Suspension sag

[Knowledge]

I don’t know enough about setting up suspension, and this probably explains why the handling on my scoot is not that good. I watched the Steel Weasel’s recent video on YouTube about fitting BGM shocks front and rear and learnt that both ends should have sag.

In this video, Steve Richards illustrates sag on his scooter. Having checked my scoot, it is sag-less.

Looking at the front, I can see that my fork links are pushed up hard against the lower buffers. What can I do to put a bit of slack into this arrangements? Shorter springs? Smaller buffers?

(Scootopia dual rate springs, I think)

[ULC Soulagent]

Steve recommends standard springs if using dampers and uprated spring if not using dampers. Try smaller fork top hats first then go the thinner bump stop buffers

[Storkfoot]

I have just watched the You Tube clip.

He mentions about the front end skipping across the tarmac. This is in keeping with what I was told by a 2 stroke bike racer probably 5 or 6 years ago. He looked at the uneven wear pattern on my front tyre and told me that my front suspension was too firm (progressive springs) as my tyre was skipping causing the uneven wear.

I have not altered the springs since but this has prompted me to finally do something about it. I believe many scooterists need to do the same as I often look at uneven tyre wear patterns on other people’s scooters. It is very common.

Martin, the progressive springs I use are firmer than the ones you refer to. Just for your information.

I shall also check for the sag he mentions.

Thanks for posting this

[coaster]

Do you have a link to the video Martin/Paul?

[Storkfoot]

https://youtu.be/GBqLIT3Pqp0

[Knowledge]

It also occurred to me that my dampers might be at their full extension, and will therefore not allow any sag.i need to check this.

I think I am going to be taking my front suspension apart this afternoon.

[bike grim]

Shortest spring I’ve got are 214mm progressive of unknown origin. The longest set I have are standard at 225mm and then some MB progressive at 219mm for one and 221mm for the other(?) I’ve rebuilt with original top hats and small buffers on the bottom and still can’t get any sag, is there shorter springs available ? (Series 2 forks) or has anyone ever shortened them successfully?

[Warkton Tornado No.1]

MB progressive at 219mm for one and 221mm for the other(?)

Hmmm. Some of us are not the greatest fans of his products, especially the re-made front sprocket bolts that are also too long & bottom out, rubbishing any torque setting thus wrecking the components bolted on, even allowing the cams to override.

Back to the plot A top Group IV racer was noted for omitting the bottom buffers completely. However, a less extreme option is: (after ensuring the links are matched upon their top & bottom faces) pairs of buffers can be 'tuned' to suit by removal of material. Regardless of top or bottom type, the smallest can be fitted bottom, which in itself may achieve sag. Whichever is selected, they can be truncated with a sharp knife, but my preference is to grind off any rubber using either a die grinder or the Makita type sanding file. Try & obtain pairs to ensure matching shore hardness & 'difficult to fit type' if using the clip in GP sort. Then the 'bottom' faces (opposite to working, rounded faces) can have the material removed, which is the preferred method. The lower buffers are rarely used on a proper set up, as full rebound occurs mainly over hump back whales.....

Dampers should never be subject to either full compression or extension &, of course, anybody using Kawasaki type steering dampers really needs more help than we can offer.....

[dickie]

Steve recommends standard springs if using dampers and uprated spring if not using dampers. Try smaller fork top hats first then go the thinner bump stop buffers

I don't really understand the first comment.

In terms of suspension development, it sort of followed this evolution:

1 springs
2 springs with rebound damping
3 springs with rebound damping and a little bit of compression damping

I'm ok with the first three

then some crazy people started adding high and low speed damping and i never got to grips with this.

Anyway, in simple suspension like most Lambrettas have, some dampers are shit. I had some once that had the same compression damping as rebound. Also, I'm about 25kg heavier than he is, so i need a firmer spring (I'd suggest most Lambretta riders are closer to my weight than his at 11stone)

So, I'd be careful about taking a single statement about suspension and using it across the board.

I think the BGM dampers he's using do have compression damping, so that makes a bit of sense for using softer springs.

