Kindergarten geometry playground

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jameso
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Joined: Tue Nov 06, 2012 1:48 pm

Re: Kindergarten geometry playground

Post by jameso »

Oder has gone in the playground, it's a free for all and I like how it's going.
I noticed how it follows differently. Tame, but also lame in a way. The feeling stuck (of course also in my head). The difference would have been about 20 mm or so.
I'm no cuttie-corner sort of rider, no loam berms here. On flatter greasier corners we have I prefer a slightly longer rear, on any SS I've had the longer setting helps me make the front stick and let the rear follow with a slide if it needs to. Could be the opposite / different on steeper banked corners that I very rarely ride.

SS cranks, I'm not sure. I use 175s on my SS Jones and 170s on all my other bikes. I've used 170s on the SS but not for a long time. I thought it was at the 20rpm end of things I needed any help I could get, spinning 120rpm isn't something I do for long. And the nice XTRs I had for the SS were 175s, they've just stayed on there.
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Alpinum
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Joined: Thu Mar 06, 2014 5:38 pm

Re: Kindergarten geometry playground

Post by Alpinum »

jameso wrote: Wed Dec 02, 2020 4:01 pm
Walt (?) the frame builder
- an OG of short chainstay 29ers. 
:lol:  quite true

The bike my mate rode (think he left it with his parents in England when he moved back to Colorado, so his dad has a bike to use. It had a bmx downtube as a top tube and the rear of a Ventana (?). Unfortunately I never rode it and have no idea how short that very chainstay was. Nonetheless, an early 29er on Swiss ground, likely a couple of years ahead of the Swiss time...
jameso wrote: Wed Dec 02, 2020 4:01 pm Been wondering about this re E-bikes, just not in any detail. There's probably a lot of assumed facts around Q-factor coming from the same place a lot of old stuff in bike design does, early road race bikes.

Many mid motor E-bikes have 190mm or more Q-factor, though new EP8 is fairly normal compared to old triples ~175-180mm. I've not heard of knee problems from riders who've suddenly started pedalling more due to getting an E-bike and statistically they're older riders on average.

Shorter riders are more likely to feel out of line on wider Q-factors so perhaps a wide crank is something a taller rider gets away with more easily?
I might be wrong, but to me it seems they are mostly used in a way where a large Q-factor isn't much of an issue(?)
The battery doesn’t last for ages, you have a constant supplemental output of what a strong rider can put down and assumingly have less forces on some of your joints.
jameso wrote: Wed Dec 02, 2020 4:01 pm There's probably a lot of assumed facts around Q-factor coming from the same place a lot of old stuff in bike design does, early road race bikes.
Exactly what I wonder and why I believe it to be important to question developments.
jameso wrote: Wed Dec 02, 2020 4:01 pm so perhaps a wide crank is something a taller rider gets away with more easily?
yeah, probably, since the angles become larger.

My girlfriend has done a few multiday trips on her fatbike (KHS 4 season) which (not measured) has a humongous Q-factor. She's 170 cm and watching her ride hurts since the pedals are so far apart. She's fine though… yet I still would ask her to change (or rather just do it for her) crankset to go narrower should we go on a multiweek trip.
marcinski wrote: Wed Dec 02, 2020 4:50 pm Interesting discussion for sure. I can't help thinking that a reasonably long FC with relatively longish RC wouldn't be  a bad compromise? Long enough front so that  stand-up space is not restricted, but short enough so that not very steep STA works and longish RC to balance the rider properly between the wheels.
I sort of did that in Rondo with Bogan (longish FC and longish RC for a gravel bike).
.
I'd be afraid to generate a dead feeling bike. With mountainbikes of different flavour and what I (would) use for offroad touring (say a tamer, granddad flavor of my mountainbiking) the chainstay length tends to feel good when shorter than 440 mm. Once it's longer, I miss more and more liveliness (and fun and playfulness and responsiveness and so on). It's of course problematic to look at this number isolated, but there… I've done it. No idea how this translates to gravel or road frames. Absolutely no clue.

Would be fun to mix things up and take back some of the wandering inspiration the different bike types have/had on each other.

Yes, that super low bb of Jones bikes for example, also looking at the gravel bikes with their huge drop.
I'd like to know how a 70 or 75 mm drop and 5 mm shorter crankarms feel like on a do-it-all (rigid or hardtail mountain) bike…
And add in some Waltworks/gravel/road bike short chainstays and a LLS front... must be wild fun to ride.
marcinski wrote: Wed Dec 02, 2020 4:50 pm I also experimented  with significantly longer  FC and short rear and while capable off road, it definitely is less comfortable than long-chainstay Bogan (all else being equal)

Marcin
Harsher because less flex due to smaller triangle and because more in-line with the rider?

I remember Ian pointing this out when getting his wonderful Shand (the rally Lancia looky one). It was something about longer chainstays and larger angle of impact to make the ride less harsh.

The hit is more direct with short chainstays, but – without doing the maths – I think it's not significant enough (?) and must be easily masked by multifold with elements like a flexy seat post, saddle and vertically compliant frame. For those who like the feel of short chainstays, I'm not sure it's worth it (to go longer for more comfort).

This is a mountainbiking/rough offroad touring perspective.

Low bb of gravel/road/Jones and the short chainstays of gravel/road bikes on a
jameso wrote: Wed Dec 02, 2020 7:53 pm Oder has gone in the playground, it's a free for all and I like how it's going.
Calvinball :-bd
jameso wrote: Wed Dec 02, 2020 7:53 pm I'm no cuttie-corner sort of rider, no loam berms here. On flatter greasier corners we have I prefer a slightly longer rear, on any SS I've had the longer setting helps me make the front stick and let the rear follow with a slide if it needs to. Could be the opposite / different on steeper banked corners that I very rarely ride.
Same here. I prefer awkward corners, off cambers, hiking paths where it's a challenge to keep momentum.
I remember playing with the chainstay length of my Summum some 10 or 11 years back and loved the short setting (435, 440 or 445 mm inserts which came with the frame). When the rear broke loose, the weight could be shifted to the front a little, to put more emphasis on the front and the rear would follow automatically, with little matter about how much grip there was. A practical lesson in how we steer over the front wheel, not over the rear (except for exiting a tight corner where you can pull the front out of it, pivoting around the rear).
jameso wrote: Wed Dec 02, 2020 7:53 pm I thought it was at the 20rpm end of things I needed any help I could get
Same here...
I'd probably need to experiment quite a bit and then I prefer to have similar setups across my different bikes, so I don't feel out of shape when swapping them.
That moment, after having ridden the geared bikes for, say, a week and leave the house with my ssp and the thumb searches for the trigger to shift, moving in the void beneath the bar.

The longer the front centre, the shorter the rear can be? If so, where are the limits though? We can only go so far forward, no matter how high the bar is and must keep a balance between the wheels.
The shortest chainstays I rode must have been, or are, 420 mm and this is also the bike with the longest reach. I can imagine that once the chainstays are eg less than 400 mm on an mtb, the reach, to stay centred, could become a mortgage, interfering good fit for comfort and handling.
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Alpinum
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Re: Kindergarten geometry playground

Post by Alpinum »

I had a beautifully classic over the bar moment yesterday on my Moxie with its 510 mm reach, 63.2 ° HTA, 150 mm fork and 25 or 20 mm stem with 20 mm rise on the bars.

The special thing was, I never felt a bike to catapult me so high, although I was going slow.
It was in hub deep snow, 30 ° steep slope and I was able to roll nicely.

Whilst it takes a lot to get you otb with a long front and slack HTA, once it does, it is quite spectacular.
Certainly felt that way.
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