Needing A New Rear Spring For My Elka

[cassandtim]

I've known that I need a new rear spring for my Elka since I got my bike back together last summer. I've currently got an 19.69 kg (1,100 lb) spring and I checked sag tonight and the numbers are as follows:

Free Sag = 3.5mm

Static Sag (No Preload) = 50mm

Static Sag (Full Preload) = 30mm

Just to clarify: I am weighing in around 245-250 lbs. These measurements were taken with no gear on. Total hydraulic preload length is 10mm. Front forks are RC51 with 1 kg springs. When I mention Static Sag I mean Rider Sag because that's the terminology that I was taught.

What I'm shooting for is 30-35mm of sag with no preload. I'd like to know if a 21.47 kg (1,200 lb) spring, 22.37 kg (1,250 lb), or 23.26 kg (1,300 lb) spring is going to get me there. I'd also like to know if I should be concerned about valving running this high of spring rate (the Elka has rebound and high & low speed compression dampening) and if my free sag will be reduced to nothing with this heavy of a spring.

I'm currently on my 3rd spring for this shock trying to get it right. I went from a 17 kg (950 lb) spring (original Hyperco spring from Elka) to a 18.8 kg (1,050 lb) and lastly to the current setup. I've got so many springs just laying around that I'm running out of space :blink: .

Any and all help will be greatly appreciated.

Cheers,

Tim

[SEBSPEED]

I would try the 22kg. Did you buy the shock new from Elka?

[Guest]

coming from a heavy (335) rider too I think the 1250 too set it up with about 3-5mm free sag and you should be right on. I am 335 and run a wilbers with a 23,9kg, and it gives me 5mm free and 27 static with no preload, at full preload I can add 200lbs. of stuff and still be at 27mm static, no need to re-valve but you will want to slow the rebound a click or 3, rebound is dependant on spring and little else. the elka should be able to still have the correct free sag with this spring if you assemble it correctly it will not be at 0.

[cassandtim]

Yes, I bought the shock from Elka on the first group buy. They provided the first two springs. Oddly enough, John at Elka was commenting on how he thought the original spring at 17 kg was going to be way too stiff.

After reading the "Race Tech Shock Spring Woes" thread Here I am having a difficult time understanding that too stiff of a spring creates more free sag and too soft of a spring creates too little free sag. If free sag is defined as the sag of the bike under it's own weight (the difference between the length if you picked up the rear of the bike and measured the rear wheel to the frame at max extension and the same measurement with the bike, sans rider, resting by itself) then it would seem that an overly stiff spring would be applying more force to keep the shock at it's max extension thereby holding the unencumbered bike at the top of the shock.

Hopefully Baileyrock will chime in and help me out.

I'll be calling our local suspension guru, Dave at GP Suspension, this afternoon to seek his guidance on this as well. I've got to get this thing sprung right soon.

Cheers,

Tim

[vfrcapn]

Yes, I bought the shock from Elka on the first group buy. They provided the first two springs. Oddly enough, John at Elka was commenting on how he thought the original spring at 17 kg was going to be way too stiff.

After reading the "Race Tech Shock Spring Woes" thread Here I am having a difficult time understanding that too stiff of a spring creates more free sag and too soft of a spring creates too little free sag. If free sag is defined as the sag of the bike under it's own weight (the difference between the length if you picked up the rear of the bike and measured the rear wheel to the frame at max extension and the same measurement with the bike, sans rider, resting by itself) then it would seem that an overly stiff spring would be applying more force to keep the shock at it's max extension thereby holding the unencumbered bike at the top of the shock.

Hopefully Baileyrock will chime in and help me out.

I'll be calling our local suspension guru, Dave at GP Suspension, this afternoon to seek his guidance on this as well. I've got to get this thing sprung right soon.

Cheers,

Tim

:biggrin: Posted in the other thread, I'd like to understand this too.

