2

I own a budget MTB (Decathlon Rockrider ST 100), with 3x7 speed and I want to upgrade the cheap derailleurs to something more reliable (Such as Shimano Deore).

I already changed the brakes and shifters by the way.

I don't wanna change the freewheel now (as it would force me to change the whole wheel if I want a cassette).

My question is : can I put a 3x9 front derailleur on this configuration ? As the only front derailleurs for 3x7 configurations are on the Altus or Tourney range, and I want something more solid.

2
  • Changed the shifters to what? AFAIK only Tourney shifters are 7 speed. – Argenti Apparatus Jul 22 '20 at 10:55
  • Apologies for late reply. The shifters I found are Shimano EF65 (Probably Acera range). Not Deore ones but it's much better compared to the Microshift grip shifters I had before... – FraJarJar Jul 23 '20 at 4:35
2

Yes. A front derailleur marketed as for a 9 speed system will work normally with your 7 speed set up. Really the front derailleur doesn't care how many cogs are in the back. Generally, using a front drive system designed and marketed for "X"-speed systems will work in an "X+/-1" system. For example, I use 10 speed crankset in combination with a 9 speed rear drive. In addition mixing brands of shifter and front derailleur is possible (a SRAM front shifter can be paired with a Shimano front der and vice-versa) resulting in normal performance. This does not hold true for the rear drive, where brand of shifter and derailleur must match to have normal performance.

Considerations should be given to the cable routing of your bike: does the front derailleur cable approach the der from the top? Or from the bottom? Front derailleur's are designed to be actuated either by cable pulling from above (top-pull) or from below it (bottom-pull). Which type you require is based on your bike's designed cable routing. Many front ders these days are termed "dual-pull" and are actuated from either a top pull or bottom pull cabling. The bike determines this requirement.

Related to this is how the front derailleur mounts to the bike. Most commonly a clamp band is used around the seat tube and this serves as a mount point and by virtue of the design is manipulated to get the derailleur in proper alignment with the chainrings. A bicycle will be built utilizing one of three different sizes of seat tube diameter, the front derailleur must have the correct size clamp band (or come with shims allowing proper fitting). There are other mounting designs of front ders too.

When a front derailleur is chosen for a particular front drive of a bike, a few important specs must be adhered to achieve nominal performance. The number of teeth of the largest chainring and the difference in the number of teeth between the largest and middle chainring. Both of these should match the specs of the front derailleur.

One further thought related to your question and desire to upgrade some componentry. Seven, eight, and nine speed hardware can be considered the same in regards to "speed." Their derailleur's actuation ratio are the same, meaning the derailleur will move the correct amount to move the chain the correct amount to achieve the correct shift distance whether the shifter is 7, 8 or 9 speed. The right numbered shifter should be used with the same number of cogs.

4
  • Are you positive of saying 7/8/9 speed, and not 6/7/8? ...where the chain widths are (almost) the same, and the inter-cog gaps are the same while the cassette gets one cog wider. At 9 speed, the cassette stays the same width as the 8 speed, but the cog spacing drops, so 8/9/10 speed freehubs (generally) take all three. – Criggie Jul 24 '20 at 12:28
  • 1
    Thanks a lot for your detailed comment ! I actually didn't know the trick about "bottom pull" and "top pull" and you helped me not to buy an unusable derailleur. My bike cable routing is a bottom-pull. – FraJarJar Jul 24 '20 at 13:33
  • 1
    @Criggie Lumping the 7, 8, 9 speed classes together, my thinking was emphasizing the rear derailleur actuation ratio was the same, inferring one needn't be limited to finding a marketed 7-speed derailleur when a 9 speed derailleur, controlled by a 7 speed shifter, will happily move the chain flawlessly up & down a 7 speed cassette. I tried to avoid the spacing issues that would need attention when upgrading to higher speeds by emphasizing pairing of shifter and cassette (same speed #). Also, text of question stated they were to remain at 7 speed FW.x – Jeff Jul 25 '20 at 1:15
  • 1
    @Criggie Your points are noted, however...especially if one is using words like "flawless" & "normal performance" in discussing what will work in a drive-train, one better be cognizant of spacing issues – Jeff Jul 25 '20 at 1:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.