40mm forks re-sprung -- huge improvement

[dlaing]

Ratchet,

I don't think you are reading the data correctly.

You recommended "Front & Rear - laden 36 mm, unladen 20 mm"

I set that as his target.

I simply plugged in the numbers to get him to the laden 36mm.

The theoretical result is that his unladen would then be about 3mm rear and about 26mm front.

The rear number indicates his shock spring is too soft.

The front number indicates his fork springs are too hard....or more likely that his measurements are off.

Sorry, if I was unclear.

Does it make sense now.

 

The only thing I said about Ohlins was "I will add that the Ohlins measurements are larger than what Traxxion, Computrack, LE, or RaceTech would recommend."

Other than that I was copying and pasting his sag numbers that included the Ohlins recommendations. Maybe I should have edited that out, or quoted it.

[Guest ratchethack]

Dave, I'm not following you. Your conclusions are at odds with what I found and used as the calculation to respring my fork, and by doing so I got my laden and unladen sag spot-on. Nuevo weighs the same. So does Jedi and (add a few lbs.) Beauchemin (to name the ones in this thread), and others who have also gone with stiffer fork springs. Not that consensus makes right, but since I can't quite follow your logic in your post, I just can't think of any other way right now to suggest that you might be incorrect?

[dlaing]

Here is the data.

Without rider:

Rear: 25mm

Front: 37mm

With rider:

Rear: 58mm

Front: 47mm

 

This is our theoretical Target:

Front & Rear - laden 36 mm, unladen 20 mm

Please note, the target is not set in stone and is subject to personal preference.

More on that, after Ratchet and I hash this out....

 

If you increase the spring weight the difference between unladen and laden will decrease.

If you decrease the spring weight the difference between unladen and laden will increase.

The theoretical target's laden and unladen numbers have a difference of 16mm, so that should be the difference of the ideal spring, theoretically regardless of preload.

 

His rear has a difference of 33mm....so his shock spring is about 200% too soft, theoretically.

His front has a difference of 10mm....so his fork springs are about 50% too firm....theoretically.

 

So, what is the the difference between theory and reality?

I am making the assumption that the spring rates are absolutely linear, when in fact they are not, but they are close enough.

I am also not taking into consideration the effect of the change in the arc in the rear suspension, but it is negligible.

And then there is the air spring effect in the front forks.

It is possible that if he increased preload, the sag would be measured with a larger, softer air spring and the difference between unladen and laden would increase, but I don't think it would increase much....but I could be wrong.

I still think it is more likely that his forks are different than yours or he is measuring incorrectly.

 

John aka Ratchethack, Chris B, and Dave A., What were your front sag numbers before and after the spring conversion?

I'll bet you all had more than a difference of 10mm between unladen and laden.

I know I did. Mine was closer to around 20-25mm difference, but I am alot heavier.

[nuevototem]

Hi to all,

 

I have read all the posts but I still have a few questions?

 

1) If the shock spring is soft can I do something changing the preload (13mm standard)?

 

2) If I have to change the shock spring, where can I order? Which spring? And more important, how do you calculate the spring rate?

 

3) If the fork spring is soft can I do something changing the preload spacer?

 

4) If I have to change the fork spring, where can I order? Which spring? And more important how do you calculate the spring rate?

 

Thanks!

[jrt]

It's like deja vu all over again....

 

1) and 3) yes, but it will not yield optimum results. You will compress the spring- effectively reducing the amount of travel (compression especially) that the fork has. It's better to get a properly wound spring for your weight. However, changing the spacer is very inexpensive and my get you the results you want.

 

2) and 4) The spring rate is calculated by the factory that produces the spring as far as I can tell. The rate you want depends on your weight and your riding style. How much do you weigh? How do you want to ride (street or track? loaded with gear or light?)

