It's on them so there's no reason not to go with the wider rim.

That said, I run 60mm big apples on a 19mm rim at 2.2bar (32psi) and never have trouble, feels rock solid. This is about as much outside of the recommendations as your configuration, and I probably run lower pressure, so you'd be fine. But it costs nothing to get a wider rim from the shop so do that.

One problem you can have with road brakes: The quick release mechanisms won't open far enough to let you extract the wheel without deflating the tire, if you go too far oversized. Part of why tourers and randos often have cantis or CPs?

Personally I believe something important is going on with how the tire sits on the bead and the curvature of the sidewalls, but I don't really know what it is. I tend to keep the rim wider with a wider tire if I can. With say, 42 mm 650b's there aren't a lot of wider rims available for rim brakes.

Yep, that's the one.

I'm wondering why my LBS says that it won't be a problem and SB's site doesn't recommend it. I want to trust my LBS on this one, but I'm not at all sure I should.

I suppose I'm also wondering if it's time to change my LBS.

I've seen discussions of this for years on different boards. I've noticed that few people have seen serious problems such as tires blowing off, so I think the LBSs won't get much extra repair traffic based on a tire-rim width mismatch. From their point of view, it's not a problem, the wheels are still round, rolling, and black. But if you value quick wheel removal, or extra security, or lack of squirminess in your wheels, it's probably best to select rims/tires along the lines of that chart given earlier in this thread.