No 20mm pedal spacers on carbon cranks...well most carbon cranks

Why do you not recommend 20mm pedal spacers with carbon cranks?
Thanks for the question. To be honest it is not so much that BikeFit recommends this but rather some manufactures do not support this.

This is a tough one for us to hold back with our actual thoughts but we will….for now.

This is what a few companies have told us. I may not have this word for word so do not hold us accountable to exact wording but here is a synopsis of a few conversations.

Use of 20 mm pedal spacers – what we think

Zipp –    Voids warranty
FSA-     Voids warranty on ALL their cranks … and they said they will void warranty even if you use a longer pedal spindle – now I did not get a range or what they actually consider a longer spindle as not all pedal widths are the same – most are close but again not all are the same
Truvativ – waiting for an update
Specialized – says they are OK if you use a 20mm pedal spacer on their carbon cranks.

So guess what I ride? I love my Specialized Tarmac S works with carbon cranks.
Right side - I go back and forth between a ½ inch longer spindle (Speedplay Zeros - which I actually pay for) or I use a regular length spindle and a 20 mm pedal spacer.
Left Side -I use a ¼ inch long spindle..

Hope I get to ride a Specialized for a long time!