GSXR1100 (1991/1992) Fork upgrade

[FJNovaScotia]

OK George,

Just watched the video and a buddy of mine happened to just drop by so these are my measurements:

With the highest spring rate setting:   10MM static and 60MM with a rider (185 lbs).   That is double what is recommended in the video.

This is also throwing off my USD fork measurements. When I get on the bike the front doesn't drop evenly with the rear.

Summary:   Rear is way to soft for my liking.

[giantkiller]

I would like to put a stiffer spring on my honda f4i shock. Haven't had the time to search one out. (Im not too good @ it) If you find one let us know.

[movenon]

I would like to put a stiffer spring on my honda f4i shock. Haven't had the time to search one out. (Im not too good @ it) If you find one let us know.

Check this out. Its good info on the spring http://cbrforum.com/forum/how-mechanical-40/how-rear-spring-change-66943/

http://www.eshocks.com/hyp_make.asp

George

[movenon]

I'll take a look at the video for sure...thanks!

Another question, how long did you make your new dogbones?   Mine are 130MM from center to center.

My bones are 125mm c to c.. With the center stand on a 2 X 8 (1.5" thick) broad my rear wheel has 1/4 clearance off the concrete floor. I estimate the bike now sits 1.5 inch's higher than stock in the rear. I put a 3/4 " "shoe" under the side stand, now sits at approx the same angle as a stock FJ. I will have to remove the center stand before I take it out to ride. I plan on redesigning the center stand if I decide to keep the shock on.
I thought about a heaver spring but again, I want to see how it works before ordering a spring. I need a valid reference point. Other wise you are just shooting in the dark. The Honda spring rate on paper is lower than the FJ but there are other things like the links, ratio's etc that come in to play. Plus factory claims and numbers are debatable.  I thought I would educate myself on the subject, let me save you some time. Don't bother, it will give you a severe head ache.  

If you order new springs make sure you get those collars from race tech. The Honda spring is tapered and the aftermarket ones are straight, you will need the race tech collars. They are cheap.

Another coil site  http://www.hrpworld.com/index.cfm?tpc=Hyperco-Coil-Over-Spring-6-Inch-Free-Length-2.25-Inch-ID-2&form_prod_id=926&action=product
George

[movenon]

I can not remember where I got the information but the spec's I have for a 1990 stock FJ shock is:

Stock 1990, 3CV-10  FJ Shock:
Coil turns= 6    Coil dia. Bottom =85.60mm  Coil dia top= 87.60mm         Coil thickness= 13.8mm   Coil length on shock= 5 13/16

1989 Stock Rear Suspension
Shock Absorber Travel              40mm(1.57in)
Spring Free Length                  163.5 mm(6.44in)
<Limit>                                  159mm (6.26 in)
Fitting Length                         151.5mm (5.96 in)
Spring Rate                            196 N/mm (20kg/mm 1,120lb/in)
Stroke                                   0-40mm (0-1.57in)
Optional Spring                        No

George

[FJNovaScotia]

Any thoughts on taking the fj coil and putting it on the f4 shock?    They look close, both are tapered and are close to the same inside diameter on both the tapered and non tapered end (I'll have to use a caliper to be sure)?

Anyone remove the spring from their FJ rear shock?

[Arnie]

George,

I don't know where you got those numbers for the OEM stock shock, but they are definitely NOT what Clymer (yeah, I'm cautious about this as a facts source too) lists as specs for that spring. 
They list 174.5mm as free length (new) and 170mm for the 'wear' limit for the 84-90 bikes.
The 91on bikes are 181mm (new) and 174mm 'wear' limit. 

This IS pretty close to what I measured after removing a few springs a number of years ago when we had some springs made.

The spring rate is also not anywhere near the 1120 lbs/in you list.  Much closer to 6-700 lbs/in.

We had 2 spring rates 'ordered' of 900 and 1100 lbs/in.  Unfortunately, the springs delivered were a bit long so the preload was higher than desired when installed, even with the ring at minimum setting.

Removing and installing these springs was a difficult and dangerous operation.  Using 2 screw type coil spring compressors with modified jaws, we stripped one of the compressors after about 8 spring changes, and broke the jaw of the other.  Luckily none of us was in the path of the flying metal. :-/

If you don't have proper tools and some experience be VERY careful.  There is a LOT of energy just waiting to be released when you have the spring compressed enough to get the keeper out.

I haven't measured the F4 shock spring rate, but it is probably in the 900 lb/in range (by feel).  Certainly stiffer than the OEM '91 or '89 springs.

I'm about 105kg (too fat) and find the F4 shock and spring suit me very well for the road solo or with luggage.  A bit soft with a big passenger added. 

Arnie

[giantkiller]

The Honda shock on mine is way too soft for a fat guy like me. The guy @ Traxxion told me the spring on the Honda f4i shock was around 780. The guy on the cbr forum switch to 900 eibach and thought it was alittle too stiff. And thought he might go down to a 850. So the original must be less than that.

I just got done ordering an eibach 900 and the bushings to fit it to the f4i. Might be a few weeks to get the spring.

Just wanted to say thanks to everybody that led the way on the Honda shock.

