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Progressive fork springs

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Al
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Progressive fork springs

#1 PostAuthor: Al » Sat Aug 31, 2013 9:27 am

Looking at these for the J1.
Anyone got any real world views about suitability, function, spring rating, pitfalls etc.

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#2 PostAuthor: Taffus » Sat Aug 31, 2013 10:39 am

Got mine from Hagon plus the oil. worked a lot better than standard but still bottom out due to my excessive girth

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#3 PostAuthor: Z1parR » Sat Aug 31, 2013 12:06 pm

Taffus wrote:Got mine from Hagon plus the oil. worked a lot better than standard but still bottom out due to my excessive girth



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#4 PostAuthor: andyb1962 » Sat Aug 31, 2013 9:00 pm

mine too are Hagon and an improvement
Andy :wink:


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#5 PostAuthor: Al » Sat Aug 31, 2013 10:10 pm

Thanks men any empirical data to back up these claims?

Got mine from Hagon plus the oil. worked a lot better than standard but still bottom out due to my excessive girth


Clearly faulty goods there, quality control is not what it used to be.


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#6 PostAuthor: pluto » Mon Sep 02, 2013 6:33 am

Not sure what 'empirical data' may be, but i put them in my B2 and they are far better than the 30 year old springs they replaced!
I run them with an additional 5 psi air pressure and they are match the koni dial-a-rides on the back for springiness and damping.
With the air assistance, dive on braking is minimal and when you hit a bump it doesn't knock your teeth out.
The konis are set on middle preload and 3 on the damping, I am 14 stone apparently.
When Practical Sportsbikes tested it last month they were very complimentary about the handling which I suppose considering the amount of different bikes they ride is a reasonable recommendation.
Dave

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#7 PostAuthor: snotie1965 » Mon Sep 02, 2013 7:54 am

zorded wrote:Thanks men any empirical data to back up these claims?

Got mine from Hagon plus the oil. worked a lot better than standard but still bottom out due to my excessive girth


Clearly faulty goods there, quality control is not what it used to be.


AL
I am over 100 kilo`s (16 stone) i put hagon progressive springs in my gpz1100 unitrack ,massive improvement over standard !
sorry i have no "empirical data" to back this other than i have done 320 miles of fast mixed motorway and country lane riding and i am still alive !!!!

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#8 PostAuthor: Al » Mon Sep 02, 2013 12:14 pm

Interesting stuff thanks glad you're OK snotie.

Mine submarines (crash dives) under braking and rears up like a startled horse after corners. Sure they are progressively wound but also very ancient.

Did a bit of reading and came up with the following.
Very long winded but also pretty comprehensive.
An impartial view of progressive versus uprated linear wound springs.
It will probably come down to availability for me.

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#9 PostAuthor: Al » Mon Sep 02, 2013 12:17 pm

Shamelessly stolen from the XT660.com website, thanks to Pleiades.
Full thread here;
http://www.xt660.com/showthread.php?t=19823

Thought it might be worth sharing what I’ve discovered with progressive and linear fork springs on the Tenere, having now tried both Yacugar progressive and Ohlins linear springs back to back. I must point out that I am no suspension expert, although I have had some advice from both FTR and Maxton. What follows is just my humble opinion based on a bit of professional advice and some first-hand experience. This may be of help to someone out there thinking about changing their fork springs, but then again you might well have changed your fork springs and be more than happy with what you’ve found (in which case I wouldn’t bother reading on!)

I never intended buying two sets of fork springs (bit extravagant), but problems setting the suspension up to work properly for me after fitting progressive springs led from one thing to another and eventually to linear fork springs.

A tale of two springs…

I fitted Yacugar 0.51-0.79N/mm progressive springs (the starting rate being very similar to OE) and recommended SAE15 oil last winter. I was initially well impressed, mainly on shorter road rides and a few light, low speed green lane jaunts: Less brake dive, less bottoming, more direct steering and all-round sharper handling on the road. However, after a couple of longer rides (on road) I noticed I was finding things more tiring than usual due to a slightly harsh, jittery feeling, rattling over minor bumps and imperfections particularly as speed increased. I put up with this for a fair while and more miles, trying to remind myself that the trade of was better handling, but eventually some experimentation was needed.

