Steering mod - 17" rims

[eeshed]

Recently I have completed the modification of 17" rims; the front is FZR1000 (1988) with FJ1200 (1992) forks + RPM spring/vales , back GSXR1100 (1992), and the riding characteristics have completely changed. I am not sure if I love the change. The bike is more "lazy" to turn, keeping upright. I am interested with quickening the steering however.  Is there any way to "quicken" the steering? I do not wish to go back to 16".

The front tire is a 120/70ZR17 (58W) CONTI ROAD ATTACK 2 GT
Thanks,
Eyal

[1tinindian]

Sounds like you forgot to raise the rear end.
That goes hand in hand with what you have already done and will quicken the steering response greatly.

Leon

[eeshed]

Leon,
How do I raise the back? I forgot to mention that on the back I replaced the shock with RPM's shock.
Eyal

[1tinindian]

What year do you have?
If you have dog bones, then shorten them.
If older, I bow to owners of same with advice.

Leon

[eeshed]

Leon,
My FJ1100 is 1985; no dog bones on the bike.
Eyal

[turbocamino]

  effectively,what you did was,at this point,is to raise the front and lower the rear...which,as you found out will slow the steering...probably,substantially.  The 17" front,now taller (vs. the 16") and the rear 18" tire is actually shorter that your typical 150/16 rear, by just a little.  That said...im pretty sure your only option is a taller rear shock...Penske makes one,Randy at RPM may be albe come up with something as well.  That last piece of the puzzle is what you are looking for...it will transform your handling into what you intended. hope this helps.

[Pat Conlon]

Leon,
My FJ1100 is 1985; no dog bones on the bike.
Eyal

Not yet that is...

Let's review shall we?  No..No...No..The difference is not with your new front 120/70-17 tire.

Tire Size Comparison
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
120/80-16         3.8in  11.8in    23.6in         74.0in        856        0.0%
120/70-17         3.3in  11.8in    23.6in         74.2in        854        0.2%

Your new 180/55-17 rear tire is the culprit (good call Leon)

Tire Size Comparison
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
150/80-16         4.7in  12.7in    25.4in         79.9in        792        0.0%
180/55-17         3.9in  12.4in    24.8in         77.9in        813       -2.6%

You new 180 tire is about 1/2" smaller in diameter than your oem donut. Allowing for tread wear figure 3/4"

A couple of things you can do;

1. Lower the front end by:
   a) Raising the stanchion tubes up in the triple clamps. Caution here: Fork dive....the RPM IAT valves uses softer fork springs than conventional cartridges or cartridge emulators, so beware of banging your fork brace on your fairing bottom, or horn. If you were using heavier springs, like a .95kg/mm or 1.0kg/mm springs I would say, go for it, give it a try....but I am unsure with the softer springs.

   b) Installing a smaller diameter front tire. A 120/60-17 (with a shorter sidewall) will fit just fine on your 3.5" wide front rim and is almost 1" shorter than your existing 120/70 tire.
Tire Size Comparison
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
120/70-17         3.3in  11.8in    23.6in         74.2in        854        0.0%
120/60-17         2.8in  11.3in    22.7in         71.2in        890       -4.0%

   c) any combination of a) and b) above

2. Raise the back end by converting your '85's swing arm linkage over to the '89/90 linkage which uses dogbones. I did this on my '84 and it wasn't that hard to do. The hardest part was finding the "relay arm" off a '89/90 FJ. The lower shock eye mount used on your '85 has to be swapped with a clevis style mount to fit the relay arm..(Randy @ RPM can help you there) Everything bolted up just fine on my '84. I used Soupy's adjustable dogbones so I could dial in the length exactly were I liked it.

Sorry for your disappointment, but no worries, we help get you there.
You made the right move by switching over to modern 17" tires (you know that right?) Now let's just dial it in

Keep the faith....Cheers. Pat

[FJmonkey]

Leon,
My FJ1100 is 1985; no dog bones on the bike.
Eyal

You have 2 options, hope and wait till the adjustable RPM shock comes out, it should be a bolt on to your existing RPM shock. Or, convert over to dog bones. You wil need an FJ 89' shock link, shortened bones and the other bits as well. I will be doing this on my 86' as soon as I can afford the RPM shock.

[Dan Filetti]

Can't he just drop the yokes further down the fork tubes?  AKA LOWER the front...  Is there a functional limitation to doing this that makes it unattractive/ impossible?

Just a thought.

Dan

Edit: Ignore this, just saw Pat's comprehensive response to this that discusses this in much more detail.

[markmartin]

You didn't by any chance, while you were working on the front end, adjust (tighten)the stem nut on your steering stem did you?  A overly tight stem nut will have the effect on the steering that you are describing.

[racerrad8]

Eyal,

Give me a call. I have the answer(s) but there are many questions to make sure everything is covered and going back & forth via the forum is not the way to address the issue.

You can post up your solution when you are done.

Randy - RPM

[eeshed]

Thank you all. I will contact Randy.
BTW, didn't touch the steering nut.
Eyal

[jscgdunn]

Going the f4i shock route will raise the rear an inch or more.

Jeff

[craigo]

Going the f4i shock route will raise the rear an inch or more.

Jeff

Why would anyone trade off the RPM shock for the F4 shock? Got to be a better way.

CraigO

[jscgdunn]

I think the RPM shock is a great option and again thanks to Randy for putting it together.

That being said, there are other options that may fit other budgets.

Jeff