FWIW, Ohlins recommended the 18.3kg spring for me and my 5th gen, I went with the 19.3kg and it's working fine, I'm about 200lbs without gear. 5g isn't the 6g, just saying the mfg's all seem to error on the light side of spring recommendations.

[Monk]

The companies are, I'm guessing. Trying to allow movment in both directions for adjustment.....

[Guest]

Yes, I bought the shock from Elka on the first group buy. They provided the first two springs. Oddly enough, John at Elka was commenting on how he thought the original spring at 17 kg was going to be way too stiff.

After reading the "Race Tech Shock Spring Woes" thread Here I am having a difficult time understanding that too stiff of a spring creates more free sag and too soft of a spring creates too little free sag. If free sag is defined as the sag of the bike under it's own weight (the difference between the length if you picked up the rear of the bike and measured the rear wheel to the frame at max extension and the same measurement with the bike, sans rider, resting by itself) then it would seem that an overly stiff spring would be applying more force to keep the shock at it's max extension thereby holding the unencumbered bike at the top of the shock.

Hopefully Baileyrock will chime in and help me out.

I'll be calling our local suspension guru, Dave at GP Suspension, this afternoon to seek his guidance on this as well. I've got to get this thing sprung right soon.

Cheers,

Tim

You are correct. Get Andrew Trevitt's "Sportbike Suspension Tuning" for a more detailed explanation.

You set the dynamic sag first. You're looking for 30 mm. If you get practically no static sag after you get off the bike, the spring is too soft. What is happening is that you are cranking in so much preload into the spring to get the dynamic sag correct that when you get off the bike, the spring tops the shock out. It all relates to how much preload you're putting into the spring. Got to remember that the preload on a spring does not change whether you are on or off the bike - only the sag changes. If you have the correct rate spring on the shock, you should get 8-10 mm static sag if you've adjusted your dynamic sag to 30 mm.

It a PITA of a process to go through. I think it took me 4 springs before I got the correct one to give me the desired numbers. That is the beauty of a Penske shock. You can change the spring without removing the shock from the bike. I started with the 1000# that Traxxion sent me with the shock, went to a 1400# per another race shop, then dropped down to 1250# (the numbers got close), and finally a 1300# put me dead on the money.

As mentioned earlier, you can get Hyperco springs from race cars shops or directly from Hyperco at about $20 cheaper than the motorcycle suspension shops charge for the same spring. A spring is a spring is a spring. Doesn't matter if it is on a motorcycle, Indy car, NASCAR, or a World of Outlaws car. Springs are based on overall length, internal diameter, and spring rate. Penske's use a 6" long by 2.25" I.D. spring.

[cassandtim]

I just ordered Trevitt's book from Amazon.

So, basically, it is a "trial and error" process of buying springs and checking sag that gets the right spring rate.

Pete, I discovered the race car shop trick on the first spring after checking on Hyperco's website for a list of distributors. Actually found one in my town.

Well, I guess with my current weight being 245-250 lbs I'll order the 1,250 lb spring and keep my fingers crossed.

[Baileyrock]

I just ordered Trevitt's book from Amazon.

So, basically, it is a "trial and error" process of buying springs and checking sag that gets the right spring rate.

Pete, I discovered the race car shop trick on the first spring after checking on Hyperco's website for a list of distributors. Actually found one in my town.

Well, I guess with my current weight being 245-250 lbs I'll order the 1,250 lb spring and keep my fingers crossed.

I don't understand where the hell some of these suppliers are getting their spring rate numbers??? :blink: If Elka is going to sell shocks with springs rates off so far then they should offer free lifetime spring exchanges so the buyer can get it right! :dry: I think they should send you another free replacement of your choice as it was their screw up that didn't even get you in the same state let alone pall park! :mad:

JD seems to have the same formula that gives these extremely light spring rates and actual numbers (free/rider sag) just don't support what they come up with. JD said he was going to look into it though. :beer:

If you go by actual VFR owners who are doing it right(like Pete) by actual numbers then you realize what a major joke it is for a 250lb rider to be sent a 17kg spring! Hell I run (almost ideal numbers) a 19kg rear spring on my Ohlins and weigh 190lbs. :huh:

There is something wrong in the formula being used by to many out there! :ph34r:

btw others here can use that 19kg your removing! :goofy:

[cassandtim]

Baileyrock,

I'm actually having second thoughts about the 1,250 lb. I'm now thinking I may go on up to a 1,300 lb.