Initially, increasing preload helped smooth things out but at the expense of sag (the bike riding too high at the front and the front wheel much more prone to leaving the ground!) Not happy; so changed the oil to SAE10 and reduced preload, with an immediate improvement in comfort (and correct sag again), but ended up with a bouncy ride over bigger bumps and rougher terrain. Adding preload now made things worse. This all suggesting to me that I was struggling to get the damping to match the spring rate at the various points in the springs travel; Compression damping being too great with the SAE15 oil giving a harsh ride, and rebound damping being a problem over large bumps with the SAE10 oil. So I thought stuff this, I’ll shell out £100 and see what linear springs can offer. Cue Ohlins 0.60N/mm springs…

Fitted the Ohlins springs a couple of months ago with SAE10 oil, the standard air gap (all as recommended by Ohlins) and wow, what a difference. Sag easily set and spot on for my weight, firmer (than stock) but compliant ride, controlled damping and no harshness in the upper part of the fork’s stroke and no bounciness in the lower part of the stroke. Dive on the brakes is a little more than the progressives, but actually I think this gives a better, more consistent “feelâ€￾ through the suspension when braking. Consistent being the key word, but then the springs would be, they’re linear!

So what's the problem with progressive rate springs then?

The first problem I think is that the initial softer part of the spring just gets used up straight away leaving a limited amount of travel for the stiffer portion to deal with, resulting in less compliance, less comfort and less traction. The second problem is setting the sag to any degree of accuracy is almost impossible. The third problem (the big one) is that damping rates need to be matched to the spring rates, in particular rebound damping; with progressive rate springs this is impossible. Damping is always a bit of a compromise but adding progressive springs to the equation just makes the job so much more difficult to achieve.

Here’s the rub with the XT, its damping rod forks. Being a very basic system (my 45 year old BSA has the same design!), it’s all a massive compromise between rebound and high/low speed compression damping; fitting progressive springs just makes the compromise greater. The high speed compression damping action is not sufficiently responsive or progressive by design and only just works with linear springs so doesn’t stand a chance with progressives, especially with heavier oil which won’t flow through the damping orifices as quickly, giving a slow response. There's not a great deal you can do to alter that other than change the oil weight/viscosity, and that mostly controls the low speed damping response... In real terms, the amount and speed of dive on the brakes rather than the ability of the forks to soak up sudden jolts and bumps in the road surface. This is why I guess the first thing that everyone (me included) notices after fitting progressives and SAE15 oil is that dive on the brakes is hugely improved – but it’s not all down to the springs.

So what did changing to lighter fork oil (with the progressive springs) achieve?

The lighter oil flows a bit better and gives an improvement by lessening high speed compression damping (rapid small movements), giving a more pliant and plush ride (the perceived improvement in comfort that I felt). Unfortunately, that brings you into conflict with the rebound damping requirements (you’re not going to have enough) which is even more of a problem with progressive springs as spring rebound is not linear (the bounciness that I felt at the bottom of the stroke).

My guess is that Hyperpro/Yacugar (and others) recommended SAE15 oil to bolster the rebound damping in order to better control the return stroke with from within the higher rate portion of the spring. The downside is that it seriously hampers the compression damping (particularly as the OE fork damping orifices are designed to work with much thinner oil), making it much more aggressive in the upper part of the stroke controlled by the lower rate portion of the spring, giving a harsh ride; in effect you’re riding on the oil (compression damping) rather than the spring!

Conclusions?

If you’re an average weight rider (90Kg kitted out) or slightly less (like me at 85Kg) I‘m really not sure progressive springs are the answer, due to the fact that you aren’t going to make best use of the higher rate part of the spring and you’re going to be rattling about in the over-damped (with SAE15 oil) softer part of the stroke. I guess, maybe progressive fork springs are better suited to the heavier rider? Then again, if you’re heavier I’m still not sure they’re the ideal because to get your sag right you’re going to have squashed out most of the soft part of the spring and be riding on the higher rate part of the stroke, nullifying much of the progressive effect of the spring, so you might as well have gone for a stiffer than stock linear spring in the first place?

