Preload - Ride height and geometry

[alex]

Front Forks.

When adding pre-load, you raise the front as a natural reaction to the force being applied to the spring.

So can I just confirm the correct way to maintain geometry when adding preload is to pull the forks up through the triple clamp. (Or drop the triple clamp down the forks however you prefer to view it).

How do you calculate the correct drop for a given preload adjustment? Is there a simple rule of thumb? I assume it's based on the spring weight being acted on to start with.

(I will be added 2 turns of preload at Portimao as I keep smashing the zip tie flat, I don't intend to worry about the geo change but I do like to understand what is possible/what a pro would do).

 

[alex]

I was asking for the theory...


- Sent from Mobile

 

[Oli]

Just out of curiosity, perhaps it would be beneficial to increase the compression damping a bit to help prevent the bottoming out?

 

[pof]

Just out of curiosity, perhaps it would be beneficial to increase the compression damping a bit to help prevent the bottoming out?

I would agree

Sent from my SM-G920F using Tapatalk

 

[alex]

Its preload first, according to Dave Moss anyway.


- Sent from Mobile

 

[pof]

If your pre load is set within parameters to get your rider sag correct and you are still bottoming out forks then surely spring rate and comp is next step

Sent from my SM-G920F using Tapatalk

 

[Oli]

If your pre load is set within parameters to get your rider sag correct and you are still bottoming out forks then surely spring rate and comp is next step

Sent from my SM-G920F using Tapatalk

+1

 

[alex]

Preload raises the spring rate.
Preload is a moving target. Depends on the track and the riders level.
Once preload is nearly used up the springs should be upgraded.
Damping controls the springs reaction to forces but not the dive under braking.

I hear what you say about sag, but again its a starting point. And to keep the geometry you drop the bike down the forks...


- Sent from Mobile

 

[alex]

https://youtu.be/sd2Z4EuLdZg

https://youtu.be/ahyObXWE098


- Sent from Mobile

 

[alex]

Rebound
https://youtu.be/sz0z5IgVGSg

Compression
https://youtu.be/vqN2Vk_qnG4


- Sent from Mobile

 

[pof]

Preload raises the spring rate.
Preload is a moving target. Depends on the track and the riders level.
Once preload is nearly used up the springs should be upgraded.
Damping controls the springs reaction to forces but not the dive under braking.

I hear what you say about sag, but again its a starting point. And to keep the geometry you drop the bike down the forks...


- Sent from Mobile

Alex, if you drop the bike down the forks then you will be shortening the wheel base, surley with the forks bottoming out the wheelbase is already shortening? Wouldnt you need to go the other way?

Sent from my SM-G920F using Tapatalk

 

[alex]

Guys, I?m not looking for ?solutions?. I was just asking if, in theory, a pro would change anything else to counter a preload adjustment in the front.

Dropping the front down the forks or lifting the rear or nothing.

I guess if I?d suggested a 10mm change to start with it may have helped everyone think about geometry alone. RR?s like to be flat. Older ZX10R?s nose down, bum up. Keeping the bike in its geometric sweet spot is an art, so the question should have simply been; If you change the ride height as a knock on effect of adding spring preload, how would a pro keep that preload change and return to the previous geometry/ride height? (Forget my bike, your bike).

NB: Preload does change ride height otherwise it wouldn?t be used to set static sag.


- Sent from Mobile

 

[pof]

My mistake al3x i mis understood what you were after.

Sent from my SM-G920F using Tapatalk

 

[alex]

Cool no probs. I guess I put too much non-essential info in the OP.


- Sent from Mobile

 

[pof]

Nice read. Just 1 part confuses me is this

surley on corner exit the forks are now starting to extend, how can this be so?

Sent from my SM-G920F using Tapatalk

 

[bananaman]

Phew, what he said ....:bananahuge:

 

[alex]

I think this helps if you look at the blue line.
The shock, off the bike (1st), without preload allows the unloaded shock to extend fully, but, the bike and rider weight (middle image) collapse the spring a certain amount. 50mm in the example. By adding the 25mm of preload in the picture you push the fork top UP the leg and everything attached to it.

 

[alex]

And fwiw I'm on 10nm with 6mm of preload in my particular setup, 90kgs kitted up. So I am going to try 7mm as Portimao has some big stops just like Almeria.

 

[pof]

Alex, back to op, when yoy say you are touching the stops, is it diving down to it or slowly under very heavy brakes?. Using whole of fork length is obviously optimal. Talking to a few guys that set up bikes on race weekends they wouldnt touch the rear in these circumstances . If its just getting to the stops then you cant be far away fr9m where you need to be especially if the bike is doing everything you want it to do

Sent from my SM-G920F using Tapatalk

 

[alex]

Alex, back to op, when yoy say you are touching the stops, is it diving down to it or slowly under very heavy brakes?. Using whole of fork length is obviously optimal. Talking to a few guys that set up bikes on race weekends they wouldnt touch the rear in these circumstances . If its just getting to the stops then you cant be far away fr9m where you need to be especially if the bike is doing everything you want it to do

Sent from my SM-G920F using Tapatalk

Absolutely, I'm trimming it out, it's nearly spot on but I do bottom out on the brakes a moment. Whilst I brake pretty hard, with the benefit of good slicks, I'm sure I have room for more to really nail the braking zones and gain meters. As grip increases you need more preload to support the ability of the rider/bike/tyres. I can return to less for road riding.

To test I will do a run as it is, make sure I use maximum brakes and record it on video (camera behind front wheel).
Review footage. Check zip tie.
Add 1 turn of preload.
Repeat.

FYI bottom of the stock forks is 8mm above the casting. So I'm looking for 12-15mm of gap from the casting to the top of the ziptie, to allow a little room for bumps under braking.