bamboobike4

Current bike:
2018 Trek Domane SL 5
Ultegra 6800 Di2
Compact 50/34 PressFit
GS long-cage RD
Wolftooth Roadlink
11-36 cassette.
Works just fine. She avoids small-small.

Proposed, for 3-4 climbing centuries (Six Gap, Triple ByPass, Cherohala Challenge, Diairyland Dare)
1-Swap in GRX Di2 FD
2-Swap in GRX 46/30 crankset (PressFit)
3-Swap in chain for shorter length.

What sayest youse folks?

I know just swapping in the GRX crankset won't work because of the FD cage reach.
I am hoping if I get the GRX FD, to work with the GRX crankset, it will all shift OK with the Ultegra Di2.

Koyote

The bike already has a low gear of 34-36, which is very low for road riding. Are you sure that a lower gear is necessary?

I've not done those rides, but I've done quite a bit of riding in CO, including some of the big climbing races. And I've found that the climbs are long but not terribly steep.

nomadmax 

You can use the grx crankset and space the chainrings inboard by 2mm with some problem solvers shim washers. I'm running the grx 31/48 crank and there isn't much that isn't doable with an 11-34 cassette. I think when I ran the gear charts a 48x11 was taller than my normal 50x12.

bamboobike4

I totally understand. My question was about the bike, not the rider.
She is a low-wattage, long-distance rider, riding by HR most of the time.
Height vs. Weight is sometimes an issue. Voss, she ain't.
If it's possible, I'd like to provide her the opportunity to do it her way.
Beats not doing it.

bamboobike4

Will I need longer chainring bolts, too?

Koyote

Thanks for the reply. I will echo nomadmax ’s suggestion, and also add that the GRX front derailer may not even be necessary. Depending on the existing crankset and the bike's geometry, it might shift just fine with the present derailleur. You’ll probably want to have that front derailer, just in case, but you might end up being able to return it for a refund.

bamboobike4

Thanks to you and nomadmax . I'd sure prefer to use 2mm spacers in lieu of a $250 FD. She already has the GRX crankset on her gravel bike, but she's not taking that, plus 4 more pounds over those mountains tends to add up, even psychologically.

bamboobike4

Forgive my naivete, but if the large chainring is on the outside, spacing it inward tends to interfere with the crank arm spider.
If I move it inward to the inside lip, do I not then lose the inner chainring lip?

Koyote

Argh, sorry, I should've been clearer: I suggest trying the GRX crankset with your Ultegra Di2 FD, no spacers. That might work. If not, the spacers are the next option, and if that doesn't work you can slap on the GRX fd.

Iride01 

I still don't understand!

What are you wanting help with? Or just an okay that your bike will be a bike with the stuff you wish to add to it?

Seems to me the important bits of information will be knowing what the cyclist is capable of climbing with the current configuration. Both in the % grade of the slopes and for the distance of them that you can ride and not be gasping for a breath or just about to pass out.

And is this being done loaded up with gear for a bike packing trip or is this just a daily ride with bare minimum needs of hydration, snacks and tire repair?

I'd think for a unloaded ride that a 34 front and 36 rear that you have already should get up most anything with a paved road. Even if there are a few places one grunts and grinds to a halt on a very brief steep section, there isn't really any shame to walk a few yards till it gets less steep.

bamboobike4

OK, I get it. I was confused by my normal assumption of road double drive side (lip outer, lip inner)
I did not realize that both chain rings already sat inward of the spider. Very cool. nomadmax sent pictures.

Plan A:
1-Swap in the GRX crankset, and try to adjust the FD outward to possibly gain the 2mm.

If that fails, Plan B:
1-Remove the rings from the GRX crankset
2-Insert the 2mm spacers (8) between the crank arm and rings, respectively.
3-Swap in the GRX crankset, see if the FD will accommodate it, now that the rings are closer.


(Forgive the artwork. I'm lame.)


If that fails, Plan C
1-Swap in the GRX crankset (no spacers)
2-Replace the FD with a GRX FD-815, which should reach outward to match the GRX crankset

bamboobike4

Appreciate it, and noted. It's about the bike setup I'd like to do.
I know the rider. (see my earlier post).
Low wattage.
Normal rpm (rarely over 90, rarely under 75)
High endurance (has done 228 in one day, 107 centuries)
Lower speed (Averages 15-16, but has a 5:29 century and a 13:29:00 for 228 ina 6-man pace line, a year ago, but that was a special year,
Rides by HR and sticks to it.

