GT STS XCR1000 - Fairly sure something is off with rear suspension geometry

simonrh

Dirt Disciple
Hi, I have recently purchased a '99 GT STS XCR1000 in nice, original condition. Lovely looking thing (if you ask me).

I was wondering if there is anyone with experience of the XCR era bike to help with what I might be looking at.

I am trying to pressurise positive and negative ends of SID rear shock to suit my weight and have queries about the sag.
On this version of the idrive system there are red markers on the various components that rotate in the bottom bracket area. To get the perfect sag, the online guide shows that the aim is to have enough positive pressure in the shock that red markers all line up with your weight on the bike (86kg). Negative is then adjusted accordingly.
However, on mine even with all air removed from both ends and the bike lifted of its wheels, the red arrows still perfectly lined up - i.e. it shows that 0 sag is the perfect position which seems to defeat the point of having perfect sag pointers and would be a bit weird.

I feel like i am missing a trick and that possibly one component in the chain is misbehaving.

Trying to start from scratch.
-Degassed shock fully
-Disconnected front derailleur cable in case it was interfering with action of rear end
-Disconnected shock, checked suspension travels correctly through its full range
-Rotated idrive components in their housing and checked for smoothenss.
-With no air pressure, checked shock travels correctly through stroke

Shock measures 6.5" centre to centre eye and looks to be the same type and design as all other STS XCR1000 i can see.

First image. With shock installed correctly, all idrive red dots line up when shock is stroked all the way out and swing arm is at full droop. This would mean I am setting no sag to hit all the red dots lined up.

Second image. With shock bottom eye disconnected (red and green lines) and allowing swingarm to drop until it is touching frame it looks like it makes more sense. Red dots are rotated apart. This seems logical as it would then mean that i have some sag and can then use air pressure to fine tune sag.

Third image (bolts either removed or undone but dog bone still correctly in place). Only other observation is that it has a BETD dog bone installed, briefly tried to disconnect it but BB lock ring will need removing first and didn't have tools to hand. If this was wrong length / version for my bike the i guess it would cause inner red dot to be rotated incorrectly. Dog bone is approx 63mm centre to centre.

shock connnected.jpg
full droop.jpg dog bone.jpg
 
Might be a while before someone knowledgeable sees this, and I'm sorry I can't help, but great post!
 
Might be a while before someone knowledgeable sees this, and I'm sorry I can't help, but great post!
Thanks, have my fingers crossed that someone with the same frame might be available ot measure off a couple of key dims. all the online photos i can find aren't resolute enough on the non-drive side to scale from.
 
Fairly sure i have found the answer.
By scaling off a photo i have found, the dogbone should be 70mm long centre-to-centre.
This then meant i can do a google search including that length which led me to this:

There is a different length dogbone required. The current one fitted seems to be 63.5mm which is 2000 and later from one of the parts list i found.

So i ordered it and hopefully it arrives from Germany (go brexit :confused:)
 
I have an xcr 4000 (non sts) at home that I can check the dogbone length on in the next week or so.

I have here (my current ride) a 2001 i-drive 4.0 plus a couple of spare dogbones, will check those tomorrow to see if there are any differences in length.

Not sure if it will be of any help to you but I have the i-drive service manual I found online sometime back:


pg7.jpg
 

Attachments

  • pg8.jpg
    pg8.jpg
    104.1 KB · Views: 3
  • pg9.jpg
    pg9.jpg
    110.9 KB · Views: 4
  • pg20.jpg
    pg20.jpg
    122.1 KB · Views: 2
  • pg21.jpg
    pg21.jpg
    134.4 KB · Views: 3
Thanks for those, that will be really helpful when i, inevitably, decide to strip it all out and regrease! Hoping the new dogbone arrives from germany and solves the conundrum
 
I've just got back from a 30 mile trek on my i-drive, longest single trip since I built it. It behaved really well so I did a decent enough job on it.

I've not had a chance to check my dogbones yet, but if not today I'll make a point to do so in the morning.

If you need any dogbone bushes I may be able to help, let me know.

I need to check mine later this week when I swap my crankset, I currently have two of the original bushes one end and two (fairly new still) of the BETD bushes the other end, slight knocking still. I've got a few spares so am going to see which type are the best fit and use four of the same.

I have a source of some almost identical to the original ones used by GT, will do as good a job, if needed.
 
When you do end up stripping it down, if either or both of the bearing are past it, BETD sell the originals in a kit, but you have to buy them with the bearing shells too. £40 plus postage.
 
Thanks, I was looking in the photos and figured they look like IGUS bearings (I am a mechanical engineer by trade so geek out on this stuff) so i figured i would measure up in case i needed a set when i pull the dog bone out.
 
the ones i've found, the dimensions are the same only theyre not quite as deep so the two sides wont quite meet in the middle if that makes sense?
Should work fine though. I bought one to compare against some originals I have for myself.

Sourcing new original GT ones seems to be impossible these days.
 
Back
Top