To the Point - Renton Coil Springs

May 13, 2013 at 0:00
by Richard Cunningham  
Renton Coil Springs, based in Washington State’s Seattle area, is a supplier to high tech industries, primarily aerospace, but its titanium alloy springs are also famous in both mountain bike and motorsports racing. Pinkbike asked Renton Coil Spring’s Kyle Cabaya to explain the differences between steel and titanium springs, and to give us a heads up on the intricacies of their manufacturing process.

Renton Coil Spring Lead photo

Renton Coil Spring photo



What kind of wire is used for MTB coil springs?

Typically, most of the steel springs on the market will be made out of chrome-silicon or a derivative of chrome-silicon. Renton Coil Spring exclusively makes MTB springs out of aerospace quality Beta-C Titanium.

What kind of machine makes coil springs?

The actual coiling is done with a CNC mandrel coiler that we have custom built in-house. From there, the ends are ground flat, the springs are heat-treated and then sent out for shot peen. When they return, we press them to solid to eliminate the possibility of them getting shorter under normal use. All springs are then individually inspected for proper dimensions and each is tested for spring rate.

Renton Coil Spring mandrel spring coiler

A partial view of the CNC mandrel spring coiler at RCS. The operator manually feeds the material into the rollers and the material is cold wound around a mandrel. After coiling, the operator trims the spring and sends it to the grinding station.


Note: Renton Coil Spring's custom-made spring coiler machine operates on a different principle. The following you tube video will give you an idea of how a typical CNC spring winder works. Video Credit here

How Most MTB Coil Springs are Made

CNC Spring Winder

by RichardCunningham
Views: 17,681    Faves: 35    Comments: 13


Does the wire need a special heat treat before or after the spring is formed?

Yes, the aging and stress relieving process is very specific for titanium springs. Both time and accurate temperature control are crucial parameters to the heat treat operation.



Renton Coil Spring manufactures only
titanium springs for its mountain
bike range. Renton Coil Spring photo
Why do springs with softer rates often have thicker wire than those with stiffer rates?

The three parameters that determine spring rate are:

• SPRING DIAMETER
• WIRE DIAMETER
• NUMBER OF COILS

Adjusting any one of these three parameters in a design will change the spring rate. All RCS Ti springs utilize an optimized spring design where we design with the smallest wire diameter and fewest coils within safe stress tolerances of the material. In all RCS mountain bike spring designs we use what’s called an optimized design. This means that we design the smallest, lightest spring based on the critical dimensions (inside diameter, spring travel, and spring rate). Optimized designs reduce weight and help to keep costs down as they minimize the amount of material used.

What kind of titanium wire is used for mountain bike springs?

We use a proprietary blend of Beta-C Titanium, which is the same material we use for our aerospace applications.

How do the wire thicknesses vary for titanium vs steel springs?

Because of Beta-C Titanium’s low modulus, a larger wire diameter is required to achieve the same spring rate as a steel spring. But by utilizing the fact that titanium is almost twice as flexible as chrome-silicon steel, we can design the spring with larger spacing between the coils, thus fewer coils are needed.

Do titanium springs have a different fatigue life compared to steel ones?

Properly designed titanium springs have more resistance to set and longer fatigue life than the highly stressed steel springs commonly
used in suspension applications. When a spring has exceeded its fatigue life, it may break, but most likely it will just take set (get shorter). If you find yourself having to add rounds of preload to your spring to
maintain sag height, it may be time for a new spring.

Renton Coil Spring ti vs steel graphic

Renton Coil Spring graphic



Is there an average weight advantage for Ti vs steel springs?

Due to Beta-C Titanium’s low modulus, low density and high strength, typical weight savings will be between 30 and 50-percent over steel springs. The performance advantages of titanium springs extend beyond the weight savings over steel springs. Advanced data recovery systems have shown that titanium springs enhance shock performance and wheel control through improved dynamic response. This is a result of the reduced mass of the titanium springs. Lower mass springs develop less inertia as the suspension is displaced. Less inertia in the spring mass enables the suspension to respond quicker, resulting in improved ground contact and traction.

What is the basic cost ratio between Ti and steel material?

The cost ratio of Beta-C Titanium vs. Chrome Silicon Steel is 70 to one.

