Hey guys, if someone with stock suspension could please max your fork preload and take a measurement between the floor and the bottom of the lower cowl. Bike needs to be straight up and down and please compress the suspension and slowly let up before taking measurements to account for stiction.

I forgot to do this before I did the fork swap and I'm trying to compare geometry between stock, reworked stock, and my current setup. My bike looks a little tall in the front right now and tends to fall in a little at slow speeds. This will help me troubleshoot the problem.

TIA

 

Greg;

If nobody does it before, I can take a shot at tomorrow. By lower cowling, do you mean the belly pan, what the manual calls lower fairing? Mine's not on and won't fit 'cause I've got a +size oil filter on. I could measure to the bottom of the engine if that would help. Also, when you say max preload, do you mean just even with the top line on the adjuster?

 

That's cool. Instead of the lower chin fairing use the little black bolt head on the left side of the oil filter housing. That's what nuhawk used when he measured with his massaged stock forks.

Max preload would be the top line even with the fork cap.

 

Good. Should be able to do it by noon here on the coast (when I'll have someone to balance the bike).

 

From the floor to the center of that black bolt head is 170mm on my bike.

That's with the preload just showing top line on each. Front compressed and allowed up slow. Bike balanced upright.

Also if it matters- my front tire has 10k miles on it and the rear is almost new. Fork tube position in triple clamps same as when new.

I have stock shock and spring on #3 position. I also have a 4mm spacer on top of shock.

So with all that the rear of my bike sits a bit higher than it did brand new. Don't know how much difference that makes in the measurement, but with the rear vs. front height I've got right now the bike is handling well and rock solid stable past 130 mph.

 

Sounds like a lot of variables there. Primarily tire diameters, rear shock length and rear sag.

The 1000RR triple clamps probably have less offset, for more trail with a steeper head angle. More trail would tend to make the bike fall into corners at low speed.

Have you raised the rear end to steepen the head angle?

I'm sure you are already on the path, but these were a couple thoughts I had.

Good luck.

 

Greg,
I'm not going to win any accolades for my note keeping. I will do better in the future.

But, I made some pretty substantial geometry changes and found my steering to be very light and very neutral midcorner. It did not tend to fall in or want to stand back up.

I can't provide you with the stock head height. I went with the fork free length and made the free axle position close to the stock position. I may have ended up dropping the nose a couple mm.

But in the rear, I increased the shock length by 10mm! That's something like 30-40mm at the rear axle. Big change. That may be why you are seeing such a noticable tendency to fall in.

I went with pretty standard sag numbers. Something like 20-25mm front, 18mm rear. I can't find my notes at the moment.

Keep us posted on what you find. And keep good notes!

 

+1 on increasing rear height. I was also in the 10mm neighborhood and it did wonders for my F4i setup.

 

I might test this out as well, as I'm having a bit of the same condition. I had pulled the rear shock shim I had in when I swapped the forks inorder to eliminate any ride height variables... but sounds like it may help to have it back in.

J.

 

I already have the Fox TC out as far as it will go - ~10mm at the shock. This tranlates to more at the rear due to the linkage. I don't know the linkage ratio though, and whether it is progressive or linear.

 

I just measured my distance between the floor and the bolt - 170mm. RK1, since you measured to the middle of the bolt and the bolt head is 4mm thick then I subtract 2mm and get the exact same measurement as you - 168mm.

BUT....I'm running 38mm of sag with 1.0 springs and you probably have 45mm of sag with progressive stock springs. It gets more and more interesting.....

RK1, I assume your forks are in their stock position, ie not raised or lowered in the triples?

 

Hmmm...

Linkage is progressive. It limits rear sag when riding 2 up. But when I was talking about rear ride height, I was thinking more about the distance from the swingarm pivot to the shock vs. the distance to the rear axle. Something like 4:1.

I don't know how the 1000RR triple clamp offset compares to the stock offset. I believe the RC51 triple clamps have about 4-5mm less offset.

I also don't know how the head tuble angle (rake) compares, but they are easy to find. I don't think you'll want to change the swingarm angle much more. I can't imagine you've changed the front end height by much, but it's a god place to start. I would be looking at triple clamp offsets and head tube angles. It wouldn't be too hard to draw up the basic geometries with a bunch of triangles for comparison. That would allow you to derive the amount of trail for the various configurations vs. the stock numbers.

I'm sure I'm not telling you anything new, but it may be useful to others as well and it's an interesting problem.

Keep us posted.

 

Yeah, Greg. I bought the VTR new and have never moved the tubes within the triples. I measured from the floor to the center/surface of the bolt head and was pretty careful about it. I've never checked my sag. I set my susp. front and rear to the recommended settings on Sportrider.com and played with them up and down from there.

Also, my usual front preload setting is four lines showing but remember I measured with one showing.

I've got the 4mm shock spacer and more tread rear than front, and my seat height is noticeably higher than before but it corners fine without wanting to fall in.

Only other thing I can think to mention is that maybe a difference in front vs. rear ride heights big enough to make a difference in handling won't show up as much (or even any) of a difference in measure from floor to that bolt. That bolt is ahead of the center point of the two axles, but not by a whole lot.

