Bicycle Mechanics - Will a SHIMANO DEORE FC-M590 48-36-26t Trekking Cranksey shift a 10 speed chain well?

I want to lower the range of my Cyclocross bike drivetrain and use larger tires. The SHIMANO DEORE FC-M590 48-36-26t 9-speed crankset has the right combination of chainrings, but I want to keep my 10 speed cassette, chain, front derailleur (105 5603 triple) and STI-Brifters. I'll use a chain guide-retainer to help avoid a dropped chain.

I'm not looking for fast and flawless shifting, but I would like the sytem to shift smoothly within one turn of the crank. Can this combination work well enough, or is a 9 speed crank not going to shift well with a 10 speed chain?

I'm running a 9-speed Ultegra triple Octalink crank (FC-6503) with 10-speed everything else, including the chain, and it shifts flawlessly. So, based on that, I expect you will have good results using the 9-speed Deore with a 10-speed chain. You will have to continue to use a "road" front derailleur if you use STI brifters.

It would be helpful to know what your current gearing and crank set is. If it is a newer shimano 3 ring crank you should be fine with some tweeking of the drivetrain, the only real issue is you may not get perfect index shifting.

It would be helpful to know what your current gearing and crank set is. If it is a newer shimano 3 ring crank you should be fine with some tweeking of the drivetrain, the only real issue is you may not get perfect index shifting.

I'm now using a ten-speed "5603" 105 triple crankset with 50, 39 and an aftermarket 26t chainring. I have a 2012 Tiagra ten-speed 12-30 cassette. The chain is 6600 Ultegra ten-speed.

What's the rear spacing of the bike--130mm or 135mm?

The DEORE FC-M590 has a 50mm chainline and is meant for 135mm rear spacing. Because it has an integrated BB spindle, you can't adjust the chainline (except re-arranging BB spacers and making the cranks no longer equidistant from the center line).

A road triple has a 45mm chainline and goes with a 130mm spaced frame.

What's the rear spacing of the bike--130mm or 135mm?

The DEORE FC-M590 has a 50mm chainline and is meant for 135mm rear spacing. Because it has an integrated BB spindle, you can't adjust the chainline (except re-arranging BB spacers and making the cranks no longer equidistant from the center line).

A road triple has a 45mm chainline and goes with a 130mm spaced frame.

The rear is 132.5mm! I'm running road hubs now, but would install a 135mm ATB/MTB wheel if I make the change.

OK, so the frame can take either 130 or 135, nice.

The MTB (50mm) crank with 135mm wheel will still be to the outside relatively 2.5mm, compared to a road (45mm) crank with 130mm wheel.

This is because going to a 50mm crank moves the crank chainline out a full 5mm, whereas going to a 135mm wheel moves the cassette chainline out only 2.5mm (the other 2.5mm goes on the left).

Edit: It should work fine, but just be aware of the change.

Edit2: Depending on the current hub, you may be able to add 5mm of spacers to the non-drive side, re-center the axle, and re-dish the rim.

Using a 10-speed chain on a 9-speed crank has been done many times before, and nearly always works. I once had a problem with a 9-speed Truvativ Rouleur road crank - when I put after-market rings on it and used a 10-speed chain then the rings were spaced too far apart. When shifting to the middle ring, the chain sometimes skated on the middle ring, almost in the gap between that and the big ring, and did not engage with the middle ring for several pedal revolutions. Since the crank didn't cost much, I filed down the outside of the mounting tabs behind the big ring to bring that in closer. That improved the situation, but did not completely solve it. However, I have not had this problem with other "9-speed" cranks and 10-speed chains, so I believe it is unlikely to happen.

I would certainly go with a 135mm hub if you use a MTB crankset with an integrated axle. Respacing a road hub from 130mm to 135mm may be possible, but going with a dedicated MTB hub should yield an advantage of having better sealing for the bearings (at the cost of a barely noticeable increase in drag). Be aware that with the MTB crank you are likely to increase the Q-factor (horizontal distance between the pedals) considerably, which may feel odd to you, or you may not notice it at all.

To get the same gearing as the Deore trekking crankset on a road crankset, which will have a lower Q-factor and better chainline, then if you want an integrated axle design then you would need to get a Stronglight crank; they have several road triples with 110mm/74mm BCDs. Unfortunately, they are not as readily available as the Shimano options. All other road triples with integrated axles that I'm aware of use 130/74 BCD, see the index here (http://www.bikeforums.net/showthread.php/617940-Index-and-Comparison-of-2-piece-Road-Triple-Cranksets-Chainsets). There are several 3-piece, square-taper designs that used this BCD combination, and so you could use the same ring sizes as on the Deore Trekking crankset. I picked up an old XTR crank from the 90's on eBay last year that is a 110/74 triple, it was still in pretty good condition. It's a shame you don't live closer, or I could offer you that because I'm no longer using it.

but going with a dedicated MTB hub should yield an advantage of having better sealing for the bearings (at the cost of a barely noticeable increase in drag).

That depends on the hubs. I recently had a Deore and Ultegra 6500 hub apart side by side and the Ultegra hub had far better sealing than the Deore which mostly relied on an external rubber boot.

Rubber seals are provided well down the price point range, these days, on hubs.