Can you help me figure out my suspension plans?

[DrImodium]

I was working on my 80 GS1000 in the garage and had it proped up on its center stand. During one of my smoke breaks, I started looking at the stance of the bike the way it was sitting. It was much more along the lines of what I had envisioned so now Im starting to put my list together for my 78 GS1000e build.

So far this is what Im thinking:

Rear:
GS1100 Alloy swing arm
CBxxxx Rear shocks (365mm 14.5")
530 Chain Conversion
Spoke wheel

Front:
USD forks (still undecided)
Spoke wheel

I currently have the front forks slid up 1.5" in the triple trees leaving me with 29" of fork measured from the top of the triple tree clamp to the center of the axle.

My main questions are these:

What size rear rim and tire should I run with the GS1100 rear swing arm and CBxxxx 365mm rear shocks?

What USD forks should I run to keep the same stance that I currently have? What size front rim and tire can I use on a USD front end? Has anyone even done this before?

The main use of this bike is spirited riding in the NC mountains but it will also be ridden around town weather permitting. Between tire diameter and fork length and offset this and offset that, the numbers have my head in a bind tonight.

*for those wondering, the 80 GS1k will be getting the same rear treatment as the 78, but the 80 got a set of Progressive fork springs and new fork seals up front.

This is the stance that inspired this thread:

 

[Hoosier Daddy]

Hmmmm, not sure I understand , sounds like you want to raise the bike 1" all the way around. Might want to see how it sits when not on the centerstand. The longer shocks you mentioned and then new springs in the forks may just be what you are after.
Love the cafe' look you got going on!

 

[Mike]

Holy crap, that is an awesome looking bike.

 

[DrImodium]

Hmmmm, not sure I understand , sounds like you want to raise the bike 1" all the way around.

Im raising the rear 1.5" and lowering the front 1.5".

Might want to see how it sits when not on the centerstand.

The goal is to get the stance similar to what it is on the center stand. Currently there is 3" of clearance between there bottom of the tire and the ground when its on the CS. With the longer rear shocks, I should still have 1.5" of clearance, assuming I can even get it on the CS after I put them on. Im thinking it actually might make it easier to put it up on the CS but well see when they FINALLY get delivered.

The longer shocks you mentioned and then new springs in the forks may just be what you are after.

This is kinda a last resort for this project. I know I can get the height in the rear Im after by swapping in the longer shocks. The upgraded handling and brakes would be the justification for doing the USD GSXR swap. My 80 GS1k is my daily and it will be getting the Progressive springs up front. The 78 that this thread is regarding, is more performance orientated. Still undecided about whats happening with the motor, but I would rather have a suspension that reacts quicker/better and brakes that stop faster, before I dig in to the motor.

The main questions are:

1. Which USD front end (Or RSU for that matter) should I run. I know that some RSU forks are better than USD forks due to valving, etc. so I havent ruled RSU forks out but they would have to be off something that would also have better brakes.

2. What wheel and tire combination to run that will give me the best performance for the twisty roads and also keep the same stance I have right now.

Current setup:

Im trying to figure out what front end and rim/tire size/combo to run to give me the closest stance to what I have now.

 

[Hoosier Daddy]

I think the factory engineered handling characteristics into the bike with the suspension geometry.:-\\\
Now if you drop the front and raise the rear a inch and a half each you will change all that, less caster = less stability... careful, tank slappers suck.

 

[Ranger]

Check out makienzies thread. I noted stuff you MAY be able to do. If you have specific questions I have a program which allows me to evaluate possible suspension set ups.

 

[bwringer]

1.5 inches at both ends is a HUUUUUGE change, especially if you're going in opposite directions. It could be a Very Bad Idea at any speed, let alone in the twisties. Change things in smaller increments, and test-ride with every change to make sure you can live with the compromises.

First, I'd get the suspension working somewhat well, then goof around with ride height. How much is the bike sagging under its own weight, or with you on board?

Up front, you'll probably want some Sonic straight-rate springs rather than the unknown-rate Progressives, especially if you might reduce suspension travel up front with spacers on the damper rods. You can order up stiffer springs to make the most of limited travel.

Out back, it can admittedly get expensive to try out different shock lengths. Perhaps some sort of spacer, so you can go back to stock ride height?

Secondly, if you're after a certain "stance", ponder whether you want that to happen when the bike is just sitting there doing nothing or when it's rolling with you on it. A bike is primarily a machine, not a piece of static driveway sculpture.

 

[DrImodium]

Check out makienzies thread. I noted stuff you MAY be able to do. If you have specific questions I have a program which allows me to evaluate possible suspension set ups.

I searched threads started by username: makienzie and came up empty. Link?

1.5 inches at both ends is a HUUUUUGE change, especially if you're going in opposite directions. It could be a Very Bad Idea at any speed, let alone in the twisties. Change things in smaller increments, and test-ride with every change to make sure you can live with the compromises

Currently (in that picture as well) I have my forks slid 1.5" up in the triple trees. When the bike is on the ground, without my weight, the bottom of the cafe seat is level with the ground.

First, I'd get the suspension working somewhat well, then goof around with ride height. How much is the bike sagging under its own weight, or with you on board?

With my weight added to the bike, the rear sags 1/2"-5"8".

Also, consider what the GS is from the factory......an extremely versatile machine. It was capable of daily riding around town, racing, and touring all from the factory.

If you look at the angle of the bottom of the tank on this Yoshi, you can clearly see that the rear has been; Longer shocks, along with alternative shock mounts and swing arm. The second one maintains the factory upper mount, but the swing arm has been switched out. Concept still applies here tho.