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    Posted: Feb/28/2009 at 5:03pm
Hey guys maybe someone can shed a bit of light here... We have been working and playing around with the CVT on our old car to try and understand how to tune them. I have read a book on tunning CVTs and how the shift. When applying all that knowledge to life something comes out wrong. What suppost to be a car geared for 38 MPH is only doing 28. Back calculating that speed it seems like the cvt is only getting to a ratio of .95 instead of the .69 it should have as an overdrive. REally can't figure out why it isn't working. Tried changing springs and weight to see if the shift RPM were too high but didn't get much out of it. The car is getting close to 3750 rpm redline (at times 3690) still something seems off. We are using a Comet 780 (an old one that was around the shop).

Any advice would be great!!

Thanks

Hector
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rob71zilla Quote  Post ReplyReply Direct Link To This Post Posted: Feb/28/2009 at 5:25pm
That sounds about right.  We use a 790 series CVT and top out at about 26mph.  Are you accounting for drivetrain loss in your calculations? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Kenneth Quote  Post ReplyReply Direct Link To This Post Posted: Feb/28/2009 at 5:27pm
Are you seeing any belt slip? With too light of a primary spring, you may not be getting enough lateral force on the belt to adequately grip the belt. We found that when using a taller (lower number) final drive, we had to go to heavier springs and weights to prevent slippage.

I'll also add that our car is geared to go 42-ish and we'll top out at 39 on flat ground (drag limited).


Edited by Kenneth - Feb/28/2009 at 5:29pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/28/2009 at 6:28pm

Your problem may be that the springs you have are the correct preload for the weights, but the spring rate is too high to allow for a complete shift.  You'll likely need to select a lighter spring (with the same weight initially) and then produce a higher preload to keep it from engaging below engine idle speed, but this will allow the engine to pull it all the way into a full shift.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote infocustrasti Quote  Post ReplyReply Direct Link To This Post Posted: Feb/28/2009 at 7:34pm
I figured that a bit of power would be lost through drivetrain but what is confusing me is that i'm on the limiter so power isn't an issue... it is a problem with the gearing... As CLReedy said i thought that the CVT wasn't shifting all the way. We tried different things. First the Driven clutch had to deep of a cam and stiff spring. Changed that and gained about 3 mph or so... Maybe being to stiff wouldn't let it shift but the driven should only be used to tune for Slippage. Try lighter springs on the drive clutch to see what even that has on the car. The car did get to the wheel speed that I would expect (38 MPH or so which is about 580 RPM on the final axle) when testing on jackstands (unloaded). So I would think it is in fact shifting all the way through but the lack of speed tells me otherwise.

Thanks and keep the ideas flowing maybe something else was overlooked.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JHrdy724 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2009 at 8:34am
well i figure that if you're at full power and 10 mph short you either aren't reaching the full range or you need to go double check your numbers. try what chris suggested but be careful...we've had cars that were engaging at idle speed and its a nightmare to deal with(gotta be hard on the brakes when you crank it). after that issues sorted out, for our tuning we have access to photogates and we just run a million accel. runs and then some. 3 distances at each weight/spring combo. distances from 75 ft. to 225 ft. we plot it and figure out where the best compromise is.  last year we made custom weights from this data and hit it pretty dead on.  tune the secondary on a hill and there you have it. should be about close to perfect.

Edited by JHrdy724 - Mar/01/2009 at 8:39am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote infocustrasti Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2009 at 1:22pm
Yeah that was the approach i was thinking. Still don't understand the issue with the speed. I guess testing will be the only way to know
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Mar/01/2009 at 4:51pm

It could just be drag limited to that speed.  When you start adding up drivetrain losses, tire rolling resistance, aero drag, etc it piles up fast.  You may want to decrease your reduction ratio just a bit, 34-35 maybe, and see if the gearing advantage nets you a higher top end.  If so then you can safely assume that you're just drag limited.  If not you may still be seeing some slippage in the system somewhere.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2011 at 10:04am
mod note: merge'd due to lack of search ability...
 
Hello again to all geniuses...
I had my CVTech cvt delivered, in whose package, i found 3 275g each metal weights...
Also got a few springs...
I understand they're for tuning, but why exactly do  i need tuning ?
Kindly help...!


Edited by Mod Squad - Dec/16/2011 at 4:16pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2011 at 10:39am
You can certainly run the CVT as it came out of the box... I've done that before.  Tuning the CVT weights and springs will affect how the pulleys shift, or at a vehicle level, how the car transitions from idle to movement, how the car accelerates, and how quickly it achieves top speed. 
 
