Hello STW

I’m building a pair of wheels for my new-to-me SB5c. I like Nobby Nic 2.35s and have bought some Pro4 hubs.

Rims though – I was going for Stans Arch EX but the 21mm internal width is very un-trendy, apparently.

Easton ARCs look cool and come in 24/27/30mm internal widths – i.e. mega wide external widths. What width is most sensible for 2.35-2.4″ tyres? Are the 30mm for 2.8″ 6-fattie wheels, or the most future-proof? Should I follow my indecisiveness and just go for the middle 27mm choice?!

Bob

Watching this with interest – having the exact same dilemma. 26″ Arch EX on my current bike have been great, but my next bike comes with Easton Arc 27 unless I spec it otherwise. Can’t help suspecting that a wider rim will increase rolling resistance, though people tell me otherwise. Arc 27 are also 50g per rim heavier than Arch.

I’ve got Arc30 and Arc27 rims. I’ve also ridden Flow ex, Arch Ex rims.

If you’re running tyres over 2.25 you’ll really appreciate the wider rim. You don’t need to go to 30mm to get the benefit, anything 25mm or above is spot on.

They don’t noticeably increase rolling resistance, what they do do is increase grip and stability.

If you’re worrying about 50g on a wheel, then the 30s aren’t really for you, as you won’t really feel the benefits over a 25mm rim.

The arc27 and arc30 are great rims, stiff, compliant enough and tubeless dead easy with a track pump.

Also, as a warning, don’t rely on the ERD provided by easton, as they’re incorrect. Measure yourself first.

Rickon – cheers, useful info. I’m not massively worried about the extra 50g – just that when I got the Arches I was really pleasantly surprised by how fast they are on a trail bike. Wary of straying back into heavy wheel territory, though I appreciate Arc 27s aren’t exactly heavy. Defo like the idea of more grip and stability, so I reckon I’ll give the Arcs a go.

Personally I think it’s a case of emperors new clothes.

I’ve got a set of wide rims (30mm internal) on a bike and they don’t grip any more than a set of other wheels with 23mm rims.

In some cases it can be less, as the wider rims ‘square’ the tyre off, so leaning the bike over becomes interesting. Also I can’t subscribe to the wider rim = lower pressure theory, a soft tyre feels like crap if you push it, squirming all over the place.

I reckon anything around the 22-27mm mark for normal tyres is about the sweet spot, with normal, sensible tyre pressures.

Generally agree, although I do notice there feels like less sidewall support on rims under 23mm. I didn’t notice much difference from 25.5mm flow exs to 30mm LB rims in terms of grip, but I did from 22mm to 27mm.

If you’re running tyres under 2.3, they will get flat, and feel a bit weird on really wide rims.

Thanks all – leaning toward the 27mm then as it seems a sensible option

When I first converted to 650b I was going to go with the 27 as my do-it-all wheel set, but I was lucky enough to get a deal on a set of built 24s, which means I’ll convert my 26 wheels to arc30 for dh use. But if I had just one I’d go with the 27s.

Id agree that 26/27 is the sweet spot for tyres right now, although for future proofing I would still go 30mm personally …. actually thats a lie. I would go 30mm XM481 rims because they don’t make a 27mm version, given the XM481 is a similar enough price in the grand scheme of things.

I looked at the Arcs but read some bad reviews of them. In the end I couldn’t justify the cost of DT Swiss wheelsets and went for some WTB Team I25 on pro 2.

I got a really good deal off a friend and I’m tempted to sell the rims and get some XM481s further down the line.

No issues here running arc 27 rear and 30 front on DT Swiss 240s with revolution spokes. 1643g

Plenty stiff and durable on my do it all HT.

went bonkers last year splashed out on a & a shiny new pair if Roval Fattie SL’s 30mm internal width the tyre profile changes a lot & gives a much better feel & I’ve not pinch flatted in a year & I’m not exactly the lightest or gentle type of rider.

Weight for the wheels comes in at just over 1500gms, but the grips levels really are impressive so for me I’d go 30mm but each to there own.

Personally I think it’s a case of emperors new clothes

this is bollox if you are a heavier rider.
a well known bike designer and trouser make told me years ago that a larger heavier rider needs a wide rim.
I trust his advice.

I had the same dilemma and settled for the 27’s as a balance of weight and width.
I’ve been running them since November, mainly across a harsh wet Winter Dartmoor.
Been very happy so far, no ‘soft as butter’ dinks as reported by one review i read.
The wheels are built up with Hope Pro 2 hubs.

I feel more confident on wider rims, not sure if that’s in my head out not,lb 35mm I’d agree you need something above 2.25 the width tho

I’m amazed that people still think wide rims and low pressures DONT offer advantages to MTB.

