What exactly is the U-Turn feature on some Rock-Shox?

hard-rider

Can someone explain what the u-turn feature is. The description given on the RS site doesn't make much sense to me.

Coil U-Turn offers 45mm of travel adjustment on a coil spring with the turn of a crown-mounted external adjuster. As the travel is changed, the spring rate automatically compensates to give riders a consistent and quality feel at every travel setting without affecting preload.

peter413

It is travel adjust feature.

Coil gives you 45mm adjustment and air gives you 30mm adjustment

ricardo666

You can adjust the travel of the fork, by an adjustment
at the top of one of the legs of the fork.

My previous bike, a gary fisher sugar 3 had this on-board
which was the rockshox duke, great fork but may be a little
heavy by todays standards.

hard-rider

Ah so instead of say 100mm you could adjust it to 45mm.

Briggo

hard-rider wrote:

Ah so instead of say 100mm you could adjust it to 45mm.

No, you could adjust it from say 120mm - 100mm - 85mm.

peter413

no. It can give you 45mm of adjustment from the original travel say on Pikes they can go between 95mm-140mm

ricardo666

When I had the dukes they varied from 85mm to 115mm

now I like my rebas, with 120mm of travel, with lockout for climbing

hard-rider

Thanks for clarifying. Must clearer now.

ricardo666

Also if your thinkING of fitting new forks to your bike, keep them within the range of the ones you already have by about 10MM , as it will drastically alter the handling of the bike.

peter413

ricardo666 wrote:

Also if your thinkING of fitting new forks to your bike, keep them within the range of the ones you already have by about 10MM , as it will drastically alter the handling of the bike.

Not to mention destroy the frame if they are to big :shock:

JamesBrckmn

it's useful to have less travel for climbing/road, or even dirt jumping, but more travel for downhill

stubs

Cant remember where I picked it up but apparently Rockshox are playing with an electrically operated U-Turn. How cool would that be just press a button and the forks go up or down

peter413

stubs wrote:

Cant remember where I picked it up but apparently Rockshox are playing with an electrically operated U-Turn. How cool would that be just press a button and the forks go up or down

Except water, mud and electricity don't usually mix to well

Would be pretty cool though 8)

Briggo

peter413 wrote:

Except water, mud and electricity don't usually mix to well

Would be pretty cool though 8)

I'm pretty sure in this day and age that they can make it waterproof.... :roll:

peter413

Briggo wrote:

peter413 wrote:

Except water, mud and electricity don't usually mix to well

Would be pretty cool though 8)

I'm pretty sure in this day and age that they can make it waterproof.... :roll:

By putting it inside the forks?

Oil is even worse for electrics.

Shouldn't they be concentrating on 2-step and making a newer 3/4-step system. That would be even better I think

supersonic

Electronics are the future. Mark my words....

fenboy369

supersonic wrote:

Electronics are the future. Mark my words....

Look at the roadies Di2...

llamafarmer

stubs wrote:

How cool would that be just press a button and the forks go up or down

You need to try out a Bionicon, it's like witchcraft!

hard-rider

Well I'm still deciding which bike I'm going to eventually buy but it'll either be Scott Scale 80 with Suntour XCR, Cannondale Trail 4 with RST first coil, or Specialized Rockhopper with RS Dart 3. But I'm considering replacing the shock stock shock with either a SH Reba SL or RS Revelation 409 Dual air (but I read that the 409's have reliability issues).

Would that be a good and worthwhile upgrade? I'm going to be doing some road, XC and rocky single track stuff.

xtreem

Here's how U-turn works.
Domain from 160mm to 115mm.

http://www.youtube.com/watch?v=EXnX0B4Yr6I

kenan

Is the amount of travel changed, or just the sanctions lowered inth the legs. Bit like coiliver on a car, lowering the car but leaving the suspension travel the same?

supersonic

The travel changes, the height changes, and the spring rate changes.

stubs

Travel is changed but not the spring rate. Means you can wind the fork down for road work or climbing a steep hill then wound out to max travel for bombing down the other side

supersonic

Spring rate does change lol, it winds a progressive coil into a spacer.

stubs

Its been a while since I saw a U-Turn coil spring but as I remember it it uses a fixed rod with a plastic head which has a screwthread engaging the coil spring. Turning the knob connected to the spring shuttles the travel up and down. The spring cant be progressive or it would jam as the coils per unit length change or the coil thickness changes.

As I understand it spring rate in a linear spring is only changed by physically altering the spring by either preloading (compressing) or unloading it and therefore changing the number of coils per unit of length.

Spring rate is calculated by the pressure needed to compress a spring a certain length. A spring a foot long with a rate of 100 pounds per inch needs 100 pounds of pressure to compress it one inch. A spring 6 inches long with the same rate needs the same pressure to compress it one inch. Assuming it has the same physical properties ie number of coils per unit length coil thickness it has the same spring rate. Changing the travel with the U-Turn does not preload the spring therefore it is the same spring so it has the same spring rate. Changing the travel just moves the spring down into the fork leg its the same spring therefore it must have the same spring rate.

The above is only an approximation and is pretty old info that has been rattling round my head for a while as you can tell with the imperial units

supersonic

It winds the linear bit into the plastic spacer - this changes overall spring rate.

From RS:

"Coil U-Turn offers 45mm of travel adjustment on a coil spring with the turn of a crown-mounted external adjuster. As the travel is changed, the spring rate automatically compensates to give riders a consistent and quality feel at every travel setting without affecting preload. "

stubs

Shortening a spring doesnt change its spring rate it is a function of coil thickness/weight x coils per unit of length

example a 12 inch long spring with 12 coils and a spring rate of 100 ponds per inch

cut the spring in half (which is effectively what U-Turn does) so it has 6 coils it still has the same spring rate

Spring rate cannot automatically compensate that is what is known as advertising ballcocks. If U-turn changed travel by compressing the spring that would change the spring rate.

supersonic

We are looking at overall spring rate.

But those 6 coils have a different rate from the previous 6 coils. If you remove part of a progressive spring, the overall rate does change.

stubs

supersonic wrote:

It winds the linear bit into the plastic spacer - this changes overall spring rate.

If you are changing the length linear part of the spring you cannot change the spring rate.

supersonic wrote:

If you remove part of a progressive spring, the overall rate does change.

I dont know if the rest of the spring is progressive wound but you havent changed that therefore you havent changed the spring rate

supersonic

I see what you are saying, and I have probably not explained myself fully or particularly well (plus having seperate discussions on springs lol). tired ;-)

The spring is linear wound at the bottom, and progressive above it. The linear bit winds into the pushrod. As it does so it will coil bind earlier (as gets shorter) and earlier into the travel.