Discover more about Renton Coil Springs

Author Info:
RichardCunningham avatar

Member since Mar 23, 2011
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92 Comments
  • 67 2
 Coil springs are useful and deserve respect!
  • 18 16
 Funfact: I know many cases of broken titanium springs (namely fox 40) Sure they might not be of Super-aerospace-B-spec-titanium but when I search on the net I find way more broken ti-springs than steel...
  • 35 1
 sounds pretty scientific... I'll never get a ti coil now that I've read your post, ib.
  • 13 1
 ti-springs.com is where its at, a lot cheaper and in 25lbs increments. recently got one on my orange and is awesome
  • 6 5
 Rcs make some nice springs, wish I had extra doe for that ti. Ti springs are more active- rebound faster. They also a bit softer than comparible weight steel springs. Steel springs never fail and always get the job done. Ti is a luxury item for racers or people with money to burn. I know people that swear by ti springs and I see the way they ride, lol could have a rubber stopper back there and get same result. As with any sport there going to be people buying stuff they not capable of using. The weight factor is not as big as some might think. Only couple ounces diff 4-5. Not dropping pounds with ti springs.
  • 6 1
 @inb4thekill, breaking a ti spring is more of an event than breaking a steel spring, of course youre going to hear about it more!
  • 4 3
 They use steel springs in F1 because they last much longer than Ti.
  • 2 1
 no mention about the actual feel of the two springs on the trail???!!!
  • 1 0
 The feel is more active meaning the shock rebounds faster, which can be controlled. Basically the effects of the ti spring can be negated by the shock adjustments, but it still has slight diff. If you run a 450 might want to go up to a 500 for ti. Tend to blow thru ti faster. Again you could disl up compression but I would rather have heavier spring then over dial my shock. I dont know about you guys but my shock feels best with less compression turned up, more natural feel. This is across the board from diff manufacturers to air also I have them all in action right now. Get the ti springs if you have the money. Its a nice 4-5 ounce drop. Change the way your bike feels a bit. Might like it or not but can ultimately control it thru adjustments on shock, if you have any decent shock.
  • 33 0
 As a Machinist in the NAVY for the past 15 years I can say, THAT MACHINE IS BADA$$!
  • 7 0
 I used to work on one of these and trust me there nothing but a pain in th ass!!
  • 2 0
 I can only imagine @Jester1826. Sure, it looks good in the video, but that doesn't show the setup and tweaking needed to get that spring to come out like that.
  • 3 0
 The trickiest part of these is lining up the steadies to get the right spaceing on the coil, but the biggest thing I hated was the thing kinking up as the wire is being fed in! It makes a hell of a bang when the cutter comes in at 20,000 psi to cut the fucker, but then it's game over and repair time! Thankfully I don't do that anymore I am now making rotor blades and missile firing mechanisms for the apache helicopter.
  • 25 0
 I'm going to go out on a limb here and say the data in your table is wrong...

The Elastic Modulus, or Young's Modulus for Chrome Silicon Springs is 207 GPa, not 79.3 GPa. The figure you have provided is not the Elastic Modulus, but the Modulus of Rigidity, or G.

Is this significant? No. But, its better that the information be correct.

Reference: www.springhouston.com/materials/alloy-steel/chrome-silicon-springs.html
  • 2 21
flag FPabst (May 14, 2013 at 5:50) (Below Threshold)
 I'm 19 yo, is it too nerdy to understand what you just said?
  • 1 2
 I just noticed the same. better have the correct information so we can focus on article instead of wondering what else is wrong
  • 4 8
flag Barnseyhcxc (May 14, 2013 at 6:35) (Below Threshold)
 I'm 17, I understand it Razz
  • 1 0
 Liberty555 is right, although i had 200 GPa in my mind. But i am not quite sure which alloy it is
  • 24 3
 That machine is punching out the $$$$
!
  • 9 0
 Can we have a To The Point on tyre tread design please?

When you look at something like Hans Dampf vs Minion DHF vs High Roller they look a million miles apart, yet all get rated as great all rounders.

