Compression and Rebound Damping

[Woodburn]

Hello!

I'm just beginning to experiment with the compression and rebound damping of the suspension on my V11 sport. I thought it might be helpful to hear how other people have theirs set up according to your weight. I'm 200 lbs. and at first I softened the damping a bit from stock and it seemed to have gotten a bit twitchy. Now I've put both forks 5 clicks from the hardest setting and it seems okay, but I need to keep playing with it. How does everyone else have theirs set?

 

Thanks!

[docc]

It's funny: on some of the other boards it's the dreaded 'oil thread' that keeps resurfacing. Here on the V11 site we just can't get enough of suspension.

 

After reading all the threads I could find on this I made some changes to my 00 V11s. I had followed the advice of an 1100i rider and gradually moved all my damping sttings to max. Recently I found some good info at guzzitech.com written by Ed. I set fr & rr rebound 75% and fr & rr compression 50%. The bike is so much nicer to ride. Much more compliant on the imperfect roads I ride.

 

Now, I'm 160# plus gear and the sport's forks sag 45mm from full extension. "Too much," everyone says. Bottom line seems to be the bikes are sprung soft and overdamped. I'm planning to change fork oil to 5wt and add a 10mm spacer, drop the triple clamp 10-15mm. Suspension tuning on the cheap.

 

For your weight most riders would recommend a spring upgrade (still pretty inexpensive). What year is you sport, which rear shock does it have and have you put many miles on it?

 

Good riding! docc

[Mike Stewart]

Wow, another suspension question!

 

Well , I was happy with the front forks when my 00 V11 Sport was new, however with mileage the forks tend to sag. With 15,000 miles give or take a few thousand (speedo still not working) I felt the fork spring rate was way too soft. I weight 200 lbs. One the other end, the rear was what I thought was way stiff. Every dip and bump I hit, the rear end wanted to spring me over the bars. I played with the rebound dampening and maxed it out. Still had the problem. A shop suggested on increasing the spring rate, I thought he was crazy. Lord and behold, the problem was solved. What was happening was, over dips and bumps, the shock would bottom out against the rubber stop which would spring me over the bars. Oh yeah, I have the rear Sucks shock, now getting the LE treatment!

 

With the rear spring rate cranked up, it is now much harder to grind the side stand. Another plus!

 

Mike

[dlaing]

Mike told me about the rear shock adjustment a year and a half ago. It took me a year to listen to him and add rear preload. Mine stopped bottoming also and became much more compliant. Set your rear sag to somewhere in the range of 1/2 to 3/4 inches (measured as the difference between rider weight and no rider weight)

To measure:

Move the rubber bottoming cushion of the shock to the point furthest from bottoming.

Set the bike upright off the stand with NO rider weight.

Gently put your rider weight on the bike, balancing the bike by the tips of your toes or the support of a wall.

Dismount the bike gently.

Keep the weight of the bike over the tires and hold the bike upright.

Measure how much the Rubber bumper moved.

That is your sag.

It helps to have someone to do the measuring or help balancing the bike.

 

To get the damping right:

Try to match the front to the rear or vice versa.

I am not sure how many clicks I am using. I do know that I am using much less damping than what I thought I needed at first.

 

There are two articles on Guzzitech.com related to suspension tuning one by Todd and one by Ed. They are both very helpful.

[Lex]

dlaing,

 

While the method you suggest is probably useful that is not sag as any person who does suspension would understand it. The geometry of the swing arm means the wheel moves much more than the shock. A quick look at my bike shows the ratio would be roughly 2 to 1, i.e. the shock moves 1/2 the distance the axle moves. The standard way to measure sag is to put the bike on a shop stand (wheel off ground, suspension topped) and measure from a fix point (I use the bottom of "V" in the decal on the rear cowling) to the axel. Take the bike off the stand, sit on it, jump up and down a bit to reduce the effects of stiction, sit as close to the normal riding position as possible and have someone take the same measurement. The difference should be between 20 and 25% of the total travel. Another rule of thumb, if you need more than 10mm of pre-load to get the sag set correctly you need to go to a heavier spring.

 

All,

 

I've said this before but I'm sorry, nobody over 125 pounds is going to get the suspension to work without stiffer fork springs. I know changing them is a pain and they cost $100 but they are soft, already have to much pre-load and appear to be really crappy martial to boot. Docc is about as light as full grown adult males of European decent get (160 pound ready to ride) and he has nearly twice the sag (he report 45mm, he should have about 25mm) he should have with a spring that is already has too much pre-load. I apologize if I sound like an a** but I have been around this problem more time than I care to think about. Pre-Telelever BMW fork springs have exactly the same problem, to soft, to much pre-load and crappy material. I started riding BMWs twenty years ago and even worked in a shop for a while. I can't tell you how much time and effort people put into fixing them. We tried helper springs, we tried replacing the spacers with Chevy valve springs, we tried air pressure, blah, blah, blah. The only thing that works is to fix the root problem. I appreciate that people like to play with their bikes but if you work with the wrong springs you are just going to frustrate yourself.

 

My way of thinking about this (and maybe nobody else's) is to think about the jobs the parts do, the springs support the bike, the dampers simply damp the motion of the springs. You can drain all the oil from your dampers and ride your bike, it won't work very well but you can ride it, try going for a ride without springs.

 

Lex

[Janusz]

My dealer when asked says there is no Moto Guzzi specific harder fork spring.

 

Did anybody located a good source for a set of harder fork springs for us?

[dlaing]

Thanks for the correction Lex.

To do the method I suggested you would have to determine the ratio of shock to wheel motion.

