werewolf

The only small wheel bike I have ever rode in my life, aside from the tricycle that I had when I was little, is my Swift, so I'm basing my assessment only on that. Might other small wheel bikes be more stable than the Swift?

EvilV

[quote=kb5ql;6742282]Yes - its a great walking route and you are never short of people to keep you company if that's what you want. I prefer to walk alone and just pass the time of day with people as I go along, but in the afternoon and at night time, it's good to be able to pal up with someone for an hour or so. Not speaking any Spanish, I was glad of an international clientele in the albergues. So far I've walked from the French side of the Pyrenees to Burgos. It's quite a long way but worth the doing of it.



I'll probably go back again at the end of September and do the stretch from Burgos to Leon. The summer is hot and very crowded in the accommodation department.

My practice was to set off at first light which at the end of April was about 7 am and walk until about 13.30 or 1400. That covered as many miles as I was prepared to do humping my worldly goods on my back. The mornings were great with really spectacular light sometimes.

Actually, The parts I've done already - mostly, I could have done them on my Merc. There are steep and rough patches though, but I'd have done it more easily overall on the little bike. Maybe I wouldn't have lost the five pounds of bodyweight I lost inside a week though.

makeinu

I know I already posted this, but and when would everything be the same? If you compare a 28mmx16" tire to a 28x700c tire then the volumes of air are not the same.

Everything is interconnected. It's hardly ever the case that you change something and only one other thing changes.

awetmore

I haven't ridden a modern Swift Folder (I had one of the earlier NYC steel models) so I can't really comment on their handling. Xootr doesn't publish the geometry of the current model, so I can't even make guesses based on that.

Using really rough estimates from the photo on their website it appears to have a head tube angle of about 71 degrees and a fork offset of about 40mm. This would give it a trail of 40mm, which is much lower than the 55-65mm found on most production bikes. I personally prefer lower trail bikes, but I think that they also benefit from a little load on the front.

The slack seat tube angle and shortish (seem to be around 41cm) chainstays of the Swift Folder will also put most of your weight over the rear wheel. That'll make the front feel even lighter.

What tires are you running? Wider tires will slow down the handling.

alex

CaptainSpalding

So you've said. Over and over. My contention is that your concept of "idealised" is so seldom found in reality that your data can't validly be used to refute the small-wheels-are-harsher claim. I'm not saying that small wheels are harsher or not - I'm just saying that the conditions of your simulation stray too far from the real world for your results to constitute proof. In addition to only having modeled a narrow set of circumstances, you also take it upon yourself on behalf of all small wheel detractors everywhere to rather narrowly define what "harsh" means. And it can mean different things to different people.

I think this is why you are meeting such resistance regarding a blanket acceptance of your findings.

With respect . . .

werewolf

Alex - Schwalbe Marathon 20X1.5's.

werewolf

Alex - Schwalbe Marathon 20X1.5's, at 100PSI tire pressure.

invisiblehand

From my personal observation, the usual suspects in the Folding Bikes forum treat everyone with respect. Regardless, it gives me a warm and fuzzy feeling to see it explicitly mentioned.

With regards to the thread ...

I think that an exercise that attempts to capture the marginal effect of something is worthwhile. As you are well aware, measuring the total effect of say tire size, geometry, and so on, with their interactions is complicated and would make the message difficult to convey.

More generally, the effort and sharing the exercise is itself laudable. At least, I think so.

One way to think about Jur's exercise, is that it moves the conversation to include something about geometry than to simply wave one's hand and say small wheels create a "harsh" ride. It also proposes a way to measure "harshness" that is reasonable or, at least, easily understood.

I don't want to speak for Jur, but I did not get the sense that he intended for the exercise to be definitive. Likewise, constructive criticism is also worthwhile since it often results in better understanding and improved future experiments.

-----

Related to something that Alex mentioned, should I infer than that to create a bike with a similar amount of trail that the head tube needs to be more parallel to the ground which goes against a motive for folding bikes; i.e., making a small portable bike?

awetmore

I'd suggest reducing the amount of fork offset, not decreasing the head tube angle. Both methods will increase trail. Decreasing the head tube angle also increases the wheel flop.

I also think that most folding bikes (including the Bike Fridays that I like) have chainstays which are too short. The bike might look funny with longer chainstays, but the rider should be between the wheels, not sitting directly over the rear. If you drop a plumb line from the back of the saddle on the Swift Folder and then do the same for photos of full sized bicycles I think you'll see that the rear wheel is closer in on the Swift. It's all a tradeoff to make the bike smaller.

alex

Fat Boy

FWIW, I'm sure you're talking about the smaller models, but the chainstays on my Air Friday are 3cm longer than my Cannondale road bike. I never really noticed it until I was fitting up a new chain not long ago.

