Serious advice needed about frame choice

[Anthony]

The first thing you need to decide is whether your bad back is caused by incorrect posture on the bike or by the frame being too stiff. Depending on which it is, your next steps would be quite different.

There's no doubt that a GT is a strong/stiff bike, about as strong/stiff as they get. A steel GT will be more compliant than an aluminium one, but still stiffer (and heavier) than some other steel frames. If you have back issues, it certainly seems sensible to keep the fork for the time being, and a Mag 21 is a decent bit of kit.

For a size 16, the lightest ti frames will be around 1.5kg, the lightest steel around 1.8kg. If you're short of money, you may be able to build a lighter bike with a steel frame, as you'll have more funds left over for the components and you'll be able to make back more than that 0.3.

I don't think there are any hard and fast rules for posture, but I agree with what has been said about getting the saddle height right in relation to a slightly bent leg and then obtaining comfort by attuning the bar height to that ideal saddle height. A stem with some rise will also make the position shorter, which may also help your back.

If it's worth the trouble to you, I would advise sending us a picture of you on your bike. I'm sure you'd get a lot of helpful comments.

 

[KillerTurtle]

Hi,

Pics of the bike are here:
http://www.flickr.com/photos/7571582@N02/3489390920/

I am 1.78 meters.
Frame is 16" (I believe 46 cm from BB till seatpost)

Greetings,
Sven

 

[FluffyChicken]

Hi,

Pics of the bike are here:
http://www.flickr.com/photos/7571582@N02/3489390920/

I am 1.78 meters.
Frame is 16" (I believe 46 cm from BB till seatpost)

Greetings,
Sven

1.78 = 5" 10' I'm that and ride a ~20" frame centre to top, (~33/34" inside leg), maybe you are too cramped on your frame. Normally 5"10' would be around 19" I would think for a typical 32" inside leg).

So my advise, buy a bigger bike it's all wrong even with odd inside leg, long body or vise versa.

 

[Neil G]

Looks like a long position to me

Could try a slightly shorter/steeper stem on there

 

[kaiser]

Hi,

Pics of the bike are here:
http://www.flickr.com/photos/7571582@N02/3489390920/

I am 1.78 meters.
Frame is 16" (I believe 46 cm from BB till seatpost)

Greetings,
Sven

Hi Sven without seeing you on the bike its hard to say but the saddle to bar drop is quite big and you also have the seat pointing downwards. Is this for comfort? Again this might suggest the frame is to small as you have to lean too far forward to reach the bars. Riser bars and a riser stem may help. Also I am 5'10" and ride have 2 GT's which are 18"

 

[Andy R]

Hi,

Pics of the bike are here:
http://www.flickr.com/photos/7571582@N02/3489390920/

I am 1.78 meters.
Frame is 16" (I believe 46 cm from BB till seatpost)

Greetings,
Sven

46cm would make it an 18" frame then, which is what it looks like from the photos - I would have thought that was the right sort of size for you.

How long is the top tube and have you tried using a shorter (70mm) stem ?

 

[Anthony]

I believe GT may have quoted size on a c-c basis, in which case size 16 would be equivalent to a c-t length of 46cm. There doesn't seem to be anything about the size of the bike that is wrong for a height of 1.78.

The drop in height from saddle to bars looks to be about 7cm, which isn't at all extreme, but nevertheless might not be helping a bad back. It's quite possible that you would benefit from fitting riser bars to reduce the drop.

It's a great bike, but there's no doubt it's an uncompromising design. One thing's for sure - you're not going to get any younger. A titanium or light steel frame could be the ultimate answer for you, or full-suspension.

 

[kaiser]

I would still think its a fit thing if your ride includes hills. Thus material or suspension wouldn't make a lot of difference.IMO

 

[Jupke]

Hi Sven,

An incorrect posture is the most common cause of injuries and pain.
Things to check:
- Framesize.
- Lenght of cranckarms.
- Height, position and angle of sadlle.
- Lenght of stem.
- Height of bars.
If these are set up correctly changing frame or framematerial could give an extra (small) percentage of comfort.

As for the (front)suspension, the discussion about the pros and cons has finished a long time ago in favour of suspension.

Ben

 

[FluffyChicken]

I just read your for sale thread, which links to you frame intro thread.
Which leads me to this.

The Forks.
The thread seems to suggest it's a mid to late 90's frame, propably around '96.
Frames where well into the suspension designs by then and built I assume around a 420mm fork. I don't know GT's so our resident expert will need to chime in here..
But the MAG21 is a shorter fork, maybe this is causing problems, lowering the front end, making the handling steeper (don't know what it started at but it'll either match racing XC or goin beyond this). Not much but the front end will be 2.5cm lower while putting the seat further forward by ~1.25cm.

You could try some orignal forks or the better matched Judy XC type if somebody is close and you want to avoid selling.
OR lengthen your MAG's but pulling them apart an either getting a kit or doing it DIY tube cutting accuratly and neatly. Picking up some JUDY's or similar for £40 is probably easier.

Just a thought, might be wrong (w.r.t. frame geometry for the bike).