Fat tyres & springy suspension sap energy & speed

[coops]

Not news I know, but I wanted to share what differences I've noticed in my bikes, one electric one not, when pedalling unassisted:

MTB: springy front suspension, fat 26"x1.9/2.0" smooth tyres speed 13-14mph

Torq1: rigid forks, front hub motor, 700Cx38 smooth tyres speed 16-17mph

(both aluminium framed, MTB ~15kg, Schwalbe tyres on each - Silento II on MTB & Marathon plus on Torq, similar pressures on each bike)

I suspect both the fat tyres and springy front forks mainly sap the rider energy & speed, although the 700C wheels will roll a bit easier anyway, I'm unclear which saps most energy though or whether there are other factors involved, but I'm struck how much easier it is to pedal a hub motor bike with its gear friction than a front suspension, fat tyre MTB.

My main thought is that, for ebikes pedalled at 15mph, such a speed/energy efficiency difference would markedly decrease range from the same battery, maybe even 20% or so less, unless the less efficient one is ridden more slowly, so clearly a trade-off between comfort and speed/range.

Front suspension forks are probably much better now than my old MTB ones, but the effect is still there presumably. Forks which lock out will help, but add to the weight, and a hard ride when locked out especially if on the front with a hub motor too.

Has anyone else also noticed similarly high losses from suspension or oversized tyres, compared to other, more efficient, bikes?

Stuart.

 

[Nick]

I should be able to give my own comparison soon as I am thinking of swapping my Continental Sports Contact tyres (700 x 37 on the rear, 32 on the front) to Continental City Contact 47s. Although I really like the Sports Contacts, I am trying to soften the ride as there is an old path I could use after the countryside part of my commute to work that would mean I wouldn't have to go on the road, thereby bypassing a few busy 'multi' roundabouts, traffic lights and bus lanes. The trouble with the path is it is old and runs between mature trees and a busy bypass, and the roots and perhaps vibration have made it extremely bumpy. I expect to lose speed but, as it is, on a still day and flat road the bike's under-geared and I spin out, so I'll see how it goes and let you know.

I was looking at a nice full suspension mtb the other day - if only I could have sussed out how to fit the battery and panniers, and where to find the £2000 on the price tag.... There again, if I could work out how I could cycle a recumbent with a knee with limited flexion, I'd get something like the Optima Cougar. It's a shame that my modified crank doesn't seem to work on recumbents.

Highpath Engineering : Cycle products : Swing Crank

I have just remembered that years ago I had a mountain bike and when I switched from nobblies to slick tyres, I could climb the local hills in a higher gear - it makes a big difference. There are a few variables I think - rolling resistance may stay the same, ceteris paribus, but of course the situtation isn't ceteris paribus - fatter tyres have a higher wind resistance (I gather this makes quite a difference on the front wheel), different tread and compound, the road itself introduces irregularities, etc.

 

[flecc]

In most cases I've found fat tyres and suspension to be far more difficult to propel Stuart, but there are qualifications:

Rear suspension is always the worst for energy loss, the softer it is, the more it saps the effort inputted.

Front suspension if quite hard doesn't occasion much loss.

A well designed fat tyre with a free rolling tread can be both efficient and more comfortable. Schwalbe's Big Apple is the prime example with many fans worldwide. Schwalbe make a big issue of this matter of tyre width in a PDF download. Their arguments are a little disingenuous since they warp the position regarding relative tyre pressures, but the Big Apples success has to be recognised.

Tyre treads can be more important than width, knobbly mountain bikes tyres often being incredibly inefficient on the road. However, with many there is a speed relationship. At low speeds the bike can drop minutely as it passes from tread block to tread block, in effect forcing it to climb a huge number of tiny hills as the wheel rolls, very inefficient. At a certain speed depending on the gap between tread blocks, there's insufficient time for the bike to drop as it traverses the tread blocks since the acceleration due to gravity at 32 feet per second/per second is insufficient. Above that speed point the bike rolls better than at the lower speeds.
Good tyre tread designers stagger the blocks laterally so that the area of tread in contact with the road is always constant, this giving the lowest rolling resistance.
.

 

[Nick]

Now they look interesting Flecc! The limiting factor seems to be finding mudguards to suit. The SKS Bluemel (?) look like they can just about handle the Continental City Contact 700C x 47, but I think the 54s would be too wide, let alone these Big Apples.