CaptainSpalding

I mention it explicitly because Jur is someone with whom I seldom disagree. I also find his posts generous, informative, and valuable. I have been part of other online communities where the best people leave because they tire of the constant negativity and rudeness of a few rabble rousers. While I may take issue with Jur on this occasion, I would hate for our exchange to be a source of future enmity, or to contribute in any way to the migration of the Folding Bike Forum brain trust to parts unknown.

Me too. Thank you, Jur.

jur

Because my friend thinks folding bikes are toys, I have looked at the Xootr Swift's geometry in minute details, and compared the various dimensions and angles with Giant and Trek road bikes, and also another website about geometry (for which I don't have the address with me here at home). The result was that the chain stays are the same length, within a few mm, of those bikes I looked at (40cm). Some sizes were slightly longer, some shorter than the Swift.The Swift falls neatly on about medium size about where the above mentioned bikes are for all measurements. The seat tube and head tube angles are the same, chain stay is the same, BB height, top tube etc etc. The only area where there is difference is the trail. And the Swift has adjustable effective chain stay length - up to 43cm.

The other thing that surprised me, is the Mini's effective chain stay length was only 5mm shorter than the Swift at 39.5cm. The R20 and the Reach are also both 40cm.

It's mainly older road bikes and touring bikes which have the longer stays AFAIK. The older bikes I have are all on the order of 43-44cm.

jur

Respect returned... Ever since I saw Nekohime's pics of your Rohloff-equipped Jetstream I thought you were much more than initially thought based upon posts...

I didn't see resistance to my conclusion at all, just discussion... interesting how peoples' perceptions differ...

Anyway, regarding harshness, I also wondered what that might mean. So I looked into that in some detail, too.

First, I don't think to one person harshness means something different to another. Harshness is harshness, like red is red. What will, differ, is one person's opinion of the degree of harshness a particular bike might have in their experience. So one person would regard a bike as harsh, and another person that same bike as OK. But I don't think harshness is a relative concept in its basic understanding, just like the color red is not basically relative.

Sooo, what is harshness caused by? I came up with 3 ideas.

One is the amount of vertical acceleration that is transmitted from the ground to the rider. Vertical acceleration is not very pleasant. However if the acceleration is constant even though a large amount, it's still not too bad. EG as a passenger in a car you can take a corner in relative comfort. So perhaps acceleration by itself is not it.

So I thought about the car cornering business, and how uncomfortable it is if you suddenly straighten out at the end of the corner such that you are shaken from side to side. From that I formed the idea that it is the change in acceleration which causes discomfort. So I also plotted that in the simulations, but the values were consistent with the accelerations - soft tyres also resulted in smaller changes in accelerations, cancelling the small wheel effect. So that didn't seem a useful idea to put forward - it might just be confusing.

The last idea I considered was the frequency content of the acceleration. That is similar to the above idea. With this idea the results were also consistent with considering just acceleration - softer tyres filter the higher frequency stuff out.

So in the end the simple analysis was what I presented as being easier to understand while not being contradictory to more realistic conditions. This is what simulations and models are all about - finding the simplest possible model with which you can represent reality for particular purposes, without compromising accuracy. I don't think the model is too simple, neither do I think the simulation of a simple step is too simple. In fact, the simple step response is the standard which is used all over the world to evaluate system response. So that was also ideal to use in this case because a pothole or pavement edge closely resembles a step response. So I think it is proof.

As to exactly what causes the experience of harshness, I think it is the combination of amount of acceleration (ie amplitude) and the frequency content associated with that acceleration.

CaptainSpalding

Uh, thanks. I think. (Having a Rohloff seems to have the same effect as wearing eyeglasses. Folks automatically grant you a few extra IQ points . . . )

werewolf

Pipes will get you some more assumed IQ points. Very professorial. Whatever happened to pipes, anyway? Nobody smokes them any more.

awetmore

Do you have the geometry information handy?

The original Swift Folders were built with 71 degree seat tube angles (source https://swiftfolders.com/spec.html). That is much more slack than any road bike sold that has 40cm chainstays. With a 75 cm saddle height a 71 degree seat tube angle puts the saddle about 2.5cm farther back than a typical 73 degree seat tube angle. That is significant.

The difference in trail is significant too. If someone is complaining about the front wheel feeling light and the handling feeling squirrely on a Swift Folder it is pretty easy to point to the low trail and the rearward weight bias compared to most full sized bicycles.

