I have a 2021 Trek Checkpoint ALR 5 with GRX 600 2x11 crankset (46/30) with 47mm chain line and the GRX front derailleur that accommodates the wider chainline. I want to put on an Ultegra 8000 50x34 crank (Shimano says 43.5mm chain line) and front derailleur from my road bike. I plan to leave the GRX 800 rear derailleur in place.
I assume the Checkpoint is designed for a 47mm chainline. Assuming my tires clear (700x35 slicks for winter road - eyeballing it I should be okay on frame and tire clearance) the narrower chain line with the Ultegra crank/front derailleur, will this work well? Will shifting performance/drivetrain efficiency be compromised? Trek used to ship the ALR 5 with Shimano 105 kit pre-GRX (like 2019 model or so), so I’m thinking this may work.
I have the crank/front derailleur on my road bike, and it is my understanding the BB is compatible, so I could just try it, but want to avoid spending the time if it ultimately won’t work, or won’t work well.
Goal is to get bigger chainrings for winter road use. I’d rather have the 50/34 on my road bike or even 52/36.
I researched this when I was building my Colnago gravel bike. Asked about compatibility of an Ultegra crankset (I had a spare w/ Stages PM) with GRX for the rest of the group and was told they would not work together.
I already own an extra Ultegra 50/34 crank and FD and I know that gearing works well for winter road use.
I can probably get by with the 46/30 with a smaller cassette in back. Don’t need the 34 in back for road and would prefer smaller jumps in the midrange so might just try an 11-28 or 11-30.
I reckon the shifting will be fine. Maaaybe you’ll get some rub on the front mech if you try to cross chain a bunch. The worry will be clearance as you say. Since you’ve already got the cranks just slot them in without messing with the front mech yet to make sure they clear everything. That’s a 5 minute job.
Check what the maximum chainring size is for the GRX mech. The two chainsets both have a 16T range so that won’t be a problem.
Are there any BB spacers in place at the moment? If there are and they are on the NDS then you could arrange them so they are on the drive side and that will push the chainline out by Xmm. The other thing to watch out for would be clearance of the rings at the chainstay.
There’s more flexibility in these systems than the manufacturers rate them for. I’m using Force Wide cranks and a Quarq power meter, 50/34 Praxis chainrings with an Ultegra R8000 front derailleur. So opposite of @Bhofstra and it works perfectly.
So, I own SL5 2021 Checkpoint with GRX RX810 Derailleurs and RX600. How to I use 50/34 drivetrain? Which components should I buy? Since I can’t efort a new bike. I really need your help.
For point of reference, I’m running R7000 series (105 11-sp, mechanical) with 52 & 33 chainrings. That’s a 19-tooth jump which is 3t out of spec for a 105 FD. Shifting is hesitant & I don’t do it under load, but it works. It went through a phase of repeatedly dropping the chain on the inside as a result of failed upshifts which I fixed by putting just a little more tension in the cable & winding out the outer limit screw a fraction. My other bike is currently running a 56t on a 105 9-speed triple, when it was designed for a max 52t. It still works well.
Ignore labels like “Standard”, “Semi-compact”, “Compact”, & you don’t have to go with the specific, recommended combinations, all that matters to you is they offer you a sufficient range of gears, & with a sufficient overlap so you’re not jumping chainrings all the time. All that matters mechanically is to keep the large ring in the ballpark (this matters because of the curve of the FD cage & its mounting point on the frame) & keep the big ring - little ring difference reasonable so that it will actually shift decently. Also check RD cage length; & if you’re at the limit, a bigger outer chainring could require an extra link or two. Good excuse to replace the chain. Shimano is conservative with its specs but the further out of spec you go, the more cantankerous the system becomes. As expected.
Interestingly, I’m going the other way for my audax rides, experimenting with fitting the RX-610 (currently with 46-30 combo), & drilling X80 holes in a Deore X64 26t inner to replace the 30t.
If you want to change your crank to a non “wide” one, just change the front derailleur too.
You might lose a couple mm of tire clearance, but probably not much.
When the manufacturer says that 50/34 is the max I’d assume they are calculating that based on a road crank/derailleur since there aren’t 50/34 rings specifically on gravel groups.
The only difference between these wide groups and road groups as of now is the chainring & FD offset. The rear end isn’t any different. Before long, I imagine most of the big-tired gravel bikes will be boost though. Why not?
