Re-springing an Alta Redshift MX

[gphilip]

Greetings!

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.

- - - - - - - -

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.

 

Edited December 29, 2017 by gphilip

[mog]

Your version 2 is well within normal sags ,I run that on my sxf 250 ,give it a try ,springs don't usually cause harshness so stiff springs won't hurt ,and you can use one spring in the fork and one old one if you want to go back to a less stiff setting

[gphilip]

Thank you, mog. I will be ordering the springs next week and will report back shortly after Anaheim 1 :-)

[ohio]

Marc from Alta here. Philip, thanks for pointing me to the thread and for posting up so much info. It's super helpful for us and for anyone considering the bikes!

You're correct that the bike is sprung fairy softly - it's set up for a rider who likely won't open up their suspension. Your variation 1 should suit you better, though you may find yourself at the edge of the damping adjustments to handle the spring rates. Also, the 4CS is extremely sensitive to oil height, and one of the keys behind our 4CS feeling better than most. I can't remember the stock setting, but you should try to preserve that after you swap springs. Mog is right that heavier springs shouldn't be too harsh - they usually allow you to run less preload which actually can increase the compliance in the initial stroke. Plus will of course help keep the bike higher in its travel and "feel" lighter.

We've been meaning to publish some tables on recommended settings for different riders and riding types, but it hasn't been the highest priority this year with everything else we're trying to build. I'll try to remember to re-post that here if we finally get those out.

[gphilip]

Thank you for the post, Marc. And thanks for making a great bike!!! 

I understand that Variant 1 is the Alta recommended stiffer set. But I generally prefer stiffer fork sprinngs compared to shock springs. On my last two new bikes I stiffened the front springs only and kept the rear stock. On the Alta I need to stiffen both ends, but I think that I need to stiffen the front more. 

The availability of stiffer springs is very limited. Race Tech has Variant 1 springs. But the best 4CS spring selection that I was able to find was at Slavens. If I am wrong I will buy Variant 1 springs. Luckily, 4CS springs can be swapped at the track in under 10 minutes!

Edited January 1, 2018 by gphilip

[mog]

You can run one stiff spring and one standard for in-between rates

[gphilip]

Yes, I know, thank you. I have done this in the past. It expands the spring selection and bridges sometimes large gaps between the available spring rates. 

[gphilip]

Ok, I have things to report back after my first MX track day...

There are good news and there are bad news. Most of the news is good though.

The good news is that the choice of springs was correct for me and my riding skill level (200 lbs, Intermediate). Not too stiff, and not as soft as before. The sag numbers are just as predicted. A very good start.

The bad news is that I also had to max out all the five suspension clickers. Both compression/rebound on the fork and hi/lo compression and rebound in the shock -- all turned all the way in. And it still feels not stiff enough. If I flat land even a small jump, the bike first bottoms out fully and then springs back and jumps once more.

I need this suspension revalved. Three years ago I had to revalve my Husky, the same 4CS fork and shock. I worked with three tuners and also I revalved it 20 times myself, learned way more about suspension tuning than I ever wanted to know, got all the dirt on the suspension tuning industry, spent a lot of time and money, only at the end, while chasing the very last 3-5%, to buy and bolt on a complete YZ450F front end. I dread having to go through this whole ordeal again.

Who are the latest and greatest 4CS motocross tuners these days? Dal Soggio? Race Tech?

Marc -- who tuned the Alta suspension for you? Can I talk to them?

One more thing I noticed is that the Alta is about 40-60mm lower than my Husky (40mm at the foot pegs and 60mm ground clearance). I cased it a few times today on flat landings. The ground clearance is not sufficient, the rear wheel-to-fender clearance is the same as the ground clearance. Can the rear shock be lengthened somehow?

The great part is that the bike is a blast to ride. It tracks like on rails, the instant power makes it super easy to control, and the acceleration pull is very hard and very smooth. It does not do anything weird, it is very relaxing to ride it fast. No more white knuckles, and a lower heart rate too. I also learned a couple of riding tricks, hearing the rear tire hook up (or not) was eye opening. After I maxed out the adjustments on the suspension, I got on my Husky 250TC. OMG, my favorite bike felt like some Harley tractor after the Alta! Lots of buzzing vibration, which I never noticed before, delayed and not very controllable power delivery, and lots of rear end wagging and sliding at all inopportune moments. That was a very sad moment today when I realized that my old favorite bike is no longer my favorite, but the new favorite is not yet properly tuned. Anyway, after a long break and contemplation, I got back on the Alta, and rode the rest of the day until the battery was discharged, trying to time the landings carefully. Let a couple of young guys ride it too, they were very excited. Overall a very good day.

 

Edited January 14, 2018 by gphilip

[Mark911]

Try Cannon Racecraft in OKC for springs.  They got EVERYTHING.  If they don't stock it they'll make it for you.  I'm 150 lbs and went with 0.54s on my Alta fork.  If yours are like mine (I heard there might have been some production changes) they'll be about 1 inch shorter (top of triple to center of axle) than the KTM 4Cs version.  They'll have about 1 inch less travel as well.  The rear linkage is just so slow so it needs a super stiff spring along with a shorter travel shock.  Even then, the wheel hits the fender.   I changed the motion ratio on mine (faster) and was able to go down to a reasonable rear spring rate of 5.0 and finally got proper race and static sag numbers.  Only problem was I needed a shock with more travel, but a stock KTM Trax shock worked fine.   