I raced a zxr400 and R6 for 10 years and got reasonably good at setting my suspension. Although setting race suspension up is actually easier than doing a road bike as it has a very controlled environment whereas a road bike has to operate in a huge variety of scenarios.

The easy way to think about it is:

- springs determine how quick/far the front drops under braking or wheel comes up when it hits a bump.
- once that is set, the damper determines how quick the wheel goes back down or front comes back up after braking.

On the subject of buffers, i'd never really thought about them until quite recently, but it seems obvious to me that you should always use the thinnest on both top and bottom. You really don't want the links making contact with them when you're riding.

[Knowledge]

I have spent the afternoon in the workshop and I have trimmed my lower buffers from about 21mm down to 11mm, and I have sag. I haven’t tested it yet, for the obviously reasons.

Sadly, that is not the end of the matter, as my dampers are now too short. I need dampers that are at least 260mm centre-to-centre, which is pretty long (having said that, I did weld-on my top and bottom damper mounts, so this measurement is probably specific to my machine)

Has anyone know of a suitable-length damper (not Kawasaki, thanks)?

[Knowledge]

The BGM slimline dampers are 238mm, centre to centre, apparently. The BGM pro damper won’t fit my forks, due to my own design of anti-dive fouling the BGM Pro body.

I have thought of another solution that will allow me to lower the position of the top mount without having to re-weld it and damage the paint.

This is tomorrow’s lockdown project.

[jonw]

Suspension sag should be set to include the riders weight i.e. sit on your scoot and check how far you "sit" into the suspensions travel using the "zip tie" method.
High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

[dickie]

High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

Yes, I just can't get my head around how it actually manages to differentiate between the two. Clever people.

[jonw]

High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

Yes, I just can't get my head around how it actually manages to differentiate between the two. Clever people.

It's probably most pertinent in off-road applications but still clever stuff as you say. The only scooter shock I've seen where it has been applied was on a PMTuning rear shock which also had adjustable length too.

[Warkton Tornado No.1]

High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

Yes, I just can't get my head around how it actually manages to differentiate between the two. Clever people.

I have a reasonable understanding of suspension set-ups, particularly the trade off between back to front with rear suspension affecting trail, therefore the sharpness & the front for turn in. Like an awful lot of motorcyclists, I personally attempt to use the benefits of dive going into corners, consequently dynamically enabling counter steering, as well as placing load onto the front end, ensuring that tyre has a larger footprint for potentially more grip. Unless I am mistaken, all manner of re-engineered front ends have come & gone in motorcycle racing, but telescopic forks with their inherent dive (albeit incredibly well controlled) still reign supreme.

Where I fall down (no pun intended) is how come so many road going scooterists convert to anti-dive Although it is widely used on the track, as far as I am aware, there is no proof that anti-dive benefits over conventional suspension. Just why some people spend a lot of money to change their suspension is beyond me, especially when there may well be a box exhaust fitted to ensure that is the limiting factor to their lean angle

[jonw]

High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

Yes, I just can't get my head around how it actually manages to differentiate between the two. Clever people.

I have a reasonable understanding of suspension set-ups, particularly the trade off between back to front with rear suspension affecting trail, therefore the sharpness & the front for turn in. Like an awful lot of motorcyclists, I personally attempt to use the benefits of dive going into corners, consequently dynamically enabling counter steering, as well as placing load onto the front end, ensuring that tyre has a larger footprint for potentially more grip. Unless I am mistaken, all manner of re-engineered front ends have come & gone in motorcycle racing, but telescopic forks with their inherent dive (albeit incredibly well controlled) still reign supreme.

Where I fall down (no pun intended) is how come so many road going scooterists convert to anti-dive Although it is widely used on the track, as far as I am aware, there is no proof that anti-dive benefits over conventional suspension. Just why some people spend a lot of money to change their suspension is beyond me, especially when there may well be a box exhaust fitted to ensure that is the limiting factor to their lean angle

Loading the front tyre in racing conditions has benefits as you say and I think a better way to deal with the dive is to use compression dampening rather than anti-dive.

[ULC Soulagent]

High speed dampening (compression or rebound) accommodates sharp or abrupt (pot hole) suspension movements as opposed to low speed which acts on gentler undulations (road ripples).

