I just bought an electric 2017 Alta Redshift MX. Love it to pieces!
I have been trail riding it on powerline roads for the last week. It has a ton of traction, a lot of instant HP, and it is always in the right gear. It weighs 260 lbs, but without a heavy flywheel if feels very light, I swear, not any heavier than my 2015 Husky 250TC 2-stroke. Very flickable and maneuverable.
The suspension is exactly the same as on my Husky. Same 4CS fork, same shock, and same linkage and motion ratios. Alta spec'ed an excellent valving, this 4CS works! The bike is very nicely balanced too.
But it feels way too soft for motocross. And it is not the damping but the springs that feel soft. I can easily tell, the bike is very well controlled but feels wallowy, slow to respond to large road bumps, whoops, etc. Compresses the suspension almost fully on even small jump. Lots of slow but very significant acceleration squat and brake dive. It definitely needs stiffer springs. I noticed this when riding two other Altas as well. And some magazines and YouTube videos are also saying that the Alta Redshift MX is sprung too soft.
I initially thought the springs were much softer than on my Husky. But they are NOT, according to the manufacturer. The stock springs are 0.52 kg/mm front and is 6.3 kg/mm rear. The bike weighs 260 lbs. It is heavy. The Alta has much stiffer springs than all my other MX bikes, including the YZ450F!
So I bought the Motool Slacker digital sag scale and measured the sags accurately.
Here is the kicker: The race sags are the same or less than on my 2-stroke Husky! The Alta suspension engineers must have copied the 2014 KTM and increased the spring rates proportionately to the weight of the bike + the weight of the rider. The static sags were a little larger, showing that the stock Alta is sprung 1% stiffer than my well-tuned Husky, when adjusted for its weight + the weight of the rider.
However, when the springs rates are compared to just the weight of the naked bike, they are 6% SOFTER. OMG!
This is why it wallows, squats, pitches and bottoms out so much! The bike itself has a lot of inertia, including the pitch inertia. There is no other way to fix this but to stiffen the springs.
So... I think I have reached a conclusion:
I have to stiffen the springs proportionately to the original specs, approximately the same percentage front and rear.
The static and race sag numbers will not match the traditional specs. I can make a reasonable static sag, or race sag, but NOT BOTH.
I wonder if there are some suspension gurus here who have experience with re-springing bikes that are much heavier, much lighter, or have a much stiffer suspension, like the pro bikes. They can't match the same 35/100mm rule of thumb rear sag numbers either.
So, please check my spreadsheet and let me know what you think. I am leaning towards Variant 2. Thank you for reading my post.
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Last thought: I cannot understand why people do not care about the decimal point in spring rate specs? For pete's sake, MXA and MX-Tech, 4.9 N/mm is NOT the same as 5.0 kg/mm! Race Tech has figured it out though, it appears.