Seems to me that it would be possible to lower the front, raise the rear a little bit more (making fall in worse) and that bolt head could still be exactly 170mm off the floor, you know?

 

After doing some reading, researching, and a bunch of calculations I think I have figured out what my problem is.

By using the specs from the 929 of 23.8° rake and 97mm of trail I was able to calculate the offset of the triple clamps to be ~33mm.

The VTR has 24.5° of rake and also has a trail of 97mm. Stock triples have an offset of about 37mm. Now, when you take the 929 offset of 33mm and put it on a bike that has 24.5° of rake then the trail jumps up to 101mm of trail.

But it's not just a function of trail, as a difference of 4mm doesn't seem like it would make the bike do what it's doing. I originally had my bike set up with the fork tubes raised 10mm and the rear shock 10mm longer than stock. These combined adjustments probably lowered my rake to about 24°. This change in rake brings trail down to about 93mm. Now the difference is almost 10mm which almost anyone would be able to feel. As the bike sits right now the forks need to be raised and the rake is probably sitting at close to stock angles. This also takes some weight off the front, making the bike feel a little flighty and loose as well as "floppy" at low speeds and difficult to turn at higher ones.

I'm going to raise the forks as much as I can in the triples to get the front end geometry down. A quick assessment says I can only raise the forks about 10-15mm before I start moving the clamps into areas of the fork that are smaller diameter but that's at least a start.

BTW, RCVTR, I'm not using the 1000RR steering stem. This one is off a 929/954.

[Edit] With the smaller offset of the 929/954 triple I will have to decrease rake a bit more than what I had before to achieve the stock trail specifications - actually it will have to be the same as the 929, which as I mentioned above is 23.8°. I don't know how much I'm going to have to change the front ride height to achieve those rake angles. I'll have to do some more calculations and post more later. All this is hurting my brain and I'm going to bed!

 

If you're trying to get it same as stock, Greg, you're going to be chasing your tail(feathers ).

I've been riding my VTR again since this season has started with my CBR down and waiting for parts (and no i'm not selling it anymore). I decided i'd take the time to set my suspension up for me rather than what was done before and i've found this bike to be amazing now. I'm no longer humping the tank and I can carve corners with much more confidence than before (one handers mid-corner on easy turns aren't a problem ).

..... BUT .....

Suspension is compromise and the low speed wheel flop and light front end (on corner exits I presume?????) are par for the course when you shrink that offset value as we have.

You're gonna have to compromise something somewhere to get it like stock (if that's what you're after, not sure as you didn't say).

 

Greg, it sounds to me like you are on the right track (I'm not surprised). Hopefully my suggestions have helped to point you in that direction.

Excessive trail will cause the wheel to rotate into the turn. Too little trail will cause you to lose some high-speed stability. That's why you want to decrease the offset when you steepen the head angle. You may be able to sacrifice some trail for lighter handling, when you get to your final setup.

You can see that Honda (and all the other sportbike mfrs) use pretty much the same trail numbers consistently. I think it's conservative to minimize headshake at high speeds. A steering damper would allow you to get away with less.

 

a lot of people only think of 'tankslappers' but one of the aspects that i really like in using a steering damper is reducing the slow speed wheel flop.
... of course you can't be a nancy, you need to have it adjusted pretty tight.

tim

 

I'm going out to lower the forks now and take a ride. I'll let you all know how it goes.

 

WOW!! That was the most fun I've had with a tankbag in a very long time!!! Whoever said 1/2" doesn't make any difference doesn't have a clue (no offense to the women on the forum ).

I moved the forks up a hair over 15mm and it's a different bike. Steering is neutral with turn in that is "right now", with no wierd steering under power or on the brakes. Before the change it would stand up under braking. I added another 1/4 turn rebound too because it was a little unstable recovering from bumpy turns and that did the trick. Slow speed steering is back to normal.

This was also the first opportunity I've had to comfortably open her up since the fork swap and the high mount Jardines. She pulls strongly and cleanly, especially from 6k up. Powering out of corners pinned in 2nd was getting the front light but she was stable as ever.

I checked tire pressure before the ride and it was at 30 so I bumped it up to 33. It's only 55°F here right now but the bike stuck like it was 85°. I'll be getting some new tires soon since I have a Pirelli Diablo Corsa on the front (3500 miles) and a fairly worn Dunlop Qualifier on the rear (4000 miles). Maybe I'll just get a rear Diablo since the front is still pretty good.

Damn, I love this bike! It's SO responsive to changes and mods. This fork swap is one mod that I recommend to anyone. Even after the monetary investment, the time, the frustration with the bars, and with the problems in this thread that 25 minute ride I just had made it worth it all.

This now brings my fork swap saga to an end. Good luck to all you guys doing the same mod.

 

So what's you're steering angle at now, Greg?

I just want a comparison note. I forgot that I moved the forks in the clamps recently to help alleviate a clearance problem with my levers/throttle cables. Mine are 14 mm up (not sure that it means much as I don't know if your 1000RR forks are the same length as my 929 forks).

