[Closed] It's not about the bike....... or is it? A SDW tale

I was blowing out my ring with a nasty wind buffering me.

you would see biggest improvement by loosing 10 - 20kg in weight

I'm 59 - 60 next year, its not the bike 😉

Haha I couldn't lose and wouldn't want to lose 10-20kg. But being 80kg would be good.........

For starters, you want a 29er.

29er, XC tyres, whoosh!
85kg will definitely be holding you back more than the bike though.

85 kilos is basically well into track cyclist/sprinter build. Unless you are 2 metres tall.

I'm 59 - 60 next year,

Well go on then are you 59 or 60 next year?

As for is it the bike? P

Haha I'd seriously not want to drop below 80kg - I'm not a cyclist build at 5'7" and with 5kg off I'd be happy. I'm a stocky gym going chap not a racing snake.

A 29er I hear, one of the lads in our group had one, he wasn't anymore rapid than me - again is there a real world benefit over my 27.5?

I've fitted XC-ish tyres To Stans Crest rims so reasonably light without sacrificing durability.

I'm beginning to think a bike change isn't going to bring about any worthwhile benefits for me.

85kg? Try being a 1.84m 100kg ex-rugby player. Don't listen to them. On my body fat percentage I could lose every ounce of fat and still not make it under 80kg.

They may be right that at 65kg you'd climb better - except you might be dead before you reached that weight.

Of course you bloody wouldn't! Would be a change in body shape, yes, but doable.

Igm were talking about a guy who is 1.7m tall. Your ideal weight depends on your hight, body shape etc. We're not implying everyone should be under 80kg. That would be dim

Agreed. But equally the OP is saying he's a stocky gym bunny type. Check he isn't 5ft across the shoulders before suggesting he could drop a lot.

I could get down below 80kg but I'd be losing a lot of muscle - which isn't great really.

Getting down to 80kg would be a mission for me tbh, let alone 65kg! There is some timber but not huge excesses to be lost.

Can't I just buy a new bike lol.

Big guns look pretty, but they are sweet FA use for climbing hills on a bike, and losing them is going to be more beneficial than a different bike.

Need to decide if you're a gym bunny or a cyclist.

@OP, yes 29er rolls a good bit faster, especially over bumpy flat sections

Big guns look pretty, but they are sweet FA use for climbing hills on a bike, and losing them is going to be more beneficial than a different bike.

[b]Need to decide if you're a gym bunny or a cyclist.[/b]

Or a human being FFS! Sorry to break it to the weight haters but you are not Chris Froome and you don't cycle for a living. Cycling might not be the OP's only passion. In fact I kind of hope it isn't. Not everyone is a one trick pony.

I am a biffer at the moment (job/recovery from a hip problem/ loss of discipline after years of living like a monk as a competitive triathlete) but even when I've finished doing something about that I'll still have an open water swimmer and kayaker's shoulders and back and not be a perfect cyclist shape and that is all fine and dandy as far as I'm concerned. It won't mean a new bike won't turn my head.

As for op's question - if the SDW is not 29er territory I'm not sure where is. If it would make any discernible real world difference to either your speed or (more importantly) your enjoyment of the ride I have no idea! Pedal strike when in some of those big deep ruts was always the thing I liked least on the SDW so a mega low BB would be something I'd avoid.

Need to decide if you're a gym bunny or a cyclist.

A lot of top mountain bikers spend more time in the gym and associated training, than they do outside on a bike.

All depends if it's 85kg of fat, or muscle.

Regardless, buy a new bike, 29ers are better for SDW type of riding

I'd second the 29er will be faster all other things being equal.

Get one. Put fast tyres on it. Revel in the fact that you're actually a fair bit faster now than your mate that was the same speed before.

Tubeless, if not already.

I've done the SDW (in the day) on HT and FS. I prefer HT (hopefully doing it again in two weeks) due to the better climbing and the lack of anything technical. The HT beats you up a little more but you get it back by not having to work quite as hard. If I was doing it on my FS I'd ride by 29er not my Orange 4, which is a bit slack for this sort of ride.

I changed my 26" for a 29" full sus last year and I live on the South Downs. It makes a difference but not as much a difference as tyres does.

I wouldn't change a 26" for a 27.5" for that sort of riding.

26" Stans Crest with Geax Saguaro was pretty much spot on for SDW bashing. 29" of the same would be faster but not, 'buy a new bike' faster if you're doing it in 3 days.

Igm were talking about a guy who is 1.7m tall. Your ideal weight depends on your hight, body shape etc. We're not implying everyone should be under 80kg. That would be dim

Er

Except it was straight in with the "lose 10-20kg" off an 85kg body before anyone knew or asked what height he was.

As someone who's 1.94m tall and hasn't been below 85kg since childhood, from my perspective the idea that a 65kg body weight would be the obvious route to better performance seemed… well, dim.

😉

Or a human being FFS! Sorry to break it to the weight haters but you are not Chris Froome and you don't cycle for a living. Cycling might not be the OP's only passion. In fact I kind of hope it isn't. Not everyone is a one trick pony.

