Randonneur Geometry
 

Does anybody have experience with the short trail geometries (3.5-4.5 cm) used by the Alex Singer and Rene Herse randonneur bikes that run with front bags and wide tires? The reason I ask is that there seem to be a lot of suitable bike frames available with more conventional trail from 5-6 cm and I am not sure that paying extra just to get the decreased trail would be worth it.

I think the point would be whether these other bikes just have rondonneuring paintjobs, or where really designed from the ground up for the purpose. If they were, then you have a difference of opinion on what kind of bike it is. Something like the PBP run out in the front of the pack might require more lively handling than some guy churning away in his own bubble. With custom frames every single detail needs to be worked towards the overall service use of the bike.

The shorter trail should give more stable stearing. Average trail is perfectly useable, slow handling when you need fast is less tolerable. So the normal trail is more versatile, you need to know the stable handling is your performance goal.

the decreased (before edit was -increased- ) trail mostly lets you get away with a loaded front bag. The obvious solution is a seat bag. I'll report back after my first 400k.

That's a reasonable way to look at it, though there are lots of bikes with front bags and standard numbers. I prefer less trail because the bike is less twitchy, I can ride the paint line with less thought. :)

my bike has fairly relaxed racing geometry. It's pretty typical of the bikes I see on Brevets. If I put a few pounds in my handlebar bag, all of a sudden it becomes much more difficult to ride no-hands.

I definitely plan on building a rando geometry bike.

Sorry, my dyslexia got the best of me again. Rando bikes have less trail/more rake.

All the frames I have built for myself are exact copies of French randonneuring frames from the 40s and 50s. I have used them with 700c/30mm tires, and my current bike uses 650b/42mm tires. I have found that these bicycles do indeed handle better with a loaded handlebar bag than without. Without, they can be slightly unstable, especially at higher speeds. This is not a severe problem; a small shimmy at 25-30 MPH while riding no hands, for example.

Unfortunately, I have never ridden a high trail bike with a handlebar bag, so have nothing with which to compare.

When it comes right down to it, "randonneuring geometry" is nothing more than larger-than-normal fork rake used with the typical 72-74 degree head angle. The simplest way to get there from here can often be just paying your local builder $100 or so to re-rake your existing fork. That may well damage the paint, and it will also decrease tire clearance somewhat, but has been done with success. It's also entirely possible to have a new fork made for considerably less than the cost of a new frame.

HTH!

"much more difficult to ride no-hands". That I can believe. The last commercial touring bike I owned would not ride no-hands regardless of front load. Kinda scarry.

I keep meaning to mention that there is an e-book: A Rider's Guide to Building the Long Distance Bicycle. Don't know anything about it myself, but it sounds interesting.

http://www.roadbikerider.com/ldb_page.htm

I was looking for something in the basement today and found all my framebuilding stuff -- finally! I have a pile of the old style Reynolds 531 narrow fork blades. My new project is to build a rando fork. Maybe I'll build one of those mini racks to go on it. Trying to decide what brazeons to put on there. I also have to decide if I should put Mafac cantis, or new style cantis on it.

I have a couple of sets of those blades myself. I haven't used any of them yet as I have never been able to find a fork crown wide enough to accommodate 42 mm tires with fenders. I am planning on building a British style single-speed touring bike copied from a 1930's frame and will be using 26 or 28 mm tires, so a crown I have should work.

What are the differences in the cantilever studs for Mafac cantis and those for "new style" cantis?

I'm pretty sure the holes for the springs are 180 degrees off. Which would be a little too much spring tension.

Huh. I've never heard of that. I have used old Mafacs, along with current cantilevers from Tektro and Shimano, and V-brakes as well, and they've all used the same studs. I have heard that the Pauls are very sensitive to stud positioning, but they still have the spring holes on the inside of the stays/blades.

Do you have any pictures?

From the Paterek Manual:

"The comfort range of trail is 5.0 to 6.5 centimeters. . . A bike with less trail will be more 'twitchy' or nervous. A bike with more trail will be more 'relaxed.'"

I've always interpreted this and other explanations/analysis of trail to mean that bikes on the lower end of the trail spectrum will turn faster and feel more responsive, but not be as stable or track as straight as bikes at the upper end of the spectrum. Thus, a racing or track bike would have less trail, while a touring or randonneuring bike would have more. It also seems that trail is mostly achieved with headtube angle, while fork rakes remain in the 4.0 to 4.5 cm range (especially when using carbon forks which come in limited rakes). Again, racing bikes have steeper HT, while touring bikes have a shallower HT.

But this thread now has me very confused. I've also noticed that some modern track bikes have as little as 2.5 cm of fork rake and trail measurements above 6 cm.

But my Surly Long Haul Trucker -- which is super stable with a heavy load -- has a trail of 6.3 to 6.5 cm depending on tire size.

Can someone help clear up my confusion?