There is a book floating around about CVT tuning, and I think a downloadable copy is linked on this site in the file sharing section. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Dec/16/2011 at 1:13pm
Olav Aaen's Clutch Tuning Handbook
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TuksBaja Quote  Post ReplyReply Direct Link To This Post Posted: Jan/04/2012 at 3:38pm
Have you looked at center distance between primary and secondary clutch? I have experience on Polaris P-90 tuning but not that much on Comets. We had a similar problem with the Polaris CVT. Make sure the distances are correct. If they are the wrong the CVT wont function as you want. After correcting angles and center distance we improved the top-end of the car by 30%.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ayushsood09 Quote  Post ReplyReply Direct Link To This Post Posted: Jan/29/2012 at 1:51pm
Hey Priyank,

I am from VIT University, Vellore. We are looking into buying a CVtech CVT. I want to know in how many days was the CVtech CVT delivered to a US address ?

Thanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: Jan/30/2012 at 1:36pm
To a US address ?
Kindly rephrase your question
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Post Options Post Options   Thanks (0) Thanks(0)   Quote knoxracers Quote  Post ReplyReply Direct Link To This Post Posted: May/29/2012 at 2:39am
Originally posted by p.lewis p.lewis wrote:

Olav Aaen's Clutch Tuning Handbook

It would be very kind of you, if you can suggest where i can get this book or if you have one can u mail that?


Edited by knoxracers - May/29/2012 at 2:40am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: May/29/2012 at 2:24pm
First, jack your tires off the ground and give it full throttle to see if the CVT fully shifts w/ no load (Note: Engine RPM CVT shifts @) .
 
Second, check CVT setup by gearing for a slightly higher & lower top speed (Note: easily accomplished by changing tire diameter).  I can't say I've ever measured one of my cars over 30 MPH w/ ATV tires on a flat surface.  However, you want to gear for higher so you can get a burst of speed downhill.
 
Third, no one said the CVT has to fully shift while driving on a flat surface?


Edited by Akron 1998 to 2004 - Jun/01/2012 at 5:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2012 at 10:38am
Originally posted by knoxracers knoxracers wrote:

Originally posted by p.lewis p.lewis wrote:

Olav Aaen's Clutch Tuning Handbook

It would be very kind of you, if you can suggest where i can get this book or if you have one can u mail that?
start here: http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=olav+aaen%27s+cluch+tuning+handbook
Also, check out the file section on this forumWink

Edited by p.lewis - May/31/2012 at 10:39am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Priyank Quote  Post ReplyReply Direct Link To This Post Posted: May/31/2012 at 3:11pm
Not to be spoil sport, but you don't really need a book...
It's more of an art...!!

Initially it looks like trial and error, but whatte fun it is to understand it :D
Just know the basics, and do the rest ! :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bsc-baja Quote  Post ReplyReply Direct Link To This Post Posted: Jun/03/2012 at 8:30pm
So what happens when my Gaged clutch doesnt shift past 1.4:1??? Cause I'm hitting a whopping 15mph right now and I don't think thats gonna cut it...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 10:21am
  1. Check your belt tension, if it's extremely loose it would cause what you're experiencing
  2. You sure nothing is interfering with either clutch? Just lift the rear end up and spin the tires at full throttle and see if the belt is shifting out all the way. Easiest way to check is to just write a line outward on the primary (drive) clutch sheaves then run the engine and see how much is rubbed off.
  3. How's your driveline? Anything rubbing or interferring?
  4. How's the engine running? Air filter clogged up? Carb dirty?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 10:25am
Does the car get to 15 mph really fast and then hit a wall?  Or is it just a slug in general?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bsc-baja Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 11:15am
No... It gets to 15 real fast and then hits a wall... I think I found the problem... Somebody put the C-C on the clutches at 7.5" instead of 8.5"... That would do it... Now I gotta decide how to fix it...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 11:29am
Get out the 'ol frame stretcher! 
 
Glad you found the culprit
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 12:34pm
If it's possible, slot the engine mount or the trans mount, our trans was slotted in the horizontal direction for alignment purposes, not the Center/Center direction, if that makes sense. Could be a real simple fix if it still lies within the frame
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 12:50pm
nah...I vote engineering a frame stretcher. Everyone would pass tech!

Slotting the engine mounts and leaving room to move the engine so you can adjust the C-C distance is definitely a good idea though. As you've already experienced belt tension has a big impact on the shift range of a CVT. If you want to use the entire shift range so you actually get close to your intended top speed you'll need to fine tune the tension.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ganeshsashank Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 1:15pm
Hello People, We are doing BAJA for the first time in our college. :)
We thought of using Comet 780 CVT for the transmission as CVTech would require manufacturing of the reduction gear train, which would be too risky for beginners.