I would concur with what you are saying about the shock manufacturers. Don't get me wrong, I think my Elka is a great product and truly the cat's meow, but I don't think their tech guys have a whole lot of real world experience in suspension setup.

I've got the 1,050 lb (18.79 kg) and soon the 1,100 lb (19.69 kg) springs that I won't be using. One cost me $75 the other was free. I'll be posting them for sale in the classifieds in the next couple of weeks to see if there's any interest. The springs are both Hyperco with a 6" free length and 2.25" inside diameter.

I will say this: this whole exercise has been very fascinating from an engineering perspective. I love to learn and also thinks it's cool that I know more about this than my local riding buddies (think free beer ).

Thanks for all of the help.

P.S. Pete, if you're out there, I still have a couple of questions for you regarding your weight, spring rate, and setup.

[Guest]

I just ordered Trevitt's book from Amazon.

So, basically, it is a "trial and error" process of buying springs and checking sag that gets the right spring rate.

Pete, I discovered the race car shop trick on the first spring after checking on Hyperco's website for a list of distributors. Actually found one in my town.

Well, I guess with my current weight being 245-250 lbs I'll order the 1,250 lb spring and keep my fingers crossed.

The "trial and error" portion of my quest was before I got Trevitt's book. Once I got his book it was fairly straight forward to figure out. Up to that point it was RaceTech says this, Traxxion says that, Phil Douglas thinks so and so, etc. Best $20.00 or so you could ever spend. I got a copy for BR and we're trying to figure this stuff out logically as opposed to a shot in the dark.

I recently purchased Tony Foale's suspension/chassis set-up software. I downloaded it on line. Waiting for the book to come in so I understand what I'm seeing on the computer. His program aims for what he refers to as "Optimum Numbers". Wonder if that is the same thing as GMD CompuTrack's "Sweet Numbers"? They had to originate somewhere. Tony Foale has been around for 20+ years or so. CompuTrack is slightly less old. I sometimes wonder how much CompuTrack relys on Tony Foale's ideas and numbers.

Based on my weight and the trials I've been through, I think you're going to be pretty close with the 1250# for your weight.

Go to the time and trouble to make sure you're getting good accurate measurements. I can't emphasize using a Baxley or something similar enough. Make the measuring device something that a non-technical person could read/use (non-technical person = wife or girlfriend). Using a Baxley you can assume your correct riding position, blah, blah, blah and not have to try and balance for 5 seconds or so while the measuring person is trying to figure out which end of the ruler to use. I made up an aluminum plug for my rear axle that is threaded 6 mm on the inside so I can literally bolt a "measuring stick" to when I measure mine. I used some half inch square aluminum rod with an adhesive tape measure stuck to it. Then I have an adhesive target stuck on the side of my Staintune.

My sag measuring sessions go as such:

Pete: OK, what does the rod read?

Wife: It's between 48 and 49.

Pete: You mean 480 and 490.

Wife: No, it says 48 and 49.

Pete: Well that means 480 and 490. How far between them is it?

Wife: Not much.

Pete: Not much how much?

Wife: Two of those little hickies.

Pete: So 482?

Wife: I guess. I'm going upstairs to watch "Reba" and leave you to play with your toys.

Pete: Good idea.

Cool on your find with the Hyperco distributor in your town. I usually use Hoerr Racing.

Pete

[Guest]

My sag measuring sessions go as such:

Pete: OK, what does the rod read?

Wife: It's between 48 and 49.

Pete: You mean 480 and 490.

Wife: No, it says 48 and 49.