Yes, totally.
There's nothing at all wrong with being a gym bunny, or a slightly tubby IT manager, or a big strong farmer that enjoys cycling. Enjoying the riding is the main thing. But in all the cases above there has to be an acceptance that its going to impact performance on the bike.
I did a riding holiday in the Pyrenees once with an ex gym bunny, he really had a remarkable set of biceps, but he had realised they were no use for climbing mountains and was happy enough to accept that limitation and enjoy the ride - just a bit more slowly than some of the skinnier people.

The OP specifically asked the question if a change in bike would be noticeably quicker for a heavy middle aged bloke, and the answer is yes a 29er will be quicker, but not as much quicker as losing 10kg, its up to him what he makes of that.

yes a 29er will be quicker

That - is absolute rubbish 👿

The sooner you people realise this the better.

JAG - Member

yes a 29er will be quicker

That - is absolute rubbish

The sooner you people realise this the better.

29ers are clearly better - they are [b]3[/b] better than a 26er, and [b]1.5[/b] better than a 650b. That's science!

Plus, they're faster.

That - is absolute rubbish

The sooner you people realise this the better.

Yes, totally.
There's nothing at all wrong with being a gym bunny, or a slightly tubby IT manager, or a big strong farmer that enjoys cycling. Enjoying the riding is the main thing. But in all the cases above there has to be an acceptance that its going to impact performance on the bike.
I did a riding holiday in the Pyrenees once with an ex gym bunny, he really had a remarkable set of biceps, but he had realised they were no use for climbing mountains and was happy enough to accept that limitation and enjoy the ride - just a bit more slowly than some of the skinnier people.

The OP specifically asked the question if a change in bike would be noticeably quicker for a heavy middle aged bloke, and the answer is yes a 29er will be quicker, but not as much quicker as losing 10kg, its up to him what he makes of that.

Ah sorry, I hadn't realised you thought the op was a complete moron and slept through his physics lessons at school. Do you REALLY think he needed pointing out that having a smaller overall mass might make going uphill easier? Really? That's so blitheringly obvious to everyone it really dosen't need stating. Which made your answer (at the point I quoted, before you edited and added the extra line) a little pointless. But this is STW so crack on.

Go ride one - it'll take you all of 2-3 mins to realise its true

Soooo someone else who.....

slept through his physics lessons at school

But this is STW so crack on 8) 😆

Soooo someone else who.....

slept through his physics lessons at school

Perhaps you'd like to enlighten us all and explain why reducing angle of attack doesn't equate to conserving momentum better over bumpy ground?
[img] [/img]

Perhaps you'd like to enlighten us all and explain why reducing angle of attack doesn't equate to conserving momentum better over bumpy ground?

But, you know, a marginal increase in weight must negate all that of course. LOL.

Reducing the torque required to overcome an obstacle (as you describe) does NOT make a bike faster. Nor does it reduce the energy required to travel from A to B.

I define faster as covering the distance quicker whilst maintaining the same energy input or covering the distance in the same time whilst reducing the energy input.

Larger wheels do not do either of these things - therefore you are wrong 😆 🙄

If you want to keep your arm muscles, ride singlespeed. You need them there.

Reducing the torque required to overcome an obstacle (as you describe) does NOT make a bike faster. Nor does it reduce the energy required to travel from A to B.

Did you really just write that?
You do realise that less torque to overcome an obstacle = need to apply less force.
And applying less force = using less energy?
On what planet does reducing rolling resistance not require less energy to travel from A to B?

Reducing the torque required to overcome an obstacle (as you describe) does NOT make a bike faster. Nor does it reduce the energy required to travel from A to B.

It's not (essentially) about torque, it's about energy. Larger wheels mean less force applied against the direction of travel, meaning less work, meaning less energy.

Try freewheeling along a potholed road on a bicycle and then try rolling along it on a skateboard.

Or consider a wheel of infinite radius. All surface irregularities of any finite size can only ever exert a vertical force: there is no horizontal component, thus the wheel is not retarded by these forces and (ignoring other losses) zero work is required to keep it moving. Big wheels tend to this point.

Fifeandy; Increased torque or energy to climb on to an object is immediately recovered as you descend off the other side - so no loss no matter your wheel size. Just temporary conversion from Kinetic to Potential Energy and back.

^ this is NOT rolling resistance. Rolling Resistance is energy loss (not temporary conversion) via material hysteresis etc...

Bez; the horizontal component of the force required to climb an object will deflect a smaller tyre more on a smaller wheel which may lead to increased loss (real rolling resistance) so there probably is a tiny gain there.

Nice to have a grown up chat about this stuff 😆

Fifeandy; Increased torque or energy to climb on to an object is immediately recovered as you descend off the other side - so no loss no matter your wheel size. Just temporary conversion from Kinetic to Potential Energy and back.

If it's lossless. It isn't. There are all sorts of losses in the system.

Bez; the horizontal component of the force required to climb an object will deflect a smaller tyre more on a smaller wheel which may lead to increased loss (real rolling resistance) so there probably is a tiny gain there.

