I had worn out the original Bontrager (apparently pronounced BON-tray-grr) tires on my 2008 Trek 7.3 FX. I did some reading about possible replacements. At a certain point, I realized this was all complicated enough that I probably should take notes.
At some point, for purposes of general reference, I found a Schwalbe webpage offering some of the information presented here, along with some information not presented here.
Figuring Out What I Had
I had replaced the stock Bontragers with a pair of puncture-resistant Continentals; I wore those out; I think I may have worn out another pair of some kind; I restored the Bontragers; and now I had pretty much worn out those too. Here were the readings from this bike’s original front wheel:
This image showed that the stock wheel size for this bike was 622 x 18 (sometimes characterized as 18-622), according to the standards of the European Tyre and Rim Technical Organisation (ETRTO). Wikipedia said ETRTO worked with the International Organization for Standardization (ISO) to develop standards. Wikipedia explained that the relevant standard for bike tires and rims was ISO 5775, which seemed to consist of Part 1, for tires, and Part 2, for rims. (I’m providing multiple links for Wikipedia, and for other sites below, because they mostly lead to different places.)
Wikipedia indicated that, under ISO 5775-2, rim measurements consisted of their nominal diameter and width, measured in millimeters (mm). “Nominal” meant something like “alleged” as distinct from “actual.” That is, the actual measurement for this wheel might or might not be 622mm (inside diameter) by 18mm (inside rim width at its outer edge), but 622 x 18 was this wheel’s official size.
The label shown here said that the effective rim diameter (ERD) was only 603mm. Apparently the 622mm value was the more commonly used one. The ERD was reportedly the distance from the far end of a spoke (inside the rim) to the far end of the opposing spoke, on the opposite side of the rim. As such, the ERD would apparently matter more to bike mechanics than to riders.
According to Wikipedia, a diameter of 622mm probably indicated that this was a straight-side or crochet-side (the latter designated with a C (e.g., 13C), as distinct from hooked-bead, designated with a HB) rim, and a width of 18mm probably meant this was a straight-side rim. Apparently hooked-bead rims were uncommon. If I’d had a hooked-bead rim, Wikipedia said, I would have needed to shop for a beaded-edge tire. But for a straight- or crochet-side rim, I could use a wired-edge tire.
The sizing of bicycle tires was something of a mess (see Schwalbe). Wikipedia‘s chart indicated that a rim having this bike’s 622mm size could have been associated with bike tires with outside diameters variously labeled as 28″ or 29″ (in the English system) or 700c (in the French system), because “Bicycle rims and tires came in many different types and sizes before efforts were made to standardize and improve wheel/tire compatibility.” Strictly speaking, according to an online converter, 700mm = 27.6″; apparently (we are amazed to hear) attempts to mesh English and French approaches could yield an imperfect fit in the pre-ISO days. (For further details, see Sheldon Brown.)
The diameter was not really a variable: I would probably have to stick with a 700c tire and my existing wheels. Replacement wheels would cost money. If they were larger, they might not fit in my bike’s frame (below), and Wikipedia said that smaller wheels would experience greater rolling resistance. In other words, as one could informally verify by watching bicyclists in the park, smaller wheels tended to mean less speed for the same amount of work.
Measuring for a Wider Tire
My bike’s Bontrager stock tire was 700 x 32, meaning that it had a width of 32mm:
The question now was, should I buy 32mm replacements, or should I go to a different width?
Wikipedia seemed to say that my 18mm wired-edge rim (above) would accommodate tires with a nominal cross-section width in the range of 25-37mm. For further insight on that point, I saw a chart evidently created by Georg Boeger and posted by Sheldon Brown:
According to this chart, my 18mm wheel should accommodate at least a tire in the range of 28-37mm. The chart came with a note: “This chart may err a bit on the side of caution. Many cyclists exceed the recommended widths with no problem.” So (looking at the rim widths on either side of 18mm) perhaps my wheels would accommodate a tire in the 25-40mm range, if not beyond.