Where to get one is a matter of some debate- I have a Wilbers spring that I have yet to install on my bike. I'm not sure they will fit later model forks. There are a few other brands mentioned in this thread. If you have a local speed shop that can reliably rebuild shocks, then you have the valving adjusted more to your satisfaction.

I'm sorry I'm weaving around a direct answer, but I've come to the conclusion that there are no direct answers for these questions- mostly trial and error.

[Guest ratchethack]

It's like deja vu all over again....

 

1) and 3) yes, but it will not yield optimum results.  You will compress the spring- effectively reducing the amount of travel (compression especially) that the fork has.  It's better to get a properly wound spring for your weight.  However, changing the spacer is very inexpensive and my get you the results you want.

 

2) and 4)  The spring rate is calculated by the factory that produces the spring as far as I can tell.  The rate you want depends on your weight and your riding style.  How much do you weigh?  How do you want to ride (street or track?  loaded with gear or light?)

Where to get one is a matter of some debate- I have a Wilbers spring that I have yet to install on my bike.  I'm not sure they will fit later model forks.  There are a few other brands mentioned in this thread.  If you have a local speed shop that can reliably rebuild shocks, then you have the valving adjusted more to your satisfaction. 

I'm sorry I'm weaving around a direct answer, but I've come to the conclusion that there are no direct answers for these questions- mostly trial and error.

72062[/snapback]

 

 

Guys, before we get ourselves wrapped too far around the ol' driveshaft:

 

Dave, I'm following almost all of your logic now and mostly agree, but not quite.

 

I think that Nuevo may have an incorrect fork sag measurement. Compounding our calculations here is the fact that we don't know if he's using a stock spacer in his fork or not. For that matter, we don't know if he has stock springs in his fork - and he might not know for sure about either if he wasn't the original owner?! The difference between his laden and unladen sag would not seem to line up with his weight, as you pointed out, Dave.

 

Jason, your last comment is well taken, but I would change it a little.

 

IMHO, there ARE in fact, direct answers to these questions, but they're in the nature of direction ONLY, (such as "more" or "less"), even though they're not exactly quantifiable, as there are many variables at work. Yep, trial and error and educated guessing plays a part in this. But logically, it's a whole lot better than a stab in the dark!

 

For example, we have the "air spring" effect, as Dave noted. I have pages of calculations that I've used on all of my preload settings over the past 2 years. After all the sag calculations are "in the can", when it comes to setting the air gap in the fork, the expected effects of changing the preload depart substantially from a linear path. It has quite an effect on laden sag.

 

All I can tell you with exact certainty is that the simple setup calculations I used in my post above are valid for the Marz 40 mm USD fork, and that they allowed me to hit my TARGET sag objectives very closely by going to considerably stiffer fork springs with 105 mm spacers and the spring mfgr. (Wilbers) recommended air gap of 100 mm.

 

This stuff is more'n a little difficult to do via Forum post. No wonder suspension shops seem to be doing so well, eh? It'd be SO much easier to do this "hands on"...

[dlaing]

I'd be SO much easier to do this "hands on"...

72073[/snapback]

Are you trying to get NuevoTotem to buy you a ticket to Barcelona?

Good Luck!

The one thing I'll agree is that if he uses your front setup, he'll be better off.

But if I were him, I would double check the sag numbers, if he still gets the same readings, I think it is essential that he change the rear spring. He should probably try a 475# rear shock spring and in the front forks put 5W or equivalent, and add 10 to 20mm preload. It is only about 50 Euros plus shipping for a hypercoil rear shock spring., the same springs that Penske uses. The most difficult thing is getting the old spring off the shock body.

Fork spring preload is increased usually using abs or pvc plastic piping cut to the right size.

These modifications will give him a much better bike, agreed? And it would be the greatest improvement for dollar spent.

Likewise for less than a hundred euros more, he could use the Wilbers fork springs or, follow Ratchethack's instructions and get it even better, agreed.

