Marz Fork Springs

[dlaing]

Hmmmmm......the plot thickens!  It seems that over a drop in air volume displaced by only 30 mm of oil, the Ohlins gain nearly 200 kgf of force from compressed air at full stroke.  That IS significant, but I have to wonder about what the pressure measurement you took on the Marz forks would be on the Ohlins - the change in pressure over this range?  It must be substantial - a LOT more than 5 lb.  As you're suggesting, the Marz and Ohlins are entirely different animals.

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The chart also shows how late in the fork movement the air assistance is.

Basically it is linear until the last 20% of stroke.

I assume the Hyperpro and Progressive springs have a more even curve.

Keep in mind that when I estimated five pounds of force at the end of the stroke, their was no oil in the forks which would be like equivalent of maybe 700mm measurement from the top.

The recommended 400cc might change the measurement by 200-400mm resulting in 300-500 of air....still not enough to provide serious anti-dive assistance.

It would be interesting to pull the springs and add oil until you need most of your body weight to compress the fork.

The draw back could be blown seals and oil leaks

So assuming my #5 at 700mm estimate was correct, then at 350mm we get #10, at 175 mm we get #20, at 87.5mm we get #40, at 43.75 mm we get #80 which with two forks you would double the amount of assistance. So one could get a fair amount of assistance. Assuming a halving of volume actually double the pressure... I am sure JRT and others would know.

The Ohlins numbers are still much higher than my guesstimates for the Marzocchi. Perhaps they are more narrow on the inside....or I am just way off!!!

Keep in mind that the higher your level gets, the more critical the balance in level between the left and right tube would be. Because if you bottom out, one fork would take a lot more of the force, possibly causing your axle to bend, loss of traction, crashing, etc.

[jrt]

Because if you bottom out, one fork would take a lot more of the force, possibly causing your axle to bend, loss of traction, crashing, etc.

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But the forks are the same length, aren't they? I imagine if you had enough force to bend the axle, the wheel is doomed as are the forks. Bail as fast as you can

 

BTW, pressure and volume are a direct inverse relationship until you get to very high pressure. I estimated a volume of 22.4 liters (1 L is more realistic, so just divide by 22.4) and 1 mole of gas. I circled the area corresponding to an estimated change in volume of the shock. You can see the pressure doesn't change significantly. And I apologise to the Europeans for using atm.

[dlaing]

But the forks are the same length, aren't they? 

I am just thinking if you bottom out on the air on one side, it will create significant torsional forces on the axle...

And thanks for the air pressure lesson

[Guest ratchethack]

This gets curiouser and curioser... So no wonder air isn't the "perfect" spring for shocks. Now that I see it graphed out (thanks Jason), I see that volume varies inversely with the exponent of pressure (I think) In any case, with an air spring, I can see that the pressure rises on a curve that wouldn't actually lend itself very well to suspension - except in tiny sections of the curve. Hence the advent of rising-rate suspensions and rising-rate (progressive) springs that follow more of an inverse geometric curve. Have I got this right, Dr. Jason?? Dr. Laing?? Dr. Moe?? Dr. Howard?? Dr. Fine??

[dlaing]

This gets curiouser and curioser...  So no wonder air isn't the "perfect" spring for shocks.  Now that I see it graphed out (thanks Jason), I see that volume varies inversely with the exponent of pressure (I think)   In any case, with an air spring, I can see that the pressure rises on a curve that wouldn't actually lend itself very well to suspension - except in tiny sections of the curve.  Hence the advent of rising-rate suspensions and rising-rate (progressive) springs that follow more of an inverse geometric curve.  Have I got this right, Dr. Jason??  Dr. Laing??  Dr. Moe?? Dr. Howard?? Dr. Fine??

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Only Dr. Frankensteeeein knows for sure!

But I think air does have its value.

Surely Big Rigs use it to keep their cargo comfortable, touring bikes use it, and it can be very useful for vehicles that need to be switched on the fly to accomodate varying loads.

On the Ohlins, the air appears to assist the springs and with enough oil displacing the air, provides an excellent bottoming out cushion.

