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Hollowtech 46/34 to GRX 46/30? Shimano 68mm BB

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Hollowtech 46/34 to GRX 46/30? Shimano 68mm BB

Old 05-31-20, 12:31 AM
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jma1st3r
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Hollowtech 46/34 to GRX 46/30? Shimano 68mm BB

First time posting, just starting to ride abit, big guy need climbing gears. I'm not really good with math and things, and with so many standard and conversion in the bike world I'm getting a headache with info overload. Pardon the newbness.

I have a 18' Kona JTS, its got 46/34 and 11/34 cassette. Just wondering what kind of crankset I can put in the front since i find some gear combo redundant and wider gear ratio would be nice.

I'm looking at the GRX 46/30 or the FSA 48/32, reason being I'd hope that without changing BB they would work somehow...

just need experts verifying/reject the idea, thx.


edit: or go with 11-40?

Last edited by jma1st3r; 05-31-20 at 12:41 AM.
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Old 05-31-20, 05:02 AM
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The GRX will definitely work without changing the bottom bracket, but you may need to change the front derailleur because the chainrings are 2.5mm further out. The FSA is supposed to work with the Shimano bottom bracket.
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Old 05-31-20, 07:47 AM
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Sorry why change the crankset when all you need to do is purchase a 30 tooth chainring and replace your 34. Am I missing something?

As for finding some gears redundant, well that is the nature of the system. You have 22 gear combinations there should be enough gears to make you happy even if you lose a few.

If you find you still can't make the hills you could go with 11-40 but you will need a road link and maybe a longer b screw. Try changing the chainring first.
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Old 05-31-20, 09:49 AM
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Originally Posted by blakcloud View Post
Sorry why change the crankset when all you need to do is purchase a 30 tooth chainring and replace your 34. Am I missing something?

As for finding some gears redundant, well that is the nature of the system. You have 22 gear combinations there should be enough gears to make you happy even if you lose a few.

If you find you still can't make the hills you could go with 11-40 but you will need a road link and maybe a longer b screw. Try changing the chainring first.
110 BCD, smallest is 34.unless theres something I missed.
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Old 05-31-20, 01:44 PM
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Originally Posted by jma1st3r View Post
110 BCD, smallest is 34.unless theres something I missed.
Yep, no 30t for your current crank. I'd prefer the GRX crank to the 40t cassette but JMO.
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Old 05-31-20, 01:53 PM
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Originally Posted by shelbyfv View Post
Yep, no 30t for your current crank. I'd prefer the GRX crank to the 40t cassette but JMO.
My current crank is 46/34 110 5 bolt bcd. No smaller chain ring than 34 is available by physical limitation. Even wolf tooth has it so.
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Old 05-31-20, 02:07 PM
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Originally Posted by jma1st3r View Post
My current crank is 46/34 110 5 bolt bcd. No smaller chain ring than 34 is available by physical limitation. Even wolf tooth has it so.
Yes, I was agreeing with you....
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Old 05-31-20, 02:39 PM
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Originally Posted by shelbyfv View Post
Yes, I was agreeing with you....
Oh crap, I've read it wrong. My bad

Guess a grx fit will have to be done. Thx

Last edited by jma1st3r; 05-31-20 at 02:50 PM.
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Old 05-31-20, 03:02 PM
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Well thank you for the correction. Yes, a new crank sounds like it is a solution for you. Hope it works out.
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Old 05-31-20, 03:34 PM
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It would probably be cheaper to look into an 11/42 cassette and a link for the rear derailleur.


https://www.bikecalc.com/gear_ratios to help you determine if a new cassette will provide lower gearing than a 30 tooth chainring
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Old 05-31-20, 04:07 PM
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Originally Posted by jma1st3r View Post
First time posting, just starting to ride abit, big guy need climbing gears. I'm not really good with math and things, and with so many standard and conversion in the bike world I'm getting a headache with info overload. Pardon the newbness.

I have a 18' Kona JTS, its got 46/34 and 11/34 cassette. Just wondering what kind of crankset I can put in the front since i find some gear combo redundant and wider gear ratio would be nice.

I'm looking at the GRX 46/30 or the FSA 48/32, reason being I'd hope that without changing BB they would work somehow...

just need experts verifying/reject the idea, thx.


edit: or go with 11-40?
I replaced my Ultegra 50/34T crank with a 46/30T (first a White Industries, and then a Shimano GRX). It works great. On one wheelset I have an 11-34T cassette. On the other (which I tend to use off-road), I have a SRAM 11-36T cassette.

The great thing about the GRX 46/30T is it is cheap (I paid $150) and is a drop-in replacement for what you have now. The front derailleur needs to come out about 3mm more (H limit screw), so if you can do that, you should be safe. It also helps to be able to lower it a couple of mm, but if you are already at 46T on the large chainring, there is probably no need to do that.
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Old 05-31-20, 04:17 PM
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Originally Posted by wgscott View Post
I replaced my Ultegra 50/34T crank with a 46/30T (first a White Industries, and then a Shimano GRX). It works great. On one wheelset I have an 11-34T cassette. On the other (which I tend to use off-road), I have a SRAM 11-36T cassette.

