fitting Longer Shocks?

[jethro10]

Hi.
I have an MTB with 100mm forks. Rockshox dual air. Very nice.
Due to an old injury, i run them a bit soft to help my back/arms. Probably meaning it runs like a shorter form and bounces a bit more

Compare to my wife's it obviously runs the bottom bracket a bit lower, and catches on obstacles a bit more often.
It's not seriously bad, but worth fixing if I can

Would it be reasonable to fit 120-130mm forks to help compensate, they would then probably run on average more like the 100mm I currently have should run.

My wife says so, but then she wants the Rockshox's for her bike

I know both way's the Geometry will be a bit wrong, but closer? or close enough?

Thanks
Jeff

 

[GilesM]

I'm trying to think about the way you are using the forks, to me lower pressure shouldn't really make the ride any softer, as your weight will just increase the sag (amount the fork drops as you sit on the bike), but the air in the main compression chamber will still be compressed the same amount, it's just that there is less volume of air, hence you are nearer the ground, all I think is likely is that you will bottom out the fork on it's full travel more often and, as you say you will sit closer to the ground, if the fork is too bouncy then this is the rebound setting, remember the oil in the shock is the main thing for controlling the rebound speed (damper control). I think that's the theory, however in practice it may behave slightly differently. The other point is that you may have a lower bottom bracket than your wife's bike, hence you will always hit more obstacles.

You could try a longer travel fork, it wouldn't really screw things up, especially if you run the air pressure lower than recommended and increase the sag, it does seem like an expensive option, however if you wife is after your forks it's not such a bad idea.

 

[jethro10]

You could try a longer travel fork, it wouldn't really screw things up, especially if you run the air pressure lower than recommended and increase the sag, it does seem like an expensive option, however if you wife is after your forks it's not such a bad idea.

Well it is an expensive option for sure, but with properly setup forks now, it feels great, but my health suffers a lot!
So I could not do as rough terrain and not enjoy myself as much?

Ok, it's a few hundred quid, but the other gets re-cycled, so we both benefit 1/2 the cost.

So at the end of the day, if geometry wont screw up my bike, looks like an option that will work and thankfully I can afford.

It may take a while, but I'l lreturn here and say how it went....

Thanks for you help
Jeff

 

[e-rider]

the sag is set by the pre-load and the main suspension is usually adjusted by replacing springs etc.

Having more sag will lower the BB and you might bottom out quicker.

There is some difference in the axle to crown length (a-c) between different brands so don't assume that all 100mm forks are the same!

What is the suspension correction of your frame? if it's; 80-100mm then you don't want to put 120mm on it but it could be 100-120mm; in which case it will be fine as you are already operating at the lower end of the scale.

My advice would be to not step outside the correction range. I once put 100mm forks on a 63-80mm corrected frame and it was really really $hit!

 

[GilesM]

the sag is set by the pre-load and the main suspension is usually adjusted by replacing springs etc.

The spring in the Rockshox dual air is air, the sag is varied by changing the air pressure.

 

[GilesM]

My advice would be to not step outside the correction range. I once put 100mm forks on a 63-80mm corrected frame and it was really really $hit!

This is a slightly grey area, I know some very good riders (one who is far too quick downhill) who have put much longer forks on bikes than the recommended value and have ended up with great handling bikes, and the opposite as you describe also happens. Changing from 100mm to 120mm will change the geometry slightly, however if Jethro10 runs with increased sag there will be no (or minimal) geometry change than with a normally set up 100mm fork.

 

[GilesM]

Well it is an expensive option for sure, but with properly setup forks now, it feels great, but my health suffers a lot!
So I could not do as rough terrain and not enjoy myself as much?

Ok, it's a few hundred quid, but the other gets re-cycled, so we both benefit 1/2 the cost.

So at the end of the day, if geometry wont screw up my bike, looks like an option that will work and thankfully I can afford.

It may take a while, but I'l lreturn here and say how it went....

Thanks for you help
Jeff

One option is to look at forks with adjustable travel, but obviously they are more expensive.

 

[e-rider]

The spring in the Rockshox dual air is air, the sag is varied by changing the air pressure.

hence the name 'dual' air!

I was refering to non-dual air forks in general - do the dual air forks have 2 valves then, or only 1 adjustment?

 

[GilesM]

hence the name 'dual' air!

I was refering to non-dual air forks in general - do the dual air forks have 2 valves then, or only 1 adjustment?

Rockshox dual air forks have a positive and negative air chamber, two valves one for each chamber, good stuff on the SRAM website if you ever want to know about the set-up details, not sure why Rockshox use the dual air system, Fox get by very well with only one air chamber on their air sprung forks.

 

[jethro10]

Well 130mm forks now fitted, set a tad on the soft side.
Manitou Minute MRD Absolute 130mm 2009 end of line model Chain Reaction £399

I am way way pleased. It's solved, or gone a long way to solving my health related issues - best I can hope for and my initial goal.
But for a bonus, I can't believe how nice they ride on the rough, like night and day compared to the previous fork - unbelievable.

Absolutley fantastic - I didn't think you could get forks this good - didn't think it could ever make this amount difference. I'd love to try a mega expensive bike now, just itching'

The altering in geometry? well I can't tell the difference to be fair, but did had to re-angle my saddle, perhaps the slightly soft setting I have has masked it? However the fork rides so much better, so perhaps the geometry change has been an advantage? who knows!

anyhow, well pleased and there's a bit of a review in the relevant section.

Thanks
Jeff

 

[spence]

Good job. The geomatry may be out but doubt your notice too much. I've not had a real problem with my hardtail, frame max 100mm currently running 130mm Rev's. Just need to get right over the front for some short sharp climbs.

Fox get by very well with only one air chamber on their air sprung forks.

Not quite true, Fox TALAS have two chambers just primed internaly with some clever valves.