john hawrylak

[QUOTE=Weatherby;16608849]Low trail bikes are wonderfully stable and easy to steer. The wide and more flexible tires change the transfer function entirely, a whole different ballgame.

I missed the wide, supple tire terms in the Xfr function, but I'll take your word for it.

Good to know leaning eliminates the RHP zero. Now let's see if Grant Peterson at Rivendell can come with a simple explanation of it.

Do you think the Wright Brother's knowledge of bicycle riding (they were always said to be bicycle mechanics) had anything to do with figuring out to turn the plane you had to dip the wing, like leaning on a bike???

Overall the slide show was great, I lost it at the 4th order equations.

Homeyba

I think I would (strongly) disagree with this. First off, narrow high pressure tires does not equal poor high speed handling. I race on high pressure tires and can honestly say that I have never (ever) been passed by a better handling fat tired, low trail bike on a high speed technical descent. On descents like that I routinely hit speeds of 60-70+mph with no instability at all. If a fat tired, low trail bike handled better and was faster we'd all be racing on them. You know how many of them I saw at the last RAAM???? zero Imagine that...
All low trail does is "slow" the steering down and it has no effect on comfort.

Weatherby

Low trail and higher pressure, low profile tired bike would be more likely to be unstable compared to a wider tired and lower inflation tires on the same bike. I did not say high pressure narrow tired bikes are all unstable. Far from it. Stability is not absolute. An experienced rider on a bike that they have ridden on for years can have a seemingly unexplained incidence of instability. Low trail is inherently less stable (at speed) with all other factors held constant. Adding wider and lower pressure tires adds stability if holding all other factors constant, no?

I did not say wider tires are faster for RAAM riders. At low speeds, the aerodynamic losses are minimal compared to the lower rolling resistence that some high wuality wider tires provide. Where does the advantage go away? Maybe 15mph? Maybe a bit less. There are online calculators and models to approximate a comparision. Remember when TDF riders mostly rode 19-22mm tires? Now, some are riding 25mm tires.

Weatherby

[QUOTE=john hawrylak;16611253]John, I suspect you are correct that understanding of bicycle steering plus watching how birds tip their wings and bank into a turn gave the Wright brothers some good ideas to pursue. They sought control and stability. Good bike framebuilders do the same. But applications are different. Who would want the slow handling of a track bike on the road or the "twitchiness" of a crit bike on a double century? I might read up on the Wright Brothers application of bicycle handing dynamics to 3-axis cotrol of flight.

Turning the bars and leaning is simple in comparision to flight. To go left, the bars are instinctively turned right and the bike rider naturally leans left and then the steering angle shifts back to the left. Anyway, I will take high speed stability any day which is one reason I like prefer large cross section top and downtubes constructed from CF or Alu, longer wheelbases, and a reasonable amount of trail. I suspect the reported handling benefits of the so-called randonneureuse bikes owes to the smaller diameter of the wheel and much wider contact patch allow the use of lower trailed front ends yielding good handling characteristics, particularly when crawling snail-like up a hill. What do riders do when the front end shimmies? They pucker up and make it worse.

Weatherby

[QUOTE=john hawrylak;16611253]No, this was pure speculation based upon my understanding of the handling patch dynamics. I have no data or reference. This is just my opinion. I came across an article by a fellow who says my opinion is wrong. Jan Heine says fat squishy tires contribute to front end shimmy. I would have expected wider tires to add dampening characteristics to lateral perturbations much like loose arms and hands on the bars do. I'll take Sheldon Brown's opinion since I am an East Coast guy.

Shimmy or Speed Wobble by Jobst Brandt
The Downsides of Wide Tires | Off The Beaten Path

thebulls

Oh, crap, now you tell me! Guess I'll have to take out the Hetre 42's that I've ridden with fenders for the last 1000km and put the Pari-Motos in.

(Photo was taken on my first ride, before I'd installed the front rack that I usually use to carry my GB28.)

FWIW, the fenders I am using are Velo Orange Fluted 48mm Fenders 700c, bought because they were on sale a few years ago. I used them with Hetre's on my '84 Trek 610, then later on an '82 Trek 728. When I got the Grand Randonneur, installation was almost as simple as taking them off the old bike and installing them on the new. I did have to drill a new hole for the rear brake-bridge mounting since it's in a slightly different place than the Treks. Total time moving the fenders over was about fifteen minutes.

