As title really, after using some cheap clincher 29″ rims on my cross bike so i can go bigger than 33mm (currently on tubs)

Yes

Skinny 23mm’s don’t work well on whopping great rims but for example I happily use 25mm on Pacentis with an inner width of 20mm.
29s are really just wide 700c

great thanks for that

Short answer: Yes

Longer answer: Check the max recomended tyre pressure on the rim. Road rims are reinforced to account the loads high pressure tyres place on a wheel, it’s why they’re often as heavy or heavier than wider XC 29er rims.

If you’re running cross tyres at sub 60 PSI you’ll probably be fine and I’m sure there are people out there who’ve whacked 100 PSI in and had no problems but it’s something to be aware of.

Where did you hear that?

You are aware the stress is higher for a wider tyre at the same pressure?

can be tough to get the tyres on some tubeless rims.

23 or 25 road tyres don’t fit stans rims that well IME.

Stans publish maximum recommended tyre pressures for their rims (on the label) which go down with increasing tyre size.

So do Mavic.

I thought the reason some road rims are relatively heavy is that they have a braking surface whereas most 29er rims are assumed to be disk only.

Stans publish maximum recommended tyre pressures for their rims (on the label) which go down with increasing tyre size.

They do, but that’s for running tubeless. Tubed tyres can be ran higher.

Indeed, also smaller tyres will spread loads out over a shorter section of rim than fat ones, so greater force on a given section of rim. Leaving aside the current trend for aero rims and low spoke counts.

Longer answer: Check the max recomended tyre pressure on the rim. Road rims are reinforced to account the loads high pressure tyres place on a wheel, it’s why they’re often as heavy or heavier than wider XC 29er rims.

Sorry but this is simply not true. Force = Pressure x Area so bigger tyre at lower pressure ~ smaller tyre at higher pressure.

As Al says. And yes, weight is to do with braking surface or absence thereof.

OP – 29er is just a marketing term for 700c rims aimed at mountain bikers. The diameter is the same. They are the same thing. For a narrower (road or MTB) tyre you’d want a narrower rim – for a wider tyre, a wider rim. So the widest (“29er”/MTB rims) would suit only 2″+ MTB tyres (and sometimes, these days, 2.5″+) and the narrowest (700c/road) rims would suit only 23c/25c road tyres – but there’s a lot of overlap in between. Fundamentally though the diameter is what specifies rim & tyre size, and they are the same.

TLDR there’s no difference in diameter, but some narrow tyres would be unsafe on wider rims and some wide tyres would be a weird shape on narrow rims.

Longer answer: Check the max recomended tyre pressure on the rim. Road rims are reinforced to account the loads high pressure tyres place on a wheel, it’s why they’re often as heavy or heavier than wider XC 29er rims.

Sorry but this is simply not true. Force = Pressure x Area so bigger tyre at lower pressure ~ smaller tyre at higher pressure.

…
Well that is not actually the reason. It is to do with the lower radius of curvature of the fatter tyre meaning that higher casing tension around the tyre is needed to hold the pressure in for a given pressure. It is that casing tension which exerts force on the tyre beads and can break the rim. Simply applying force=pressure x area is difficult because the forces on the inside of a tyre are pointing in all directions and you need to add them all up vector wise and when you do there is some cancelling out.

Road rims are reinfoced/heavier, but not so much to account for the pressure on the sidewall. The higher pressure in the tyre is forcing the entirety of the rim into compression. This can be seen when you build a wheel. Built on its own, the wheel may be perfectly tensioned, but as soon as you apply a tyre to the rim and inflate, the compressive force can cause a drop in spoke tension, this is especially true for lightweight spokes.

As road rims are under a uniform 700KPa (240KPa for MTB) they’re under almost 3* the compressive force.

I once tried 28mm Conti GP4Seasons on Stans Crest (for one winter) and they were ridiculously tight. Way too tight to get off with non-metal levers.

The high pressures, even about 60psi, eventually destroyed the rims too. Better to use decent road rims, like the Archetype or new Hydra.

Well that is not actually the reason. It is to do with the lower radius of curvature of the fatter tyre meaning that higher casing tension around the tyre is needed to hold the pressure in for a given pressure. It is that casing tension which exerts force on the tyre beads and can break the rim. Simply applying force=pressure x area is difficult because the forces on the inside of a tyre are pointing in all directions and you need to add them all up vector wise and when you do there is some cancelling out.

