T500 fork spring specs or dimensions

[jabcb]

Anyone have the specs for the T500 fork springs or a NOS spring they can measure?
I need the OD, wire thickness & free length (length with no load).

The T305 & early T350s also have external springs.
They have a spring rate of 26 lb/in & have a free length of 7".

Some people have used the T500 springs in the T350 with OK results.
But by guessing the specs, I got a spring rate of about 40 lb/in.

From what I've read Suzuki generally used overly stiff springs & not enough preload.
I've found a possible alternative that might fit the T305/T350 & T500.
The alternative provides about an inch more preload & has a spring rate of 30lb/in

The alternative's OD is 50mm, which is a smidgen larger so I'm not yet sure they will fit.

Link to my topic on the T305/T350 spring:
viewtopic.php?f=2&t=10574&p=148574&hili ... gs#p148574

[Bloop2]

Outside diameter 47.9 mm
wire thickness 4.55 mm
overall length 178mm

Cheers...Fred

[jabcb]

Thanks.

The T500 springs have a spring rate of about 40 lb/in.

The OD of the Triumph springs is approx. 2 mm bigger.
I hope they fit -- looks like they will provide better sag & a better ride than the stock springs.
At $37 they could be an excellent deal.

The bike is already put away for winter so this project will have to wait for spring.

[oldjapanesebikes]

The bike is already put away for winter so this project will have to wait for spring.

I was wondering whether you'd managed any progress on this idea jabcb ? I will be taking my MK1's front end apart again in a couple of weeks, and was thinking about possible spring replacement options. Thx !

[jabcb]

I've started working on the bikes but the queue is pretty big.
Worse yet, a mechanic that does some work for me is down for the count for a while with rotator cup problems.

There were some posts a while ago of forum members ordering replacement springs that are stiffer than the stock T500 springs.
They weren't happy with the results.

I'm certainly no expert, but I think that stiffer springs is a change in the wrong direction, and what's needed is softer springs with more preload.
I think these Triumph bobber springs have the potential to be an improvement for both the T305/T350 & T500.

This is the comparison for the T305/T350 per my calcs:

T350_ForkSpringComparison.jpeg

I don't know what the preload & stroke are for the T500.
I would be interested in seeing the calcs for the T500 if you can determine the preload & stroke. (I wouldn't be surprised if they are the same).

[oldjapanesebikes]

I don't know what the preload & stroke are for the T500.

At the risk of displaying my ignorance ! I've never seen a spec for either - the stroke I could measure, but for the pre-load, in the absence of a spec wouldn't you need a set of original new springs to check this ? I'm thinking mine likely have sagged too much to be useful for measurements, and the spacers that are used with the spring really don't amount to much.

These bobber springs - the diameter fits the T500 spring holders OK ?

[jabcb]

My calcs for the T305/T350 spring were consistent with the spec per the T305 manual.
I guessed that the T500 spring was the same except for having fewer active coils.

The Triumph bobber spring has a marginally larger OD.

To check the fit without taking my forks apart, I got a NOS fork spring guide, part # 51573-11010.
It sits at the top of the spring & locates the top of the fork boot.

The spring is supposed to fit inside of the guide, but unfortunately the spring is a bit too big to fit.
I'll post pics later to explain this.

Double quadruple rats.

But the consolation is that the bobber springs might still be useable if you aren't using fork boots.

[jabcb]

I found an interesting alternative spring that should fit the spring guide.
Its a stock spring that costs $26 with a minimum order of 4 springs.
http://www.thespringstore.com/pc177-187 ... gi-in.html

InterestingSpring1a.jpeg

My T305/T350 calcs for this spring:

InterestingSpring1calc.jpeg

InterestingSpring1b.jpeg

[jabcb]

I think the Cycle World suspension mods article from back in the 70s is a useful reference.
http://www.ozebook.com/compendium/suzi/ ... AtHome.pdf

Their fork mods for the GT380/GT550:
spring rate: 26 lb/in
preload: 1" more than stock
travel: 5.5"

Their fork mods for the GT750:
spring rate: 38 lb/in
travel: 5.4"

The T-series bikes are lighter than those bikes.
So a spring rate of 29 lb/in looks reasonable given what we have to work with.
But I'm not sure how much preload would be needed.

Any thoughts?

[oldjapanesebikes]

Any thoughts?

Not yet - but this is something I will be looking at in May when I get home (still in the EU). Ideally I'd like some progressive rate springs but perhaps that isn't realistic.

I'll get back to you.

[oldjapanesebikes]

jabcb - have you seen these ? I was thinking of trying a pair. The vendor can't provide any specs ( ), but does say they are a bit stiffer than the originals. The issue really is the price with shipping to get them across the pond.

Anyone else on the board tried them ?

[jabcb]

jabcb - have you seen these ? I was thinking of trying a pair. The vendor can't provide any specs ( ), but does say they are a bit stiffer than the originals. The issue really is the price with shipping to get them across the pond.

Anyone else on the board tried them ?

I've been really busy lately & haven't made any progress.

Some time ago there were some forum posts about some members having had T500 fork springs made.
If my memory is correct, they were stiffer than stock & the members switched back to stock springs.

The bobber springs didn't work out -- the OD is just a bit too large.
Probably will order the "interesting spring" that I found.

[jabcb]

Finally getting back to this project.

I purchased a set of the “interesting springs” from The Spring Store.
Here are pics comparing the spring to a T350 spring. The interesting spring is gold.

Pic with the springs sitting in part # 51573-11010. Which is the boot guide that positions the top of the fork boot on the 69 T350 & the T500.
The interesting springs fit the boot guide.


The second pic shows part # 51173-11010. Which is the dust seal that sits on top of the oil seal.
It drop into the stock spring with some clearance.
Its a snug fit on the interesting spring & rubs a bit when you push it in.


The interesting spring OD looks good.
But the ID might be an issue — it potentially will rub on the dust seal due to normal motion of the fork.

Will need to do some math. A spring’s diameter increases a bit when its compressed.
Hopefully the spring preload will minimize the rubbing.