The big wheels versus small wheels. Serious question.

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  • The big wheels versus small wheels. Serious question.
  • Premier Icon epicyclo
    Subscriber

    Any time there’s a discussion about 29ers, someone is sure to chime in about how rubbish big wheels are and gives several technical reasons:

    eg 26″ is less rotating mass so faster acceleration, is a stronger wheel, and gives nimbler handling.

    So if small wheels are better, why aren’t mtbs built with 20″ wheels? There’s plenty of suitable components being used in trials bikes.

    The original Moulton proved that small wheels in a long wheelbase with a bit of suspension gives a bike that handles as well as a full size bike.

    So why haven’t small wheel mtbs taken off?

    (There was a small wheel mtb manufacturer called Burro in the USA, but they are out of business)

    tomlevell
    Member

    Easy
    20″ is for BMX.
    700C is for road bikes.
    26″ is for MTBs

    Premier Icon epicyclo
    Subscriber

    I was hoping for a more technical reply rather than a declaration of faith 🙂

    Premier Icon nedrapier
    Subscriber

    It was all about 24″ wheels a few years ago. They were the future. So many advantages.

    tomlevell
    Member

    So why haven’t small wheel mtbs taken off?

    I answered that though ;0)

    For starters.
    Chainrings would be massive.
    Working out what angles would make them work would be a PITA.
    There aren’t any tyres other than for properly dry weather and groomed trails. ie dirt jumps.

    jambon
    Member

    I don’t think they go over bumps as well. Low slung rotating mass is surely a good thing though? Love the way Bromptons carve turns!

    Premier Icon epicyclo
    Subscriber

    tomlevell – Member
    …Chainrings would be massive.
    Working out what angles would make them work would be a PITA.
    There aren’t any tyres other than for properly dry weather and groomed trails. ie dirt jumps.

    Chainrings – good point. Could be avoided with a suitable hub gear though, but probably the major hassle.
    Angles – nothing that isn’t done on every new frame design. Doubt there would be anything radical needed.
    Tyres – had a look at the Schwalbe BMX range – they look as good as anything we’re riding on the trail.

    jambon – Member
    I don’t think they go over bumps as well…

    A bit of decent suspension design would fix that, but a longer wheelbase helps iron out bumps. (You can have a long wheelbase with small wheels and still keep the bike within the length of a normal bike.)

    Wibble89
    Member

    Imagine a graph with 2 curves on it, one being a positive trend with wheel size (for example ability to role over obstacles, etc) the other being a negative trend with wheel size (for example strength, acceleration, handling etc). Now where the two curves cross might dictate the best size of wheel.

    As you go through the spectrum from infinitely small wheel to infinitely large wheel you will notice the apparent issues along the way. Too small doesn’t get over the bumps / inefficiencies in large suspension movements. Too large and overall size/length of bike becomes an issue.

    jambon
    Member

    And may cross somewhere between 24″ and 26″???

    tazzymtb
    Member

    Too large and overall size/length of bike becomes an issue.

    well given the silly slack head angles and monster wheel bases on hardcore 26ers it’s no wonder that a good 29er is more agile these days 😀

    emanuel
    Member

    look,it’s simple.
    play canvasrider/freerider2,swithcing between bmx and mtb.the handling differences are pretty well done between the diff sized wheels.

    It isn’t big vs small, it’s a little bigger vs a little smaller, only about 10%. In fact my 26er measures 27″. Wibble’s example of curves describing gains and losses vs diameter is a good one – but it needs many curves in many dimensions and then the application (terrain, speed, style, rider size/strength/inclination, etc) describes a multi-dimensional locus within that space – and the optimum wheel size for that application is within that locus.

    From a marketing perspective 29ers are genius because they allow you to sell much more stuff. They also have clear performance benefits for various situations. And even better, they’re often a good fit with older (wealthier?) more wheels on the ground riders, giving a nice upgrade path. If they didn’t work they wouldn’t be getting more popular but they’re no panacea.

    tazzymtb
    Member

    big wheels can go this

    looks like one of epicyclos builds 😀

    bencooper
    Member

    Simply, a small wheel falls further into a hole than a big wheel. Same with logs and other obstructions – larger wheels roll more easily over things. I’ve built and ridden 20″-wheeled bikes off-road, and the wheels just won’t go over anyhitng bigger than about kerbstone-size.

    Downside of big wheels is more inertia, so slower steering response and slower acceleration, and they’re not as strong.

