the stones

Randy Grein randygrein at comcast.net
Tue Sep 8 18:54:13 PDT 2009


Correct. To expand on this a bit spring compression is relative;  
preload just moves the balance point between weight and spring force  
up. Visualize the spring from the side fully installed (but visible)  
on the bike and it will become clearer. Assume a spring rate of 100  
lbs/in; a 300 lb front end will compress the spring 3 inches. That's a  
lot of sag for a standard ~ 6" travel, so we shim (preload) the spring  
by 2 3/4 inches and sag is now 1 3/4". The bike now sits 2 3/4" higher  
unless you slide the forks up in the clamps.

This is important; the spring rate is unchanged and optimal damping  
rate for an idealized spring is unchanged. (Yes, when in a hurry a  
small change in preload can substitute for a ride height change, and  
vice versa.) What is different from the classic idealized damped  
spring problem in physics is the stops: hard parts abruptly stop  
travel at top and bottom. Jo was likely near to bottoming with the  
090s and stiffer carcass of the 003 likely caused the suspension to  
bottom, which would of course cause it to slide.

If I remember correctly Bridgestones are much stiffer than Pirelli  
(which are soft as butter); I had best keep an eye on my preload at  
least if I do try them.

Randy Grein, WMRRA #141

On Sep 8, 2009, at 9:12 AM, Ernest Montague wrote:

> Spring rate on a linear spring does not change until the far end of  
> the compression stroke. A relaxed spring compresses at its given  
> rate. A spring loaded enough to compress a tenth of its length still  
> compresses at the same rate.
>
>
> On Sep 8, 2009, at 9:07 AM, Chris Burgess wrote:
>
>> Ah...preload isn't just ride height.  It affects the initial stroke  
>> of the
>> suspension.
>>
>> On Tue, Sep 8, 2009 at 9:05 AM, Ernest Montague  
>> <afm199 at earthlink.net>wrote:
>>
>>> preload is ride height.  Not stiffness. Only at the extreme does  
>>> it make
>>> the ride "stiffer"
>>>
>>>
>>>
>>> On Sep 8, 2009, at 8:59 AM, Chris Burgess wrote:
>>>
>>> Do you think the carcuss of the 003's are stiffer than the 090's?   
>>> That
>>>> would make you need to stiff the suspension since the tires can  
>>>> do less of
>>>> the work than they did before.
>>>>
>>>> On Tue, Sep 8, 2009 at 8:17 AM, Jo Rhett <jorhett at fastlizardracing.com
>>>>> wrote:
>>>>
>>>> Sorry FYI I meant 003s.  I was switching from the 090s to the  
>>>> 003s ;-)
>>>>>
>>>>> I had to stiff up the front and rear preload.  Note: this may be  
>>>>> only
>>>>> because I needed to anyway, but I found that when I went out on  
>>>>> the 003s
>>>>> I
>>>>> was sliding around at the same pace that the 090s were stable.
>>>>> Increasing
>>>>> the preload on both sides made the tires grip better and I  
>>>>> dropped my
>>>>> time
>>>>> significantly.
>>>>>
>>>>>
>>>>> On Sep 8, 2009, at 5:29 AM, Randy Grein wrote:
>>>>>
>>>>> What did you have to stiffen up? Springs, compression, rebound,
>>>>>> everything?
>>>>>>
>>>>>> Randy Grein, WMRRA #141
>>>>>>
>>>>>> On Sep 7, 2009, at 11:05 PM, Jo Rhett wrote:
>>>>>>
>>>>>> On Sep 7, 2009, at 2:10 PM, Randy Grein wrote:
>>>>>>
>>>>>>>
>>>>>>> Bridgestone finally has SV sized DOT tires and they're like  
>>>>>>> $140 less a
>>>>>>>> set.
>>>>>>>>
>>>>>>>>
>>>>>>> Yeah, $260 a set is a sweet deal.  The 090s have sweet grip  
>>>>>>> too but I
>>>>>>> had
>>>>>>> to stiffen my suspension both front and back to make them  
>>>>>>> pay.  But
>>>>>>> after
>>>>>>> that change they ran well -- I dropped 2 seconds immediately  
>>>>>>> after the
>>>>>>> suspension fix.
>>>>>>>
>>>>>>> --
>>>>>>> Jo Rhett /  velociRaptor Racing
>>>>>>> #553 WERA / AFM
>>>>>>> #53 SMRRC
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>> --
>>>>> Jo Rhett /  velociRaptor Racing
>>>>> #553 WERA / AFM
>>>>> #53 SMRRC
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>> --
>>>> WERA #104
>>>> OMRRA #104
>>>> WMRRA #104
>>>> http://www.burgiracing.com
>>>> http://www.sponsorhouse.com/members/thatman
>>>>
>>>> 2009 Sponsors
>>>> I-90 Motorsports
>>>> Vortex Racing - http://www.vortexracing.com
>>>> Motorex - http://www.motorex.com
>>>> Lockhart Phillips http://www.lockhartphillipsusa.com
>>>>
>>>>
>>>
>>
>>
>> -- 
>> WERA #104
>> OMRRA #104
>> WMRRA #104
>> http://www.burgiracing.com
>> http://www.sponsorhouse.com/members/thatman
>>
>> 2009 Sponsors
>> I-90 Motorsports
>> Vortex Racing - http://www.vortexracing.com
>> Motorex - http://www.motorex.com
>> Lockhart Phillips http://www.lockhartphillipsusa.com
>>
>



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