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Mid & rear engine placement safety implications



 
 
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  #31  
Old September 9th 13, 07:48 PM posted to rec.autos.tech
jim beam[_4_]
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Posts: 3,204
Default engine onnatop placement implications

On 09/09/2013 02:49 AM, wrote:
> On Friday, September 6, 2013 6:33:48 PM UTC+3, AMuzi wrote:
>> On 9/6/2013 9:17 AM, jim beam wrote:
>>
>>> On 09/06/2013 02:19 AM,
wrote:
>>
>>>>>>>

>>
>>>>>>> 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 **** 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.

>>
>>>>>>>

>>
>>>>>>>

>>
>>>>>>

>>
>>>>>> Good overview.

>>
>>>>>> That rear spoking pattern for disc/drum rears is also

>>
>>>>>> the preferered

>>
>>>>>> 'old guy' way for fronts, which need no particular bias.

>>
>>>>>

>>
>>>>

>>
>>>>

>>
>>>> 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

>>
>>>

>>
>>> "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.

>>

>
> 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.


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?


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