Grouperdawg

I just bought the giant advanced revolt 2 with the grx mix and praxis crank 48-32 and 11-34 cassette

I bought a hed Ardennes plus from a friend at a good price and I put conti 5000s on it

This bike will serve a few purposes, one is a road bike for my son to ride with me on pavement. The second is a gravel bike every so often for me to ride, probably mostly gravel roads and fire roads. Maybe some light single track. The third is a back up road bike if mine is in. I’ve never ridden gravel before just road and MTB

Im a little worried about chain rub , the shop where I got it worked a while on it and still rubs the one cog below the big big.

I have a friend with a brand new Ultegra 50-34 that I can have and not sure if it would fit ? I know I would need a new bottom bracket at
minimums

Wondering if it does fit should I replace praxis with ultegra , is the easier gearing that big a deal on gravel ? Not sure how much climbing I’ll do but my current road is sram 12 speed with 11-28 cassette but I think a 48-35 up front. When I do mountain climbs I’d like more on that bike but that’s only a few times a year at most

Should I replace with an 810 crankset if can find one ?

If I want to add a power meter should I take that into consideration before replacing the crankset?

Thx for any help!

mstateglfr 

Chain rub isn't due to the crank, its due to the drivetrain needing to be adjusted.
I have 2 praxis zayante cranks- a 50/34 and 48/32. Just like any other system, when there is chain rub, I adjust the FD and its gone.

In general, gravel road riring benefits from smaller chainring sizes. This is in part because a larger tire effectively changes the ratios so a 32 ring on gravel with a 40mm tire is like a 34 ring on pavement with a 28mm tire(those numbers are just for visualization).
Slightly easier gearing for a gravel bike really is beneficial for most. Between larger tires and a looser slower surface, slightly easier gearing helps.

Use whichever crankset has the gearing that you want for the highest % of riding time.
As for power meters, 4iiii can fit their power meter to the left arm of either crank.

Grouperdawg

Great info thank you

msu2001la

When you say "chain rub", are you talking about the front derailleur rubbing on the chain when you're in the big-big or small-small combo? If so, a new crank isn't going to solve this problem. As mstateglfr mentioned, this is a derailleur adjustment issue. You should be able to adjust the FD so that it doesn't rub on either end of the spectrum.

Unless there is something specific about the Praxis crank that you don't like, I'm not sure there's anything to be gained from swapping it to an Ultegra crank. Your bike has a BB86 pressfit bottom bracket, so the Shimano crank should work. I'd just run whichever crank gives you the best gearing - with either you'll need to adjust your FD so that it doesn't rub.

Grouperdawg

Yes, the shop worked on it for a while and it helped but never could get rid of it….my guy here also worked on it but no luck

dwmckee

If the chain is rubbing the side of the large chain ring when in higher gears on the small front chain ring it could be due to a chainline problem. GRX cranks are spaced outward an additional 2.5mm compared to most regular cranks to eliminate that rub and give you better overall shifting performance with clearance for wider tires. An Ultegra or most other cranks will not be set as wide as a GRX crank so may be more likely to have chain rib against the large chain ring wnen on the small ring and in higher rear gears.

Grouperdawg

Ok, I found this same thing on a google search today as well as on another forum for that specific bike. If this is the case not sure why they put the praxis on in the first place that makes no sense

Motorazr

I have a 2020 Specialized Diverge with a Praxis Alba M30 48/32T crankset and a Sunrace CSMS1, 11-34T cassette. I just now tried cross-chaining from the 32T (small, inner) chainring to the 11T (smallest, outer) cog and, indeed, the teeth from the idle, large 48T chainring do lightly tug at my chain. On the other hand, I always avoid such cross-chaining and so this is zero problem for me. Though I shouldn't, I do sometimes cross-chain the other way (48T chainring to 34T cog) and that works just fine. I don't see an issue here.

Grouperdawg

Not sure if you read my original post , but it rubs one cog below the big big. I had a third guy work on it today and we got it a little better. I’m no mechanic but each subsequent guy was confident the others didn’t no what they were doing until they themselves tried. I’m not sure if it will go away completely with three different shops getting the same result: I’ll live with it for now and do more research maybe upgrade to the grx at some point idk. Great bike otherwise

unterhausen

I read that and really don't know what it means. It rubs on the crank? It rubs on the front derailleur?