[mog]

Marc or Russ or Pete Payne or Kevin Stillwell depending on where you are

[gphilip]

 

22 hours ago, Mark911 said:

Try Cannon Racecraft in OKC for springs.  They got EVERYTHING.  If they don't stock it they'll make it for you.  I'm 150 lbs and went with 0.54s on my Alta fork.  If yours are like mine (I heard there might have been some production changes) they'll be about 1 inch shorter (top of triple to center of axle) than the KTM 4Cs version.  They'll have about 1 inch less travel as well.  The rear linkage is just so slow so it needs a super stiff spring along with a shorter travel shock.  Even then, the wheel hits the fender.   I changed the motion ratio on mine (faster) and was able to go down to a reasonable rear spring rate of 5.0 and finally got proper race and static sag numbers.  Only problem was I needed a shock with more travel, but a stock KTM Trax shock worked fine.   

The Alta's 4CS forks are the same length as 4CS on my '15 Husky, they just have a thicker front axle from the '14 4CS. The rear shock is exactly the same. The Alta's linkage is different, but the overall travel is the same ~325mm.

19 hours ago, mog said:

Marc or Russ or Pete Payne or Kevin Stillwell depending on where you are

I will try to keep things simple. Move the YZ450F front end from my Husky onto the Alta and install stiffer springs. The Alta's fork springs are 12% stiffer, so maybe the SSS holds up.

But I must revalve the shock. The shock spring on the Alta is 20% stiffer.

Kevin Stillwell is a friend, we did some work together. Pete Payne appears to be with MX-Tech. I do know know others. I think I need someone with a dyno. Not having to deal with the 4CS widens the tuner selection quite a bit.

 

Edited January 16, 2018 by gphilip

[mog]

Kevin knows the 4cs better than anyone ,why would you not use him ?

[gphilip]

I might do that, if I conclude that the SSS needs a revalve for these extra stiff springs as well. But, if it works, then it would allow me to go riding right away. No need to spend extra time and money. Then I will only need to work on the shock. 

 

[gphilip]

Alta just emailed me a spreadsheet with the shim stack specs that Josh Grant ran at the Red Bull Straight! I am pumped!!! 

[mog]

That's amazing

Did he use the 4cs and STD shock ? I would thought he used a trax and cone valves?

[gphilip]

11 minutes ago, mog said:

That's amazing

Did he use the 4cs and STD shock ? I would thought he used a trax and cone valves?

That's what I thought too, but apparently he just ran the stock suspension. 

Wouldn't it be nice if Musquin ran a stock suspension too and KTM shared the stack specs with us? LOL. 

[gphilip]

Back from testing a stock KYB SSS (2015 YZ450F) front end on my Alta. It worked! I put one 0.54 kg/mm and one 0.56 kg/mm spring in it. I ended up with almost the same clicker settings that I ran on the 2-stroke: Compression - 10 clicks, Rebound 8 clicks. The KYB SSS saves the day!

I am getting the tools to revalve the shock. Will start on it mid-week. The MX track will be closed next weekend though, and then I will be away, so it might be mid-February before I get to track-test the revalved shock.

Today's experience was "spoiled" by a local pro rider, with whom we switched bikes for a few laps. He said he had a Showa A-kit revalve on his CRF450, revalved by the same Showa technician who does Roczen's bikes, so I became curious. We both loved each other's bikes. He said that the Alta was the funnest bike he has ever ridden. Lots of instant power and super easy to rear-steer. And I loved his A-kit suspension. His CRF450 engine felt sluggish and lacking an over-rev after the Alta, LOL. But the suspension, OMG, it was so plush in the beginning, almost too soft, absorbed every little bump in the track. But it stayed high in the stroke, and when I flat-landed it it soaked in the impact beautifully and immediately stuck right back to the track like glue. Damn, I now have a new suspension benchmark to look up to.

[gphilip]

I have revalved the shock last weekend, following the new specs that Alta gave me. IT WORKED! I set both the compression and the rebound at 15 clicks at home and did not have to touch them at the track. The bike is well balanced, and I can jump much higher and farther. And the traction is still good.

Turns out that these shims stack settings are not from the Red Bull Straight Rhythm. They are however, well-developed settings that Alta's pro riders have used on the 2017 MX. These settings are working well for me.

Next, I will try to revalve the 4CS fork and see whether it works better than the KYB SSS or not.

[gphilip]

I revalved the stock 4CS fork this week following the specs that Alta sent me.

The local MX track is closed for two seeks. So I went to my favorite off-road trail to test it. OMG! The ravalved shock worked before but now the fork works too! This was not a motocross track test with jumps and landings, but judging by how the fork felt compared to the YZ450F KYB SSS that I ran before, I am excited to report that it felt much better on the trail.

I DESTROYED the trail today. I am not a trails rider, and I hate the random rocks that are plentiful in Arizona, but I felt so much in control of the bike today that the rocks did not faze me a single bit.

I am very hopeful that the fork would handle the flat landings well. We will see. If I can manage the MX track landings, then hell, I am going to claim that this revalved WP 4CS fork is better than the stock KYB SSS!

[pavetim]

Little off topic but i'm really considering this bike instead of a new KTM 450. Realistically how does it compare to a 450? I now it has a ton more torque which me being 230lbs would be good but i'm worried at the HP level they claim it may not be as fast as a 450. Whats your thoughts on that? They claim the new one correlates to a 300cc