The Wheel Size Debate – The Theory??

I was out riding with my ‘smarty pants’ cousin today, and got chatting about wheel sizes and the ongoing debate that continues in cycling circles (no pun intended there). He is a nice guy and a great trail rider, but a confusing smarty pants, as he has a maths and physics degree. I thought I would share his thoughts here.

It started with me stating that I have no problem with the new ‘650’ and 29′ sizes, but that I will always be a 26′ wheel man, as I favor power and handling over speed. He then confused me a bit with some mathematical thoery and mechanical physics which sounded good, but went straight over my head and it’s grey hairs!

But he concluded that he had ‘proven’ that for a mountain bike (that was not purely a downhill speed bike), that 26′ wheels were THE perfect size, an optimum size, for general off road riding. He said, this was the ideal size for optimal acceleration and delivering (uphill) power, assuming a suitable standard gearset was used (such as my SLX rings and a 34t – 11t cassette). This is particularly true, because the priority with an offroad machine is delivering power and acceleration, for offroading generally, and NOT speed, he says.
He also mentioned that it makes no sense at all, to increase wheel size to 29′ on a MTB, unless you want to prioritise speed over a slight loss in power and acceleration (ie, by slightly raising the effective gear ratios used), which more or less turns a MTB into a speed machine. He also claims, that the ‘650’ size (27.5?) is a complete and utter waste of time, and just a marketing con, as if you want more speed, you opt for a 29′, and for more traditional power you use a 26′, and that there is such a very minimal variation in using a 650 that it’s pointless…. etc etc etc….

He started talking something about old pennyfarthing bikes with huge driving wheels, being very high ‘ratioed’ due to too large a wheelsize, blah blah, when I started to get a headache and stopped him talking by pointing to a non existent “amazing bird”!!!

Anyway, what do you all think about this theory? It sounds logical, but I’m no expert. It got me thinking because if the cycling industry does abolish the 26′ wheel, it does strike me it could be a move in the wrong direction for the sport (unless of course, you seriously compete and want more and more speed over trails. You could simply use 29’ers for traditional power riding by lowering your gear ratios (slightly smaller rings?), but that leads to the question my cousing concluded his rant on…. in that case, why bother increasing standardised wheel sizes at all, if there is no clear net gain in output? (ie, you could acheive the same increase in speed by just increasing chainring sizes?)

I’m starting to go crosseyed….! I shall stop thinking about wheel sizes now..!

GBR.

For future reference, this is the correct response for when someone tries to start a debate on wheel size:

Why did i read all that? 😥 Im going to bed…goodnight

Don’t be a spoil-sport Jamie, we haven’t had one yet today

Not sure what he’s getting at – all bikes (apart from penny fathings) have gearing, larger wheels can just have a lower ratio to make the speed for a given pedal rotation the same.

Bigger wheels don’t fall as far into holes as small wheels, but have more inertia so are slower to accelerate and turn. It’s that simple.

Haha!!

I suppose this is a bit of a sore spot issue for some people, which is understandable! Wheely understandable. Sorry to be a spokes-man on the issue! :o)

My cousin needs no hi-vis clothing… you tend to hear him coming from a mile away with his motormouth! :o)

GBR.

He may be smart but he’s not correct. Ask him about conservation of momentum, and ergonomics and fun. Or how much suspension you have / need affects it. Or riding terrain, style etc. See if physics can balance all that : )

you could acheive the same increase in speed by just increasing chainring sizes?

unless you want to prioritise speed over a slight loss in power and acceleration (ie, by slightly raising the effective gear ratios used),

and surely he isn’t suggesting that big wheels are faster because they go further per crank revolution on the same gear?

Apologies for engagement of the debate – only intent is to suggest maybe he’s better with sums than practical examples.

Why did i read all that? Im going to bed…goodnight

Sounds like you took one for the team. I only managed the first paragraph.