Yes, I have been watching the shock therapy videos, Justin there is a great source of information, very clear discussion of technology, very pragmatic approach. I just watched one on IQS and how it is used on UTVs.. very interesting. I have also been spending a lot of time on the mountain bike side looking at some of the absolutely awesome info there. Much more technical than what you see discussed on UTV/Snowmobile/ATV sites.
When I say I find the "balance of the sled is very good", I mean specifically the SRX, and in this case my reference is handling not weight (absolute and/or distribution) yet as I simply do not know until I do a 4 corner on it but also I want to make sure I understand to some degree the dynamic envelope (weight transfer, my own input, etc) hence my bottom up approach. As to where that opinion comes from I have never raced snowmobiles, I just rode what I had which has been an apex attak prior to the srx, and prior to that a mishmash of touring and trail sleds going back to the rupp oh and a deere before that. My background is track cars, race boats, street bikes, ATVs, dirt bikes, mountain bikes where I was either the driver, wrench/engineer of some form or both. Getting on the apex I found its handling to be pretty poor (suspension was a bit beat up when I got it) but I did get it into reasonable shape eventually with some help from Stubbs. The motor got me excited about snowmobiling again but life got in the way of paying any more attention to the apex so it became a gas and go machine. So jumping on a new SRX out of the box and following guys that were 'fast' trail riders (their words) I found the SRX to be a pretty sizeable upgrade to the Apex, not just the bump absorption, it was more that the machine is very poised, very reactive to body english, and very linear in power delivery and predictable in handling up to its limits. The balance of a machine and by that I specifically mean the overlap in the venn diagram between power, traction, cornering, suspension, etc is very good. It actually surprised me. I prefer very slight predictable push to unpredictable oversteer and the SRX was right there. I was riding a buddies 2022 XRS earlier this season and I found it to be skittish, the power delivery was urgent but not very linear (and it ran out juice quickly), and the front end is in need of some help *for the way I ride*. Not sure I agree on the weight distribution as it intuitively (no proof to back this up) limits your own input through body english. I was the chassis architect (fancy way of saying I came up with the suspension solutions) for a team where they had two very different drivers with completely different driving styles. Machines were otherwise identical. Since this was buggies, not bikes, it wasn't about body english, it was more about power delivery, braking dynamics, and cornering. Both guys were competitive but for different reasons due to their different styles. I know from that experience that riding style, terrain, etc will dictate the targets for improvement more than anything else. If you watch motogp it is an interesting study in chassis dynamics and riding styles (also the best racing on TV bar none).
When I say I find the "balance of the sled is very good", I mean specifically the SRX, and in this case my reference is handling not weight (absolute and/or distribution) yet as I simply do not know until I do a 4 corner on it but also I want to make sure I understand to some degree the dynamic envelope (weight transfer, my own input, etc) hence my bottom up approach. As to where that opinion comes from I have never raced snowmobiles, I just rode what I had which has been an apex attak prior to the srx, and prior to that a mishmash of touring and trail sleds going back to the rupp oh and a deere before that. My background is track cars, race boats, street bikes, ATVs, dirt bikes, mountain bikes where I was either the driver, wrench/engineer of some form or both. Getting on the apex I found its handling to be pretty poor (suspension was a bit beat up when I got it) but I did get it into reasonable shape eventually with some help from Stubbs. The motor got me excited about snowmobiling again but life got in the way of paying any more attention to the apex so it became a gas and go machine. So jumping on a new SRX out of the box and following guys that were 'fast' trail riders (their words) I found the SRX to be a pretty sizeable upgrade to the Apex, not just the bump absorption, it was more that the machine is very poised, very reactive to body english, and very linear in power delivery and predictable in handling up to its limits. The balance of a machine and by that I specifically mean the overlap in the venn diagram between power, traction, cornering, suspension, etc is very good. It actually surprised me. I prefer very slight predictable push to unpredictable oversteer and the SRX was right there. I was riding a buddies 2022 XRS earlier this season and I found it to be skittish, the power delivery was urgent but not very linear (and it ran out juice quickly), and the front end is in need of some help *for the way I ride*. Not sure I agree on the weight distribution as it intuitively (no proof to back this up) limits your own input through body english. I was the chassis architect (fancy way of saying I came up with the suspension solutions) for a team where they had two very different drivers with completely different driving styles. Machines were otherwise identical. Since this was buggies, not bikes, it wasn't about body english, it was more about power delivery, braking dynamics, and cornering. Both guys were competitive but for different reasons due to their different styles. I know from that experience that riding style, terrain, etc will dictate the targets for improvement more than anything else. If you watch motogp it is an interesting study in chassis dynamics and riding styles (also the best racing on TV bar none).