Yes, I just can't get my head around how it actually manages to differentiate between the two. Clever people.

It’s to do with the shim stacks inside the cartridge and oil helps as well

[ULC Soulagent]

Steve recommends standard springs if using dampers and uprated spring if not using dampers. Try smaller fork top hats first then go the thinner bump stop buffers

I don't really understand the first comment.

In terms of suspension development, it sort of followed this evolution:

1 springs
2 springs with rebound damping
3 springs with rebound damping and a little bit of compression damping

I'm ok with the first three

then some crazy people started adding high and low speed damping and i never got to grips with this.

Anyway, in simple suspension like most Lambrettas have, some dampers are shit. I had some once that had the same compression damping as rebound. Also, I'm about 25kg heavier than he is, so i need a firmer spring (I'd suggest most Lambretta riders are closer to my weight than his at 11stone)

So, I'd be careful about taking a single statement about suspension and using it across the board.

I think the BGM dampers he's using do have compression damping, so that makes a bit of sense for using softer springs.

I raced a zxr400 and R6 for 10 years and got reasonably good at setting my suspension. Although setting race suspension up is actually easier than doing a road bike as it has a very controlled environment whereas a road bike has to operate in a huge variety of scenarios.

The easy way to think about it is:

- springs determine how quick/far the front drops under braking or wheel comes up when it hits a bump.
- once that is set, the damper determines how quick the wheel goes back down or front comes back up after braking.

On the subject of buffers, i'd never really thought about them until quite recently, but it seems obvious to me that you should always use the thinnest on both top and bottom. You really don't want the links making contact with them when you're riding.

If using uprated progressive spring along with dampers makes the front end too hard as mentioned b4 will cause skipping of the contact patch of the tyre. So use standard springs if using dampers too get the all important static sag

[Storkfoot]

Steve recommends standard springs if using dampers and uprated spring if not using dampers. Try smaller fork top hats first then go the thinner bump stop buffers

I don't really understand the first comment.

In terms of suspension development, it sort of followed this evolution:

1 springs
2 springs with rebound damping
3 springs with rebound damping and a little bit of compression damping

I'm ok with the first three

then some crazy people started adding high and low speed damping and i never got to grips with this.

Anyway, in simple suspension like most Lambrettas have, some dampers are shit. I had some once that had the same compression damping as rebound. Also, I'm about 25kg heavier than he is, so i need a firmer spring (I'd suggest most Lambretta riders are closer to my weight than his at 11stone)

So, I'd be careful about taking a single statement about suspension and using it across the board.

I think the BGM dampers he's using do have compression damping, so that makes a bit of sense for using softer springs.

I raced a zxr400 and R6 for 10 years and got reasonably good at setting my suspension. Although setting race suspension up is actually easier than doing a road bike as it has a very controlled environment whereas a road bike has to operate in a huge variety of scenarios.

The easy way to think about it is:

- springs determine how quick/far the front drops under braking or wheel comes up when it hits a bump.
- once that is set, the damper determines how quick the wheel goes back down or front comes back up after braking.

On the subject of buffers, i'd never really thought about them until quite recently, but it seems obvious to me that you should always use the thinnest on both top and bottom. You really don't want the links making contact with them when you're riding.

If using uprated progressive spring along with dampers makes the front end too hard as mentioned b4 will cause skipping of the contact patch of the tyre. So use standard springs if using dampers too get the all important static sag

It was me that mentioned this. I get no sag either but have the large buffers fitted. Out of interest, do you use the standard springs on a scoot you use for rallies ie laden down with stuff? What rear shock do you have too please?

[jonw]

Personally I use 3 stage progressive springs (soft at start of stroke, hard mid rage and hardest near top out) accompanied with dampers that have compression dampening.
This gives me a soft start to the suspension travel and helps to give sag and be compliant over small bumps and the increasing spring rate along with compression dampening helps combat rapid dive and bigger suspension hits. The springs were Charlie Edmonds 3 stage progressive spring bought from Cambridge which were relatively cheap but have been fantastic.

I have set up my sag to be approx 25% perecent of total travel measured with me in normal riding gear on my scooter which gives a compliant road ride and a small amount of static sag.