Ohlins springs and sag...

[HansJ]

I've been struggling with my front end on the track. Basically it has felt pretty good, but it's been softish, making the bike dive deep when braking hard. I've also not had a good feeling for what the front wheel was doing.

I've had Wilbers progressive springs, Racetech emulators set to 3 turns, 15w oil, 110 mm gap, and the loaded sag has been ca 30 mm with 5 rings visible on the pre-load. (Re-bound is set by changing oil when using Racetech emulators, as the rod has to be ditched).

Now I've put in Ohlins linear springs, 85N/mm (admittedly, i am a bit on the heavy side, 90 kgs without clothes). According to Racetechs spring calculator, I should have gonne for 1.05 kg/mm springs for the track, but 8.5 was all Ohlins could offer. I've ditched the spacer, and adjusted the pre-load to minimum. My sag is now just over 20 mm The emulator takes up some space, but not more then ca 1 cm. Bike feels OK when driving a short testdrive, but I am nowhere near using up all available damping length. That the front would be that much harder is a bit odd to me as the original springs should be 75N/mm.

Anyone with Racetech/Ohlins that can come with some input?

The old and new setup:



BTW, this is how my fork oil looked after less than 15000 kms...

[phuk72]

You need to take into account that progressive forks are progressive and soft at the top so the fork travel will initially be greater than with linear springs (hence the sensation of having harder springs now)

[HansJ]

Yup, that's already in the equation. Original, are they progressive as well? Racetech springs are probably not progressive, or?, and they recommend even harder springs. I am concerned that I won't have enough negative damping now, otherwise I am fine, so far...

[AHTHUD]

Just a thought, But isn't there a correlation between spring rate and lenght? the Ohlins springs have a lot more coils as they are full lenght where as Wilburs/ Maxton etc are a lot shorter. I have Maxton springs which are only 260mm long and are .90 (I weigh 80kg fully kitted). I believe the Ohlins are about 515mm so a load more coils. so would they be a lighter rate?

[HansJ]

Could be right there, but that's beyond my current knowledge... Keen to learn though! Racetech's springs should be 340 mm, and Ohlins are,like you said, clearly a lot longer. My thought is to take away the upper washer, which would give me a couple of mm less pre-load, it's not only the washer thickness itself, but it would allow the spring to go further up. Backside is, I'll have to skip pre-load adjustment, but that's not much use if i can't get the right sag at all...

[bazzee]

Hi,

I am using Racetech springs, rated 0.9kg/mm which is what they recommend for a 70kg rider. They don't seem exceptionally harsh compared to the stock springs which according to the Yamaha manual are 0.75kg/mm.

According to Racetech the static sag should be in the range of 25-35mm for road use, 20-30mm for race use. So your sag of 20mm is at the minimum suggested for a track bike.

I think that removing the washer would be a bad move, the spring rotates as it compresses and expands, this would wear away the preload adjuster at the top of the forks.

Shortening the spring actually increases spring rate, so that's not an option. (I think)

Can you remove the gold valves temporarily in order to test fork action and handling with a larger amount of static sag?

bazzee

[HansJ]

Hi,

I am using Racetech springs, rated 0.9kg/mm which is what they recommend for a 70kg rider. They don't seem exceptionally harsh compared to the stock springs which according to the Yamaha manual are 0.75kg/mm.

According to Racetech the static sag should be in the range of 25-35mm for road use, 20-30mm for race use. So your sag of 20mm is at the minimum suggested for a track bike.

I think that removing the washer would be a bad move, the spring rotates as it compresses and expands, this would wear away the preload adjuster at the top of the forks.

Shortening the spring actually increases spring rate, so that's not an option. (I think)

Can you remove the gold valves temporarily in order to test fork action and handling with a larger amount of static sag?

bazzee

Good point! I can put another washer in, with a larger hole, that would let the pre-load adjuster pass through, but allowing the washer to rotate against the fork-caps though. I can take out the emulators, but that would leave me without any compression damping at all, so no...

[trixynut]

As far as I know, the length of a spring, or the ammount of coils is irrelevant: if it is rates at a certain Kg, then that is the amount of compression you will get, and it will be constant all the way until the spring will compress no more. So more/less washers won't make a difference?

The original springs are linear, not progressive, and are probably shorter with a spacer for economic reasons.

Progressive springs are rubbish: how can you set up your front end to be right for two different spring weights? And why do you need harder suspension when it is being compressed? You don't.

(admittedly, i am a bit on the heavy side, 90 kgs without clothes).

..and I would advise against you riding nudey!

[HansJ]

As far as I know, the length of a spring, or the ammount of coils is irrelevant: if it is rates at a certain Kg, then that is the amount of compression you will get, and it will be constant all the way until the spring will compress no more. So more/less washers won't make a difference?

The original springs are linear, not progressive, and are probably shorter with a spacer for economic reasons.

Progressive springs are rubbish: how can you set up your front end to be right for two different spring weights? And why do you need harder suspension when it is being compressed? You don't.

(admittedly, i am a bit on the heavy side, 90 kgs without clothes).

..and I would advise against you riding nudey!

True, i will even avoid driving in shorts. took a small testride around the block last night, and attracted the coppers' attention, Helmet, gloves, jacket, shorts and sneakers After a brief license check, they waved me away, not bothering about my loud exhaust nor the lack of mirrors

No, you're absolutely right. (suspension is logically challenging, at least for me...) 10 mms compression requires the same force, regardless of springlength (until it's been compressed to far as you say)

But to challenge a bit, in the end of the dampíng movement, you ideally want to have harder damping, thus the airgap. But that's extreme...