kinger
VIP Member
I understand what you are saying and agree. I have said this before, out of the box the winder is comparable to a heavily modded apex. The apex got screwed with a crappy suspension that was comfort based instead of performance based. It also just had way to much unneeded weight, the seat, exhaust, suspension, all the misc steel brackets, etc. However once modified I can't keep up with it on my winder. Now that said mine is not a SRX like yours, I am sure yours handles even better then my winder BTX although I will have more traction. I really want to believe 70/30 is bad but I am becoming more convinced with more real world testing. A sled is so different then a ATV or anything else I decided to just let real world feel take over from spreadsheets and research.
I made this vid to show you how the weight transfers when moving around a sled this is on my 65/35 twincharged. I will do the winder someday when ever it gets a new motor from Yamaha. You can create deltas of 50-80lbs just leaning forward backward and sideways. I will be curious what you ultimately decide is the secret sauce on handling for your SRX. I find mine front heavy because it has 50lbs MORE on the front skis when I sit on it. However in deep snow it walks out and feels light as a feather in front. Modded apex is opposite light steering, hooks and wheelies hard but in deep snow trenches and overall sucks.
I made this vid to show you how the weight transfers when moving around a sled this is on my 65/35 twincharged. I will do the winder someday when ever it gets a new motor from Yamaha. You can create deltas of 50-80lbs just leaning forward backward and sideways. I will be curious what you ultimately decide is the secret sauce on handling for your SRX. I find mine front heavy because it has 50lbs MORE on the front skis when I sit on it. However in deep snow it walks out and feels light as a feather in front. Modded apex is opposite light steering, hooks and wheelies hard but in deep snow trenches and overall sucks.
Thanks for that. Like I said, working backwards from the 4 corner test will be an important component of understanding why it handles the way it does. I have a good feel for the shock geometry at least on the front, I am working from my measurements to create a model containing predicted spring weights/spring constants/critical frequency to then pick components and compare to what's really on the sled. My expectation is to be wrong, I hope I am surprised but, probably wrong and that's okay, it will force me to dig deeper.
I found the shock therapy iqs demo to be really interesting, the individual iqs components (without shocks) are available for UTVs as it appears they can be added to existing shocks. One interesting thing was that for a UTV the IQS controls are a 3 way switch that gives you instant access to what mode the shocks are in. The yamaha/cat implementation leaves a lot to be desired because it requires you to look at a menu, futz around with buttons that have a serious glove hate going on, and if you are in soft, you have to click multiple times to firm. That quick access 3 way would be fantastic as you could, without looking, predict what mode you need to be in and make the switch as soon as you see the trail/conditions change and before you get there (unlike smart shocks).
Of secondary interest would be intercepting the individual IQS command sent to each front shock to create a semi-automatic roll control (rebound dampening) for the inboard ski. Call it a semi-smart shock. That would help cornering at speed.
The other thing I found interesting was that between the lines of what he was saying (he loves all shocks like a good suspension tuner) is that dynamix and potentially smart shocks are great for the gas and go guy but they cannot predict of course they can only react to sudden changes. To me this says that in the right conditions the shocks can get it completely wrong.
Back to the front/rear split. Static tests of weight transfer are fine and necessary, but its important to understand or predict what is going to happen to the weight distribution while under real riding conditions and much of this comes down to riding style. For me, 50/50 or something like it (with rider) is an important starting point because you want the center of gravity and the center of rotation be in the same (or nearly the same) spot as your center of mass (body) so your envelope of movement can maximize control. Your center of mass is largely dictated by riding position (seated and otherwise) so you sort of have to make the sled work for you. Any weight that is not centered becomes weight you end up fighting at some point.
The four corner or 2 corner plus 2 test on the SRX is going to be interesting because I am coming at it unbiased except through experience riding it. If I find out that the weight distribution isn't what I think it will be I will be scratching my head to figure out why. My intuition about a rearward weight bias is that while keeping the sled, nimble and fun it is going to be problematic in a high speed corner. That is why I asked earlier about the trackers. If you unload an apex in the front without trackers you are going to become intimately familiar with the depth of the snow and smell of the woods off the trail at the first high speed corner. I hate the idea of trackers, I love how they work. For the apex it ended up being the better solution despite bugging me every time I thought about it.
