Tech FAQ: E-Bike impacts, chain friction, tubeless tire talk
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E-Bike impacts and maintenance
Is there any way to measure the difference of impacts on soft surface trails caused by the on-again off-again delivery of pedaling power versus the smooth and constant application of power of an electric assist motor? If I am riding at 150 watts, half from me, and half from pedal assist, how can the improvement in traction be measured? How much longer might tires last with very-smooth application of energy produced by pedal assist versus the not-so-smooth application of energy produced by pedaling?
Thanks for your continuing education for all of us.
In 2015, IMBA conducted a study that concluded Class 1 eMTBs (Class 1 are those limited to 20mph and have only pedal assist—no throttle) are not likely to have any more impact than traditional mountain bikes or other trail users. It seems to me that the study’s methodology could be used to quantify the first impact you are wondering about. It makes careful measurements of the trail bed and indicates that there is little or no measurable difference in trail wear.
The assumption that e-bikes damage trails more than pedal-powered bikes is one of the most common reasons cited as to why Class 1 eMTBs should not have trail access. However, it is generally seen as a misconception, and this study makes that clear. IMBA posted a number of resources on its website related to e-bikes on trails that you can see here.
I imagine that measuring the traction difference could be done in a lab with a roller like the one used in this test. Or perhaps by testing traction on incrementally steeper and steeper trails made of the same dirt.
As for tire wear differences, that could be quantified by over-and-over riding on the same trail over a long period of time and measuring the change in tire tread depth with the number of laps. I suspect that, while the smoother application of power from the e-bike might reduce slips while climbing and hence reduce tread wear, that will be counterbalanced by the extra weight of the motor and battery adding to tread wear. I would not be surprised if it were close to being a wash.
On the road, without slips, tread wear is unquestionably higher on the rear tire than on the rear tire of my non-e-bikes.
My family rented electric mountain bikes in Italy and the mechanic mentioned that they have a higher rate of cog wear, especially in the small rear gears. Perhaps that’s because people are more able to use the smaller gears and start from stop positions. Have you encountered this? I asked because we just bought my wife an e-bike and I want to keep up on maintenance issues.
Any other electric bike maintenance issues that you’d suggest keeping an eye open for?
Yes, I have certainly encountered this. In order to avoid frying cogs, I measure my chain elongation frequently and replace the chain as soon as it has exceeded the elongation on the gauge. I go through chains faster on my e-bike, and I tend to ride more on smaller cogs, accelerating the wear there. I have yet to let a cog wear to the point where it actually skips. However, I have been concerned enough about the 11T cog that I have replaced that prophylactically a couple of times.
It is not so much that the wear is concentrated on the smaller cogs as it is that, on high output levels (Sport and Turbo settings on my Bosch system), I tend to be on the 11T cog exclusively for long periods on flat roads. This happens to me often because I use my bike for transportation and often am in a hurry to not be late for appointments and hence spend a lot of time in Turbo mode.
My bike is a Class 3 e-bike, meaning that the motor assist cuts off above 28mph, rather than 20mph as with Class 1 or Class 2. At 28mph and above, any bike rider tends to be largely on the 11T cog.
The 11T cog is easy to replace, relative to the other cogs that are attached to spiders or, in the case of SRAM, are machined in a single piece. That’s another reason why I replace that cog alone.
Just a quick point on chain articulation. True, the larger the ring, the less a link bends engaging it. However, the number of links that engage per revolution increases proportionally. So the total articulation (angle/link x number of links) is always 360 degrees per crank revolution irrespective of ring size. What changes is chain tension for a given torque. This suggests it’s the decrease in tension, not any difference in articulation angle, that makes larger ring-cog combinations more efficient.
More tubeless tire talk
To answer the questions in your recent column, the rims are from 2017 and are the Plus model. The tires were the new Continental tubeless Grand Prix 5000 in the 25mm width.
Just reading your column. There was some question about what Hed Ardennes rims are tubeless compatible. Here’s an email from Andy Tetmeyer from 2017 about this rim – it was in response to my inquiry about a replacement rim after hitting a rock on a descent.
We had one 23mm rim that was tubeless-ready, and it is the one that Art references on the link you sent me. That particular extrusion comprised less than one percent of our 23mm rim production. I do not have any more 24-hole rims in that extrusion, only 18s. The other 23mm extrusion is the C2, and that is not tubeless compatible.
Repository of Knowledge
Hed Cycling Products
So, it does seem like a small percentage of the 23mm wide Ardennes were tubeless compatible (not just the plus size). My rims are Hed Ardennes SL and I have ridden two Haute Route Alps on them without incident.
I have found that I can deal with difficult to mount/remove tubeless tires by using the Tubeless Solutions Bead Biter levers. They can be hard to find. I bought mine on Amazon. They are stiff enough to pull tires with tight beads off, and the other end can grip the rim, creating a barrier that prevents the bead from coming off the rim when I lever the last section on.
I also depend on the Tubeless Solutions Bead Biter levers for really hard to mount or remove tires. They can be a bit hard to squeeze and get to clamp onto the rim bead. Once on there, though, they keep the bead from regressing from the point you had advanced it to with the tire lever. They are far better than fighting with multiple standard tire levers.
I use a Sector 28 as my rear tire and never even noticed that the minimum pressure is so high. I wonder if the limit has more to do with the impact on ride. I have experimented with lower pressures, but I have experienced resonance at higher speeds on rough descents. I am a tall rider (6’5, 205) and am happy with 80psi.
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”
He holds a bachelor’s in physics from Colorado College.