Bicycle Rolling Resistance is a website run by Jarno Bierman in the Netherlands. Jarno* uses a roller to measure tire rolling resistance. The attraction of Jarnos’s work is that he uses a consistent method for a large number of different tires, and he uses a textured roller in an effort to account for energy loss from vibration as well as tire flex. The consistent test procedure gives me more confidence in his results than I have in roll-down test of just a few tire models, and the textured roller presumably approximates a real-world road surface better than a smooth roller.
However, he focuses on a narrow range of road tire sizes, staying close to 25 mm width. He treats stouter touring tires as a separate class, and he sticks to tires of around 37 mm for that group. Road and touring tires are all 700c. He has not yet directly explored the characteristics of wide light and supple tires.
He has, however, compared the rolling resistance of a particular model of high-performance road tires in different widths and concluded that the widest (28 mm) had the lowest rolling resistance (conti GP link ) . And he performed a similar test with a touring tire, showing that the 37 mm tire had lower rolling resistance than the 40 mm or 47 mm tire, while the 32 mm version had the highest rolling resistance for this tire model (Marathon link ).
However, the real outlier is in the mountain bike category. I am a little dubious of the usefulness of this test on knobby mountain bike and fat bike tires (since the knobs are larger than the roughness elements on the test roller — it seems to me that a more pertinent test would involve a rougher roller**), but the relatively smooth tires in this category should behave like road tires.
The best-performing tire in the mountain bike class has a rolling resistance that is competitive with the best 25 mm road tires, even with each class at inflation pressures appropriate to their widths. As one might expect, it has a very light tread and casing but measures 47 mm wide.
These results seem to show that wide/light/supple tires can be as fast as their proponents claim. Jarno has a long list of tires that he wants to test and not a lot of capacity to do the testing, but I would love to see him test some performance-oriented tires in the 38 mm range.
*I understand that you go straight to first names in the Netherlands rather than referring to someone with an honorific (e.g. Mijnheer Bierman) as you might in English. I prefer that informality, but I don’t want to sound disrespectful, and I apologize if I am incorrect.
**I think it might be useful to test tires on a series of rollers with different size roughness elements, comparable to Nikuradse’s experiments with pipes. This additional experimental data might provide some insight about optimum tires, width, and pressure for different surfaces.
As I am sure all of you bike geeks out there know by now, there are two mechanisms by which rolling is resistance is generated. One is the energy consumed by flexing of the tire as it rolls (hysteresis loss). The other is vibration, which converts forward motion to vertical motion and consumes energy within the body of the rider.
Hysteresis loss can be minimized by using a hard tire. As an extreme example, rolling resistance is very low for steel train wheels rolling on smooth steel track. High air pressure in a bicycle tire can minimize the amount of flex.
Two other factors influence hysteresis loss. A tire with a light and supple construction tends to lose less energy to flex at any pressure. Thick tread, heavy casing construction, and puncture-resistant belts all tend to increase energy losses.
A wider tire can lose less energy to hysteresis at the same pressure as a narrower tire because of the shape of the contact patch. However, the maximum pressure a tire can handle is limited by the tire’s width.
Historically, many of the measurements of bike tire rolling resistance have been made on smooth rollers. These measurements ignore energy loss due to vibration and have helped encourage an emphasis on narrow, high-pressure tires for most applications. Recent research has used more real-world conditions and has shown that, because of energy losses to vibration, wider tires at lower pressures can be faster on the less-than-perfect surfaces that we are likely to experience in our daily riding lives. In addition, wider tires provide greater comfort and control, especially on rough surfaces and with heavy loads.
It is worth noting that light tire construction, including both thin tread and a light-weight fabric casing, reduce both hysteresis loss and vibration loss. Thus the fastest tires tend to be the lightest tires, and they also provide the most comfortable ride.
There are circumstances in which the best tire is narrow and hard, but they are restricted mostly to competition on good pavement or at the velodrome. Outside of those conditions, it makes little sense to be stuck with skinny tires that ride harshly, require frequent inflation, and can be steered and bounced by surface irregularities. For riders not involved in competition (and many who are), a 28mm tire is the narrowest that is needed, and tire widths of 42 mm and wider are very practical, and can be as fast as narrower tires.
