We have a long-time customer in our shop who has been having what we swore were freehub body issues for a little bit. Previously, she was complaining of what sounded like a loss of engagement, primarily on big descents. This prior wheel had a pretty old Bontrager Hub and the freehub body was looking at little tattered inside. At her request, we laced a DT350 hub onto her old rim and called it good. We have a light coating of grease in there, and looking around. nothing appears wrong between splines/ratchets.
A few months later, she’s back with the same complaint. “I’m not getting traction going down these big descents!”. She’s confirmed that she’s in the big chainring and in the smallest cogs in back. She claims it also only happens after some time spent coasting, then when trying to pedal again, is immediately spun out. Since she’s not able to pedal, eventually she will slow down when the hill eases off, and only then she’s able to get engagement and “traction” again.
Is this making sense to anyone? We’ve spent an embarassing amount of time test riding this bike, trying to recreate the symptoms on appropriate hills around here, but just can’t get any misbehavior. We’re inclined to think it’s user error, but she is an experienced cyclist…
Fair enough, we’d been thinking the same. However, I don’t think she is that strong of a rider, and knowing the grades she’s descending and gearing she’s running, it seems unlikely.
Mechanically, it doesn’t make much sense if there’s no slipping in any other condition. The only thing I’d try would be to degrease and use just a light oil.
On the user error side, I’d try putting on a cadence sensor and have her record her rides. If you can see speed and cadence and know the gearing, it should be clear if there’s a problem.
Or ask another rider you trust to ride with her and try to match cadence?
Pretty hard to imagine the engagement of 2 consecutive hubs being worn to the point of slipping. The point that the client doesn’t seem to be a strong rider also corroborates the point that she’s probably on a friendlier front chainring setup, i.e. 50/34 for 2x. So, given that the problem surfaces only “on big descents”, could point that she’d run out of chainrings pretty easily, even on say, a 50x11 combination.
The point that the client needs to “slow down until the hill eases off” before she’s able to regain engagement pretty much sums up the issue, imo.
Sounds like spinning out to me too. If the gearing and wheel circumference are known, and have access to a fit/tcx file with speed and cadence data this can be checked. Bonus, if it’s Di2 you can confirm the gear selection too.
Is it a Ratchet EXP freehub? The first production batches of that freehub ended up with a known issue where the single moving ratchet would get stuck in the freehub losing engagement with the hub, typically on a descent. My 2022 Roval Control SL wheels with a Ratchet EXP freehub recently was warrantied by DT with a full star ratchet replacement and freehub replacement, no questions asked after providing the hub serial number.
Really appreciate all of the thoughts in here, generally pointing to the customer simply being spun out. Today she came back in, saying she just had this happen going 15mph downhill. Having this happen at 15mph was surprising, kind of ruled out the spun-out notion IMO. She does not use a power meter nor cadence sensor, so it’s tough to get that data from her Wahoo (though we have been tempted to let her borrow a cadence sensor).
This is an older rig, 10 speed Ultegra 2x chainrings. She is going to ride an older bike of hers from her garage, and see if she has the same experience. This isn’t a totally fair comparison though because she may have taller gearing on the old triple chainring setup.
The final notion of a bouncing chainring not engaging on the cassette teeth is an interesting one. She claims one of her friends looked at the drivetrain, and only commented that the chain “seems to be bouncing around a bit”. We checked the chain length, assuming maybe it was cut too long, but the length seemed perfect. The is a road bike used exclusively on the road, no clutch in the RD.
Did you ever get around to check what cassette/chainring combination her original bike was on? The 6700-series groupsets had cassettes that started at 12T, instead of the usual 11T, and the chainrings could possibly be a 50/34…
FWIW, I had a non EXP DT 240 hub lose engagement. One of the aluminum rings that one of the ratchets slid in became damaged and the ratchets slid erratically. I replaced it with a steel part from a 350 hub and problem gone. DT replaced the part licketty split, with a steel part. All of which is to say, I guess that your clients 350 probably is not losing engagement. But, if you want, take off the cassette body and see if the ratchet slides smoothly, to further satisfy yourself and your diagnosis. Good luck!
@Babs if I may ask, any ideas how that aluminium ring got damaged? It seems curious to me, since it’s usually “sandwiched” between the hub axle and the ratchet ring, and should only slide along the axle, while in use.
In any case, just intrigued at the possible causes.
I think it was just under built/not the right auminum, or not treated/anodized correctly? My weight in the 200lbs range couldn’t have helped. : (
And - I’m talking about the ring that threads into the hub shell, annd stays put, and the star ratchet slides in the grooves in the ring. That thread in aluminum ring is what gave out on me. The grooves on its interior circumference were chewed up and the star ratchet would get hung up.
Ah, okay, got it, and thanks for highly detailed explanation! I had assumed it was that bit (thought it’s steel and not aluminium) in the photo instead. Glad you’ve got it sorted out , though I’m thinking that it must have been painful removing that ring if the teeth had been worn off
Teeth were still there ( just not lookin very good) fortunately. Those rings are tough to get out even under good circumstances. I had the right tool and treated myself a nice long breaker bar.
, though I’m thinking that it must have been painful removing that ring if the teeth had been worn off 
