Tech guru Lennard Zinn takes reader questions on air compressors, SRMs and sweaty workouts

By Lennard Zinn

Dear Lennard,
I saw the Prestaflator tool showed on VeloNews.com. Looks cool, but what kind of compressor is reasonable and affordable for road tires?  I have looked at compressors in the past and I generally only find industrial-like ones for nail guns, etc.  Is there an affordable one just for low volume higher pressure road tires?
Samuel

Dear Samuel,
I don’t know what you consider affordable, but at hardware store sales, you can often find a compressor for around $100 that runs on 110V and has a 5- or 6-gallon capacity and 150psi maximum pressure. I have a 6-gallon Porter Cable one that I got at the McGuckin Hardware garage sale for something like $120 last year, but there were a lot of similar ones of different brands for the same or less money. And this is definitely not a nail gun machine — it cannot keep up with a high-volume air tool like a nail gun or a die grinder, but it can certainly pump up bike tires well.
Lennard

Dear Owen,
Well, while it’s commendable that you have the capacity to machine the arms, there’s an overriding issue that you would need to confront, and that is that the original SRM spider design was essentially flat, whereas the 7800’s external bearings would require the spider to reach inboard.

Since the original SRM crank mounts on a standard bottom bracket spindle, the base of its spider is already at essentially the proper chainline, so the spider can reach out flat to the chainrings. But the 7800 external bearings move the inner face of the crankarm, and hence the base of the spider, too far outboard for proper chainline, so it needs to somehow reach inboard to mount the chainrings. So your question of whether the center of the SRM unit is large enough to accept the larger spindle is not the question — the question is whether you can bore a hole big enough in the power unit to swallow the entire external bearing cup, since the chainrings need to surround it to be at the proper chainline. And I would doubt that this would be possible.
Lennard

Basically, is there any reason to worry about damaging a frame by being hooked up to a trainer for workouts?  I use the trainer setup for race warmup and also for indoor workouts when I don’t have time/weather to get outside.
Jay 

Dear Jay,
I’ve answered this in the past, but I continually receive this same question, year in and year out, so I’ll continue to answer it periodically.

While the stresses are different on a bike constrained to a trainer than on the road, they are nonetheless far smaller than the kinds of stresses commonly encountered when riding on the road. So, no, you need not worry about damaging it by riding it on a trainer. If your bike can’t handle the abuse of a trainer, you sure don’t want to ride it on the road!

Of course, you will wear out your rear tire rapidly and need to replace that before blowing it on the road. Furthermore, the danger of corrosion from sweating on a bike on a trainer is an issue with a steel, aluminum or magnesium frame, but it’s generally not with carbon.
Lennard