michaelr

I have looking all over the Internet for a solution to this problem but I can't figure it out.

My son has a Trek Madone with a 2x12-speed SRAM groupset. It's great but unfortunately its not compliant for UCI racing. The groupset is 48/35 at the front and 10-32 at the back.

I have worked out that with the 48 at the front, to be compliant with the UCI restrictions on gearing, the biggest ring he can have on the back is 15.

So I am trying to work out how to put something together at the back that has 12 speeds with the smallest ring being 15T and that is compatible with the SRAM RED AXS gear on the bike.

Any suggestions much appreciated!

cpach

The best solution is probably https://www.williamsracingproducts.c...-sram-axs-12sp run 1x.

Also pretty easy to swap back in a year.

There's no real (sane) way to customize a xdr cassette.

FBinNY 

A cheaper alternative is to simply remove the outer ring and convert the bike to a 1x12.

You can use 4mm spacers to take up the space, or buy a set of 1x, aka "track" chainring bolts. Also the remaining chain ring can be mounted either inside or outside to optimize chain line.

You may be less than thrilled with this approach but it's much cheaper and for all practical purposes the 37 tooth isn't much different than a 35 that's there now.

Another option might be to remove all the smallest sprockets from the cassette and replace them with spacers. The spacers can be placed on either side to center the cassette and optimize chain line. This allows more gear selection with what's left but depends on the existing cassette being made of loose sprockets. It will require setting the derailleur limits so that the bike cannot shift to the dead space. It might require replacing the limit screws with ones a bit longer because the originals probably won't reach far enough.

BTW it might pay to check with a USI commissar about the exact rules. If my memory serves, (not assured) eons ago they used to allow the derailleur to be adjusted to lock out the illegal sprockets. If that is still legal it's a cheap easy solution.

cxwrench

Not possible to 'remove' sprockets from an AXS road cassette. We need to know what level the OP's group is before we can talk about changing the chainrings as well.

FBinNY 

I believe I qualified that suggestion.

I've been away from new bike components for a while but unless SRAM changed the spline pattern the OP could buy an intermediate quality, loose sprocket cassette and go from there.

cxwrench

Yes, there is no splined freehub anymore. 12 speed SRAM uses a proprietary XDR driver for road 12 speed. You should look into it.

Bike Gremlin

May be a silly idea, but my first thought was to use the RD adjustment screw and limit the RD movement to the 15T rear sprocket. If it will go that far (the limit screw).

michaelr

Many thanks for the responses.

I was looking at various options including switching the read derailleur for the older 11-speed eTap and then putting on a Shimano-compatible 15-32 cassette.
But it sounds like that would not work because of the driver. Is that right?

If I switch to the 1x, does mean new cranks as well? Sorry, I have not worked with these parts before!

EDIT: As the groupset is electronically controlled, I cannot lock out gears. Also, SRAM cassettes cannot be broken down. I think they come as one piece.

cxwrench

Does this bike have Red, or Force, or Rival?

HillRider

A different rear wheel with a freehub that will accept a "conventional" cassette is probably the least difficult and expensive approach.

michaelr

it is SRAM RED AXS.

michaelr

That's something that I was wondering about. That deals with wheel/driver questions.

if I want to avoid changing the RD from the existing 12-speed, then the question becomes how to come up with a 12-speed cassette with a smallest cog of 15...

Looking at, say, Ultegra, I think only have 9 distinct size rings on the 12-speed cassettes which are 15 or bigger... I was wondering if you could mix and match 105 and Ultegra or something, just to get more options... Sounds pretty niche but I can't think of anything better.

jccaclimber

The first hit I found on Google searching for this was a post about that rule changing, so it might be worth doing some research there.
Changing out or removing the large front ring seems the easiest solution to me, what is the problem with that?

cxwrench

The rule changes for next season. No more junior gearing. And here is another example of people just not knowing enough about newer parts to be able to give correct advice. Red chainrings are machined from 1 piece of metal...it's a direct mount and not possible to 'remove one'.

jccaclimber

Then change the crank for a year as was also suggested above, or is it a proprietary BB interface to the frame too?

Re:rules change, “changing”, implying in the future, not “changed”, implying already completed. How long this change needs to work for speaks to the quality of fix required.

alcjphil

What I am asking is why you bought this bike unless you didn't know about junior gearing? Are you and your son new to competitive cycling?. The bike you bought represents a significant expense and the regulations for his racing category should have been taken into account before the purchase. Your profile shows that you are a very new member, so there is no way to know how experienced you are with cycling. As others have pointed out, rules for juniors are about to change, but for now your son needs a bike that is legal. You may have to buy a stopgap bike that he can use until he ages out of junior racing or until rules change.

cxwrench

I don't know how to be more clear. Next year...2023...there are NO junior gearing restrictions. There is no proprietary frame interface, but there are many bb standards. The OP hasn't said which standard his bb/crank are but it's usually not an issue.

jccaclimber

We're saying the same thing about the gearing restrictions change next year, but you can keep being all argumentative about it if you want. Whatever the OP chooses to do, it only needs to last through this season.

I'll skip trying to explain the sarcasm in the rest of it. There are a couple workable solutions in this thread already, though the suggestion to get a whole new bike might be excessive.