Twin shock rear suspension set-up?!!!

[John Orchard]

I'm trying to get my rear suspension sorted, I'm keen to hear what spring & sag settings you guys use?

The springs I have on my rear shocks are progressive (tighter coils on one end), I feel if running modern sag measurements (20-25mm unladen, 1/3 of total travel laden) finds the action un-responsive in the middle of its stroke and limited available travel left to absorb big hits.

Plus I feel it is packing down after a rapid succession of knarly bumps and the ride height is too low in the corners causing front end washout.

I don't think I agree with big sag measurements with progressive springs.  I've just fitted straight-rate springs with only 16mm unladen sag and it feels better in the garage, soon to find out on the track but I'm interested to see what combination you are running, progressive or straight rate springs? Laden & unladen sag?

[crossedup2]

I'm having a very similar problem with the suspension on my RT1.
New shocks with the second lowest rated variable springs. I'm getting about 10mm to 12mm of sag combined and about 4mm static.
The shocks pack up hard after the second wop and is terrible to ride for the next 30 seconds until the springs unload!
I'm planning for less rebound but I don't think the spring rate is anywhere near right!

What are the right measurements for a set of shocks with 80mm of travel????And is going after less rebound before springs the right (or wrong) way to go?

Peter B

[John Orchard]

So Pete, are you getting 4mm of sag with only the weight of the bike and only 12mm with the rider aboard?!!  If that is the case I'd say the springs are miles to stiff.

Maybe the suspension is compressing further on the second hit and firing back too fast because the spring is too stiff?

I think I agree that rear suspension should compress about 1/3 of total travel when seated on the bike...... 25mm if only 4" (100mm) travel.

The modern mx bike likes 100mm laden (with rider aboard) sag as it has a total of 300mm travel.  My KX has a total of 265mm travel so I'm running 80mm laden sag.

[Davey Crocket]

What brand shocks are you guys using?

[Tim754]

Good question John. I have found I cannot jump over a beer can as I used to and my guts sorta hangs over my belt a bit. Yep have lost my spring and compounding it with to much sag .

[JohnnyO]

If you're using modern bike settings to set up the rear end of a twin shock bike you are off the mark. Modern bikes have a rising rate rear suspension linkage system and twin shock has a linear rate, you can't run as much rider sag on a twin shock bike, it will ride too low in the stroke and bottom everywhere.

[John Orchard]

If you're using modern bike settings to set up the rear end of a twin shock bike you are off the mark. Modern bikes have a rising rate rear suspension linkage system and twin shock has a linear rate, you can't run as much rider sag on a twin shock bike, it will ride too low in the stroke and bottom everywhere.

Yep that's what I'm saying but it is interesting to know what laden & unladen sag riders are using with either straight rate or progressive springs?

[EML]

Pre 75 it was(is) more to do with how you held your tongue and the angle of your shoulders. Gritting your teeth is important  too as it never seemed to matter a hell of alot  
Most jappers I rode then had no working rear shocks and any Euro stuff I saw had Girlings or Konis but they were all well past their use-by date so guys just pointed them and shot at whatever was in their way.
It wasn't until the 1st RMs came out that gas shocks that actually dampened anything became a topic of  conversation. Before that we only spoke about tyre pressure and handlebar width/bend. The 21" front wheel did more towards making it handle than spring rates or fork oil.

[JohnnyO]

If you're using modern bike settings to set up the rear end of a twin shock bike you are off the mark. Modern bikes have a rising rate rear suspension linkage system and twin shock has a linear rate, you can't run as much rider sag on a twin shock bike, it will ride too low in the stroke and bottom everywhere.

Yep that's what I'm saying but it is interesting to know what laden & unladen sag riders are using with either straight rate or progressive springs?

To be quite honest a lot of riders in vmx have no idea about suspension setup, they just ride it how it is or bolt on any set of shocks not even built for that bikes suspension geometry. I've seen shocks from a long travel Evo bike bolted onto a pre 75 bike and they are nowhere near the correct spring/damping rates and feel like rigid rear end. Even some well known suspension shops are selling the wrong shocks to customers because the buyer knows no different.

[huskibul]

   The only thing most point and shooters did in the old days was adjust the spring preload  maybe or upgrade to a set of koni's ,s&w or mullhollands,the A graders didnt go around revealing their setups - looking for that edge  !  interesting thread

[crossedup2]

The shocks are brand new from a well known dealer.
The spring rate was discussed at purchase and suggested springs installed. It was also advised by seller to buy the better type of shock for a number of additional benefits.

The thing is that I have been running around on a set of 1972 Yamaha shocks on an AT1 for 4 years now and they are still almost perfect for that bike. The RT1 has now had 3 different set on it, the first set where stuffed Yamaha ones (possibily from a CT1), second set where $75 imports that was just for sorting the rest of the bike out. I crushed the top eye on both sides (they weren't steel) after 2 races and as a mental note they definitely seem to offer zero damping anyway. The third set were not cheap but not a $1000 either. I'm certainly not a complaining customer (was told of pitfalls at time of selection), just dissapointed that I have to actually fine tune something that I would ordinarily take for granted would work out of the box. Unreallistic I know! It does seem obvious now that the rebound is way off, so I'll pull them down shortly and have a play.