Are we at a point where tread designs are becoming increasingly similar for a given purpose, and it's just tyre manufacturers don't really bother explaining the purpose very clearly? Or is it that there's still alot of diverging opinion and art to it?
  • 5 0
 Cost ratio of 70:1? Ouch - that's quite the difference and a very expensive titanium coil. The titanium coils are obviously better and all but at 70:1, I don't know...it's going to take a while for it to pay for itself that's for sure.
  • 5 0
 Not really. You don't have to buy one, first of all, and 2nd, it's probably the cheapest way to drop half a pound on a high end bike. The only other component changes that can drop that many grams is typically coil to air shock lighter crankset or lighter wheels. So in that sense, Ti springs are cost effective as well.
  • 3 3
 Plus, half of the spring's mass is unsprung weight - acting against the response time of the suspension.
  • 3 0
 I think 70-1 refers to the raw material cost, as a consumer you wont pay 70x more for a ti spring
  • 1 0
 Yeah otherwise you would be looking at £2100 a spring if the cost ratio was 70:1 for the consumer assuming the average steel spring is £30. Just as an idea the most expensive spring Renton show on their site is $310 so it is more like 7:1 for the finished product.
  • 2 1
 Interesting. I have an RCS Ti coil on a Fox DHXRC4. Besides a .45# wt loss, the faster rebound of the Ti was the most noticable (I had to slow down the shock's damper). I thought it was due to the different modulus, not the lower mass.

However, I just swapped that set up for a Cane Creek DB Air and so far, air is much nicer... Ask me Whistler this summer though.
  • 2 1
 70:1 is the material cost. A steel spring has about $1.00 worth of steel in it, when bought in bulk. The ti is $70.00. You have the same costs in terms of overhead in each spring: labour, electricity, heat treat, equipment, maintenance, marketing, payroll etc.
  • 2 0
 THe RCS springs look great, and I could watch that spring winding video over and over, but the photo brings up a pet peeve. Why do we see so many shocks with the heavy end attached to the suspension? It's a pointless way of adding unsprung weight. If we did that in any motorsport, we would be laughed out of the pits. I know some frames are designed so there is not enough room for the reservoir in the proper position, but why WHY??
Cue flogging dead horse emoticon...
  • 1 1
 Half the springs weight could be approximated as unsprung weight, however it's still behind the leverage of the shock linkage, so a better approximation would be 20% of the springs weight is unsprung.
  • 8 5
 I just got my RCS Ti spring...It's a world of difference.The advantages of the Ti are ridiculous. Yeah the weight savings are awesome but the suppleness and how much better the shock reacts is crazy. I will never own a dead-non-working steel spring again. Spend the money, you won't regret it!
  • 2 1
 haha excellent
  • 3 1
 Wondering where you sourced one in the US? I need to sheed some weight on my Entourage. I looked at the list of MTB suppliers on their website and didn't see any in the US.
  • 3 3
 I'm with you.... I swapped out my steel spring for a NukeProof Ti spring - a world of difference! jtorlando, order em from chain reaction cycles!
  • 3 2
 CRC here too. The feel is much better with Ti, plus the weight savings. Get the correct rate nailed in steel first, or you end up with expensive lightweight paperweights. I found 1 rate lighter on ti worked well for me. YMMV.
  • 6 1
 Very cool, was wondering about titanium springs for a while, would also be interesting to see info about carbon springs as well, maybe in another article!
  • 6 1
 Got on a YouTube bender after watching the machine clip, came across this, I'll never look at iron railing the same way again!:
https://www.youtube.com/watch?v=8qGHWZm0C-o
  • 2 1
 HA! I watched that same video a few weeks ago, after a similar bender that started with industrial shredding machines like this one:
www.youtube.com/watch?v=0sPs4HSiaSc
  • 4 1
 With all of the advantages listed in this article, why doesn't every world cup DH racer use a Ti spring? Are there disadvantages of using a Ti coil? Maybe they use a Ti spring painted black to look like a stock steel coil?

