Herzlos

So I currently have a Giant Revolt 1 (2021) which comes with an FSA Omega Adventure 48/32T 2x10 setup with an FSA MegaExo press-fit BB, but I do a lot of hilly rides so looking to change to a 46/30T to make life a little bit easier at the expense of a top gear I rarely use.

There seems to be an Omega 46/30T which I assume would be a straight replacement, but I can't find one anywhere.

Can anyone recommend an alternative? Ideally one where I don't need to change the BB, to do as little work as possible and giving me less scope to getting it wrong

Thanks!

Edit: It seems that the older FSA Omegas that are 2nd hand are a square taper so won't fit, but FSA claim that the MegaExo is compatible with Shimano, and it looks like a GRX-400/GRX-600 would fit without changing the BB but I'm not sure. Would I be able to fit a Shimano GR without needing to take out the BB?

tdilf

Can't you just replace the rings on the crankset?

Herzlos

Unfortunately they are riveted so it looks like I'd need to replace the whole thing.

Edit: I'm wrong. There are some rivets but I'm not sure what they do (chain catcher?). The rings are bolted on.

So changing the chain rings seems to be the way to go. It looks like the front derailleur (Tiagra) can only handle a 16T gap so I'll need to change both rings. Can I use any 10 speed chains that have a 90mm BCD / 30T and a 120mm BCD / 46T? Any recommendations?

Typically, I can't seem to find any in stock, and wondering if I'm better just buying a crankset and taking the rings off.

Polaris OBark

JIS is one of the two "standards" for Square Taper.

If it were me, I would get a GRX 46/30T crankset and a compatible Shimano BB. I have this on a bike where everything else is Ultegra, including the front derailleur. The chainline is +2.5 mm, so if you have a little bit of room on your H-screw, you should be ok.

Helderberg

I have a 105 Topstone with an Omega FSA. I replaced it with an FSA AGX 46/30 with a new BB. I didn't go with the Shimano because the front derailer would not match so going with the FSA AGX was and is a drop-in and has worked perfectly. The crank was more expensive than the Shimano but it ended up less as I didn't have to change the front D.
Frank.

cyclezen

PressFit MegaExo <> Shimano Hollowtech BB - may be compatible, but I would have a real (good) Shop tech, who has worked with this combo confirm...
If you go full shimano, you'll need a pressfit shim/adapter to then put on a Shimano BB.
...But you can try the crankset in the current BB and see how it runs...
Other option I might suggest looking into... Get a 30 ring for the current setup and have 48/30 .
Sure Shimano says it won;t work, but...
I had heard that some Shimano users went down 2 teeth on their inner rings - no problem....
SO
I'm getting older... and slower... and weaker... and having gone to an Ultegra Mid-compact last year (52/36), I now find that the verdammte climbs/hills my groups are now riding are killing me at the speed I need to keep up !!!
so, I checked around... and sure enough, seem like plenty of riders have done the FORBIDDEN change to a 52/34 setup...
I'm using Ultegra 10 spd Drivetrain group w/ short cage RD, with Ultegra R8000 crankset... 52/36 - NOW 52/34 - 0ver 1,000mi. and for sure 25K+ ft of climbing. not a single issue, shifts like it was designed that way, FD, RD, rings, cassettes (13-28).... ALL GOOD
Don't worry what shimano says about the FD ring handling... it will work with a 30 as well as it does a 32, and if the RD is shimano also, it will also work, as long as chain length is good. If you're not changing the cassette ratios, the chain will prolly work fine as is.
Problem would be - can you FIND a 30 ring for that FSA Crankset ???
Ride On
Yuri

jonathanf2

If your bike came spec with an 11-34t 10 speed cassette and a GRX 400 RD, you can just swap out the 10 speed cassette for an 11-36t cassette and stay within Shimano spec (GRX 400 is spec'ed for 11-36t). If 11-36t is still too high of a gear, you can then swap out the crankset for a GRX 46/30t setup. In regards to 10 speed cassettes, I'm using the 10 speed Shimano XT 11-36t cassette and I tend to like it due to the higher quality plating and the ability to swap out cogs. SRAM also has 10 speed 11-36t cassettes of similar weight and quality.

