Michael Lamach
Analyst · Vertical Research.
Yes, Jeff. There's a number of things that I think that we can count on and, in some ways, drive and control even with the trailer decline forecast for 2020, and that's one of them. So if the standard aftermarket growth rates would be something kind of in the normalized 3% to 5% range, as an example, if all 35,000 North American units that are probably up for replacement wouldn't be replaced, which would be an extreme view, you'd likely see something in the high single digits. Our experience has been something maybe 8% to 10% if that were to be the case. So that tends to always pan its way out.
The other thing that is interesting when you look at the auxiliary power unit bolt-on rate, think in 2016, we were talking about something in the 10% to 11% kind of bolt-on rate there. And we said, look, we think we can move this thing. And for every 2.4 units of APUs we sell, it equates to 1 trailer unit. That was a strategy to help us through 2016 and '17. We actually have increased that bolt-on rate by 10 points, so we ended the year kind of in the low 20s. The remarkable thing about that is that's with the denominator, right, increasing dramatically in terms of what was built in terms of OEM tractors put out into the marketplace.
Other interesting thing there is the replacement factor that we see out there for APUs going into 2020 is roughly 102,000 units that are available. That's compared to a 99,000-unit market. So here, you've got a replacement rate opportunity that's actually bigger than a new complete. So by taking the same experience we've had around bolt-on rates moving 3, 4 points a year with even a more aged APU fleet out there, that's an opportunity for us.
The NPD launches I've talked to, the new platforms, should be good. And we've worked 3 years to get these things ready for the market. And as I said in my remarks, truck, bus, rail, those will all grow, too, small truck, in particular, bus, rail, all grow, too. So those are sort of factors that we can count on, I think, in 2020.