fork length?

[drlapo]

I'm still working on the forks on my Thruxton and am calculating spring preload now
I have Progresive springs and they reccomend 2.5" spacers for the Trhuxton, 3" for Bonnevilles and 4.8" for Scramblers???
as the springs are the same I assume the inner fork tube lengths are different
can anyone confirm this?

 

[drlapo]

i may have found the problem
the Progressive springs are .63/.89
stock is .72
RaceTech reccomends straight .90 for the Thruxton for my weight
the Progressives are too soft
this explains the front end dive when hard on the brakes or diving into a turn
I'll try more preload before I put the Progressives up for sale

 

[beemerrich]

That's the problem I have with progressive springs...by the time you dial in enough preload to get the sag right, the spring is no longer 'progressive'!
In your case, the firmer part of the progressive spring is pretty correct for your weight - so you might be OK by simply increasing preload until the lighter weight portion of the spring is compressed.

BTW, despite having longer fork tubes than the bonnie, the thruxton takes shorter spacers to account for the extra length of the preload adjustable fork caps...

Regards,

--Rich

 

[drlapo]

its a bitch getting the fork caps back on with longer spacers
I added an inch of preload, spacer, and have the adjustesr wound down to 3 lines showing
its off for a test ride now

 

[drlapo]

more preload is the right wy to go
almost there but I'm going to get RaceTech .90kg springs
so the almost new Progressive springs will show up on this site for sale soon

 

[beemerrich]

yeah, I made that same mistake in the past...the only way to go is straight-rate springs specified to your weight/riding style. With F3 forks & wheels, single rate springs, and sportbike rubber, my bike corners like its on rails...

Regards,

--Rich

 

[drlapo]

the .90 RaceTech springs are in but it's raining
the Progressive springs are for sale $50 shipped (in classifieds)

 

[tooblekain]

yeah, I made that same mistake in the past...the only way to go is straight-rate springs specified to your weight/riding style. With F3 forks & wheels, single rate springs, and sportbike rubber, my bike corners like its on rails...

Regards,

--Rich

Yep, I had did the F3 fork conversion (but forks only) and used the progressive springs that came with the F3. What a nightmare. Straight spring rate springs is the only way to go. I installed Racetech .95 springs and cut an 80mm spacer to get my sag proper sag numbers, but preload is taken all the way out. Luckily I also cut a 70mm spacer and for my next fork oil and seal change I will change to the 70mm spacers and that should bring my preload adjusters around the halfway mark. Plus I plan on losing more weight so more reason to switch. I also found out that my F3 fork tubes are bent, so I will be ordering new fork tubes soon from Racetech.

 

[drlapo]

so I've been f--king around with the forks for months
RaceTech emulators and straight wound springs, different oil
true and balance the wheel, even a new tire
but it still will not handle small ripples and bumps
so yesterday, after my son rode the Thruxton to BritJam, i light up a cigar and just look at it
bad bushings?
i loosened the axle and bounced on the front end, I loosed the pinchbolt too
then i smacked the end of the axle with a hammer and the right fork tube "sprung" out a bit
now the suspension is smooth and supple
the axle was binding in the right fork leg even though i tightened the pinch bolt after tightening the axle and bounced the forks before tightening the pinch bolt
i used a wooden broom handle to push the fork leg out and let it move back
now things are looking good; time for another test ride