One thing I meant to ask you earlier one, the video you posted where you were first getting the dash running, is the motec generating standard ODBII messages? Did you have to decode the CAN ID or was there any proprietary messages?
I found the shock therapy iqs demo to be really interesting, the individual iqs components (without shocks) are available for UTVs as it appears they can be added to existing shocks. One interesting thing was that for a UTV the IQS controls are a 3 way switch that gives you instant access to what mode the shocks are in. The yamaha/cat implementation leaves a lot to be desired because it requires you to look at a menu, futz around with buttons that have a serious glove hate going on, and if you are in soft, you have to click multiple times to firm. That quick access 3 way would be fantastic as you could, without looking, predict what mode you need to be in and make the switch as soon as you see the trail/conditions change and before you get there (unlike smart shocks).
Of secondary interest would be intercepting the individual IQS command sent to each front shock to create a semi-automatic roll control (rebound dampening) for the inboard ski. Call it a semi-smart shock. That would help cornering at speed.
The other thing I found interesting was that between the lines of what he was saying (he loves all shocks like a good suspension tuner) is that dynamix and potentially smart shocks are great for the gas and go guy but they cannot predict of course they can only react to sudden changes. To me this says that in the right conditions the shocks can get it completely wrong.
Back to the front/rear split. Static tests of weight transfer are fine and necessary, but its important to understand or predict what is going to happen to the weight distribution while under real riding conditions and much of this comes down to riding style. For me, 50/50 or something like it (with rider) is an important starting point because you want the center of gravity and the center of rotation be in the same (or nearly the same) spot as your center of mass (body) so your envelope of movement can maximize control. Your center of mass is largely dictated by riding position (seated and otherwise) so you sort of have to make the sled work for you. Any weight that is not centered becomes weight you end up fighting at some point.
The four corner or 2 corner plus 2 test on the SRX is going to be interesting because I am coming at it unbiased except through experience riding it. If I find out that the weight distribution isn't what I think it will be I will be scratching my head to figure out why. My intuition about a rearward weight bias is that while keeping the sled, nimble and fun it is going to be problematic in a high speed corner. That is why I asked earlier about the trackers. If you unload an apex in the front without trackers you are going to become intimately familiar with the depth of the snow and smell of the woods off the trail at the first high speed corner. I hate the idea of trackers, I love how they work. For the apex it ended up being the better solution despite bugging me every time I thought about it.
One thing I meant to ask you earlier one, the video you posted where you were first getting the dash running, is the motec generating standard ODBII messages? Did you have to decode the CAN ID or was there any proprietary messages?
kinger
VIP Member
Get your four corner weights first then let’s talk theory, you’re already approaching this with a biased point of you that you know what you want those scales to say. I’m just telling you I have a similar experience as you I have an RX7 that is V8 swapped and painstakingly made weight distribution efforts to keep it at a 50-50 split. Snowmobile is different.
Motec runs its own Canbus and my dash uses preprogrammed language to understand the Motec CAN IDs. I was merely trying to decipher the correct addresses in the right spot in the software.
Motec runs its own Canbus and my dash uses preprogrammed language to understand the Motec CAN IDs. I was merely trying to decipher the correct addresses in the right spot in the software.
Bias is from
(inserted)
Creating a bottoms up model is how you remove bias, that is part of why I am doing it the way I am. I have an expectation, I fully expect the model to tell the truth expecting the model to be wrong. In other words, the model is a derived/predicted mathematical one, its basically a spreadsheet with a few calculations. Once that is done I will match it up with what's actually on the sled looking for the alignment between calculations and reality (what the chassis designers chose). This will remove bias completely because:
A. I like how it handles now
B. The real world is the truth in this case which means that the model has to adjust to that truth.
There is no room for bias, the scales will say what they say. That's why I am working backwards first and why I haven't done the scale test.
(/inserted)
Just curious what you had to go through to get the gauge dialed in. I did a bunch of canbus sniffing to figure out my bike, it wasn't fun.
Last edited:
kinger
VIP Member
My sidewinder 153" BT-X balance is crazy. 167.2 lbs clutch side, 182 turbo side, 42lbs front arm, 219lbs rear arm for a 57% front and 43% rear bias.