For those of us who are low-performance riders, low rolling resistance still matters. In fact, because we cruise at a lower speed, wind resistance is lower than it is for faster riders, so rolling resistance becomes a higher proportion of total resistance. The difference between a very fast tire and a slow tire result in as much as 2 mph cruising speed on a flat road for a 100-watt rider.
On the down side, light high-performance tires tend to be relatively easy to puncture or cut and are more prone to stone bruises (broken cords with no external damage). And, as one might expect, they wear out relatively quickly. I get between 1500 and 2000 miles from light tires on the back wheel (3000 to 4000 miles for a pair that is judiciously rotated), and wider tires do not seem to last appreciably longer than similar narrower tires (at least in the range of 28 mm to 42 mm). I don’t have a lot of problems with punctures on the roads that I ride on my weekend peregrinations, and I have the skills to fix them easily when I do, so the greater speed (and therefore greater range) and comfort are worth it to me under these circumstances. However, when I do have flats, some are caused by very small objects, such as tiny thorns or miniscule slivers of glass that would not penetrate thicker tread and casing.
I use stouter tires for commuting and utility riding and accept any loss of speed in exchange for the practicality and reliability. City streets are littered with more broken glass and other sharp things than are country roads. When I have to stick to a schedule and when I am wearing office clothes, I really don’t want to repair a flat, and I seldom need to do so when using heavier tires with protective belts. Most of these tires last significantly longer than performance tires, on the order of 2500-3500 miles, even while hauling groceries and other loads. The Schwalbe Marathon currently on the back of my utility bike has about 2000 miles on it and looks like it just getting warmed up. From an economic perspective, a good quality tire that is heavier and more robust can cost half as much as a light tire and last twice as many miles.
For me, touring is more similar to utility riding than it is to sportier weekend jaunts. Tires wear faster and are more likely to puncture with the dead weight of a load of camping gear. Light tires are okay for a fast weekend trip, but a journey to the opposite coast would require tire replacements (maybe more than one) along the way, perhaps at an inopportune time, and the risk of tire failure that would leave the traveler stranded would be increased. And repairing flats on a loaded bike is considerably more trouble. I am still not sure how much priority durability should get compared to rolling resistance.
Although the general tendency is for lighter tires to be faster but more fragile, manufacturers seem to be able to do some tricks with rubber compounds and casing design that make some tires behave differently than expected looking at only weight, or at least mitigating the performance impacts of added weight. Some of the tricks seem to be expensive (tire costs range by a factor of four or more), and it appears that you get what you pay for to some extent if you are discerning about ride quality. I would recommend doing further research about any tires you are considering.
The renaissance of the 650b tire has paralleled the rediscovery of the advantages of wider tires. The 650b size allows a wider tire to work with a traditional road bike design, whether as a retrofit on an existing frame or on a frame designed for that size. Under the marketing designation of 27.5”, the size has become quite popular in the mountain bike world (and now on fat bikes), but is still not entirely mainstream on road bikes. However, there is now a wide range of 650b tires available, from extremely light tires that roll fast and float over rough surfaces to massive and possibly bullet-proof trekking tires. There is also some bleed-through from the off-roaders, providing road tires that fit those 650b mountain bikes.
I have assembled a list of 650b road tires available as of late November 2016, posted below. I expect that assembling a list like this in the future will become an impractical undertaking because the number of options will continue to increase. I probably missed a few in my searches, but I hit the major tire manufacturers and marketers of this tire size. I cut off the maximum width for the list at 50 mm because there are few road frames that accept a tire any wider than that and because there are very few road tires that are wider. I did include some all-surface knobbies in the list, up to the 50 mm Continentals.
Finding all of these tires on the manufacturers’ web sites illustrated the lack of standardization for tire size nomenclature. Tires were listed as 27.5 (inches) x width in inches, 650b, 650 x zzb) (where “zz” is the width in mm), zz-584, or 26 x 1 ½ (with some other number to designate the actual width). Even in the same web site, it could take multiple searches using these different designations to locate all of the 650b tires.
Because I am too lazy to add references to the text of this blog, I will leave it to the reader to search out the details. Here are few links to get you started.
