somethingchange

Hi everyone, I'm a new owner of a Jamis Renegade S3, which includes a GRX 400 groupset with 30/46 crankset (FSA) and 11-36 cassette.
I was surprised to find that the extreme four gears in the cassette aren't really usable, due to scraping on the front derailleur or the chain rubbing against the other chainring.
e.g. when on the 46 at the front, the four largest at the back create issues, and when 30 at the front, the four smallest create issues.

I understand that cross-chaining is to be avoided, but with the large teeth difference up front, this means I'm missing a large range of gearing. Jumping from the 'hardest' combination on 30 to the easiest combination on 46 is a big difference of 38%. (A jump from ratio of 1.58 for 30/19 to 2.19 for 46/21). And that's right around the sweet spot of flat to undulating hills for my weary non-competitive legs.

I'm not bothered by a lack of overlap in ratios, but this gap in the range isn't practical.

Has anybody else here experienced gaps like that, and is that just a price to pay for having a wide range of gearing? What do you think about the usable gears - should I be able to cross-chain further and use one more gear at each end to close that gap, without all the scraping at either extreme? Am I expecting too much to be able to use gears without them scraping on the derailller and chain rings, so should I just use those gears and not be bothered by the scraping and inevitable wear? Hopefully any advice can be useful to others. Thanks.

somethingchange

Self update: looking at the Dealer's manual, it looks like the FD can be adjusted to be more forgiving. If I can squeeze one or more gears out at either end then the problem will be solved. I will update further.

shelbyfv

Shimano seems to expect rubbing with small ring/ four smallest cogs.

somethingchange

Thanks for that. Going the other way, I reckon if I can get it running cleanly on the fourth or third largest on the cassette and the largest chainring then that will solve the problem.
I've been spoilt by a Shimano 2x9 that let me run all combinations without any scraping. (a Shimano Nexave front derailleur with clutch system).

masi61

I’ve been considering using the GRX 400 2X10 shifters for a disc road bike build since they are 10 speed rear and hydraulic disc.

I would use a mid compact road crank such such as a Dura Ace 9100 and then run a 7900 Dura Ace 10 speed cassette in more road friendly (tighter) ratios such as 12-25. I’m not going to use a GRX rear derailleur since I don’t need to run the super low gears. I heard that the GRX 400 shifter is incompatible with the older 10 peed rear derailleurs since the pull is different (despite being 10 speed). I also heard that the GRX 400 shifter works fine with 11 speed Shimano rear derailleurs. For this reason I was going to use a Dura Ace 9100 (11 speed) rear derailleur with these 10 speed GRX 400 shifters.

This leads back back to your experience with the GRX front derailleur performance. I’m just curious - does the GRX front derailleur have trim clicks? Would the GRX 400 front shifter be compatible with road front derailleurs Such as the Ultegra 8000 or Dura Ace 9100? Or is the front derailleur tied only to the “GRX” for the shifter and the FD?

SalsaShark

The GRX front derailleur and crank can be setup to function without rubbing in all gear combinations, but requires precision in initial setup physically and with regards to cable tension and trim adjustments. The cable tension has effects on both derailleur travel as well as trim stops, and it took me a number of adjustments to get the trim adjustments just right. You will end up with having to trim the FD while in the middle of the cassette when it is adjusted properly, meaning that the inner half of the rear cluster will need the FD trimmed inward, and the outer half of the cassette trimmed outward on the FD. If you set it up so that it would rub in the middlish part of the cassette without the FD being trimmed to the proper side, you should have just enough adjustment inward and outward to access all the gears in both chainrings without rubbing. It is a precise balancing act, however!

trailangel

You should be getting 7 usable gears on the big chainring. Probably 8 on the small chainring. Adjust your derailleurs.

Cyclist0108

I also have a GRX 46/30T crank and an 11-36T (sram) cassette on one of my wheelsets. I am able to use all of the gears, including the cross-chained ones. My derailleurs are older Ultegra Di2 ones that aren't officially rated for this capacity. My chainstay length is 426mm.

So based on this, it should be possible, unless your setup is radically different.

AlmostTrick

So OP is getting 12 usable gears out of 20, but "should be" able to get 15 when derailleurs are adjusted properly. And Shimano says "If noise is a problem, shift the rear sprocket to the next larger gear, or the one after. (!)

