DArthurBrown

I've tried reading the Shimano spec manuals but can't find what I am looking for.

I'm considering upgrading the crankset on my road bike. Right now I've got a 9 speed setup. I have the option of getting a new Tiagra crank for dirt cheap.

Is the triple chainring spacing (the space between chainrings) the same on a Tiagra crank and 105 crank.

I know the 105 chainrings are slightly narrower to accommodate a 10-speed chain.

As far as I can tell, the spacing between any Shimano chainrings should be 5 mm, but my LBS said the spacing on 10-speed cranksets is narrower. In the event that I end up upgrading to a 10 speed setup, I'm wondering if I could simply put 10-speed chainrings on a Tiagra crank and have an identical setup to a 10-speed crank.

Jeff Wills

Yes. The difference in spacing between 9-speed and 10-speed is built into the chainrings, and is small enough that you won't notice the difference if you use the "10-speed" chainrings with your 9-speed chain.

DArthurBrown

So, just to clarify, there is no difference in the crank spiders themselves, only in the chainrings?

DMF 

Whoa there, cowboys! The spacing is the same. That does not mean that the chain rings are interchangeable! Spacing is achieved by a combination of ring thickness, mounting surface location, and tooth offset. The wrong combination can change the spacing from e.g. 5-5 to 7-3. Furthermore, ring sets are designed to have complementary shifting aids. Mix those up and even if the spacing is the same the shifting may suck.

See my thread nearby for more details.


Now, all that said, the result of mix-and-match might be acceptable to you. There are very different levels of expectation.

DArthurBrown

Well, I was hoping to have an identical setup, meaning that just by swapping chainrings I could exactly duplicate 10-speed spacing. Sounds like that just isn't possible, or is at least a huge hassle.

My reasoning was that Tiagra cranks are only about 30g heavier (according to Shimano) than an equivalent 105, but are often $100 cheaper. Both are significantly lighter (.5 lbs) than what I have now. Since my drivetrain is 9-speed anyway, and I'm perfectly happy with it, I don't intend to replace the shifters or anything else unless it wears out.

I guess the follow-up question is: What issues would a 105 crank give me if I have an otherwise 9-speed drivetrain. I know people say it works "fine". But if the teeth are narrower, they'll almost certainly wear faster, and the Tiagra front der I have is designed for a 9-speed crank as well...

DArthurBrown

Follow-up:

Shout out to Peak Sports in Corvallis, OR for helping me sort this out. They went the extra mile to get some info for me, and have secured my business indefinitely.

A 10-speed crank can be made to fit 9-speed gearing with spacers between the spider and chainrings. In order to get the correct tooth-to-tooth spacing, you must then use 9-speed rings.

A 9-speed crank cannot be made to exactly fit a 10-speed crank, no matter what you do. I t can be made close, but not exactly the same.

This whole deal has vindicated my bike stuff buying rule of thumb, which is buy for what you have, not for what you think you can make work "okay."

EDIT: I should also mention that according to the Shimano rep, the spiders are different between 10 and 9 speed. The chainrings are also different. The effective chainring spacing is therefore dependent on both.

DMF 

Which *may* be true if the 10-spd rings are thinner rather than thicker (assuming 0 tooth offset). The problem is that these spacers are mythical beasts. Unless you're a better man than I you can't buy (in half-dozen lots) exactly what you would need.

Now, as to tooth dimensions, if you're describing what they told you correctly, then what they told you is wrong. The *inside* dimensions of 9-spd and 10-spd chains are identical. Therefore teeth from either set will fit the chains identically. However, tooth shape is also one of those shifting aids I mentioned, so it's not a non-issue.

All that said, your conclusion is excellent. Buy for what you have, not for what you think might work. Well said.

Kontact 

This thread is full of misinformation. There is no functional difference in chainring spacing and virtually any speed chain will run on virtually any speed crank without issue.

urbanknight

Well, I just put 10 speed chainrings on a 9 speed crank and the chain rubs the outer chainring when I’m in the middle ring and two smallest cogs. So... anybody know what size spacers I need and where? I’m going to visually inspect the chain line to try and estimate, but wouldn’t mind if someone here has an experienced recommendation.

Andrew R Stewart 

I will tolerate some cross over chain rub (on the inside of the large ring when the chain is on the small ring) as I avoid these combos for any amount of actual use (as opposed to "passing through" that combo along the way to a different combo).

To further confuse the mixing and marching of front of drivetrain parts is the presence (or not) of the front shifter's trim features. We see a lot more chain rub on the cage with older set ups that have shifters lacking trim capability then with shifters that have trim points. Andy

alcjphil

A lot we don't know here. Did you change anything other than the rings? What size are the large and middle rings? The larger the difference in tooth count between the large and middle rings the more likely it is to have chain rub against the outer ring. If you are still using a 9 speed chain the more likely it is to have chain rub. The shorter your chain stays the more likely it is to have chain rub. If you only changed the chainrings it is more likely that you will have chain rub

urbanknight

Thanks. You actually have me thinking. It's a tandem (so not short stays, but a wider rear spacing) and I don't know if the rear BB is the stock 123mm width or not (I had to replace the front one, and 118 was the closest I could get), so maybe measuring that would give me a clue. FWIW I changed the 52/42/30 to 50/39/26 while keeping with a 9s chain, and I'm sure just a little spacing on either chainring will make it work fine. As Andrew mentioned above, I don't make a habit of cross chaining, but still prefer to get proper spacing.

oldbobcat

Instead of doing this piecemeal for negligible or questionable results, I suggest saving your money for a complete Tiagra 4700 kit. It will shift like 11-speed 105 but for 10-speed, and you won't have to replace your rear wheel.

Its major advantage is, it's the slickest shifting 10-speed system Shimano ever made. Its disadvantage is, except for the crank, cassette, and chain, none of it is compatible with anything else Shimano ever made.