Then sit on it. Goes to 175/182/281/205 respectively for a 42% front and 58% rear bias.
Then stand on it goes to 189/199/266/183 respectively for a 46% front and 54% rear bias.
No canbus decoding thankfully. This was my first experience with Canbus and its so cool! That said I am like a carb guy looking at a EFI fuel map wondering what in the earthly h*ll am I looking at. I only figured it out because Powertune support is really good and gave me the Motec address I needed for the dash and Motec to talk.
Then sit on it. Goes to 175/182/281/205 respectively for a 42% front and 58% rear bias.
Then stand on it goes to 189/199/266/183 respectively for a 46% front and 54% rear bias.
No canbus decoding thankfully. This was my first experience with Canbus and its so cool! That said I am like a carb guy looking at a EFI fuel map wondering what in the earthly h*ll am I looking at. I only figured it out because Powertune support is really good and gave me the Motec address I needed for the dash and Motec to talk.
Canbus is fun right up until someone uses proprietary IDs and coding to hide telemetry (big squinty stink-eye towards BMW). Most companies these days use standard IDs which gives you options and there are more and more canbus tools out there every day.
We are in the same boat with the fuel maps. I understand the concept, but have no experience with how to translate that into the real world. I did start to build up a model for AFR and flow looking at the intake path. Based on the WAI/CAI discussion thread I ripped the top plastic off the sidewinder to look at design and possible restrictions. What I discovered is the stock intake is pretty much a good potential CAI to begin with but it has serious restrictions that ultimately limit performance.. but there is space there to make the appropriate modifications. I am ordering parts so I can modify the upper intake plate when I add the tune as several tunes work with/without their CAI. I want to leave that front opening on the sidewinder strictly for cooling (clutch and engine bay). Wide open, the air demand for a stock winder should be 275 CFM or 134.5 Linear feet per second (based on the smallest restriction in the air path). I haven't validated that yet but should be a good approximation to start. At least the model is in place and I can modify it later if needed. The point of the exercise however was to work my way all the way up to the fuel maps so the model will take into account (without timing) how the sled consumes both fuel and air and what the respective maps mean. That is an ambition waiting for some serious alone time though. Its like looking at a 1000 piece puzzle, you know its solvable but where to start.
That weight change is interesting and very good info. (thinking out loud) The implication is that pre-sag/sit-in weight is carried by the rear shock and the center shock is softer in spring rate and doesn't even start to engage until you add that weight, the implication here is that when the sled unweights (look I can fly) the geometry and resulting ability to absorb bumps gets interesting. Do you have the limiter strap pulled up beyond the default position or is there even one on a BTX, I don't know. The rebalancing of the left/right when you get on makes sense. In its natural state the sled is right side heavy (muffler/turbo/exhaust), but the spring rates are equal. When you get on it the left side which has done less work up to this point has more free travel/less resistance and will take up some of the slack. Sitting to standing impact makes a lot of sense.
kinger
VIP Member
I actually have the stingray spring on the front shock. Limit strap is stock position. Mine is uncoupled not sure how your coupled suspension will react, I assume it will carry more weight on the front arm but I am not sure.
My winder has been broke more then not so I haven't been able to dabble much in handling, but last ride I remember grading it as a B- where the Apex is a A. The ape can fly in the corners, yet pull the skis with throttle, and is a blast while riding nice. The winder wsa firm, direct, tippy, and doesn't transfer as nice. The only thing it does better is deep snow, it literally just crawls out of it.
My winder has been broke more then not so I haven't been able to dabble much in handling, but last ride I remember grading it as a B- where the Apex is a A. The ape can fly in the corners, yet pull the skis with throttle, and is a blast while riding nice. The winder wsa firm, direct, tippy, and doesn't transfer as nice. The only thing it does better is deep snow, it literally just crawls out of it.