The great thing about the GRX 46/30T is it is cheap (I paid $150) and is a drop-in replacement for what you have now. The front derailleur needs to come out about 3mm more (H limit screw), so if you can do that, you should be safe. It also helps to be able to lower it a couple of mm, but if you are already at 46T on the large chainring, there is probably no need to do that.
I think i've came across a post like this before about white industries' crankset on this forum... cant remember where..

its very good news! thanks!
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Old 05-31-20, 06:26 PM
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You can get a 30 tooth ring for your crankset. There are 46-30 oval chainrings for your crank from Absolute Black. Works for me with Ultegra 6800 crank and front derailleur. Oval rings make it easier to "get over the top" but let you apply real power on the downstroke.
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Old 05-31-20, 07:04 PM
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Originally Posted by jma1st3r View Post
I think i've came across a post like this before about white industries' crankset on this forum... cant remember where..

its very good news! thanks!
Probably me. Short version: I like the $150 Shimano GRX more than the $650 White Industries.
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Old 05-31-20, 07:05 PM
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Originally Posted by qajaq View Post
You can get a 30 tooth ring for your crankset. There are 46-30 oval chainrings for your crank from Absolute Black. Works for me with Ultegra 6800 crank and front derailleur. Oval rings make it easier to "get over the top" but let you apply real power on the downstroke.
Can you keep the non-oval outer ring and replace just the 34T one with the 30T oval one?
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Old 05-31-20, 07:32 PM
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Unfortunately no you can't just replace the inner ring. The Absolute Black outer ring has bolts that screw into the small ring. That's what allows them to make a ring smaller than the usual 34
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Old 05-31-20, 08:25 PM
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The absolute black 46/30 fits 4 bolt cranks and is more expensive than a whole GRX crank. I have the AB 46/30 rings on my 105 crank and if I were doing it now I'd just get a GRX 48/31 crankset and a new FD.
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Old 05-31-20, 11:03 PM
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You probably don't need a new front derailleur. I am still using my Ultegra (Di2) derailleur with the GRX 46/30T.
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Old 06-01-20, 12:21 PM
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Yes the GRX crank costs less than the Absolute Black 46-30 rings but the AB rings are oval. While my install predated GRX (they are on a 6800 crank) I still think oval chainrings are worth the price difference. That's just me of course. Some folks like them; some don't. BTW They have different "timing" than the earlier, failed Shimano BioPace rings and feel easier to get the pedal "over the top". Something that may appeal to the OP.
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Old 06-01-20, 12:34 PM
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FSA omega crankset supports a 30/46. Overall setup is realtively cheap compared to other options. I've been running this 6 of my last 10k miles with the same cranks and BB with no problem and most of that is in gravel, grit, and moisture (along with a 36 or 32 big in the rear). I am not light and I've done many trips with various touring gear strapped on. I can't speak for different front derailleurs but I have a CX70 and it works perfect with both a Tiagra 34/50 HT2 and my FSA 30/46 that I swap around.
General notes for this option..
- You can get the Omega with 34/50 and swap to FSA 30/46 rings or just get the FSA Omega "Adventure" which come with 30/46. The price is about the same for either route as the 50/34 seem to be cheaper and more readily available last I looked.
- There is exactly one and only one BB choice for the Omega cranks and 68 shell, a BB-4000 (cranks are 19mm spindle, not ~24 like the HT2 and similar). It costs more than a HT2 and probably not on the shelf at many LBS but it does seem to last.

EDIT: I did not know the GRX 30/46 was as cheap as it was, I must not have looked in a while. If you have the front der and the shifter pull ratio already if required, seems to be a great option.

Last edited by u235; 06-01-20 at 12:59 PM.
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Old 06-01-20, 05:09 PM
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Originally Posted by u235 View Post
FSA omega crankset supports a 30/46. Overall setup is realtively cheap compared to other options. I've been running this 6 of my last 10k miles with the same cranks and BB with no problem and most of that is in gravel, grit, and moisture (along with a 36 or 32 big in the rear). I am not light and I've done many trips with various touring gear strapped on. I can't speak for different front derailleurs but I have a CX70 and it works perfect with both a Tiagra 34/50 HT2 and my FSA 30/46 that I swap around.
General notes for this option..
- You can get the Omega with 34/50 and swap to FSA 30/46 rings or just get the FSA Omega "Adventure" which come with 30/46. The price is about the same for either route as the 50/34 seem to be cheaper and more readily available last I looked.
- There is exactly one and only one BB choice for the Omega cranks and 68 shell, a BB-4000 (cranks are 19mm spindle, not ~24 like the HT2 and similar). It costs more than a HT2 and probably not on the shelf at many LBS but it does seem to last.

EDIT: I did not know the GRX 30/46 was as cheap as it was, I must not have looked in a while. If you have the front der and the shifter pull ratio already if required, seems to be a great option.
as we speak...ebay pricing on GRX crankset is sub 130 shipped in states. Oakley shades are on mass discount right now.
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