xbr 500

[Propellor]

Must have been the beer.......

Hee. Good on yer.

[Propellor]

Maybe the bottoming out in spite of extra spacers can be explained by the fact that spacers set preload and suspension sag but don't (can't) affect spring rate? A "soft" spring is soft no matter how many spacers are applied, no? The position the forks end up under heavy braking surely will be determined by the reaction into the forks under braking. For any given reaction (edit: and any given spring rate) won't this compress the springs to the same point to equal this force every time? Regardless of the number of spacers (amount of preload). Unless the force is less than the preload force, in which case no movement will occur at all.

Pretty much but if the springs are ie 35lb/in then you need another 70lbs of force to overcome the effect of the spacers.


Edited to correct units of force

Hi rhinoman (and steveC).

The above proposal and a comment by steveC have had me scratching my head, as to what actually happens when you add spacers.

This is how I see things. When you add your own weight to that of the sprung portion of the bike the springs will settle to a certain position to counter that force with a force of their own exactly equal to it. That force will equate to a certain length on the spring, according to the spring rate. With the same spring the same position (spring height) will occur each time, except for differences caused by stiction, but hopefully you see my point?

By adding (or subtracting) spacers we are changing the preload. But, as long as there is still some suspension travel ABOVE our static ride height, then we won't have changed anything about the height the spring settles to and therefore way the spring acts under braking. We will have changed the bikes "attitude" (so, indirectly, we have changed the way the bike behaves). Also, we will have altered how much travel is available, as a ratio, above and below static ride height (suspension sag). If we spacer all available travel above static ride height out, then that changes things as the bike acts as a rigid until a certain force is exceeded.

Is that right? I must admit, I'm not entirely sure I'm right! Certainly a confusing, but juicy, topic.

Hopefully I'm making some sort of sense, at least.

Cheers.

[Propellor]

Quoting from Race Tech's motorcycle suspension bible.

"Spring preload is one of the most misunderstood concepts when discussing suspension. Often we hear riders talk about adjusting their motorcycle's spring preload to make the spring stiffer or softer. This is a misconception. Changing spring preload does not change the spring rate at all. The spring has the same rate regardless of how the preload adjustment is set."

And again, same chapter;

"With a given amount of preload force on the spring it will take that same force to initiate suspension movement when the suspension is fully extended. As preload is increased, it takes more force to cause the fork or shock to begin to compress. ... It is important to note that when the motorcycle is resting on the ground with the rider on board, the suspension is compressed. When preload is changed the sprung mass is held higher or lower. This means more preload does not require more force to initiate movement once the weight of the bike has compressed the suspension. "

Quoting from Kevin Cameron's sportbike performance handbook.

"A fair number of people intuitively believe that increasing preload makes the suspension stiffer. It does not! All the preload adjuster does is raise or lower the point at which the bike rides on its suspension, by setting the load on the spring with the suspension fully extended. ... the only way to make the spring stiffer is to replace it with a stiffer spring."

I'm happy that I've cleared up any doubts I had about that aspect of a fork spring!

It seems to me that a spring which has settled to the lower free length tolerance or less will have a softer rate than it started life with (a higher number of coils per inch). We can surely be confident now, that adding spacers won't rejuvenate its spring rate (ie won't make it stiffer again).

[Moto63]

Thanks for all the info propellor , very informative . What I can add is that I went out on my XBR cafe racer based special last night (fitted with hagon springs up front) and gave it some serious beans on the country roads where I live, I was carrying some serious corner speed at times (approx100mph in places) and they behaved impeccably. So in conclusion I would recommend them

[Propellor]

Thanks for all the info propellor , very informative . What I can add is that I went out on my XBR cafe racer based special last night (fitted with hagon springs up front) and gave it some serious beans on the country roads where I live, I was carrying some serious corner speed at times (approx100mph in places) and they behaved impeccably. So in conclusion I would recommend them

You're welcome.

Not sure how/if my diversion has helped the opening post? Sorry!

Why are you looking for different springs?

If I've done my conversion right, then the hagons do seem slightly softer at the initial rate than the srx ones put forward by rhinoman, but seem to end up the same stiffness at the final rate. The gb springs mentioned in rhinoman's posts also seem to start stiffer but don't end up as stiff as the other two. We don't seem to know the rates of the standard springs.

The other thing to bear in mind is that the rates given are just the initial and final rates. This tells us a lot, but not everything. It doesn't tell us whether the springs are truly progressive or simply a dual rate. If they're dual rate, we don't know how much travel occurs before the stiffer rate fully kicks in. A lot also depends on how much preload you apply. This seems to affect the feel of the suspension more than might be imagined.

No easy answers, but a few options for rab. Let us know why you're looking to change.

[guest564]

When preload is changed the sprung mass is held higher or lower. This means more preload does not require more force to initiate movement once the weight of the bike has compressed the suspension.

That doesn't apply if the forks have been moved in the yokes as well - in my case I added 1/2" of spacers and lowered the front end 1".

[Propellor]

When preload is changed the sprung mass is held higher or lower. This means more preload does not require more force to initiate movement once the weight of the bike has compressed the suspension.

That doesn't apply if the forks have been moved in the yokes as well - in my case I added 1/2" of spacers and lowered the front end 1".

Hi rhinoman.