If I was going to choose something other than the stock 32mm, should it be narrower or wider? In my earlier years, the standard wisdom was that a skinny tire would have less road resistance, less wind resistance, and less weight. But apparently there were other factors at work. Jan Heine (2018) of Compass Cycles (makers of Compass Bike Tires, and now known as Rene Herse Cycles) found that, holding tire construction constant, at least up to 54mm, wider tires could have lower rolling resistance than narrow tires — even on smooth pavement, and more so on rough pavement — while also offering much better riding comfort and grip in turns:
To me, tires narrower than 38 mm don’t really make sense any longer. 38 mm tires still give you the “connected to the pavement” sensation that makes a racing bike feel so fast. Below 38 mm, all you gain is harshness. The bike doesn’t feel any better, just more jiggly.
Mavic offered additional commentary toward the same conclusion. I had lost skin, more than once, due to loss of traction, so I was receptive to Heine’s preference for a wider tire, with more rubber on the road. To figure out how wide I could go, Heine (2013) suggested measuring the width of the existing tire, and checking that against the clearance at various points on the bike.
It looked like my tire was just a tad over 1.25″ — call it 32mm. So its actual width seemed to pretty much equal its (700 x 32) nominal width. In deciding whether I could replace it with something wider, the points to check included the top of the front fork, the seatstays and chainstays (i.e., upper and lower rear forks), the brake calipers (when squeezed), and the fenders and cargo racks (if any). My narrowest clearance seemed to be at the chainstay. That was hard to measure — to get my head in there next to the tire, I mean, and view it closely. The chainstay was kind of curved around the tire, so there was not a single obvious point of closest clearance. It helped to take a bunch of photos and crop the best ones to get a close-up measurement.
The point of nearest clearance seemed to be just under 14/32″ — so, about 11mm. Heine said I should allow no less than 3mm of clearance on each side of the tire: “Any less, and you run the risk of having your tire rub, under hard acceleration or if the wheel develops a slight wobble.” That gave me up to 8mm (i.e., 11 – 3) of expansion space on each side of my stock 32mm tires. By Heine’s calculation, that meant I could go up to a 48mm (i.e., 32 + (8 x 2)) tire. But that would be well beyond the ~40mm capacity of my wheel.
Then I realized that I might have overlooked what was actually the point of nearest clearance. It wasn’t on the sidewall but, rather, on the crown of the rear tire (i.e., the high point of the tread). Heine said, “Some inexpensive tires can be much taller than they are wide, but high-end tires usually are relatively round.” So as the tire’s width increased, its height would increase too, presumably by about the same amount. A tire that was, say, 8mm wider would also be an estimated 8mm taller.
That called for another look at the rear tire. Once again, it was hard to see down in there. It looked like the rear tire’s point of nearest clearance was no more than 7mm between the crown and the kickstand area. I wasn’t sure I would have to allow a full 3mm of clearance there: hard acceleration or wheel wobble would presumably not affect the crown. But if I cut it too close, the frame next to the kickstand would be scraping the tire clean of mud and gunk. The other thing was, no doubling at the crown: Heine’s formula would give me a total of only 4mm (i.e., 7 – 3) of expansion space. It appeared that I would be limited to no more than a 36mm (i.e., 32 + 4) tire on back.
This was not an exact science. It could be that my stock Bontragers were taller than the tires that would replace them — or, on the other hand, if I bought something like a Schwalbe Marathon tire, maybe its thick layer of anti-puncture rubber would make it even taller, though one source said it was actually “quite flat across the tread” (though it might still be tall, and flatness could pose concerns about traction when cornering). Heine (2013) said that, whatever the tire’s official size, its working size might be larger: “High-end tires tend to expand over time as the casing ‘relaxes,’ and you don’t want your tire to rub every time you rise out of the saddle and flex your wheel.” One rider said he was able to install 40mm tires on his Trek 7.3 FX, though that was as tight a fit as he would care to attempt. But his was the 2011 model; maybe that model didn’t have the tight fit I was seeing at the kickstand. A StackExchange discussion tended toward the conclusion that I should be able to install 35mm tires, but even that small increase was not a sure thing: one participant recommended buying from a retailer who would let me return them if they didn’t fit.