A good friend of mine has a Boulder Bikes All Rounder which he rides with Hetre's and hammered Honjo's. It's a very nice looking frame; and the fork, particularly, has an elegant bend and is more shock-absorbent than the GR's chunky fork. Since the All Rounder frame is made by Waterford it's no surprise that it is a much nicer frame than the GR, but it had better be for triple the cost. I thought long and hard about buying an All Rounder, but ultimately the fact that I am putting two kids through college swayed me to buying a frame that's "good enough".

Nick

Homeyba

I'd argue that a low profile tire would actually handle better. A high profile (by high profile I'm assuming a tall sidewall), low air pressure tire is much more likely to have tire roll (unless it has an especially stiff carcass which would negate it's cushy ride) and instability. That is the complete opposite of normal high performance tires. Generally speaking, tires made for comfort are not the best for performance at speed.
If you are just cruising around at 10-14mph then what you said is perfectly fine. I don't think so if you are going faster.

Six jours

JFWIW, low trail does not increase stability. In fact, it is just the opposite. The idea of decreased trail is to restore the lost "liveliness" caused by fat tires and a handlebar bag. Riding a low trail bike unloaded can be irritating, because the bike begins to take on a mind of its own. Riding a low trail bike unloaded and with narrow tires is downright unpleasant, and sometimes frightening.

I personally do not like the very low trail espoused by Heine. I built several frames with exact copies of the geometry he likes so much and found that under ideal conditions they are slightly too nervous for me, and that under less-than-ideal (i.e. typical) conditions, they were actively obnoxious. I ended up preferring the British approach to geometry: 73 degree angles with two to two-and-a-half inches of rake, which results in lower trail than modern racing-inspired bikes but higher trail than the typical French rando. To me, this results in perfect, predictable handling - IOW, a bike which does what I want it to when I want it to and can otherwise be ignored.

Short version: different people want different things from a bike and none of them are wrong or right.

Re. descending: In my racing days I was probably among the top 10% of downhillers, but could not stay with the top 3% or so no matter how far out of my comfort zone I went. So I am not a great descender, but I am competent, anyway. Today, as a purely recreational rider, I never venture out of my comfort zone on descents. On my 700x25 bikes I tend to stay near the front of the main group but never anywhere near the fast guys. On my 650x42 bikes, I tend to hang on to the tail end of the fastest guys, at the same level of perceived effort/risk/whatever. So from my perspective, fat tires are easier to go fast on during curvy descents.

Does that mean high level racers would be faster on them during that type of condition? I honestly have no idea, but I suspect they would. The argument that they don't currently use such tires carries no weight with me, partly because high level racers almost never try anything significantly different from other high levels racers, and partly because that type of condition plays such a small part in most races that it would be foolish to sacrifice performance in other areas (weight and wind resistance, as the two most obvious ones) just for a small advantage in a twisty downhill.

Weatherby

Put a set of 19mm Schwalbe or Conti tubulars pumped to 170-200psi and do some high speed dives into corners on real roads with less than perfect pavement. Swap the wheels out for say 25mm Schwalbe One or Conti clinchers run at 90-100 psi. Repeat. The difference will be obvious. Sidewall flexbility equates to not only lower rolling resistence but also to better handling on bumpy roads because the contact patch is held more constant making it easier to control and hold a tight line. The sidewalls are like little shock absorbers. Average humans will corner with more confidence and apparent skill on the clinchers in this example. The Pros? Who knows. They aren't human.

Homeyba

Can't agree with that more.



I respect your opinion on that but it is still contrary to what I've experienced through my years of racing but that just might be our different perspectives.


This though flies in the face of everything I know about racing (and I've been doing it for along time too). People are competitive and if anyone has an advantage no matter how small, they will be right there exploiting it. We were always trying different things to get that little extra advantage and if you weren't you'd get left behind. You might be right that the difference isn't enough but you'd think that someone on some big race would switch bikes at the saddle of a final climb before a technical descent into a finish if it was any real advantage.

unterhausen

agreed, high trail is what you want for stability. Makes sense for racing where quick movements precede crashes. I understand why people like low trail -- it definitely feels livelier. I am not real fond of lower trail for gravel where the road can steer the bike

Homeyba

That's just ridiculous because nobody uses 19mm tires at 200psi unless they are on a track. We're not talking about riding on rocks. People generally run between 70-120psi depending on what tires they are running. I run 23's and 25's (Conti GP4000 because Conti sponsors my race team) all the time very aggressively and I can't tell the difference between them unless I look. The mechanic has done that to me several times. I would bet that there are very few if any people who could could tell the difference.

Six jours

Have you ever tried 650x42 in a race? No? Why not? And don't you think your reasons for not trying it might be the same as all the other racer's reasons for not trying it?