1:1 is wrong and I think 1:2 is also wrong, but closer. If we knew what it is, we could set it using the bumper method. For now, forget I mentioned it.

I measured mine by the axle with the help of a friend. The bumper method could be done more easily by yourself, if the ratio was known.

Thanks for the tips Lex! You are no a**, maybe I am...

It makes sense what Lex said about measuring as a percentage of total shock travel, rather than just the difference between rider and no rider. I did a litlle calculation and 20-25% of 120mm is 24-30mm or about 1-1.25"

The following is hypothetical, let me know what you think:

Assuming the springs are straight weight rather than progressive and that half of the bike's 500lb weight (250lbs) is on the rear tire, and the rider weighs 250lbs, we might assume that the spring should ideally sag about 12-15mm with just the bikes weight, and 12-15mm further with the rider's weight.

A 125lb rider would want the bike to sag 18-20mm with just the weight of the bike, and 6-10mm further with the rider's weight.

So one might be able to draw a chart of what the rider only sag should be based on rider weight and given our model bike with 120mm travel and 500lb weight. ex. A 185 lb rider would than want the rider only sag to be about 10-11mm.

Too mathematical? Too many assumptions?

Also, Why is preload is not a good substitute for spring weight?

[Lex]

dlaing,

 

Defiantly not to mathematical. Just to make sure I am clear, I am not an expert. I've been lucky enough to know a few, read a lot and have done some messing around. That said...

 

I measured roughly 16" from the swing arm pivot to the axle and 9" from the swing arm pivot to the rear shock bolt. That should give a ratio of 16/9. Being lazy I rounded to 2 to 1.

 

The only thing I would question about the rest of what you said is the weight distribution, Guzzis are notoriously "tail heavy". Making a complete SWAG I'd guess the 500 LB would be distributed something like 60%R (300 LB) and 40%F (200 LB). Anybody actually weight one? Other than that it makes sense to me. That doesn't mean its right, I'm not that trustworthy. (Sorry, I love Japp's smilies)

 

As to why preload doesn't work to replace spring rate, that is one I had to have explained to me. The important thing to remember is that pre-load doesn't change rate. Lets say you have two springs that both have a rate of 100 LB/ In. and five inches of travel. Spring A is pre-loaded two inches, spring B 1 inch. If you add 100 pounds neither spring moves, add a second 100 pound and spring B compresses one inch. Add a third 100 pound block and both springs compress one inch. See the difference? All that changed what that spring A didn't move at all until it had twice as much weight as spring B. Do that to your forks and you get can get the proper ride height (that is good) but the spring will still be to soft when you hit a bump, nail the brakes or hit a bump while nailing the brakes (bottom out, big shock through the bars, tire off the road when you need it most, etc.). Moto Guzzi "solved" this by specifying way too much high speed (non-adjustable) compression damping. This a brilliant solution, not only is your fork still going to bottom (remember, the damper just slows the movement, it can't change it) but the bike rides like an empty cement truck to boot.

 

Back to the important (non-theoretical) question if your local dealer comes up blank I'd try Race Tech (http://www.racetech.com/) for springs. They don't show any application for the V11 but they handle Eibach and show applications for the Ducati SS, some of which came with eye-talian forks. If it helps, my stock springs are 35mm by 295mm. LE put a 1.05 Kg/Cm spring in but remember I'm a lard ass, 260 LB. Someone (maybe Todd?) suggested 0.90 Kg/Cm for normal sized people. Hopefully someone familiar with these bikes or Race Tech can tell you what you need for your size, that is past my knoladge.

 

Anything here helpful?

 

Lex

[Mike Stewart]

I just returned home from picking up my suspension parts at LE. The front spring rate for my 200 lb. weight is .90, the rear spring rate is 550 lb. (you do the conversion). I can feel the stiffer spring rate on the forks just by pushing down on them (one at a time). The rear Sach shock had its seal replaced by replacing the seal head assembly. This was a extra $60.00. Now I just need to sneak into the garage to put these bad puppies back on.

 

Mike

[dlaing]

Thanks Lex, Great explanation! The other info could be very helpful too.

Mike Stewart, You have a full project for the weekend!

Can't wait to hear how you like the set up or if you need any preload.

[Lex]

Mike,

 

I feel your pain. The only encouraging this I can say is that you will get a chance to torque/ loctite lots of bolts the factory probably didn't set correctly and with the rain we are getting you wouldn't want to be riding anyway.

 

I am really happy there is a work around for the seal, I have been nervous ever since this issue came up. In the fun filled world of suspension "only" $60 is getting off cheap.

 

I'm taking my forks back to LE next week, I think they got a little carried away on high speed compression. I can set the adjuster low enough to mask it but then the bike is mushy on the low speed stuff. This is a pain but they were very cool when I called. "Sorry, you bring, we fix same day, no charge".

 

= Mike on mines road next Saturday?

 

Cheers,

 

Lex

[Mike Stewart]

Hi Lex,

 

I put my bike back together this morning and went for a quick ride to check everything out. My first impression is boy this bike feels different. I can't put my finger on it as of yet but it does feel better. The first thing I noticed was the lack of dive when braking. The old springs in the forks were pretty tired and sagged. I also noticed when hitting a dip, the bike does not even notice it. Before there would be a steering change and one had to hold on. There was a lot of debri out on the road today from the storm last night, and I couldn't or wouldn't force the bike around the turns like I normally do. I did hit a few sharp edged bumps and do have the fly over the handle bar sydrome. I need to crank up the rear spring preload (rear sag with rider is 1.250 inches). I will change it to .750 of sag and ride it hard tomorrow.

 

 

 

Mike