Hollowtech 46/34 to GRX 46/30? Shimano 68mm BB
05-31-20, 12:31 AM
#1
Scrubby duff
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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?
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.
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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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.
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.
05-31-20, 09:49 AM
#4
Scrubby duff
Thread Starter
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.
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.
05-31-20, 01:44 PM
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05-31-20, 01:53 PM
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05-31-20, 02:07 PM
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05-31-20, 02:39 PM
#8
Scrubby duff
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05-31-20, 03:34 PM
#10
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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
https://www.bikecalc.com/gear_ratios to help you determine if a new cassette will provide lower gearing than a 30 tooth chainring
05-31-20, 04:07 PM
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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 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?
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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05-31-20, 04:17 PM
#12
Scrubby duff
Thread Starter
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.
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.
its very good news! thanks!
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.
05-31-20, 07:04 PM
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05-31-20, 07:05 PM
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Can you keep the non-oval outer ring and replace just the 34T one with the 30T oval one?
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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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05-31-20, 08:25 PM
#17
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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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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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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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06-01-20, 12:34 PM
#20
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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 Ø19mm 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.
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 Ø19mm 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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06-01-20, 05:09 PM
#21
Scrubby duff
Thread Starter
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 Ø19mm 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.
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 Ø19mm 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.
