Suspension Education

[Rooster]

Hi All,

I am trying to educate myself on suspension and would like your educated input. I am 5'6'', weigh 135lbs, and ride solo 80% of the time. I am interested in giving my bike an overall "flatter" stance.

From what I can figure my rear shocks are 340mm (13.38 inches). Here are my questions:

1. How does one calculate how much lower the rear will go by lowering the shocks? Is it a direct ratio? I have looked through the threads and understand that lowering the rear is not a popular route, I am merely gaining some understanding at this point.

2. How much lower can you make the front forks with the Progressive Springs?

3. How does lowering the rear and/or front effect ground clearance?

4. Do 18" front tires exist that will work with my 81GS650G?

Outside of this, I would appreciate any further direction in understanding suspension.

[Steve]

1. How does one calculate how much lower the rear will go by lowering the shocks? Is it a direct ratio? I have looked through the threads and understand that lowering the rear is not a popular route, I am merely gaining some understanding at this point.
It's not quite a one-to-one ratio, but close.

2. How much lower can you make the front forks with the Progressive Springs?
Have you installed the springs yet? Some bikes require a spacer, others don't. If you do not install the spacer, your bike will be that much lower, but will also have that much less travel available. You can also raise the forks in the triple clamps a bit to lower the front.

3. How does lowering the rear and/or front effect ground clearance?
Well, it doesn't effect it at all, but it does affect it some. If you lower the rear one inch, you will be one inch lower at the rear axle, nothing lower at the front axle and various amounts at various points in between. Halfway between the axles, you will be 1/2 inch lower.

4. Do 18" front tires exist that will work with my 81GS650G?
Some 450s use 18" front wheels, not sure if they are a straight bolt-in or not. Note that you will only drop the front end 1/2" by going to an 18" wheel. That's about the same as sliding the fork tubes up in the clamps.

.

[RichDesmond]

Hi All,

I am trying to educate myself on suspension and would like your educated input. I am 5'6'', weigh 135lbs, and ride solo 80% of the time. I am interested in giving my bike an overall "flatter" stance.

From what I can figure my rear shocks are 340mm (13.38 inches). Here are my questions:

1. How does one calculate how much lower the rear will go by lowering the shocks? Is it a direct ratio? I have looked through the threads and understand that lowering the rear is not a popular route, I am merely gaining some understanding at this point.

A tape measure, graph paper, protractor and a knowledge of basic trig. No easier way, unfortunately.

2. How much lower can you make the front forks with the Progressive Springs?

With any spring, you can lower the front end by reducing your preload. You never want to go negative though, i.e. when the fork is assembled and fully extended the spring should be compressed at least 5mm. The downside of doing that is that you will bottom the suspension more frequently on big bumps. Although at your weight that won't be a huge problem.
A further step would be to fab a spacer that goes under the damper rod. That will directly lower the bike by the length of the spacer, and reduce fork travel by the same amount. You also need to shorten the upper spacer by a like amount.
The simplest and most direct way to lower the front is by raising the tubes in the triple clamps. The amount you can do that is limited by the clearance the fender and sliders have at full compression. Typically 10-15mm is the most you can safely do, but you need to check your bike to see what it's limit is.

3. How does lowering the rear and/or front effect ground clearance?

It has a large effect. If you like riding aggressively in the twisties it will cause major problems.

[Rooster]

Thanks for the response,

2. How much lower can you make the front forks with the Progressive Springs?
Have you installed the springs yet? Some bikes require a spacer, others don't. If you do not install the spacer, your bike will be that much lower, but will also have that much less travel available. You can also raise the forks in the triple clamps a bit to lower the front.
No I have not. I am just researching what the options are to see if it's something I want to do. I will check out what other threads have been posted regarding these springs and get back to you here if I have any other questions.

4. Do 18" front tires exist that will work with my 81GS650G?
Some 450s use 18" front wheels, not sure if they are a straight bolt-in or not. Note that you will only drop the front end 1/2" by going to an 18" wheel. That's about the same as sliding the fork tubes up in the clamps.
The 18" wheel swap would be strictly for aesthetic reasons. Now if someone does this, I imagine it's a good idea to maintain the original "pitch" of the bike from the front to the rear right? As in, if there are two 18" wheels, the bike will be more or less level across. Is that bad for handling and such?

[Rooster]

@RichDesmond - "A tape measure, graph paper, protractor and a knowledge of basic trig. No easier way, unfortunately."
Care to steer me in the right direction? I am trying to educate myself..

"With any spring, you can lower the front end by reducing your preload. You never want to go negative though, i.e. when the fork is assembled and fully extended the spring should be compressed at least 5mm. The downside of doing that is that you will bottom the suspension more frequently on big bumps. Although at your weight that won't be a huge problem.
A further step would be to fab a spacer that goes under the damper rod. That will directly lower the bike by the length of the spacer, and reduce fork travel by the same amount. You also need to shorten the upper spacer by a like amount.
The simplest and most direct way to lower the front is by raising the tubes in the triple clamps. The amount you can do that is limited by the clearance the fender and sliders have at full compression. Typically 10-15mm is the most you can safely do, but you need to check your bike to see what it's limit is."
I will search the threads for more info on this. Thank you for the brief description. If you have any links that I could study, please feel free to send them.

"It has a large effect. If you like riding aggressively in the twisties it will cause major problems."
Please go on... This is what I am trying to learn about, so as to avoid making a dumb decision.

