- This topic has 11 replies, 7 voices, and was last updated 11 years ago by chiefgrooveguru.
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29 Vs 26: Rolling circumference
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crotchrocketFree MemberPosted 11 years ago
accepting the fact that the bike:human system is a complex interface, that people have different needs and requirements and blah blah blah. I got to thinking a min ago about rotating weight.
I read somewhere (unsubstantiated, received wisdom – I stand to be corrected) that rotating weight is equal to 3 times as much “sprung weight” (frame/rider/drive chain etc).
I have also seen the length some will go to to reduce rotating weight – 120g/£10 to swap wire for kevlar on a folding tyre.We can assume that where 29ers originate (California) is largely dry, I can attest to that. In fact many CA dwellers have said “Americans don’t ride in the wet. we don’t have to so why would we.” As we know we have a very different climate in the UK.
The other thing I noticed is that Each 29er I’ve ridden was supplied with super light paper thin race tyres.Another point I would like to make “Engineering is compromise”
so here is my quandary: how much extra rotating weight is added by a chunky 29er tyre with the mud that would stick to it & at what point does it become less efficient than a 26er.
tinsyFree MemberPosted 11 years agoDunno, but please factor in that the 29 wheel is rotating slower for a given speed into your calculations.
I hope this helps. 🙂
ampthillFull MemberPosted 11 years agoAll atempts to give a multiplying factor for rotting mass fail as moving mass from the frame to wheel reduce accleration but doesn’t make it harder to carry or ride the bike up hill
But where all 26 vs 29 wheel arguments fall down is tyres.
you migth think that its fair to test both with the same size tread and carcass. But the 29 er can probably get away with a narrower tyre and shallower tread for the same traction. This is due to the longer contact patch.
My final thought is this. I’ve only done one cyclo cross race, this was on my mountain bike. Whilst being lapped by the cyclo cross bikes in deep mud at no point did i think, “I pitty those poor fools with their longer rims weighed down with all that mud!!!”
crotchrocketFree MemberPosted 11 years agofor example:
Stans Arch Wheelset 29 – 1575g plus 580g for a kenda SB8 DTC
Stans Arch wheelset 26 – 1420g plus 520g for the same
215g ‘claimed’ difference in dry/race componentsfor the sake of simplicity lets add on fat tyres rather than calculating the weight of wet mud.
945g for a kenda nevegal dtc/sct 29
827g for the 26a further 58g over the top combination.
all suggestes to me that: if you ride in muddy conditions and are looking for tougher components you to gots to go 26.
another way to look at it: 29 is more suitable for dry conditions, lightweight race type applications.
Dare i say – horses for courses?
imnotverygoodFull MemberPosted 11 years agoDare I say: try riding one & see what it is like in mud?
crotchrocketFree MemberPosted 11 years agoAmptill: you are missing a few other key factors.
total bike weight of a CX bike is itro 18lb? I’m willing to bet your MTB was >25lb
gearing
tyre width
It’s what the thing was designed to do – see above “engineering is…”crotchrocketFree MemberPosted 11 years agoimnotverygood> CBA, TBH I’m not really in the market for one.
But I am interested in the feedback of someone who has a balanced opinion, someone who can be balanced. someone who is not invested in me buying into one size wheel or the other (as opposed to the “I bought one, so it must be great or I’ll look an idiot” which is the usual fodder on forums).Perhaps an idea for a proper funded article: a scientific trial?
imnotverygoodFull MemberPosted 11 years agoYou don’t need to buy one. Take one for a demo. I was hugely sceptical of 29ers until I did. Still haven’t bought one yet.
eshershoreFree MemberPosted 11 years agono idea about the physics but certainly found my 29er a much better performer in snow and mud than any of the dozens of 26″ mountain bikes I have ever owned?
running Specialized Purgatory Control tires with tubeless on the 29er, certainly not a paper thin tire….
ampthillFull MemberPosted 11 years agocrotchrocket
I don’t seem really see my race performance as evidence. Other than it is clealry possible to form a good for the mud rim combination from a 700c rim.
I think the whole premiss of the original question is wrong as bike with the longer rim can simply fit a narrower tyre so that it cariies less mud. If the 26 rim firs the same size tyre it will sink deeper due to the shorter contact patch
for the record I own 2 off road bikes both 26 inch rims.
chiefgrooveguruFull MemberPosted 11 years agoI haven’t noticed any 29ers I ride with having more trouble than usual in mud, and only very occasionally struggling with tighter lines. The better riders still are, the others aren’t! 😉
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