Offset Bushings – must be a trade-off, reduced rear travel?

I think I know the answer to this, but not really seen it discussed before. If using offsets slackens your head angle by shortening the shock length, then they must also reduce the shock stroke and the amount of rear travel.

So dont you need to weigh up the benefits of a slacker head for descending vs less rear travel with the disadvantages that brings?

I’m about to stick a set of these on my BLT, which already has 20mm more travel at the front than rear, but which also had a fairly steep head angle (hence the bushings).

Yeah there will be a bit less travel. Also check the frame clearance at full travel? If tolerances are tight damage could occur!

Who said it shortens the shock length? Are you not just adjusting the shock position with the off set bushings?

no it only changes the eyes to eys length, not the stroke.

Yup, op is incorrect.

it doesnt change any shock length or eye to eye, it justs shifts the frame and rear triangle closer together (or further apart)

You sure Al…

Offset bushings change the effective shock length without affecting its stroke. Because the stroke is unchanged, the travel remains the same (caveat for the pedants – I know if does affect it fractionally due to geometry and angles of linkages but it’ll be negligible for any design actually in use)

Would it depend on whether the offsets were both pointing “inwards”, which would compress the shock slightly when mounted, or both pointing in the same direction, which would effectively move the shock forwards or backwards.

Sorry, I geuss the stroke length doesnt change, but the shock will be compressed in its mount (more sag), but would presumably have scope to expand slightly?

Mmm, so follow up question, how much sag should you set in a shock mounted in 2 offset bushings – a little less than normal?

no. if it ‘compressed the shock slightly’ you wouldnt be able to get the shock in to fit it, unless you took off the spring/let all the air out. and then when you refitted it it would extend again.

shock length and stroke remain unchanged, travel the axle moves remains unchanged (assuming it doesnt hit your seattube a la old konas/222’s etc.)

Agent-wrong.

there’d be no point to have one inward and one outward.

As for sag you’d expect to set it very similar as the shock and wheel travel are essentially unaffected.

So, what happens if you only use one offset bushing (which isnt unusal), this has to affect the eye to eye length of the mountings.

I can see that using 2 bushings can maintain the length, but will shift the shock fore to after (or up and down on a Reign, Cube etc)

You’re only playing with the available space of the eyelet to get a shorter shock ‘length’ which drops the bike at the BB (as if a light person was sat on it) which has the effect of slackening the seat and head angles as the forks are still at full length.

And another thing, the bushings will always settle so to give the shortest length of shock. You can’t put them in to extend the length – they’ll always eventually work their way round. It’s easier to hold a CD (for example) with finger and thumb closer to one side and push against the side closest to your fingers. Push against the other side and it will always want to flip round.

I didn’t think it changed anything except the unsagged shock’s position relative to the frame/linkage?

If you think of the the shock eye to eye as the radius of a circle, and one end as the centre of that circle (for inserting a single offset bushing) aren’t you just moving the position of the other end around the circumference a fraction of a degree, changing the relationship between the rear and front triangles?
And if you use two bushings, then that moves the centre as well, but still doesn’t change the shock length.

OK, from the guy who makes and sells them:

What do these do exactly?

Compress your suspension; you’ll notice your bike gets lower and slacker as the shock shrinks in length. This is what these bushings effectively do. By offsetting the hole in each bush, you can shrink the shocks e2e (eye to eye length) by as much as 7mm. This will usually give a 1-1.5 degree head angle change and lower the bb substantially too.

How do I install them?

1. Remove your rear shock.

2. Press your old bushings out (these usually come out very easily).

3. Take your new, offset bushings and slot them in. Make sure the hole is facing the inwards if you wish to slacken the bike , outwards to steepen it.

I dont have any vested interest in the outcome of this discussion, I’m quite prepared to be right or wrong (Al!), just interested in the science.

he’s written that the wrong way round.

Well he has not described it clearly. But if you want to believe that it compresses the shock then do carry on.

edit – and as nick says he has written it the wrong way round.

What this thread needs is a pie chart.

Stroke is not reduced.
Eye to eye effectivly reduced so gives the affect of the shock being compressed slighty BUT not actually compressing it.

As for negatives, it could be argued that the bushes put the suspension system into parts of the travel it not designed for.
Due to the bolt hole not being concentric in the bush, wear on the eylet bush is increased, so it’s best to check them regularly.

its not that hard to understand. assume the shock is a rigid bar.

if you bolt it to your frame further back in your linkage, the linkage has to move up a bit to meet the end of the shock, slackening the bike – as if it was using a bit of travel.

but it isnt using any travel to do this. ergo, travel remains ultimately unaffected, just the starting position is different.

They don’t compress your suspension – how can they? They merely make the suspension shock length shorter ‘as if’ the suspension is compressed by 7mm, thus lower BB, etc.

EDIT – too slow, beaten to it by LoCo.

exactly, its the same as just moving the drilling in the mount by a few mm.