Just take a look at every off-road discpline involving wheels.

My ancient D321s are looking better all the time. I just need to stretch them a little…. maybe if I loosen the spokes they’ll expand?

Scienceofficer
Just take a look at every off-road discpline involving wheels. Couldn’t agree more.

I’m completely with you, I raced school boy & adult motocross in my youth, (Soooo many years ago) we ran mega low pressures to spread the tyre and increase grip, the lower the pressure the great the contact patch. Narrower rim & Higher pressures the more rounded profile = smaller contact patch, less grip simples…

A friend recently installed Pro Core on 27mm wide DT rims, ok he’s a light rider but running a TL Rockrazor with 18 psi in the lakes doing fast boulder descents with no issues with massive increased grip was impressive, I chased him down descents at speed that really we should know better & he straight lined them, you had to be there to see it, so anyone considering pro Core to allow them to run low pressures I’d go for it.

A glance at all the varied Specialized bikes in my LBS & most seem to have 30mm internal rims & 2.3″ Spesh tyres.

Just take a look at every off-road discpline involving wheels.

And look how many have an engine driving them.

Low pressure = slower rolling, so more effort required, tyres folding over in corners & feeling like crap, and if you’re really lucky, burp central.

Really not interested in adding 1kg to my wheelset with Procore so I might be able to run lower tyre pressure in the hope it might work (plenty of very public failures already).

Just take a look at every off-road discpline involving wheels.

I’ll bet these have massively heavier sidewalls than are run on MTB’s. Therein lies the compromise.

Id do some more reading hob-nob. Your ideas on slower rolling speed from lower pressures are somewhat out of date and mostly disproved now, at least off-road.

Stevet1 – for sure! The MTB market is still learning this bit at the moment IMO. Plus size tyres are, I reckon, at least in part a response to managing rim strikes from low pressures by giving more volume as a safety margin. Personally, I’m increasingly heading to stiffer sidewalls, since lower ground pressure from super wide tyres isn’t always what you want – see references to plus tyres not turning in mud.

Id do some more reading hob-nob. Your ideas on slower rolling speed from lower pressures are somewhat out of date and mostly disproved now, at least off-road.

So they are, I guess there is a threshold point though. I know if I ran 15psi in my tyres for example, it wouldn’t roll very well.

And notwithstanding the other points, it would ride like crap & probably result in tearing the tyre off the rim on the first, half decent corner at speed.

For me (key part) wide rims & low pressures offer me no benefits.

Yeah. I agree. There has to be a sliding scale of lower pressures versus stiffer, more robust sidewalls/casings. Balance point along the line is going to be based on weight a nd riding style I would have thought. For sure, DHers don’t seem keen on low pressures, but for general trail riding, it suits me.

I hate low pressures. I don’t need more grip than I get at high pressure (XC riding) and I don’t want tyres feeling like they are going to roll off the rim on corners that are hard surface and I don’t want a tyre squirming away as I power up a standing climb.

I do however feel that my 2.3 Race Kings look too big for my Stan’s Alpine rims (21mm internal) but live with it as I like the 340g weight of them.

Low pressure = slower rolling, so more effort required, tyres folding over in corners & feeling like crap, and if you’re really lucky, burp central

All of the above Pro Core eliminates bar more effort on the climbs.
I was skeptical until I saw it in action & rode the bike, a light weight thin wall Rockrazor flat out down boulder descents in the lakes normally would be in tatters but not so, but hey were all different huh.
I think back to spindly mavics & the rounded tyre profile compared to more recent rim developments & profiles I feel I have far more grip.

After demoing a spesh fattie for a full days ride in the lakes I was hugely impressed with it’s grip & climbing ability but not keen on the slightly vauge wandering sensation when going at it on the descents.

Really not interested in adding 1kg to my wheelset with Procore so I might be able to run lower tyre pressure in the hope it might work (plenty of very public failures already).

it’s, er, 200g/wheel – roughly the same as a tube.

of those public failures, you can almost guarantee that they’d have been failures without procore, and who knows how many extra failures would have occurred without it…

An update that anyone buying ARCs might be interested in…

I went for the ARC 27 and have just built up the front wheel on Hope Pro 4.

ERD is published as 558, but you need to add the height of the nipple head to that. Easton describe it as 558++ on the website (but not on the rim itself) where each + is the nipple head.

My DT Swiss brass nipples are about 1.5mm high, so I calculated spoke lengths from 561 (I also measured across the rim with spokes attached to nipples and got 561), and they were just about right.

Only the third wheel I’ve ever built but I’m pretty chuffed with it. No idea how these things ride yet though!