Sunday spring rates for a light rider?

T-Rex

Template denier
I'm loaning out my old Sunday for Interschools in a few weeks, the rider is a beginner, 55kg without kit.

It's got a Marz Roco and pre '09 Boxxers, the 32mm steel spring jobbies.

The 300lb spring in the back is about right for me at 85KG, I've got a 250 and a 200 I could put in it. The spring calculator suggests 200.

Looking back at some old RB threads on the subject, S. and Udi suggest that the quoted rider weights for the Boxxer springs of the era are a bit understated, and that the springs can support a heavier rider than what the chart says. My rider is between a white and a silver spring, but if the boys are right, we should be running a white spring.

So in summary, for my 55kg (excluding kit) beginner, does a 200lb rear spring, and a white (the softest) fork spring sound right?
 

MARKL

Eats Squid
Finally got my computer working again.

According to Linkage, 2008 Sunday, 35% sag:

(kitted riding weight)
55kg - 220.8 lbs/in

60kg - 240.9 lbs/in

65kg - 261.0 lbs/in

At 35% sag the leverage ratio is 2.70 if you want to do your own calcs. The leverage ratio varies through the travel from 3.17 - 2.59. Depends on how accurate model is but it should be better than the straight calculator. All of the above are with 0 pre-load.

Hope it helps, if you want me to run a different assumption let me know.
 

driftking

Wheel size expert
Best bet would be spend an hour one arvo and test the bike for him with the different rates. He could probably run either in the rear, he will be siting right between them, the issue is you than have variances with the springs themselves so your 200 might actually be a 190/210 and your 250 might be a 260/240 as an example so testing is best bet. Is that possible for you to do?

Older boxxers I have no idea on weights so cant help there.

The short option is just go with sag, if the kid is a newbie it wont matter about getting perfect rates, it will take too long to test every combination of
soft and hard
soft and soft
hard and hard
hard and soft

Every change will take a retune of the changed part as you will know so it would be a massive under taking for a newbie really.

My vote is get him set up with the right sag springs then spend like 30min tuning it a little at a track than leave it alone.
 
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MARKL

Eats Squid
Spotted your weight at 85kg, according to the calculator that is 282.5 lbs/in allow riding kit so say 90kg is 299.2 lbs/in. So Linkage seems to agree with your experience. As DK says you need to allow for the fact the spring may not be that accurate - as a starting point I would be tempted to let rider speed/strength be the determining factor if fast go hard, if slower/learning go softer option.
 
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