EXPERIMENTING WITH LOWER TIRE PRESSURE? — TROY’S TECH TALK

Q: I want to try a larger road tire and experiment with lower tire pressure. Can I use my older wheels with “narrow” rims, or do I need to invest in new wheels, too? Also, if I can use my old wheels, is it okay to put a tubeless tire on a non-tubeless rim with a tube?

 A: This is a great question, and in short, yes. You can definitely use your old wheels with a larger-volume tire. A wider rim profile can offer better overall performance but is not mandatory. If you try it and the new size is something you are planning to stay with, then I would recommend a wider internal rim profile, maybe 19–22mm for most road applications. This can boost the volume of that tire, so make sure you will still have room in the rear triangle and between the fork legs.

As far as a tubeless tire on a non-tubeless rim, that is also a yes. Just ensure you do not try to modify your old rim to run tubeless. Using a tube in a tubeless tire is no problem at all. Some tubeless tires can be a bit snug, but proper installation technique makes it easy enough. If all works out and you do decide to go for a wheel upgrade, choosing a set that is tubeless-compatible is a great idea, too. 

 

Q: I was an early adopter of road disc and have loved it for years. Recently, I changed my brake pads, and I feel like they are not feeling as good as they once did. What else should I do?

A: Disc brakes are like anything else on a bike; in order to work properly, they need to be maintained. Brake pads are important, but there are a few other things to consider doing at least once a year. Bleed the system and flush the old fluid. As brakes heat up and cool down, this can affect the properties of the fluid, and replacing it is good practice. It doesn’t take long, and if you don’t have a bleed kit, most shops charge around $25 per brake.

The next thing to consider changing are your rotors as they, too, are a wearable item, and after multiple pad replacements, they can lose a substantial amount of its material. This can become a problem when it wears too thin and the calipers struggle to move the pads the extra distance. This means you have to pull the lever further to reach the rotor, offering a less predictable feel or a lever that bottoms out on the bar.

SRAM indicates that their rotors are 1.85mm new and should be replaced if below 1.55mm. Shimano is very similar, their new thickness is 1.8mm, and the replacement thickness is 1.5mm.

Q: Why doesn’t anyone refer to bottom bracket height anymore?

A: For years, brands and all the content around bicycles referred to bottom bracket height. This is the distance from the ground up to the center of the bottom bracket. This measurement has phased away, and you will notice that bottom bracket drop (BB drop) is what it has been replaced with. 

Most of this has to do with the evolution of cycling. There are so many different wheel sizes and combinations of tires. When you measure from the ground up to the frame, it changes drastically depending on the tire and wheel
you choose. 

Bottom bracket drop is the distance from the horizontal axle line down to the center of the bottom bracket. Using this unit brings a level of comparability that is not affected by wheel/tire selection. The larger the number, the closer the bottom bracket is to the ground and the smaller, the higher it is.