1x10 or replace spider?

General CX/MTB
1

I was upgrading my cranks on the TT bike to a wireless SRM unit yesterday with the intention of transferring the current wired SRM cranks to the CX bike using compact chainrings (crank has 130BCD outer and 110 BCD inner). Unfortunately noticed one of the 130BCD holes has a hairline crack…

I have already emailed SRM Oceania and I could get a wireless FSA SRM spider for 50% retail to replace the wired FSA SRM spider. But I’ve been thinking today that another option would be to convert my CX bike to 1x10 using something like a Wolftooth 110BCD chainring and bolt a bash guard if necessary to the outer 130BCD.

Questions about such a conversion.

Is my current Shimano 5600 105 rear derailleur spring strong enough or should I replace the front derailleur with a chain guide or just keep the front derailleur? Will the 105 shifter mind not have the gear cable in place or rattle away? What size front chainring is ideal with a 1x10 set up and 12-25 cassette if there is an ideal?

Or should I just bite the bullet and and use this as an opportunity to upgrade the crank to wireless?

2

My thing with 1x10 and a 105 rear is that it will give you bugger all range if you want to gravel grind/light tour it or any thing other than race cx.
So either get the 50% off srm and sell it( I don’t think power helps in cx much at all)
Or go an clutched rear that can handle more range and fix the slap problem and run 1x10

But hey that’s just my thought?

3

If adventurous, you can rebuild the 105 mech to a stronger spring position for the cage. That plus a locked out mech as a guide and maybe a BBG bashguard for the outer (PM me and we can both order one, I need another) would be fine unless you do a Jeff Curtes and jam your chain under your keeper/catcher.

Your mech is rated to 28T max rear IIRC, you may go further if you have a long hanger. 6700A would do 30T.

But realistically, even a 12-25 with a 38-42 is going to be fine for CX racing. Any lower and you should be running. For non world cup racers, I’d probably err towards a 38. Can you spin out a 38-11 (93") at the end of a race?

If you want clutchy, you’ll need a SRAM RH shifter (last gen Force would be nice, but apex will work) and an X7 Type 2 to get out of it cheapest.

4

And very much appreciated!

I can see power during the race is pointless and find it is the same on the velodrome, but do find it invaluable reviewing the data afterwards…

Given how 2nd hand SRM’s have dropped in price I’d only expect I break even if I got the replacement as it would then be a new spider but my old less popular K-Force arms. So would only bother if I use the replacement.

I’ve been told if the zero offset is still stable (and even with a cracked spider it often still is supposedly) I could just keep riding it 2*10 till the offset starts playing up?

5

Thanks AL9000. More to consider!

I already have a 42 inner ring, though Stronglight CT2 may not be suitable for CX. If I go down this route I’ll be in touch about the bash guard.

6

Don’t think you really need clutch for CX. I was ‘racing’ on a 39 ring to a 11-32 cassette. Means you can sit on some little climbs and keep traction. But it also sounds like you’d have more power than me.

could just get a 9 speed shadow slx/xt in medium cage. They have better spring tension then whatever cassette you want. Pity they don’t come in short cage.

And a n-gear jump stop is lighter than a front mech and with some mods works well with a guard.

Main plus of having a bigger range is probably not racing but other stuff as dayne said.

7

Yeah sorry I meant the heavy shadow mechs not the clutched SRAM stuff,
I don’t think power is a bad thing in racing I just think that it’s not real accurate in a cx race because the course is so different and has so many variables but if you already own it I guess why not.

8

I ran my CX bike with a 5600 RD, 27/12 cassette and a 42T chainring. Worked fine but you do notice the bad chainline at the extremes.

I also had a Paul Chainkeeper so I can’t say for sure that the RD spring tension was enough to keep the chain on without it.

I’ve also run 1x8 and 1x9 setups with Shimano 6401 RDs and never had any chain jumping problems, but they weren’t ridden off road.

9

Derailling (punpunpun) the thread for a second, how big have you gone on the rear cassette with a 6401 rd?
I’m thinking of running 1x with a 32 or 34 max cassette.

10

It would’ve been a max of 25T I think, maybe 27T.

11

As AL9000 alluded, I also saw on one of the sites for chainrings (possibly Wolftooth site) had instructions on how to adjust the spring to increase tension… So sounds like a worthwhile mod.

Was mainly contemplating just racing, but pictures from the gravel grinds do make them look appealing! I just got a reply from SRM USA (I emailed all the service centres to see what they would offer in regards to swap / fixes) they would replace the whole unit including PC7 and all accessories for only a few hundred more than to swap just the spider from NZ! Will cost a little more in postage as I need to send my spider and PCV (I have a few so would send in one in poorest condition) but still far better than retail and all new with full warranty! Problem is clutch in the car is on the way out so trying to save for this…

12

Dam cars.

13

Agreed. Barely drive mine but it seriously impedes my bike budget. Rego is due next month too!