rear spring swap

Vintage Veloce

Vintage Veloce

pro rider
Joined
Oct 7, 2020
Messages
1,087
Location
San Diego
In a separate thread I brought up the idea of swapping out the rear spring on my 2020 Svartpilen 401.

Today, I swapped out the rear spring.
I had purchased an H&R HRF 180 60 130 (180mm free length, 60mm ID, 130 N/mm). This spring rate was recommended by some experts for my weight, 165 pounds (75kg) with all my gear.
The spring was approximately US$ 70 including shipping.

It was harder to swap the springs than I had anticipated. The shock bolts were rather tight, with either a locking compound or maybe poor bolt machining. I found other bolts on the Bajaj manufactured bike to be a bit rough on the threads too... so I recommend having a tap and die set available to clean up the threads. You also need a spring compression tool and a way to unweight the rear suspension, so many might prefer to have a professional do this kind of thing.

Here is my bike on the my lift:
PXL_20201122_195623716.jpg

Here how I unweighted the rear wheel:
PXL_20201122_224944085.jpg

This is the original (white) and the new (red) spring:
PXL_20201122_214637842.jpg

Putting the new spring on:
PXL_20201122_215126344.jpg

Pictures of the new spring installed:
PXL_20201122_234912642.jpg
PXL_20201122_234921754.jpg

I actually like the red color. I had planned on painting the spring black, but red matches the plastic trim on the front fork and I like it!
I checked the free and rider sag, and it seems good. The stock spring is progressive, and this new one is a flat rate. This does help to provide less sag, as there is no soft beginning to the spring.
I did set the bike up with less rider sag (26mm) than I had with the original spring, as I thought I had too much there. Pushing down on the seat, it does feel good, I think that is just because it isn't progressive.

How does it work? Well I only had time for a short test ride around the city tonight. It does seem somewhat better than the stock spring. But I need more riding to test it out. Frankly, I did still hit the rubber bump stop going over a harsh bump... and that was the primary thing I was hoping to fix. But You should hit the rubber bumb stop over the harshest bumps... so we will see. I'd like to be able to adjust the compression damping, but the stock shock does not provide for that. So I may still need an aftermarket shock. I need to do some more riding to figure that out.
 
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Nice write up.

Yes, using the whole range is good, I find that mine usually gets to about 3 or 5mm from the bump stop when no hardcore travel is required and it barely touches it when it needs to. By barely touching it, I mean I dont feel slam, it I just see it on the o-ring and think "oh yeah that was good one..."

I am curious about your sag though, without rider, how much do you use? (On the stock shock I would guess 4 clicks?)
 
Current settings with the new spring
With the preload set to #3 notch from max:
Free sag, 2-3mm
Rider Sag: 26mm
Generally, that is a small number for rider sag, IMO. But I am trying to reserve some travel for the bumps.
 
I want to say I have 10mm static sag and like 50mm sag.

Does it still bottom out when you take it to 6 clicks out from max stiffness, maybe would create less inertia as the downwards dip is already loaded to a different angle of the arm,... maybe?
 
BISavage said:
I want to say I have 10mm static sag and like 50mm sag.

Does it still bottom out when you take it to 6 clicks out from max stiffness, maybe would create less inertia as the downwards dip is already loaded to a different angle of the arm,... maybe?
Click to expand...
I'll be playing with the preload some... but first I just want to ride it a few miles and see what I think. Before it was hitting the bump stop hard and way too often. So far it feels better... but I can't tell really with one loop around the neighborhood.
 
So far the new spring still seems definitely better. But I still haven't gotten out for a long ride on curvy back roads, so a full report is still pending.
 
Vintage Veloce said:
Current settings with the new spring
With the preload set to #3 notch from max:
Free sag, 2-3mm
Rider Sag: 26mm
Generally, that is a small number for rider sag, IMO. But I am trying to reserve some travel for the bumps.
Click to expand...
With all the snow around here I've been holed up, trying to learn about suspension setup. I'm a total noob, my experience riding was 30 years ago on a tiny enduro that I had growing up. But I thought that I'd try to learn about and set up static sag. I'm a pretty lightweight guy, 127lb. without gear. But in researching how to set up static sag, I see that Racetech recommends 25-33% of total travel (therefore 35.5-46.86mm), Touratech says 30% (therefore 42mm) yet the Svart manual suggests 20mm. In your comment above, you feel that even 26mm is a small number. So what gives with the manual suggesting 20mm, does anyone here run with that much preload? I'm not concerned (yet) with bottoming out, I just want to set up a baseline.

(FWIW it seems that "static," "race," and "rider" sag are all referring to the same thing, i.e. sag with the rider in full gear sitting on the bike. That's what I'm referring to as "static" sag above.)
 
First, your naked weight doesn't mean much... the wait of people's gear varies wildly and some wear a backpack or carry a tank bag, etc.

