Mid & rear engine placement safety implications

beats me how you survive in the giant air conditioner by the bay

so you were implying never buy /read jobst book or that was not was you implying?

I have other people do the wheel assembly and tensioning for me so I wonder about the need vs want vs just for laughs

besides, I think I'll go mtb where wheel quality is of lesser importance than on a road bike

Reply to
isquat
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unfortunately, i don't think there's any one magic bullet on wheel building books. jobst's book will allow you to calculate spoke length from first principles [although, not allow for the elongation that happens as they tension], lace, true and tension, but it'll also have you over-tension, bend spokes unnecessarily, and he gives you a very iffy "stress relief" method. you'll also have no initial clue on how to position a hub so the label aligns with the valve hole, as per conventional practice.

gerdt schraner's book will solve the hub label position problem, and have you stress relieve better, but you'll be reliant on others for spoke length. his lacing method is also unnecessarily complicated.

sheldon brown's online guide is very good on lacing, hub positioning, but repeats a lot of the garbage that jobst bullied into him. and his stress relief method blows chunks.

if you can find it online, the mavic wheelbuilding guide is pretty good. absolutely the best stress relief method. but it tells you nothing about spoke length calculation, presumably because if you're rebuilding a mavic wheel, you're already using spokes of predetermined length.

so, "don't read that book in isolation" is my advice. and if you're thinking you want to understand wheel mechanics and don't already have a strong understanding of mechanical principles and materials, it'll badly f*ck you up because a lot of what he says is just plain wrong.

as to building wheels for yourself, we've discussed this before. there are definitely benefits to learning in that most people don't have access to a good builder. statistically, that includes you. once you can build yourself, and you take the time to do it right, which most shops seldom invest, you can have a wheel that remains true and stable almost indefinitely. that's a rare beastie in "other people built" wheels. my mtb wheels, complete with unconventional rear spoking pattern*, have remained completely true despite some fearful abuse. same for my townie fixie on san fran's pot-holed, cable car tracked streets.

  • convention is that you go trailing-leading-leading-trailing when looking at the four hub sides, theory being that this allows the spokes with increasing tension from drive torque to distort the wheel's dish less. with a disk braked rear, if you're following this principle, you need to lace leading-trailing-leading-trailing because braking reaction opposes drive torque. it's a little more complicated to lace, but it's specified in the shimano hub manual.
Reply to
jim beam

Good overview. That rear spoking pattern for disc/drum rears is also the preferered 'old guy' way for fronts, which need no particular bias.

Reply to
AMuzi

interesting.

in that vein, old guys used to tie and solder. jobst went out of his way to pour scorn on that practice, but doesn't do it in what is an actually scientific way, just a pseudo-scientific way - i.e. the scientific way is "objective, methods, results, conclusions". he just leaps from method to conclusions, omitting actual results. yet he blithely accepts spoke interleaving as "stabilizing the spoke structure" with no analysis whatsoever.

[i know, broken record, but i really can't understand why other people don't see this stuff when reading - you don't need to be an engineer to have logical inconsistency slap you in the face.]
Reply to
jim beam

thanks for the comprehensive wrapup, took the time to setup thunderbird w eternal september again so I can crosspost at will ;-)

My CXP-33 is laced over-4 whatever that means and the ceramic open pro is over-3 not sure how that meshes with leading-trailing-leading-trailing and trailing-leading-leading-trailing

For next year cross competition I wonder if I'd reuse my roadbike to get a 26"er or 29"er. Though the latter is a bit too portly for competitions, I think

it's the "blond gene". you don't have to understand it, just accept "as is"

Reply to
isquat

"three cross" is conventional with an open pro. "4x" on a cxp33 is not something i'd do because it's not got as much socket angle available as the open pro - which is precisely what "4x" requires. i'd therefore expect spokes to be more likely to break at the threads.

presumably the builder was looking to make the cxp33 a slightly "softer" ride - the cxp33 is very deep and thus rigid so it can ride "harsh" compared to others. ["4x" spokes are longer and thus theoretically slightly more elastic.] i'd have gone with a lower spoke count and "2x" personally.

[another criticism of "the book" - jobst has succeeded in making most people think of "spoke crossing count" as one of the parameters for spoke length calculation. this is somewhat misleading since you can compute a result for 2.7179 "crossings", even though no such thing is possible. the fact is, the "crossing" number is in fact the number of hub hole offsets from the "key" position, and this doesn't have to be an integer.]

doesn't for "crossing" count.

cringe.

Reply to
jim beam

Not enough information.

4x 48 spokes builds to an optimal spoke angle. 4x 40h is good, better than 3x. 4x with 32h is a clusterf**k. 4x 36 is failure prone, far from ideal, not recommended. And yet guys do it with 50-50 results, despite our admonition.
Reply to
AMuzi

indeed. so as we know the rim is cxp33, 4x is inappropriate given that it's either 28 or 32 hole.

Reply to
jim beam

4x36 was developing figure8th before I changed the wheelbuilder and last guy apparently did a faitly good job, that or I haven't ridden long enough after the last rebuild

it is a 36 hole cxp-33

I could recount the spokes but I belive I did ask for 36 and that's what I got. In fact the open pro is similarly overbuilt being 36-holy (but cross 2)

can't get cxp-33 in 40 or 48 hole versions. I think.

for 40 or 48 I guess I'd have to get some sort of a touring rim not that it's a bad thing since I value reliability over weight/speed

what are my options for mtb rims in 26" and 28" in 40 or 48? (if any)

Reply to
isquat

Maybe I have cross 2 in front and cross 3 in the back. Tell me how to count and I'll tell for sure :^)

I wanted higher rigidity for the rear to I asked for higher cross count for the rear wheel. To tell the truth it's probably an overkill for the amount of power I deliver to the wheel anyway, but ferrari owners don't use even half of the capacity also. So what the heck.

Reply to
isquat

crossing count doesn't really make much difference for rigidity [and decreasing count - shorter spokes - are technically more rigid than longer spokes, higher crossing count] but total spoke count does. so, cxp33 [old stock] with 36 spokes is about as stiff as you can get without getting into tandem wheels.

what made you want more rigidity? many people don't like the harsher ride. does your bike have a shimmy problem?

Reply to
jim beam

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