Yeah, it's a tiny gain but it's on every single bump you hit during a ride. Which adds up to a significant amount.

That's aside from the issues of larger bumps, eg at a number of places on the SDW you'll be trying to roll the wheels over large rooty/rutty lips while climbing fairly steeply. There will be a slim margin where a smaller wheel pushes you to the point where you have to either give it an exceptional effort or dismount, while a larger wheel would just about avoid that. Again these occasional things, where smaller wheels cost time and energy, may be shrugged off in isolation but they add up over a 100 mile route.

Fifeandy; Increased torque or energy to climb on to an object is immediately recovered as you descend off the other side - so no loss no matter your wheel size. Just temporary conversion from Kinetic to Potential Energy and back.

^ this is NOT rolling resistance. Rolling Resistance is energy loss (not temporary conversion) via material hysteresis etc...

Actually, it is still rolling resistance, just not the traditional type you highlighted.

What you said regarding energy loss would possibly be true (you'll still get friction losses) if all the forces involved in rolling over an object were vertical, but they aren't (see the diagram below). Increasing the wheel diameter decreases the horizontal component of the force resisting forward motion.
[img] https://static1.squarespace.com/static/57ca085ec534a5dcc423c9d0/t/57fc11e4d1758ec2a160b1d1/1475457703510/?format=1000w [/img]

Fifeandy/Bez; the losses that you refer too are created by tyre deflection. Tyres are mostly elastic - therefore as you roll off the 'object' the tyre returns to shape and imparts the energy to the forward motion of the wheel. So energy is again recovered.

There is a tiny amount that is lost to material hysteresis - so tiny that the tyres barely get warm. I honestly don't believe that anyone would find any advantage created by wheel size increase.

But YMMV 8)

Fifeandy/Bez; the losses that you refer too are created by tyre deflection. Tyres are mostly elastic - therefore as you roll off the 'object' the tyre returns to shape and imparts the energy to the forward motion of the wheel. So energy is again recovered.

There is a tiny amount that is lost to material hysteresis - so tiny that the tyres barely get warm. I honestly don't believe that anyone would find any advantage created by wheel size increase.

No, the losses from tyre hysteresis are FAR preferable to the losses in the diagram above - hence why its now commonly accepted that lower pressures are faster off road. The force depicted above is the somewhat futile attempt of our bikes to accelerate the earth.

Take the image above, and imagine what would happen if the obstacle were 3ft high rather than 3 inches - in that case it would be near enough all horizontal force and no vertical force.

What you are neglecting is that there are two components to rolling resistance. The traditional material resistance which you seem well aware of, and the so called suspension loss which has only really had widespread exposure over the last 5-10yrs.

The smaller the bump (and the larger the tyre and the lower its pressure) the more the energy loss is reduced by tyre deflection. But not all of the energy loss from a bump can be mitigated by the tyre, and once the bump size approaches the tyre size the tyre can't have any more effect. A wheel probably encounters quite a lot of 2"+ bumps on most rides.

But, aside from discussing the inescapable physics involved, I would think that there are numerous tests of varying rigour which demonstrate that big wheels lose less energy rolling over irregular surfaces…

OP, maybe just have a big jobbie before you set off. A 5 or 6lb'r is ideal. And a red bike is normally faster. What colour is the orange?

[img] [/img]

^^ 75mm object 😆

Christ; lose some weight, graphs, hypothesis, physics...... I wish I'd never asked lol.

Ah well it is what it is eh 🙂

I darent ask what 29er FS............

It all comes down to marginal gain-saying 😉

Opened this thread expecting some interesting chat about a long-distance XC ride, maybe with some nice pictures. Instead it's gone full physics ****athon.

Hope all the DH teams don't see this thread, they'll be throwing their new 29ers in the skip just days before Fort William WC.

50yr old, 183cm, 85kg rider of a 29er. 🙂

29er's are nice for XC if I didnt have one I would buy one. Losing weight is also great but takes some conviction post 40 and the occasional pie and pint would be missed.

Hope all the DH teams don't see this thread, they'll be throwing their new 29ers in the skip just days before Fort William WC.

full physics ****athon

maybe with some nice pictures

[img] [/img]
Approaching Cocking from the west on a drop bar 29er with file tread cx tyres. What physics for slating my wheel choice?

.

[img] [/img]
Study the photograph above. Have I fallen off here due to hitting an obstacle with the wrong size wheels, or have I stopped for a rest?
If I've stopped for a rest, would I have stopped for a rest earlier or later if I'd been riding a 26er hardtail with 2.2" semi slicks? (Assume 22psi)

You know the reason they have gone 29er in the first place right?
Because underneath the external appearance of baggies and a cool laid back persona, they are all really just excited by having a

full physics ****athon

I read the interviews with Santa Cruz and Trek bods saying they'd tested the bikes against the clock and found them convincingly faster.

They didn't go into what kind of theoretical analysis they'd carried out though.

What physics for slating my wheel choice?

It's the SDW, it's more flinting than slating 😉

Yes lots of flint, not much slate, although there was a very odd cobbled bit.