Cyclocross - Wide gearing on a Cross bike using road bike componients

The Shimano Ultegra "GS" (long arm-road) rear derailleur has huge chain wrap and cog size capacity that is much greater than stated on the Specifications.

I've combined a 50, 39 & 26 Crankset with the 10 speed Tiagra 12-30 cassette. This provides the range of a Compact with a 12-26 cassette using just the large and middle chainring. The 39t middle chainring is good to 25 mph at a 100 rpm cadence. The 26t small chainring and 30t rear cog combination can crawl up a 20% slope at 4 mph with a 60 rpm cadence.

The chain-wrap limit of the Tiagra/105/Ultegra GS, according to Shimano, is 37. I'm operating safely, with every gear combination, using a chain-wrap value of 42. It is also possible to exceed the 27t Cog size capacity and use a 32t.

The practical chain-wrap capacity, with a correct length chain, of the road "GS" RD allows the big-big combination of 50t front Chainring & 30t rear cog with a little safety margin and also allows the small-small combination of 26t & 12t without any slack in the chain.

I also used a Sram 11-32 cassette with a compact last year and had no issues with a 32 size cog. This may not work on all bikes, YMMV.

http://i289.photobucket.com/albums/ll210/wildcat-bucket/001.jpg

Nice Set up - What FD and Shifters are you using? There's a race in Ontario, every spring- Paris to Ancaster - that mixes rail trail, gravel road, single track and a brutal climb at the end that most will walk. This looks like the perfect setup for speed and final climb.

Thanks for posting

Canflyboy

Good to hear. I just got one of those 12-30 cassettes and I was hoping I wouldn't have to get a new derailleur. I had some problems with an 11-32 with my old Tiagra 9-speed rear derailleur. It nearly worked, but bounced a bit in the big cog. The rear derailleur I'm intending to use now is the Ultegra SS model (capacity = 29), but I'll be using it with a 46-34 crankset, so I think I'll be alright.

Nice Set up - What FD and Shifters are you using?
Canflyboy

I'm using a 105 series FD-5703 front Derailleur and older 5603 brifters. I also installed a system like this on my road bike and used a chain-catcher from K-Edge;

I've assembled the K-Edge Chain deflector for triple, Shimano FD-5703 front derailleur and the Shimano SM-AD15 clamp band for front derailleur (34.9mm size). The three part assembly is pictured below;

http://i289.photobucket.com/albums/ll210/wildcat-bucket/CGpart2004.jpg

http://i289.photobucket.com/albums/ll210/wildcat-bucket/CGpart2002.jpg

I was concerned that the K-Edge Chain deflector needed a braze-on plate to install, but it fits properly on the Shimano SM-AD15 clamp band. On the road bike I'm using the same 50, 39 & 26 crankset, but use a 12-27 cassette and a new 6703 Ultegra "GS" RD;

http://i289.photobucket.com/albums/ll210/wildcat-bucket/CG2011-1.jpg

Good to hear. I just got one of those 12-30 cassettes and I was hoping I wouldn't have to get a new derailleur. I had some problems with an 11-32 with my old Tiagra 9-speed rear derailleur. It nearly worked, but bounced a bit in the big cog. The rear derailleur I'm intending to use now is the Ultegra SS model (capacity = 29), but I'll be using it with a 46-34 crankset, so I think I'll be alright.

Yes the front triple with a 50, 39 & 26t adds 12 units to the chain wrap value compared to your 46 & 34t double. You should have the same outcome and be within the practical chain wrap capacity of the "SS" RD.

There's a race in Ontario, every spring- Paris to Ancaster - that mixes rail trail, gravel road, single track and a brutal climb at the end that most will walk. This looks like the perfect setup for speed and final climb.

Thanks for posting

Canflyboy

Here is a side by side contrast of 50, 39 & 26t triple with the 12-30 cassette a 50 & 34 compact double with a 11-28 cassette.

http://i289.photobucket.com/albums/ll210/wildcat-bucket/image-1.png

The middle ring on the triple is a ideal range and covers 80% of my time on the bike. Almost any cycling in the 10 to 25 mph speed range can be done on the middle gear. The big ring only is needed with descents and faster pace-line riding, but provides 35 mph powered cycling. The little ring is only needed for very steep climbs at speeds less than 10 mph and improves climbing cadence by 40%.

It's a great range for just about any type of riding, including gravel road, light touring and hilly century rides.

nice touring bike drivetrain..

nice touring bike drivetrain..

No.

Loading touring bikes are better off with a 48, 36 & 24t chain-rings using a 110 & 64 BCD crank. A 12-36 cassette with a MTB RD would be needed for hilly routes using a touring bike with enough camping gear for self-sufficient camping in damp weather.

Yes the front triple with a 50, 39 & 26t adds 12 units to the chain wrap value compared to your 46 & 34t double. You should have the same outcome and be within the practical chain wrap capacity of the "SS" RD.

Confirmed!

I put the new cassette on this weekend. I didn't change the chain length or adjust the derailleur cable tension -- just put the new cassette on the wheel and tried it out. The chain length is pushing the limit, but seems to be acceptable (the chain was cut to accept a 12-27). The shifting is outstanding. If anything, it shifts better than it did with the old 105/Ultegra cassette. That may be because of accumulated grime in the hyperglide bits of the old cassette, or it may be that the old cassette was just worn.

I just posted a full review on the Commuting forum (http://www.bikeforums.net/showthread.php/772972-Review-Tiagra-4600-12-30-10-speed-cassette).

barretts, you've mentioned your setups before, and I agree 100% on how versatile the 39 tooth is. While I am intrigued by compact doubles, I really think I will always be a triple fan, especially as I can often have a pannier with stuff on a bike, and then also because I like you, find the middle chain ring to be so versatile for so much of my riding and not having cross chaining.

tks for the charts. Us gearing nerds find those neat.

Your triple gave me an idea. I'm building up a triple and will us it for one race this coming spring. It's a 60 kms point to point done on a cross bike. Country roads, single track, rail trails and steep climb at the end that I (and 80% of others) have to walk. Last year I used a standard compact with an Ultegra 11-28 which was perfect for everything except that final climb.

I want to use a 50/34 chainring, so that means I need a 110 bcd. Sugino makes such a crank. It's 110/74 bcd with a tapered square drive. My set up will be 50/34/26 and an 11/28 in back.

I'll let you know how this works out in the spring

Canflyboy

No.

Loading touring bikes are better off with a 48, 36 & 24t chain-rings using a 110 & 64 BCD crank. A 12-36 cassette with a MTB RD would be needed for hilly routes using a touring bike with enough camping gear for self-sufficient camping in damp weather.

I think what fietsbob is getting at is.........

Its great that your bike can climb a 20% grade at 4mph at 60 rpm - great math - but in a CROSS race, you're better off jumping off and running :)

Whats the gear spacing on that cassette? Given the range, I'd imagine theres some considerable gaps in the gearing - many prefer the tighter gearing gaps of a 12-25 and a cross compact (46/36).

I think what fietsbob is getting at is.........

Its great that your bike can climb a 20% grade at 4mph at 60 rpm - great math - but in a CROSS race, you're better off jumping off and running :)

Whats the gear spacing on that cassette? Given the range, I'd imagine theres some considerable gaps in the gearing - many prefer the tighter gearing gaps of a 12-25 and a cross compact (46/36).

Your statements could be correct, if I was cross racing. I am not. I've used, and would use again, a 44t single chainring if I was racing cross. I would not use a triple. Did U read the prior posts?

Sure did...just seemed like you scoffed at the term "touring", despite describing your bike as such in your signature.

But I digress - I have a race tomorrow......