120mph on “Dream-o-meter” = ?

mmordan

mmordan

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Joined
Jan 13, 2019
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Location
Richmond Michigan
I had my Viper out this weekend up north and was hitting it hard. The trails were in great shape. I hit one straight that was at least a mile and 20-25’ wide... I and had it pinned! Speedo touched 120... I know that isn’t my real speed but does anyone have an estimate on what my actual speed would be. I have an 02 Viper and it was on hard pack snow not ice... Was hanging around 118-119 for at least 5 seconds and touched 120.
 
8600-8800ish but I wasn’t staring down at my gauges at that speed. The guy behind me on a new 600 skidoo said he was doing 75 and I pulled a 1/4 mile gap on him in the straight.
 
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That sounds about right on your srx

How accurate are the magnetic pick up speedos on the 4 strokes?
 
Accuracy of the gauge to actual track speed isn't the biggest difference. Most are close if the sled hasn't been altered. Track slippage is the biggest reason. At 100 mph it doesn't take much to be 15 mph off.


opsled
 
Yeah I get the slippage factor opsled... It hung pretty consistently at that speed though for 5 seconds or so I’m guessing. Within a mph or two anyway so I discounted much track spin. I was on hardback... Out on the lake I would tend to think I would have more slipping than on the trail. As far as I know and can tell everything looks to be in stock condition... Bought it used... Next investment gps or radar gun lol



:sled1:
 
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mmordan said:
Yeah I get the slippage factor opsled... It hung pretty consistently at that speed though for 5 seconds or so I’m guessing. Within a mph or two anyway so I discounted much track spin. I was on hardback... Out on the lake I would tend to think I would have more slipping than on the trail. As far as I know and can tell everything looks to be in stock condition... Bought it used... Next investment gps or radar gun lol




:sled1:
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You still had slippage. I'm not talking "spin" Big difference. As I said it doesn't take much to throw a speedo off 10 to 15 mph when fully shifted at WOT.

Stock Vipers don't do 120 mph.. Not in the best conditions. SRX yea, Viper no.

opsled
 
opsled said:
You still had slippage. I'm not talking "spin" Big difference. As I said it doesn't take much to throw a speedo off 10 to 15 mph when fully shifted at WOT.

Stock Vipers don't do 120 mph.. Not in the best conditions. SRX yea, Viper no.

opsled
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Yeah I realize that the speedo isn't accurate hence my 1'st post saying "I know that isn't my real speed..." What do you mean by slippage vs. spin I'm not following you? It is possible some of my internals aren't stock I haven't inspected the reeds and I couldn't tell you if any of the clutching has been changed. Just learning more about some of this stuff now... I bought the machine this year and have cleaned the power valves and carbs but the guy I bought it from didn't know much about it... He had bought it as a "barn package" guy he knew through work was moving and selling everything. He bought all his toys and equipment in his barn as a package deal. The guy I bought from had only had the sled for a couple of months and never rode it or had any intention to and knew very little about it. After a few years of not riding it's great to get back out there.

:winterrul :2strokes:
 
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Slippage --- Example is if your track is 10ft long and you had no slippage you would travel 10ft per revolution.

If you only travel 8ft per revolution on a 10ft track you have slipped 2ft.

That would be a 20% difference. If you equate that to MPH a 100 mph reading on a perfectly accurate speedo would have you only going 80mph.

You don't have to spin the track to slip and a 10 to 20% slippage is hard to feel when you're on the sled. High speed = heavy wind that is really holding the sled back. Very hard to achieve 100% traction unless you are on ice with sharp picks or on asphalt.

opsled
 
EVOVII_SWE said:
That calculator assumes an exact 1:1 clutch ratio to work but the clutch is a "Continuously Variable Transmission", how can you know that you really achieve a exact 1:1 ratio?
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You don't know. You can calculate what speeds should be at certain RPM's and certain shift positions in the CVT system but there are no indicators of exactly where the shift position is at any certain time. Only approximate calculations can be done with RPM and they could be way off. To many variables.

Speed is counted off drive axle so if the math has been done correctly by the manufacturer and nothing on the sled has been altered speed should read correctly if there are no traction issues.

opsled
 
opsled said:
Slippage --- Example is if your track is 10ft long and you had no slippage you would travel 10ft per revolution.

If you only travel 8ft per revolution on a 10ft track you have slipped 2ft.

That would be a 20% difference. If you equate that to MPH a 100 mph reading on a perfectly accurate speedo would have you only going 80mph.

You don't have to spin the track to slip and a 10 to 20% slippage is hard to feel when you're on the sled. High speed = heavy wind that is really holding the sled back. Very hard to achieve 100% traction unless you are on ice with sharp picks or on asphalt.

opsled
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Ok so what is spin then? I’m still not understanding the difference. In drag racing when your tires “spin” your speedo runs up higher as well as the tach... Isn’t this the same as what you are describing just applied to a snowmobile?... Tires vs Track... I think we are both talking about the same thing... The track is not applying all of its rotation to the ground/snow/ice/whatever... However I question whether the track was moving 15 mph faster than me and my snowmobile were or if the calibration from the factory is just off and on the generous side...?
 
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To me spin is when the track is going twice (or more) as fast as ground speed. Up until then I call it slipping.

You can call it whatever you want.

opsled
 
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