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  • 31.8 alu bars Vs 35 carbon Vs 35 alu and Trek knock-block.
  • weeksy
    Full Member

    Ok, stay with me here. It’s a dreary damp day, my legs are dead and I’ve watched the cycling.

    So.

    I’ve got a Trek Fuel ex9.8 with a knock block headset.

    After attempting to swap the stem I’ve just found out my headset spacers are also knock block.

    So they slot into frame/headset/stem together and are locked in place

    So I’ve currently got 35s fitted, alu with 38mm rise and 780mm width

    I have standard bars, carbon 35s, 800mm and 28mm width.

    But I wanted to try some 31.8s I have with 760mm width and 28mm rise, why, well, why not.

    Now Google shows me these

    https://www.tritoncycles.co.uk/components-c9/headsets-c79/knock-block-1-1-8-lockring-spacer-p19463/s59011?utm_source=google&utm_medium=cpc&utm_term=trek-knock-block-1-1-8-quot-lockring-spacer-545523&utm_campaign=product%2Blisting%2Bads&cid=GBP&glCurrency=GBP&glCountry=GB&gclid=Cj0KCQjwqPGUBhDwARIsANNwjV6PRtnOi4TvuOVXa_Bxf-kjq6mk0-JXcjJ_ijkjXR5WwZZO4w7FoOcaAjq_EALw_wcB

    Which means I lock that in place? Why? I can then fit a standard stem?

    I get the stiffness discussions but can normal humans/riders really notice a difference between 31.8 and 35s?
    I could also remove the knock block headset aspect completely if there is no way they can hit eachother of course.

    Posted 1 year ago
    greyspoke
    Free Member

    So if I understand correctly you want to try 31.8 bars but the Trek stem fits 35 bars so you want to use a non-knock block stem?

    I have 31.8 bars in the Trek stem with spacers I got from ebay but I can’t find a link to the exact component ATM.

    I have read on the internet that you can dremel the knobs off the Trek spacers and use a standard stem or make recesses in a standard stem to knock block it (not for the faint hearted).

    Posted 1 year ago
    weeksy
    Full Member

    Yeah, just checked frame and indeed the knock block would be needed by the look of it.

    So I guess I need a 31.8 knock block stem.

    https://www.trekbikes.com/gb/en_GB/equipment/cycling-components/bike-stems-and-accessories/bike-stems/bontrager-rhythm-comp-knockblock-stem-no-packaging/p/28828/

    Posted 1 year ago
    tomhoward
    Full Member

    Or a shim for your narrow bars?

    https://www.ebay.co.uk/itm/153969037607?hash=item23d9451127:g:zo4AAOSw4rte4Y1T

    Posted 1 year ago
    weeksy
    Full Member

    Good thought. Not sure I fancy that though

    Posted 1 year ago
    bowglie
    Full Member

    I’ve used one of Trek ‘knock-block to normal’ adapters on my bike so that I could use my old stems. The adapter is effectively a locking 10mm spacer that means the knock block system still works, but you can stick non Trek stems on. Oh, and I’ve used some 31.8 carbon bars on my heavy Trek ebike and they didn’t feel like noodles (even with my fat old ar** handing off them!)…er, I do think they were a bit more comfortable though – but that might be down to the slightly different shape.

    I think I might have an unused adapter in my garage, so if you’re interested I can have a look and let you know if I find it.

    Posted 1 year ago
    bowglie
    Full Member

    Just been in the garage and put my hand straight on it – I also found that knockblock lock spacer;) I think I bought it for a Fuel EX I used to own, and never got round to fitting it. It’s still in its unopened packet marked £17.49. I’m open to a reasonable offer, so if you’re interested just PM me. If you’ve found an alternative solution, no worries, I’ll stick it on Fleabay.

    Posted 1 year ago
    weeksy
    Full Member

    Why does the spacer need to be a locking type then guys ? I must be missing something here but i can’t really think of a reason it would need to be so.

    Posted 1 year ago
    b33k34
    Full Member

    Why does the spacer need to be a locking type then guys ? I must be missing something here but i can’t really think of a reason it would need to be so.

    this was news to me so I just went and looked at a trek video. The headset cap, spacers, and stem all lock together. Theory being the stem has the strongest connection to the fork steerer.

    Posted 1 year ago
    madhouse
    Full Member

    I thought the whole idea of the knock block was to get around the issue of your crown fowling the downtube.
    They went with a straight downtube and as such you can no-longer 360 the bars, so they had to do something to stop that happening. Didn’t think it had anything to do with stiffness (edit – of the steering, the straight downtube is all about stiffness) or connection between bars & fork. Only the bottom spacer that’s doing the blocking needs to be there, the rest is probably just there to help stop people putting the stem on at a jaunty angle or maybe the marketeers decided to have a bit of fun.

    Posted 1 year ago
    weeksy
    Full Member

    Yeah that’s why i don’t quite grasp the locking aspect of the spacer. Rigidity, stiffness, can’t say i’ve ever considered that aspect.

    I’ve currently now got the carbon bars on there which i’m debating whether to leave at 785 or so with grips, or trim a smidgen…

    Posted 1 year ago
    b33k34
    Full Member

    I think to stop bar mounted stuff hitting top tube. It all locks together to try to stop bar/stem rotating independently of fork.

    Posted 1 year ago
    weeksy
    Full Member

    my part from @bowglie arrived, so i’ve now got the choice to try the 31.8s…

    Not sure when i’ll get to it yet as i’m not seeing me riding anything tech for a few weeks.

    Posted 1 year ago
    ballsofcottonwool
    Free Member

    25.4mm bars were stiff enough when they were only 580mm long
    31.8mm bars were stiff enough when they were only 680mm long

    Thats why they make 35mm bars now that they are 780mm+ long

    Posted 1 year ago
    honourablegeorge
    Full Member

    ballsofcottonwool

    25.4mm bars were stiff enough when they were only 580mm long
    31.8mm bars were stiff enough when they were only 680mm long

    Thats why they make 35mm bars now that they are 780mm+ long

    I have 810mm 31.8 bars that are plenty stiff. 35mm is just a daft new standard that wasn’t needed.

    Posted 1 year ago
    Saccades
    Free Member

    My 800mm 35mm bars are too stiff, uncomfortably so (raceface 6c).

    Posted 1 year ago
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