# 10 speed crankset and 8 speed drivetrain compatibility



## difficult (Aug 28, 2008)

Looking to do some upgrades to my bike and wanted to see if anyone else has tried this out. 

Currently I have an 8 speed Shimano drivetrain and I'm looking to upgrade my crankset to a new, lighter one, possibly Sram Rival. What I'm seeing is that most of these models that I'm looking at are 10 speed. In order to avoid excessive cross-chaining and compatibility issues I was wondering if anyone else had experience running Sram 9 speed chains on an 8 speed drivetrain. 

On the Sram website all of their 9 speed chains are described as 8/9 speed compatible. 

I am thinking that a 9 speed chain would run fine on an 8 speed drivetrain and not be too wide for the 10 speed cranks. 

Does anyone have any advice to offer?

I should also mention that I plan on upgrading the drivetrain to a 10 speed in the next year, so buying an older model crank is not my preferred option.

Edit: maybe using Siri to dictate my posts is a bad idea?


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## Randy99CL (Mar 27, 2013)

Will likely work just fine.

The FSA cranksets I have are marked 9/10 compatible.


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## bikerjulio (Jan 19, 2010)

A 9-spd chain will work very well on an 8-spd drivetrain. Better than an 8-spd chain in my experience.

Better shifting and quieter.


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## pmt (Aug 4, 2009)

Sure, no trouble at all.


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## Kontact (Apr 1, 2011)

Any crank will work fine - 9, 10, or 11. I'd stick with 8 speed chains because they are tough and cheaper and work fine with those cranks. KMC comes to mind.


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## danl1 (Jul 23, 2005)

If the crank is 10v, an 8v chain might rub in the crosses earlier, and could potentially shift just a little wonky. They tend to run the rings on a 10v crank a little bit closer.

But since there's no problem running a 10v chain on an 8v rear (I'm currently running one on a 6v freewheel, for reasons not worth mentioning) you have no problems.


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## Agent319 (Jul 12, 2012)

I have found that drivetrain on bikes seem to be accommodating. I have a 9speed cassette, an 8 speed crank, and 10 speed chain and it cycles through the gears smooth as butter. I understand the 8,9 is compatible and I came across a new KMC 10 spd chain real cheap when I needed a new chain and thought I'd try it. It worked so I haven't taken it off.


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## brucew (Jun 3, 2006)

I wore out the middle ring on one of my commuters. Its 8-speed Sora crank now has a 10-speed 105 middle ring. Everything else remains 8-speed. No problems.


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## Kontact (Apr 1, 2011)

danl1 said:


> If the crank is 10v, an 8v chain might rub in the crosses earlier, and could potentially shift just a little wonky. They tend to run the rings on a 10v crank a little bit closer.
> 
> But since there's no problem running a 10v chain on an 8v rear (I'm currently running one on a 6v freewheel, for reasons not worth mentioning) you have no problems.


8 speed chains have more internal bearing surface to their rollers so they last longer, as well as being 1/3 the price of a 10 speed chain. And many ten speed cranks are spaced the same as older cranks to increase chain crossover clearance. 

"Might rub", not "does rub". My experience is that 8 speed chains don't rub any more than anything else, so I'm not sure why we need to worry the OP with a _theoretical_ rubbing concern while encouraging someone with a Sora bike budget to buy expensive, shorter lived chains.

Especially when the added "rub" an 8 speed chain has over a 10 is .5mm, or less than the variance in cassette location from one brand of freehub to another, or the amount that any two frame's chainlines might vary.


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## danl1 (Jul 23, 2005)

Kontact said:


> 8 speed chains have more internal bearing surface to their rollers so they last longer, as well as being 1/3 the price of a 10 speed chain. And many ten speed cranks are spaced the same as older cranks to increase chain crossover clearance.
> 
> "Might rub", not "does rub". My experience is that 8 speed chains don't rub any more than anything else, so I'm not sure why we need to worry the OP with a _theoretical_ rubbing concern while encouraging someone with a Sora bike budget to buy expensive, shorter lived chains.
> 
> Especially when the added "rub" an 8 speed chain has over a 10 is .5mm, or less than the variance in cassette location from one brand of freehub to another, or the amount that any two frame's chainlines might vary.


