Bumpy Ride / Suspension

[XX]

okay, i'm going to put :oops: here first because i'm really confused and this is probably confusing to only me, but i thought i'd ask:

History:

Givi wingrack and E35 trunk on rear. Stock front and rear suspension, no adjustments. bt57 front, bt020 rear, running approx 38-40psi.

Change:

Upgraded front springs to 1.05 (as recommended for my weight, riding style etc etc). Cut shims so that new springs + new shims are same length as old springs + old shims.

Perception: Front end up higher, handling affected, not hugely, but affected.

Conclusion: Front end where it's supposed to be (or darn close), rear end sagging because of stock setting of preload in spring, and weight of givi bags.

Tried solution: remove Givi bags. Holy cow batman, the rear end of the bike is bouncy bouncy, boing boing boing, to the point of causing back paid and actually desiring to drive the 3 hour traffic standoff.

I also dickered with the rebound to no resolve, although dialing almost all of it out (full stop) helped a little, but made the rear end squirrely.

So, if i stiffened up the front end, and removed weight on the backend, wouldn't the bike now, be more closely weighted correctly to not pogo like this?

and how come if i ADD weight to the back (i put the givi's back on today), the bike settles.

the wife, she's smarter than me, says the givi racks and trunk simple makes the bike more stable.

my next step is to cut the front fork preload shims down 1/4" and ride for a week (700 miles) to see if that helps.

is it that simple? :???:

[jrdxx]

I'm going out on a limb here, because of all the science and mechanics involved in a motorcycle, I am definitely most ignorant in suspension setup; sometimes it seems to me to be more like a black art. However, if only for the sake of discussion, I'll get the ball rolling by throwing my two cents in, then someone more knowledgable can correct me.

What was the measured difference in the static sag in the front with the replaced springs and spacers, as compared to the stock setup? The reason I ask is that I have trouble understanding the premise that the replacement springs/spacer total length should equal the stock springs/spacer length. If the 1.05 springs are slightly stiffer than stock, then it seems to me they should require a shorter than stock spacer in order to achieve the same preload. I back my suspicion with your statement that the front stands higher. It's affecting handling for several reasons (here's where I get lost in the black art). For one, it sounds like it's less compliant, not more, and is transferring this supension load back to the rear, making it work harder. It's also altering the front steering geometry.

This is all just a longwinded way of saying that I think you're on the right track with reducing the length of the shims. Someone here can probably tell you accurately what the length should be. Leave the rear end alone for now, and get the front more closely sorted out.

[XX]

The new shims are shorter than the stock shims because the new springs are longer than the old springs. But shims plus springs in length are equal. :wink:

I'm thinking of shortening the new shims, therefore increasing static and rider sag up front.

Measuring? Shame on me, haven't done any of that yet... i'm afraid i might have to.

I'm just shocked that when i lighten the rear end that the bike doesn't ride better, in fact, very worse :???:

[jrdxx]

More ignorance here: what is the length of the replacement shim? How much length do you have to work with? I suspect when you bring the front back into compliance, the rear will improve as well.

[SwampNut]

and how come if i ADD weight to the back (i put the givi's back on today), the bike settles.

The stock spring is too heavy. A stock bike with a 220# rider should have a 16.5kg spring, while the stocker is 16.8. Adding more rebound should help control it some, but not much. You can back off the preload to correct the spring issue somewhat, but then you have the height issue. For that you can shim up the shock to add height.

Make sure you separate all the issues and adjustments. Preload to set sag, shims to set height, and rebound to control the spring (set it just stiff enough to be stable in hard cornering).

[XX]

The stock spring is too heavy

wow :shock: didn't know that. so you are saying that the rear spring is stock for a heavier rider.

as opposed to the front stock springs are too soft? that would explain why it's happier with more weight. I remember my 97, back then i had an s.o. (hopefully my wife is not reading my posts!), and we'd ride all day saturday and all day sundays and that bike handled so much better with her on the back, than for my commute m-f....

[jrdxx]

Where does the 16.5 Kg spring measurement come from, and how does it correspond to the Kg/mm value I've seen regarding straight-rate replacement springs (the 1.05 replacement springs cited, for example)?

[Northman]

The lighter springs are the fork springs (.89 stock, with most replacements being 1.0), while the rear spring is stock at 16.8, with 16.5 being optimal according to Racetech.

[SwampNut]

as opposed to the front stock springs are too soft?

