earlethomas
I'm converting a '86 Trek Elance 400D. The original drivetrain is 52x40  by 6spd freewheel. Way too high in the front. I'd like to move to 36x22 if that's possible. The new 650b wheels are spec'd 10spd. I'd also like to swap out the downtube shifters for triggers.

I have some sram shifters that are 8x3, bought for another project but unused along with an sram rear derailuer, med cage. I could buy a 8 spd cassette and spacers? 

Can anyone help me make a meal out of this stew?

thanks
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clarksonxc
I have used an 8spd cassette on a wheel with a 10spd freehub body.  I cant remember which spacers were needed (if any), but it is definitely compatible.
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ljsmith
If I recall correctly, an 8 speed cassette has much thicker gears, so it actually takes up the same space as a 10 speed cassette.  So I don't think you need any spacers.  My only question would be whether the rear wheel fits in your frame.  I assume the new rear wheel has 135 spacing, but I would guess you frame has 130mm or less being that it is a 6 speed.  But if its steel you can just pull apart the dropouts and jam the wheel in I suppose.  
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BluesDawg
Most 8-10 Sram and Shimano drivetrains all use the same freehub dimensions, so you should be fine. There were a few 10 speed specific freehubs, but at worst, that would mean you'd need to add a spacer to the freehub before installing the cassette.
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babylou
I think 6 speed is 126mm spacing.
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HollyBoni

8-9-10spd cassettes are the same in terms of overall width, some Shimano 10spd road cassettes require a spacer. You won't need any spacers to run an 8spd cassette if the freehub is listed as 10spd.

But as babylou said the rear of that frame is most likely 126mm. If the new wheels are 130mm you can spread out the rear and you will be fine (if you want to do some research there are millions of forum threads about this all over the internet).

However if the new wheel is 135mm and your frame is 126mm personally I would not push it that far even though it's steel. 

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earlethomas
Thanks to all for your replies. My wheelset is spec'd at 130mm chainstay spread and 8 to 10spd cassette, so I'm good (the old Trek is 130mm rear spacing). Next concern is a crankset The BB is old school road, 68 x 24 I think and I'm looking to reduce my gearing from 52/40 (way too high) to something much lower, say 38/24. Any recommendations? I've been looking at Sram and Middleburn, no love yet. I'd rather avoid Shimano if at all possible. I have an Sram x4 medium cage rear derailuer which could be brought into the mix.  Thoughts? 

Thomas
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HollyBoni

If the bottom bracket is 1.370" X 24 tpi 68mm that's english thread, so you can basically use any modern threaded BB and crankset. 

38/24 is mountain bike gearing, and for that you will need a mountain bike front derailleur too. Sadly I don't know of any new 8 speed MTB cranksets with that gear ratio. 8spd is kind of dead so new components are rare. 


For derailleur compatibility check out the chart in this article:

http://blog.artscyclery.com/science-behind-the-magic/science-behind-the-magic-drivetrain-compatibility/

However SRAM in the past made shifters that were compatible with Shimano rear derailleurs, so check the exact model you have. The X4 rear derailleur most likely uses the 1:1 pull ratio. 

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nalax
What are your plans brake-wise with this bike? 700c calipers don't match up with 650b rims in most cases.
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drwelby
Rivendell sells the Silver crank in 24 x 38. Also take a look at the Sugino XD. They sell a version in 26 x 40. Or you could buy the bare cranks and get the specific chainrings you want.

Any 110x74 bcd crank would work with either short bolts or a chainguard on the outside. Lots of options on Ebay.
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earlethomas
Thanks again, folks...to answer Nalax, I'm looking at some Tektro long reach calipers, they are widely available and will fit. As to Hollyboni and drwelby, I am looking into your info, thanks so much...

thomas
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breadfreak
Regarding crankset, have a look at the Spa Cycles TD-2 triple we discussed in this thread http://ridinggravel.forumchitchat.com/post/new-subcompact-crankset-option-9469036 - all the details are there. 74mm inner BCD will take you down to 24t
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