FordTrax

I was planning on putting the Shimano Shimano FD-RX400 front derailleur on my space horse. With the GRX 10 speed 46/30 crank and 11-36 rear. 650b Flintridge 45mm tires.
I just saw that there was a tire width limitation on the FD-RX400 front derilleur. It states compatible up to 42mm tires. I have not seen this before on a front derailleur but then I am more of a road guy than a fat tire guy.

Will I have an issue with the 650b 45mm tires and this derailleur - I thought GRX was made for gravel. Why is the tire a limiting factor here my space horse frame can take up to 47mm?

Never thought to look for a tire limitation before I bought the Flintridge tires (which look very nice - and I am a Panaracer fan) that I was looking forward to trying.

Will I still be okay with the 45mm tires and the RX400? If not would the Microshift Sword FD-G7000 front work?

BTW: I am putting on the Microshift Thumb shifters10 speed full friction on Mokolo Bars.

FBinNY 

It's a question of geometry. Key dimensions include tire to chainring distance, and tire to seat tube clearance.

Given that GRX may be intended for sportier use, it's chainline might be more inboard and closer to a road bike's. If so, that might explain the limitation. Of course Shimano tends to be conservative, so there's likely some fudge room.

BTW, FD brand or controller won't make a difference if th we problem is tire to inner chainring distance.

Polaris OBark

I've used it with 55mm x 700c tires without issue. It all depends on your frame (mine is a Soma Saga steel touring bike, fwiw).

Iride01 

Did it not have GRX on it before? If it had a road crank on it before such as a Tiagra 2x10, then the chain line of your rear cassette is expecting a crank with a chain line around 43.5mm. The GRX FC-RX600-10 has a chain line of 47mm. If it has some other crank on it, then you should check what it's chain line is. You can simply measure from the centerline of your seat tube to the middle of the space between your two current chain rings. Or if it's 3x now, the middle ring.

If may shift well enough for you without doing anything. However if it doesn't, then depending on that bikes rear spacing, and hub, you may or may not be able to adjust it's chain line outward to match. If the BB for the FC-Rx600 crank uses spacers between it and the crank, then those also might allow you to move the chain line inward.

As for wondering if a 41mm tire will rub the DR, then just measure what your distance from the tire is to the current FD when in the small ring. Though remember if your current FD is a road FD, it will be set up for a more inward chain line.

GRX was made for bikes with wider tires. But obviously there are limitations. If your current FD cages overlaps the tire, then you should take that limitation seriously if everything else about your bike put that FD and crank at the 47 mm chain line. Might be better to just get the 42mm tires and see how much more clearance you have for the next set of tires.

FordTrax

I thought there might be a bit of conservative thinking in Shimano's number. IRide's post made me think ... while this is a new build so there is no history for me with this frame. But then I remembered that All City sold this bike in GRX configuration. So I went to the AC website to see what their GRX had on it:

• Front derailleur = Shimano GRX RX400
• Rear Derailleur = Shimano GRX RX400
• Tires = Teravail Rampart 650bx47mm, 60tpi, Light & Supple, Tan Wall (43cm~61cm

So if All City sold the GRX version with the GRX 400 front derailleur (and rear) and 650b 47mm Teravails I should be okay with 650b 45mm Kenda Flintridge.

Thanks for the assistance!

cpach

Try it out and see. On my personal bike, I have a Shimano Metrea front derailleur (I built it before GRX was available, and Metrea is designed around a 46/30 crank) and had to replace the cable anchor bolt and washer to get clearance on a 40mm tire on my Surly Midnight Special.