Lowering dilema

[gentlemanjim]

I swapped out the stock 15.5" shocks for 13.5" shocks believing that would lower the bike (seat height) about 1.0"to 1.5".  The under frame is now sitting on the fender bottom.  I plana to drop the fork tubes a similar amount to level the bike, but somehow, I don't think I have my doubts.  Where did I go wrong in my calculations?

[Perazzimx14]

Yes you have lowered the bike by pulling the rear wheel up two inches. You've taken out 2 inches of travel out of the equation on a bike a bike that only had  4.4" (V7-II?) of suspension travel to begin with, its a lot.

I'd be inclined to send the shocks back and put the stock length back on then have someone rework the seat thickness to get you lower to the ground.

[gentlemanjim]

My objective was to lower 1".  Thinking angle of the shock mounting would work.  Going with a 14.5: shock give the 1" drop?.  And yes, of course the trimming the seat in height and width would be a big help too.

[DoubleGuzzi]

I'll be playing around with shocks on my V7s soon. I bought used Bitubo ones to try out on the V7III, which will free off the current TEC ones. Although shorter than used on my V7C, the TEC ones are ride height (shock length) adjustable by up to about 15mm. Additionally, they are supplied with "slugs" that screw on the bottom, to lengthen them further. This give a lot of scope for adjustment - important for my ~29" inseam. To coin a phrase: an inch can make all the difference!

Example of "slug"/extender/riser


 

There are a number of cheap Chinese shocks that have that same length adjustment,if you can bring yourself to try them. There are also much more expensive versions from some of the big names.
Food for thought?

I also have old Hagons that came with the 750 Breva and a used set of Hagon Nitros that I bought erroneously for the V7III. Both are the standard length for the V7 Classic, however. The Nitros are a bit "flash" for the scabby looking V7C though. 

Here's a pair of Lawless ones for an Indian Chief



Notice the silver nut at the base.This indicates the lower eyelet can be removed and/or the shock lengthened to some degree.

You haven't said which bike but I managed to source a lower profile rear tyre for my Breva, which slightly reduced the seat height.

[TOMB]

NOTE!

You should / must keep the rear axle even with the swing arm pivot bolt when seated. Or slightly lower than the universal.

If not, you might/ will have the rear diff oil migrate into the universal boot leaving the rear diff with lower level of oil and if that happens it gets $$$$$$$$$$$$$.

So plan ahead but also consider the unknowns.

There is/are plenty of experienced Guzzi gurus here that have experienced plenty of let's say unusual problems , so ask away, the problem you have may have a ready answer found here.

My personal ride is a 1976 Convert, and that is a bike that can/does deliver many memorable miles/memories.

TOMB

[Huzo]

Because the shock is not at right angles to the swingarm, the axle does not move in a linear relationship with the shortening of the shock.
Imagine the shock was at a more extreme angle, say 45 degrees to the swingarm, a one inch movement of the shock mount would be a 1.4 inch movement on the axle.
Suffice to say that shortening the shock by “x” moves the axle 1.4 times as much.
Also as the angle between the shock centreline and the swingarm centreline becomes more acute, the compressive force on the shock begins to magnify.
You are losing both ways.

[gentlemanjim]

Interesting.  As I understand it 1" reduction in shock length lowers the bike or raises the axle 1.4 "  so, the 3" used lower the bike 2.8"  And 1/3" will lower .7".

[Huzo]

If you used a 3” shorter shock and it was at 45 degrees to the swingarm, the bike would sit 4.5” lower.
Now the effect will not be that much because your shock is not 45 degrees.
The thing to do is, take your shocks off and block the bike up to the height you want with the rear wheel touching the floor and then measure the eye to eye distance, that will be before the sag occurs so allow some length for that.
That’s where to start.

[SIR REAL ED]

If you used a 3” shorter shock and it was at 45 degrees to the swingarm, the bike would sit 4.5” lower.
Now the effect will not be that much because your shock is not 45 degrees.

You got this part backwards Huzo.  Think in terms of seat height measured perpendicular to the ground (vertical), and shock angle measured from vertical.  Vertical is one leg of the triangle, the shock length is the hypotenuse of the triangle.  Then it is simple Trigonometry.

If the shocks are 45 degrees from vertical, seat height will be lowered by Cosine 45 (.707) times the change in shock length.

The thing to do is, take your shocks off and block the bike up to the height you want with the rear wheel touching the floor and then measure the eye to eye distance, that will be before the sag occurs so allow some length for that.
That’s where to start.

But you redeemed yourself by getting this part right!!  When in doubt, tape measures and to scale sketches are great for verifying or disproving initial ideas.  Especially for people like me who have dyslexia!

go get them Buddy!

[Huzo]

You got this part backwards Huzo.  Think in terms of seat height measured perpendicular to the ground (vertical), and shock angle measured from vertical.  Vertical is one leg of the triangle, the shock length is the hypotenuse of the triangle.  Then it is simple Trigonometry.

If the shocks are 45 degrees from vertical, seat height will be lowered by Cosine 45 (.707) times the change in shock length.


But you redeemed yourself by getting this part right!!  When in doubt, tape measures and to scale sketches are great for verifying or disproving initial ideas.  Especially for people like me who have dyslexia!

go get them Buddy!