So, a longer spring only gets you more suspension travel! Right? (Provided all other components allow that...) But with that comes also, that when the original spring is bottomed out, teh Ohlins will still give way, but, the force needed to compress that extra bit is a lot more than the original springs can handle. 120 mm suspensionway, 7.5 N / mm = 900 Newtons, approx 91 kgs. With a spring rate of 8.5 N, it gives ca 104 kgs. To compress further, it's still 8.5 N / mm (never mind the air gap).

With this in mind though, with less pre-load (changing washer), as the weight is constant, but the compression of the spring is less from the beginning. Right?

[dandywarhol]

Shortening a spring WILL alter the spring rate.

The emulator is roughly 2.5 cm long as I remember. The Ohlins spring won't allow for that so shortening (by grinding it)the spring will raise your spring rate a little and give you the sag you need.

I find 3 turns on the emulator screw gives pretty harsh compression damping, albeit on TDM forks - try taking it back to 1 turn - you'll soon know if it's right or wrong! then work back towards 3 turns. Once the damping is set it's pretty much right for street or race

[HansJ]

Shortening a spring WILL alter the spring rate.

I've seen that before, but how does that work?

The emulator is roughly 2.5 cm long as I remember. The Ohlins spring won't allow for that so shortening (by grinding it)the spring will raise your spring rate a little and give you the sag you need.

OK, so I'll have to try some alternatives. I won't cut the spring initially though. Since my cutting won't leave the same nice falt surface as from the factory.

I find 3 turns on the emulator screw gives pretty harsh compression damping, albeit on TDM forks - try taking it back to 1 turn - you'll soon know if it's right or wrong! then work back towards 3 turns. Once the damping is set it's pretty much right for street or race

I've had 3.5 turns (it's tricky to tell what 3 turns really is though, where do one start to count? I've come up differently every time...), with the old springs. Rubber's been good looking, and I have not had any real issues with grip. I backed off a bit now, from what i initially had.

But main thing is to get sag right first, then go from there to see what the new springs demand for compression/rebound.

[dandywarhol]

Take a spring out of a pen and feel how much pressure it takes to compress it - then cut the spring in half with pliers and try again.........................more pressure required eh? You're reducing the number of moving coils so there's more pressure needed to compress whats left.

I begin counting the number of turns on the compression damping screw from the point that I can't freely revolve the light spring under the allen screw head.

Isn't the standard TRX spring a 0.5kg mm?

[bazzee]

The Yamaha manual specifies a fork spring rate of 0.75kg/mm.

The Racetech website says that it is 0.5kg/mm. Maybe they made a mistake, didn't press the '7' key in between the '.' and the '5'?

I would offer to try to measure the rate of the originals from my bike, but don't know when I'll get an opportunity to do it.

bazzee

[dfh]

As far as I know, the length of a spring, or the ammount of coils is irrelevant: if it is rates at a certain Kg, then that is the amount of compression you will get, and it will be constant all the way until the spring will compress no more. So more/less washers won't make a difference?

A spring is a simply a metal rod coiled to save space. Remember when you were an annoying grommet at school putting a rule on the edge of the desk and flipping it like a diving board? Try it again. Hold one end on the table, push down on the other end and reach a deflection of 50mm. Now slide the rule in to shorten the free length by 50% and try to deflect the end 50mm. It will take twice the effort to deflect the end as you have halved your leverage, even though the material (the rule) is unchanged.

Springs are the same. Cut some coils off and you shorten the length of the rod, increasing the force needed to compress the spring over the same distance.

I have two sets Race Tech supplied Eibach forksprings, one set .9kg/mm & the other .95kg/mm. The wire is the same thickness but one spring is shorter than the other requiring different spacers that I change over when I swap the springs over. As both pairs of springs need spacers to fit the forks it is a simple matter to shorten the spacer to accomadate the emulator.

The bad news for HansJ is its obvious that Ohlins have used a wire diameter thicker than Eibach for whatever reason and to achieve the desired spring rate the coiled length of the spring is too long to use in TRX forks with a Race Tech emulator and quite possibly without it as well. The first option for HansJ would be to cut down the spring, especially as the rate is a little soft for his weight... but by how much? Cut too much off and the springs will be ruined so the better option would be to return the Ohlins springs and get some that fit. All the big brand names sell a quality product so unless being able to say "I have Ohlins fitted" at the pub then its just a matter of finding ome that fit.... sorry HansJ I just remembered what "fitter" means in Swedish

Cheers

DFH

[HansJ]

Hmm, I objected at first, but i think i got it at last, the example with the ruler... (Mixing things up, since i thought, hey, you don't want to press the ruler 50 mms, only 25, as this is how far the ruler would go down at the middle in the first example). "Uncoil" the spring, and the explanation makes sense. But, an uncut spring, with a stated stiffness will be constant, right?

I'll do some more testing, first "as is". Even though the springs, according to Racetech's calculator would be a bit soft, i was no where near bottoming out. A too small dynamic sag, what would the negative consequences be? What I can understand, risk of topping out negatvie damping, and too harsh as the pre-load is too high?

Then I'll see what the sag will be without the emulators. If it fits, then I know with how much i have to cut the springs. Then it's just a matter of either cutting, or deciding to order springs from Racetech instead. Cutting springs, the end won't be "square". Will that not have negative coonsequences? Sheering? (if that's the word?)

DFH, are you running with emulators as well? The spring rates you have, do you find them good, what weight are you? (I heard someone on a Swedish site mentioning that the Ractech calculator had been found to give faulty recommendations in many cases...)

(And i don't know whether i should be impressed or scared, from your Swedish knowledge. What were you doing here? )