Technical FAQ: Tires for riding rollers
I have a question that I cannot find the answer to anywhere. I have been following you for years, have two of your books, and I just read your VeloNews article, “Where the rubber meets the road.” So you are eminently qualified to answer this question. I hope you can.
I just purchased a set of Elite Arion Mag Rollers, and I love them. They are the best rollers I’ve ever used, by far. One problem I am having, though, is that I’m getting some bumpiness. I’m fairly certain it’s due to my tires, and possibly the tubes. The tires, for sure, are fairly old and have imperfections in them. I’d like to correct this problem and make my roller experience as smooth as possible, but I just don’t know the best way to go about it.
PLEASE NOTE: The tires and tubes will be used on the rollers ONLY; no road or turbo trainer usage.
What characteristics do I need to look for in a tire? Weight, puncture resistance, and handling are obviously not a concern, so what does matter? TPI? Suppleness? Outer materials? Casing materials? Does tire width matter? (Ex 700×23 or 700×25?) Will using a latex tube make a difference? What about tire pressure?
There has been so much written about these issues in regard to turbo trainers, but I can’t find a single word on the subject for rollers. I just want to get the best experience out of them as I can, but also without spending hundreds of extra dollars.
In the late 1970s, before turbo trainers, any indoor training I did was on rollers. The drums on my Cinelli rollers were not machined; they were made out of large-diameter, thin-wall steel tubing, and they had open cup-and-cone bearings, rather than cartridge bearings. Consequently, I had few expectations for smoothness (or quietness). My roommate, however, had some early Kreitler rollers with machined drums, and his were nice and smooth (so I tended to use his!). There were no decent clincher rims or tires at the time, so we rode tubulars for training as well as for racing. A good racing tubular glued on straight onto a true (especially a radially-true) wheel made for a smooth ride on the Kreitlers, but if the valve stem were cocked or if there was a bulge in the tire, it made for rough roller riding.
In the rolling-resistance article you cite, I did not publish the test results performed on the (very large-diameter) smooth roller surface at Wheel Energy Oy because it was unrealistically smooth, making the rolling resistance numbers unrealistically low and showing only that rolling resistance continues to go down as tire pressure goes up. (In the real world, even small imperfections in the road surface will cause rolling resistance to increase after a certain tire pressure with a given tire has been exceeded, so I instead only published the results of the diamond-tread surface on the roller, which revealed this effect.) Even with smooth rollers, however, as the roller diameter decreases, the tire’s rolling resistance will increase, due to the deeper deflection of the tread and casing. And while the drums on your Elite Arion Mag rollers are smooth, they are also relatively small in diameter, so they will push more deeply into the the tires than bigger drums. This will tend to compound any rolling issues due to inconsistencies in the tires.
Kreitler service manager Billie Uriguen says, “Any tire can be used on the rollers. However, the smoother the tire, the quieter the ride. The knobbier the tire, the louder the ride. We recommend a set of used tires, as they seem to have less rubber buildup than brand new tires.”
So, you will be looking for a used tire with a very smooth tread, and my contention is that you should also seek one with a consistent, supple casing. This generally means a higher-quality tire, as the construction will not only tend to be more consistent, but the thread diameter in the casing will also be smaller, allowing the casing to deflect more easily as the roller pushes deeply into it. To answer one of your questions, yes, this means higher TPI (threads per inch). And yes, better-quality inner tubes, especially latex ones, enhance the suppleness of the tire and hence, the smoothness of the ride.
To answer another of your questions, a larger tire size will also result in a smoother ride, as it will distribute the load over a wider area. So go for that 700x25c, rather than the 700x23c tire.
As for tire pressure, you obviously want it high enough that you won’t feel the valve area as it rolls over the roller. That said, lower pressures will provide smoother riding, and, as I discussed above, the rolling resistance will increase with decreased inflation pressure. If the tire were completely smooth, you could run super-high pressures, and your rolling resistance would be at or near its lowest. But no tire and wheel will be completely smooth and round. Furthermore, nobody pedals completely smoothly, and less rider-induced bouncing will be absorbed in a harder tire, so the amount of bouncing on the rollers will increase with higher tire pressure. And you don’t want the tire to be so hard that you could risk explosion with the added heat of friction on the rollers.
The tire pressure will also need to be lower with larger tires. As pressure is force per unit area; the force on the sides of the tire (and, in the case of a clincher, on the rims and beads holding tire onto the rim) at a given pressure go up as the square of the tire’s cross-sectional diameter. That’s why even high-quality mountain bike tires have a much lower maximum pressure written on the side than small road tires of similar-quality construction. It’s not that the listed number is for the smoothness of your ride, but that the bigger tire cannot contain as much pressure before exploding. So bigger tires will ride more smoothly on the rollers also because the pressure will be lower, thus increasing the size of the contact patch on the roller.
Of course, you also want to have as perfectly true and round wheels as possible. No combination of tire and inflation pressure can make up for a wheel that is bouncing up and down.
Feedback on last week’s column:
Just wanted to report that IRD’s 11-speed (with 32t as the biggest cog) seems to shift as well as the OEM cassette on the wife’s Athena 11 triple setup.