Yup. Too soft front, too stiff rear. I don't know what the fuck Honda was thinking. But hey, at least it's easy to upgrade that, and we got a flawless motor.

how does it correspond to the Kg/mm value I've see

It's the same, kilos/mm. The rear suspension works differently, through a lever arrangement, and has only a single spring, so it must be a lot stiffer. The 16.5 recommendation comes from Racetech, with a stock bike and 220# rider.

[XX]

this answers lots of questions for me :worship:

thanks!

[kg4fku]

i second the to stiff idea. When I ride two up the bike is a totally different beast. A lot easier to control in fact than when I'm alone.

[jrdxx]

OK, my bad. I didn't realize you were talking about the rate on the rear shock. It's becoming slightly clearer than mud now. It sounds as if the 16.8 rear is actually about right for my fat ass. My complaint is with the front seeming so "busy." It is apparently undersprung for my weight; is it underdamped as well?

XX, I don't mean to hijack your thread; I've just been anxious to talk through some of the suspension issues and get a clearer picture of what's going on.

[SwampNut]

It is apparently undersprung for my weight; is it underdamped as well?

The front is undersprung and then overdamped to compensate. What you get is a front end that dives under pressure, even just from cornering, but jumps around and seems skittish from the overdamping.

I sound like a broken record, but...the fork valve job makes a HUGE difference. More than you'll ever imagine.

[XX]

put the givi wingrack and trunk back on and she rides totally different.

she's a little sloppy on the handling.

definitely need more height in the rear, and less preload up front - looks like i'll be cutting down the shims a little, and maybe i'll actually measure my static and rider sag.

not to ask for somethign thats been posted repeatedly, but what mm figures should i be looking for up front?

[RodeRash]

I would try for 30 mm in front with you and your riding gear on the bike.

It's best to get 2 helpers. One to measure and one to hold you and the bike.

[AlphaBird]

1) your geometry is harleyed--its to be expected when you probably reduced fron sag by 15mm

a) measure sag in front--should be approx 30mm

set sag in rear via spring preload approx 30mm

c) jack up rear total of 12mm via washers/spacers--this will return geometry back to what it was prior to front spring change

2) To reduce bwonginess INCREASE--rebound---whan you add pre-load--you need to ADD rebound as the rear is too fast--

Then add your bags--add preload/more rebound---this is where an adj Ohlins helps a ton--if you get one--you can ad rear preload by turning the hydraulic adj--then add a few clicks of preload

Basically after you did the froks, you kind of went backwards to remeding both the geometry issue (lowering preload) and the bwonginess(reducing rebound)

All these changes also slowed the steering down--as the bike is more rear biased --thus the Harlization

Good Luck

[XX]

OMG :shock: i added 15mm of sag (it measured at 20mm!) to the front by shimming it off the shims and this bike is smooth as silk.

it's so smooth it's eeerie.

it's so smooth I don't want to change my fork oil for fear that it won't be the same afterwards :shock:

:bike:

[TimXX]

Just came back from a trip from Vancouver to Kelowna [sports Bike West] and then back. I rode with 2 loaded GIVI E45 and a tank bag plus a passenger [150lbs with gear] for part of the ride, and solo with 1 Givi bag for the Sport bike tours.

My front spring is a Hyperpro with 2.5wt fork oil and the rear is a stock shock with Hyperpro spring. I have no idea what the spring rates are, but they are continually progressive. The front HP springs are longer than stock and use the same length preload tubes-so more preload and less sag [15mm-bike; 27mm with me [210lbs with gear] + 2 Givi bags; 29mm fully loaded with passenger. Rear was really compressed from 227 to 213mmspring length and sag was 6mm bike; 23mm with me + 2 Givis, 53mm fully loaded with passenger.

Net result: the bike felt pretty good fully loaded with passenger. I could keep up with most of the sport bike people on tight twisties and sweepers. I did ride more cautiously with a passenger- but felt secure.

Riding solo with most of the same people was fun. The bike felt very secure but was a little stiff in the rear. If the XX had decent preload adjustment I think the ride would have been great with maybe a spring length of 215 -217mm. Why did Honda make it so HARD to alter the preload? It is impossible without removing the tank. What the hell are they thinking?

I think this is a pretty good fairly cheap way to improve the stock suspension. I still will want to eventually get a rear shock with easy preload, comp and rebound adjustment. It pisses me off that this was not included with the bike.

The front seems to be fine whether solo or loaded; so maybe preload adjustment is not so critical here. But damping adjustments would be nice-why isn't this included with this bike?

TimXX

PS: Thanks Peter and others for the help when I got a flat tire. I was able finally to get a Pilot Road in Kelowna for an outrageous price. You US riders have it good re: tire prices- but I was desparate and paid $339CAD to have it installed :shock: .