In my day, at least, bike racers were actually a fairly conservative bunch. Sure, we'd be willing to try some little thing if the possible downside wasn't too great, but that pretty automatically meant that we wouldn't try anything really radically different. I mean, hell, the advantage of 25mm tires at slightly reduced pressures is actually pretty clear in typical pro road racing situations, but look at how slowly that little change is taking place, and look at how the racing "masses" are still being dragged kicking and screaming into it. No, as far as I can see, bike racers' willingness to try new things is severely limited both in scope and in practice. "Sure, I'll try it, as long as no one will make fun of me for it, and long as someone else tries it first."

Homeyba

I don't have one. Can I borrow yours? I wouldn't mind taking one out and giving it a run down the mountain.

If you win with something nobody will be laughing at you. They'll be using the same thing you were using. I think that is kind of a hollow argument. 25mm tires haven't caught on because there hasn't been anything to prove they are a definitive advantage. There are a number of teams using them but none of them are consistently beating the teams on 23's. In fact the only reason some teams are on 25's and others on 23's is because the teams on 25's are sponsored by wheel manufactures who are making the new , more aerodynamic, wider wheels. The teams on 23's are using standard width wheels. I think the pro teams are like me and cannot tell the difference between the two.

Six jours

Even though you are wrong about every single thing you have ever done, posted, or even just thought about, I like you just fine and you are welcome to try anything I've got (wife excepted) if you are ever in my neighborhood.

WRT 25s, they are actually used by the winningest riders, on anything but the smoothest surfaces. At worst, they are no faster than 23s. At best...

And that is my point entirely. Racers are willing to experiment with tiny little differences, maybe, if it can be demonstrated that there is no significant downside. The ten+ year debate over 2 mm of tire width exemplifies that perfectly. Suggest a 20 mm difference and you will be instantly disregarded as a crackpot.

<post script> In all seriousness, wide, soft tires are pretty amazing in downhill corners, probably for the same reason motorcycle road racers use them. That big, sticky, bump-absorbing contact patch allows you to do all sorts of things that would be frightening at best on narrow high pressure tires. With Hetres, on technical descents, I can comfortably ride past the same people who easily leave me in the dust when I am on 25 mm clinchers. Does that mean that Hetres are better all-around racing tires? Of course not - but in that particular niche, I think they are the best bicycle tires that have ever been made.

Homeyba

Even though we don't always agree, I really do enjoy your conversations and you may not believe me but I do respect your opinion, even if you are wrong.

Don't know if you know but before I ever got a "proper" road bicycle I raced motorcycles professionally (back in the early 80's). That's where I learned to go around corners fast. The problem with talking tires and performance is that there are so many variables involved it's not even funny. Motorcycle racing tires have changed dramatically over the years depending on technology. There was a time when we used skinnier tires because they actually were faster. The main reason they are using wider tires now is because they have dramatically shortened the sidewall length. If you compare old racing tires vs newer ones they are about half as tall on the sidewall. The sidewall on the rear of my GSXR is about an inch. Not much taller than your Hetres. This extra stiffness allows the wider profile and significantly reduces chances of the tire rolling on the rim or feeling loose in the corners.

When I first started doing team long distance races I was usually the designated down hiller because of my technical skills and being big I have good descending muscles. I thought that a larger tire might with a flatter profile like a motorcycle tire might be fun to try but nobody makes such an animal. I did tried a number of larger tires and always returned back to the 23's and 25's. The bigger tires always felt too loose when I pushed real hard in the corners. I always associated that with the taller sidewall. To be stiff enough a larger tire has to be significantly heavier.

Six jours

Well, I have had my turn with road racing motorcycles over the years myself, and I disagree that narrower tires are ever faster, except when horsepower is seriously limited. That is to say, narrower tires make sense on a 125 GP bike, but not on one of the 1000cc MotoGP monsters now in use. The 125s don't generate nearly the lean angles of the big bikes, and IMO that has everything to do with contact patch. But putting a 6" wide tire on a motorcycle with 50 HP doesn't make sense, because anything you might gain in the corners is more than lost everywhere else.

The parallels in bicycling are obvious; otherwise we'd all be riding around on two inch wide slicks. So we balance (or at least pretend to) the various factors and mostly come up with the idea that Hetres are not ideal for racing in general. None of which has much to do with the fact that I pretty much guarantee you'd go faster on a technical descent with a 42mm tire as opposed to whatever racing clincher you are currently using.

