Tire and Rim Width Compatibility: Is There a Definitive Answer?

[XXtwindad]

This is still confusing to me. I was considering buying a buddy’s used ENVE 4.5 AR disc wheelset. The specs are 25 interior width and 31 exterior width. They are optimized for 28c tires, according to ENVE.

My LBS said, unequivocally, that a 28c tire WILL NOT work on this rim, because it’s narrower than the exterior. That seems to make sense. I trust my LBS. Very knowledgeable. OTH, ENVE has some pretty savvy people working there as well.

Thoughts? Is there a definitive answer? Thx.

[jkbrwn]

Definitive answer? Probably not. Your LBS's advice? Nonsense.

You said it yourself, ENVE are one of the few rim manufacturer's who've gone to the trouble of testing tyres on their rims. I would absolutely trust ENVE.

[jtakeda]

This is still confusing to me. I was considering buying a buddy’s used ENVE 4.5 AR disc wheelset. The specs are 25 interior width and 31 exterior width. They are optimized for 28c tires, according to ENVE.

My LBS said, unequivocally, that a 28c tire WILL NOT work on this rim, because it’s narrower than the exterior. That seems to make sense. I trust my LBS. Very knowledgeable. OTH, ENVE has some pretty savvy people working there as well.

Thoughts? Is there a definitive answer? Thx.

According to Jan Heine your LBS is correct.

The tire should be 20% wider than the rim youre using. (internal measurement)
https://www.renehersecycles.com/myth-18-wide-tires-need-wide-rims/

Personally I would not ride a tire that narrow on those wheels

[weiwentg]

This is still confusing to me. I was considering buying a buddy’s used ENVE 4.5 AR disc wheelset. The specs are 25 interior width and 31 exterior width. They are optimized for 28c tires, according to ENVE.

My LBS said, unequivocally, that a 28c tire WILL NOT work on this rim, because it’s narrower than the exterior. That seems to make sense. I trust my LBS. Very knowledgeable. OTH, ENVE has some pretty savvy people working there as well.

Thoughts? Is there a definitive answer? Thx.

Your LBS is wrong.

OK, your LBS is not wrong if we are going by the book, i.e. we are following the ETRTO tire-rim compatibility guide (https://bikerumor.com/2016/08/12/tech-story-match-bicycle-tire-width-rim-width-best-results/), which Bikerumor reproduced. To read this, the left column is nominal tire width. Let's assume your Enves are hooked rims (i.e. crochet style). The rightmost column is the rim internal widths that are compatible with the given tire width. So, by the book, you should be fine with 15 to 19mm internal rims.

If those are hookless rims, then you are doomed, and your buddy should be dead by all accounts. The smallest tire compatible with 25mm internal diameter hookless is probably 47mm, maybe a bit less.

However, the book is wrong. This is an old specification. It's currently undergoing revision. Also, if you want to maximize aerodynamics, refer your LBS to the rule of 105 - the rim's max external width should be no less than 105% of the tire's mounted width to accomplish that. (Admittedly, that is an older rule as well. It originates with Josh Poertner, currently with Silca, but used to work at Zipp.)

My main wheelset is also way out of compliance with the ETRTO chart. I've got 19.4mm internal width, 25mm nominal tire. By the book, I should be on no more than a 17mm internal width rim. And yet, here I am.

I have a wheeset with 25mm internal width built by November Bicycles. It's on my gravel bike. I believe that November's said that they wouldn't mount anything under 28mm on it, but I'm not sure if they did testing or if that was based on their opinion and experience. Either way, I'm pretty sure they have said that a 28mm tire would be fine on that particular rim (I believe it's a Light Bicycles rim, but I can't confirm).

I suspect that many of us are on wheels that are outside the ETRTO tire/rim standards. If it were an issue, more of us would have crashed.

[jkbrwn]

This is a 28mm tyre mounted to an ENVE AR rim.

https://www.slowtwitch.com/articles/images/1/186461-largest_ENVE-SES-AR-3.4-all-road-gravel-disc-brake-wheel-review-10.jpg

It measures 32.4mm wide. I don't see a problem here and I do not see what issue your LBS would have either.

Edit - yes^ as stated above.

[ColonelJLloyd]

I can't see that anything bad is going to happen. The tire doesn't know how wide the exterior of the rim is. I do think this is near the extreme and not something I would run, but that's mostly because I believe I'm done with tires narrower than 32mm probably forever.

If these are hookless design and you're going to run tubeless then that would further push me into the "perhaps you can, but I wouldn't" column.

[jtakeda]

These are hookless rims I believe, which is what led me to say I probably wouldnt do it but Enve does say its ok to do it

[Mark McM]

You're LBS's reasoning makes no sense. The outside width has nothing to do with the what tires will work- the tire attaches to the inside of the rim (and the tire neither knows nor cares what the outside width is).

In regard to the Jan Heine's recommendation, this appears to be based on rims based on ERTRO standards. The ERTRO standard allows quite a loose tolerance for the depth of the tire well inside the rim; hence, tire retention is based almost entirely on the bead interlocking with the rim "hook". There is a limit to the range of tire widths with which the bead will be reliably retained by the hook, so Jan Heine's recommendation makes sense for this type of rim. But many tubeless ready rims have an additional method of retaining the bead, namely a distinct "shelf" of a well controlled circumference, upon which the tire bead seats tightly against. When mated with a tubeless ready tire, these rims can work with a wider range of tire widths.

