Topic: Shock Length As A Way To Control Rake

[spiritof67]

A question about high performance handling for CB750's: since adjustable ride height is difficult and expensve for twin shock bikes, for two-up fast travel is it recommended to use a longer rear shock as a way to control rear sag? I have seen 13", 13.25", 13.5"and 13.75" rear shocks for CB750's.Is this how we control the proper front end rake? And if so, what's the recommended length for a fast ride two-up? I'm assuming my NOS S&W air shocks are a non-starter!

[FunJimmy]

I'm assuming my NOS S&W air shocks are a non-starter!

Considering sag is an indication of correct or incorrect spring rate, I would think your air shocks would provide the adjustability nessesary for two up riding. Longer shocks are not the answer to high payload. You need the correct spring rate for the rider/passenger weight and air shocks would allow you to add spring rate when required.

[turboguzzi]

shock length is indeed a common way to sharpen steering in twin shock bikes.

but until you find out what works best for you, there's another path: shock extensions.

they can be made either as milled blocks that bolt between shock and swingarm ears or as triangular side plates, lets you try quickly the impact before committing to a shock length

take into account that if you go real long, as well as reducing rake you are also reducing trail and you'll need custom triples with less offset to compensate, but that would be a track oriented setup.

another limit is chain rub on the top of the swingarm right bearing, that is a real physical limit to shock length

bt +10-20mmm should be pretty safe on both accounts. 

[Jerry Rxman Griffin aka MuthaF'er]

I used S & W pumpers and found them an easy solution back in the day after my Honda shocks took an early dump. Kinda bouncy but they served a purpose and that was not knee dragging. I never tied them in together and it was difficult to keep the pressures the same. May still have a few bits and pieces of hardware around if you are interested. I'm running a 75 F. I drilled 2 holes on each side of my license plate and mounted the valves there. Clean install but I would recommend tieing them in together.

[Old Scrambler]

I have fading bruises on my back from my wife wanting me to 'slow-down'   I installed Mulholland HD springs and was very pleased. I have since seen even stronger units on a 2-up ride.

Yes, you need to measure the sag to try and equalize the loaded 2-up with the normal amount. That will benefit chain-wear and should keep the trail at the desired amount.

[Retro Rocket]

shock length is indeed a common way to sharpen steering in twin shock bikes.

take into account that if you go real long, as well as reducing rake you are also reducing trail and you'll need custom triples with less offset to compensate, but that would be a track oriented setup.

Its relevant to road set up on a 750 too TG, they only have 3.7 inches of trail and if everything isn't perfect, can be prone to tank slappers, I wouldn't reduce rake, and therefore trail, on a road based 750 without having new triples made with less offset, also a steering damper would be recommended...

[spiritof67]

I'll have to look into that - I only thought of blocks as a lowering device. Good idea.

[spiritof67]

I have a new/never used set WITH the join valve. I never liked them before,but now I think I didn't do enough tinkering with pressure. IF they hold air after 40 years of dry storage I think they'll be interesting. If not, a set of Hagons, maybe 13.5" instead.

[NobleHops]

If you explore this I really encourage you to do so in small increments - 5mm at a time up front, maybe a bit more out back - 10mm at a time? Stability can become an issue as noted. Raising the rear and lowering the front did magical things to a slow-steering VStrom I owned, but the side and center stands became less optimized and you needed 34+ inch inseam to ride it.

[NobleHops]

P.S. In my experiments I tried as much as 15 mm drop in front without raising the rear at first and positively SMASHED my feet in a few tight corners before I backed off. I ended up down 10 mm in front and 15mm up in the rear to restore some cornering clearance, and that was a great setup for that bike.

[NobleHops]

I'm assuming my NOS S&W air shocks are a non-starter!

Considering sag is an indication of correct or incorrect spring rate, I would think your air shocks would provide the adjustability nessesary for two up riding. Longer shocks are not the answer to high payload. You need the correct spring rate for the rider/passenger weight and air shocks would allow you to add spring rate when required.

This is the money post in this thread. Spring rate is the critical element for getting sag right when loaded. Ride height can be tuned as desired to optimize chassis geometry, but those are completely separate factors. Works and a few others offer dual spring setups for this very purpose of optimizing spring rate for two very different loads. Threaded or ramped preload collars are a poor substitute for the correct spring rate.

[turboguzzi]

the silencer is covering the top bolt that attaches the shock, but you get idea...

those triangles are super easy to in any dimension you want. i hit my sweet (track) spot after two tries

[spiritof67]

Thanks to all for some real meat to chew on in this endeavor. Here's what I'm contemplating: I have an NS set of S&S air shocks I am dying to try, so I'll start there but with braided stainless hoses instead of the NOS plastic fittings. I also have the accessory air pressure gauge and mini pump. I'll start with them and see where it goes.If they prove to be intractible, I'll give Works a try.