And here is the table of 650b road and all-surface tires
|Model||Width (mm)||Series||Advertised Weight (g)||Comment|
|Schwalbe||One H 462a||25||Evo||215|
|Schwalbe||Pro One HS 462||25||Evo||225|
|Panaracer/ Compass||Cypres||32||Extra Leger||261|
|Panaracer/ Rivendell||Nifty Swifty||34||406|
|Panaracer/ Compass||Loup Loup Pass||38||Extra Leger||333|
|Panaracer/ Compass||Loup Loup Pass||38||standard||354|
|Panaracer||Col de la Vie||38||500|
|Schwalbe||G-One HS 473||40||evo||420|
|Schwalbe||Marathon plus HS 440||40||performance||920|
|Panaracer/ Rivendell||Fatty Rumpkin||41||green label||480|
|Panaracer/ Rivendell||Fatty Rumpkin||41||force field||620|
|Panaracer/ Soma||Grand Rando||42||SL||300|
|Panaracer/ Compass||Babyshoe Pass||42||Extra Leger||362|
|Panaracer/ Compass||Babyshoe Pass||42||standard||390|
|Panaracer/ Soma||Grand Rando||42||EX||390|
|Schwalbe||Marathon supreme HS 469||42||evo||470|
|Panaracer/ Soma||Grand Rando||42||Blue label||610|
|Panaracer/ Bruce Gordon||Rock n road||43||520||knob|
|Schwalbe||Marathon Cross||44||performance||620||semi knob|
|Schwalbe||Marathon HS 420||44||performance||820|
|Panaracer/ Compass||switchback hill||48||Extra Leger||413|
|Panaracer/ Compass||switchback hill||48||standard||478|
|Continental||Race King Performance||50||580||knob|
|Schwalbe||Marathon supreme HS 469||50||evo||600|
|Schwalbe||Hurricane HS 352||50||performance||670||side knobs|
|Schwalbe||Marathon Almotion HS453||50||evo||750|
|Schwalbe||Marathon Mondial HS 428||50||evo||780||semi knob|
|Continental||Double Fighter III||50||845||knob|
|Schwalbe||land cruiser||50||active||900||semi knob|
Lather was sixty years old today
And Lather came home from his cage.
He looked at me eyes wide and plainly said
Is it true I’m no longer middle aged?
And I should have told him “No, you’re not old.”
And I should have let him go on…smiling…babywide.
— Apologies to Grace Slick
So I am officially old now, and to console myself and demonstrate that 60 really is the new 59, I took the day off and rode. I rolled up to Elkmont in the Great Smoky Mountains National Park. The weather was perfect and traffic in this most-visited national park is still relatively moderate in early May. The ride followed the Little River, which is a serious of cascades and pools carved into bedrock and boulder. There were also cascades of penstemon and maiden hair fern, and the mountain laurel was just coming into bloom. The odometer read 99 miles when I got home after about nine hours on the road, including a stop for pretty good burger at the Riverstone in Townsend on the return leg.
A couple of weeks later, a change of travel plans created an opportunity for a camping trip to Citico Creek.
So I loaded up the touring bike and headed out. The plan was to follow the proposed route of USBR-21 (with minor deviations) from Knoxville, south to Vonore. There, my route takes a left off of USBR-21 (which is on the wide shoulder of US-411 at this point) and onto SR-360. I went straight where 360 turns right, and it becomes Citico Road. This road rolls eastward for a few miles before picking up Citico Creek, which it follows into the Cherokee National Forest. The pavement ends at about mile 70 on this route, measured from my house. There are no major climbs, but it is all hilly, and there are some steep climbs.
Camping on the Citico Creek corridor is limited to areas specified by signs, and the two developed campgrounds have limited services. Most notably, they do not have water, so a bike camper needs to be prepared to filter a lot of water. If that does not sound appealing, Indian Boundary Campground is available further on down the road and up a significant climb. The bike camper can skip the Young Branch Horse Camp, where a premium is charged for the extra facilities to support horses. But I find it worth the $6 per night at Jake Best (mile 75) for a table to sit at, and the pit toilet beats finding fresh spots in a field of TP flags. I have been in this area on busy summer weekends when it was difficult to find a camping spot, so arrive early or visit at off-peak times if you want your choice of a spot.