Alternately, he could get a straight rate fork spring set. I think the consensus is about a .95Kg/mm pair of springs is about right for his weight. Does anyone disagree? I think this would be a waste of money as his front spring weight may be fine, and he just needs 15mm more preload in the forks....but we disagree on this, if his measurements are correct.

It is interesting that his measurements change when he adjusts the damping.

Here are Traxxions instructions for measuring front fork sag:

First you need a fully extended measurement. I've found that the only way to get this measurement with any consistency, is to make sure the front wheel actually leaves the ground slightly. You can do this with a jack under the pipes or a couple of helpers. Measure the exposed area of the fork slider. On a conventional fork, this will be from the bottom of the lower triple tree to the top of the dust seal on the slider. For an inverted fork, this will be from the dust seal down to the top edge of the axle clamp (See Figure 6). Record this measurement on your log sheet. Push down on the fork hard three times to settle the suspension. Now measure the same two points again. Subtract this number from the fully extended number to get your "bike sag" or "free sag" number. Finally, you get on the bike and push down three more times, while a friend balances the bike. Have your friend with the tape take the final measurement. Subtract that from the fully extended number to get your "rider sag". The measurement we are looking for on the front fork is 35mm. If your spring is of the correct rate, the static sag should be about sixty percent of the rider sag, or about 20mm. The front fork has to have a great deal of static sag so that the front wheel may move down into a hole as well as over a bump. If your fork has too much sag, turn the preload adjuster in. If you don't have preload adjusters, then you will have to remove your fork spacers and cut longer preload spacers. Adjust in five-millimeter increments. These numbers and this method represent a guideline for you to get a starting point. Although measuring sag sounds simple enough, a thousand people can measure the same bike, and they will get a thousand different numbers. If you are concerned about the numbers you get, contact us. While this method works well for most people, perfectionists may call in and ask for details on a method that takes into account for "stiction".

 

 

Still he would be best off going completely to Ohlins But that is an expensive option.

Other options are that he send the forks to somebody like traxxion, LE, computrack, or racetech and have them revalve and respring it.

And there are many rear shocks to choose from.

[dlaing]

Hi to all,

 

I have read all the posts but I still have a few questions?

 

1) If the shock spring is soft can I do something changing the preload (13mm standard)?

 

2) If I have to change the shock spring, where can I order? Which spring? And more important, how do you calculate the spring rate?

 

3) If the fork spring is soft can I do something changing the preload spacer?

 

4) If I have to change the fork spring, where can I order? Which spring? And more important how do you calculate the spring rate?

 

Thanks! 

72055[/snapback]

Sorry, I don't think I am making myself clear.

1) adding pre-load will help your rear shock spring, but not nearly as much as replacing the rear spring.

2)http://www.hrpworld.com and get the Hypercoil 2.25 inch by six inch spring. 475# may be about the right weight. Probably 450# would be better for touring and 500# for racing. Any other opinions? What is your riding style? Do you have a large girlfriend on the back?

3)preload does not change softness of firmness. It just increases the amount of force required for you to bottom out. It also changes your bike's geometry as the ride height changes.

I subscribe to the theory that if the sag numbers are in the range of OK and you are not bottoming out, your spring rate is firm enough. Others like bikes so firm they never get to within and inch of bottoming.

4)Ratchethack or JRT can tell you where to get the Wilbers fork springs.

I guess Todd at Guzzitech.com sells them, but if you are in Barcelona, you could save on shipping buying from Europe.

Otherwise I'd recommend a Traxxion 0.95 to 1.00KG/mm spring.

If you are an agressive rider, the Traxxion springs are probably a better choice because they are linear. The Wilbers are progressive, so they should be more comfortable.

[jrt]

Well, I'm blind- my apologies- when I read "spring" and "fork", I did not distinguish them in my mind. Reading Dlaing's post I see it's clear you're talking rear and front. I'm educated, not necessarily smart.