So those were my thoughts as I looked at that point of close clearance, down by the kickstand. But it pays to take another look. Eventually the light came on and I realized that what I was seeing was not the bike frame but, rather, the kickstand itself. It had been on there for some years, and there was some gunk, but finally I saw that, if I moved the kickstand, the chainstays would truly be the real point of closest contact. So I didn’t need to worry that my replacement tires might be too tall; width was the only constraint. (As it turned out, I wound up with a 35mm tire and still had a bit of room left, even with the kickstand.)
Assuming I could find a way to try (and, if necessary, return) a larger (say, 700 x 35) tire, the next question was, which kind of tire should it be? That would depend on individual priorities. Various sources talked about such standard characteristics as speed, weight, durability, comfort, noise, price, and valve type, along with special features that might be prized in certain situations (e.g., foldable tires, for packing; studded tires, for winter; ease of changing, as an argument against tubeless tires).
I have already mentioned the two competing priorities that mattered most to me. On one hand, I could quickly get tired of fixing flat tires every time I ran over a speck of glass. That would be especially true in winter cold or under a blazing sun. So a tire made of solid steel would be great: never a flat. On the other hand, a steel tire would have no traction (and, of course, it would be heavy and slow). In my vehicles, I preferred softer rubber that would wear out more quickly but would give me superior traction on slick pavement. A bike tire with lots of thick, hard rubber would have better traction (and, of course, lighter weight) than a steel tire, but in rain it would still skate and slide, where a tire made of sticky rubber would help me survive the moment, even if random highway junk did soon slice it to pieces.
My balancing of those priorities said that punctures came first. I wanted a puncture-resistant tire. But I wasn’t prepared to die for it. Bearing in mind that the Schwalbe Marathon Plus was famed for its puncture resistance, I found it sobering to consider the results of research by Chain Reaction Cycles (CRC):
This chart said that the Schwalbe Marathon Plus came in last, or nearly last, in every test except puncture resistance (TP) and durability (D). Like a steel tire, it might survive nuclear war, but it would also offer me exceptional opportunities to find myself lying on the pavement due to exceptionally poor braking (B) and cornering (C) in both wet and dry (d) conditions. Oh, and abysmal rolling resistance (RR) to boot.
Was that research correct? You’d have to explore the details of CRC’s research to know for sure. Their webpage offered an interactive feature, where the user could change the weight given to those several criteria, and would receive a customized recommendation for the best tire. When I tweaked the settings to emphasize puncture resistance and cornering, the interactive tool told me I needed Continental Gatorskins, which happened to be what the local bike shop guy recommended as well.
The topic of cornering raised another question: did I want tread or slicks? Some people said slicks were best: the goal was just to put as much rubber on the road as possible. Slicks wouldn’t work on cars because of hydroplaning in wet conditions, but bikes didn’t have any problem with hydroplaning. Others said slicks were worst. Jan Heine (2016) said that his testing demonstrated that slicks provided poor grip in wet conditions. He said slicks were necessary on racing cars and motorcycles because they had too much power — they’d just shred any fine detail on their tires — but, especially on its shoulders, a bicycle tire should have ridges that would interlock with irregularities on even a wet road surface. The ridges should be little, not big: “Knobs will squirm in corners and thus make cornering unpredictable and dangerous,” though they could be useful in mud and snow.