I feel a phone call coming on Ed.

[gentlemanjim]

You guys are great, thanks.  I always thought if the shocks were 90 degrees vertical an inch shorter would lower the bike 1" and every degree inclined would be less than an inch.  Correct?  And my shocks are inclined 50 degrees.

[SIR REAL ED]

You guys are great, thanks.  I always thought if the shocks were 90 degrees vertical an inch shorter would lower the bike 1" and every degree inclined would be less than an inch.  Correct?  And my shocks are inclined 50 degrees.

you are correct.  If the shocks are inclined 50 degrees from vertical, then seat height will be lowered by the change in shock length times the Cosine of 50 degrees, or 0.64 times the change in shock length.

Anyone who takes a little bit of time to understand the Unit Circle, which is the origin of Trigonometry will be amazed how often they will use it going forward when trying to figure things out dimensionally.

[SIR REAL ED]

I feel a phone call coming on Ed.

I always enjoy those phone calls my Love....  (insert heart emoji here)

[gentlemanjim]

If you are correct then 2" shorter shock length x .64 = 1.28" . Fact is the bike dropped over 4" all the way down to resting on the tire.  Your calculation is what I expected about 1.0" inch 1.5"'s

[Kev m]

If you are correct then 2" shorter shock length x .64 = 1.28" . Fact is the bike dropped over 4" all the way down to resting on the tire.  Your calculation is what I expected about 1.0" inch 1.5"'s

The geometry/math is fine.

But if you're saying the bike dropped further than the geometry said it should, then you're forgetting the physics.

The geometry is only good if the shock is equipped with an appropriate spring that holds the bike up to the full length of said shock. If the spring rate is too low or the preload is not set, then the bike may sag under its own weight, changing the geometry.

[Dirk_S]

The geometry/math is fine.

But if you're saying the bike dropped further than the geometry said it should, then you're forgetting the physics.

The geometry is only good if the shock is equipped with an appropriate spring that holds the bike up to the full length of said shock. If the spring rate is too low or the preload is not set, then the bike may sag under its own weight, changing the geometry.

I was wondering the same thing about the preload.

Since I’m the stinker who sold you the barely used stock V7 III shocks, I thought I’d chime in with a drawing if it helps. Keep note of the following:

• the photo probably shows the shocks under static sag.
• it’s merely an estimated drawing, not a precise CAD schematic.
• the swing arm radius/circumference is not (quite) at the axle, but rather at the shock mount, which is maybe two inches higher than the axle

And if they end up not working out at all for you, shoot me a message.

[gentlemanjim]

That's what I thought.  I really appreciate your input.  The shocks are stock V7 13.5" and I cranked the preload all the way to the maximum with the threaded collars.  Weak springs, I guess, very weak springs.

[Kev m]

Oh, this is a stock V7III shock? Yeah, mine are near useless. I've got the preload set literally all the way up to the end of the threads and they just kinda work like shocks now.

[DoubleGuzzi]

I cranked the preload all the way to the maximum with the threaded collars.  Weak springs, I guess, very weak springs.

I've got the preload set literally all the way up to the end of the threads and they just kinda work like shocks now.

Hmm. Minus my biking clothing, at ~144lbs I need the preload backed off for the standard V7III shocks to perform with any comfort. The currently fitted TEC ones are also too harsh and need preload lessened. I haven't bothered yet, as I'm about to try out the Bitubo ones.

[Kev m]

Hmm. Minus my my biking clothing, at ~144lbs I need the preload

Aww how cute

I think my 12 y/o son is about that big.

I'm in the 230's.

[DoubleGuzzi]

Aww how cute

I think my 12 y/o son is about that big.

I'm in the 230's.

My bad : I forgot how to count in vintage measurements, actually 169lbs but overweight by about 20lbs!

[Kev m]

My bad : I forgot how to count in vintage measurements, actually 169lbs but overweight by about 20lbs!

A long time ago I used to fight < 180#.

[gentlemanjim]

I'm back and ready to ride, had a business trip. 
Should I consider buying stiffer strings or just buy new shocks?  I weigh 165 lbs.
Where can I get springs only?  Are they easy to change?  Can I use the springs off the original 15.5" VII shocks?  Which held the bike up fine at the lowest preload setting. 

[Kev m]

I'm back and ready to ride, had a business trip. 
Should I consider buying stiffer strings or just buy new shocks?  I weigh 165 lbs.
Where can I get springs only?  Are they easy to change?  Can I use the springs off the original 15.5" VII shocks?  Which held the bike up fine at the lowest preload setting.

I think the length of the old springs would be a problem. To install them on the shorter shocks you'd already be giving them ~2" of preload at the minimum setting.

[gentlemanjim]

Latest update:
1. installed springs from the original 15.5" shocks on the V7iii 13.5' shocks.
2. Cranked the preload collars to the max.  Now its a true hardtail no suspension movement at all.
3. Seat height 29" from the original set up at 31.4"
4. In spite of all the math and science the regardless of the 50-degree shock angle the bike was lowered 2" exactly the difference of the two shocks (15.5' to 13.5")
5. Conclusion going back to stock shock length and springs.  Reduce the preload a bit and modify the seat, as was suggested.
Thanks for all  the help and guidance