Halycon

First time poster. I bought a brand new Trek 520 Disc frameset from my LBS this past February. Wanted to do a custom commuter bike build with a SRAM Apex 1x drive train. I also liked the fact that the frame could accommodate wide tires. On paper, all component i bought should fit together. Spent hours watching Parktool youtube vids on how to build a bike. This was my quarantine project. Then I hit a brick wall... (figuratively speaking)...

The 42T chainring that came with my SRAM Apex 1 crankset appears to be too big to fit into my Trek 520 frame. The teeth of the chainring are physically touching the chainstay on the driveside when I tried installing the crank. Can't figure out if I have the wrong BB (got a SRAM GXP for BSA-68 shelf size)... or maybe I need more spacers (is that even safe?!)... or I need to get a smaller chainring than 42T so it won't touch the chainstay.

I'm assuming that I have the wrong equipment, not that am I installing it wrong. The crank has to be installed so it's flush with the drive-side BB bearing, right? UGH.

Any advice would be much appreciated!

Andrew R Stewart 

IIRC the 520 is designed for a triple crankset with a mid 30's middle ring. (Of course there have been some spec drift over the years). S assuming this is correct and that both the spec crankser places the middle ring spot on WRT chain line AND that you have done the same with the 42T you installed then it's no wonder that the 6T larger ring might get close to the stay. Solutions are a smaller ring, a longer BB axle, a different crankset, placing a clearance crimp in the stay, spacing the ring further out on the spider (unsure if this can be done given the crankset). Andy

tFUnK

Can you move the ring to the outside of the spider?

dsaul

You should not be able to push a GXP crankset all the way against the drive side bearing. It should stop when the step in the spindle hits the inside of the non drive side bearing. There should always be some exposed spindle on the drive side.

In case you didn't know, you should not be using any spacers with an Apex crankset and a 68mm bottom bracket. 2 spacers come with the GXP bottom brackets, but they are only used when installing an MTB crankset in a 68mm shell. They are never used with a road crankset for any reason.

If you have a spacer installed on the non drive side, take it out and that will give you another 2.5mm of space on the drive side. It still may not be enough to allow the 42t chainring to clear the stay.

shelbyfv

Did you have any info that would indicate a 1X would work with this frame? If not, you are probably stuck with either a chainring that is too small to be useful or moving to a 2X or 3X. Bummer.

ctak

Pretty sure Apex 1x rings are already mounted to the outside

tFUnK

It could be that the frame was designed for a MTB crankset and BB (73mm).

Halycon

Thank you for all of the responses! Looks like you guys are absolutely correct about this being the wrong crank for the frame.

I revisited the Trek website for the full 520 bike. This bike was originally designed around a Shimano Alivio T4060, 48/36/26 triple chainset. .

Shimano's website for the Alivio crank indicates it has a 50mm chainline (presumably at the 36t chainring) and a 181.7mm Q-factor. In contrast, the Sram website for Apex 1 Cranks i bought have a 42t chainring, a 45.5mm chainline and a Q-factor of 149mm. So it's no wonder the Apex 1 Crankset doesn't fit.

My confusion comes from the Review pics posted on Trek's website. Several of these review pics show Trek 520s that have 1x setups. (This forum won't allow to me link the pics because i'm a newb member). I just can't figure out the components they're using.

I'm don't wanna abandon the 1x project. And I don't wanna start from scratch on components as I already installed SRAM Apex 1 shifters, an Apex 1 Rear Derailleur, and brakes. In order to find a crankset/chainring combo that fits the Trek 520 Frame, i'm thinking about two options:

Option 1 -- The SRAM NX Crankset. On paper, it looks like this crankset should fit into the GXP bottom bracket i've currently installed if I add the included spacers. I'm not sure if the crankset will cause any problems when used in conjunction with my Apex 1 derailleur. I wanna use dropbars, so I don't wanna switch to a the NX shifter. This crank has a 32T chainring (upgradeable to 38T), a 49mm chainline, and a Q-factor of 169mm. I think that should be more than enough to clear the chainstays.

Option 2 -- The Shimano GRX RX-600 1x Crankset. I don't know if it's ok to mix a Shimano 1x crank with a Sram Apex 1 derailleur. Hoping this will work as an alternative after switching out the bottom bracket, even though it's a more expensive option. This crank has a 40T chainring, a 49.7 mm chainline, and a Q-factor of 151mm. This also looks like it will be enough to clear the chainstays.

If anybody have any thoughts, or other alternatives for cranksets, please let me know!

Thanks again!

tomtomtom123

For touring you'd need wide gear range and I don't think a 1x would give that to you. Let's say that you use an 11 to 46t cassette, that's only 418%. Then your stepping between gears is huge, and you might not find an optimal rpm on a constant gradient and stuck either to high or too low.

I have a 12-34t 10 speed cassette with 44/24 double chainrings which gives me 519%. With 406 rims I get 14-72.6 gear inches. Very low for comfortable slow climbs but many people don't approve such low gears, but I use them.
I assembled my own cogs to get 12,13,14,15,17,19,21,24,28,34 so that I have close spacing at the top where I use more often and wider spacing at the bottom where I don't use as often. 72.6 gear inches is a bit low and I would prefer 76 or 80 at the minimum, but it's ok. I only max out for 1 minute per 2 hours, which would have only saved me maybe less than 30 seconds if I had a higher gear.

A triple with 22t or 24t jump would give even greater range.

But maybe you have strong legs and perhaps the 1x with narrower range may work for you.

70sSanO

I think a 1x for commuting is great. Since you have it setup, how much more of a chainline do you need?

Will 4mm do the trick?

You are talking about less than 1mm difference between your options. Maybe an additional 1mm spacer might work.

Personally, I think you should look at chainring options also for whatever crank you get. I assume you will eventually consider a narrow-wide. How does that play out?

For a 1x there are no compatibility issues to RD, other than a really bad chainline.

John

dsaul

The NX crankset will work fine with the GXP bottom bracket and the 2 included spacers. The rear derailleur will not care what crankset you use, as long as it is a single chainring.

Given the Q factor of the original spec. crankset, I would be concerned about any crankset with a narrow Q factor having the crank arms hit the chain stays.

Darth Lefty 

I have wanted to use the Apex 1 drive train on a project and it seems like the crankset is an odd duck. The arms are very wide for a road bike, giving it a large Q factor, like a MTB crank. But it goes on 68mm BB and the chain line is road width, not mountain bike. So in your touring bike with trekking chain ring clearance it’s a problem.

If you use a direct mount crank you might accrue some options. Often the road version and mountain version of the chain ring have different offset and there may be a different PF30 or Boost version as well with additional offset options. But they might not have the teeth you want at each offset. You can also look at the Wolftooth and other aftermarket ring options.

The recent Salsa Stormchaser uses a Race Face arrangement to get a 50mm chain line with a smaller than MTB but bigger than roadie Q factor

tFUnK

Good suggestions/considerations in the comments above, but to answer your question simply, my guess is a MTB crank, with the BB spacers mentioned, should work.

Leebo

One option would be a square taper BB, many spindle lengths available and a road double or mt bike triple crank with whatever chainring you need. SS crank options too. Thinking less than $ 100 for crank and ring.