Road rims are reinfoced/heavier, but not so much to account for the pressure on the sidewall. The higher pressure in the tyre is forcing the entirety of the rim into compression. This can be seen when you build a wheel. Built on its own, the wheel may be perfectly tensioned, but as soon as you apply a tyre to the rim and inflate, the compressive force can cause a drop in spoke tension, this is especially true for lightweight spokes.

As road rims are under a uniform 700KPa (240KPa for MTB) they’re under almost 3* the compressive force.

Fair comments, there’s much more going on than the simplistic explanation I gave, for sure.

mikekay – Member

As title really, after using some cheap clincher 29″ rims on my cross bike so i can go bigger than 33mm (currently on tubs)

You can get wider tyres than 33 on road rims. I’ve had 38s on pretty standard road wheels. Admittedly wider wims might give you a better contact patch but having run 29er wheels on my commuter they are far heavier than a lighter cross set.

Superstar were my cheap set. My nace wheels are veloxity A23 on hope hubs. The novatec or Kinesis ones look good for an allrounder. There are quite a few off the peg CX wheel sets and disc road set. For racing I’d go with a disc road set but for general riding I’d get something tougher with 32 spokes. Wiggle’s cosine range could be worth a look?

I’m 100kg and have used my 29er wtb i19 for 3000 km with a selection of tyres on my road bike.

Pave 27c (very tight, under the recommended width, rode well in summer until the tyre was cut by glass)
Schwalbe 1 28c (tight, running very well).
Verdestein 28c senseo winter extreme (tight, running well)
Hutchinson 35c contact sport (I think, about time to stick them back on), wired and tight.

I think the tightness is the rims I think rather than the tyres, as the Pave was fine on mavic Open Pros for fitting. I pump them to ~80psi and ride not well cared for country roads without a bother.

My “road bike” has Mavic XM719 29er rims. They work fine with all the road tyres I’ve tried but do look a bit funny with low volume 23 or 25mm tyres.

jonba
Yes but i’m currently on tubs so 33mm is the biggest tire i am aware of, trying to find disc wheels that are sub 1700g for less than £400 is not easy but i found some 29″ wheels that fit the bill and will run 40mm tires (need to check whats the largest i can get in my frame).
Hence the original question.
Mike

jonba
Yes but i’m currently on tubs so 33mm is the biggest tire i am aware of, trying to find disc wheels that are sub 1700g for less than £400 is not easy b

Kinesis Crosslight wheels fit that bill perfectly.

Link to CRC

this is what i found, crc100g lighter and £50 more.

Okay, but they’re 650b…

The 29er versions are all heavier and more expensive than the Crosslights, they are tubeless right out of the box though.

Linked the wrong ones 😳
so your right the crosslights are a bit better

Ah I see. You could try custom but I don’t think you’ll get below 1700g. Mine came from JustRidingAlong. AL23 rims on hope hubs. 32h which bumps up the weight but has meant they’ve survived 3 goes at the 3pks and 4 seasons of cross racing.

You could try spokesman wheels.

Otherwise browse the usual suspects. I would look at Wiggle’s cosine wheels, merlin, ribble etc. I’ve also had good experiences with Rosebikes and for a £400 purchase you’d probably be on to a good thing. I bought a £2k roadie from them and love it!

Sheldonbrown has recommendations on tyre widths I think the ball park is no narower than 1.5x the internal rim diameter. I run 32mm tyres on a superstar mtb rim no problem. Very old so don’t have specs, I believe they are 19mm internal though. There are far more wide clinchers available as most on tubs want to follow UCI rules which limit to 33mm. Fatter clinchers are being pushed by gravel bike marketing. Can’t actually remember the BC rules but at a regional level I’ve never known anyone check widths – probably likely at a national trophy round.

Yes but i’m currently on tubs so 33mm is the biggest tire i am aware of, trying to find disc wheels that are sub 1700g for less than £400 is not easy

Mine were less than 1700g and cost £370: Stans Grail rims (24 spoke), Novatec disc hubs, Sapim CX-Ray spokes, brass nipples.

Built by Spokesman.

You could also try Hunt wheels.

Had 32c on the Bontrager Rhythmn Elite last summer. The wheels looked fine, but they made the bike look weird with it’s 29+ compatible fork. Lots of mud clearance 🙂

Bike rode nicely though.