Date: Mon, 19 Apr 2010 16:46:40 -0600
Reply-To: Tom Buese <tombuese@COMCAST.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Buese <tombuese@COMCAST.NET>
Subject: Re: Why go to big tires?
In-Reply-To: <l2l5c80974c1004191532lda28759br59b2709a00b33b14@mail.gmail.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes
On Apr 19, 2010, at 4:32 PM, Sudhir Desai wrote:
> ...................
>
> (as far as tire/wheel combinations go, you can always get a lighter
> wheel to somewhat offset the heavier tire. the stock steelies are
> pretty heavy, as are the stock alloys)
& you forgot to calculate what brand of tires we should use & whether
the whitewall is on the inside or outside! LOL!
YMMV,
Mr. BZ-less is more
>
>
>
> I'm not going to offer to do the actual calculations, as I'm sure
> there is a solid modeler out there that could do ALL of them
> correctly. (I had to rewrite that email four times because of bad math
> on my part) ;)
> Sudhir
>
>
>
> On Mon, Apr 19, 2010 at 18:07, Jake de Villiers
> <crescentbeachguitar@gmail.com> wrote:
>> Nice explanation Suds but... you've left out the other half of the
>> equation.
>>
>> As the wheel diameter grows the weight of the wheel also grows,
>> especially
>> the tire mounting section which is at the far end of the 'lever'
>> system
>> which is the tire's diameter.
>>
>> So that 5600in/lbs is no longer sufficient to stop the more massive
>> rotating
>> 'lever', you need even more brakes.
>>
>> On Mon, Apr 19, 2010 at 2:39 PM, Sudhir Desai
>> <sudhir.desai@gmail.com>
>> wrote:
>>>
>>> Sorry about the simplicity, I figured I would gloss it over
>>> HARDCORE.
>>>
>>> the 0 represents the hub, the ) the brake rotor/drum, the | the
>>> outside of the tire.
>>>
>>>
>>> STOCK
>>> distance of force from hub:
>>> 0--5"----//---12.5"
>>>
>>> direction of force:
>>> 0--up-------down
>>>
>>> illustration:
>>> 0--)-----//----|
>>>
>>> lets say the car is rolling along, and the torque needed to stop the
>>> wheels abruptly (ignoring/subtracting any sort of rotational
>>> inertia,
>>> and friction, etc) is 5000in-lb.
>>>
>>> that means, we would have to exert a force of 5000in-lb/12.5in =
>>> 400lb
>>> (at 12.5" out from the hub) to stop the wheels abruptly.
>>>
>>> now, we go in more to where we can stop the wheels, the brakes. at
>>> 5"
>>> out from the hub, that 400lb force needed is now (400lb*12.5in) =
>>> (xlb*5in), or x = ((400lb*12.5")/5"), so
>>>
>>> x = (5000in-lb)/5" = 1000lb
>>>
>>>
>>> SO... to stop the wheel abruptly, we need 1000lb of force at 5" out
>>> from the hub, and that's the torque our stock brakes can put out.
>>>
>>>
>>>
>>> when we increase the tire size to a 28" tire:
>>>
>>> OVERSIZE
>>> distance of force from hub:
>>> 0--5"----//---14"
>>>
>>> direction of force:
>>> 0--up-------down
>>>
>>> illustration:
>>> 0--)-----//----|
>>>
>>>
>>>
>>> SO NOW WE GO BACKWARDS!!!! lol~
>>> due to our original assumption of 1000in-lb,
>>> we have just increased the diameter of our tires to 28".
>>>
>>> this means that our 1000 lb force (5000in-lb) that was enough to
>>> stop
>>> the 25" tire will not be enough to stop a 28 inch tire by the
>>> following equation.
>>>
>>> 5000in-lb/12.5in = xin-lb/14in, or xin-lb = (5000in-lb*14in)/12.5in
>>>
>>> x=(5000*14)/12.5 = 5600in-lb is our new stopping torque needed.
>>>
>>> our stock brakes can only exert 1000in-lb of torque, so we won't be
>>> able to stop the wheel abruptly anymore.
>>>
>>> hopefully y'all are following me still...
>>> we just increased the amount of force needed to stop the wheels, and
>>> we see that our stock brakes are not enough to do so.
>>>
>>> NOW, we need to calculate the size of brakes we need to stop the
>>> tire
>>> abruptly (ignoring all other factors).
>>>
>>> we take the known stopping torque, and our original brakes (10"
>>> brakes
>>> LOL), and see how that compares with our new 5600in-lb
>>> x-in/5600in-lb = 5in/5000in-lb
>>>
>>> x = (5*5600)/5000 = 5.6in
>>>
>>>
>>>
>>> so we'd need 11.2" diameter brakes to put out the 5600in-lb torque
>>> needed to stop the wheels abruptly.
>>>
>>> which is another inch diameter of brake needed.
>>>
>>>
>>> I hope my simple explanation (with calculations to show i wasn't
>>> just
>>> pulling numbers out of the air) was satisfactory. :)
>>>
>>> Sudhir
>>
>>
>>
>> --
>> Jake
>>
>> 1984 Vanagon GL 1.9 WBX 'The Grey Van'
>> 1986 Westy Weekender/2.5 SOHC Suby 'Dixie'
>>
>> Crescent Beach, BC
>>
>> www.thebassspa.com
>> www.crescentbeachguitar.com
>> http://subyjake.googlepages.com/mydixiedarlin%27
>>
>>
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