Dogtrousers
Kilometre nibbler
Today, while riding up a steep (15% or more) hill, standing on the pedals. my transmission slipped resulting in a fall (no injuries, just bruising). When I remounted and continued up the hill it slipped again, but I was seated this time. I was in my bottom gear at the time and in neither incident did the chain come off. This wasn't the first time I've had slips in bottom gear, just the most dramatic.
Later in the ride, on a lesser hill, I put the bike into a moderately high hear and stood on the pedals. I managed to elicit a small slip.
Note also that this doesn't have anything to do with changing gear. I'd been in my bottom gear for a while when this happened, and the rear indexing seems fine. Just when there is a lot of stress on the system (like when I stand up on a steep hill).
This left me rather nervous in traffic: what if it happened when I accelerated onto a roundabout, for instance.
THe transmission is SRAM Apex 50/34 & 11-32. The kit is relatively new - the bike has done about 3,000 miles or maybe a bit more. The wheels are slightly older and have done maybe 800 miles more than that.
So what can it be?
Chain stretch? I measured the chain (while still on the bike, so not all that accurate) using a vernier caliper and got 6.107" for 6 link pairs, so less than 2% "stretch".
I'm not super fast or a racer so I doubt I'm putting all that much power through the system. On the other hand I'm a big lump (> 90kg) and do tend to ride up a lot of hills, which I guess will take its toll.
Stiff link? I've checked the chain and not found one. And anyway that would give me a "clonk" each time the sitff link went through the rear mech. Which doesn't happen.
I also fail to see how a chain could momentarily disengage then re-engage with a sprocket. If it had jumped off the gear altogether maybe. But it didn't. At least I don't think it did. I'm beginning to doubt my memory now.
Could it be the freehub perhaps? This is my favourite theory.
One other thing. It's always worth checking to see if it could be your own fault. I replaced the BB a while back. When I did this I think the chainrings ended up a smidge further out from the BB. I know this because the front mech can sometimes throw the chain off the inside when changing down if in a large sprocket at the back. I've been meaning to re-adjust it but as it's easy to get the chain back on without stopping I haven't bothered. I don't know why this could elicit these symptoms, but it's worth considering.
Any thoughts?
I'm thinking of asking my LBS to service the freehub (that's not a job I've ever done, as real bikes have freewheel blocks, not freehubs).
As I said in another thread I suspect that the underlying cause will turn out to be the fact that All Modern Bikes Are Rubbish, Not Like In My Day.
Later in the ride, on a lesser hill, I put the bike into a moderately high hear and stood on the pedals. I managed to elicit a small slip.
Note also that this doesn't have anything to do with changing gear. I'd been in my bottom gear for a while when this happened, and the rear indexing seems fine. Just when there is a lot of stress on the system (like when I stand up on a steep hill).
This left me rather nervous in traffic: what if it happened when I accelerated onto a roundabout, for instance.
THe transmission is SRAM Apex 50/34 & 11-32. The kit is relatively new - the bike has done about 3,000 miles or maybe a bit more. The wheels are slightly older and have done maybe 800 miles more than that.
So what can it be?
Chain stretch? I measured the chain (while still on the bike, so not all that accurate) using a vernier caliper and got 6.107" for 6 link pairs, so less than 2% "stretch".
I'm not super fast or a racer so I doubt I'm putting all that much power through the system. On the other hand I'm a big lump (> 90kg) and do tend to ride up a lot of hills, which I guess will take its toll.
Stiff link? I've checked the chain and not found one. And anyway that would give me a "clonk" each time the sitff link went through the rear mech. Which doesn't happen.
I also fail to see how a chain could momentarily disengage then re-engage with a sprocket. If it had jumped off the gear altogether maybe. But it didn't. At least I don't think it did. I'm beginning to doubt my memory now.
Could it be the freehub perhaps? This is my favourite theory.
One other thing. It's always worth checking to see if it could be your own fault. I replaced the BB a while back. When I did this I think the chainrings ended up a smidge further out from the BB. I know this because the front mech can sometimes throw the chain off the inside when changing down if in a large sprocket at the back. I've been meaning to re-adjust it but as it's easy to get the chain back on without stopping I haven't bothered. I don't know why this could elicit these symptoms, but it's worth considering.
Any thoughts?
I'm thinking of asking my LBS to service the freehub (that's not a job I've ever done, as real bikes have freewheel blocks, not freehubs).
As I said in another thread I suspect that the underlying cause will turn out to be the fact that All Modern Bikes Are Rubbish, Not Like In My Day.