BicycleRollingResistance (BRR) offered another comparison tool. Within the Tour/E-Bike category that interested me (as distinct from Road Bike, Mountain Bike, and Fat Bike), they provided a chart comparing a number of tire models by various test results, with an apparent focus on rolling resistance (RR, measured in watts) and what they called the puncture factor (i.e., force needed to puncture the tire, multiplied by tire thickness), which they considered a realistic measure of a tire’s puncture resistance.
In BRR’s chart, tires seemed to be ranked according to their RR at 60 pounds per square inch (psi) of inflation. (Some sources used “bar” rather than psi, where 1 bar = 1 atmosphere = approximately the atmospheric pressure at sea level = ~14.5 psi.) Up to this point, I would normally have expected to run at or beyond BRR’s maximum tested pressure of 75 psi, where RR (and the risk of pinch flats) would be lower, at the expense of some lost traction. That might be something I would want to reconsider at some point. For now, I saw that the RR differences among tires could be substantial. In their review of a high-RR tire (i.e., the Vittoria Randonneur), BRR said,
Rolling resistance is very, very high. … At the lower end of the air pressure range, rolling resistance skyrockets to over 50 watts per tire. That’s more than 100 watts for a pair of tires, this will seriously slow you down.
When using these tires, you should monitor air pressures very closely. Don’t let these drop under 60 psi EVER.”
Even at 75 psi, the Randonneur’s RR of 29W would impose almost twice the drag of BRR’s fastest touring tire, the Marathon Almotion (RR = 15.8W). That sounded bad. But would I even notice the difference? They said that 100W was a lot. But how about 50W? That value was of interest because the Schwalbe Marathon Plus (SMP) would consume 25W per tire. In terms of RR, as noted above, the SMP was at the bottom of the list of tires tested by Chain Reaction Cycles. So how could BRR give the SMP five stars?
While this post was focused on puncture-resistant tires, there were other ways of trying to reduce flats. One was to use a tube sealant like Slime — a liquid that would coat the inside of the tube and congeal in the hole when it was punctured. I had not found Slime to be very effective, and it could make a mess of things, including congealing in the valve stem. Another was the tire liner, a tape-like layer installed between tire and tube. Some found these useful; others reported that they did not help and could even cause flats by abrading the tube at the point where the tire liner ended. On the other side of the tube, everyone seemed to agree that rim tape (covering the heads of the spokes) was essential. There was also the retro tire saver, not presently available from many merchants — a device (or, in one DIY version, a leather bootlace) attached to and dangled from the brake, rubbing lightly on the tire’s tread as it rotated, so as to wipe off loose pieces of glass and other tire threats as soon as they were picked up, before additional rotations could drive them into the tire. Solid tires (by e.g., Bell, Tannus) were another possibility, though the science and the price did not quite seem to have come together yet.
Some reported that the best tire liner was actually an old tire, with its bead (i.e., wired edge) cut off, cut to remove a bit of its length (unless its diameter magically happened to be a bit smaller) and then slid inside the new tire — though presumably this additional rubber would make the tires heavier and perhaps slower. My search turned up several webpages offering details on this approach. A BikeForums discussion said these were a great solution for goathead thorns. ThoughtCo suggested that the inner tire should be a narrow racing tire (~23mm). Instructables proposed a remarkable system, not requiring such a narrow inner tire, in which one would add the flexible steel of a dismantled tape measure as a tire liner sewn to the outside of the inner tire, using a strand from a steel cable to do the sewing. Conceivably a layer of Plastidip or some other painted- or sprayed-on glue or plastic could supplement or replace that sewing task.
Rider Power Output
To solve that mystery, I looked for information on how many watts a bike rider might produce. According to Wikipedia,
During a bicycle race, an elite cyclist can produce close to 400 watts of mechanical power over an hour and in short bursts over double that — 1000 to 1100 watts …. An adult of good fitness is more likely to average between 50 and 150 watts for an hour of vigorous exercise. Over an 8-hour work shift, an average, healthy, well-fed and motivated manual laborer may sustain an output of around 75 watts of work.