    Premier Icon epicyclo
    Subscriber

    I should add I’m thinking more along the lines of trail bikes rather than gnarly dude hero machines, although that would be worth considering too.

    Looking at the wheels in isolation, obviously a small wheel will drop into holes etc, but if you use a longer wheelbase then the CoG isn’t displaced as much so it won’t feel too bad. This is nicely demonstrated by the original Moulton which has around 43″ of wheelbase.

    emanuel
    Member

    I had a 20″ fs.honestly it was shite.took it to some proper steep trails,the same I’m riding on a hustler now.
    It was so shit.I rode around the same trails(slowly) on a road bike with moustache bars and 28mm tyres,that was pretty sktechy in some bits,but not as bad as the tiny bike.oh,epicyclo-getting a gryphon.thanks.
    Havig said that,I had a gf who had just bought a 16″ wheeled folder(curve).took her mtbiking.
    she did pretty well.but never came again.and left me soon afterwards.
    little wheels’ break your heart.

    Premier Icon epicyclo
    Subscriber

    Confession – I sometimes enjoy riding small wheels offroad.

    There are swings and roundabouts. I don’t recall feeling particularly disadvantaged while riding which is why I wonder how a purpose designed bike would go – maybe a project for summer?

    A stopwatch may have revealed otherwise, but I was just out riding. The small wheels feel trickier in rocky stuff, but they do allow you to dodge a lot.

    Not to mention bashing my 45yr old Moulton round the ‘Puffer course – sorry no pic of that.

    (That orange Dahon has taken me over most of the Great Glen way – bit sketchy in places with the skinny tyres though.)

    I do prefer proper large wheels for most riding though (and I do mean large 🙂 ).

    emanuel
    Member

    I had the very same folder,put a fox on the back though.better brakes,etc.
    It was horrible on rough,steep,rocky stuff.
    roots were similarly bad.besides,it flexed like mad.
    and the skinny tyres had no grip.

    I’ve seen some really wide small tyres.like a 20″ pugsley,they’d be interesting.
    and you can get decent susp forks for 20″,from german:a.

    Premier Icon aracer
    Subscriber

    Tyres – had a look at the Schwalbe BMX range – they look as good as anything we’re riding on the trail.

    Yep – I bought myself a Mow Joe for use on my 20″ uni, and it works pretty well.

    I also have a 26″ uni, so very direct comparison of the merits of 20″ and 26″ wheel sizes (granted neither has suspension, which appears it may be very important for the smaller wheels) – arguably more direct than riding a bike. I’d tried off-roading with the 20 before I got my 26, and was thinking that muni was really pretty hard – even smallish bumps were causing me problems. Was amazed at the difference the bigger wheel made – far more than I was expecting. It really does roll over bumps far better.

    However to get back to the 29er debate, my understanding is that the difference in rolling is far less pronounced – it is after all only a 10% difference from 26 (bearing in mind it’s really a 28.5er) compared to the 30% difference between 20 and 26. You’re also at the point where the disadvantages of larger wheels start to some into play. So as mentioned above, what’s best depends on what you’re doing. I have to admit I’ve actually become convinced of the merits of a 29er for a lot of the riding I do, without even owning one!

    I’m sure at some point I’ll get a 29er uni at any rate (the chances of getting a 29er MTB are rather low due to my investment in 26, and decreased disposable income nowadays). Unis do make you think about wheelsize a whole lot more, as there’s a whole other level of compromise going on (bigger wheel means a higher gear which could be either an advantage or a disadvantage – bigger wheel also means more stable, less manoeuvrable and higher off the ground, so harder to get on and further to fall!)

    Oh, and wow at epi’s little wheeled bikes. Just wow!

    Premier Icon andyh2
    Subscriber

    A 20″ wheel with Pugsley type tyre volume would be interesting. Maybe get a 25% weight reduction on current fatbike wheels / tyres.

    I know the trend is for fatter tyres, but for trial riding probably be better to have a 26″ tyre between current ‘normal’ and full on fatbike. Something that weighed as close to a kilo as possible max and could be used with standard 135mm rear end and able to use an IGH, SS or keeping 5/6 cogs of a 9 speed cassette. So maybe a 3″ tyre.

    Premier Icon epicyclo
    Subscriber

    Thanks emanuel. That’s a good find.

    emanuel
    Member

    nae bother, 😉

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