However, I am struggling with the static / dynamic sag settings for older twin shocks. I know sag validates the spring rate (soft or weak) but with only 4" of wheel travel, I really don't want 1" taken up when sitting my fat as* on the seat!

It is a black art and a huge time taker to get right. Any helpful points taken with great respect at stage.

Peter B

[John Orchard]

The shocks are brand new from a well known dealer.
The spring rate was discussed at purchase and suggested springs installed. It was also advised by seller to buy the better type of shock for a number of additional benefits.

The thing is that I have been running around on a set of 1972 Yamaha shocks on an AT1 for 4 years now and they are still almost perfect for that bike. The RT1 has now had 3 different set on it, the first set where stuffed Yamaha ones (possibily from a CT1), second set where $75 imports that was just for sorting the rest of the bike out. I crushed the top eye on both sides (they weren't steel) after 2 races and as a mental note they definitely seem to offer zero damping anyway. The third set were not cheap but not a $1000 either. I'm certainly not a complaining customer (was told of pitfalls at time of selection), just dissapointed that I have to actually fine tune something that I would ordinarily take for granted would work out of the box. Unreallistic I know! It does seem obvious now that the rebound is way off, so I'll pull them down shortly and have a play.

However, I am struggling with the static / dynamic sag settings for older twin shocks. I know sag validates the spring rate (soft or weak) but with only 4" of wheel travel, I really don't want 1" taken up when sitting my fat as* on the seat!

It is a black art and a huge time taker to get right. Any helpful points taken with great respect at stage.

Peter B

I see your point, I guess you don't want the spring firing the shock back so that it tops-out with a thud, maybe so it settles back a few mill from topped-out?

The last time I played with 4" travel was my TM125 with a Skunkworks linkage and that was way soft, little did I know then lol.

[JohnnyO]

The shocks are brand new from a well known dealer.
The spring rate was discussed at purchase and suggested springs installed. It was also advised by seller to buy the better type of shock for a number of additional benefits.

The thing is that I have been running around on a set of 1972 Yamaha shocks on an AT1 for 4 years now and they are still almost perfect for that bike. The RT1 has now had 3 different set on it, the first set where stuffed Yamaha ones (possibily from a CT1), second set where $75 imports that was just for sorting the rest of the bike out. I crushed the top eye on both sides (they weren't steel) after 2 races and as a mental note they definitely seem to offer zero damping anyway. The third set were not cheap but not a $1000 either. I'm certainly not a complaining customer (was told of pitfalls at time of selection), just dissapointed that I have to actually fine tune something that I would ordinarily take for granted would work out of the box. Unreallistic I know! It does seem obvious now that the rebound is way off, so I'll pull them down shortly and have a play.

However, I am struggling with the static / dynamic sag settings for older twin shocks. I know sag validates the spring rate (soft or weak) but with only 4" of wheel travel, I really don't want 1" taken up when sitting my fat as* on the seat!

It is a black art and a huge time taker to get right. Any helpful points taken with great respect at stage.

Peter B

If you only have 12mm of sag sitting on the bike your springs are way too stiff and if it takes 30 secs for the springs to unload then the shocks are over damped also. You've been sold a pair of shocks not suitable for a pre 75 bike and more likely to suit an Evo.
Like I said before there are well known dealers selling the wrong spec suspension to customers and you've just confirmed it! There are also certain suspension brands that have been around a long time and always get it right.
I'm rebuilding twin shocks for vmx customers pretty much every week so I see plenty of them and you're not the first with this complaint and you won't be the last!

[80-85 husky]

The hot poop years ago was the koni  damper units which they only make road bike ones now??

I had a set on an XL 250 and they tied it down nicely c/w the stocker shockers!

Without the spring on, you could push them in about twice as fast as pulling them out (from memory ).

a mate purchased some mulhollands or S&W's i cant remember which but they were over damped and packed down after consecutive hits.

We had a nice 300m section of 6 - 12 inch ruts across a wide track which was good standard to test suspension out and a few of us learnt to sort comp from rebound and we developed a rudimentary knowledge of feeling what worked and what didnt. A lot of riding up and down that section was done on saturday afternoons!

One of the "tests" was to push down on the back brake lever and foot peg together and the suspension at both ends should compress ~together.

Until the RM 125S came along, most bikes improved significantly with the fitting of Koni dampers.

In respect to the DTI, try and find a set of older koni units or get a suspension expert to sort the spring and damping issues.

cheers

[JohnnyO]

You don't need to buy an old pair of koni's you just need to get shocks built with the correct damping and spring rates to suit a pre 75 bike. Pre 75 use lighter damping and spring rates to pre 78 and different again to Evo.
Ohlins and Works Performance are 2 reputable brands that build their shocks correctly to suit specific applications.