First custom build

Started 2 months ago | Discussions thread
OP Gnine Contributing Member • Posts: 823
Re: First custom build

windmillgolfer wrote:

Sounds like you’re lucky to still able ride a bike (and breath too). I despair at the carelessness of today’s drivers on a daily basis.

What’s the purpose of the fat tyres, presumably grip and comfort but they must quite inefficient from a rolling resistance viewpoint?

Yeah, I've given up riding on the road now. I didn't really ride on the road previously, just to get to the bike tracks a km or so from my house, but that's no more. I'll chuck the bike in the back of the ute, drive to the bike tracks, bush, or mountain bike parks, & ride from there. I hate doing that, but you've got to do what you've got to do.

You pretty much nailed it on the fat tyres, but they're not that inefficient, if you're careful about choosing tread patterns & air pressure. Or worried about travelling fast. Relatively of course. The engineering side of me has seen my curiosity spike a few times, and seen me test a LOT of different widths, tread patterns & pressures. My other mountain bike runs the same size wheels as road bikes/racers, so I've fitted skinnies, & other various tyres to that, & timed each of them over a set course a number of times. Of sufficient length (about 10 kms or so) where, at my fitness level, an unconscious preference or bias towards a certain tyre shouldn't be able to create large deviations in the statistical data. ie I'll run out of energy well before covering the set distance, finish slower, & things should even out. Yeah yeah yeah, it's not scientifically precise & controlled, a power meter is really the only way to do it properly, but in real world situations -which I'm riding in, it's close enough. I can't see any meaningful difference in average speeds, on average surfaces, running skinnies (23mm) at 100 psi, or the fatter tyres (2.25") at around 50. The fatter tyres are definitely more comfortable though.

What I've found, is that aerodynamics probably make the biggest difference, once you get to around 25 km/hr. The slight difference in rolling resistance of the fatter tyre on smooth surfaces, seems to be of less significance than the air resistance increase by travelling faster. On a rougher surface, even on a coarse chip sealed road/path, the fatter tyre will actually roll faster. I tested that quite a few times, in an aero tuck, down quite a long steep hill where, where speeds were around 60+ km/hr. No pedaling involved. The fatter tyre was a few km/hr faster. Every time. I see that even some of the pro riders are starting to gravitate to slightly wider tyres now, so there must be something in it.

Another advantage of the fatter, larger volume tyres, is rim protection. There's simply more distance between the road, & the rim, to absorb any sharp irregularities in the road surface, before damaging the rim with the fatter, higher profile tyres. I dinged the rims when running the skinnies, just riding over the joints in concrete pavements, that the fatter tyres hardly even noticed. Forget about taking the skinnies off road.

Also, on softer surfaces, such as loose gravel, and sandy soil, the fatter tyres have a lot less rolling resistance than a narrow tyre. Surface area and all that. That's why fat bikes with their 4" wide tyres can ride through snow, & over sand, where even your mountain bike will be bogged. There's lots of data out there on various tyres rolling resistance, but most of that is generated indoors, on a roller, under lab conditions, and don't take into account factors such as surface roughness, air resistance & the like. It's heaps more fun doing your own tests anyway, than just reading test reports For me, at the speeds and conditions I ride at/in, I'm perfectly happy with the wider tyres, at lower pressures. As I can't find any advantages with the narrower tyres. Only disadvantages.

Oh dear, that got a bit long winded. Sorry about that.

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