PDKL45

Has anyone here attempted to mate a compact road double with a wide range modern MTB rear cassette? This is just a thought experiment at this stage, as I see a lot of bikes I would like as an N+1, but their gearing just does not work for me.

The specific set ups I am thinking about are:

1. A 10-speed Shimano Tiagra 34-50 crankset, a Shimano Tiagra Double Front Derailleur, an 11-42 tooth Sunrace 10-speed cassette and a Shimano RD-T8000-SGS rear derailleur.

2. An 11-speed Shimano 105 34-50 crankset, a Shimano 105 Double Front Derailleur, a Shimano or Sunrace 11-42 tooth 11-speed cassette and a Shimano RD-M8000-SGS rear derailleur.

Both rear derailleurs have a total capacity of 47 teeth, and the RD-M8000-SGS has a maximum low gear of 42 teeth in 2x11 configuration (40 teeth in 3x11 and 46 teeth in 1x11) with a maximum front teeth difference of 18 teeth. The 11-speed set up looks like it would work, going by the math alone. Can anyone see a problem with it?

The 10-speed set up is more difficult. The RD-T8000-SGS has a maximum low gear of 36 teeth, but maybe a Wolftooth goatlink could offset the position of the derailleur enough that it could shift onto the lowest gear?

I am aware of the problem between drop bar and flat bar width and I know that a tanpan will not work with Tiagra shifters.

My main questions are if anyone has ever mated a road compact double with an 11-40 or 11-42 cassette and if anyone thinks that a Wolftooth Goatlink could position a 10-speed derailleur to properly shift an 11-42 teeth cassette.

nfmisso

Wolftooth link may or maynot be required - depends on the hanger on the bike, some are longer, some are short. Shimano tends to be conservative, so the 36T rating is for the shortest reasonable hanger including tolerances.

gsa103

The main problem is the shifters. You'll need a tanpan for any configuration.
Tiagra 4700 shifters use the same cable pull ratio as a 11-sp (just with 10 positions). Which means they're basically incompatible with everything. If you want 10-speed, you're better off using 5700 (105).

PDKL45

The specific bikes I had in mind for conversion were the Giant Fastroad SLR 1, a flat bar road bike with Tiagra components, and the Giant Fastroad CoMax with 105 components, so I would be adapting to existing components with flat bars.

It's just an idea at this stage, though, nothing more. I may get a new bike in a year or two, so it's good to know what is possible when looking at candidates.

And thanks for the info on hanger lengths, it's useful. Maybe a goatlink would help with chain wrap at least? I have not seen them used with 2x drivetrains, though.

Eggman84

I understand its only a thought experiment but what you are considering wont work unless you change shifters on both bikes you are considering. For Option 1, the 2017 Giant Fastroad SLR 1 comes with Tiagra 4600 2x10sp Flat Bar Shifters, which are not compatible with Shimano 10 speed mountain rear derailleurs like the RD-T8000-SGS. For Option 2, the Giant Fastroad CoMax comes with Shimano RS-700 2x11 road shifters for flat bars which also are not comparabile with himano 10 speed mountain rear derailleurs like the RD-M8000. Note the RD-T8000 is just the touring version of the RD-M8000; no real difference.

Shifters and derailleurs have to work together, or use a converter like a shiftmate. Good luck.

nfmisso

not at all. Chain wrap is a function of the the distance between the two RD pulleys and the angle the RD arm can swing.

PDKL45

You make a good point. I would have to use an XT rapidfire shifter for the rear derailleur.

I actually assumed that the derailleurs were basically the same, but got hung up on the different specs on the Shimano site. I think they give specs on the assumption that the T8000 would be always be used with a triple trekking crankset. Thanks for your reply.

PDKL45

It's genuinely useful replies like this make this such a good place to educate yourself about bikes. Thank you.

RubeRad

FWIW my CrossCheck has a 50/34 compact and an 11-32 9sp cassette with a Deore M510 RD straight on the hanger, and it works fine.

I think it would be fun to go 1x with a 11-42 or 11-46 cassette, but I'd also have to upgrade my shifter from 9sp to 10sp or 11sp -- and a granny that big might require a tanpan or similar. And there's not much point going 1x unless I actually replace my double crank with a 1x crank (although I could just take off the FD) and replace my left retroshift with a regular brake lever.

ExpertTools

I can feel for your problems. There has been a trend where current MTB drivetrains with either single front chainrings or compact doubles are the norm. Great for off-road or cross country, but if you try to use that type of drivetrain on the road, you run out of high gearing.