Please advice:
Is COMET 780 Reliable?
Since we are from India, How much time will it take for the entire CVT set to be delivered? (In the Comet industries site, they mentioned that they would provide the CVT, The FNR Gear Box, the Limited slip differential)
What problems will CVTs face on the track?

We are thinking of mounting the CVT by raising the engine, mouting the FNR on the ground floor and to connect it to the differential by mean of a chain and sprocket.

PLEASE HELP!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ganeshsashank Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 1:20pm
Hey Priyank,

You used CVTech CVT right? How did you use a reduction gear train? Was it an FNR Readily available in the market? Or did you get the gear train manufactured?

Please help!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 2:03pm
Originally posted by sandres913 sandres913 wrote:

If it's possible, slot the engine mount or the trans mount, our trans was slotted in the horizontal direction for alignment purposes, not the Center/Center direction, if that makes sense. Could be a real simple fix if it still lies within the frame
 
Or just a few spacers/washers under the engine to raise it vertically.  This assumes it won't poke out of the cage envelope of course.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/04/2012 at 8:26pm
Originally posted by collinskl1 collinskl1 wrote:

Originally posted by sandres913 sandres913 wrote:

If it's possible, slot the engine mount or the trans mount, our trans was slotted in the horizontal direction for alignment purposes, not the Center/Center direction, if that makes sense. Could be a real simple fix if it still lies within the frame
 
Or just a few spacers/washers under the engine to raise it vertically.  This assumes it won't poke out of the cage envelope of course.

Another viable option! Big smile
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7.5 inches vs 8.5 inches? I guess that would definitely make you lose top speed as the belt wouldn't ride in as much on the secondary. When we adjust our cvt center to center through a range of about 0.5 inches our max ratio only changed between 0.88 and 0.94 which makes me feel that there are other problems afoot. You said your only getting 1.4 ratio vs gaged quoted value of 0.90. Do you get his same ratio with your wheels off the ground, or is it only limited when driving the car? If it seems like a hard limit like you said I can tell you that in the past we have made the weights on the primary too large such that they hit the housing before allowing to primary to fully shift out. A good way to test this is to use a paint marker or sharpie on the primary sheave and then hit full throttle with the rear jacked up off the ground. If the top of the belt isn't about flush with the OD of the primary at 3800 rpm engine speed then you have a problem. Of course this could also be due to having too high of a spring rate or extremely light weights as mentioned previously.

The only definitive way to test if the dimensions of the weights are causing the problem is to take the spring out of the primary and then reassemble it. Once assembled move the primary all the way in with the bottom of the sheaves touching each other. Then check the weights for clearance with the housing and also make sure the rollers are touching all the ramps. Not having clearance is more of a problem on the gx8 than in the gx9 as you only have 3 vs 4 arms to distribute the total weight. The quickest fix is to modify the housing with a dremel and file so the the weights don't hit. If you have slightly more time you can remake weights to more efficiently use the space in the housing. It can be done on the gx8 you just have to be clever or use a denser metal such as tungsten.

If you still have questions bill fredenburg from gaged with be out at competition with a trailer full of parts and im sure he'd be more than happy to help you out.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote knoxracers Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 5:31am
Hello Everybody
We just received our package from CVTECH, After doing research i have a query here regarding FNR Gearbox. We are using the CVT first time and we are thinking to customize the FNR. If i am right i studied in the forums somewhere that a gear reduction from 7:1 to 10:1 is good for doing events like hill climb,acceleration. But last time we used manual transmission with final gear reduction from 1st gear is around 45:1( with briggs engine only) i.e. FNR should have gear reduction around 15:1, and in INDIA mini baja most of the teams are using this gearbox and doing well on hill climb and acceleration events. So guys what is your suggestion in this context??
And what are your views about RPM Gearbox?

Thanks And Best Regards
Team KNOx
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 9:17am
Originally posted by knoxracers knoxracers wrote:

Hello Everybody
We just received our package from CVTECH, After doing research i have a query here regarding FNR Gearbox. We are using the CVT first time and we are thinking to customize the FNR. If i am right i studied in the forums somewhere that a gear reduction from 7:1 to 10:1 is good for doing events like hill climb,acceleration. But last time we used manual transmission with final gear reduction from 1st gear is around 45:1( with briggs engine only) i.e. FNR should have gear reduction around 15:1, and in INDIA mini baja most of the teams are using this gearbox and doing well on hill climb and acceleration events. So guys what is your suggestion in this context??
And what are your views about RPM Gearbox?

