Your Lightning: A Custom Fit

Taking the measurements

For correct frame sizing, up to four measurements are needed:

  • Height
  • Weight (Note: Weight limits apply to both seat and frame. Weight limit is for the rider only, an additional 50 pounds can be carried on a rear rack)
  • Ex-seam (see diagram below). Measure with your riding shoes on.
  • Inseam, measured standing up and barefoot, from crotch to floor.
Ex-seam measurement


  1. Use the Height to determine the Seat Size. Normally this will be the same as the frame size.
  2. Use the Ex-seam dimension to determine the Frame Size.
Size Rider Height Ex-seam Rider Weight Limit
Small 5′ to 5′9″ 37 to 42″ 200 pounds
Large 5′7″ to 6′6″ 41″ to 47″ 250 pounds

P-38, F-40, and R-84

These models are available in three or four frame, seat, and stem sizes. The seat and stem interchange with different size frames for a custom fit.

Note: Only the P-38 is available in a small size.

  1. Use the Height to determine the Seat Size.
  2. Use the Ex-seam dimension to determine the Frame Size.
  3. Use the Inseam dimension to determine the Stem Size.
Frame, seat and stem size Rider Height Ex-seam Inseam Rider Weight Limit
Small 4′9″ to 5′3″ 35 to 38″ 23 to 27″ 160 pounds
Medium 5′2″ to 5′8″ 37.5 to 41″ 26 to 30″ 200 pounds
Large 5′7″ to 6′1″ 41 to 44.5″ 29 to 33″ 220 pounds
X-Large 6′0″ to 6′6″ 44 to 47.5″ 32 to 36″ 250 pounds

Here’s how to determine the size of a P-38 frame:

Frame size Crank tube length
Small 7 inches
Medium 8 inches
Large 9 inches
X-large 10 inches
Lightning P-38 frame sizes


The Thunderbolt was available in the following frame sizes:

Size Rider Height Ex-seam Rider Weight Limit
Small 5′ to 5′10″ 37 to 42″ 220 pounds
Large 5′8″ to 6′6″ 42 to 48″ 250 pounds

Extended bottom bracket fitting

An extended bottom bracket is available for slim riders with a short torso and long legs.

This results in a lighter bike, since the next smaller frame size can be used. This option is not recommended for strong or heavy riders, as frame flex increases with the smaller sizes. Follow the directions above to determine the correct seat, frame, and stem size when the extended bottom bracket is used.

Frame and Seat Size Height Ex-seam Inseam Stem Size
Small 4′9″ to 5′3″ 37 to 41″ 25 to 30″ Medium
Medium 5′2″ to 5′8″ 40 to 44″ 28 to 33″ Large
Large 5′7″ to 6′1″ 43 to 47.5″ 31 to 36″ X-Large
X-Large 6′0″ to 6′8″ 46 to 50.5″ 34 to 39″ XXL

Note for bikes equipped with optional Tilt Steering: Because this option adds 2 inches to the total stem height, a smaller size stem should be used so that the handlebars do not end up too high. If you order a bike from the factory with the tilt steering option, we will automatically install the appropriate shorter stem. But for later upgrades or repair work, be sure to obtain the appropriate size stem. For example, a Large P-38 with tilt steering should have a medium stem.

P-38 forks

The following forks are available for the P-38. When replacement forks are ordered, please indicate the size, type, and brake mount.

Size Type Brake Mount Use
16-inch Rigid or Suspension V Brake or Caliper Small Frame, 16×1 or 1⅜ tire
16×1⅜ Rigid or Suspension V Brake Medium Frame, 16×1⅜ tire
20×1 Rigid or Suspension Caliper (dual pivot) Med/Large/XL Frame, 20×1 tire
20-inch Rigid or Suspension V Brake Large/XL Frame, 20×1.25 tire

If you have any questions about all of this, give us a call!