<edit> Or put another way, how fast do you think you'd corner on a road racing motorcycle if you had 23mm tires on it?

Bandera

I spent a bit of time doing Long Distance road motorcycling where the clock is running and various routes & challanges are met (or not) around North America.

Always interesting hardware debates:

"An Advernture type bike will give you the long travel suspension for bad roads & a big tank for fewer stops & greater saddle-to-fuel-stop time. Give me a GS!"

"No! A dedicated Touring design with plush rider comfort & electronic cruise control & heated seat will keep the rider alert and comfortable for extreme distances. Give me a Gold Wing!

I Hate Analogies, but I submit this for your amusement w/ two communites trying to challange themselves to go as far as possible on two wheels with the clock running.

More than 1 way to skin the cat.
My modified VFR is sitting in the garage ready to do 1,000 miles in <24 hours on demand, and a couple of bicycles hang next to it.

-Bandera

Weatherby

Obviously you have no scientific background or experience on the track. Continental makes 19mm tubulars that are designed for 160-220 psi. The nature of my thought experiment was for you to think of the performance at the two extremes. Narrower tires must be inflated to a higher pressure than wide tires. For a a 200+ lb rider, it is quite possible that the proper inflation pressure for the rear "narrow" tire could be in excess of 140 psi and it won't have the same cornering adhesion on normal, rough bumpy roads with flecks of gravel and sand compared to say an equivalent skinned 28mm tire inflated to say 85 psi. I can tell the difference. Read what tire engineers have written on the subject. Again, I am speaking about real world roads. Not those with smooth, swept corners.

If I remember right, Avocet did a study about a million years ago. real data. I'll try to find a link to it. Might have been Jobst Brandt.

Weatherby

Has anyone ever rolled a clincher?

Why do we reduce tire pressure in the rain?

Below a certain speed, the aerodynamic loss of a wider tire is irrelevant because both frictional and aerodynamic losses are approximately linear whereas once we ride at speeds exceeding about 30kph, aero losses take over. Anyone who is sponsored and has a personal mechanic, this "linear" part of the curve does not apply to you. Stick to 23mm or 25mm at the widest. For normal century or double century riders who do them in 5-7 or 12-16 hours, a 28mm or wider tire will roll faster and corner better than an equivalent 23mm pumped to the proper pressure. Vendettes=23mm, Randonneurs=28mm, Touristes=Jan Heine's recommendations

Cycle Tyres and Tubes

Road Tubeless Tire Benefits & Disadvantages | Bicycling Magazine


https://www.bccclub.org/documents/Tireinflation.pdf

Tech FAQ: Seriously, wider tires have lower rolling resistance than their narrower brethren - VeloNews.com

Weatherby

So, what is the attraction to bikes like the Soma Grand Randonneur versus what road bikes have become over the past 20-30 years?

For me?

It is only about the ability to mount wider tires. the geometry? Not so much.

thebulls

Depends if you like to carry your load in front or in back. My high-trail Rivendell Rambouillet can handle 650Bx42, if I wanted. And with a rear load the handling is fine. But with a ten or fifteen pound load in a handlebar bag, you take your hands off the bars at your peril. I like to carry the load in front. Why? Because then I can easily get what I need, often without stopping, but even if I have to stop I can stay astraddle the bike instead of having to get off to dig into a saddlebag. But as far as I can tell, there is no "right" answer, just personal preference.

Nick

Weatherby

I guess I have been lucky with my handlebar bag on various bikes but then again, I never ever put 15 pounds up on the steering axis, which could require some gymnastic ability to steer no hands or the hips of a ballerina (partial joke). Any bike that cannot be ridden "no hands" at 13-18 mph is worthless in my opinion since this the speed I want to take a jacket off or put one on and below that speed, the physics don't give much margin for stability. Keep the poles out of the right plane or keep your hands on the bars.

If your Soma Grand Randoneur can take 15 pounds in a handlebar mounted bag, can be ridden no hands in the 20kph+ range, and is stable at low and high speed with hands on the bars..........and is comfortable. What else do we need to know?

The dampening and dissipative effect of the tires turning is described somewhere in the following link(s). I thougth they were pretty good but it has been many decades since I studied control systems, but I think this fellow does a good job taking a very complex subject and explaining qualitatively and then bringing it to a more mathematical treatment.

It seems to me that the kink effect of big soft squishy tires tends to soewhat offset the lowered feedback of a handlebar ladden with a heavy handlebar bag while lower trail gives you a lower critical velocity which helps remain on the bike while crawling up hills. I know that my handlebar bagged bike was really easy to ride with the front panniers were loaded with the heaviest part of the touring gear and that makes sense since these "lead" bags stabilized/dampened the perturbations at the top of the inverted pendulum.