Perhaps that is why the Ohlins are favored over the Marz in addition to 'better' damping.

As for the Marzocchis, I am not sure.

Perhaps they just need more oil to increase the air spring and the damping modification that Brian did.

And a thicker axle would not hurt.

I have got Ohlins forks on order, so I am very excited about that, but now that I have read what Brian did, and what I have learned about the 'air', I think there is room for improvement on the Marzocchi.

I always thought a fork brace would help, but it is too much trouble to fabricate one...

Ratchet, love your Marty Feldman avatar! It is always disturbingly appropriate to our conversations.

[Guest philbo]

Only Dr. Frankensteeeein knows for sure!

 

I have got Ohlins forks on order, so I am very excited about that, but now that I have read what Brian did, and what I have learned about the 'air', I think there is room for improvement on the Marzocchi.

 

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Just curious but what is the damage for the Ohlins? I've heard number around $2K but I'm not sure how accurate they are.

 

Cheers

 

Phil

[Guest ratchethack]

I think air does have its value.  Surely Big Rigs use it to keep their cargo comfortable, touring bikes use it, and it can be very useful for vehicles that need to be switched on the fly to accomodate varying loads.

On the Ohlins, the air appears to assist the springs and with enough oil displacing the air, provides an excellent bottoming out cushion.

I think there is room for improvement on the Marzocchi.

I always thought a fork brace would help, but it is too much trouble to fabricate one...

Ratchet, love your Marty Feldman avatar! It is always disturbingly appropriate to our conversations.

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Dave, this discussion has really helped me think differently about air in suspensions. The graph that Jason came up with showing that volume varies inversely with the exponent of pressure (I think) means that air can't be the main component of the spring, because it just doesn't provide the right action through normal suspension travel. Now I think of air's capability more like you do - being limited to something resembling the rubber cushion on the shaft in rear shocks. It adds an essential VERY RAPIDLY RISING rate at the end of travel. It looks to me like this is how it's designed to work in the Ohlins. As you pointed out, big rigs and touring bikes need exactly this.

 

I'm even more convinced now that in the absence of a rising-rate rear bell-crank setup, properly matched progressive springs are the way to go - at least for Yours Truly. I'm going to give Doug at Micron North America an order for the Hyperpro kit, since it looks like he couldn't match up the right springs from shelf stock.

 

There's certainly room for all kinds of improvement with the Marz 40mm fork. Not to throw cold water, but I reckon there's room for improvement with the Ohlins too, since there's no perfection to be had here - suspension is always going to be a great balancing act, juggling a mix of interdependent trade-offs. Me, I'm not too put off by the asymetric compression/rebound design of the Marz, and not worried about flex (I've never detected this, nor ever actually heard any reports of it either). Since I'm not riding anything like racing conditions 99.99% of the time, I don't think I'm likely to push it too far past it's capabilities very often.

 

Disturbingly appropriate. I like that. Feldman has a face that for me, will always say, "Welcome to my world. Walk this way, please!"

[BrianG]

Ratchethack:

I think you have absolutely come to the proper conclusion with regard to the utilization of the airspace in the fork tube.

 

In terms of a single-rate spring, the linear graph of the spring's increasing force will intersect the parabloic graph of the compressed air's force at some point in the fork's stroke. While the compressed air always contributes somewhat to the total-spring-force of the fork, it is at this intersection point that the air actually becomes the more-significant factor. Since the air's force-rate at that point is rapidly rising I would propose that it becomes the critical spring-factor, in fact.

 

The suspension tuning goal in altering this air volume is to have it small enough to provide the "anti-bottoming snubber" that you related to, and at the same time large enough that this force does not substantially limit useful fork travel. With a single-rate spring, this provides for the specific fine tuning for the racer context, where work-cycle variables are minimal, and full-range suspension compliance is sought.

 

Arguably, this is not the same contextual consideration for a street-bike where load and ride-quality (comfort) are expected variables.

[dlaing]

Just curious but what is the damage for the Ohlins? I've heard number around $2K but I'm not sure how accurate they are.