[Big Rich]

Rooster, I'm unfamiliar with your front brake setup - does your bike have dual calipers? The 18" mags from the GS450 won't accept a rotor on the right side. Plus, the 18" mags are only 1.6" wide while your current wheel is probably 1.85" wide (so your tire selection is greatly reduced).

[RichDesmond]

@RichDesmond - "A tape measure, graph paper, protractor and a knowledge of basic trig. No easier way, unfortunately."
Care to steer me in the right direction? I am trying to educate myself..

Umm, that's what I did. If you know the needed trig/math it should be obvious how to proceed, if you don't then I can't do much more for you via a forum.

..."It has a large effect. If you like riding aggressively in the twisties it will cause major problems."
Please go on... This is what I am trying to learn about, so as to avoid making a dumb decision.

Lowering the bike means that it will drag parts sooner, i.e. with less lean angle. If you ride hard, with lots of lean angle in the corners, a lowered bike can drag solid parts, levering the tires off the pavement and causing you to crash.

[Rooster]

@Rich - I appreciated (and learned something from) your response regarding the springs and various ways to use them. The trig comment, was not helpful and only belittles my efforts at learning something here. Regardless thank you for your info on the springs.

[Rooster]

Rooster, I'm unfamiliar with your front brake setup - does your bike have dual calipers? The 18" mags from the GS450 won't accept a rotor on the right side. Plus, the 18" mags are only 1.6" wide while your current wheel is probably 1.85" wide (so your tire selection is greatly reduced).

Yes, it has dual calipers. Thanks for the info! I will look around for something that will accept dual calipers. Can the difference in width be compensated for with a spacer/washer if I do find something that has dual calipers or would that be unsafe?

[tom203]

My L has the smaller 16 tire and the stepped seat lets me at 5' 7" be flatfooted at stops. My shock length is the same as yours. I've had 180 lbs behind me with no problems with rear shock travel. I'd try a 1/2 inch shorter shock at rear and slide front forks up.

[RichDesmond]

@Rich - I appreciated (and learned something from) your response regarding the springs and various ways to use them. The trig comment, was not helpful and only belittles my efforts at learning something here. Regardless thank you for your info on the springs.

Didn't mean it that way, sorry that's how it came across.
It's not something you can calculate without the trig, so I threw it out there on the off chance it was something you knew. That's about as good as I can do on a forum.
Now if you want to pop over for a visit we can sit down at a table and go through the procedure. The beers are on me.

[Big Rich]

Yes, it has dual calipers. Thanks for the info! I will look around for something that will accept dual calipers. Can the difference in width be compensated for with a spacer/washer if I do find something that has dual calipers or would that be unsafe?

I think you misunderstood - the width of the bead is different. That's why your tire selection would be so limited. The GS450 18" mag can fit a 3.00-18" tire (about 80/90-18 in modern sizes) while your current wheel probably has a 100/90-19 tire mounted.

The only way I know to fit an 18" wheel with dual disc brakes is with a spoke wheel (but you would need a new rim and custom spokes).

[Rooster]

Didn't mean it that way, sorry that's how it came across.
It's not something you can calculate without the trig, so I threw it out there on the off chance it was something you knew. That's about as good as I can do on a forum.
Now if you want to pop over for a visit we can sit down at a table and go through the procedure. The beers are on me.

No problem Rich, thanks for the clarification. I am obviously a newb at working on bikes and am essentially trying to avoid making a dumb decision regarding the suspension.

Where are you located?? I just might take you up on that!

Also I looked into your springs, and was curious what the main differences are between yours and Progressive? Sonic has a calculated spring rate, which seems pretty awesome. What's the spring rate on Progressives...?

[RichDesmond]

No problem Rich, thanks for the clarification. I am obviously a newb at working on bikes and am essentially trying to avoid making a dumb decision regarding the suspension.

Where are you located?? I just might take you up on that!

Also I looked into your springs, and was curious what the main differences are between yours and Progressive? Sonic has a calculated spring rate, which seems pretty awesome. What's the spring rate on Progressives...?

Oklahoma City, so a bit of a ride from where you're at.

The spring rate on the Progressives varies as it compresses, so it's not just a single number. Typically they're spec'd with the starting rate and the ending rate, although you really need more info than that to completely characterize the spring's behavior. I don't have a chart of their rates, so you would need to get that info from them.

We believe the straight rate design to be superior, here's a Tech Article from the website that explains it.

http://www.sonicsprings.com/catalog/straight_vs_prog_tech_article.php

Lest I sound like too much of a salesman I should point out that any aftermarket spring is going to be a huge improvement over the stock ones.

[Rooster]

Oh I see what you're saying, sorry about that. Were there any other bikes with 18" mag wheels with dual discs? Tire wise i was thinking about Firestones or something similar:

http://www.performanceplustire.com/products/tires/productID/11990/subSection/antiqueTires/antiqueTireDataID/3766

Also, my bike has a shaft drive so I don't know if spokes would even be workable for the rear..?

I think you misunderstood - the width of the bead is different. That's why your tire selection would be so limited. The GS450 18" mag can fit a 3.00-18" tire (about 80/90-18 in modern sizes) while your current wheel probably has a 100/90-19 tire mounted.

The only way I know to fit an 18" wheel with dual disc brakes is with a spoke wheel (but you would need a new rim and custom spokes).