Trail is just one tiny piece of the puzzle.

[QUOTE]It is generally believed that a trail is absolutely necessary for the stability of an autonomous bicycle. This was recently shown to be incorrect (Kooijman et al. 6,7). Stability requires a sufficient gain in the negative feedback loop. The negative feedback is basically provided by the handle bar transfer function T[SUB]f-σ[/SUB](s). For a standard bicycle geometry, the trail is instrumental for the negative feedback. If, hovever, another effect causes a negative feedback, i.e. causes the handle bar to turn into the lean with a sufficient amplitude, the bicycle remains stable against capsizing[/QUOTE]

https://sites.google.com/site/bikeph...n-and-synopsis

https://sites.google.com/site/bikeph...ium-conditions

https://sites.google.com/site/bikeph...-steering-axis

Six jours

For a while I was a complete believer in everything Jan wrote about trail. I even took up framebuilding, as a hobby, so that I could experience the things he talked about without mortgaging the house to pay custom framebuilders. And so my experience gradually showed me that, while Jan may have found a geometry perfect for him, it is not necessarily perfect for anyone else.

One of the most critical lessons, for me, was a long ride with a Rivendell-mounted friend. I fully believed that his high trail bike would be essentially unrideable with the handlebar bag he'd recently installed, but he seemed to have no problem with it. We swapped bikes for awhile (I was on a faithful copy of the Rene Herse 650b bike Jan had written so glowingly about) and we both noted that there was very little difference in the way the two bikes handled. I liked mine slightly better, and he liked his slightly better, which just goes to show that familiarity plays a large role. But the reality was that both bikes were perfectly pleasant. (We both noted that the tires made a much larger difference than did geometry - I was on Hetres and he was on Schwalbes - which has helped convince me that Jan is more right about tires than anything else.)

In that time I also have ridden bikes with handlebar bags mounted in several different ways, and I have decided that that makes a much larger difference than the actual existence (or non-existence) of a handlebar bag in general. In my firm opinion, a handlebar bag mounted securely and low will work fine with any standard geometry, while a handlebar bag attached directly to the bar and allowed to flop around without adequate support will work poorly regardless of geometry.

Short version: if you want a handlebar bag, first you need to get a good rack and mount it with minimal tire clearance. Having done that, handling will be fine no matter how your fork is raked. If you can't or won't do that, then do yourself a big favor and buy some panniers instead. In all other respects, you're probably best off following Grant Peterson's lead and refusing to think about geometry at all.

thebulls

I think I mostly agree with this, particularly getting the "handlebar" bag off the handlebars and low down onto a front rack. From 2007 to 2010 I rode with a handlebar bag attached to the bars, riding either a Rivendell Rambouillet or a Gunnar Sport. The bag was a Lone Peak Atra 100, which attaches to the bars with a Klikfix system and in that respect is much like the Ortlieb bags that are more popular. Then from 2011 to now I have been riding almost exclusively with a Gilles Berthoud 28 mounted on a front rack, on various "low-trail" early-80's Trek's, my Gunnar Sport with a low-trail (62mm offset) fork, and most recently on the Grand Randonneur.

Where I experience the biggest difference between these various bikes is that with the higher-trail bikes with a handlebar-mounted bag, I can't take my hands off the bars for more than a moment before the bike starts to veer. That's basically not a problem because I seldom have any desire or need to ride no-hands. But it does mean that I am doing more-constant work to keep the bike on course and that contributes to a little more fatigue that becomes more noticeable on long events (600km or more). Getting the bag lower on these bikes definitely helps with this. My current commute bike is an '82 Trek 728 that I initially used for randonneuring for a year with the GB28, low rack, and 650Bx42; but now in commute service it is using the Lone Peak on the handlebars, with 700x32. It is noticeably more of a handful when I stand up on a hill ... more "torque steer". But still nothing to write home about. If I was going to ride a brevet and discovered right beforehand that my two main brevet bikes had mysteriously melted down overnight, I'd have no hesitation riding the 728 instead.

I do wonder how much rider-weight matters to all of Jan's results. He's taller than me but probably weighs only 3/4 as much. A frame that "planes" for him might feel soggy to me, and a frame that "planes" for me might feel too stiff for him. Though I can't say I've ever felt much of a "planing" effect on any bike I've ever tried. Maybe I just don't know what to be looking for.

Where did you learn how to build frames?

Nick