Pete: Well that means 480 and 490. How far between them is it?

Wife: Not much.

Pete: Not much how much?

Wife: Two of those little hickies.

Pete: So 482?

Wife: I guess. I'm going upstairs to watch "Reba" and leave you to play with your toys.

Pete: Good idea.

Cool on your find with the Hyperco distributor in your town. I usually use Hoerr Racing.

Pete

LMAO!! Absolutely CLASSIC! :huh:

[Guest]

Yes, I bought the shock from Elka on the first group buy. They provided the first two springs. Oddly enough, John at Elka was commenting on how he thought the original spring at 17 kg was going to be way too stiff.

After reading the "Race Tech Shock Spring Woes" thread Here I am having a difficult time understanding that too stiff of a spring creates more free sag and too soft of a spring creates too little free sag. If free sag is defined as the sag of the bike under it's own weight (the difference between the length if you picked up the rear of the bike and measured the rear wheel to the frame at max extension and the same measurement with the bike, sans rider, resting by itself) then it would seem that an overly stiff spring would be applying more force to keep the shock at it's max extension thereby holding the unencumbered bike at the top of the shock.

Hopefully Baileyrock will chime in and help me out.

I'll be calling our local suspension guru, Dave at GP Suspension, this afternoon to seek his guidance on this as well. I've got to get this thing sprung right soon.

Cheers,

Tim

:wheel: Posted in the other thread, I'd like to understand this too.

FWIW, Ohlins recommended the 18.3kg spring for me and my 5th gen, I went with the 19.3kg and it's working fine, I'm about 200lbs without gear. 5g isn't the 6g, just saying the mfg's all seem to error on the light side of spring recommendations.

Ok here goes, if the spring has too high a rate, you can get into the situation of having too little tension left when the bike is un-laden thus its static sag is too great, this is when you get off it will maybe raise say 10 mm from your dynamic sag of 30mm, but then you can still lift the bike rear another 20mm if you pull up on the rear (you are running out of the linear region of the springs force curve). This leads to what we used to refer to as lofting of the rear, you will generally try to compensate for this by running a ton of rebound damping and then the rear starts packing badly. It is in effect like running a spring that is too short, you do not evenly control or the rebound and tend to get a bucking spring board effect. If the spring rate is too low and you have to run a to of preload for that same dynamic sag there is more spring pressure supporting the bike when you get off, and thus the rear end tops out and has no static sag.

the big problem is the shock makers cannot test every bike, and they very often only have weights to go by, they do not have weight distribution front and rear data for most bikes with the rider in the saddle. so if the bike you are setting up is lighter or heavier in the front by 10% that makes a huge difference. Even the Gurus in many places will be in the trial and error mode some if they see a bike they have not had a ton of exp. with. When you order a shock it is best to send actual weights with the rider in gear in riding position with a full tank of gas to the builder, this requires a scale under each wheel and someone to help hold the bike up. this will get you started pretty well. send the front and rear weights to the shock builder. (since you have the shock trial and error is your choice, but a good guy can make a close guess based on what you have tried and have now)

A classic example, is the vstrom (which can be a brilliant handling bike) has a weight bias to the rear and is very tall(lots of wt transfer to the front). based on its weight every spring calculator will get the fork rates a full kg./mm. too high., and the rear too low

most mfg.s go light because most folks ride on the street and given the potholes broken pavement etc. going light will get fewer complaints of the it is beating me too death kind. also most people over estimate their level of aggression while riding.

You also need to read Motorcycle dynamics, by Vittore Cossalter, to really understand :huh:

just as an aside usually a bike set up to handle very well at speed will be rough slow around town

ps Elka is absolutely famous for going light on the spring, I think they believe every bike is a big bmw

[Guest]

Another indication of too stiff a spring is what I experienced when I tried a 1400# spring on my 6th Gen as recommended by Traxxion: Even with absolutely no preload cranked in, I could not get 30 mm of dynamic sag. 25 mm is about all it would sag.