After trying out both spring types I’m not convinced the progressive springs really work (for me), mainly because you can only achieve the correct damping for either the higher rate or the lower rate part of the stroke, but crucially not both (or for that matter the bits in between). Adjustable high/low compression and rebound damping would be much more effective and would have cured most of woes (but unachievable with XT forks), but even clever cartridge/USD forks can’t vary damping within a single stroke to match a progressive spring. As mentioned earlier, I think the improvement that most people who fit progressive springs notice first is reduced brake dive, but I reckon that’s more likely down to the original springs that were replaced being too soft in the first place and the change to heavier oil, not the fact that the replacements are progressive.

Basically I reckon progressive springs might be an issue if…

• You’re heavy, they’ll blow past the soft part early then ride hard and too low, so you’ll attempt to increase preload to get the ride height back and make the ride even harder.
• You’re light, the damping will be too great in the soft part and ride harsh (plus you’ll never use the stiffest part anyway), so you’ll attempt reduce oil weight and end up with too little damping in the hard part and bouncing.

Of course, everyone is different, every bike and the way it’s used is different. You may think what you have just wasted the last five minutes reading is a load of twaddle! On the other had you may not? You may, perhaps, have fitted progressive springs to your beloved Ten and love them, but for me, this is what appears to work best…

• Linear springs correct for rider weight/conditions and damping oil that exactly matches the spring rate (and matches what the damping orifices in the forks can cope with at speed).
• Use the air gap/oil level (not the springs) to control bottoming resistance and progressive stiffening at the end of travel.

Or better still fit WP forks (if you can afford them)!

Notes:

Whilst asking around I found that apparently Yacugar and Hyperpro fork springs are one and the same product, made in Holland in the same factory, but supplied in a different box (and also I’m informed that Hagon and Wirth progressive springs are the same as each other too.)

All the fork oil I used was Fuchs-Silkolene, so I could make direct comparisons, also Fuchs is one of only a handful of oil companies that use SAE grading which is comparable between other brands that also use the SAE designation ( a lot use just # weight, # w and Ohlins their own numbering system all of which aren’t really comparable, although Ohlins do supply a comparison chart to SAE spec).
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#10 PostAuthor: Garn 1 » Sat Sep 07, 2013 9:40 am

Zorded, well stolen script..... an interesting read.
RegardZ.
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#11 PostAuthor: Strebe » Sat Sep 07, 2013 12:35 pm

I have Hagon progressives fitted to my Z1000A2. At least with the supplied oil at the recommended level they have made the front end very harsh. Would be fine on a smooth racetrack, but with the tired roads around here it is no fun at all. I weigh about 95kg ( too many pies). Until I read the excellent post above I had been thinking of trying lighter weight fork oil. Now I am thinking of going back to the original springs with oil a little heavier than standard.
On an unrelated topic, what pressures do people run BT45s at?
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#12 PostAuthor: Al » Sat Sep 07, 2013 9:42 pm

Thanks, more interesting views.

Contacted Maxtons to see what their solution would be.

Make sure youre sitting down if reading the following.
These are theyre cartridge inserts.

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#13 PostAuthor: Al » Sat Sep 07, 2013 9:46 pm

Maxton Engineering
Laurel Bank
Kingswood
Frodsham
Warrington
Cheshire
WA6 6HX
U.K.

TEL : +44 01928 740531
FAX : +44 01928 740635


Thanks for your enquiry, we can help you out with the problem on your
forks but have no spec sheet for you to read.

We convert your forks, but not by modifying the existing internals. We
throw everything inside the fork away and start again with our internals.
The internals we supply is our own GP20 cartridge style damping system.
The cartridge system is the same type of internal as what you would find
in any modern front fork. It has been manufactured and developed by our
own engineers and has pistons and shim stacks for the rebound and
compression damping. The Cartridge also has needle valves so you can
adjust the
damping. The damping adjusters are external, so you can change the damping
without having to strip the forks down, but we hide the adjusters to keep
the classic appearance. As part of the conversion we also machine new
fork tops to take the new cartridges and damping adjusters. We also fit
new springs.