 

Cheers

 

Phil

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MSRP on the R&T is about $2500 US. But people sell for $2250 or so... Their Superbike series are quite a bit more expensive, especialy for tuning and replacement parts.

If you order the R&T (Road and Track) or the Superbike you will also have to do something to make your wheel, axle, and fender work with it. You will probably need new axle, new bearings, new bearing spacers, and a new fender. If you sort it out yourself, the parts should not cost more than $500, but if you pay a shop to figure it out for you, the sky is the limit. So, maybe $3000 for the whole setup. People on this list can help tell you what you need.

The OE Ohlins equipped bikes are well worth the extra price, in my opinion.

If you get a genuine Guzzi Ohlins, from a Scura or Corsa or whatever, there may be less to do, I am not sure...

I am buying Mike Stewart's used Ohlins, so he has already done all the hard work for me, and will provide, the fender, axle, bearing and spacers. I just have to reassemble and make sure the spacers are right for my bike.

Look for a thread titled, "Hollow Axle", lotsa good info there.

 

Maybe somebody could write a clear FAQ on upgrading.

Paul M. and others have already provided valuable information....you just have to search for it.

[Guest ratchethack]

Thanks for the clearly articulated feedback, Brian.

[Guest philbo]

MSRP on the R&T is about $2500 US. But people sell for $2250 or so... Their Superbike series are quite a bit more expensive, especialy for tuning and replacement parts.

If you order the R&T (Road and Track) or the Superbike you will also have to do something to make your wheel, axle, and fender work with it. You will probably need new axle, new bearings, new bearing spacers, and a new fender. If you sort it out yourself, the parts should not cost more than $500, but if you pay a shop to figure it out for you, the sky is the limit. So, maybe $3000 for the whole setup. People on this list can help tell you what you need.

The OE Ohlins equipped bikes are well worth the extra price, in my opinion.

If you get a genuine Guzzi Ohlins, from a Scura or Corsa or whatever, there may be less to do, I am not sure...

I am buying Mike Stewart's used Ohlins, so he has already done all the hard work for me, and will provide, the fender, axle, bearing and spacers. I just have to reassemble and make sure the spacers are right for my bike.

Look for a thread titled, "Hollow Axle", lotsa good info there.

 

Maybe somebody could write a clear FAQ on upgrading.

Paul M. and others have already provided valuable information....you just have to search for it.

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Thanks for the info. It's definitely a good chunk of change but undoubtedly well worth it. I’m starting to get the feeling that by the time I do the suspension and engine work (another $6K), I could have put a down payment on a Harley rather than owing a thoroughbred goose -

 

I think I'll go for beefing up the Marz springs first (cheap and quick) then do the rest over the Winter.

 

Cheers

[dlaing]

Here is some more good info:

http://teamiguana.com/FZ1/Suspension/springchart.htm

FWIW the FZ1 spring fits our Marz, so this data is right up our alley.

It looks like the FZ1 OE spring is progressive like the hyperpro, while the Traxion is straight rate like the racetech.

Surprisingly the HyperPro is softer than the OE in the 2nd and 3rd inch of travel.

Search eBay for an OE FZ1 spring!!!!

Here is the thread

http://www.yamahafz1oa.com/forum/showthrea...p?threadid=6694

associated with the chart....and with graphs like this one:

[BrianG]

Very nice representation of the 3 springs!

 

It's nice to see that Max's springs are, in fact, linear. I am quite surprized to find that the HyperPro spring is softer than OEM. Common wisdom is that the Japanese bikes are typically under-spung at the front and over-sprung at the back.

 

I can say that I am very pleased with the new 1.05 kg straight rate spring in my Marz forks, now that Max has done the valves. I'm not sure what rate the OEM springs were, but I can say that they were both longer and of finer wire, so obvioulsy substantially softer.

[Guest ratchethack]

FWIW the FZ1 spring fits our Marz, so this data is right up our alley.

It looks like the FZ1 OE spring is progressive like the hyperpro, while the Traxion is straight rate like the racetech.

Surprisingly the HyperPro is softer than the OE in the 2nd and 3rd inch of travel.

Search eBay for an OE FZ1 spring!!!!

