17" Wheels - What rear shock length?

[Royalratch]

Hi all.

Looking to order some new rear shocks to suit my build specifically.

Z650 frame, USD Ninja forms with 17" wheels front and rear.

How do I calculate what rear shock length I need? As a new Ohlins shock for a Z650 may not be right as they had much bugger wheel and longer forks.

Tips appreciated.

[steve.w]

id get a piece of wood or metal drill holes every halve inch and use it as a dummy shock ..youll then find were ya wanna be ..level is good ..or some like the rear raised ..i dont

[harrythemagnum]

..or some like the rear raised ..i dont

Agreed.

These guys do different lengths, look nice for the money.
http://www.ebay.co.uk/itm/Adjustable-Tw ... 4d1505482b

[Royalratch]

Ohlins say these shocks come only in 350mm eye-to-eye.

Custom lengths need to be built specially.

Good tip on the wood!

How does altering shock length affect damping? Shorter means less travel?

Setting up static sag and preload is still a mystery to me.

Then there's the bikes new weight which is lighter plus the completely different geometry due to smaller and matching wheel size.

[garyd]

Most manufacturers change the length by putting longer threaded fixing at the bottom...so that doesn't alter the way the shock functions.

I bet the weight won't be hugely different and don't forget they can compensate for different riders weights. So I wouldn't worry about that much unless your onle 7 stone.

[Ginger Bear]

Ratch,

ZRX1100 spec Ohlins are 365mm eye to eye & adjustable for length.

http://www.ebay.co.uk/itm/Ohlins-Twin-S ... 4897.l4275

I had them fitted to this;

[Royalratch]

They're also 3 times the price!

I'll set the static height first as suggested to get the bottom frame rails right then measure the distance from top and bottom shock mounts - then just order the closest shock length to that.

[Ginger Bear]

They're also 3 times the price!

Don't tell me you're gonna start scrimping at this stage of the build.

[Royalratch]

The standard S36 are more than enough for me.

Besides - the adjustable ones are for the next bike!

Anyway, got some measurements to help select the right shock length.

Here is the bike sat dead flat under its own weight - the changes from stock Z650 are 17" wheels, 06 ZX6R forks and pretty regular tyre profiles. The rear 'shock' length here is 300mm.



Obviously there are no Ohlins options for a modified Z650 - only for the Z900/Z1/Z1000 and some 750s / 500.

So, the Ohlins S36P KA140 is 350mm eye to eye. That's 50mm long so allowing 25mm static sag (under bikes own weight) means it'll be jacked up 25mm at the rear. Can I dial that out by adding preload? Or is it too much?

Is a custom built set worth the bother?

Cheers all!

[tlc]

I'm pretty sure Yam XJR shocks are shorter. However……

I would fit your seat and bars and try it out by sitting on it. You will then probably find that with the new forks it sits a little low.
Even using the longest newer type forks I ended up raising them by 1 1/2 inches. This then gave me an ideal shock length of 1 inch longer than original. Bearing in mind that I am also using 17's front and back this made sense. Also the side stand makes the bike sit correctly now.

[Royalratch]

Hi mate.

Yep - XJR shocks are 326mm so may be perfect. Weight an issue?

It's not on the side-stand at the mo it's dead upright just balanced against the wall if thats what you meant?

The forks have also been extended about 50mm via dropped yokes - still not as long as the standard fork / wheel combo tho. Should it be level when sat on? What's the ideal target sag when sat on?

[tlc]

I don't know about sag. That's a modern thing. Our old bikes wore pretty much bone shaking legs.

Looking at your other thread I assume you are looking for the wrench monkey bobber type look. You've pretty much achieved that haven't you. Looks good IMHO.

Seeing as XJR shocks could well be right I would personally see if you can blag a set to borrow.

Otherwise, I got some of these as a temporary measure. £79 only.
http://tecbikeparts.com/site/mobile?url ... .html#2654