Thanks And Best Regards
Team KNOx
www.knoxracers.in


Hill climb and acceleration are fairly simple events, not a whole lot of calculation for the gearing necessary. If you assume a 45-degree or 50-degree hill, you'd probably be fine and just do free body diagrams to figure out how much torque you'd need to get over the hill. Acceleration is even easier. How fast do you want to be going at the end of 100 ft, 150 ft, 200 ft, etc?

A little hint too: for hill climb, depending on how you gear your car, your engine will not be at max rpm the whole time, likely won't hold constant rpm, the belt might WILL slip, and other factors affecting CVT ratio. Just a little something to keep in mind. The CVTech has about two or three threads on this forum alone.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Soccerdan7 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 9:50am
Originally posted by sandres913 sandres913 wrote:

If you assume a 45-degree or 50-degree hill, you'd probably be fine and just do free body diagrams to figure out how much torque you'd need to get over the hill. 

That seems like an awfully steep hill. I know this was discussed in depth in the Rochester competition thread, but anything over 30 or 35 degrees is frankly ridiculous and you'll likely never see it. At 45 degrees, half of the cars would rollover backwards due to their CG locations.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 10:02am
Originally posted by Soccerdan7 Soccerdan7 wrote:

Originally posted by sandres913 sandres913 wrote:

If you assume a 45-degree or 50-degree hill, you'd probably be fine and just do free body diagrams to figure out how much torque you'd need to get over the hill. 

That seems like an awfully steep hill. I know this was discussed in depth in the Rochester competition thread, but anything over 30 or 35 degrees is frankly ridiculous and you'll likely never see it. At 45 degrees, half of the cars would rollover backwards due to their CG locations.

Right, but the way you figure it, it would give you a little more power. Kinda like a safety factor, even though that's probably not the right term to use here. You could probably break it down so you can determine how quick you would traverse the hill too, and I bet a few teams actually do that...but if he's posting asking about this, I figure this is an ok place to start. Quick calculation.

For the record Washington 2012 felt every bit of 40-45 degrees from my seat!....of course I was a total n00b at the time Wacko now I'm just a semi-n00b Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 11:55am
15:1 reduction sounds way to high for just the gear box.  The best advice I could offer you is to figure out what the top speed of last year's winner was and then calculate the gear ratio you'd need to match it.
 
I don't know anything about RPM Gearbox except it's probably much better than what you could design and build on you're own. http://www.rpmgearboxes.com/
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 12:12pm
Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

15:1 reduction sounds way to high for just the gear box.  The best advice I could offer you is to figure out what the top speed of last year's winner was and then calculate the gear ratio you'd need to match it.


We have used 15.2:1 in 2010 to 14.5:1 in 2011 and 2012 for the CVTech so it's in the ball park albeit on the highside since people also use 12:1 with good success.

We use 22-23in tires.


Edited by jeiB - Jun/19/2012 at 12:12pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 12:16pm
Not really all that high, we've used around 10:1 for a few years, not great in acceleration due to weight. We used 24's in the rear until this year - huge 26's in the back! Big smile looked good, but worse for acceleration obviously

Of course that reduction is overall, including the diff
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 1:20pm
Originally posted by jeiB jeiB wrote:

Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

15:1 reduction sounds way to high for just the gear box.  The best advice I could offer you is to figure out what the top speed of last year's winner was and then calculate the gear ratio you'd need to match it.


We have used 15.2:1 in 2010 to 14.5:1 in 2011 and 2012 for the CVTech so it's in the ball park albeit on the highside since people also use 12:1 with good success.

We use 22-23in tires.
There just isn't enough information to give an accurate gear ratio recommendation (nor would I).  12:1 still seems high for 22" tires.  But whatever works for you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 1:51pm
Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

Originally posted by jeiB jeiB wrote:

Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

15:1 reduction sounds way to high for just the gear box.  The best advice I could offer you is to figure out what the top speed of last year's winner was and then calculate the gear ratio you'd need to match it.


We have used 15.2:1 in 2010 to 14.5:1 in 2011 and 2012 for the CVTech so it's in the ball park albeit on the highside since people also use 12:1 with good success.

We use 22-23in tires.
There just isn't enough information to give an accurate gear ratio recommendation (nor would I).  12:1 still seems high for 22" tires.  But whatever works for you.


