What is chain growth?

I’ve had a number of single pivot bikes over the years and currently ride a VPP. I’m looking at a new bike and thinking I’ll go for a single pivot again as I’ve always been fine with them but I’m told chain growth and brake jack are serious issues and I should stick with multi link etc etc. CAn’t say I’ve noticed much difference with VPP but seems a bit more difficult to pop of things on my VPP.

What does it all mean and more importantly will a rider like me of modest talent, speed and cohones actually even notice the difference?

Ta.

if you setup your chain to short, it’ll snap the first time you fully compress the suspension in a high gear.

It’s how the distance between bottom bracket and rear hub changes as you move through the travel.

OK I get that but why would it be a problem is what I’m asking, assuming the bikes set up right.

joolsburger – Member
OK I get that but why would it be a problem is what I’m asking, assuming the bikes set up right.

None at all it’s a problem if it’s not, the issue will be more chain at the wrong time and bouncy bouncy if the shock isn’t playing ball

It isn’t a problem. Pretty much everything you read about bike suspension is wrong – if you can get your head around the graphs on the linkagedesign blog then it’ll all start to make sense.

Like how Mike’s post above refers to a single-pivot needing the shock to stop it bouncing. Not true at all but people keep repeating it because they’ve heard others say it or experienced one example which does.

So why do single pivots behave much worse than other designs with a fully open shock? (experience all I have ridden including oranges on demo where the rep set them to max Pro Pedal (LSC) to stop the bobbing?)
I guess I’m just wrong again….

Have your parents never sat you down to have this talk?

http://linkagedesign.blogspot.co.uk

Look at lots of anti-squat curves and you’ll start to see what really matters. Much of it is chain pulling force and tyre driving force interacting with the effective pivot location.

You’ll see that in terms of anti-squat (pedalling) and anti-rise (braking) that the two real groups of suspension design (single pivot inc. linkage driven single pivots vs four bar inc. short link and Horst link) have huge variance in pedalling/braking performance and there’s a clear relationship between the graphs and the actual or projected pivot point. Four bar gives more design freedom allowing you to optimise one characteristic without compromising others so much.

Get a demo ride, make sure shock/bike is setup for you and see how you go. Chain growth, brake jack etc are all semantics for most of us, does it ride how you want it to?

I have an SP, you can tell the difference without pro pedal (bob) or when climbing in granny (stiffens up, soon to be remedied by going 1×10 🙂 ) neither are deal breakers tho. Not sure I can identify brake jack over and above the usual ill effects you get from hitting the brakes. I’ve had a couple of multi pivot, they feel more supple when climbing and don’t “suffer” from dropping into granny ring. More pivots to replace tho.

Current “bestest” bike is 4bar, no idea what I’m going to replace it with when it goes, if it’s a new bike I’ll be doing some demos and getting whatever rides best ignoring the number/type of pivots.
(but chances are it’ll be another 2nd hand so what ever comes up at my price 🙂 )

I’m told chain growth and brake jack are serious issues and I should stick with multi link etc etc

Rubbish : ) Ask someone who says that to explain when chain growth is and isn’t an issue or how brake jack works .. hard to generalise or go into detail but there’s as many inherent flaws, pros and cons etc with most multi-link bikes as there are with SP bikes. It all depends on where the pivots are or how you like a bike to feel and much of the design work out there is about avoiding other designer’s patents.

First, buy what you like not what somebody else says you should like. If you like the feel of a Single Pivot then fine, you are hardly alone.

Second, brake jack is complete BS. I don’t think there is a singgle mountain bike in production today that jacks up under braking. They pretty much all squat down a bit.

Finally, as has been said, chain growth refers to the way the distance between the bottom bracket and rear hub increases as the suspension compresses. A certain amount is considered to be a good thing as it helps to prevent the suspension from compressing when you apply the power (and your weight shifts back). How much is ideal is a different question, but you can pretty much engineer in as much (or as little) as you want with any established design.

roverpig – Member

Second, brake jack is complete BS. I don’t think there is a singgle mountain bike in production today that jacks up under braking. They pretty much all squat down a bit.

I think partly the terminology’s just used very badly tbh- people often just mean “brake feedback”, rather than distinguishing between jack and squat, and mix that in with chain growth effects too. Which is wrong, but pretty understandable I think because people mostly don’t care exactly why their braking affects the suspension, they just care that it does.

You’re right, I’m being pedantic (for a change 🙂 ). Some designs are affected more by braking than others. Mind you, they all work better if you don’t brake.

Well I dunno, I don’t think it’s really pedantry- it’s a real difference and the misuse of the terminology muddles the issues.

as above, on a single-pivot design, ‘brake-jack’ gets used when really ‘brake-squat’ might more more accurately describe the phenomenon of rear wheel braking forces compressing the rear suspension. Caused by wheel torque acting on the system, or, tpiaw, wheel-rotation becoming swingarm-rotation.

it’s not a bad thing, it’s just a thing.

some bikes even have widgets to create brake-squat:

see? – the caliper could be mounted on the vertical element – which also contains the rear axle, where wheel torque wouldn’t have any effect on the suspension. but instead rotec have added a complicated little 4-bar link, so that the caliper can sit on an extra element, which moves parallel to the main swing arm, the effect of this is… brake squat when there could be none.

it’s easy to argue that braking and suspension forces should always be kept separate, but brake squat can be quite handy for keeping the bike level and composed under heavy breaking.

in summary: don’t worry about it.

Very illuminating thanks all.