The ride started with pleasant, cool temperatures, but there was some storm activity approaching and scattered showers during the day. I was not feeling that great, and after about 50 miles, I considered the alternative of a shorter trip to Abrams Creek Campground on the southern edge of the Smokies Park. I found a place where I had a connection on my cell phone (which was being charged by the dynohub). I discovered that, as I feared, Abrams Creek would not open until the next weekend (Memorial Day). So it was back to plan A.
The rest of the ride was slow but uneventful until it started raining lightly. For the last fifteen miles or so, there was a light intermittent rain, necessitating bringing out the raincoat. Being a wool guy, I was comfortable, even when a little soggy.
I set up camp mostly between showers. A serious thunderstorm came through at about 4:00 AM. I could feel a light mist through the rainfly of my MST Hubba tent at the peak of the storm, but I just got damp.
After the storm passed, the weather got very pleasant. I spent most of day 2 hanging around camp, including a short ride to enjoy the scenery. For the fluvial geomorpholy geeks out there, Citico Creek goes through the sequence of Rosgen A, B, and C classifications in about 10 miles.
Different route choices on the return trip on day 3 added close to 5 miles. The weather stayed pleasant but breezy.
I was remarkably slow on this trip. In the past, I could figure on a net average speed of about 10 mph, including stops. I was just over 8 mph on this trip. The weight of all the food I could eat in three days might have been a factor. I was not in great shape, and of course I am now old. This was the first time I have traveled with front and rear panniers, and the wind was against me in both directions — the wet weather was coming from the south and southwest and the fair weather was from the north. The bike handled the weight and the distribution of the weight well; it felt solid with no handling quirks.
Wildflowers, wildlife (deer, turkeys, coyote) and great scenery made this a wonderful trip for a long weekend.
I noted in a previous post that my old touring bike had some shortcomings. The following post goes into excruciating detail about the history of that bike, a history which might be interesting to a few bike-history obsessives, but likely not anyone else.
The Brown Bike was built in 1978 under the tutelage of Gary Hale, who was a fellow employee at Stu’s Bike Shop in Eugene. This bike was intended to be a gravel-road camping bike.
There is, of course, nothing new about riding a bike on surfaces other than asphalt. There were no good roads in the early days of cycling and a lot of roads remained unpaved into the middle of the last century. Stages of the TDF were run on gravel into the 1960’s and maybe later. But by the late 70’s, unpaved roads were retreating into remote rural areas and bike tires were getting skinnier and skinnier. It was common knowledge that wide tires were slow and heavy. An all-road bike in 1978 seemed downright radical.
Figure 1. Anquetil and Bahamontes, TDF 1963.
I think the seeds of the idea of an all-road bike were planted on a backpacking trip when I was about 8 years old. My memories are fuzzy, but I remember bicycle tracks on the back country trail in the Three Sisters Wilderness Area. One of the grownups teased me that we might meet up with the the ice cream dealer making the tracks at any time. As I got older and continued to enjoy hiking and backpacking, the idea of riding into the wild and remote places grew in appeal.
The seeds were watered by Cyclists’ Touring Club accounts of British rough-stuff riding (CTC Link) and the few references that I could find to French touring bikes with 650b demi-ballon tires. I also saw an “expedition” bike around Eugene that was made in Missoula (I don’t remember the builder) that was in the same spirit. The 650b tire size was not available in the US then, American balloon tires seemed too wide, and the British three-speed 26 x 1 3/8 seemed like the best available compromise.
Alloy rims for this size, triple cranks, and cantilevers were all pretty exotic in Oregon in 1978, and it took some looking to find the pieces I needed, but I was happy with the results. The bike rode well on pavement and on gravel, and the gears were low enough for long steep climbs.
I used this bike to explore the back roads, USFS and BLM roads in the vicinity of Eugene, Oregon. And I rode it on the longest bike tour of my life so far, from Nevada City, California to Eugene, up the crest of the Sierra and the Cascades. This trip was all on pavement except for a short segment of railroad shoulder (would have been shorter if I had not missed my turn the first time) to avoid getting on the freeway at Weed.