Participants in a Bike Forums discussion similarly estimated (based presumably on their experience with bike power meters) that a “good fit cyclist” could sustain between 100W and 200W, and up to 500W for short bursts of no more than a few minutes, while the sustained value for a recreational rider, not of racing caliber, might be closer to 100W. In a famous demonstration, Olympic medalist Robert Förstemann, with 29-inch thighs, was barely able to power a 700-watt toaster long enough to toast a slice of bread. PowerPedals noted that, at peak professional doping (e.g., Lance Armstrong), power output would remain in the vicinity of 450W for only 30-60 minutes.
Of course, 1 kilowatt = 1000 watts, and a kilowatt hour (a term familiar to many payers of electrical bills) is a one-kilowatt power consumption that lasts an hour. So when we say that a bicyclist put out 500W, we mean that was the power being exerted and consumed at a specific moment; it is not a cumulative measure of the power used in order to achieve a task (e.g., bicycling a mile).
Various (e.g., 1 2) bike power calculators solicited input on assorted variables (e.g., rider weight, tire type, distance) to estimate power output. Using Steve Gribble’s calculator, filling in the few variables that I knew, it seemed that I might be producing a little over 100 watts on a 27-mile, 16 MPH average route I rode sometimes on my hybrid bike. One interpretation of results from that calculator noted that maintaining 15 MPH could require twice as much power as 11 MPH, and 20 MPH twice that of 15 MPH. Responses to a question posed by a 54-year-old, 115 lb. female Ironman triathlete who described herself as BOP (“back of the pack,” presumably) seemed to concur that a 100-watt output would actually be much better than BOP for someone of her size and age. ScienceShareware offered a graph for a 40-year-old casual rider who had several 20-minute workout sessions per week at 10 MPH: his peak was about 160W, and the average looked more like 60-80W.
The size of the rider was an important factor in determining the difference his/her power output would make. Bicycling suggested that the rider’s power-to-weight ratio (i.e., watts per kilogram of body weight) provided a more accurate indication of how fast s/he would actually go: a lighter rider might beat a bigger and stronger one in hills. Bicycling indicated that a top rider could produce over 6 w/Kg (i.e., 13 W/lb.) on a major hill, while a competitive amateur or older racer might be around 4 w/Kg (i.e., 9 W/lb.), and “an untrained person would struggle to produce 2.5 w/Kg” (i.e., 5.5 W/lb.). Cycling Weekly offered a chart suggesting that, over a one-hour ride, power-to-weight ratios would range from 6.0 for a professional rider to 3.0 for an amateur competitor to 1.8 for a recreational rider. Another Cycling Weekly chart showed how wattage outputs varied. For example, to keep up with an amateur racer whose power-to-weight ratio was 3.0, a rider weighing 50kg (i.e., 110 lbs.) would need to produce 150W, while a rider weighing 90kg (i.e., 198 lbs.) would need to produce 270W.
This information suggested that a pair of tires requiring an extra 30W would make little difference to a Tour de France rider on vacation, but the impact could be significant for a recreational rider with a 100W power output. Along those lines, I read with interest the comments in a sometimes heated discussion of the speed difference that puncture-resistant tires could make. Several participants claimed that they had calculated or experienced a theoretical or actual speed reduction ranging from about 0.75 to 1.5 MPH. The latter figure, for a participant whose average was 15 MPH, would be 10%. At that rate, s/he would do the work to ride 100 miles, but would actually travel only 90.
The conclusion seemed to be, then, that tires with high rolling resistance (RR) would probably make my riding noticeably harder. As I had found, the places where I rode would flatten unprotected tires — small glass shards were a common sight — but I didn’t necessarily need my tires to be bulletproof. Based on what I had learned so far, I decided it would probably make sense to compromise, to look for a tire that would protect against the vast majority of threats I was likely to encounter, while accepting that I would still have to fix a flat tire now and then.
