Tuesday, August 18, 2009

Reader Question: 1x9 dual bash guard setup

Does anyone have an answer to this +1lap reader's question?

Hello. First off let me say I really like your website. Now I have a question. I have a stock Truvativ Touro 50/36 compact crankset with a 68x108mm BB and a 45.5mm chain line (?). And a 12-26T 9-speed cassette. I'm leaning towards a 40T chainring.

I'm trying to get the straightest chain line for this setup. Should I get a 68x107mm and run the chain ring on the outside (I'm adding 2 bash guards) or get the 68x113mm and run the chain ring on the inside?

Also, assuming I'll need chain ring bolts for a triple crankset, what size spacers? I'll be getting 2 42T BBG Super lights. Do people normally get bash guards 2T bigger? Obviously this is all new to me. I bought a 54cm Moto' Fantom CX for my introduction to cyclo-cross. Thanks for your time and expertise.


Shawn Small said...

I have been running 2 chainguards for years now with CX and have never dropped my chain once. I am more of weight weenie though and prefer a carbon set-up.

Unknown said...

If you use a bashguard on the inside, you won't have the choice of running the chainring on the inside, so you have to put it on the outside. I run 2 BBG ultralight 42T bashguards with a 42tooth chainring. You will need to get spacers as thick as the crank spider so that you have the bashguards equally spaced around the chainring. I ran this with a 9-speed cassette on a Phantom Cross last year with no rubbing issues. Get the 42t instead of the 40t chainring.

Matt Surch said...

As an ex downhill mtb racer, I understand the appeal of two guards sandwiching the ring. Its a great set-up in general. But for the cross bike this seems overkill in a sense. Yes, I see how two carbon guards are really light. But the chainline is going to suffer in my mind...perhaps I am mistaken. The ring should fall in the centre of the cassette; if this is achievable, great, but I'm thinking this is unlikely. Again, I may be mistaken. Rather than fuss around so much, why not run a chain device off the seat-tube? The Third Eye device is pretty good, and the new Paul's Chain keeper might be an option with some simple modification (remove outer 'plate' with dremel). Yes, the latter option is likely heavier than a carbon guard, but the upside to running just the single bash guard is that you are less prone to mud and debris fouling the system.

I personally use a 42 with a Salsa Crossing Guard, and an old Shimano 600 front derailleur funcitoning as the guard. I have not dropped my chain with this set-up since I set it up last year (about 6 races and lots of other riding on it).

Matt Surch said...

Great site, I dig it.

I just lost my first response, so here is a shorter version.

Two plates seems like overkill. If the chainline can work, great, nice clean set-up. Proper chainline seems unlikely. I may be mistaken.

I suggest considering a Third Eye or modifying Paul's Chain Keeper to cover the top of your ring and chain. Derailing at the bottom of the ring only matters if it also derails at the top. A good guide up there will keep that from happening. The advantage, chainline aside, is the reduced potential for mud and debris fouling the system. Two plates always packs up.

I personally run a 42 ring with a Salsa Crossing Guard and an old Shimano 600 front derailleur. I have had zero derails in a year. This combo is not light, but it is cheap and cheerful. It is a similar set-up to what many have and continue to use on mountain bikes.

Urethane said...

I would concur with Matt. I originally bought two guards and was setting up the sandwich approach but the chainline and excessive hardware were issues for me once I got it setup. I reverted to a single outer guard with a third-eye on the inside and am into my second season with this simple setup with 0 chain drops. I race in Colorado where it is extremely bumpy at times and while I can hear the chain bouncing all over the place it never drops...very effective solution.

KidCog said...

I am running the same set up. 2 40t BBG bashguards and a 39t chainring. Get old school sugino triple bolts if you want it set up right (get them from jensonusa). I found that with a standard road bb and a little grinding down of the inner chainring you don't get any chain noise/ grinding. The standard road bb is good because you get nice q-factor. I am running this on a kona Jake the snake if that means anything also