All of the folders that you mentioned have geometries and designs closer to a hybrid or rigid mountain bike than a folder. Typical mountain bike geometry from the early 90s had 16.5" chainstays (42cm), 73 degree seat tube and 71 degree head tube angles. Hybrids are often similar, except the chainstays are closer to 44cm and the seat tube angle usually drops a degree or two.

alex

awetmore

100psi is overly hard for a 1.5" (38mm) tire unless you are running them on a tandem or cargo bike. You might find that you prefer the handling, and you'll certainly find that you prefer the comfort, if you run those tires at about 60psi. It's unlikely that you'll have any measurable difference in rolling resistance.

alex

cyclistjohn

Jur,

https://www.blackwellresearch.com/pdf...and%20Drag.pdf

may be of interest in your wheel research, assuming you've not already seen it?

The main site has some other interesting info' too.

Speedo

Sorry dude, but what you originally wrote was self contradictory, and your recent blast:

Directly contradicts what you said in your original post:

What I thought was funny, and pointed out, was that you made blanket statements like the ones above and then simultaneously recognized that it wasn't so simple.

Sorry to have offended you, but it's not like your posts have been examples of clarity.

Speedo

werewolf

I'm trying lower pressures. So far it seems about like you said...however the jury is still out. Shouldn't I be using pressures on the high end due to my large size - 250 lbs. or more with clothes and gear?

jur

Here are some figures I culled from the web:

bike/ Xootr Swift / Trek WSD2.3 M / Giant OCR M / Giant touring
headtube angle/ 72* / 72.1* / 72.5* / 72*
seat tube angle / 72* / 74* / 73* / 73*
chain stay / 40cm / 40.9cm / 41.8cm / 43cm
wheel base / 1029mm / 980mm / 992mm / 1021mm

Seat tube angle is a non-issue to me - if the Peter White approach to fit is used, then the saddle will end up in the same spot wrt the BB for any frame (assuming a seatpost with correct set-back can be found).

The geometries site I referred to is https://home.comcast.net/~pinnah/dirt...-function.html

cooker

people are smarter now...

Fat Boy

It was a rhetorical question along the lines of "How long is a piece of string?"

Speedo, I think your shorts might be riding up a little bit or it's time for a bran muffin. All of my posts could have been prefaced with, "Keeping all other variables constant". Anyone with one eye and 1/2 sense could have figured that out, of course.

I think it's great that I'm considered the heretic. I've own 2 folders and ride them quite a bit. Since I am saying that there are situations where they are not perfection, I'm considered an A-hole. I think I'm going to go over to the 'Living Car Free' forum and write about why I love my Hummer.

kb5ql

soooo.... good going Jur. You may have inadvertently created your first locked thread!!!

HOORAY.

Fat Boy

The weird deal is that Jur's information and sim work is really interesting. There are numerous ways to debate the best way to compare apples and oranges, but I bet there isn't a folding company around that has done the work he has.

I agree with Jur in that the change in acceleration, or jerk, is probably the biggest player in terms of human perception of harshness. Certainly, the frequency distribution is of the disturbance is going to be a big player. The human body is not uniformly tolerant of different frequencies. In general, we _really_ start to not liking things over about 10 Hz. This brings another variable into play. In general, a road bike and a folder travelling over the same piece of road will see a different frequency profile because the road bike will be travelling faster. In my experience, the difference is about 30% from my Downtube to my road bike. The Bike Friday is significantly closer to the road bike in terms of speed, more like 5% and maybe less. The speed difference alone will cause a rider to perceive a different feel even if the displacement of the axles are exactly the same for a given series of bumps. Is anyone interested in doing this type of homework? Most bike companies aren't.

I would like to see the comparison of a 700c bike and a 16" bike when both tires were set at low pressures for 'impending pinch flat'. This would give us a good idea of the 'best' ride of both bikes. It would also be interesting to see the 700c bike set at 'impending pinch flat' pressure and the 16" bike set at a pressure that had the same rolling resistance as the 700c tire. This would be a way to compare ride quality at a constant rolling resistance, which I would guess would favor the 700c bike.

Last, you could keep rolling resistance constant and then try all sorts of tire sizes until you come up with an 'optimum' tire size/inflation pressure. If I were going to guess, I'd say a 700/28 cyclocross tire would be a hard 'all-arounder' to beat. Of course, we're not bring tire construction into any of this, and that has a massive effect which is probably enough to outweigh most of the changes we can test.