Rocky Mountain 2018 Altitude Sizing: Compare Reach and Stack at One Setting
For 2018 Altitude sizing, write down the chip setting beside the frame-size letter. The same Rocky Mountain frame has different listed reach and stack across RIDE-9 positions. A viewing or fitting demonstration must also wait until the recall requirement (https://www.cpsc.gov/Recalls/2018/Rocky-Mountain-Bicycles-Recall-Mountain-Bicycles-Due-to-Crash-Hazard) is resolved: stop using a covered bicycle and obtain authorized-dealer verification of its inspection and repair.
Compare 2018 Altitude sizing with the setting fixed
The 2018 RIDE-9 PDF (https://resources.bikes.com/sites/default/files/resources/2018_Ride9_Altitude_EN.pdf) gives a useful medium-versus-large example. At neutral position 5, medium has 435 mm reach and 601 mm stack; large has 458 mm reach and 610 mm stack. Subtracting the published figures gives a 23 mm reach difference and a 9 mm stack difference. Those arithmetic differences describe the frames, not a guaranteed fit for particular rider heights.
Now hold the medium size fixed and compare configurations. Position 1 lists reach 430 mm and stack 604 mm. Position 9 lists reach 441 mm and stack 596 mm. A size comparison made with one bicycle slack and the other steep would therefore include a setup difference as well as a frame-size difference.
Bring a consistent measurement record
The guide defines reach as a horizontal distance from the bottom bracket to the head tube. It is not the same as the horizontal top-tube entry, the fitted stem length or a measurement taken along a tube. Identify which number a seller is quoting before comparing it with a bicycle you already know.
The neutral medium and large seat tubes are listed as 432 mm and 470 mm. That is another distinct dimension. It does not turn reach into a saddle-height measure or provide a complete dropper-insertion specification. A useful fitting conversation keeps frame geometry and installed contact-point components as separate records.
Source choice also matters. The online archive (https://resources.bikes.com/en/bikes/altitude/2018) lists neutral medium stack as 600 mm, whereas the PDF used here gives 601 mm. Other cells differ too, including questionable XS wheelbase values. Retain the source and configuration with each figure rather than silently replacing one value with the other or presenting the tables as identical.
For an actual purchase, confirm the frame identity and size, note the RIDE-9 configuration and record the currently installed bar, stem and saddle arrangement. Ask a qualified fitter to evaluate the complete bicycle once its recall status permits use. The historical figures support that discussion; they do not supply an unsourced rider-height range or guarantee comfort.
FAQ: Fit comparison questions
How much longer is large reach at neutral position 5?
The PDF lists 458 mm for large and 435 mm for medium, a calculated difference of 23 mm.
Does a medium retain the same reach in every position?
No. The PDF lists 430 mm in position 1 and 441 mm in position 9.
Why identify the source beside the stack measurement?
The PDF and archive differ in some cells; neutral medium stack is 601 mm in the PDF and 600 mm online.
The bottom-bracket discussion explains another setting-dependent dimension. Use the Rocky Mountain topic for the historical model context.
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Original title: Rocky Mountain Altitude C50 2018.jpg
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