1981 GS1100 fork swap... HELP

tacocart

New Member
I have an 81 gs1100e. I want to replace the front shocks with something newish. Maybe from a GSXR. I found that these have the same bearings. How hard is this swap? What's involved?

Suzuki GSXR1100 (90-93), GSXR1100F (88-92), GSXR1100G-M (86-91), GSXR1100WP/WR/ WS/WT/WV (93-98)


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GSXR1100K forks are pretty nice, the 1st gsxr cartridge forks. 43mm conventional (RSU). A bit shorter than the GS1100 forks though.

The best swap to retain correct height for the GS frame is Bandit 1200 43mm cartridge forks. these have excellent damping and good height and spring rate for the older GS big fours.
Much larger axle however. A guy on the GS forums had some axle adapters made up to use the stock GS axle on the bandit forks. Seems the best swap so you can keep your speedometer drive and keep geometry similar
1993-2005 or 2007 Yamaha VMAX 1200 triples are 43mm fork tube aluminum triples with a 50mm offset to retain proper steering geometry on an older bike like ours, or improve. Most modern fork swaps add better brakes and damping to our old bikes, but threaten to totally ruin the handling of the vintage bikes due the modern triple clamp offsets are designed around frames with substantially steeper rake AND 17" wheels with low profile tires. Therefore using a modern triple on an old frame and a 19" front wheel gives you such a massive amount of trail that the old bike steers like a truck with the "upgrade."

A few guys on the GS forum like the late 80s gsxr 750/1100 triples (bikes that still used 18" wheels - wheel diameter and head tube rake are the primary dictators of steering quickness or slowness), but still those triples withe even taller rear shocks and dropping the front ride height will leave you in the low 4" range in terms of trail. Modern sport bike triples will give you high 4" range (closer to 4.5" or 5"!!!) of trail. 3.75-3.9" is the preferred sporty/crisp handling range, no more than 4.1" or so unless you are just looking for high speed straight line stability. 3.75" of trail is more geared towards tight twisties type road riding, & on a flex frame like an early CB or Z1, would without a doubt require a steering damper.

Look up an article and illustration of trail if you are not 100% familiar with this most critical spec of steering and chassis geometry.

I'd say do the 89 gsxr1100k swap and 18" gsxr front wheel from that era with gsxr or GS1150 3.5" wide rear wheel (popular GS upgrade) & slightly taller rear shock upgrade ($300+ quality), or do the bandit 1200 with an adapted VMAX 1200 triple and whatever brake adaptation that it takes to run that width triple (mags may be fine running the band it calipers). The opposed piston calipers that bolt to those come inboard quite a bit of distance toward the wheel, so wire spoke wheels may have spoke to caliper clearance issues. Not sure on mags but typically not as wide as wire spokes there.

I'm in the process of figuring out how to swap an aluminum gsxr/Hayabusa steering stem into the VMAX triples for both my Rickman CR900 GS racer build (RF900R or GSXR1100K forks) and a second set either for Bandit 1200 forks on my GS750 or RF900R (same but shorter) or RF900R forks on my 79 GS425 489cc racer brainstorm project.

Stay tuned, I'll add more details later. Cbr600f3 (& last year of f2) are also great and zero brake clearance issues. There are a few triples that work well with these 43mm cartridge forks (84 Honda interceptor, late model CB Nighthawks, etc). Bigger axles still however. Nothing a machinist can't adapt for you though.

There are some great Honda late model floating rotors that bolt to GS wheels and come in the needed 296mm and 310mm diameters.

Look on the GS Resources Forums for the Bandit 1200 info. The recommended gsxr1100k triples they talk about will still give a lot of trail, so best to try for an 18" 80's GS 2.15x18 front mag swap (850G? GL?) or 2.15/2.50x18 early GSXR double 3 spoke front wheel. Smaller diameter front tire o.d.'s reduce trail, so does steeping the rake of the frame by adding up to 1" taller rear shocks and dropping the front down by sliding glass the triples down on the fork tubes. Don't want to drop the front too much however, or else you will lose much needed cornering clearance and scrape pegs/engine cases/exhaust and also smash the bottom of the nice 4 into 1 exhausts on steep approaches and speed bumps...

I did a very in depth thread on http://www.thegsresources.com/_forum/showthread.php?237305-More-modern-cartridge-fork-options-retaining-GS-wheels-amp-proper-revised-geometry
 
I've been running bandit 1200 forks and wheels for years. No handling issues at all.
 

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