Widest tyre on a 25mm internal rim ?

I had 2.0 race kings and Fat Franks on 14mm internal open pros in my monstercross/graveltype bike.  Rode them fairly hard for a gravelbike, raced a bit.  It was absolutely fine.  I wouldn't want to use the same on FS bike, riding how and what I ride on that.

Most DH riders still use 25mm internal, I think?  So I reckon you can use whatever you like, short of plus size tyres over 2.6?

There's prob a recommend width of upto 2.1 - but you could prob get away with going wider, but.... The shape of the tyre will be come rounder the wider you go which will affect grip and rolling resistance.

I ran 2.8/2.6 on 25mm rims as an experiment before building up proper plus rims a few years ago. Worked fine, but tyre profile ended being a bit rounded.

Schwalbe say 3.2"

Light Bike say 2.6"-2.8"

I'd say 2.4"-2.6" is about right.

@daffy - I reckon those larger numbers would be a bit problematic for heavier riders so you're more in the right area.

(PS did you get that link to the XL Fatbike I sent you @ton ?)

The answers seem to be all over the place here

I run some 25mm rims on the rear and 2.4in works really well on them.

Could probably get away with 2.5 depending but it might be starting to get sub-optimal in performance, though some 2.5s come up small anyway.

@scotroutes

No mate. Please send it again.

The answers seem to be all over the place here

As somebody who talks tyres for a job, please let me intervene...

What works and what is ideal are 2 different things... 2.5" is probably an ideal maximum width on a 25mm internal rim, but that's not to say you can't run a 3" tyre on it if you wanted to... I know people that have! Christ, back around 20yrs ago, me and my mates were all running 2.8" Michelin Comp 32's on Mavic 721's (21mm internal) on the front of our bikes for a week in Morzine!

Also depends how you like the bike to handle... A big reason a lot of DH riders still use 25mm rims is to give the tyre a more aggressive shape than a 30mm rim would, so it's easier to bank it over and not fall off the edge knobs. A trail centre bimbler that never leans the bike over will likely much prefer a much wider rim that gives the tyre a flatter profile and engages more of the knobs, more of the time, but is quite limited when leaning hard into corners.

As above 2.5" is a reasonable max, there's no issues running 2.35, 2 .4 ime so 2.5 won't be asking too much,  I wouldn't push it to 2.6 though.

@mboy that makes so much sense! 721 was rated up to 3.0 (mmm Gazzas ) so would definitely be rounded out.

Almost anything can work, 2.5" tyres have been around for years including back when rims didn't go wider than 21mm. I'm running a 2.6" tyre on a 25mm rim and I find it fine.

The issues are more likely to be around what pressure you are able to run and whether the tyre will be the right shape (too square or too round)

I run 25mm rims on my bikes, mainly be default as one bike came with them and the other is down to the rims the wheelset was built on, they both run 2.25" XC tyres absolutely  fine down to around 20psi dependent on conditions, I'm 79kg BTW

WTB say 60mm optimal 70mm max compatible

https://www.wtb.com/pages/tire-rim-fit-chart

That’s about 2.5 inches optimal, 2.8 inches max.

Got a 2.6" on the front of a rigid mtb with 25mm internal rim. It's fine but I'm on the light side of rider weight. And it's a fairly slim 2.6" tyre, barely wider than some of the larger 2.4"s I have.

Mavic say 64mm (2.5") on a tubeless-compatible rim, run tubeless, with a max pressure of 3.1 bar

Hookless, tubeless is 54mm (2.1") at 2.7 bar max

Abridged version of the original Mavic article here... https://capovelo.com/getting-right-tire-width-right-rim-width/

It's worth saying that not all 25mm rims are equal.  25mm hookless give a much better profile to a tyre than hooked 25mm rims.  I'd be fine with a 2.6 on a hookless rim.

I don't think anyone has mentioned casing, unless I missed it

I run a 2.6" on the rear of my hardtail and never have tyre stability problems, but it's an enduro tyre so the stiff casing helps

I used to run a 3.0 Minion on a 29mm internal width rim and I found that to be great. When I added a Rimpact insert, I had the pressure down to 10 psi and it was still stable

In contrast, I ran a Schwalbe 2.6" with an XC casing on a 23mm or width rim years ago and it was genuinely dangerous

Hope Tech Enduro rims were only 23mm internal a few years ago remember