The new CVTech's ratios are different than most CVTs hence your confusion. The low is 3:1 and the high is 0.43:1 although we have never seen it fully shift.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 2:04pm
Originally posted by jeiB jeiB wrote:

Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

Originally posted by jeiB jeiB wrote:

Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

15:1 reduction sounds way to high for just the gear box.  The best advice I could offer you is to figure out what the top speed of last year's winner was and then calculate the gear ratio you'd need to match it.


We have used 15.2:1 in 2010 to 14.5:1 in 2011 and 2012 for the CVTech so it's in the ball park albeit on the highside since people also use 12:1 with good success.

We use 22-23in tires.
There just isn't enough information to give an accurate gear ratio recommendation (nor would I).  12:1 still seems high for 22" tires.  But whatever works for you.


The new CVTech's ratios are different than most CVTs hence your confusion. The low is 3:1 and the high is 0.43:1 although we have never seen it fully shift.

I'm curious if anyone will ever achieve that 0.43:1. Your car would have to squeal like hell and be geared super low, killing your top speed just to do it. Most we've experimentally seen is around 0.9:1, at least that we have numbers to back up that is.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ErikHardy Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 2:23pm
.9? Wow, Whats the fastest you have measured vehicle speed at?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 2:39pm
We've gotten up to between 23-25mph, measured through a 100' gate entered at (roughly) top speed, assuming no acceleration through that 100', and checked by GMC speedo. that was the summer directly after Peoria. The engine wasn't at peak power throughout (some odd rpms instead) so the primary wasn't fully adjusted, but it was better than when we first took it out of the box from Canada.
We weren't able to re-tune before Wisconsin due to some gearbox issues and sealing issues (RTV cure time stinks Cry ) or I would have caught and corrected the belt slip earlier and probably machined some custom tuned weights...oh well. coulda woulda shoulda! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 2:46pm
Originally posted by sandres913 sandres913 wrote:


I'm curious if anyone will ever achieve that 0.43:1. Your car would have to squeal like hell and be geared super low, killing your top speed just to do it. Most we've experimentally seen is around 0.9:1, at least that we have numbers to back up that is.
I've gotten a Comet 790 to shift down to 0.6:1 on test bench but the propaganda says it should go to 0.54:1 (Don't trust the propaganda).
While driving the car, I've just marked the plates to ensure a full shift took place.
CVTs are most efficient when at 1:1.  I bet the CVTech is not very efficient if/when it shifts to 0.43:1, that overdrive may only be useable down hill. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Akron 1998 to 2004 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 2:52pm
Originally posted by jeiB jeiB wrote:


The new CVTech's ratios are different than most CVTs hence your confusion. The low is 3:1 and the high is 0.43:1 although we have never seen it fully shift.
0.43:1 CVT does make 12:1 gearbox seem more reasonable.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sandres913 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/19/2012 at 3:22pm
Originally posted by Akron 1998 to 2004 Akron 1998 to 2004 wrote:

Originally posted by sandres913 sandres913 wrote:


I'm curious if anyone will ever achieve that 0.43:1. Your car would have to squeal like hell and be geared super low, killing your top speed just to do it. Most we've experimentally seen is around 0.9:1, at least that we have numbers to back up that is.
I've gotten a Comet 790 to shift down to 0.6:1 on test bench but the propaganda says it should go to 0.54:1 (Don't trust the propaganda).
While driving the car, I've just marked the plates to ensure a full shift took place.
CVTs are most efficient when at 1:1.  I bet the CVTech is not very efficient if/when it shifts to 0.43:1, that overdrive may only be useable down hill. 

But propaganda is always good! Everything on the internet is 100% correct all the time!....kidding of course!

Unfortunately, it doesn't really help much on the downhill. You almost need an overrunning clutch after it, the thing doesn't shift much further, it actually turns into more of an engine brake. The video we took from Wisconsin shows a bit of acceleration downhill, but not enough to justify a full shiftout. But again, we had a ton of belt slip and it wasn't even close to tuned right. So it might act differently if its adjusted the right way, we just haven't had the opportunity to do so.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bantu Quote  Post ReplyReply Direct Link To This Post Posted: Sep/24/2018 at 11:39am
Hi Guys...I am working on a Comet 780 series CVT. Does anyone knows what equations can I use to determine Pressure spring Force, Mass of the roller weights, and Roller weights Force or the clamping Force of the roller weights.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sujandinesh Quote  Post ReplyReply Direct Link To This Post Posted: Sep/25/2018 at 11:29am
I see that again you have directly posted a question here without doing proper research. Multiple articles and some thesis reports are available online, which give a detailed description of all the equations used in a CVT. 

Best of luck! 
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