I'm off to Google - shout if you have any ideas on wide mudguards!

 

[Tiberius]

Schwalbe have also got the Marathon Supreme. I think its a new introduction but it looks to have the benefits of the Marathon Plus in the Big Apple size, id est, up to 2". I have them on my new 26" build, which isn't on the road yet.

There is a 50-622 size, which I am sorely tempted to try on the front of the Torq. As the other Nick says, it looks like new mudguards will be needed, though.

Nick

 

[flecc]

I'm afraid I know little about mudguard availability Nick, but the Big Apples also need fork vertical space to accept them. I don't think the Torq 1 forks would be a problem, but I'm not certain.

The Marathon option is interesting, though I doubt it would have quite the Big Apple comfort.
.

 

[coops]

Excellent points everyone, thanks.

I'm erring towards it being mostly the very soft MTB suspension thats sapping energy - its really oversoft for roads and I'm uncertain it can be adjusted either. What surprises me most is that it doesn't just absorb energy on bumps/potholes, as one might think, but its continuosly stealing energy from forward motion too, to compress it, as you pedal along...

At least better or no front sus forks might help that; I'd always thought too that rear sus would cause worse energy loss.

Tyres-wise, the smooth treaded schwalbe silento II on the MTB transformed the riding ease from the previous very basic knobbly tyres, so how bad must that have been! The silentos roll easily and the width gives plenty of cushioning, but I think must cause somewhat greater air resistance, especially because of their knobbles on the outside edges, for offroad grip in mud - which have worked several times for me in slippy mud, saving what seemed a certain spill!

I find with tyres that cushioning tends to increase steeply (non-linearly) with tyre width, which I'm sure you're aware of Nick, so those 47s ought to give a much softer ride than the 37/32 you have: my 1.9/2.0" MTB tyres are exactly 47mm wide & look monstrously huge next to the 38s on the Torq! Well worth it to avoid busy roads though if necessary and probably more 'traditional/authentic', aesthetically pleasing & efficient (& cheaper!) than going down the full suspension route - depends how much suspension you need though to make it work - hope it goes well for you if you make the swap. I certainly find my MTB suited to muddy & bumpy tracks, but how much that would change with less springy front forks remains te be seen. I'm really thinking of changing them now - maybe for harder ones with a lockout too - so that I can better use the MTB for shorter road trips too.

It does raise the question of which is the best compromise for such bumpy routes - especially with hub motors - good (maybe adjustable) full/part suspension forks or good, adjustable (though tyre pressure) 'pneumatic' suspension? I guess tyre pressure is more finely adjustable & can also improve grip as well as less energy loss than full sus, as long as it does enough to absorb shocks, and no weight penalty or complexity of moving parts/lockouts for on-road use either.

Stuart.

 

[flecc]

As Schwalbe say about the Big Apple, Stuart, "Suspension for rigid bikes".
.

 

[coops]

And presumably it slides smoothly & effortlessly over mud too...!

 

[the_killjoy]

How can a swing crank cost £200 ?

 

[flecc]

Highpath stuff is all hand made individually to high standards, the sort of craftmanship that's extremely rare these days, but necessarily expensive.
.

 

[Nick]

A local cycle engineer made mine for considerably less than £200. It was built as a prototype maybe six or seven years ago but it worked so well that we've never done another one, although I'm thinking of asking him to do me a revised one.

 

[flecc]

And presumably it slides smoothly & effortlessly over mud too...!

I don't think a Big Apple would have any traction on mud, very much a slick tyre.
.

 

[Nick]

Well, thanks to the comments here I've just ordered a couple of Schwalbe Supremes - 50mm wide! And to think I started off with Ultra Gatorskins at about 25 or something silly! I think the Supremes will fit on the bike but time will tell... The reviews I found were very good and they seem to roll better than I was expecting, so I'll see if they're all they're cracked up to be. I got them from dotbikes.com. If they do work, maybe I didn't need to buy that Cancreek Thudbuster a while back. Hey ho.

Tubes seemed hard to come by but Flecc's frequently recommended SJS have some so thanks for that.

And after more Googling, I've ordered some SKS Beavertail mudguards that look like they'll do the job, although perhaps not as well as the close-fitting guards I have at the moment.

So, thanks for all the pointers, and I'll let you know how it goes.