All fair commentary. Perhaps better if I phrased it as "If you do experience any problems, a narrower chain will address them."

Except maybe for the last bit. It's not exactly about chainline or cassette location. Trigonometry is a such that a little difference in available space between the little ring and the big amounts to a multiplied difference in chainline / cassette location for the small-small cross. A 0.1mm space difference between the rings (especially on a compact) can give rub-free access to an additional two (and occasionally three) cogs. We weren't strictly talking about ring spacing, but plate thickness has exactly the same mathematical effect.


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## difficult (Aug 28, 2008)

Thanks for all of the great feedback. It seems like the best option would be to purchase the crank and then measure and compare with the current one. This way I can choose the best chain for the situation. 

Knowing that folks here have had success with similar mixed systems makes me more confident in going ahead with the purchase. 

Thanks again!


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## Kontact (Apr 1, 2011)

danl1 said:


> All fair commentary. Perhaps better if I phrased it as "If you do experience any problems, a narrower chain will address them."
> 
> Except maybe for the last bit. It's not exactly about chainline or cassette location. Trigonometry is a such that a little difference in available space between the little ring and the big amounts to a multiplied difference in chainline / cassette location for the small-small cross. A 0.1mm space difference between the rings (especially on a compact) can give rub-free access to an additional two (and occasionally three) cogs. We weren't strictly talking about ring spacing, but plate thickness has exactly the same mathematical effect.


That .5mm I mentioned is chain side plate thickness, as the total width difference from an 8 speed chain to 10 is 1mm total. I agree that little differences do add up, but the chain thickness is the smallest of the important variables to angled chain rub.


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## danl1 (Jul 23, 2005)

Kontact said:


> That .5mm I mentioned is chain side plate thickness, as the total width difference from an 8 speed chain to 10 is 1mm total. I agree that little differences do add up, but the chain thickness is the smallest of the important variables to angled chain rub.


right, meaning that it's functionally equivalent to a .5mm difference in ring spacing. I don't have the numbers handy, but I'm pretty sure the difference between dedicated 8v and 10v cranksets is more than that. This isn't really about "adding up", it's about "multiplying out." It's a trigonometric problem.

The difference in the radius between a 34 and a 50 ring is a bit more than 3cm, while the distance from where the chain leaves the ring to where it hits the cogs is the chainstay length - 41 cm's or so. in other words, the interference at the rings is multiplied by a factor of approximately 12 or 13 out back. So that "meaningless" .5 mm's in front will account for perhaps as much as 6mm difference in rub clearance in back.

As a practical matter, it's slightly less than that. Due to the chain leaving the small ring at a tangent, that 3cm is really closer to 5 - but I'm not near enough to a compact to measure it right now, and that math is slightly more bothersome than I want to deal with at the moment. But even at 5cm, it's still an 8x multiplier over the length of the stays. 4mm is more than a full cog's difference. 

In comparison, a .5mm difference in chainline would change the impact at the rear by slightly less than .5mm. The sideplate thickness (or the ring spacing, if you prefer) is actually the most important factor in getting the rubs out.


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## Kontact (Apr 1, 2011)

danl1 said:


> right, meaning that it's functionally equivalent to a .5mm difference in ring spacing. I don't have the numbers handy, but I'm pretty sure the difference between dedicated 8v and 10v cranksets is more than that. This isn't really about "adding up", it's about "multiplying out." It's a trigonometric problem.
> 
> The difference in the radius between a 34 and a 50 ring is a bit more than 3cm, while the distance from where the chain leaves the ring to where it hits the cogs is the chainstay length - 41 cm's or so. in other words, the interference at the rings is multiplied by a factor of approximately 12 or 13 out back. So that "meaningless" .5 mm's in front will account for perhaps as much as 6mm difference in rub clearance in back.
> 
> ...


I don't understand your post. The "rub" I thought we're discussing is when the chain rubs the big ring because it is cross chained from the small ring to one of the smaller (11, 12, 13t) cassette cogs. The added clearance a narrower chain gives is used in the 5 or 6 cm between touching the big ring and engaging the top of the small ring. Changing that chain width is not going to change the geometric arrangement of 34x12 combination, just how close that combination puts the chain to the the 50 ring. Trig doesn't play into this when the only variable is chain sideplate width.


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