And there was one particularly epic camping trip on jeep trails on the edge of the Waldo Lake and Three Sisters Wilderness areas.
A few months after the Brown Bike hit the road, Charles Kelly’s article about the nascent phenomenon of mountain biking hit Bicycling Magazine (Clunkers) . This article marked a turning point in bike culture and merchandising and made my attempt at an expedition bike seem a lot less radical. (And of course the more-recent development of fat bikes and the gravel-grinder fad makes this bike almost conventional.)
Later that year (1978), a young footloose man came through town. He tried my bike and loved it, and offered to buy it. I declined the sale, so he knocked out a copy in a few weeks in Gary’s shop. He then disappeared into the sunset only to appear again a year or so later on the cover of Bicycling. That’s him just right of center (under the second “i”) on the orange bike with relatively skinny tires. The scene is Pearl Pass and all the culture heroes of mountain biking are in the picture. I wish I could remember his name. He was obviously an interesting and dynamic person, and I would like to know where he ended up. (The Bicycling cover shot is from Charles Kelley’s site )
After a few years, and after a couple of seasons of road racing, I got the cyclocross bug. The only knobby ‘cross tires available in the early 80’s were sew-ups, which of course are the same rim diameter as 700c. I moved the cantilever studs (including heating the tubing to remove them and heating it again to add new studs) to accommodate the larger rim diameter, and it became a reasonably capable cyclocross bike.
During one cyclocross training session, I hit a big root (or something) buried under the leaves on a trail. The obstacle was big enough to stop the bike and launch me over the handlebars. The result was bent top tube, down tube and fork blades, but not so severely bent that I could not straighten it out again.
Some years later, long after my cyclocross days were over, the bike was again a utility and touring bike. The 700c wheel size limited the width of tire that could be mounted, and I mostly rode 28 mm tires; anything bigger was a problem with fenders. In addition, the extremely high bottom bracket with the larger tires was less than optimum under most conditions. By this time (2005 or so), 650b tires had become somewhat available, promoted mostly by Grant Peterson. In order to restore the bike to its original function, I again moved the cantilever studs and converted to the bike to 650b. This was quite successful, improving the ride and opening the tire options.
I originally designed the bike thinking about some fairly technical riding, and the BB is high to allow pedaling through rough sections. Frame angles are 71° parallel head and seat tube. I figured this would make the bike stable and cushy on rough surfaces. The chain stays are as long as I could get them with untrimmed Reynolds 531 stays and long Campi horizontal dropouts, and they come out to about 445 mm (17.5”). Of course the main reason for long stays is to get good weight distribution (and heel clearance) for a rear load, but the length of the stays also allows a reasonably wide tire between the plain round-oval-round stays. The original 1 3/8” (about 35 mm) tires fit fine. I can fit a 38mm wide 650b tire, but there is not a lot of room left for mud. The width of the fork crown also limits this bike to a tire not much wider than 35mm.
The high bottom bracket is good for rocky trails, but it makes the bike feel less stable and grounded than would a lower BB. The head angle is okay, but the seat tube is too slack for a good riding position over the BB without sliding the seat all the way forward.
The fork offset produces a conventional amount of trail (60 mm or so), and I would prefer a little less trail. The offset is also small enough that, combined with the short top tube, I kick the front fender at low speed, which is not a critical flaw but it is mildly annoying, and one would think it could be avoided on a 60 cm frame.
The best I can reconstruct from my memory and the Proteus catalog (Proteus catalog link ) , it appears the frame was constructed with a .8/.5/.8 top tube, a 1/.7/1 down tube and probably .8/.6 chain stays, and it has a .9/.6 seat tube.
After 36 years of use and abuse, two cantilever conversions, one major realignment, and a moderate amount of rust (it never got anything better than a rattle-can paint job), the bike still rides great and serves on an occasional tour, but I felt like the bike might not reliable for the long trips I dream of, and it was relegated to occasional use and replaced with the new bike.