I think that's a chainline problem if not an issue with rear triangle alignment. Does the praxis have a wider chainline? Seems unlikely.

Grouperdawg

Its hitting the front derailer when it’s in the big ring up front and the largest two cogs in the back. I try not to ride in the big big so I’m ok with that rubbing and would let me know I’m in it but the one below I want to use

I honestly don’t know enough about bikes to understand what the triangle alignment is or chain line issue would be but I can ask one of the mechanics about that

dwmckee

If you do not cross-chain drastically then not such a problem. And very precise tuning can get it pretty good. You could see if the mechanic could shim out your crank to the right side a millimeter or so as a possible fix. Or just shift to the big ring sooner. Or change to a GRX crank and derailleur (need both to match). Also a different brand chain might be just enough of a difference to eliminate some of the rub. Or a couple thousandths shim stock under the inner ring crank bolts might pull the inner ring in just enough to give extra clearance between the rings to solve the problem. We use brass shim stock for all sorts of fixes like this, but that is a dying art in many shops these days where the mechanics are increasingly just part replacers instead of true problem solvers.

dwmckee

In square taper cranks it is very easy to shim out jist the drive side of the crank with a piece of shim stock on two sides of the square taper, effectively making it a wee bit thicker and that forces the crank outward slightly while still seating cleanly on four sides of the square taper.

Grouperdawg

The derailers that came with it are the grx 810s; seems like it would make more sense to pair it with grx crank idk.

I wouldn’t mind a little noise but none of my other bikes are anywhere near this loud where people are asking why it’s making so much noise

My son road it today and said it was also noisy in the big and 11 & 13 cogs in the back, not sure what that is I’m going to ride it tomorrow

zandoval 

In the old days we just did not do that, or that combo...

It's a real skill to select your gears front and rear with friction shifters on the down tube using thumb and fingers. I have been humbled when trying to find my favourite gears on a handle bar indexed shifter bike.

zen_

I ran an Alba crank for 7-8K miles last year and honestly didn't mind it at all for an entry level crank. It shifts good, and I think I had a whooping two chain drops even though I don't pay much attention to the front mech adjustment until it's obviously bad, and I shift a ton going up and down gravel rollers. As others have mentioned, there's always going to be a bit of rub cross-chained. Just run the Alba until you are either A) certain you want a crank based power meter or B) are actually spinning it out regularly, and really need bigger rings.

Grouperdawg

thx that’s good advice, I need saddle time on this bike to figure out what gearing I really want/need and I’ve never ridden a gravel bike before so I’m not sure what to expect. I don’t ride completely cross chained on my road bikes but I’d like to use the cog below like I do on my road bikes.

xseal

I had a GRX crank, wanted a power meter and did a bunch of research. www.power2max.com is the way to go. Replace the crank, has GRX like spacing, same chain rings, and for a couple hundred $$ more than 4iii or Stages, you get (my view) a much higher quality PM that requires no zeroing. I've been super happy with mine, totally reliable, accurate readings, no need to change BB.

NumbersGuy

I assume that you and/or the mechanics are aware of the front derailleur trim setting, correct? You mention not knowing that much about bikes, so perhaps you do not.

While in the big ring, just barely press the shifter like you are shifting into the small ring, just until it clicks. This moves the front derailleur ever so slightly inward which gives a better chain line for the larger cogs in back. If your son had gotten into this position, it could explain noise when using the smallest cogs in the rear. To go back from the trim position to normal, simply press the shifter like you are shifting from the small to big ring and it'll move the front derailleur back outward that slight amount, which will give a better chain line for the smaller cogs in the rear.

I don't have the same bike, but my Niner RLT 9 RDO has GRX derailleurs and an Easton 47/32 crank which is a pretty similar setup. I generally don't go that far up the cassette in the big ring, but as I get to the 3rd or 4th biggest ring on the cassette, I'll get a very slight rubbing and shifting. Shifting to the trim position completely eliminates the rub/noise.