Rear shock and Seat Height

[Guest captain nemo]

I am curious about how the rear shock relates to seat height with rider. This weekend I softened the back monoshock by lengthening it by an inch. It seemed to make my riding position on the seat a tad higher. Someone on 'Wild guzzi' says I have it backward - that this would make my seat lower. I don't get it. Which is it and why?

 

The other thing is that it seemed to make more weight on my hands - that's why I think the back end got jacked up.

[al_roethlisberger]

Hi Cap'n, yep already replied to your post on Wildguzzi

 

Hi there again Cap'n 

 

To concur with the posts above, if you are "letting out" the preload, that is "unscrewing" the preload collars so that the spring is lengthening, all-things-being-equal(that is, you aren't also lightening the bike accordingly at the same time)... you will be lowering the bike.

 

It is true that as you reduce preload by "unscrewing" the spring, it is getting longer(to a limit) but you are also reducing the compression on the spring, while it's spring rate and weight of the bike remains the same. The effect is that the rear suspension will become softer and the bike will settle.

 

If you were "lengthening" the spring and the rings holding it were static(i.e. inserting a longer spring, with the same rate), then yes the bike would get taller, but as you unscrew the preload collars with the existing spring, they are moving down the tube, while the length of the shock itself it unaffected(more or less). So, since the only thing changing at that point is the "load" the spring is seeing, and that is now reduced(the spring is less compressed), the bike settles lower.

 

If you want to raise the bike significantly, you can crank up preload, not reduce it... or get a longer custom shock. However, be aware that changing ride height, front and/or rear... can significantly change the geometry and handling characteristics... for good or ill... sometimes for "tragically" ill. So take care, and change only one thing at a time, ride, then adjust again...

 

I would encourage you to experiment to find what is best for you, but if you are really unsure about suspension settings, you may want to find someone local that can take a bit of time to review the basics for you. And anyway, to really and effectively setup suspension sag... it takes 2 to 3 people 

 

Good luck!

al

 

If you are reducing preload, by "letting out" the spring... and the weight of the bike is not changed... the rear will drop. This is why some Sport-Touring bikes have a remote preload adjuster to increase preload(crank down on the spring) for heavier loads like 2-up riding or luggage.

 

Hope that helps.

al

[al_roethlisberger]

BTW, an "inch" of preload adjustment is a rather large adjustment. Often we are talking 10-15mm and that's sufficient for many applications. If one has to adjust a spring by an inch, a couple things to consider...

 

1) If that gross adjustment is legitimate and justified, then it sounds like a new spring with the correct rate for one's weight may be in order

 

2) It may be possible that with the bike unloaded, this extreme adjustment may possibly indeed have unexpected results... but I don't think it would raise the rear, especially once you were on the bike since the spring will be very unloaded at that point and should take-up a lot of sag once you get on.

 

Maybe the previous owner had the preload way too high? If so, then maybe the inch you took out isn't such a big deal But I'm concerned with that much being necessary.

 

As I mentioned above, you may want to check with someone familiar with suspension, especially MG suspension. Because having the suspension potentially mis-adjusted at such an extreme can introduce some dangerous handling misbehavior.

 

Your post about lowering the clip-ons even lower increases my concern here, as it sounds like your riding position is becoming more severe and aggressive, and that combined with the steep steering angle of the early Sports, and my suspicion that the suspension(especially the arguably rudimentary rear suspension) is poorly setup... could wind up presenting a bad surprise in a corner one day, or even on uneven pavement. You really don't want a bad head-shake or worse a suspension induced tank-slapper.

 

Apologies if I sound too apocalyptic ... but based on your question, I just want to make sure we don't lose another Forum participant over a simple lack of knowledge. I mean heck, we have a hard enough time finding more people to post

 

...just kidding

 

Just do a "google" for "Motorcycle Suspension Basics", or something similar, and I'm sure you'll find some great info. Also, your local MC shop or Amazon probably has some good books on the subject.

 

Good luck with it!

al

[Guest Brian Robson]

Captain Nemo,

Hope that Mr Roethlisberger's reply quantifies my initial post (brian9) on wild guzzi forum, and can only agree that gross adjustments in preload can really upset a bikes handling, especially a Moto Guzzi

[docc]

True. I must of confused the driver of the BMW when he rolled down his window to look at me lying in the road after the low side bounced the Sport off his air dam.

 

"You OK?" says he.

 

" Nah," says I, " the preload's too high to compensate for the soft springs and the damping's noncompliant."

[Guest captain nemo]

Al,

 

Your explanation is excellent and very clear. Now I get it. I've added here a clear shot of my spring. The nice thing about running pods is that you can see how easy it will be to adjust this thing. I had a thought about judging preload among the members here. This spring is now exactly 15 cm long from ring to ring and I weigh 170 lbs. This would form a ratio that can be compared to other guys and their own weight.

 

One of the reasons I want to figure all things out the hard way is that, over the years, many people I PAID to know better didn't know crap. Take 'my mechanic' for instance. He took my bike out for a spin to determine the feel for the shocks, and then made a pronouncement about it - however, he didn't even take in consideration he out-weighs me by 40 lbs. See?

 

I took the Guzz out for a nice run today down to the beach, up a steep, wet hill, around many corners, cruising at 50 mph over a washboard type road with 'washout' bumps, over speed bumps and RR tracks at various speeds with my butt on the saddle and off.... I can say it is much better than when I took possession of it - that's for sure. I still think there is some slight tendency for the front tire to 'bounce' too much when it is trying to both turn and handle small bumps. Do you think I should increase 'rebound' up there?

 

Here is my spring and its length:

 

[Guest Brian Robson]

As a rough guide, if you feel that the fork is not handling small bumps, then back off compression, not rebound by a minimum of 2 clicks (a fair balance is to always make any adjustments in 2 click increments, as most shocks show very little change with only one click).

Do your rebound adjustments before you set off, ensuring a smooth controlled return of the shock at both ends, you will have already set the sag (preload), and this leaves you only the compression to worry about.

If the rear kicks you off over a series of small bumps, back it off and if the front does what you have described, again, back it off.

Always write down some notes as you do this and try to ride over the same stretch of road to find out the comparisons.

Good luck in your setup and as a rough guide most Italian bikes can do with the compression backed off.

[Kiwi Dave]

I've also just backed off the preload on my rear suspension. The specs in my handbook sez the preload range is from 8mm to 14mm from a free spring length of 165mm, i.e. a preload of 157mm minimum to 152mm.

 

I measured mine as delivered at 145mm, so after removing the seat, tank, side panels, air cleaner and battery I got access to the castle nuts. I reduced the preload by increasing the spring length to 150mm, but I could have sworn that the castle nuts moved more than this. I'm yet to evaluate the results in anger on a twistie road.

 

But I'm confused about seat height. Surely if the spring is under some compression at rest, the overall length of the suspension unit is governed by the limit of the extension of the shock absorber, and independent on the amount of preload applied.

 

Where am I going wrong here ....?

[Lex]

Al,

 

Nice post on pre-load. Do you think it is about time for a suspension FAQ? We seem to be going over the same ground more than once.

 

I'd be happy to provide any assistance I can and if somebody who is good with graphics could help I think we could cover the basics pretty well.

 

JMHO,

 

Lex