I’ve got a set installed on my DH bike they do nothing to the shock itself, merely have the effect of making the effective eye to eye length shorter all you install is a pait of mounts where the hole through the centre is eccentric rather than concentric allowing you to cheat a few millimeters off at either end of the shock…

The difference it makes will all be down to the specific frame and it’s configuration, it’s worth taking your shock out and measuring how far beyond its normal fully compressed position the frame can go before components start contacting one-another in an unwanted way.

Doing it has had an effect on the ride of the bike, in combination with some other tweaks, it didn’t make a huge impact on it’s own really, certainly noticeable but not huge, it all depends on what you want from the bike really…

it will slightly slacken the Head Angle and Seat Angle, drop the BB an tiny amount and extend the wheelbase at the front by a weeny bit too… you can get a similar effect by running a little bit more sag in the shock, not quite the same but similar…

What bike are you considering it for?

What bike are you considering it for?

I’m about to stick a set of these on my BLT

So, what happens if you only use one offset bushing. I can see that using 2 bushings can maintain the length, but will shift the shock fore to after (or up and down on a Reign, Cube etc)

I’ve got one on order for my Reign. Despite using just one bushing, the stroke or i2i of the shock is still unaffected. All that happens is that the linkage centre will effectively be 1-3mm lower than normal.
Think of it as if you had part-cpmressed the suspension, except that you haven’t, you still have the available travel and stroke but the bike is sat ever so slightly lower.

Offset Bushings – must be a trade-off, reduced rear travel?

(among other things)

slacker seat-angle.

which can make climbing more difficult.

But, in what sence is the quote above the wrong way around?

Ha, sorry, think I get it now after reading the posts I missed while typing that last one.

Doesnt clear up the instructions on offset.com site though

dude. concentrate. think about it again.

if you use two bushes they are opposing each other, not facing the same way. you arent just moving the flinking shock along a bit, that would be pointless.

aha ok. instructions are wrong way round. i.e if bushes face in then they push the linkage out, which steepens the bike.

if bushes face out than the linkage can overlap the shock a bit, bringing the back end, slackening the bike.

all clear? or time for pictures?

I think its a bit less significant than that, I’d refer to it as the penny dropping… 🙂

Sorry to offend your religious sensibilities! I came into work at 7.30 today to sort out what I though was going to be an horrendous problem and it turned out to take just 10 minutes of quiet thought, clearly I stuggled much longer with this one…..

Not sure I’m the only one who struggled with this concept though, see the “Rotating CD” arguement above, which cant be correct, or it wouldnt be possible to use these bushings to steepen your head angle.

indeed, and if bushing were loose, he’d have a point.

however the ‘cd’ doesnt rotate as it is bolted nice and tight between flaps of metal on your swingarm and mainframe

Not sure I’m the only one who struggled with this concept though

Penny must have been stuck in the same place..

I have heard of them bushes moving around, but I did wonder if they hadn’t been done up tight enough.

however the ‘cd’ doesnt rotate as it is bolted nice and tight between flaps of metal on your swingarm and mainframe

Ah, I suppose. When I fitted mine I did the bolts up but not tight. Bounced on the bike several times to get the bushes to settle in their natural preferred position then tightened them up.

another way to look at it if anyone still confused: you take a bit off the beginning of the travel, and add back the same amount to the end.
(only a few mm so not a problem on most frames).
your geometry then is exactly like running more sag all the time, but without losing travel or changing your shock action.
to work out the height drop you will get, take the bush offset(s) and multiply by your linkage ratio (ignoring that on a single pivot it’s an arc not a straight line up and down but close enough).

Ah, I suppose. When I fitted mine I did the bolts up but not tight. Bounced on the bike several times to get the bushes to settle in their natural preferred position then tightened them up.

I did exactly the same, not had any issues with them since fitting, if they’re moving about then I think the issue is probably that you’ve not got the bolts done up!

I have to be honest I can’t really see how the concept of eccentric mounts is dificult to understand.

No offence* OP but you do sound properly Blond…

(*clearly some offence intended)

Cookeaa – I think there are enough variations in opinions on this thread to suggest that the concept isnt obvious, including an apparent mistake from the guy who makes them posted on his own website. Some people struggle with very simple concepts, such as how to make a good chilli for instance… 😉

No offence taken though, despite not being blonde…

I’ll persist a little longer…

I’ve got a set installed on my DH bike they do nothing to the shock itself, merely have the effect of making the effective eye to eye length shorter all you install is a pait of mounts where the hole through the centre is eccentric rather than concentric allowing you to cheat a few millimeters off at either end of the shock…

So, does it matter how you rotate the bushings when you install them, or do they rotate themselves, presumably pointing outwards (which would increase the e2e length)?

3. Take your new, offset bushings and slot them in. Make sure the hole is facing the inwards if you wish to slacken the bike , outwards to steepen it.

I’m struggling to see what’s wrong with this.

yes there is nothing wrong with the instructions on that site, except for “substantial” being exaggerated imho and i would not try to use these to extend a shock, has anyone done this successfully, they didn’t try to rotate?