I'd also consider crank length as well. A longer 175mm crankset will give you more grinding torque, but at the expense of possible toe overlap on technical trails.

Herzlos

I've ordered a Shimano HG50 11-36 10 speed cassette (Deore) which should be a drop-in replacement and making my lowest gear about 5% easier which will be significant when I'm slogging up hills!

I was actually wondering about that and whether or not it'd work because...

I've actually been able to find the 30T ring on a few sites (one reputable, some on ebay/amazon), but not the 46T except for an Amazon listing that doesn't mention the BCD. If I can get away with running 48/30T with the Tiagra front mech that'd give me the best of both worlds and save me $40.

cyclezen

Quote:
Originally Posted by cyclezen View Post
Other option I might suggest looking into... Get a 30 ring for the current setup and have 48/30 .

The idea of going to 11-36 is great ! Also a way to get that little bit extra, without any tech re-do...

The 16 tooth spread No-No came about back in the day of 8 & 9 spd... Because of chain width, the ring sizes were much more critical. IF you had a large ring and a small ring spread greater than 16 teeth, going to the 2nd smallest cog, while on the small ring, could often cause the chain to rub on the inside of the big ring...
I had a FSA 50/34 crank (forgot the crank name...it'll come to me... in about 2-3 weeks... LOL!) ) teamed up with a 13-21 shimano 9 spd cassette (uniglide back then) and it did exactly that....
I was able to work-around by 'McGivering' the chainline outward 1.5mm (that was back in the day of ISIS & Octalink BBs...)
Not necessary these days - BECAUSE - the 10 & 11 spd chains are significantly NARROWER than 8 or 9 , so the bike's chainline for the setup would have to be 3mm off for the rub to even be possible...
The other thing which would cause a chainline issue is old school steel & Alu BBs which might have been 'faced' with a heavy hand... Too much off, and the chainline goes inboard... not good.
Can't imagine a big, legit bike company doing that...
Hence using a big ring like my 52 with the small 34 is No Problemo !
I would expect the same would be true for the 48 & 30 combo...
Shimano is playing it safe (and adding some low hanging revenue) by staying with the 16 tooth spec...
Ride eOn
Yuri

dwmckee

It is possible you may need to lengthen the chain if you go to a 36 T cassette.

Herzlos

I was originally thinking adding 2 teeth to the back and removing 2 teeth from the front would cancel out. But even assuming I keep the 48T at the front, presumably the worst case is that I can't use the big-big, which is a combo I'd want to avoid anyway?

Herzlos

So would my only potential problem be the chain rubbing on the inside of the ring on changes? Is that likely to cause something to catch and cause an accident or just be a bit of extra wear/friction when trying to change?
In the same vane, if I fit it and I can change back and forth without anything colliding when on a repair stand, then I'm good to go?

Chilepines

An FSA 46/30 crank with 11-36 cassette is what I ran on my last bike. 46/11 is a pretty big gear. But you should also be able to go with a 48/30 setup even though that is above what they spec.
Your current FSA crank takes an FSA 90 BCD inner (which bolts to the big ring) and it looks like 30 tooth rings are available. Just be sure that the hole pattern matches - they are unfortunately are not all the same.

cyclezen

Most modern big rings have chain pickups on their inner face, so you would definitely want those to clear the chain when on the inner ring.
AS I said, my Ultegra 52/34 has no issues like that and shimano rings are noted for all the pickup features they have to assist the UP chain shift...
All this assuming (as with all multi-chainring setups) that you're not using the small/small crosschain...
... an interesting tech tidbit - what is the actual distance/spacing between rings ??? I think when I have a moment later, I'll see if I can mic that distance on my Ultegra and 105 Mid-Compacts including the the new 'deep' Mid-Compact 52/34...

my thoughts on chain - If you're not cross-chaining 'Big to Big', then given just a 2 tooth jump on the 2nd to largest cog, would at the most be a one full chainlink diff.
And depending how the current chain was cut, most RDs have no problem handling that... especially the newer clutch RDs designed to work with wide range cassettes (or your std long cage RD...)
Most you, might have to add is one full link - wide/narrow.
if there's 2K miles on the current chain - prolly a good time to do a 'chain check' for wear/'stretch anyway...