I take it all back. I just went and looked at my mafac installation of old, and they are the same as the newer ones.
I know the brakes fit on the newer studs, I started to install some Mafac cantis on a cheap trek before I realized half
of the studs were broken.


As far as Paternak and trail goes, it isn't that easy. I don't think that trail tells the whole story. Head tube angle, and rise/fall have something to do with stability. Clearly a more relaxed head tube angle and longer rake will be a more relaxed ride. This would mean less trail.

Trail is made up of head tube angle, wheel radius and fork offset (aka "rake), so by talking about trail we cover a range of variables. If you increase head tube angle without changing radius or offset, you get more trail (more stable, less twitchy). If you increase rake without changing the other two, you get less trail (less stable, more twitchy, faster response to 'bars). If you put on a smaller wheel (less radius) without changing head angle or offset, trail will decrease. But doing anything that will raise or lower the front relative to the back changes head angle a bit, so it affects how much trail change you'll get.

I think Paterek has it right.

Another source of confusion is that in motorcycle literature the terms are used in different ways than cyclists do.

Road Fan

Question:

How do low-trail rando bikes handle no-handed, with a front load and the wider tires? I've been thinking of a brevet bike, too, but I want to be able to no-hand. I generally believe that if the frame and wheels are aligned and the headset is good and adjusted right, it can be no-handed.

Road Fan

Paterek et al. oversimplify trail quite a bit, IMO. I agree with the Paterek POV when we are talking about narrow high pressure tires with no load. Beyond that it gets more confusing. There is little agreement, as can even be seen right here on this thread.

In my experience...

Standard trail (+/- 6 cm) works just fine with 20-25 mm tires and no load. Especially at higher speeds (20 MPH+) it makes for a comfortable and stable bike. At lower speeds, like below 10 MPH, you will start to notice the wheel flop caused by excess trail. The "standard" test is to slowly roll down a hill with no hands. At first you cannot do it, because the front wheel will flop to one side or another. As speed increases, steering stabilizes. In my experience the typical standard trail bike will stabilize somewhere between 8-12 MPH.

Now, putting a bag on the handlebars of this bike sends things straight to hell, as weight on the front wheel really brings out the tendency for the wheel to flop. A handlebar bag combined with 6 cm of trail may mean the bike doesn't stabilize until 15 MPH or higher -- at least according to what I have read. This, I think, is why handlebar bags have such a poisonous reputation in some circles.

At the same time, wide tires work fine with standard trail at moderate speeds, but as speed increases, wide tires tend to emphasize the stability provided by higher trail. This can get to the point that you feel like you are "plowing a furrow" with the bike, as it really starts to resist rider inputs.

Now, I think the key with low trail is that you are minimizing wheel flop. This is important with the handlebar bag, again bearing in mind that the bag really emphasizes flop -- which, BTW, is amply illustrated by simply rolling your handlebar bag equipped bike around the garage: watch out for top tube dents! So the goal of minimum trail is to restore the "neutral" handling of the 6 cm trail bike which was lost by the addition of the bag. The downside is that, as speed increases, inadequate stability can become an issue with a low trail bike, especially if you ride the bike without the bag. Frame alighnment is supposedly more critical with a low trail bike than with a higher one. This too is where the fat tires come into play, as they tend to have a stabilizing effect upon the whole affair while not significantly affecting wheel flop.

So essentially, we are using low trail to negate the effects of the handlebar bag, and the wide tires to negate the effects of low trail. My current bike is a copy of a 40s "mule path" bike with 42 mm 650b tires and about 25 mm of trail. It handles fire roads and general riding beautifully, can be comfortably no-handed down to about 6 MPH, and gets a little bit nervous above 45 MPH. I find clamping the top tube between my legs gives me a bit more courage. As a home built frame, I doubt the alignment is up to professional standards, which may have something to do with it, but it is not a significant problem. Taking the bag off actually allows me to ride no hands at about 4 MPH, but the bike becomes unpleasant at above 35 MPH, with a bit of shimmy that I have never tried to "ride through".

And now you see why I consider the Paterek "two sentence explanation" to be a bit of an oversimplification. :)

Six jours, thanks for all that detail! Great description. I didn't mean to trivialize the topic - I recognize that my confusion with all the details of steering performance is a result of the topic's complexity.

I find my racy bikes reasonable to no-hand down to about 10 mph, as you suggest. I don't think I ever get much above 20 except on downhills. It sounds like at speed (10-20 mph) the rando bike with bag and 28 mm tires might have decent no-handing ability.

What do you think about a bike getting wheel flop at low speeds while going uphill? I seem to find this issue mitigated by more trail. Do you have any experience or ideas about that? It seems to run counter to the idea that with less trail there is less tendency to flop at lower speeds - or am I getting dyslexic again? It also seems like nose-up versus nose down is a significant factor. This sort of flop causes me concern because of traffic. I feel if I am flopping I am more likely to get sideswiped.

