A question on the effects of tire wear on bike performance on indoor rollers. I recently changed my rear tire after wearing down to the threads and experienced an immediate major decrease in bike speed (15-20%) with the new tire on my roller setup. Thought initially it was the bike or rollers, but that clearly is not the case. Switching between the old worn tire and the new tire several (same type) times clearly pinpoints the problem, but is not a solution for obvious reasons.
Tire diameter is clearly reduced by the wear, but it seems unlikely that subtilties in how the bike sits on the rollers would have such a large effect. Any thoughts on what cause this or similar experiences?
A question on the effects of tire wear on bike performance on indoor rollers. I recently changed my rear tire after wearing down to the threads and experienced an immediate major decrease in bike speed (15-20%) with the new tire on my roller setup. Thought initially it was the bike or rollers, but that clearly is not the case. Switching between the old worn tire and the new tire several (same type) times clearly pinpoints the problem, but is not a solution for obvious reasons. Tire diameter is clearly reduced by the wear, but it seems unlikely that subtilties in how the bike sits on the rollers would have such a large effect. Any thoughts on what cause this or similar experiences?
Assuming the pressure on the tire from the roller remains constant, for a given power output, you should actually go faster since rolling resistance for a tire decreases as the tread wears. Of course the pressure on the tire from the roller doesn't remain constant if the roller doesn't automatically set the pressure. See, the tire starts wearing (immediately) and so the diameter starts to decrease, and that decrease will decrease the pressure on the tire from the roller. This happens slowly and is only a very small change, so it's entirely possible that you won't even notice it. If you do notice it, it'll most likely be in the form of increased tire slippage or "squeal" when accelerating. Otherwise there is absolutely no reason for a major decrease in speed, especially a decrease on the order of 15-20%. Something has occurred or was changed that you either forgot about or haven't mentioned.
Thanks for your response. True - tire tread wear as a source for significant speed variability on rollers sounds ridiculous, and was certainly my last guess as well, but after eliminating the other possibilities I was surprised to see reverting to my older tire corrected the problem.
The effect is clear and immediate, but my sense is that you may be right - there's another overlooked issue that's the real problem. It's is not an obvious one (such as brake pads/truing etc.) but I will check again. In the meantime, any other ideas would be appreciated.
What kind of trainer are using, and how is the pressure between the roller and the rear tire set? Is set automatically or by hand? Are the tires you've described the same model and size? If they're not the same model, that could be the issue. For a given, stated tire size, the actual tire size can vary significantly between manufacturers and between models from a manufacturer.
Since you are on rollers and not a trainer I figure the pressure (from weight) and everything else remained constant except for tire wear. Thus you probably have more friction (less slippage) with the new tire so your wheel is turning a little slower now with the same effort.
If you could measure the rpm of your roller and the rpm of your wheel when using each tire, you would know. But what else could it be?
Thanks again for the ideas. After double checking my roller setup, it seems that the free rear roller (the one not belted) has more resistance than I'd assume it should have. It spins slightly less freely than the belted one - possibly indicating a developing bearing problem.
Maybe this free roller is designed that way to turn with the same resistance as the belted ones (anyone know?). If not, the new tire may slip more relative to the older worn tire because of the increased resistance. Checking the RPM of both wheel and roller is a good idea, but technically difficult for me. Perhaps a new set of rollers is in order (given age and wear).
Originally Posted by JTIBdma[IMG]/img/forum/go_quote.gif[/IMG] Checking the RPM of both wheel and roller is a good idea, but technically difficult for me.
I was not actually suggesting you do this. Just that was the only way I could see how you'd determine if one tire was slipping more than the other. I can't help you with the bearing as I know virtually nothing about rollers.
