I’m looking at upgrading my gravel bike via a new frame (keeping the components) that can take up to 50mm tires from my current that is limited to 40mm. How much, if any, of a difference would also upgrading from 21mm internal width rim to a more “modern” 25mm+ internal width for a 45mm or maybe 50mm tire?
Define “difference”…..
In general, you will end up with more width for the same time on the 25 IW rim. This increases comfort, traction, etc. and can also lead to having to sue slightly lower PSI.
If you are getting a new bike, I’d say it isn’t worth limiting yourself with 21mm IW rims in 2026. If anything, 25mm IW will soon be seen as too narrow. Zipp is 32mm, rumors of incoming rims from ENVE at 35mm and many DTC brands at 28mm.
For clarity, I’m just looking at getting a new frame and using my existing components
More precise on my question: how much of an improvement in comfort / traction would there be going from a 21mm internal width rim to a wider (25? 28? ???) internal width rim on top of going from a 40mm to either a 45mm or 50mm tire?
There are a lot of variables that factor into the answer….tire choice, pressure choices, rim depth, etc. If is almost impossible to quantify the improvement.
Will it be noticeable? IMO, yes. Will it be “significant”? Unfortunately, “it depends” applies.
Personally, I would do it….as long as the budget allows it.
2 Likes
You will very materially notice the improvement, so long as you buy the right tires
I’ve got 2 sets of wheels set up for my gravel bike with identical tyres - 50mm Bontrager RSL Betassos.
One rim is “optimised for wide tyres" and has an internal width of 25nm, the others are old road wheels with just 19.5mm internal.
The difference in inflated tyre width is barely 2mm and the tyre profiles look identical side by side - you literally need a set of calipers to differentiate.
The only noticeable difference is because the narrower wheels are 50mm deep carbon so look Sick AF and combined with the big tyre are a real handful in crosswinds!
1 Like
According to the ETRTO chart i21mm rims are good for tyres with nominal widths from 25-65mm and i25 from 29-71mm. Back before wide rims became ubiquitous people survived with even narrower rims(!) - and usually didn’t die. FWIW, I ran 2.2” MTB tyres on ~i22mm rims for a roughly 7000km loaded off-road tour BITD and they were fine, even at low pressure.
Tyres matter quite a bit, rim widths not so much. (Having said that, I’d go a bit wider now if buying new wheels, but there’s no rush to do so given how many wheels I have kicking about.)
1 Like
Yup BITD the rim to have on your CX MTB was the Mavic 717 because it came in cool colours, and as the name suggests had a 17mm internal width.
In the beginning of the year I’ve changed old aluminium stock 23 inner width wheelset with Miche Graff Aero 48 - 27 mm inner width
so the only difference which I see about internal width is more confidence to run it with much lower pressure than before. But also tire size is going a bit up, in my case Schwalbe RX/RS both increased up to 47 from standard 45
2 Likes
It is significant. I have this exact comparison - swapping Wheelsets on my Giant Revolt and Specialized Crux. I have Roval C38 wheels - which are 21mm internal - and Roval Terra wheels - at 25mm internal. The C38 wheels are okay with gravel (or road) tires to around 32mm but after that the shape they take on is not optimal. I have done 35mm and 38mm (for CX races) and the shape they take on is not optimal for higher speed gravel. In contrast I regularly run 40 or 45mm gravel tires on my 25mm wheel set and I run around 30 - 35 psi (or 40 if on a lot of road). I ran a 2.2 in tire once as well (not optimal LOL). When I used those wider wheels for CX racing I usually limit myself to 38mm tires but am running more like 20 psi (and low speeds).
So to sum up based on my experience, the wider rim will let you run a 40 - 50mm and at a lower pressure with an optimal tire shape. If you get a new frameset - IMO modernize the wheels set as well. Keep the old wheels to swap on when you want a dedicated road setup with 32mm tires.
2 Likes