I'd love to try raising the rear but everything I know says not a good idea. You're tempting me to try otherwise with some washers between the shock mount and frame.

I must be missing something that's going on with the rear of the bike that balances it all out, yes? Better traction out back to help pick up the nose a bit? But does that not make the front end even lighter???

 

Glad to hear you got it all worked out...

 

Got your trail right, I see.
Fantastic! This was fun and informative.

You had too much trail before (rake was too shallow for the fork offset).

Go a little farther. See how light you can make the steering without affecting stability.

 

Just so I can compare, where was the head of the bolt on the oil filter when you got it to work? I'm a little concerned about how I account for the difference between 139 mm's on mine and 170 on others. I suppose I could have 20 mm's of sag - now that I think about it I think this is where it settled out after the first set of forks. No, wait a minute - I'm still missing 20 mm's. Does this sound right or within range, Greg? Glad things worked out for you. I suppose now your bars are truly perfect

 

that is overall about where I ended up when swapping the RC front end. I figured I'd lost about 5mm offset with the RC triples and raised the forks about 10mm hoping to maintain stock trail. I raised the rear about 7mm. I think it is slightly quicker than stock, but completely neutral and very stable.

A most helpful thing at this point is if we could get measurements with say, 30mm front sag with rider, from the ground to the bolt on the filter housing. Or if you prefer a different sag, but just so we can compare on-road ride heights. wait, is sag measured differently on the 1000RR forks? I suppose as long as you are at faststreet/track sag settings and get the height with rider, it would be a good reference point.

 

I'm with RK1. It seems to me thet there are infinite combinations of front and rear ride height for any given height at the chin spoiler.

What you are really interested in is chassis attitude. I think it would be great for people to post their setups for comparison, using a standardized set of measurements.

I am thinking that you could measure front and rear height from the axles, but it would vary with tire diameter, or you can measure from the ground. You could set a level across the rear subframe, behind the seat holddowns, havea friend hold the bike level and measure the rear height, then measure to a bolt on the front fairing stay for the forn height. Something like that. If everybody does it the same way, you will have a good comparison.

the good thing about measuring from the axles is you can then take measurements with the bike in a stand. You would then compensate for different tire diameters (radius, acually).

And as Bill mentioned, sag numbers should be included.

Just a thought...

 

Slim, I can't accurately measure rake angle now. I used calculations from the stock bikes and an estimate of what I thought my bike may have been before the fork swap. You should try raising the rear. Go a little at a time and see how the bike responds.
I'm going to keep it the way it is for now. The bike gave me a small wiggle in some bumpy stuff while hard on the throttle in 2nd, just enough to tell me that I'm close to my limit of comfort for stability.
I'm not sure these measurements would really mean anything, for reasons discussed below. Also, I have my rear Fox TC shock maxed on ride height, something not a lot of folks have. It is difficult to try to do an apples-to-apples comparison with suspension. My bike is different than most, not everyone weighs 230#, not everyone rides the same way I do. Suspension setup should be an individual effort. Sure, you have baselines, but you almost always deviate from those settings to fine tune the bike to you.

With that said, the 1000RR forks operate best with a sag of 38mm, which is what I have, and I have the 06 forks which have different springs and valving than the '04-05. The 38mm sag number is significantly more than the 25-35mm that stock VTR forks work well at. This is due to completely different internal design and long top-out springs which actually help keep the front wheel tracking while hard on the throttle. VTR top out springs are about 1" long. 1000RR top out springs are about 3" long!

Now Doug, I do think that your measurement of 139mm was a little low. You have .95kg/mm springs, and even though you're raised 10mm in the forks, this is to make up for the extra ride height of the stiffer springs. Did you measure in inches and then convert? It may just be a math error.
I think that the information in this thread alone should give more than most people are looking for. As I said above, 38mm front laden sag is the optimum setup for the 1000RR forks. With those forks raised 15mm I think this is the sweet spot.
I agree that the chin spoiler is probably not the best place/way to get a measurement. It is the easiest place to get a measurement and is probably one of the farthest forward points on the chassis itself, which is why I chose to ask for it, but as discussed above these measurements don't mean much because there are so many variables that come into play from one bike/rider to another.

 

Greg - got it, thanks! I'll see how it goes.


I like the idea of a baseline/settings thread for those of us that have done the front end swap, but I also realize that it's about as convoluted as carb tuning settings! Too many variables, although the end result is typically the same thing - a happy rider.

Should we start a thread about this? (or does it already exist?)

 

Are the fork springs stock or aftermarket? Have they been cut or even installed properly? With the differences you're noting i'd be getting in there to check what's going on.

 

Ouch! I'm hurt!

I worked Doug's forks. He has .95kg/mm Eibach springs with GSXR-600 compression valves and stock rebound valves. I instructed him to raise the forks by 10mm when I sent them back to him.

 

DOH! I uhhh ...... errrrr ..... ummmm .....

(closes mouth)

(crawls under rock)