And why doesn't Fox, Rockshox and most of the other high end shock manufacturers offer Ti springs on "race" models, or at least aftermarket upgrade options? If Fox offered a RC4 Ti that was a half pound lighter than the standard RC4, I would definitely buy the Ti version!
  • 2 0
 $$$$ Probably.
  • 2 0
 I believe the fox 40 coil and air both have ti springs in them (the new air one actually has two coil springs in it).
  • 3 0
 40 are standard equip[ped with a ti spring.. the shocks are a good question on the other hand,.. .
  • 2 0
 Marzocchi have offer Ti springs in there forks for the last couple of years as their top versions. But again no sight that I know of of anyone using Ti in a factory equipped rear shock!!
  • 2 1
 Have you guys not noticed all the whining about prices here? Most of the guys on the WC circuit do run ti, and a lot use air now too.
  • 1 0
 Yeah I have and price wise get the best value for what you can afford! At the end of the day the technology used in the WC stuff is much more advanced than my car!!
  • 4 2
 Any performance increase is miniscule. Ive owned an RCS coil on a previous bike. Now Ive got a steel one, and I dont find myself wanting to spend £100-£200 on a Ti spring. Even half a pound in weight isnt going to make much difference to the feel of a DH bike at speed.
  • 6 1
 Am I the only one who was like whoooooooaaaooooo ont the video.
  • 2 1
 Not the only one!
  • 2 1
 Good!
  • 6 5
 With all this new air technology in shocks and stuff I find that the coil is losing reputation; however I personal think that it's just as good as an air shock if not better....Just my thoughts.
  • 24 2
 Air = good .... Coil = Better .......... you're welcome!
  • 11 1
 I 100% agree. i have a Ti coil on my Demo and ill be honest, i bought it for the .7lb weight reduction, but if a $250 Ti spring gets me closer to air shock weight, with the performance and feel that i love about a coil. It's worth it
  • 5 2
 My vivid Air feels more supple with better small bump compliance than my vivid coil with Ti did. That being said, the Vivid isn't a 'great' shock. So it would be more beneficial if this was a test between a CCDB Air and a CCDB with Ti . . . but I'm not that rich
  • 2 2
 @Andrews: Air only is not really a complete shock. It serves its purpose in light duty AM/XC/Enduro scenario and DJ. You want to build a light frame and an airshock softens the loads on the frame and you get a little bit of comfort.

Coilsprung dampers are an altogether different beast. They have adjustable damping and variable spring rates and are tunable. Ride a 951, Foes, Supreme or any other highly developped coil bike. Comfort and "roadholding" are way way better.

Something that I completely missed on ti springs is that fewer spring windings mean more travel and probably a 50lb lighter springload. Probably the single most important design feature. Must have, now.
  • 2 0
 adjustable spring preload.. and are pressure serve the same purpose..
and you now summing up foes with it.. the new dhs mono 2:1 is delivered with an air shock nowdays..
so i think air has come up a long way the last few years..
  • 1 0
 Coil springs for life! Smile
  • 1 0
 @cyberhawk: Springs are linear, "Airsprings" are not. Preload and pressure are entirely unrelated concepts - except in marketprose.
Progression is something you design into the suspension by means of changing leverage. I think that is what you mean.

There is no "new" dhs mono. My 2013 Foes Hydro has coil-dampers allaround. The rear has a Fox DHX with 200mm spring...
8.25 inch of progressive suspension travel; 2.3 : 1 suspension leverage ratio. The 2.3 is important to know. Solid number.

So 21cm theoretical spring travel before coil-binding occurs with a steel spring. If I change to a ti-spring with less coils - binding will occur later, giving me either a safety margin before explosive coil binding or I could ride a softer ti-spring and crank less endprogression into the dhx - giving me buttery linear travel to the endstroke.
  • 1 0
 frame design is a different story.. but with bottoming out control and air chamber ajustments.. i FIND that results are somewhat identical these days..
and as for foes..
www.pinkbike.com/photo/9279369

and another guy on here also has an air shock
  • 4 2
 If I'm using a 400lb x 2.8 steel spring now, is it the same for Ti? Or will the numbers be different to achieve the same feel?
  • 6 0
 Lbs = Lbs in any material. It will be the same in both.
  • 5 2
 To my knowledge Ti springs undergo a bit more scrutiny when it concerns actual measured weight. Steel springs can vary + or - up to 15lbs, so you should still use a 400lb spring, but it may have a very slightly different feel
  • 1 0
 Thanks for the advise!
  • 2 0
 Such an awesome read. Thanks for this. Know things now what I didnt know before.
  • 3 0
 Ok, where can I actually buy one!
  • 1 0
 Universal Cycles sells the RCS Ti springs.
That is where I got mine.
www.universalcycles.com/shopping/index.php?category=136
  • 3 1
 This was my article idea, nice to see when you send in an idea to pink bike they actually listen. Great work PB!
  • 2 0
 i make this shit in the uk....boring job.love riding but what a shit job being a spring maker is lol.its EASY!!!!!!
  • 1 0
 try power coil spings in the uk.excellent build quality springs and cheaper than big brands too.a 25 year old business that knows all about springs and performance.
  • 2 0
 Mmmmm. Ti springs. You gots to have one Smile
  • 2 0
 Lots of themmm...!!!
  • 1 0
 Are these available in the US?
  • 1 0
 If I could get a ti spring I might want a coil shock!
  • 1 0
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