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Dave, Jason at Moto International had incorrectly posted 18 months ago on GuzziTech that FZ1 springs fit the Marz forks. When I spoke with Jason a few months back, he confessed that this turns out not to be the case. I suggested that he update GuzziTech, which he finally got around to doing. See:

 

01.14.04 - V11S Fork Spring Upgrade Info by Jason of M.I. ***Revised***

 

I would expect the Hyperpro to be softer in the first few inches of travel than a comparable straight rate spring - why wouldn't you? What I wouldn't expect is that the Hyperpro graphs as close to the stock spring as this graph shows. I do like the differences I see, however.

 

Now Gents, leave us not fly off the handle here. There appears to be potential for unfair and misleading aspects to this graph. Brian, the data accompanying the graph doesn't include part numbers, so we don't know which of the many available springs - and rates - from Hyperpro and Traxxion Dynamics are being compared. I submit that without knowing exactly which of the many available springs from each mfgr. are being compared, the graph is not entirely useless, but pretty nearly so. For example, I don't think it's at all fair to make a blanket statement that Hyperpro springs are "softer than stock", unless we know what we're looking at.

 

I'm not defending any spring here (I ain't got no dog in this fight to defend yet!) However, by this graph, the Traxxion D. spring appears to be LESS progressive than the stock FZ1 spring, AND it has an significantly lower (end to end) rate than the stock spring tested. Again, since we don't know which springs we're looking at, I'd be unfair in saying that TD springs are softer than FZ1 stock springs.

 

I would also point out that we have no kind of comparison data whatsoever here that would graph the stock Guzzi springs in comparison to alternatives that we know for sure would actually fit the Marz forks, let alone be matched up correctly by rate from the many available from each mfgr.

 

But this is great info, and I'll take it up with the Hyperpro distributor.

[BrianG]

Dave, Jason at Moto International had incorrectly posted 18 months ago on GuzziTech that FZ1 springs fit the Marz forks.  When I spoke with Jason a few months back, he confessed that this turns out not to be the case.  I suggested that he update GuzziTech, which he finally got around to doing.  See:

 

01.14.04 - V11S Fork Spring Upgrade Info by Jason of M.I.  ***Revised***

 

I would expect the Hyperpro to be softer in the first few inches of travel than a comparable straight rate spring - why wouldn't you?  What I wouldn't expect is that the Hyperpro graphs as close to the stock spring as this graph shows.  I do like the differences I see, however.

 

Now Gents, leave us not fly off the handle here.   There appears to be potential for unfair and misleading aspects to this graph.  Brian, the data accompanying the graph doesn't include part numbers, so we don't know which of the many available springs - and rates -  from Hyperpro and Traxxion Dynamics are being compared.  I submit that without knowing exactly which of the many available springs from each mfgr. are being compared, the graph is not entirely useless, but pretty nearly so.  For example, I don't think it's at all fair to make a blanket statement that Hyperpro springs are "softer than stock", unless we know what we're looking at. 

 

I'm not defending any spring here (I ain't got no dog in this fight to defend yet!)   However, by this graph, the Traxxion D. spring appears to be LESS progressive than the stock spring, and it has an significantly lower (end to end) rate than the stock spring tested.  Again, since we don't know which springs we're looking at, I'd be unfair in saying that TD springs are softer than stock.

 

But this is great info, and I'll take it up with the Hyperpro distributor.

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In terms of the FZ1 cross-application, my 1.10 springs were FZ-1 spec, and they fit quite well into my 2000 Marz fork. The coil diameter was identical, the wire diameter was heavier, and the free length was slightly reduced. What is the reason for the new assertion of incompatability?

 

As for the spring rate graph, I was simply stating that I was pleased to see that Max's "straight-rate" springs are, in fact" straight rate........ on never knows exactly what they are getting in the absence of the appropriate test equipment.

 

Also, the comment on the "usual" springing of Japanese motorcycles was just a communication of something I've heard repeatedly, amongst motorcycle suspension tuners............. along the same lines as the assertion that Japanese bikes are typically sprung for a rider of 170 lb, in his gear.