[movenon]

George,

I don't know where you got those numbers for the OEM stock shock, but they are definitely NOT what Clymer (yeah, I'm cautious about this as a facts source too) lists as specs for that spring.  
They list 174.5mm as free length (new) and 170mm for the 'wear' limit for the 84-90 bikes.
The 91on bikes are 181mm (new) and 174mm 'wear' limit.  

This IS pretty close to what I measured after removing a few springs a number of years ago when we had some springs made.

The spring rate is also not anywhere near the 1120 lbs/in you list.  Much closer to 6-700 lbs/in.

We had 2 spring rates 'ordered' of 900 and 1100 lbs/in.  Unfortunately, the springs delivered were a bit long so the preload was higher than desired when installed, even with the ring at minimum setting.

Removing and installing these springs was a difficult and dangerous operation.  Using 2 screw type coil spring compressors with modified jaws, we stripped one of the compressors after about 8 spring changes, and broke the jaw of the other.  Luckily none of us was in the path of the flying metal. :-/

If you don't have proper tools and some experience be VERY careful.  There is a LOT of energy just waiting to be released when you have the spring compressed enough to get the keeper out.

I haven't measured the F4 shock spring rate, but it is probably in the 900 lb/in range (by feel).  Certainly stiffer than the OEM '91 or '89 springs.

I'm about 105kg (too fat) and find the F4 shock and spring suit me very well for the road solo or with luggage.  A bit soft with a big passenger added.  

Arnie

Arnie,

On these projects you gather up all the data you can find but there is no substatute for seat of the pants. I don't trust any of the numbers that are published at least to a point. I also think the 1120 lb figure was high. But having no real data you just start digging for answers.

My spring is stock right now and after I ride it I might change the spring, but I need to know where I am before I go changing springs. I have changed motorcycle shock springs in the past. They can be intimidating. I have never had a close call but,,, I was keenly aware of what I was doing.   Ever changed a garage door spring ?   It will get your attention..

Good point on the aftermarket spring being longer thus adding some built in preload.

I am a shade under 98kg and trying to hit 90-91kg. I started the "bio engineered suspension improvements" in Nov. at 116 kg.

The last post from "giantkiller" he mentioned someone going to a 900 lb spring and thought it was a little to stiff. That comes into alignment with what you discovered at 900 lbs of spring. He mentioned going to 850lb spring. He didn't mention the guys weight and preffered riding style.  I lean more toward touring with a little power to play with.....  

Thanks for the input Arnie.

giantkiller:

If you can, keep us posted on the spring change. Its all good information. Another member in Utah is also doing the same shock conversion and I am sure he is following this post also.
George

[giantkiller]

The guy that said he thought the 900 was maybe too stiff, was on a Honda f4i( lighter bike). And I believe he said he was 180lbs. The guy @Traxxion that I talked to on the phone said I should go to 1000-1100lbs. But he wouldn't even sell me a 900 without him doing a revalve. Even after I told him I would send him the shock if it didn't work.

[FJNovaScotia]

Hey Arnie,

You mention that the stock f4 shock works for you.    Would you be able to measure static sag?  Perhaps the nitrogen charge is low or non existent on mine.

I'm going to have mine looked at by a local bike suspension guy but that won't be for another couple weeks (he is on vacation).

Jason

[Arnie]

Just measured static sag at 12mm and rider sag at close to 50mm.  Not exact on rider sag doing it myself.  I'll crank in another notch or two of preload to see how that feels.

Note: I ride torn up roads and not smooth racetracks, I don't want it too stiff for my old bones :-)

Arnie

Hey Arnie,

You mention that the stock f4 shock works for you.    Would you be able to measure static sag?  Perhaps the nitrogen charge is low or non existent on mine.

I'm going to have mine looked at by a local bike suspension guy but that won't be for another couple weeks (he is on vacation).

Jason

[FJNovaScotia]

Thanks Arnie that is close to my measurements 10MM/60MM.    I'm going to swap the fj coil into the f4.   Can you describe how to seperate the fj rear shock?   The top part of the shock screws off, is that part under load?   Do I have to remove that first, then compress the spring and remove a clip inside the shock to allow the bushing and spring to be removed?

Jason

[Arnie]

IIRC
I compressed the spring until I could slip the upper keeper/seat out. 
The spring then just slips over the upper mount eye.

Arnie

[FJNovaScotia]

Hey guys,

Still researching to see what I can learn about the f4 shock.   Based on my research thus far I believe that the shock needs a stiffer spring to handle the heavier FJ.   I have been researching VFR forums as this is an option for that bike as well.   Even using the VFR as a platform the consensus is the same: the f4 shock spring isn't enough to handle the load.   Here are the sites I have been reviewing:

http://www.vfrdiscussion.com/forum/index.php/topic/32986-cbr-f4-shock-in-place-of-vfr-shock/
http://www.vfrdiscussion.com/forum/index.php/topic/73424-shock-option-vfr1200-rear-shock-on-vfr800/
http://www.vfrdiscussion.com/forum/index.php/topic/19712-vtec-shock-options/


I still think the best option right now is to replace the f4 spring with the fj spring and see if the dampening can handle the heavier shock, if not then will I revalve or buy a new shock?   I'll be on vacation for the next 2 weeks.  I'll post my updates when I get back.

Jason