9 and 10 Speed Compatibility

greymarauder71

I am sure this Newby Question has been covered before but I couldn't find where so...

I have an SRAM GXP 10 Speed 42 tooth single front ring. Can I use an 8 or 9 speed rear cassette with it or is there an actual difference in chain spacing etc. I am building my first bike from scratch I have been offerred a PG950 cassette...

Cheers

Ouija

10 speed chains are narrower. However. A 9 speed chain should work on the front ring just fine so long as the 42 outer and the next ring in aren't sat closer together than is normal for a 9 speed. This, however, tends to be decided more by the thickness of the spider on the crank than the actual rings themselves. If they do sit close enough together that the chain rubs agains the outer ring when on the inner/middle ring you can easily space the outer a fraction of a millimeter further apart by cutting some helicopter tape into washers and putting them around the bolt holes in the spider before bolting the ring on.

greymarauder71

Thank you so much for clearing that up. I only have a single front ring so I guess that should not be a problem. Cheers.

njee20

Helicopter tape washers won't do a damn thing anyway!

It'll be fine. Not sure I'd be using a ramped 42t ring as a single ring though.

greymarauder71

Thank you again. Were you unsure of the 42 ring due to ratio or something else...?

cooldad

Both I would think. Pretty useless for most mountain biking, and due to it being ramped, which is to aid shifting.

Ouija

njee20 wrote:

Helicopter tape washers won't do a damn thing anyway!

Ever tried it? I imagine not.

The Rookie

Just to clarify, as a single ring set up, the external chain width is irrelevant (8,9 & 10 have the same internal width)and so even if ouija's post is right, it has nothing to offer you.

greymarauder71

I understand the ramped issue helping the chain to 'slide off'- maybe a chain guide will solve that? As for the size of the ring surely it is the ratio of the front ring to the rear ones that counts, not the actual size of the it? James

jimothy78

greymarauder71 wrote:

As for the size of the ring surely it is the ratio of the front ring to the rear ones that counts, not the actual size of the it? James

Yes, but given that there's very limited scope for changing the sizes of the rear ones (I think the greatest available spread for 9 speed cassettes is something like 11-36T), using such a large chainring as the only one up front is very unusual. Most people would use something between 32T and 38T for 1x9.

Lets say you use your maximum 36T sprocket at the rear with your 42T ring. This is your easiest gear, but is only the equivalent of using a 30T sprocket with a 36T ring, or 27T sprocket with a 32T ring (that's not far off the middle gear of a standard tripple ring setup - so it's going to be hard going on any real climbs.

The Rookie

^^^This I wouldn't see myself getting up many hills with a 42/34 (34 is the largest avaialable in 9 speed bar a few exotica), in fact my 1x9 MTB runs a 32T mated to 11-34 which is just the right spread for me for most places I ride.

njee20

greymarauder71 wrote:

Thank you again. Were you unsure of the 42 ring due to ratio or something else...?

As said, for both reasons. The chain retention will be worse because of the ramps, and that's quite a tall gear.

greymarauder71

I see your point. Using my pitiful logic I looked at single speed MTB and the ratio they seemed to use a lot was 36 - 18. I then figured a 42 - 21 would be the same, and thus an 11 - 32 cassette would place a 21 rear cog (or something close to it) in the middle somewhere, giving me some variation each side of that. Where did I go wrong with this chain of thought (no pun intended)...

And thank you for all of this info; if I had found this place earlier I could have saved a lot of hours studying the different headsets and BB spacing! James

Chunkers1980

It is in the percentages. So frinstance, 10-11t is 10% more. To get the same at 30t, you need to go from 30-33t, 3x more teeth to get the same percentage.

The Rookie

greymarauder71 wrote:

I see your point. Using my pitiful logic I looked at single speed MTB and the ratio they seemed to use a lot was 36 - 18. I then figured a 42 - 21 would be the same, and thus an 11 - 32 cassette would place a 21 rear cog (or something close to it) in the middle somewhere, giving me some variation each side of that. Where did I go wrong with this chain of thought (no pun intended)...

Single speeders get off and walk on longer steeper hills, geared riders ride up, 2:1 is a common compromise, but as in all things the compromise means it doesn't work all the time, as the majority of riding is on the broadly flat SS gear up enough to make it tolerable and accept walking up longer steeper hills.

Ouija

The Rookie wrote:

Just to clarify, as a single ring set up, the external chain width is irrelevant (8,9 & 10 have the same internal width)and so even if ouija's post is right, it has nothing to offer you.

I realize that now. But he didn't state a single ring setup in his original post.

As for the other thing. I just thought it slightly odd that someone would think that washers can't be used to space things further apart. If you have tried spacing rings further apart (i did on two old 8 speed bikes i had with narrower 9 speed triple ring cranks) you'll know you can't find metal washers that are thin enough or have a hole wide enough, paper washers come in thin enough sizes to work but disintegrate in the wet, hence the DIY option of making your own washers out of helicopter tape to space the rings the tiny fraction of a millimetre apart needed to allow for the differences in chain widths.

cooldad

Ouija wrote:

I realize that now. But he didn't state a single ring setup in his original post.

greymarauder71 wrote:

I have an SRAM GXP 10 Speed 42 tooth single front ring.

Ouija

cooldad wrote:

Ouija wrote:

I realize that now. But he didn't state a single ring setup in his original post.

greymarauder71 wrote:

I have an SRAM GXP 10 Speed 42 tooth single front ring.

He said "ring", not crankset. Which suggests he was trying to fit a ring to an existing crankset (with possibly other rings on it).

greymarauder71

The percentage answer makes it clear - thanks. I have a couple of rings so will try out the 42, and work my way down until I get something that works across a range that suits me. I will add a chain guide to combat the ramped teeth, and start off with the 950 cassette as I have it already(even though it did not get a great review)... I'll post what I end up working with.

greymarauder71

Doh, ok - get it now. Thanks for taking the time to explain.