 

Ratchet- I'm not saying it's a complete stab in the dark, but since I haven't had a chance to set mine up yet, it still seems a bit 'waffley' (if that's a word). I'm prolly going to follow your set up as close as I can, having let you do all the trials. I weigh about 180, if I recall that's not too much heavier than you are.

[Guest ratchethack]

Nuevo - I didn't mean to leave you hangin' there, my friend. I got pulled away from the keyboard unexpectedly right in the middle of trying to de-confuse things...

 

Sorry about the small cluster****, my friend. At this point, I think we should at least put some effort into getting you through this if at all possible!!!

 

Re-reading the last batch of posts again, there seems to be some doubt about your fork sag measurements. If you can clarify the following, we'll see if we can take it forward from there:

 

1. Do you know if you have stock springs and spacers in your fork? If you do NOT, can you find out what springs are in there (by rate and length) and the length of the spacers. OTOH, you might know for certain that both are stock. Please advise.

 

2. Can you take another run at laden and unladen fork sag measurements just to make sure? It still makes no sense that the damping settings are having an effect on your sag, and we'll have to see if we can get thru this somehow...there's gotta be an explanation.

 

I'll do my best to walk you thru it if y'er still game. Dave and Jason, et al will also no doubt continue their contributions as well...right, guys?

 

Bst Rgds.,

 

RH

[big J]

Ah for gawds sake, just take it out and play with it.

 

Have some fun and put the smile back on your face.

[Steve G.]

Ah for gawds sake, just take it out and play with it.

 

Have some fun and put the smile back on your face.

72160[/snapback]

No kidding!!

Ciao, Steve G.

[dlaing]

QUOTE(big J @ Dec 29 2005, 02:07 AM)

Ah for gawds sake, just take it out and play with it.

 

Have some fun and put the smile back on your face.

*

No kidding!!

                                                                            Ciao, Steve G.

72189[/snapback]

Nothing wrong with just riding it stock and never improving it.

Biggest smiles I've had were:

day one on the bike

day two

day three

etc.

But also, there were many days where I smiled because the bike was better than the day before.

The day I put the PCIII on.

The day I got the PCIII dyno tuned

The day I put the Ohlins forks on

The day I put the Quat-D on

The day I put the FBF lidless airbox kit in

The day I put the Hyperco spring on

The day Ratchet hack helped me dial in the Hyperco spring

The day it did not ping on 89 octane after a few modifications to the ECU.

The day I put in the bearing spacer that JRT arranged to be made

The weeks that followed with the GEI relay not failing.

Everyday I contributed to or observed a discussion here that helped someone to enjoy their ride more.

[Guest ratchethack]

Nothing wrong with just riding it stock and never improving it.

...

But also, there were many days where I smiled because the bike was better than the day before.

...

Everyday I contributed to or observed a discussion here that helped someone to enjoy their ride more.

Well put, Dave. I've had lots of those days too. Makes me thankful that this Forum provides such a valuable service. Without it (particularly the Tech Topics), I'd probably never have found the best ways to get the most out of my Guzzi - the best has been "releasing" all the great stuff that'd seemingly been there all along, but previously hidden within!

 

BAA, TJM, & YMM certainly V

[dlaing]

BAA, TJM, & YMM certainly V

72259[/snapback]

so, you don't remember your front sag numbers before springs and spacers.

I wish I had written mine down....oh well.

But I looked back throught the threads and found that you and I both ended up with the same numbers.

You wrote,

I just cut the spacers down again and my laden sag is now 33% (38 mm). The unladen sag now reads 21% (26 mm). I'm not at all displeased with this (what're the chances it'd match your figures exactly with about a 50 lb. weight diffential between us and entirely different kinds of fork springs!?!), though I missed my target unladen sag by a tad.

Your unladen target was 21mm

I think if you got to your target the spring may have been too soft.

And we both have a difference of 12mm, which I think is fine.

But if I had a choice of going a little firmer or softer, I'd go firmer.

So I think a front sag difference of 16mm would be too much, for all but touring.

What do you think?