Road Fan

Six jours:

That was great. Thanks for taking the time to write it all. If you don't mind one more question: I have a Lemond, titanium frame, 90s vintage, road bike that handles just fine. I don't know the front end specs, but it has a carbon fork, so I'm assuming nothing out of the ordinary for a road/racing bike. I did a lightly loaded tour on it last year with a rear rack to hold my gear which was about 25 lbs. I also clamped two water bottle cages to the forks. No handle bar bag. I found that the steering had a pretty bad shimmy that totally prevented me from riding no hands or even riding with only a light grip on the bars. It didn't seem to be affected by whether the water bottles on the forks were full or emptly, so I'm assuming that the problem had to be the extra 25 lbs on the rear end. The shimmy was also more pronounced at certain peddaling cadences. I didn't notice that it was particularly speed dependent, but it was certainly a problem at my average traveling speed of around 15 mph.

I'd like someday to build a sport touring frame that could accomodate a lightly loaded set of rear panniers without having the same shimmy problem, while still performing well unloaded, say for century rides, etc.

What kind of front end geometry would you suggest?

Frankly, I don't think anyone has a complete understanding of bicycle handling. If I'm being honest, I can think of at least one example to contradict everything I have said so far. For instance, you note that wheel flop seems decreased to you, at low speeds. This is the opposite of my experience, but obviously is no more or less valid. I think that bicycle handling is almost certainly the product of many, many factors, including body weight, positioning, and stem length. That is the only way I can explain so many different findings from so many people. At the least, it is probably fair to say that everything written about bicycle handling is a generalization and cannot be counted on as an absolute.

Can you elaborate on nose-up vs. nose down? Are you talking about the saddle? It does seem to me that putting more weight on your hands via a downward tilted saddle would change handling -- although exactly how I couldn't explain.

Fun, huh? :lol:

Yikes. Way out of my league. I've ridden a bike with a five pound saddlebag, which was just fine. Twenty-five pounds on a rack is way beyond anything I have any experience with. Jan Heine has written of decent experience with a Mercian touring bike with a very slack head angle (70-71 degrees, IIRC) with typically moderate fork rake of perhaps 4 cm. I believe he said this bike was quite nice with a rear load and nearly unrideable with a front load. Overall though, I'd recommend you get advice from someone who actually knows something about it, ie. not me!

Oh, one other tidbit: I understand that wheel flop is exacerbated by a shallow head angle, and that reducing trail cannot completely compensate for it. (No, trail is not the whole story!)

So theoretically, at least, a 71-72 degree head angle is going to result in excessive low speed wheel flop no matter what else is involved. That may be why some people report low speed instability on certain bikes regardless of trail figures.

Ok, well my Woodrup, the low speed offender, has about a 72 degree front end, due to its smallish 52 cm frame size. Maybe this is one of the rarely-discussed compromises of small frames designed for 700c to 27 inch wheels. It also has a high BB, and a 74 degree seat tube. Maybe I should be going towards a French fit and base my brevet bike on a 55cm c-c platform in the first place, with a 73 degree head angle.

My purely personal opinion is that the upsloping top tubes, extended head tubes, and other tricks meant to get the handlebars high enough for long distance comfort are ugly and stupid. Going to a larger frame is such an obvious answer but between the weight weenies and the CPSC telling everyone they'll neuter themselves if they don't have at least an inch betwixt crotch and bike, it seems the fad is to make the bike as small as possible. Those foot long seatpost extensions still haven't stopped looking silly to me, but I'm told I'm a hopeless codger...

I've gone to the old "fistfull of seatpost" method and have been quite satisfied. I have never in my life felt the need to straddle a top tube with both feet on the ground, so really don't see the problem.

</grump, grump>

I've been riding since 1969, and I'm not on board with teh weight weenies and the CPSC. Safe fork ends are such a PITA, and since 1969 I've never failed to clamp my QR levers properly. That said, getting good geometry with a little more standover clearance is a good thing.

I don't think you can be a weight weenie if you are thinking about a reliable bike for over 100 miles at a shot.

I think Fistfull = French Fit, or at least more Gallic than I have now.

I also like this bigger frame approach because it will let me have a lower BB. I like how a 7.5 to 8 cm BB drop feels when pedaling.

I'd rather see a sloping top tube than some of the outlandish stem extensions I've seen. I'm of the "fistfull of stem" camp. Seems like most rando bikes have flat top tubes though. (Then I go to Rivendell and see this with a sloping top tube and borderline stem extension. Oh well.)

I was looking at where I should put brazeons on my new fork. Didn't find any dimensions for the Mini Front from Nitto Also looked at the Velo Orange Randonneur Racks which state that the attachment points should be 3 .75" below the bottom of the fork crown.

I'm also trying to figure out how the boss under the fork crown for racks and fenders is usually done. I've never seen one.