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Hooked
Rally180
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Hooked
Rally180
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What is the advantage of using a P series front fork and suspension conversion on the earlier large frame bikes? Does the P fork have significantly more suspension travel?
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a lambretta or two
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@sfvsr avatar
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UTC quote
Those forks would be a bad idea in any Vespa frame other than an actual P-series. The rake would be aweful. But I imagine the benefits of a P-series fork is the options for disk brake, better shock/damper.

I don't think it would be a good idea.
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Hooked
Rally180
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UTC quote
My bad. What i really meant was what is the advantage of the conversion kits where the new forks are very similar to the PX.
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@sfvsr avatar
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UTC quote
I like the PK fork. You can change how low the arm sits with different dampers. Those conversions are cool. I've done it three times. I'd have done it a fourth, but I am selling that project.
@ginch avatar
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Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and '66 Blue Badge Smallframe
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@ginch avatar
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UTC quote
SFvsr wrote:
The rake would be aweful.
I understand your feelings about the fork conversion, but I just want to point out that there seems to be a common misconception about the rake on these scooters. Here's a couple of pics from the guy with the frame straightening jig somewhere in the UK.

You can see there's no adjustment for rake.

External inline image provided by member with no explanatory text

Here is the only adjustment:

External inline image provided by member with no explanatory text

External inline image provided by member with no explanatory text

http://vespaframejig.piczo.com/vespaframejig?cr=6&linkvar=000044

You can also adjust the height on P/PX fork with dampers. Here's a Sprint guard, PX fork and PK shock. There's a Zip shock that is another 30mm or so shorter.

[URL=http://s803.photobucket.com/user/cuckoobird4/media/6035d040-3096-49c8-a7bf-612011e18aac_zps1f5f4758.jpg.html]External inline image provided by member with no explanatory text[/URL]
@rob_hodge avatar
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Molto Verboso
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Molto Verboso
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UTC quote
ginch, i'n not quite sure what you're getting at with that frame jig. no one is arguing that the different frames have significantly different rake angles, but because the lower bearing races are at different heights swapping forks definitely alters the rake and handling.

the rake is truly bad putting a P fork into a vintage frame- because the P fork has one of the longest lengths from the center of axel to the lower bearing race of pretty much all shifter vespa forks. (yes, you could go with a shorter shock, but then this alters the angle of the suspension swing arm and that changes handling in yet other ways.)

when the distance between the axle and the lower bearing race is increased (as it would be by putting a P fork into an older frame), this lifts the front of the bike up, and increases the rake angle of the bike.

to answer the original question, the ease of retrofitting a disc brake combined with the plethora of aftermarket shock options are the main reasons.
up until about 3-4 years ago unless you had a P you pretty much had at most two or three options when it came to choosing a front shock.

another reason is that on 60's 8" bikes it's one of the better ways to put a 10" wheel on the front ad the only stock-style way to do it right is to track down a GL or GS 150 fork - rare birds these days.
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UTC quote
Rob is a vglb/vgla fork the same as a gs150 or 160 fork




just curious as they share a vs5 mudguard but use a vna frame
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Molto Verboso
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Molto Verboso
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UTC quote
joshzingzing wrote:
Rob is a vglb/vgla fork the same as a gs150 or 160 fork




just curious as they share a vs5 mudguard but use a vna frame
should be the same as a GS 150, with possibly the exception of a slightly different column lock tab on the tube.

GS160 is a whole 'nother bird altogether.
@ginch avatar
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@ginch avatar
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UTC quote
rob hodge wrote:
ginch, i'n not quite sure what you're getting at with that frame jig. no one is arguing that the different frames have significantly different rake angles, but because the lower bearing races are at different heights swapping forks definitely alters the rake and handling.

the rake is truly bad putting a P fork into a vintage frame- because the P fork has one of the longest lengths from the center of axel to the lower bearing race of pretty much all shifter vespa forks. (yes, you could go with a shorter shock, but then this alters the angle of the suspension swing arm and that changes handling in yet other ways.)

when the distance between the axle and the lower bearing race is increased (as it would be by putting a P fork into an older frame), this lifts the front of the bike up, and increases the rake angle of the bike.

to answer the original question, the ease of retrofitting a disc brake combined with the plethora of aftermarket shock options are the main reasons.
up until about 3-4 years ago unless you had a P you pretty much had at most two or three options when it came to choosing a front shock.

another reason is that on 60's 8" bikes it's one of the better ways to put a 10" wheel on the front ad the only stock-style way to do it right is to track down a GL or GS 150 fork - rare birds these days.
I'm only saying that the rake angle on the frames is exactly the same. It's a good point regarding the longer lower leg altering rake however. Mine is shortened and sleeved the same way that Scooter and Service do their conversion forks.
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Rally180
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UTC quote
Checking the SIP catalog, they have a conversion fork which allows fitting a shortened PX shock and a disk brake. This must be what I see the Rally bikes with. It also implies that a P bike has more suspension travel than a Rally.
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@joshzingzing avatar
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UTC quote
rob hodge wrote:
joshzingzing wrote:
Rob is a vglb/vgla fork the same as a gs150 or 160 fork




just curious as they share a vs5 mudguard but use a vna frame
should be the same as a GS 150, with possibly the exception of a slightly different column lock tab on the tube.

GS160 is a whole 'nother bird altogether.
thanks rob could be interesting if i put where to put a kitted p200 in my vb1 frame and put a GL fork ala poor mans gs150 style
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Molto Verboso
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UTC quote
crock wrote:
Checking the SIP catalog, they have a conversion fork which allows fitting a shortened PX shock and a disk brake. This must be what I see the Rally bikes with. It also implies that a P bike has more suspension travel than a Rally.
no, that's a converse busing a PK fork.

regardless, these conversions don't have significantly more travel. and it's far from as straightforward to convert it and maintain good handling characteristics as they make it out to be.
@jackson85 avatar
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T5 Pole Position, T for thoroughbred
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UTC quote
SFvsr wrote:
I like the PK fork. You can change how low the arm sits with different dampers. Those conversions are cool. I've done it three times. I'd have done it a fourth, but I am selling that project.
Half the 'project' Pk you get for sale over this way are missing the fork for this very reason. Very popular here
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'69 Vespa Sprint, '59 Lambretta LI125 (S1)
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UTC quote
This conversation is not boding well for my wideframe resuscitation project.

I have a 1954 Allstate body and I was planning to put the engine and fork from a P200 in there. (I'm not thrilled about the undamped 8" Allstate fork.)

I haven't done the rake and trail measuring and math yet. Any other front fork suggestions?
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Molto Verboso
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Molto Verboso
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UTC quote
fciron wrote:
This conversation is not boding well for my wideframe resuscitation project.

I have a 1954 Allstate body and I was planning to put the engine and fork from a P200 in there. (I'm not thrilled about the undamped 8" Allstate fork.)

I haven't done the rake and trail measuring and math yet. Any other front fork suggestions?
sure. make a bushing for the bottom, move the top bracket on the fork and run a small frame shock in place of the spring on your stock allstate fork.
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UTC quote
Cool. That makes sense.

Thanks, Rob Hodge.





Anybody need any P forks? I have two.
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