But I'll get specific on the route(s):
-Triple Bypass, 106m/10,900' event support though we're hoping for an extra stop or two.
-Cherohala Challenge, about the same, event support
-Six Gap, roughly the same
-Dairyland Dare, shorter and steeper.
-----If successful at the first 4, probably Horrible Hilly Hundred.

Last year was an endurance year, and we trained for it.
Coming off a rough winter/early spring, we're planning Colorado, and then go from there.

I'm asking about the bike setup, specifically, for this ride and 3 others, using what works now on the rear and gaining some improvement on the front.

All the advice is great, though.

Andrew R Stewart 

I won't say how to achieve it but my rule for mountain touring is one can never have too low a gear. Depending on the HR limits wanted one might be riding up one hill for an hour+ (my personal longest is about 4 hours for one hill in the Sierras, twice on the same self contained tour). Have a lot of fun and bring a camara ability. Andy

Iride01 

When I looked up those routes only one was in the Rockies proper. Unless I found the wrong ones of the same name, then they stretch from the Smokies to the Rockies. Most between.

If your friend is use to that much pedaling on a ride and does it regularly then I don't think you have much to worry about. Those aren't super steep routes IMO. Just long periods of climbing. The Six Gap might be the most arduous as it has the longest distances of steady climbing and you'll be at higher elevations where O2 might leave you gasping for a breath. But just pedal on, despite the gasping, you'll have plenty of energy for it. At least that was my experience with going up to 14,000 feet on Mount Evans CO.

The other routes seemed low enough elevation not to be an issue. Also not sure why you think the DairyLand Dare is steeper. It looked like it averaged a much lower grade over all. However since it was shorter, the scale of the vertical compared to the horizontal distance made it's profile appear like a steeper road.

If I was doing them unloaded, I'd be happy with the 34F / 36R... even just a 32 rear which is what I did Mt. Evans with and I only needed it for the few times the grade kicked up briefly. Otherwise the 4% average grade was just steady grinding away on the cranks.

If loaded with stuff, that might be a different matter. And I have no idea what would work for a loaded down ride as I just don't carry anything with me other than hydration, snacks and stuff for a flat tire. Luggage and other stuff can go in a car with my wife.

rm -rf

My road bike low is 34F-32R. It's good for the local climbs: up to 8-10% sustained, with some 15-18% portions of some climbs.
I want to stand up when the grade goes beyond 10-12%.

My heavier gravel bike is a triple, with a 30F-34R low gear. I like that I can stay seated well past 12%, often at 15%. It made some of the harder local climbs quite easy to finish. It's amazing to climb 15% grades at easy to moderate pedal pressure at 3.5 to 4 mph! Low gears are good!

But I'm wondering if the swap is worth the trouble. Here's the 70-90 rpm that your rider favors, with a Sram 11-speed 11-36 and three chainrings to compare: Red=30 chainring, black=34, blue=46.
From the useful Mike Sherman Gear Calculator -- here's the link to this setup.
How steep are these hills?

The 30 is just one more shift easier than the 34 chainring that you have already.
And the rider will want to shift from the 30 chainring to the big ring at about 13-15 mph, instead of 15-17 mph with the 34 chainring. That might be a bit annoying. But it is Di2, so front shifts are simple and efficient.

rm -rf

I downloaded and looked at the Wisconsin HHH 200k route in ridewithgps.com. The 200K -- 127 miles, 7500 feet, has lots of 300 foot climbs, and a few 600 foot ones. rwgps thinks the grades are mostly below 10%, no obvious sustained 12%+ climbs. (It can underestimate shorter pitches, though.)
I'm thinking that this ride doesn't really require ultra low gearing. That's a long day and a lot of climbs, maybe 30+ climbs, though.