 

[Caph]

I'm erring towards it being mostly the very soft MTB suspension thats sapping energy

It's probably worth pointing out that front suspension saps upward force, not forward force. So it's not absorbing energy from the rider, but energy from bumps in the road that would otherwise move your handlebars upwards/downwards accordingly. In other words, the upward/downward force is present no matter whether you have suspension or not and absorbing it or not is irrelevant to forward force.

Personal experience bears this out. I find that changing from thin tyres to thick tyres has a big effect on my riding efficiency but changing from thick tyre with front suspension to thick tyre without front suspension has no noticeable effect.

 

[flecc]

It's probably worth pointing out that front suspension saps upward force, not forward force. So it's not absorbing energy from the rider, but energy from bumps in the road that would otherwise move your handlebars upwards/downwards accordingly. In other words, the upward/downward force is present no matter whether you have suspension or not and absorbing it or not is irrelevant to forward force.

Personal experience bears this out. I find that changing from thin tyres to thick tyres has a big effect on my riding efficiency but changing from thick tyre with front suspension to thick tyre without front suspension has no noticeable effect.

Not entirely true Caph, suspension can and does sap forward forward force in more complex manners. It can also sap rider pedal input when the downward thrust is absorbed into the springs. Here's the relevant extract from my article on suspension in the Technical section:

"In practice when cycling, pedal downthrust effort is absorbed by the springs, a small proportion is lost as heat, and the rest is then returned in useless modes. Half is sent down into the road at the forward sloping angle of the forks and slowing the bike as it's in the opposite to the direction of travel, the other half is sent back up into the bike. The only time that second half has no effect is when the pedal cranks are vertical, at all other points the upwards rebound force directly opposes the rider's pedal effort and has an ill effect on cycling rhythm and muscle action. Therefore, the suspension having lost some of the original pedal effort into the spring, almost half of the lost portion returns to have a second go at wasting the rider's effort. Added to these, insufficient damping of the spring motion which is common on bike suspension causes excess rebound bounce, and this multiplies the forward energy loss."

If you want to read the full article, here's the link:

Suspension
.

 

[coops]

Nice going Nick, I hope it works out well & let us know what you think of the Supremes too won't you - I've also been pondering these for quite a while, though still not actually even seen any for real!

I think I'll be converging from the other direction & switching to rigid forks on the MTB if I can find some reasonably priced ones.

Caph - To be honest I thought the same thing, and I expect the difference depends on many factors, not least the quality of forks, tyres, pressures, riding surfaces, styles etc. and the sus forks I have seem particularly soft & unsuitable for roads and definitely seem soak up forward motion, like a sponge! It was my surprise at this apparent situation which prompted me to post it.

I think a basic bike's simple & efficient design means its performance can be subjectively quite drastically affected by even quite subtle changes, so perhaps the effect doesn't have to be great to be particularly noticeable.

Stuart.

 

[Caph]

pedal downthrust effort is absorbed by the springs

Possibly in theory but not enough to be noticeable in practice. Simply riding a bike and watching what happens bears this out. Downward pedal thrust can be and is absorbed by the rear suspension but there simply isn't enough rider weight being applied down the front forks for it to be absorbed by the front suspension. The simplest way to prove this is to just watch your front suspension while you pedal. Also switch from non-suspension to front suspension and notice the lack of difference it makes.

 

[flecc]

I knew in advance you'd disagree Caph, suspension proponents always do.

You're in a minority though, you won't find suspension on any road race bike for precisely the reasons explained, and it's only used to a limited degree in some forms of off road competition like downhill in particular to prevent frame or fork breakage. Even then it's very restricted in it's action to avoid the power sapping losses described.

Personal physical experience is no way to measure the losses described, them being far too complex to readily detect by rough comparisons in unlike situations. From that you might conclude the losses too small to bother with, but given human limitations, any loss is undesirable

Equally you won't find any bike designer of any worth agreeing with you, and the knowledgeable parts of the cycle trade often only sell suspension bikes under silent protest, but happy to voice off about its ills if asked.

However, you're entitled to believe as you will and I respect that.
.

 

[JohnInStockie]

Funnily enough where I am it seems the opposite now Flecc. Most/all of the shops I go in, and they seem to be competent bike engineers, tend to gree in prinicpal that sus-forks are only really needed off road, but "they would use them on road" and for commuter bikes "..it'd be better with rock shox" Ive heard a dozen times.

Weird init

John