/ Going compact - maybe...

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Martin W on 17 May 2017

I have made a few alterations to my much-loved Specialized Tricross Sport over the years. The main one being switching to a disc brake at the front, which also required a replacement carbon fork. The improvement in stopping power was undoubtedly worth the money, though.

I've recently been pondering whether to switch to a compact chainset. A play with Excel suggested that I'd only lose the very lowest ratio by changing from the OEM 30-39-50 triple to a 34-50 double. I had an idea that I could experiment by just putting a 34T ring on the triple crank, but that seems to be ruled out by the non-availability of 34T chainrings with either a 74mm or 130 mm bolt circle.

The next least disruptive approach would seem to be sourcing a 9-speed double crankset - either a used Tiagra of the same vintage as the bike, or a modern Sora. The kicker seems to be the cost of replacing the triple STI shifter with a double: I never realised how much those things cost on their own! Would it be wholly daft to try to run the double crankset with the triple shifter, and just use the top and bottom range adjustment screws on the triple front mech to avoid shifting off the rings? Or could I run a double front mech with the triple shifter? I am also unsure of whether I'd need to swap out the BB.

I suppose that the 'proper' way to do it would be to source a whole new drivetrain, such as the latest Tiagra 10-speed. That would obviously cost a fair bit more (although even taking the cheapskate route of just swapping the crankset I would spring some more cash to replace the worn cassette and chain as well). Sourcing the individual components of would would be more or less a complete drivetrain does start to rack the bill up in to three-figure territory (although I was surprised to see that if I shop around I can buy a full 10-speed Tiagra groupset for not much more, which would leave me with a pair of brand new road brakes that I could perhaps sell to recoup some of the cost).

The purist approach would probably be to invoke the n+1 rule and buy a new bike. But I actually really like my Tricross. I built it up myself from the delivery box, and there's just nothing about it that niggles me apart from the occasional lure of shiny new "bits".
Post edited at 11:29
RX-78 on 17 May 2017
In reply to Martin W:

check out: http://singletrackworld.com/forum/topic/triple-front-mech-with-double-chain-rings

seems it depends on how old your set up is, I have used a triple with a double but then my bikes are getting old, just like me.
jrck2 - on 17 May 2017
In reply to Martin W:

My experience of using a triple shifter with a double front mech is that it is possible to make it functional, but it'll never be quite right.
Chris the Tall - on 17 May 2017
In reply to jrck2:

Depends on the shifter - Shimano XT can be switched from triple to double merely by adjusting a crap plastic screw and swearing profusely
Martin W on 17 May 2017
In reply to jrck2:

Thanks, I don't think I'm looking for it to be "just right", I'm really just interested to find out how I get on with a compact double Vs the triple I'm used to. If I decide that I can live without the lowest ratio then I'd be happy to put in more time and money to get a properly fettled setup.
ablackett - on 18 May 2017
In reply to Martin W:

How about try riding up a hill without going into 1st gear. if you can live with that I suppose you would be fine.
Martin W on 18 May 2017
In reply to ablackett:
> How about try riding up a hill without going into 1st gear. if you can live with that I suppose you would be fine.

I've already been doing that! That's one reason why I'm considering taking the next step in that direction.

I spent a few minutes last night costing up a new 9-speed double compact crankset and associated bits. It came to ~£200, of which roughly half is the cost of the STI levers. Obviously that could be cut by buying some stuff eg the crankset itself used (there appear to be some on eBay ATM) and retaining the triple STI lever. But I'd still want new chainrings, chain and cassette.

Going a bit further and upgrading to a new 10-speed compact powertrain would be ~£300. Still a lot cheaper than a whole new bike, which I don't necessarily want anyway.
Post edited at 08:09
Hardonicus - on 18 May 2017
In reply to Martin W:

Just get a new 10 spd groupset and flog the old one on ebay, then your future proofed and for not much more money. Changing to compact has been a revelation, but then I live in a very lumpy part of West Yorks.
Martin W on 18 May 2017
In reply to Hardonicus:

Your rationale is tempting. As is the thought of shiny new stuff, and funky new features like all internal cable routing on the shifters. Likely to be an exercise for the latter part of the year, I think, rather than risk having the bike u/s for too much of the summer.

The only problem with buying a complete groupset seems to be that ones with the crank length I want appear to be in short supply. So I might end up having to buy the components individually anyway, hey ho. (I've also discovered that the 4700 GS derailleur can accommodate up to a 34T sprocket, but no-one seems to do the groupset with that cassette - not sure how much of a show-stopper that really is, though.)

One thing I'm still not 100% sure about is the bottom bracket. All I know about the BB currently on the bike is that it has English threads and a 68mm shell, and it fits the Tiagra 4503 crankset currently on the bike which I believe has a 24mm diameter hollowtech axle. As far as I can tell that BB spec matches that for the 4700 crankset, so I believe that:
(a) the 4700 groupset BB would fit my bike, and
(b) if buying components individually, I might not need a new BB (unless the old one is shagged).
Does this sound right, or am I utterly deluded?
RX-78 on 18 May 2017
In reply to Martin W:

On rereading the thread, why are you going from a triple to compact? I can understand going from a standard double to a compact but you already have the low gears you need with the triple. What is your cassette? maybe get one with narrower jumps in the teeth to give nice shifts and then you might end up using the triple?
r0b - on 18 May 2017
In reply to Martin W:

There's no benefit in changing shifters if going from triple to double; triple front shifter will work fine with a double chainset and you will notice no difference to a double front shifter.
Martin W on 18 May 2017
In reply to RX-78:

A double is so much simpler (and lighter) than the triple, though. And the only way to get narrower steps between the ratios while still getting the same overall spread of ratios would be to go for 10 or 11 speed, which would mean a whole new drivetrain.
Martin W on 18 May 2017
In reply to r0b:
> There's no benefit in changing shifters if going from triple to double; triple front shifter will work fine with a double chainset and you will notice no difference to a double front shifter.

Yes, but...but...shiny new things!!!

CRC have the best price on the Taigra groupset, but for some reason don't list the 175 crank option. The next cheapest is less than £40 cheaper than the equivalent 105 11 speed groupset. Shiny new things!!!

But not for a few months yet, whatever I eventually decide to go for.

Thanks to everyone for the input and ideas.
Post edited at 22:14
Martin W on 02 Jun 2017
Brief update: I went for a donder on some of the steepest roads I know locally the other night and there was one that I couldn't get up in anything other than lowest gear on my triple. Hence I am going to go for the 11-34 cassette. (I can always swap it out if I find myself getting better at climbing at some later date.)

Vanilla Bikes are now showing the Tiagra 10-speed compact groupset as due in next week, available with all the options I want and at a stonking price
Rigid Raider - on 02 Jun 2017
In reply to Martin W:

The Tricross is a comfortable but unexciting bike. It's also pretty heavy so the triple chainset suits it well in use as a commuter or tourer, which is what I used mine for until I sold it.

If you want more excitement sell it and buy a naughty little carbon road bike with a compact double and an 11-28 or 11-32 cassette. You won't regret it.
ads.ukclimbing.com
Martin W on 04 Jun 2017
In reply to Rigid Raider:

I don't recall mentioning anything about wanting more excitement. And I'm not sure how well a carbon road bike would cope with some of the landrover tracks my Tricross takes me down. At ~£1,000 minimum for the road bike compared to <£300 for the upgrade...sorry, I'm out!

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