At the end of a long day of climbing, I'm standing on minor, easy roller climbs that I'd hardly notice near the start of the day. Some extra low gears would be nice right then.

bamboobike4

Yes. Triple ByPass is in the Rockies, and the 3 peaks are over 10,000' Cherohala and Six Gap are in the Appalachians/Smokies, and Dairyland Dare/Horrible Hilly Hundred are in the driftless area of SW Wisconsin (well known to racers from St. Louis)

I didn't realize Six Gap in Georgia was higher then 10,000' elevation, just knew a lot of climbing. I've done Cherohala, Dairyland Dare, and Horrible Hilly Hundred. We are going to CO 2 weeks early, will likely do (formerly known as) Mount Evans, and run over and try the Copper Triangle route.

Having done the Dairyland Dare (6x) from 100K to 200K, the climbing is relentless, often shorter, and certainly seemed more brutal. Perhaps it's just the constancy. There is a climb on Horrible Hilly Hundred (right at the end) that Lemond made famous/infamous in the Juniors. ATV's have tipped over backwards on it.

We did (formerly known as) Mount Evans on CompuTrainers, took awhile. The only real-life comparable climb we've done together is Thunder Ridge in VA, 12.75 miles at 5.6% average. "just steady grinding away" is apt.

I'd do that, but she'll be riding whatever modifications I do here!

Thanks again for the information. It will be useful. Our last training ride here is Saturday, 104 miles and 7,000' of climbing. No mountains, though.

Iride01 

I spelled it wrong. I meant the triple bypass in CO. My fingers didn't listen! <grin>

Besides, I'm so confused!

Oh, in CO, around the higher elevations, the convenience stores and other places have some little bottles of O2 that look like the little pocket size asthma inhalers. Might want a couple of those just in case. My son needed to use his a few times on our trip. Check what the temps are running near the peaks in those routes at higher elevations. I almost got hypothermia when I stopped to admire the views for 30 minutes in August.

bamboobike4

Join the club. A mechanic, I ain't.

I only know "little in front, big in back" is better for climbing.
Making it all work, fun.
I finished my climber last night: 50/34 front, 11-34 rear, DA9100 with a Roadlink DM.
Hits all the gears just fine, both big and small rings, but not real happy getting in/out of 11T.
1996 frame, maybe it's just mad about it.

I'll ride it tomorrow night on hill repeats and see what's up. We do 6 climbs, 11 miles, 1900'. Repeat if time permits.

Racing Dan

Doesnt DI2 have some function to see what gears in the current configuration is used the most? Id say only if there is sustained riding in the 34/36 combo an expensive swap of crank and FD is warranted.

pdlamb

Cherohala tops out over a mile high (5,600'?), but IIRC Six Gap is under 4,000' elevation. Total climbing is over 10kft, but not elevation -- you won't run out of oxygen except, perhaps, dealing with the grade. IIRC Cherohala grades are limited to about 6% (except for the wonderful downhill to the dam!), and Bull Gap has something like a 9% grade to the top.

bamboobike4

I was responding to his earlier post.
He cleared it up in #18

bamboobike4

You'd be correct. There is. The lass likes to hit the big cogs at the first sign of incline. Again, she rides by HR and if I can gear her down, I will. Simple as that. I asked a mechanical question, not a technique or fitness or financial one. But thanks. I understand.

Iride01 

I don't remember if any said it, but your best bet for reducing the gearing is to get another crank with smaller rings. Otherwise you are going to get into mountain bike parts on a road bike and the compatibility issues which might crop up between them.

Shimano crank already? Not certain they offer any inexpensive or expensive 11 speed road set with smaller rings than a 50/34. The GRX Shimano crank will probably fit without changing your BB. However it's chain line is 47 mm and the current crank on that Domane is probably about 43.5 mm. So even if the crank fit the BB shell width, the shifting will be crappy trying to get to the low ratio cog on the back. If it would even get there. Though maybe FSA or some other that makes cranks with the same spindle size has something that will fit without requiring a BB change and then you can put the other back in after your adventure.

Still I bet you both will make it on your current setups. Like I did for my big climb last year, you are probably worrying too much. I did way more training and prep than I needed too. Though in the end, being prepared is what makes it easy.

Canker

Absolute Black makes sub compact chainrings that will fit a 6800 crank. I'm running their 46/30 rings on my 5800 cranks and I didn't need a new FD. AB's rings are expensive so you'd have to decide if it makes more sense to go GRX or AB rings. If I were doing it now I'd go 48/31 GRX.