Suspension - reading between the bu!!sh!t

[Cav]

My ZX6R has long been needing some TLC. I decided my suspension would get looked at over winter. A race shock was on the list but sadly Santa never delivered, because of this I looked at other options - suspension service and re-valve seemed like a good deal.

I researched countless websites, some genuine gurus were found but they were few and far between amongst the jungle of internet idiots - you know the sort, the ones that know everything and have jumped over 17 more buses than you have! If they haven't then they know someone who has.

It wasn't until today that I stumbled across a particular website that finally made what I have been researching sync.

The picture below shows a graph with an ideal spring curve. It reaches full suspension travel (fully compressed) then returns to it's original length (free length) in the same time taken to fully compress. Rarely people have the 'correct' spring for their weight so I'm going to explain as concisely as I can what you can do about it.

TOO SOFT:
If the spring is too soft a lot of people think "it's okay, I'll just up the preload". WRONG. Increasing preload does nothing beside change the geometry and amount of travel in the forks. What needs to be done is increase the compression. Obviously there is a limit to the amount of compression you can add and this is down to the valve stack.

Changing the valve stack allows the compression to be firmer. When the compression is made firmer you also want to reduce the rebound damping (usually this is done by turning both compression and rebound adjusters the same way).

TOO STIFF:
If the spring is too stiff you will have the opposing problem to having springs that are too soft. In this case you need to reduce the compression damping and increase rebound damping.

THE SCIENCE:
A stiff spring is harder to compress than a softer spring, because of this you need less compression damping (compression damping can increase the force required to compress the fork springs). Because a stiffer spring contains more energy when compressed it needs more rebound damping to counteract it (therefore you increase rebound damping).

This enables the suspension to work nearly identical regardless of spring rate.

I hope this helps at least one interested person.

Thanks

[Kwacky]

So who is doing your suspension?

[Cav]

Tillit at Cheltenham. The guy who runs the place is a real nice chap called Darren - very helpful

[Kwacky]

What's he quoted if you don't mind me asking?

Parkitt quoted me:-

a service on the rear is £135 and a service and a re-valve is £185 all in.

rear springs are approx. £85 depending on where we go for them.

the front is £112.

delivery back to you £10

we will also provide a £50 set-up included in the price FOC.

[Monty]

See, it's magic!

[Blade]

Tbh Cav the comments Preload just changes the geometry and amount of travel in the forks is not really correct. The geometry and travel changes do occur but they are consequential and not the specific reason for adding preload or why preload is adjusted.

In very simple terms preload is added to adjust the starting point of the springs compression.

Expanding further increasing the preload means you have to exert more force on the spring before the spring compresses. For example if you give a 100kg/mm spring 70 kg of preload you now have to exert enough force to overcome 170kg before the spring will start to compress. Once it has started to compress and travelled 1mm it will then continue to compress at a rate of 1mm per 100kg of force (not 170 as the initial 1mm of travel). The preload is exactly what it says i.e PRE or in laymans terms inital force.

By adding preload as a by product we alter the shocks length and thus the geometry is changed but this is a by product of adding preload and not the reason for adding preload or what preload does and is often confused. If you want to alter geometry you should be looking at changing ride height by adding length to the shock using the ride height adjuster.

It may also be worth adding the comment "lighter spring fitted" to the statement when the compression dampening is increased the rebound damping can be decreased as the rebound damping is independent of the compression dampening and is governed by spring rate alone. Therefore if you increase the compression dampening because a lighter spring has been fitted then yes you would reduced rebound dampening to compensate for the reduced spring rate.

Suspension is always a compromise and one change effects another change.

Hope the comments are helpful and add some clarity.

[Blade]

Your very right in saying there is alot BS on the subject.

The best advice I can give anyone interested in the subject is by a decent book on the subject and learn the basics then when talking to a supension techicinan you understand what's going on as in my experience quite a few experts talk BS also. But then if customers are ignorant on the subject and they stand to make money people will be played every time unless of course you find a guy who is both knowledgable and honest but those are few and far between sadly.

[Perkles]

back in 2003 k-tech revalved my rear shock and front forks on my old gsxr 750 they also fitted a spring matched to my weight and a suitable oil
Go to an expert that has good feedback and who you can trust,sorting my suspension had the biggest impact on my riding especially when on track

[Blade]

Ktech have a very good reputation both on their products but also their knowledge and experience as a suspension company .

If you go for ktech be wary who fits it as although the product is good the installer may not be. If possible always have it installed by ktech themselves.

[Perkles]

k-tech are based in hinckley so I called in one day had a good chat with a technician who advised me on whats best value for money etc
I took out my forks and shock and got them back in a week,great service and it wasnt expensive as I recall

[Blade]

Good service and they have a good reputation at hinckley. The owner and founder is still very much hands on I believe.

[Cav]

£135 including the re-valve.. couldn't turn it down really plus they're local.

Yes you are right and I should have made it clearer what I was saying. I didn't mean it was the sole reason why people adjust preload, just that most people think "if my spring is too soft I will just add more preload and it will be fine". Also, some people think that having the correct static sag means their suspension is set up - you and I both know this simply isn't true.

I was simply trying to touch on areas of suspension that you don't hear about very often besides, "add a couple of clicks". I found it quite facsinating and wanted to share my new found knowledge

[Kwacky]

£135 for a service and revalve is good value.

[Blade]

It's a very interesting subject Cav and rewarding to learn and play with the settings.

[Kwacky]

It's not, it's boring AF

I don't care how they work, so long as they work

[Blade]

So how do you know they work if you don't understand what's going on ?

What you think is the best is only the best you know doesn't mean there isn't better

[Kwacky]

If the engine goes and the wheels turn and the brakes make me stop it's working.

I'm not a physicist but I know when the microwave is working

[Monty]

Cav, please don't take this the personally as it very definitely not meant to be, but I think you have greatly undervalued your audience in this thread.

Some of these old buggers have been messing up suspension way way way before you got your hands on it.

[duke63]

Best way to get a feel for what each adjustment does is to wind each adjuster (one at a time) fully in then go ride and the fully out and then go ride to see what difference it makes.

A lot of standard adjusters are limited in what they actually adjust though unless you have decent quality suspension.

Preload adjustment is really to make sure the forks or shock are working fully within the limits of top and bottom without hitting either top or bottom whilst out riding.

[Blade]

If the engine goes and the wheels turn and the brakes make me stop it's working.

I'm not a physicist but I know when the microwave is working

Fair point and not meant in anyway argumemtative, its a genuine question why the revalve then ?