The usual assumption is that significant part of the ride characteristics of a frame is determined by its rigidity. An excessively flexible frame feels inefficient for power transmission and can be more difficult to control on rough surfaces or with a load. On the other hand, an excessively rigid frame rides harshly, transmits shock and vibration to the rider, and feels less lively.
Custom builders talk about the importance of using the appropriate combinations of wall thickness and diameters for a particular rider and the use to which the bike will be put (but they usually keep their design procedures proprietary). Jan Heine advocates for the improved ride quality and desirable flex in a frame constructed of extra-thin-walled traditional-diameter tubing (Jan’s blog). On the other hand, some influential figures in the business of building steel bikes downplay the importance of tube diameter and/or wall thickness to the ride of a bike (Sachs in forum discussion, Gordon link).
It is difficult to make an objective judgment about the influence of bike tubing. There are design fashions and fads, the power of suggestion, and the placebo effect. There are also confounding effects of frame angles, chain stay length, fork design, individual fit, and tire characteristics. And it is difficult to get a statistically significant sample size, both in the number of human subjects and the availability of bikes that are identical except for the factor being compared.
Without objective experiment, all we have is experience. For decades, the standard high-quality bike frame was made of Reynolds 531 tubing. The usual combination was a 1” diameter top tube with 0.8 mm wall thickness on the ends and 0.5 mm wall thickness in the thinner (butted) section in the middle of the tube (.8/.5/.8) along with a 1 1/8” diameter down tube with .9/.6/.9 wall thickness and a single-butted 1 1/8” .9/.6 seat tube. There might have been millions (I am completely making up a number here) of frames built with these specifications by Peugeot, Raleigh, Schwinn, and a host of competitors. A bike built using this tubing was responsive and reliable, and could win races, tour the world, or get the rider to work in the morning. The comparable Columbus tubing was a little heavier. The Columbus SL sticker designated tubing with .9/.6/.9 top and down tubes, and Columbus SP was 1/.7/1.
By the late 70’s, Reynolds advertised variations on the basic set of tubes with options for touring and larger frames. Heat-treated Reynolds 753 appeared in 1978, which was offered in wall thicknesses down to a .7/.5/.7 top tube and .8/.5/.8 down tube on road bikes; other tube manufacturers soon followed with their own heat-treated offerings. The mountain bike revolution created a need for steel tubes durable enough for the abuse of off-road riding, and larger-diameter tubing became available to fill the demand. Fat-tubed aluminum frames began to compete with steel. As tubing for mountain bikes and aluminum frames grew in diameter and this look began dominating the market, the traditional tube diameters started to look oddly skinny by comparison, and road-bike builders began to use oversize steel tubing partly to fit that new aesthetic.
We are currently in a golden age for the hobby frame builder. We can buy quality steel frame tubing for road use in three different diameter standards. Traditional construction, as noted above, uses a 1” diameter top tube and 1 1/8” diameter down tube and seat tube. Oversize (OS) employs 1 1/8” top tube and 1 ¼ down tube; double oversize (2OS) uses a 1 ¼” top tube and a 1 3/8” down tube. The default for all three standards is a 1 1/8” .9/.6 single-butted seat tube, but there are a number of variations available. Wall thicknesses of .7/.4/.7, .8/.5/.8, and.9/.6/.9 are available in all diameters and 1/.7/1 is available in some sizes, along with variations on seat tube, seat stay and chain stay diameter and wall thickness. Fork blades are available from light to stout.
In spite of all this variety, I have not found any analytical methods for helping choose tube diameter and wall thickness, or even any specific guidance on ride characteristics. Clearly, a heavier-wall tube is more rigid than a thinner-wall tube of the same diameter and same material, but how do tubes of different diameters and wall thicknesses compare?
In order to answer this question, I did some rough calculating. Deflection of a tube in bending is inversely proportional to the moment of inertia (MI) of a tube. The variable part of the MI is (D^4 – d^4) (where D is the outside diameter of the tube and d is the inside diameter). Using that as a basis, I created a stiffness ratio table (Table 1) for a range of readily available main tubes. It is common practice (and this shows in most Reynolds tube sets) to use a thinner-walled top tube than down tube, so there are nuances not shown in this table. However, this seemed like the clearest way to present the information.