That looks like fun. The coupled/uncoupled as I understand it should only really impact when there is rearward weight shift (under power). Prior to that they (SRX/BTX) are probably reasonably close. When you get on power however, say coming out of mid-corner, the BTX will not carve like a coupled skid. It just wasn't designed to do that. Launching I imaging the BTX is better just straight out of the hole. I have to go look at the parts fiche to understand the difference between the two. Funny story, my first experience with the apex in deep powder was while on our way to the trails we had to do some ditch banging session alongside a major highway. I hit a bump wrong and got thrown off the semi-packed and wooped out trail and into the 3' of powder/soft snow on the side, right where it goes through a swamp. I tried like hell to keep momentum up but eventually (and not long later) the snow depth and cattails won and I was stuck... deep and of course it pushed me further into the frozen swamp. As we are digging out (long straps, etc) a car pulls up that looks suspiciously like my wife's. I am looking up at an angle from 10 feet down so I wasn't absolutely sure but still, it looks like hers. Sure as sh*t she gets out and asks if we need help. I quickly close my helmet (we all look the same in helmets I guess) and shake my head violently no. She asks if we are sure, and I keep shaking my head no like a bobblehead on a truckers dash while emphatically waving her off with arm gestures. She looks at us puzzled because its obvious that we are stuck deep. I wasn't about to admit to her that I got stuck on my way to riding. She jumps back in the car and drives away, my buddies of course had new ammo to snipe me with for the rest of the day. The apex, rip 1 track, and deep snow are no bueno 
It took me several days to clean all of the cattail fluff out of the deep corners of the apex. To this day my buddies will go out of their way to bring a piece of cattail along to remind me. All of which is better than her finding out because having your wife call you out constantly is way worse.
It took me several days to clean all of the cattail fluff out of the deep corners of the apex. To this day my buddies will go out of their way to bring a piece of cattail along to remind me. All of which is better than her finding out because having your wife call you out constantly is way worse.
kinger
VIP Member
That's hilarious!
I still can't figure out why the BTX crawls out of deep snow. Its a 40" stance, I also had 40" width as a custom lightweight set up on my Apex. Track angle is worse on the BTX (has 8T drivers), track is 1.75 BTX vs 1.5 Ape, 7" wide skis on both, BTX weighs more in front then ape, makes no sense. If I can crack mine then I can stand it on its tail and walk through almost any depth of snow, but starting out from a stop slowly it will just trench and bury itself where the BTX you can use 1% throttle and it will just crawl out. It was fun to play in the deep with it! Maybe I will get it back by 2024...
I still can't figure out why the BTX crawls out of deep snow. Its a 40" stance, I also had 40" width as a custom lightweight set up on my Apex. Track angle is worse on the BTX (has 8T drivers), track is 1.75 BTX vs 1.5 Ape, 7" wide skis on both, BTX weighs more in front then ape, makes no sense. If I can crack mine then I can stand it on its tail and walk through almost any depth of snow, but starting out from a stop slowly it will just trench and bury itself where the BTX you can use 1% throttle and it will just crawl out. It was fun to play in the deep with it! Maybe I will get it back by 2024...
kinger
VIP Member
kinger
VIP Member
@earthling !! I couldn't help myself and had to run to weight Doo. Check it out!!
This is crazy I am only 102lbs more on my twincharged 4 stroke with ZERO lightweight stuff in my build (aside from Impulse turbo kit which removed weight). I was expecting 150-190bs difference. 4 weights: FL,FR,RF,RR: 135.5/137.8/181.6/158.5!! Look at the ski weights my "front heavy pig" is 7.5/8.5lbs heavier. Also remember I am 12 gallons fuel compared to 10 on the Doo, and 151" compared to 136 on the Doo.
I think I can shave almost 100lbs from my build as crazy as it sounds I could be lighter then a 600cc two smoke!
This is crazy I am only 102lbs more on my twincharged 4 stroke with ZERO lightweight stuff in my build (aside from Impulse turbo kit which removed weight). I was expecting 150-190bs difference. 4 weights: FL,FR,RF,RR: 135.5/137.8/181.6/158.5!! Look at the ski weights my "front heavy pig" is 7.5/8.5lbs heavier. Also remember I am 12 gallons fuel compared to 10 on the Doo, and 151" compared to 136 on the Doo.
I think I can shave almost 100lbs from my build as crazy as it sounds I could be lighter then a 600cc two smoke!
I did a log of paper weighing so thanks for making that effort. The doos feel lighter than they are because doo wants them to feel that way. But I guess if you stop to think about it, part of the whole 'skis to the sky' mentality means that they would have to run a light front end and geometry that allows for good transfer. The total weight sitting on the skid is still a surprise, I would have thought that it would be lighter. I would have bet money that you couldn't get close but looks like you really don't have that far to go.
