Fork Spring Mod

[bikerphil]

No problem, Drum. As I understand it, a spring can't perform properly if it is preloaded too much. This will explain it much better than I can...

http://www.sonicsprings.com/catalog/...ch_article.php

More good info on progressive vs. straight wound springs...

http://www.sonicsprings.com/catalog/...ch_article.php

Bullet, I haven't tried them in any 37MM XS forks, yet. They are designed for 36MM XS 650 forks. I made them fit the 41MM forks on my Standard with some adapter sleeves.

[bikerphil]

Ok, I built a fork spring rate tester using a piece of sprinkler pipe with a bolt thru the end as a stop and a bathroom scale. A fixed piece of wood attached to a cabnet door makes a good 1" increment guage. I just make a mark on the PVC pipe and line it up with the top mark on the guage, then press down until it reaches the lower mark, then read the scale.





Here's the data I recorded for several types of XS11 fork springs....

78-78 Standard non-air progressive wound factory springs (short type)
27 lb/in (0.48 kg/mm)

80-81 Standard straight wound air type factory springs (short type)
20 lb/in (0.36 kg/mm)

80-81 Special air type progressive wound factory springs (long type)
30 lb/in (0.53 kg/mm)

Progressive brand replacement springs for all XS11 P/N 11-1110 (short type)
30 lb/in (.53 kg/mm)

Unfortunately I did not measure the 79 Special straight wound springs (long type) before I cut them , but after cutting...

35 lb/in (.63 kg/mm) definitely stiffer.

The experimenting continues...

[natemoen]

Hmmm very interesting. Maybe this winter when I start pulling things apart I could test out the 78 spring uncut.

[bikerphil]

Yep, just about all bikes coming from the factory seem to be undersprung. The springs I cut down are better, but still not stiff as I'd like them. I think next I'll try cutting the 80-81 Special long type and remove the progressive wound part as they seem to be pretty stiff. On my other XS with the FJ forks, I'm running 50 lb/in (0.90 kg/mm) straight wound springs and they feel great.

Here's the spring calculator if anyone is interested....

http://www.sonicsprings.com/catalog/...pring_rate.php

[fredintoon]

Please don't think that I am arguing with you. If there is something to be learned here, I would like to learn it.

Hi Drum,
there's two different things here.
One is the spring rate. That's the pounds it takes to compress a spring one inch (or the metric equivalent).
The spring rate depends on the wire material and temper, the wire diameter, the coil diameter and the number of coils in the spring.
Once the spring has been made the ONLY thing Joe Amateur can change is to cut the spring short.
Shortening the spring INCREASES it's spring rate because each coil has to be compressed further to compress the spring through that inch of movement.
So what Bikerphil did by cutting his springs shorter was to increase their spring rate.
The other thing is the spring preload. That's the amount the spring is compressed when the fork is fully extended.
By using plastic sleeves to replace the coils he'd cut off Bikerphil kept his preload the same.

[cywelchjr]

Yep, just about all bikes coming from the factory seem to be undersprung. The springs I cut down are better, but still not stiff as I'd like them. I think next I'll try cutting the 80-81 Special long type and remove the progressive wound part as they seem to be pretty stiff. On my other XS with the FJ forks, I'm running 50 lb/in (0.90 kg/mm) straight wound springs and they feel great.

Here's the spring calculator if anyone is interested....

http://www.sonicsprings.com/catalog/...pring_rate.php

On the specials and the later standards you have to remember that the spring rates were designed about part of the suspension being provided by air pressure. XJ shocks work the same way.

[bikerphil]

On the specials and the later standards you have to remember that the spring rates were designed about part of the suspension being provided by air pressure. XJ shocks work the same way.

Yep Cy, I've found both straight wound and progressive wound springs in the Specials, but the 78-79 Standards are all progressive wound. In the 80 Std air forks, I've only found straight wound.

Today, I cut down a set of progressive wound Special springs about 6" (25%). Cut the progressive end off, now they are straight wound. Got 'em up to 42 lb/in (0.75 kg/mm). Only running 3/4" of preload, took 'em for a short ride and I like them so far. These were 30 lb (.53/kg) before the chop.

[skids]

Ok, I built a fork spring rate tester using (snip)

Here's the data I recorded for several types of XS11 fork springs....

78-78 Standard non-air progressive wound factory springs (short type)
27 lb/in (0.48 kg/mm)

80-81 Standard straight wound air type factory springs (short type)
20 lb/in (0.36 kg/mm)

80-81 Special air type progressive wound factory springs (long type)
30 lb/in (0.53 kg/mm)

Progressive brand replacement springs for all XS11 P/N 11-1110 (short type)
30 lb/in (.53 kg/mm)

Unfortunately I did not measure the 79 Special straight wound springs (long type) before I cut them , but after cutting...

35 lb/in (.63 kg/mm) definitely stiffer.

The experimenting continues...

Yes, I would say that you changed the spring constant!

[bikerphil]

I just got back for a spin with these newest springs and they feel great. Spring preload now is 1", the caps can be installed with your fingertips, no struggle, just the way it should be.

[79XS11F]

Go for the gold valve emulators!!!! My bike handles a billion times better. If you don't want to spend the 150 on them there are 40 knockoffs on mikes xs. I have been out running my friend with an 04 r6 easy. You pedople have to try them

Will they fit the XS11s forks? Are the 650 forks not of a smaller DIA?
Rob

[bikerphil]

Rob, next week I'm gonna make a set of those Mike's emulators work in the 37MM forks, I'll let you know how it goes.

[79XS11F]

Rob, next week I'm gonna make a set of those Mike's emulators work in the 37MM forks, I'll let you know how it goes.

Yes in deed. If you sort out a mod that will allow for use in the XS11s forks I am interested.
Rob

[yamahansolo]

The goldvalves are a direct fit. Plus they have to be a little smaller to fit inside. I think even if the stock knock offs were 1mm smaller they would be fine. The spring rests on top of them.

[justme1100]

Has anyone tried this on an XJ ? I am wondering on how to proceed with stiffening up my front end.

[fredintoon]

- - - I am wondering on how to proceed with stiffening up my front end.

Hi Mike,
by reading those naughty magazines?
Oh, the XJ, right?
let's discuss progressively wound springs. In theory they are wound with the coils getting closer and closer together along the spring length so that as each coil touches it's neighbor it stops working so the rest of the spring gets stiffer. That's costly to do so the ones you buy have the first ~8 coils wound tighter together than the rest to give what is actually a dual-rate spring that's just called a progressive.
Going back to Bikerphil's first post, the progressive (actually dual-rate) springs he'd fitted to his Special are the same springs that Progressive sells for the Standard. The Progressive spring kit contains plastic sleeves that need to be installed in the Special to take up the extra length of the Special's stock springs so that one kit will work with both bikes.
What phil did was to shorten his carefully saved stock springs and make spacer sleeves to take up the length of the missing coils.
What this did was to give him stiffer single rate springs that made his suspension stiffer.
The other thing that can be done is to increase the spring preload.
You can see this done with the external ratchet on the rear shocks. On the front you need to put a spacer sleeve atop the existing spring.
Stiffer springs keep the front wheel lifting as far when you hit a bump.
Increased preload keeps the fork from sagging as far when you sit on the bike.
Two different things, don't confuse them.