On rider sag: The books and magazines do give some ranges, but it is very dependent on your riding style, preferences and the roads you ride. Basically, you want enough room to absorb the bumps but also enough left to extend into depressions. In my case, I have been having trouble with bottoming the rear shock and so I went for less sag. I haven't noticed any trouble with topping out yet, but that may be harder to sense with my mild riding.

Where does your manual suggest 20mm rider sag? I don't see that in the 2020 USA 401 manual...
 
weird at 75kg rider weight, you feel the need to go stiffer on the spring?
you'd think that's the 'average' weight of this bikes general riders?
 
hannesd said:
weird at 75kg rider weight, you feel the need to go stiffer on the spring?
you'd think that's the 'average' weight of this bikes general riders?
Click to expand...
The stock spring is progressive, and thus gives up a lot of travel at low weights. Really, I mostly went to a linear spring. It's both stiffer and softer. ;-)
The stock spring is claimed to be 100 to 150 N/mm
My replacement spring is 130 N/mm. So that's stiffer than the softest part of the stock spring but softer than the stiffest part of the stock spring.
The big benefit of a progressive spring for the manufacturer is that it will cover a broad spectrum of rider weights, but crudely. The negative is that it is hard for a tuner to understand what is going on... what area of the spring is getting used by a given rider on a given road? Now I know I am at 130N/mm.
I will say, it's not perfect. Better than stock for me, yes! It still does bottom on harsh bumps and I am trying to decide if I am OK with that. Sadly I haven't done much riding lately due to some back issues...
 
Vintage Veloce said:
Where does your manual suggest 20mm rider sag? I don't see that in the 2020 USA 401 manual...
Click to expand...

You know what, you're right. I pulled that figure from the service manual, not the owner's manual. And now re-reading that more carefully, their use of "static sag" does not seem to include the rider, so I think in reality they are referring to "free sag." Facepalm.
 
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20mm would be a lot of free sag! Too much. By the Race Tech Bible, Static Sag is with the rider on the bike. I use the word Rider Sag, because it's easier for me to remember it means with the rider on the bike.
I highly recommend the Race Tech bible, especially if you really want to understand the tech details.
Sportbike Suspension Tuning is another good book, but much less detailed.
 
Vintage Veloce said:
The stock spring is progressive, and thus gives up a lot of travel at low weights. Really, I mostly went to a linear spring. It's both stiffer and softer. ;-)
The stock spring is claimed to be 100 to 150 N/mm
My replacement spring is 130 N/mm. So that's stiffer than the softest part of the stock spring but softer than the stiffest part of the stock spring.
The big benefit of a progressive spring for the manufacturer is that it will cover a broad spectrum of rider weights, but crudely. The negative is that it is hard for a tuner to understand what is going on... what area of the spring is getting used by a given rider on a given road? Now I know I am at 130N/mm.
I will say, it's not perfect. Better than stock for me, yes! It still does bottom on harsh bumps and I am trying to decide if I am OK with that. Sadly I haven't done much riding lately due to some back issues...
Click to expand...
really nice to know, good to be well informed (y)
nonetheless, i don't have problems with it, even when i haven't adjusted it yet from previous owner (all the way soft) i do avoid big bumps and ride street only.
i'll just try to balance it out with the stock front and be done with it :-)
 
pudding said:
Touratech says 30% (therefore 42mm) yet the Svart manual suggests 20mm. In your comment above, you feel that even 26mm is a small number.
Click to expand...

Interestingly enough, the manuel with the hyperpro says to adjust the free sag (without rider) to a specific value.

And that free sag adjustment put the sag with rider in the perfect range.

Also, there is a notable change to the suspension performance with changes in chain length; with the axle at the front of the adjusters it needs less preload, than with the axel at the back, to achieve the same sag.
 
as with dirtbikes, most important is race-sag (riders sag, fully dressed up and feet of the ground,and bike held up perfectly straight) as this determines the handeling characteristics of the bike.
this value for dirtbikes is around 100mm. for road bikes i have no idea.
if you really want to do it right, you set race sag and then you check the free sag,if this is still withing the range, then your spring rate is suited for your weight.
 
hannesd said:
if you really want to do it right, you set race sag and then you check the free sag,if this is still withing the range, then your spring rate is suited for your weight.
Click to expand...

Fortunately, when purchasing an Aftermarket Setup, the supplier can provide the setup best for your weight / style.

They got it covered, so you can worry about more important stuff... like choosing the right oil.

:cool:
 
BISavage said:
Interestingly enough, the manuel with the hyperpro says to adjust the free sag (without rider) to a specific value.

And that free sag adjustment put the sag with rider in the perfect range.
Click to expand...
The Hyperpro does use a rising rate / progessive spring, so setting that up may be somewhat different. It may more easily accommodate a range of rider weights (I've heard that is typically why they are used.)
 
Guess the bottom line is preference, i am happy to pay an specializing company a few pennies to engineer the best suspension for me.

On the otherside, there are alot of things I would rather take the time to do myself before payin 1 cent.
 
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