Rear shock sizes - does it have to be EXACTLY the same ?

[trek_y]

I've just bought myself a Canondale RZ120 frame with the idea of swapping across everything from my Prophet as I want something a bit lighter and less bouncy to suit my kind of riding these days. But thanks to a mis-read of the online owners manuals I now realize the rear shock is not the same length (i2i) and stroke. Bugger !
The Prophet has a Fox RP23 200x50 (which would be lovely if I'd bought an RZ 140 :facepalm: ) but the smaller RZ 120 needs a 185x45 shock. I not even going to try fitting the RP23 as it's too far off I expect but seems finding a decent one to fit the new frame isn't easy - must be an OEM size ?
So how close to the specs do I need to be as looking on Ebay etc there lots of 190x50 or a few 185x51 shocks about so could I realistically get away with one of them or do I really have to find an exact replacement.
I realise the slightly (5mm) difference will affect the geometry a little and the longer stroke will give more rear travel but seeing as shocks need setting up with 10%-20% sag etc then can I just dial this out ?
Help !

 

[OllieJones]

If you managed to get hold of a 185 x 51 mm shock the geometry of the bike will be fine, BUT, the extra 6mm of stroke would equate to more travel. The problem is that you may find bits of the frame may come into contact with each other as they travel further than designed, the rear wheel may continue and contact the seat tube of the frame before the shock actually bottoms out which would could be dangerous.
If you used the longer 190mm or 200mm i2i shock you may have the above problems plus the added problems of the frame linkage being extended further than designed in the opposite direction, plus the geometry would be off even if it did fit (bottom bracket would sit higher, head angle would be steeper ect).
Hope some of that makes sense??

 

[02gf74]

If you have size 10 feet, would you wear size 8 or size 13 doc martens? I think not.

185 fox shocks are not hard to find nor overly expensive.

The rear shock fitted on my ibis was shorter than spec and it felt very much sit up and beg, when correct 200 mm was fitted, it just rocked.

I was surprised it made such noticeable difference so id say dont do it.

 

[ishaw]

Re:

Stroke is very important I've learned. I2i you can get away with a bit more or less in some cases, but stroke/travel can cause problems as indicated above. If you want a home for your rp23, I'm looking for one in that size/stroke. I've not got a shock in the size you need to trade, closest I have is a 190 i2i float r, or a ctd that needs a new can, but stroke is 50mm on these.

 

[trek_y]

Re:

Thanks all, thats pretty much what I thought and appreciate the advice. The RZ120 was designed around a 120mm fork up front as well so I'm thinking if I were to go for an extra 5mm stroke on the rear shock then I'd end up with about 13mm more rear travel if the ratio's remain constant and that might be good as I could also put over my 130mm Lefty Max Carbon fork so it may well balance things out albeit with a slightly higher BB and front end - right ? The sister RZ140 looks to be pretty much identical frame with a different linkage to accommodate a longer shock so frame clearance for the rear wheel shouldn't be an issue. There's a few fairly cheap Fox / RS in 185x50 floating about on Ebay so perhaps I'll try one of them and see how it goes for frame clearance and feel. I'll keep the RP23 on the Prophet frame though as expect it'll be more desirable that way when / if I come to sell it but thanks for the offer ishaw.

 

[The Malcolm]

Re:

I have the opposite dilemma to you I bought an RZ120 off ebay at Christmas and only realized this week that the linkage in the centre has been changed for the one for a RZ130\140 suspension. As you note above the frame is the same size it is just the centre linkage that differs

I have a spare 100DLR lefty that I wanted to use thinking that it would maybe work given that there is only 20mm of difference. Now I have a 30-40mm difference between the front and back to deal with. Mine came with a manitou swinger shock which I have tried to measure as there are no markings on it and it looks like it is a 200 x 50 which I understand is correct size for the pivot. My research for the shock size for the RZ120 is 200 x 57

Having replaced all the bearings, pivots, cable guides and shock bushes I am at the stage of I wish I had never bought this frame.

I take it you bought the black RZ120 that was on ebay the other day.

I have put in a wanted add in the wanted section for a 130 or 140 lefty. Not sure whether to cut my loss and sell the thing.

 

[trek_y]

Re:

Hi, sorry didn't reply sooner as have been away from keyboard thanks to a PC meltdown !
Yes I did buy the black RZ120 on Ebay and was heading in the same direction like you of wishing I hadn't after the shock size error. I've now picked up a RockShox Monarch XX for it in the correct 184x44 size but have yet to receive it so fingers crossed it works out for me as I'm quite taken with the RZ frame and hope it'll team up nicely with my Lefty 130.
For your issue I guess the easy option is to fit a longer Lefty fork if you can get one or maybe go for a standard 140mm fork which'll be far more readily available unless like me your are also tied to Lefty wheels ? Alternatively change the linkage for the standard 120 version but then like me you'll have a shock which is too long and round we go again !
Hope it works out.

 

[The Malcolm]

Re:

I have managed to get a lefty 140 from the wanted section on here which should come next week. So hopefully that's the last big expense. It all seemed so straight forward before I bought this frame. I have never had a full suspension bike so not sure what to expect with it.

 

[The Malcolm]

Re:

Well I can confirm changing the top suspension link does not upgrade an Rz 120 into a Rz 140. The 120 Rz frame I bought at the beginning of the year had the top link changed to the link for 140 link by the previous owner. The manitou shock that came with the frame is on its way out so I sourced a 200 x 50 shock on e-bay in great condition but it is too big.

The frame geometry of the Rz120 and Rz140 are identical but the difference in travel and shock length is created by a combination of the top link and the size of the connection point which is welded on the underside of the top tube.
You can see the difference in the two attached images from the manual. Its all obvious after the event.(Ignore the arrows they are from the manual)


Now I have a 200 x 50 fox damper to sell. The joys of second hand parts!

 

[alric]

Re:

if its any use, the Giant trance x 2011 fox rp2 shock is 185x46.
bbut the 190xx50mm fits jjust fine