Are Wide rims too wide?

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bm0p700f
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by bm0p700f

I thought a 29er can't be much better than a 26er bit when my main MTB died I thought I would build one up and wow I am converted. The point is until you try doing miles on wider rims you won't know why other use them. I have some narrow rimmed wheels left in my stash and every time I use I wonder why I have not sold them or re mimmed them. That I have to get round to as I don't like the the ride anymore and speed loss over rougher roads which Britain aplenty.

Wingnut
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by Wingnut

Yeah I've heard 29 seems to roll over obstacles better than 26 but my understanding is 26 can take a heavier load which is why I use them for touring...

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petromyzon
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by petromyzon

I agree with CycleClinic - I recently built up a set of new shape Pacenti SL23 rims and I am running them with 23mm Conti GPTTs. Hands down the best feeling wheel/rubber combination I've ever had.

I have yet to try them with a thicker tyre and feel that the rubber may be a key factor here, but the fact that you can run them at incredibly low pressures without any detectable squirm is really impressive. As for rolling resistance, I would really like to see someone put a 15mm IW rim and a 20mm IW rim on a rolling resistance rig and test it. Am I sacrificing a lot of speed at these low pressures??

Regarding safety, I note that HED put a pressure limit of 100psi max on their 20mm IW rims - seems reasonable. Beyond that and the fact that very wide rims might leave sidewalls more vulnerable I think Mavic's concerns might be overblown. What I do think is unsafe is large, non-standard bead seat diameters and very low sidewalls - I have popped an open tubular type clincher off a Stan's Alpha 340 with just a few strokes of a track pump and now will only use meaty road tubeless tyres at low pressure on those rims.

The new shape SL23s are absolutely superb - incredibly stiff, 30grams/rim lighter than an open pro, much better finished and allegedly with a thicker spoke bed which should eliminate cracks. Would never go back and would recommend to anyone - Pacenti is a genius.

bm0p700f
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by bm0p700f

Stans 340 rims should only be used with tubeless tyres the tyre blowoff problem is well know and is due to the unique/crap hook design they have. Well it not crap for tubeless tyres I suppose.

I have tyres from 23mm to 30mm on my 25mm wide rims. the wider the tyre get the better it all feels. My 30mm tyres absorb take potholes in there stride. so for me tyres cant be too wide. I dont think the extra width and low pressure slows me down when just riding, if racing then that maybe different but my race bike will only take a 23mm tyre on a wide rim and no more.

wingnut you can build a 29er wheel that can take daft loads reliably so there is an solution to every problem. Its not just rolling over obsticles that a 29er has an edge even on smooth roads rolling resistance is lower (as it proportional to wheel radius) so a 29er feels more like a road bike in terms of pace on the road than 26er can. I should do a club run it really maybe I will this sunday.

dmulligan
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by dmulligan

At what width do rims start to be too big for brakes?

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Calnago
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by Calnago

That depends, on the brakes, and the tire you want to use. The new shimano brakes can open up to accommodate wider runs without concern for tire size (to a point obviously). The clearance underneath the brake arms remains the same regardless of how wide you open them up. But with campy brakes it's a little less cut and dry, especially when using clinchers. The reason is that as you open up campy brakes to accommodate a wider rim, the arms of the brakes come down lower on top. This can be a problem if you want to run even some 25mm clinchers on a wide rim because although you may be able to get the brakes open wide enough to accommodate the rim just fine, the larger tire will sit taller and sometimes hit the brake arms. So best to experiment with the setup you want to use to be sure. Sorry I can't be more definitive but it does really depend on the setup you're running or want to run.
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by Marin

I did some rolldown/rolling resistance test with nicely reproducible results in our condo's indoor car park.

As expected, my fastest combo were Conti Force/TT with Latex.
I was hoping my Panaracer Evo L 23mm would be similar, and with R'Air butyl tubes they were pretty close.

So I tried them with latex as well, and moved them from 15c to 18.5c rims too. The Tires went from 22mm to 24mm on the wide rims.

Result: Slower than before! What gives?

I'm pretty sure I didn't introduce any other factors. The only thing could be wheel bearings / freehub drag, but I'd expect this to not be visible in a rolldown. Rolling times were around 1 minute to 1:10.

