Does reducing travel reduce a to c

[Harryburgundy]

Just mocked up some 100mm forks on my M2 1996 build, and they look a bit tall, the frame wasn't meant for 100mm of course.
If I reduce the travel to 80mm does this 'shorten' the fork?
Would it bring the a to c down by 20mm?

 

[fjpshaw]

What forks? I think it depends on how you intend to reduce the travel. For example, fitting a 20mm shorter spring to original internals, but making up the difference between it and the original spring with some kind of 20mm spacer would reduce your travel, but not your a2c.

Simply installing a 20mm shorter spring (without making up any difference) effectively introduces 20mm of sag, and would reduce travel and a2c. But I wonder how it would affect the handling of the fork in terms of negative travel, as you would have 20mm worth of 'slack' not taken up by your rebound cartridge? Not sure that would be advisable.

 

[mattr]

The damper doesn't actually care if it uses 20mm less of its travel, might not really be optimised for it, but it won't damage it.

It usually shortens the a-c of the fork. (I've not come across any it doesn't, but that's not to say there aren't any that keep the same a-c) The extra sag/negative travel is usually accounted for by the change you make, I.e. pace moves springs about, fox use travel spacers, RS use tokens IIRC.

Still, Best to say which forks!

 

[fjpshaw]

No, it shouldn't cause damage to the cartridge, but (and I am thinking about Bombers as I say this) installing an 80mm effective travel spring on to a Z1 rebound cartridge designed for a 100mm travel spring, means the 'top' 20mm stroke of that cartridge is now redundant. If the fork was to become fully extended for some reason (e.g. a jump, or drop off), then the rebound cartridge is free to extend beyond the maximum extension of the spring. Upon recompression, there would be a jarring down to the point where the spring comes back into play.

Thinking about it, the timescales involved between drop off and landing are probably small enough (certainly in my case! ) that the cartridge wouldn't fully over-extend, however, i just dont think it is an ideal setup.

 

[foz]

I reduced a set of Reba's down to 80mm (their shortest travel setting) by inserting the extra spacers, and I'm 99% certain it reduced the a-c (at least I hope it did, because that's what I wanted to do, but it was a couple of years ago and to be honest I can't remember!

 

[Harryburgundy]

Re:

Ah...good point. They are Rockshox SID RTL Ti forks.

 

[GSB]

Re:

I once shortened the travel on a set of RS Judy's. The manual described the different orientation of internal components to shorten the travel from 100mm to 80mm.

Doing so dropped the stanchions into the sliders by 20mm, so yes, it did shorten the axle to crown distance.

 

[Raging_Bulls]

I reduced a set of Reba's down to 80mm (their shortest travel setting) by inserting the extra spacers, and I'm 99% certain it reduced the a-c (at least I hope it did, because that's what I wanted to do, but it was a couple of years ago and to be honest I can't remember!

Reducing a Reba's travel does indeed shorten the a-c.

Unless my own Reba blows up spectacularly as soon as I finish my modern, 80mm only is the shortest recommended setting. You can make it shorter.
Mine is at 60mm but I haven't tested it yet because my shifters have been in backorder for months now.
Initially I set it at 50mm, but found that I had to exceed the maximum recommended 200psi just to get the right sag.

 

[FluffyChicken]

No, it shouldn't cause damage to the cartridge, but (and I am thinking about Bombers as I say this) installing an 80mm effective travel spring on to a Z1 rebound cartridge designed for a 100mm travel spring, means the 'top' 20mm stroke of that cartridge is now redundant. If the fork was to become fully extended for some reason (e.g. a jump, or drop off), then the rebound cartridge is free to extend beyond the maximum extension of the spring. Upon recompression, there would be a jarring down to the point where the spring comes back into play.

Thinking about it, the timescales involved between drop off and landing are probably small enough (certainly in my case! ) that the cartridge wouldn't fully over-extend, however, i just dont think it is an ideal setup.

But you don't just switch springs. If a set is designed to be reduced then there will be spacers at the damping end to move around.
You never just switch to shorter springs.

 

[JamesM]

I reduced a set of Reba's down to 80mm (their shortest travel setting) by inserting the extra spacers, and I'm 99% certain it reduced the a-c (at least I hope it did, because that's what I wanted to do, but it was a couple of years ago and to be honest I can't remember!

Reducing a Reba's travel does indeed shorten the a-c.

Unless my own Reba blows up spectacularly as soon as I finish my modern, 80mm only is the shortest recommended setting. You can make it shorter.
Mine is at 60mm but I haven't tested it yet because my shifters have been in backorder for months now.
Initially I set it at 50mm, but found that I had to exceed the maximum recommended 200psi just to get the right sag.

If it's a dual air Reba then set the positive chamber to the normal amount for your weight and set the negative chamber to whatever it takes to get the right amount of sag. The negative chamber will then be at a lower pressure than the positve chamber.