Eliminating Most Contenders
Armed with that perspective, I returned to the BRR website. I noticed that the touring tires given a five-star rating all had puncture test scores of at least 12 for tread and 4 for sidewall. Indeed, on closer examination, I saw that (despite giving it a five-star rating) BRR was critical of puncture resistance in the Vittoria Voyager Hyper. In other words, BRR seemed to prefer puncture test scores of at least 13 for tread and 4 for sidewall. I also observed that, except for the Schwalbe Marathon Plus, the touring tires to which BRR gave five stars all had RR scores no higher than 21.5 at 60 psi.
Armed with those criteria for what counted as a five-star touring tire, I looked at BRR’s list of road tires. Several tires on that list met these criteria as well. The tested versions were narrow, as befit the classic concept of a road tire, but some of them came in wider versions. Possibly those wider versions would have higher RR, though what I had learned (above) suggested they might not. BRR did not report puncture factor scores for road tires, nor tire thickness values for touring tires, so that was the limit of my ability to filter the two lists by one another’s criteria.
That effort gave me a list of 20 tires. (Gatorskins were not among them: their RR was even higher than that of the Schwalbe Marathon Plus.) I looked on Amazon and Nashbar to see which ones came in 32-37mm sizes. I ruled out those that didn’t, or at least those for which I couldn’t find listings of that nature, as well as tubeless tires. Unfortunately, that eliminated most of the otherwise qualifying road tires after all. BRR’s reviews gave me grounds to rule out a few others. I also ruled out the Schwalbe Energizer Plus, as BRR found it functionally identical to Schwalbe Marathon (Greenguard).
Of course, there were many other tires that BRR did not review. For instance, Amazon listed 214 results (some of which were probably duplicates) for 700c tires averaging at least four stars in user ratings. At this time of repeated scandals involving paid fake reviews, there seemed to be a fair chance that some of those entries (especially those with relatively few ratings) may not have reflected the experiences of actual users. It was not clear whether or where I should set a floor on the minimum number of reviews required before I would take seriously Amazon’s ratings.
Within BRR’s limited list of tires with acceptable RR and puncture resistance, I suddenly found myself with only four contenders. I looked at their prices. The Continental Sport Contact II (32mm) was $32 (backordered) at Nashbar (backordered) and available (apparently in the earlier version, for $45) at Amazon. The 32mm size was not my preference, so I didn’t hunt too hard for alternatives. The Schwalbe Marathon Almotion (38mm) was available for as low as $57 through various stores or $93 at Amazon. The Schwalbe Marathon Supreme (35mm) was $70 at Amazon but as low as $47 elsewhere. Finally, the Schwalbe Marathon GreenGuard was rather confusingly priced in a number of listings at Amazon and elsewhere, due possibly to a welter of similarly named versions.
The hunt for deals led, ultimately, to a mixed set. For the front, where looked like the frame would accommodate a somewhat wider tire, I managed to find a 38mm Schwalbe Marathon Green Guard Reflex. I wasn’t sure whether that was identical to the Marathon GreenGuard, which BRR described as “THE tire to beat in the Tour/E-Bike class.” But for $28, I felt I could try to cope with it. For the rear, mindful of the narrower chainstay clearance, I went with a 35mm Schwalbe Marathon Supreme for $47 (including shipping in both cases). Unfortunately, the ad for the GreenGuard tire was somewhat misleading; it wasn’t for my wheel size, so I had to return that and try again. I wound up getting both tires from Chain Reaction Cycles, for $29 with shipping. They were in Ireland, but they must have had a warehouse in the U.S., or anyways I got it same-week for $8 shipping. (Note: this blog has no paid endorsements.)
So at this point, the mission was to get the tires, use them for a few weeks (as some advised) in order to break them in, and then decide how I felt about traction, rolling resistance, and puncture prevention. At some point, hopefully I will return here to provide an update on those factors.