Please bear in mind the above quote is not mine. I quoted that from Race Tech's suspension bible.

With regard to the first sentence of the quote, yes, I would agree that lowering the forks through the yokes will compensate for the raise in height, but of course it won't compensate for the difference in sag, which is also important. Would you agree with that?

With regard to the second sentence of the quote, that is entirely a different matter. Lowering the forks through the yokes won't change that aspect of adding spacers. Well, only very slightly as it will alter the weight distribution. That second sentence is very subtle and very important. You would need to add preload to the point of eliminating sag to change the whole crux of that sentence. And why would anyone set their bike up like that?

I look forward to your opinions.

Cheers.

Edit:when I say "lowering" forks through yokes I should have said "raising" forks through yokes.  I'm meaning "lowering" the front end. Making the rake steeper. Confusing terminology on my part. Apologies!

[Propellor]

Ok, how about this one:

Does increasing preload shorten OVERALL suspension travel? Does increasing preload make your fork operate with less overlap?

Currently trying to get my head around this. I think it might.

Neither of those things sound beneficial, if true.

[guest564]

Adding the springs will reduce the overall travel because you will have already used up some, but you gain some up travel. Reducing sag is usually the point of adding preload, you must have some sag so the suspension can work, usually you would set it to around 1". Theoretically it doesn't make the suspension any stiffer but it takes more force to move the forks so it will firm up the front end a little, the XBR also has progressive springs so say you have 25/45 springs, take up the first part of the travel and you now have maybe 26/45 springs. I wouldn't go over 1/2" additional spacers, if you can't set the sag correctly without using silly length spacers then the springs should be changed. I chain drilled and then filed my spacers from some scraps of 1/4" ally plate, I also drilled holes through the middle of them to make it easier to hook them out.

[Moto63]

Hi rhinoman,  must say I have found the posts both yourself and propellor have been putting up regarding the spring rates etc very informative indeed. Keep up the good work (both of you ). I might even be able to sound like I know what I,m talking about to my mates if I carry on reading your posts LOL.  Ps sounds like you have a nice bike in your racer, any chance of a couple or three photos?

[Propellor]

Ok, how about this one:

Does increasing preload shorten OVERALL suspension travel? Does increasing preload make your fork operate with less overlap?

Currently trying to get my head around this. I think it might.

Neither of those things sound beneficial, if true.

I think the first sentence I proposed above is right so long as the spring itself is the limit to suspension travel ie going fully coilbound. But, to my knowledge, the spring is generally not the limit to suspension travel. In that case I would say that my proposal above is wrong, because it doesn't take into account that the spring is kind of superimposed over the fork (or shock) travel itself. This is shown clearly in race tech's book. Clear diagrams and a clear graph explain the concept well.

[Propellor]

Hi rhinoman,  must say I have found the posts both yourself and propellor have been putting up regarding the spring rates etc very informative indeed. Keep up the good work (both of you ). I might even be able to sound like I know what I,m talking about to my mates if I carry on reading your posts LOL.  Ps sounds like you have a nice bike in your racer, any chance of a couple or three photos?

As well as being knowledgeable, rhinoman is a gentleman. He must be to keep tolerating me! I appreciate that.

[Moto63]

Flattery will get you everywhere propellor I,m sure  LOL

[Propellor]

.........Theoretically it doesn't make the suspension any stiffer but it takes more force to move the forks so it will firm up the front end a little, the XBR also has progressive springs so say you have 25/45 springs, take up the first part of the travel and you now have maybe 26/45 springs. ............

A spring (progressive or straight rate) will only counter whatever force is placed on it by moving to a certain length. For the same force and the same spring it will achieve exactly the same length each time, excepting for differences caused by stiction. I understand what you mean about effectively increasing the starting rate but it will only take more force to move the forks when they start off fully extended.

[Propellor]

I run Progressive Suspension springs that were designed for an SRX600, I had to cut down the stock spacers to suit. The PS springs are a little stiffer on both initial and final rate but I found that the stock springs were bottoming out with upgraded brakes and stickier tyres even though I was running 12mm of additional spacers. At the time no one was selling springs for an XBR.

Edit: I had the forks lifted 25mm through the yokes so they may not have been bottoming out but the front mudguard/fork brace was hitting the bottom yoke.

Hi rhinoman.

Maybe the bottoming out in spite of extra spacers can be explained by the fact that spacers set preload and suspension sag but don't (can't) affect spring rate? A "soft" spring is soft no matter how many spacers are applied, no? The position the forks end up under heavy braking surely will be determined by the reaction into the forks under braking. For any given reaction (edit: and any given spring rate) won't this compress the springs to the same point to equal this force every time? Regardless of the number of spacers (amount of preload). Unless the force is less than the preload force, in which case no movement will occur at all.

I believe the above is correct except for a subtle point, which I missed.

If the spring going coilbound was the limit to suspension travel then, yes, spacers wouldn't affect bottoming out. The exact same braking force which bottomed the suspension without spacers would also bottom the suspension with spacers. BUT! The spring going coilbound isn't (usually) the limit to suspension travel. So adding spacers will allow access to the stiffer zone of the spring at the extreme end of maximum suspension travel, by the amount equalling the spacers. So, for exactly the same braking force it will take the spring to the same length, but it may not bottom out the suspension.

Apologies.