And users are ok with this?

It seems deficient to me.

Cyclist0108

Lucky for you, SRAM makes some really high-quality, competitively-priced drive train parts.

trailangel

Huh? Depends on which plate in front your are in.
You can go to your 1x and get 11 usable gears.... or you can get at least 15 usable gears with 2x... 2 plates in front.
Might want to check your chainline as well.

HTupolev

Does the GRX400 front shifter not have trim clicks?

somethingchange

Yes, it has trim clicks. I've come from a flat bar bike, so this system was new to me. It may well have worked better had I been aware of trim clicks before I started playing around with it...

somethingchange

Thanks everybody for your advice. I've followed the dealer's manual (I can't post URLs but the file name is DM-GAFD001-00-ENG.pdf) and now have the combinations working happily up to the third-last cog at each extreme, and the second-last with a bit of noise. That will let me ride on flat-to-undulating surfaces fully on the 46 without needing to swap back and forth on the front all the time. I might be able to improve it further, but that's a big improvement!

wsteve464

Does the FSA crank have the same wider chainline as the GRX crankset? If not you may want to condsider using the correct crank for the GRX derailleur or switch to regular road derailleur.

jlaw

+1

I have a lower-end SRAM x5 crankset with a 10 speed Shimano RD (11-32 cassette) on a road bike - no problems running all the way up and down the cassette when on the large chain ring. I don't normally run it large-to-large because the chain line looks too 'cranked', but even in this combo it doesn't complain (much). The x5 crankset came with a SRAM GXP threaded BB - I don't have exact numbers for the chain line.

I'm surprised to hear that the new GRX drive train is limited as described. The whole idea of using a 46T large ring is so that you don't have to shift the FD until you hit steep terrain.

redlude97

you may need a touch more rotation of the FD to get 1-2 more useable gears, and/or a couple more turns either in or out of the reinforcing bolt. The FD setup is a bit more nuanced than the guide specifies so its a balancing act between usuable gears. You may need to open up the upper limit a hair so you have a bit more range in the tension adjustment

Cyclist0108

It was meant to be sarcasm.

(They focus on 1X systems now so the problem doesn't arise.)

Cyclist0108

It is not. (See above.)

My setup is with a sub-optimal component mis-match, and, even then, this isn't a problem. I think the drivetrain must not have been adjusted correctly in the shop, and the OP stated he wasn't initially aware of the trim functionality.

somethingchange

Good question. There are marking on the crankset that suggest it's compatible with 10 and 11 speed, whereas Shimano make one specifically for 10 speed. What specifications should I be comparing? I can see on the Shimano site specs for chain line, P.C.D. and Q-factor. I haven't yet found the exact model of FSA crankset that I have. I'm happy to change to a full-GRX setup.

I'll see how I go. Otherwise I'll need to find a good bike shop that will be able to make the right adjustments.

You're right about the adjustment. I had already asked the bike shop to adjust it before I left the store, and their adjustments didn't seem to help. So I don't have much faith in them getting any where near the nuanced adjustments needed. Being unaware of the trim was only a small part of it. I couldn't even use the smallest two at the back while fully on the 'top' at the front. So they'd somehow managed to limit the gears in both directions.

Cyclist0108

Sounds like the limit screws weren't (or still aren't) set properly. It might be good to work through it yourself. These aren't difficult adjustments, and I think you only need an Alan wrench.

https://www.parktool.com/blog/repair...eur-adjustment

https://www.parktool.com/blog/repair...eur-adjustment

somethingchange

Thanks again. I'll give that a go.

I'm grateful for all of the advice and discussion received on this post. I was expecting my share of sarcastic replies (why didn't you take it back to the shop, why did you mess with it, how did you not know about the trim noob, you're an idiot, etc.). But instead, I received a host of constructive advice. That's a breath of fresh air.

rosefarts

I have been looking at grx600 and have thought this might be a problem.

I think a much better crankset would be 46-34 and keep the 11-36. Even 32 would be a major advantage over 30. 44-32 might be really good too, if it was on a bike that doesn't do double duty as a road bike.

I currently have a low of 40x42 that is more than enough for everything but steep rocky mountain bike trails. Unless you are fully loaded, then we have a different scenario.

In the 1x world, a sram 1x12, 44 x 10-46 might be better and would avoid this futzing around.