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by mr4fox

Veloflex, Vittoria and Schwalbe all told me that their 25mm clinchers/open tubulars are not compatible on my Pacenti SL23 rims. I usually ride tubulars and because SL23 rims are such a nightmare to mount tyres on i usually just use my carbon tubs in bad weather too so have probably only done about 1500km on the clinchers in the last 12 months. I havent had any problems with tyres popping off the rims unexpectedly. The tyres are on so tight i can't ever imagine one popping off. Ive recently mounted Schwalbe Pro One road tubeless. Now that was a challenge! the only way that tyre is ever coming off is with a knife and some elbow grease!! ...im scared of getting a puncture that the sealant cant fix.

I dont get why the etrto chart suddenly jumps from a 28mm tyre being ok on a 19mm IW rim but then they recommend a 35mm tyre as the minimum for my Pacentis with a 20.3mm tyre...at east according to Schwalbes email. I don't know how the etrto measurements were derived but they clearly never foresaw this tyre/rim combo. plus the shwab Pro One 25mm tyre measure 27.8mm wide on the SL23 rimsand when i laid them flat against a 25mm Conti GP4000s tyre they were a good few mm wider bead to bead than the conti...so should it be regarded as a 25 or 28mm tyre on the etrto chart??

I wouldn't recommend Pacenti rims to my worst enemy (i don't really have enemies...well may kirk Pacenti) because mounting tyres on these rims is just a royal pita until they've already been on the rims for a few months and stretched....which i believe doesn't happen with road tubeless tyres. plus breaking tyre levers or puncturing a tube on installation is a 50:50 chance. But at least due to his lack of quality control or possible engineering skills I'm confident i wont die from a 25mm tyre popping off his rims.

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by beatle

I have a rear Pacenti23 rim and I have had no trouble mounting IRCs or Schwalbes by hand.

mr4fox
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by mr4fox

Ive read a lot of reports of people struggling with the Pacenti SL23 v1 rims but ive also read of others not having issues. i can onnly assume its a quality control thing. ive never had issues moutning tyres on anything else be it tubeless ready rims or normal clinchers. Ive changed huge motorbike tyres by hand with less drama (and force!) than is needed to get a Schwalbe Pro One tubeless onto my rims.

jeffy
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by jeffy

please to hear from cycleclinic and others are running 23mm tyres on a 25mm rim. Am think of doing the same next tyre swap and was a little concerned - wanted to try to get a 25mm measured tyre on a 25mm OD rim and thought the 23mm would be closest.

What difference to the 'measured when mounted' size does internal rim diameter contributed.

Eg which of the below rims would the same tyre measure wider/narrower?

25mm OD 17mm ID
vs
25mm OD 20mm ID

bm0p700f
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by bm0p700f

The weird thing is roadies worry about things like 23mm tyres on a 25mm wide rim. MTBer having for decades been ignoring the ERTRO charts for tyre size and you know we are all still alive although some of the combinatons did not feel that great.

In a down hill race one rider recently proved that tyres are in fact optional.

Tyre mounting of some tyres to Pacenti SL23 rims is a pain but then again there are always some tyre rim combo's that is a pain. Conti GP4000s tyres slipped on the SL23 V1 and even easier to the V2. One of the hardest tyres/rim combo's I have tried is a gatorskin hardshell 25mm on a Mavic GP40 rim (well it was something similar in name anyway) I swore cursed and eventually it went on. There are a couple of combinations that I have found not to be even possible.

Tubeless tyres opens up a whole can of worms. To get tyres that seat with a hand/floor pump they have to be tight. I have carbon tubeless rims that need help to get IRC tyres to seat but once they have they are secure. The old schwable one on the V1 Pacenti rim is one I mount by hand (had to do it once at night on a cold winter nights when I got a sidewall cut that sealant would not plug). My hands are of average size and strength maybe a bit above average but I am not a Gorrilla with hands the size of shovels.

Internal width dictates tyre width and height. Eternal width tell you how wide the rim is.

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by glepore

As far as cornering feel goes, yeah, 25's don't feel as "crisp" on initial turn in, but the bigger contact patch makes for more ultimate grip, at least that's my subjective feel.
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by HermesSport

I'm not familiar with the circumstances of how the ETRTO guidelines were developed originally, however I feel that by now it's safe to say that they're unduly conservative in terms of dictating what tires can fit on what rims. It's been safely demonstrated for years that you can mount tires well beyond the established guidelines, however there has been no effort on the part of the ETRTO to revisit the matter. As I recall, the criteria for establishing their guidelines were pretty opaque too.
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