LM3 Front Inner Tube

[Vince in Milwaukee]

Went and bought a new front tire for my Le Mans 3, but forgot to get the inner tube.  The tire size is 100/90-18.  I believe that translates in to 3.5 x 18 (?). There seems to be some slight variation in the ones for sale.  I bought the wrong one for the rear tire last year, but luckily the Guzzi Doctor (our own Joe Walano) had the correct one on hand.  Also, prices are at a low of around $15 and a high of $40.  Why such a difference?  Thanks in advance.         

[Antietam Classic Cycle]

I use these: https://www.americanmototire.com/motorcycle-tubes/irc-tube-3-25-3-50-4-10-18-tr-4/

[Groover]

The ones made of natural rubber are higher cost and then there are different thicknesses.

[Stevex]

Gone tubeless on my LM2.
No problems in 5 years and my risk of instant deflation are now almost nil.