As an example, HED recommends using tires of 22-23mm width on their HED Jet Plus and Belgium Plus rims, which have an inner width of 24mm.

[weiwentg]

You're LBS's reasoning makes no sense. The outside width has nothing to do with the what tires will work- the tire attaches to the inside of the rim (and the tire neither knows nor cares what the outside width is).

In regard to the Jan Heine's recommendation, this appears to be based on rims based on ERTRO standards. The ERTRO standard allows quite a loose tolerance for the depth of the tire well inside the rim; hence, tire retention is based almost entirely on the bead interlocking with the rim "hook". There is a limit to the range of tire widths with which the bead will be reliably retained by the hook, so Jan Heine's recommendation makes sense for this type of rim. But many tubeless ready rims have an additional method of retaining the bead, namely a distinct "shelf" of a well controlled circumference, upon which the tire bead seats tightly against. When mated with a tubeless ready tire, these rims can work with a wider range of tire widths.

As an example, HED recommends using tires of 22-23mm width on their HED Jet Plus and Belgium Plus rims, which have an inner width of 24mm.

Actually, I believe the Jets' external width is 25mm, and the internal width is 21mm (https://store.hedcycling.com/jet-plus-rim-brake/). Nevertheless, 22-23mm tires are still far out of the ETRTO spec for 21mm internal width hooked rims, so your broader point remains.

[Toddykins]

The point of this thread was that you should find new bike shop right?

[Mark McM]

Actually, I believe the Jets' external width is 25mm, and the internal width is 21mm (https://store.hedcycling.com/jet-plus-rim-brake/). Nevertheless, 22-23mm tires are still far out of the ETRTO spec for 21mm internal width hooked rims, so your broader point remains.

Oops, you got me, I mis-remembered the spec. of those rims.

It might also be good to mention "the rule of 105" for wheel aerodynamics. During Zipp's testing of tire and wheel combinations, they found that for best performance, the rim width should be at least 105% of the tire width. This has lead to many aero wheels being developed with toroidal shaped rims, which bulge out beyond the width of the tire. So not only are tires narrower than rims often allowed, but sometimes they are even recommended.

[XXtwindad]

Oops, you got me, I mis-remembered the spec. of those rims.

It might also be good to mention "the rule of 105" for wheel aerodynamics. During Zipp's testing of tire and wheel combinations, they found that for best performance, the rim width should be at least 105% of the tire width. This has lead to many aero wheels being developed with toroidal shaped rims, which bulge out beyond the width of the tire. So not only are tires narrower than rims often allowed, but sometimes they are even recommended.

Hey Mark -

Since you’re one of the people whose opinion I have often sought out is my LBS (and by extension Jan Heine I guess) mistaken? A simple “yes” or “no” would be great :)

[sparky33]

LBS experts are on par with internet experts.

[mj_michigan]

I think the answer is in the max pressure the rim is rated for versus the tire pressure you would want to run.

I used a 25mm tire with an inner tube on hooked DT-Swiss 540 rim (19mm interior) and it blew off the rim in the middle of the night. I pumped them up to 105-110psi as I usually do (I weigh 200 lbs). When checking why this happened, noticed that the rim showed max pressure of 6bar (90 psi).

[Mark McM]

Hey Mark -

Since you’re one of the people whose opinion I have often sought out is my LBS (and by extension Jan Heine I guess) mistaken? A simple “yes” or “no” would be great :)

For this particular wheel, no, your LBS is not right. The LBS's advice might have been the right years ago for older wheels and tires, but not for the newer rim and tire designs.

[XXtwindad]

For this particular wheel, no, your LBS is not right. The LBS's advice might have been the right years ago for older wheels and tires, but not for the newer rim and tire designs.

Thx. I’ll consider it settled.

[November Dave]

Mark is correct, the LBS is incorrect.

There are a lot of things to consider when putting together a rim/tire combo. The first is safety - will it work and stay on the rim? The answer here is yes, more through having been proven in comprehensive usage.

The second is "will this do what I want it to do, and at what cost?" Using a 28mm tire on a 25mm inner/32mm outer rim or similar will maximize aerodynamic speed, but will reduce the tire's contribution to bike suspension (and in this case the tire is probably providing all of the suspension) and leaves the rim more susceptible to damage from potholes etc. Wider tires fold over the rim edges when compressed, narrower tires tuck into the rim cavity when compressed.

Generally, road tires will have the closest match between rim and tire width. Gravel and mtb tires do better with a wider disparity between tire and rim width, both for the benefit of suspension and traction, plus the rim protection feature noted above. A tire on too wide a rim will have vertical sidewalls which will reduce suspension and may square off the tread too much, increasing tread squirm in cornering and creating very on/off traction in cornering. This post details this more with illustrations (https://novemberbicycles.com/blogs/blog/wider-is-better-until-it-isnt?_pos=1&_sid=d3484a92c&_ss=r).

[RoosterCogset]

The linked article is relatively newer than the old ETRTO guidelines, and I like the charts near the end because they use that use a 4-factor compatibility matrix (rim type, rim width, tire width, and max PSI recommended).

For OP's example, a 28mm tire on a 25mm internal hookless rim (TSS column) shows as compatible (since there's a BAR value posted) but only inflated up to 4.1 Bar = ~60psi

https://engineerstalk.mavic.com/en/the-right-tyre-width-on-the-right-rim-width/

https://engineerstalk.mavic.com/wp-content/uploads/2015/09/tableau1-1.jpg

https://engineerstalk.mavic.com/wp-content/uploads/2015/09/tableau2-1.jpg