On the plus side, there are some pretty wide gear spreads seen on road bikes these days, with the assumption that riders at somewhat less than "pro" levels will want to tackle some pretty big hills or carry packs. This combination of trends kind of leaves the riders looking for a more upright ride for city or just general use with something that is either geared too low for the roads, or too high for steep hills. While hybrid bike tend to have a lot of gears, most makers assume that their riders aren't going to be tackling major hills.


This has been something of a concern for me as well, as I have very bad knees, and would much rather spin than hammer up hills, and we've got some pretty steep ones around where I live. I found a somewhat different solution; MTB drivetrains USED to be available with much wider gear ranges than today. So instead of a modern 'hybrid" bike, I bought an older XTR equipped Litespeed 26" hardtail, and put skinny tires on it.


So I have 26-36-48 front and 11-28, (8speed) in the rear. This set-up works great for me as I can make it up some very steep hills without getting out of the saddle, and can get to well over 20mph without running out of gear. The bike originally came with 22-32-44 up front and 11-32 in the rear but it was geared too low for the road. Granted this bike may be very slightly heavier than that Giant, but only because of the modern suspension fork and a sprung seatpost; both of which I like due to the rough bike trails in my area. Compared to the Giant, I have lower gearing for the hills, (and could choose even lower if I wanted,) and although just slightly lower on the high gear side, it seems to be plenty high on the other end.


I also own a Stevens flat bar bike which is very similar design to the Giant, and comes with a wide range triple, (AL frame, 700c wheels, and a light duty suspension fork). I know it's also made with no suspension fork. It's made in Germany. I found that one in a pawn shop in Florida, I'm not sure how it got there as I don't think there are any US dealers. But it's pretty much exactly the gear range you're looking for, slightly wider range than even my Litespeed. It's in the exact price range of the Giant, (1,000 Euro). I think the European market sees more variety of flat bar bikes that we do here in the US.

Abu Mahendra

Look at a SRAM DualDrive hub. One of my rigs with it gives 18.5-112 gear-inches with a 1x11-36T drivetrain.

PDKL45

I have a bad lower back, so with a few further modifications, like a high rise stem, a flat bar road bike like the Giant Fastroad would be okay for my back while riding. I am based in South Korea and have started to participate in randonneuring rides--brevets--so I like the idea of a brevet bike that is easy on my back while being lighter and faster than my Specialized AWOL, which I would keep as a touring bike/daily commuter.

Some of the brevets here feature climbs of 500 to 1000 meters (1700 to 3300 feet) with some seriously steep grades in places. Having a bike allowing for good posture and providing some ease in climbing with rubbery legs after a full day of riding is the goal. Shaving a few hours off ride times with a light bike would also help in brevets, allowing me to take relatively unhurried meal breaks and have some sleeping time on the longer rides (600, 1,000 and 1,200 kms).

I actually have a new 26-36-48 crankset that I got for a great price from CRC, destined for my AWOL. That crankset, with an 11-32 cassette, provides basically the exact gear range I want. Still, that crankset is a 9 speed triple, and part of the idea, for me at least, is modifying existing bikes to keep costs down. The Giant Fastroad SLR 1 is relatively cheap in Korea at about US $900, so with a few new parts and accessories, I could have the brevet bike I want for around US $1300.

I like the Stevens Strada bikes, they're the equivalent of the Giant Fastroad in many respects, but there is no dealer for Stevens here in Korea. Plus, I would probably get all deranged engineer on their drivetrains as well. That Stevens P-Carpo is a dream bike, though.

RubeRad

Had to look it up, that's kinda cool, can't believe I've never seen that before.

invisiblehand

If you need a super low bottom but can give up a bit on top ... a 50-11 top gear is roughly 120 gear inches ... why not try a 46-30 crank?

Velo Orange Grand Cru 50.4 Crankset

Or if you want something more modern, look for the Sugino ...

https://www.suginoltd.co.jp/us/products/road/ox.html

It should work well with Shimano cyclocross front derailers designed for 46 tooth big chanrings.

This way you can avoid crazy large big cogs in the rear and maintain more granularity between gears.

PDKL45

Those are really good suggestions, thanks. Like I said above, I got a good deal on an FSA trekking crankset after thinking along the same lines for my Specialized AWOL, but I hadn't seen those Sugino cranksets.

I actually went and had a look at a Giant Fastroad today at one of my LBS's and realized I tend to go overboard with my desire for lower gears at times. I had a quiet chuckle to myself while thinking "You could probably just HTFU and see how it goes."

Still, mixing road and MTB drivetrain components interests me. I put a 12-36 cassette and a Deore RD on my AWOL, with a 30-39-50 crankset. I will probably go even lower, with 26-36-48 on 12-36, but that's for taking a full touring load up a couple of climbs of around 1000 meters (3000 feet).