Gear Ratio Question for bike build---looking for real world opinions

10 replies · 271 views

rockymountainhigh
33 posts
#1May 28, 2019, 9:27 PM
My current setup is a Specialized Diverge Expert...
50/34 up front and 11-40 in back.
Building a kitted out monster gravel rigid 29er and will be doing a 1x XX1 Eagle setup.
Cannot decide how big to go in the front....I have done all the gear ratio calculators online but I am looking for some real world input.
34/36/38 up front?
Bikes will weigh roughly the same...about 18-18.5 lbs. maybe a tad more with full kit.
I know I won't ever have the top end with the 1x setup but I am more interested about what a good compromise is for the front chainring. I want to be able to utilize the 50 in the back so I can pedal up anything but also want to be able to at least feel like I can ride it on the road if I want to.
Right now the 50/34 11-40 setup can get me up just about anything. If I cannot make it up it is more than likely due to my 35 tires and not the gears I have.
Thoughts?
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drwelby
531 posts
#2May 28, 2019, 9:59 PM
44 is almost the same range, just a little bit tighter but would feel the same more or less.

38 would give you a low gear that feels like almost one "shift" lower., and you lose your top gear.

34 is like you lost your top two gears, low is would feel like two "shifts" lower than the Diverge.
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droitaubut
58 posts
#3May 29, 2019, 1:23 AM
If 34*40 works for you as lowest gear now, this is 0.85. If you want some extra margin If you want roughly the same (or a bit lower), you get 42/50, with the Eagle cassettes easiest gear being 50.
Another way of looking at it is that road can currently go as low as 1 (34/34) or (33/33). Mtb Eagly as low as 0.6 (30/50). So exactly in the middle is 0.8, this would require you 40 up front, 50 at the back (40/50=0.8).
So keeping things the same go 42/50, slightly lower would be 40/50.

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Slim
300 posts
#4May 29, 2019, 8:31 AM
Will the new bike be used the same way as the Diverge? Or will you be bikepacking(extra weight, longer days) or maybe riding rougher and steeper trails and roads? If the latter, you might want to gear down.
On the other hand, if you start with a bit bigger ring in front, and you find it’s too tall, you can easily swap to a smaller chainring and shorten the chain. The other way around is not so nice (new chain or two quick links close together).
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velogeorgia
54 posts
#5May 29, 2019, 8:57 AM
Last season I used a 1X with a 38T and 9-46 from ethirteen. It was a good combo from the flats to the mountains of north Georgia and western North Carolina.
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droitaubut
58 posts
#6May 29, 2019, 9:06 AMedited
velogeorgia wrote:Last season I used a 1X with a 38T and 9-46 from ethirteen. It was a good combo from the flats to the mountains of north Georgia and western North Carolina.

Of course it depends on your fitness level, duration etc. of rides as well, but 38/46 gives you an easiest gear of .826, very close to the 0.8 I deem ideal for gravel. I think this particular set-up is very good as well.

However that's for 1x, I expect bike mechanics to quickly establish the knowledge that you can run 46/30 with 11-40 with a tiny B-screw adjustments in 2 months. It's already possible with the former Ultegra RX derailleur, and the new one even has 3t extra chain wrap capacity, so I expect it to be as good as flawless. But not sure, eagerly anticipate posts we will see on this topic in July/August.
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velogeorgia
54 posts
#7May 29, 2019, 9:11 AM
droitaubut wrote:

Of course it depends on your fitness level, duration etc. of rides as well, but 38/46 gives you an easiest gear of .826, very close to the 0.8 I deem ideal for gravel. I think this particular set-up is very good as well.

However that's for 1x, I expect bike mechanics to quickly establish the knowledge that you can run 46/30 with 11-40 with a tiny B-screw adjustments in 2 months. It's already possible with the former Ultegra RX derailleur, and the new one even has 3t extra chain wrap capacity, so I expect it to be as good as flawless. But not sure, eagerly anticipates posts we will see on this topic in July/August.

I certainly hope that’s the case!
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rockymountainhigh
33 posts
#8May 29, 2019, 5:08 PM
Thanks everyone!
I am probably going to start with a 36t and go from there if necessary.
I am planning on riding the new bike similarly to the Diverge. Mixed road and trails/gravel/whatever the "roads" are up here.
Hoping to extend my riding into places that are higher and more off the beaten path. The Diverge with 35 tires is sweet up until I get above 12500 feet and the road/trail gets variable with larger rocks etc. and steep.
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ccand51997
265 posts
#9May 30, 2019, 12:40 AM
I just built a go-anywhere bike and went with a 30x42 low. I really like it better than the 30x36 as I can get up stuff I could not before and other stuff is just more comfortable.
I think the bike has changed the way I view cycling. Before I thought of road rides, mtb rides and more recently, gravel rides. Now it is all just cycling and I go from one surface to another without thinking.

(I paired a 105 R7000 shifter with a Shadow+ SLX derailleur (with a Tanpan) and a Sunrace 11-42 cassette. It works really well.)
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dangle
465 posts
#10May 30, 2019, 10:08 AM
What size 29 tires do you plan on using? If you're making a true monster cross and running something like a 2.3" tire, that's going to affect the gearing quite a bit compared to a 35 mm. That's a 'gear inch' change of going from a 46 chainring on your 35 mm tires to a 50 chainring. The wider diameter of the tire really affects gearing.

I think your decision to go 36 is pretty solid. I feel like anything over 100 gear inches isn't seeing much use on a true gravel bike and you're right there if you're using a 2.1" tire or larger.
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rockymountainhigh
33 posts
#11May 30, 2019, 10:30 AM
It will have Maxxis Pace 2.1 29ers to start out with. See how those work and go from there.
But ya I agree about the larger tire. Even though the bike will weigh the same I will lose a bit with tire width.

dangle wrote:What size 29 tires do you plan on using? If you're making a true monster cross and running something like a 2.3" tire, that's going to affect the gearing quite a bit compared to a 35 mm. That's a 'gear inch' change of going from a 46 chainring on your 35 mm tires to a 50 chainring. The wider diameter of the tire really affects gearing.

I think your decision to go 36 is pretty solid. I feel like anything over 100 gear inches isn't seeing much use on a true gravel bike and you're right there if you're using a 2.1" tire or larger.
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