Tube diameter is the most important determinant of rigidity, and there was only a little overlap in the rigidity of different diameters (less than I expected). Traditional 1/.7/1 is essentially the same rigidity as OS .7/.4/.7, and OS 1/.7/.1 is very similar to 2OS .7/.4/.7 (the butted section of the smaller diameter tubes are relatively more rigid, so calling these as ties is a judgment call). I might note that traditional 1/.7/1 is not readily available, probably because of that redundancy.
The heaviest 2OS tubing (1/.7/1) is about three times stiffer than traditional .7/.4/.7. In general, progressing from one rank to the next increases rigidity by 13% to 19%. The Bruce Gordon link above suggests that most of us would not notice a change in one rank level (although Jan Heine would disagree). I would speculate that it would be easier to detect a change in 3 ranks or more—traditional .7/.4/.7 should feel noticeably different than OS .7/.4/.7 with no other design changes.
A critical piece of information in choosing frame tubes is the frame size. Deflection is proportional to the cube of tube length (based on the equation for deflection where loading is applied to the free end of a cantilevered beam). This should be a conservative approach, since frame tubes are part of a truss and not really cantilevered and torsional deflection is proportional to tube length. However, we still are not including the effect of increased weight of the rider.
The following chart (Figure 1) shows the rank (from Table 1) of top and down tubes that would be used to match the ride of a frame made of traditional tubing of specified wall thickness (everything else being equal) using the cube of the ratio of tube lengths.
If the ride quality of a 58 cm traditional-diameter 7/.4/.7 frame is desired, it is easy to duplicate in larger frames, but smaller riders are out of luck. A lighter seat tube and perhaps a 1” down tube might get close. On the other hand, the ride of a traditional 1/.7/1 frame can be duplicated in the full range of frame sizes. Using oversize tubing means that there is no need for lateral tubes or double top tubes on large frames even for applications that require extra rigidity.
My touring frame is a bit long in the tooth, having been built in 1978. It was the first frame I built. It has never gotten a proper paint job and is suffering some from rust, although not as much as one might expect. Damage and changes over the years make it less reliable for a long trip. It also has a few design quirks that I would like to correct.
So I built this new frame. It has a standard touring design of 72° head angle and 73° seat tube angle. It has a fairly low bottom bracket for stability. Tubing is on the stout side for durability and rigidity with a load on rough surfaces. There is plentiful clearance for 42 mm tires.
The Rohloff 14-speed hub with Paragon sliding rear dropouts is one feature that is a little out of the ordinary, but the biggest deviation from standard design is the long chain stays.
Most production touring bikes have chain stays no longer than 18” (460 mm) or so (for comparison, a competition bike’s chain stays tend to be about 16” (406 mm) or a little shorter).
The longer stays on a touring bike allow the panniers to be mounted far enough behind the rider to provide clearance between the rider’s heels and a loaded pannier while pedaling without forcing the weight of the load too far behind the rear axle. It is possible to mount a rack and panniers on a bike with short stays in a manner that allows the rider to pedal without kicking the luggage on every stroke, but a load cantilevered out in space behind the bike tends to pick up the front wheel. This messes with the weight distribution, which results in vague, unstable, and/or wobbly steering. At best, this change in handling is something the rider has to get used to; at worst, it is downright dangerous. I would theorize that the tendency for Americans to try to tour on bikes with short chain stays had a lot to do with the shift in fashion from rear loads to front loads.
The 21” (535 mm) chain stays on this frame place the center of a loaded pannier about an inch in front of the rear axle. There is almost no change in handling when a 50 lb. load is placed in the bags. The stout Tubus rack also contributes to this loaded stability.
I went for a classic British three-speed aesthetic. Most made it to the US in black, though several other colors were available. A steel VO stem and a steel Campagnolo Sport crank (manufactured briefly in the early 1970’s) fit in with the “all steel bike” theme, as do the SPD pedals styled to look like rubber pedals. The road handlebars spoil the look somewhat.
The bike hit the road in August, 2014, and it has been in regular use as a commuter/utility bike since. I have ridden it regularly on weekend excursions and two camping trips. I am very happy with the design and, for the most part, the components.
More details than anybody cares about will follow.