Every Maxton GP20 cartridge is built to order, the reason for this is to
valve and spring the cartridges to suit the fork, the bike, the riders
weight and what they are using the bike for. Once the cartridge has been
manufactured we then fit the cartridge to the fork to make sure it works
correctly. In most conversions we have to modify the original bottom
sliders and stanchions so our cartridge will fit and work properly. The
forks are then returned to you fully serviced with new seals and the
spring preload and damping set up.

The Maxton GP20 cartridge costs between £330.00 and £530.00 + V.A.T.
Depending on how adjustable you want the cartridge to be.

- for £340.00 + V.A.T the cartridge is adjustable for rebound damping.

- for £540.00 + V.A.T the cartridge is adjustable for rebound and
compression damping.

All adjustment can be made without having to strip the forks down.

To service the forks with new seals and install the cartridges costs
£140.00 + V.A.T. In some cases there are also charges for any extra work to get the forks to work correctly. In Norton and Seeley conversions we machine new bushes for both top and bottom sliders, the bushes are made from a hard wearing frictionless plastic called Delrin. The bushes cost an extra £80.00 + V.A.T. In some cases we also have to get the original sliders honed as the bore of the slider is not machined very well. The cost of honing the sliders is £80.00 + V.A.T for the pair. In some
Triumph forks the seal is held in place with friction on the outside
diameter. We machine a groove in the bottom slider, so the seal is retained with a cir-clip. This costs an extra £50.00 + V.A.T.

The cartridge conversion fits inside most forks with stanchions that have
an outside diameter of 35mm or bigger. In some H**** forks the stanchions are 35mm outside diameter, but the internal diameter of the stanchion is too small for the cartridge to work. For these forks we supply new Hard Chromed stanchions with a larger internal diameter. These cost £200.00 +V.A.T a Pair.

If you need any more information about the modification we carry out you
can ring me on the telephone number above, if you cannot get through fax
me your number and I'll ring you back as our phone can be very busy.

IF YOU LIVE IN A COUNTRY WITHIN THE E.E.C THEN YOU WILL HAVE TO PAY U.K
V.A.T, UNLESS YOU HAVE A TAX CODE FOR YOUR COUNTRY.

Regards

Richard
Maxton Engineering
1981 J1

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#14 PostAuthor: Strebe » Mon Sep 09, 2013 11:26 am

That sounds like the perfect solution - apart from the cost!
I don't know whether anyone sells Race Tech products in the UK, but their "Gold Valve Cartridge Emulator" kits have a good reputation.
http://racetech.com/html_files/vintage_testimonial.html


They cost about $170, and Race Tech can supply springs of the "right" rate for about $125.
http://racetech.com/ProductSearch/2/Kaw ... 00/1977-80
It might be worth giving them a call to see what they can do.
Fear is temporary, regret is permanent: JFDI
But was falling in love with a woman 32 years my junior really a sensible move? Perhaps not, but it's been a hell of a ride!
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Linear v Progressive

#15 PostAuthor: Fred the Zed » Mon Sep 09, 2013 6:29 pm

An interesting post... in the good old days when I was racing in the Hornet Cup, everyone used Ohlins Linear springs as progressive springs gave inconsistent feedback and were too soft. To start with, I used Ohlins linear springs with 10% firmer rating and I really liked them as they had plenty of travel (good for weight transfer and getting the front tyre to grip when on the brakes).

On recommendation from another racer, I changed these springs for ones that were firmer still and then I started crashing with alarming regularity. Part of the reason was that when I let off the brakes (turning into the corner) the bike would rebound too quickly and unload the front end. (Tinkle tinkle crunching sound to follow) the other reason was that the bike wouldn't dive enough on the brakes and there was insufficient weight transfer to prevent a front wheel skid. Losing faith in the front end of your bike is horrible.

My recommendation is to go for linear springs from a reputable manufacturer but don't go too firm..... (Oh and don't get drawn into using heavy weight oil as this just masks your suspension problems)

Fred
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