Trials Australia Forums

Hi All,

A few weeks ago I had a new rear shock spring made up for my Sherco. I had the old spring tested and based on a typical 75Kg rider, the tension was lowered on the new spring to suite me. And that side of things has worked out fine.

The Sherco standard spring was made using 8.5mm wire. But that is apparently non-standard (and uncommon) in the spring industry. The local manufacture did not have (and could not get) 8.5mm wire. So he adjusted all the figures to work with 9.5mm (3/8”) wire. In theory, the new spring is under much less stress and should last a lot longer. I was also told that the standard Sherco spring is made “over-stressed” ….Although I’ve not heard of many Sherco springs breaking??
Now the only problem is…. if I do something like a cat jump above a meter or so. The new spring bottoms out (or closes flat). Which I know is not so good

So my main question is…..does anyone know where I can get hold of about 1.5 meters of 8.5mm Spring wire???

Best of balance.

Neo

Neo

Maybe it isn't the diameter that is the problem. If the tensions are right the spring should take the weight. You might find the answer is to make a new spring in 3/8" but increase the desired load to higher than you had but have the spring progressively wound so it is softer in the earlier stages of compression. That should solve the bottoming out but still give you the softer setting you seek.

Hi BJ,

Thanks for the feedback. But increasing the load would defeat my objective. The Spring feels great. But what I need is more dynamic range. The distance between, what they call "Free Length" and "Solid Height".
As there are 6.5 coils on this spring. All being the same, Using 8.5mm wire would effectively give me 6.5mm of extra travel. And I intend to have the next spring made 7mm longer (Solid Height) too.

I know it sounds like a long shoot....but my bike lands more like a Beta (softer) now ....so I feel it worth a go.

If anyone can help me...please speak up


Best of balance.

Neo

Neo wrote:Hi BJ,

Thanks for the feedback. But increasing the load would defeat my objective. The Spring feels great. But what I need is more dynamic range. The distance between, what they call "Free Length" and "Solid Height".
As there are 6.5 coils on this spring. All being the same, Using 8.5mm wire would effectively give me 6.5mm of extra travel. And I intend to have the next spring made 7mm longer (Solid Height) too.

I know it sounds like a long shoot....but my bike lands more like a Beta (softer) now ....so I feel it worth a go.

If anyone can help me...please speak up



Best of balance.

Neo

Neo,

Ever thought that 6.5 mm might just drive the damper shaft into the end of the shocker housing

It may be all right to play with the spring rates but the stroke of the shock internally relys on the spring fully compressing if it bottoms out, otherwise the shaft takes the brunt. 6.5mm might smash the damper valves off the shaft or bend the shaft when it thumps out. Don't forget that the extra travel at the swing arm axle point will be somewhere between 30-50mm and you are likely to run into problems with the tyre/guard clearance and maybe chain tension issues. When a new shock will cost you $1oo's be sure you get your facts right before you bugger it right up

Just sell the thing and buy a Beta if you want a plush rear end or get a bike with a seat on it like me

Hi BJ,

I had exactly the same technical concerns as yourself. And I believe they are covered OK now. It's a long story (too long for a TA post) but I did consult with the Spring manufacturer, over a two week period, before he made up the spring I have now.

It's funny but I spoke to an engineer (about two years ago) about getting a spring made. He told me then, that there's much more to it than meets the eye. And it would be tough job getting it right. So over the last two years I've given it some considerable thought and I think I've covered most bases now.

It's certainly a pleasure to ride a bike with the suspension tuned to your weight and riding style. I've found balance and traction on sections that previously dab'd on. So I'm happy with the riding results so far.... I just gotta fix this last thing

Best of balance.

Neo

Howdy Y'all,

Neo, are you using much preload on your new spring or not? Instead of getting a longer spring (which will need more preload to fit your shock), you might want to go just a little bit stiffer, with less preload.

Sounds the wrong way round i know, but i have been looking at weight tuned springs for my Scorpa, so I have done a few calcs and that was my best solution: a stiffer spring with less preload would give me a plusher feel and more bottoming resistance than a less stiff spring with lots of preload. If I could remember what I did with compressed length/force curves I'd post them so it would make more sense.

Oh and weight tuned springs for me? I would have had to use a bent crowbar...

Cheers,
Your friendly neighbourhood ScorpaMan,
Scorps

Thanks for the advice Scorps.

On a Sherco the tuned rider weight, of the standard spring, is 75Kgs. But I weigh a mear 57Kgs (yes, you read that right!!!). On the old spring the pre-load was backed right off but the ride was still too hard for me. That why I just had to try a tuned weight spring.

But on the new spring. Because of the thicker wire, the gap between each coil is much, much less than the original spring. Another reason for this, is that the new spring has more turns on it than the old one (to lower the stress factor). So in practise, I have to keep the pre-load right off the new spring too. Otherwise it would bottom out on the smallest of bumps

This all adds up to the fact that I really need 8.5mm wire to solve this problem.


Best of balance.

Neo

Howdy Y'all,

That makes sense Neo, from memory, stiffer (thicker) wire needs a smaller pitch to be as stiff as thinner wire, hence your problem of your coils hitting. I will have a chat to our company's onesteel rep on Monday see if I can get some details or catalogue on their automotive spring wire range, and see what sizes they actually have.

For ultimate bling, why not go titanium?

Cheers,
Your friendly neighbourhood ScorpaMan,
Scorps

Scorps

Titanium??? Isn't that what the plate in my head is made out of????

It hasn't me ride any better so how does help a bike

Gee, and I`ve got all this 8.5 Titanium rod lying round, wonder what it`s worth ??????