UPDATE: so I tried to mic the spread/distance between the rings on my R8000 Ultegra crank, and there was just no way to get the mic in there to measure properly... But, if a crank is design for 'compact' type 16 tooth spread, then the distance between rings should be same for most all cranks... course, it always, depends... LOL ... still thinking that 2 tooth small ring difference - 18 tooth spread - would be workable...

Polaris OBark

Often, you don't have to. The 2.5mm chainline increase is often within the adjustment window of the H-limit bolt. I have an Ultegra derailleur with a GRX crankset, which works fine, and perversely, a GRX front derailleur with a non-GRX crankset. All seem to work interchangeably.

Finding a GRX crankset now is however a challenge.

dwmckee

We have found than more often than not, a standard Shimano derailleur will not work well with a GRX crank because of teh extra 2.5 mm spacing, but there are lot if variables in setup that may make the combination possible.

zen_

I admit to not reading through the whole thread here, but you can get Megaexo (FSA's smaller spindle) Omega cranks from FSA's website directly for $145 looks like without changing out your BB or front mech. You might be able to find it cheaper from a European merchant.

Herzlos

This is it here, but it's out of stock: https://shop.fullspeedahead.com/en/p...omega-crankset
Just the rings (also out of stock): https://shop.fullspeedahead.com/en/t...chainring-3580

I've ordered this for the 30t ring: https://www.bikeparts.co.uk/products...7e89692d&_ss=r

It looks like I need to buy a 120 BCD 46t ring that's compatible with the 30t, though I don't quite understand the fitting.. From looking at the crankset (without taking it off, which I was hoping to avoid until I had the new rings to go on), both chainrings connect to the spider with the same bolts, and that seems to be at 90mm.
That doesn't fit with the sizing there or the 90/120BCD printed on the 48T chainring. So is it really a 120BCD for the outer ring, with a 90BCD mount for the inner ring?

Not that it really helps, because the only 46t rings I can find in stock are FSA road rings (vs adventure, if it makes a difference) and much more expensive than I would expect (£50+ vs £20), or completely undescribed on Amazon.

I had no idea that cranksets would be so complicated or incompatible! That said, I'll try the 48/30t combo first whilst I keep looking.

cyclezen

so I checked out the FSA Omega Adventure, and sure enough it's 120 outer & 90 inner - a weird complication... maybe needed to enable a 30 inner ???
and so they also list a 46/30 combo, besides the 48/32... so, at some point there should be stock for the 46.
When you get the 30, let us know how the 48/30 combo works out.
Will be good for future reference and anyone else who wants to change a wide spread compact combo...
Ride On
Yuri

Herzlos

I suspect that if I need to get a special 46 to fit the 30 that it won't fit on the 48, so I've attempted to cancel the order. If it turns up anyway I'll try and fit it to see what happens.

I managed to find a full 46/30 crankset for a not-crazy price (£80) imported from Germany so I've ordered that. It gives me the chance to go up to the 175mm cranks which should make hills a tiny bit easier, and gives me a few new combinations to work with.

Thanks all!

t2p

What bottom bracket did you use ?

I might go this route on a Topstone I recently purchased

Craptacular8

I just had my lbs order the fsa gossamer pro modular agx+ in a 46/30. I think they were ordering from the qbp catalog, but I see them on fsa's site as available too. I was getting it for a new to me Midnight Special that came weirdly (to me) specc'd with a sram 2x11 with a 50/34 crankset. Be nice to be able to re-use the bb, but certainly not a deal breaker.

I thought the bike rode fine, and looked as I'd expect a well used bike to be. I also thought the rear cassette was black until I degreased the drive train. Turns out it was silver after all, lol, which has now got me thinking I'd better have them check out the whole bike when I'm having the crankset swapped.

t2p

if you have the budget - consider a new chain and cassette also

Helderberg

Sorry, it took so long to get back to you. I could not find the box but I did last night.
Frank.

t2p

Thank you !

Now gotta see if that crank / rings will work with 9 spd (chain etc)

The Topstone I got is a lower model ... 3 ? ... has Sora components and a low end FSA crank ...