Putting a TAV 30 series in Baja DB30 comes with 12T 35 chain jackshaft would a 14t or 15t jackshaft sprocket help to improve top speed?

GustoGuy

Well-Known Member
#1
Gearing question. I have a stage 1 Predator 212cc in my Baja DB30 and tired of dealing with the chain tensioner and clutch setup I currently have. I bought a 30 series TAV and it comes with a 12T 35 chain jackshaft sprocket. I want to soften the acceleration and get a little better top speed and I can choose between a 14T or 15T jackshaft sprocket . I would like to have a top speed of just over 40mph like I currently do with my 14T centripetal clutch. Which jackshaft sprocket would be the better choice?
 
Last edited:
#6
Between the two, I would choose the 15T. The sprocket and chain will wear more evenly and slowly with odd number tooth count than with even number.
 
Last edited:
#7
How do you apply a fixed gear calculator to a variable ratio CVT?
The TAV 30 ratio to the sprocket varies. The Comet asymmetric systems achieve slight "overdrive," their ratio range being from about 3.2: 1 through around .83:1.
You can calculate the theoretical highest and lowest ratios. I've seen multiple sources stating the ratio range as 2.7:1 to 0.9:1 so I will use those plus 15 and 70 tooth sprockets for an example.

70/15=4.67 (rounded), 4.67:1 ratio
4.67x2.7=12.61 (rounded) Highest ratio (AKA: lowest gearing): 12.61:1
4.67x0.9=4.20 (rounded) Lowest ratio (AKA: highest gearing): 4.20:1
 
#8
Torque converters suck on Doodlebugs. The wheelbase is too short and they just want to wheelie all the time. I've had one set up that way and it wasn't a fun bike to ride. Even with a TAV installed, you still may want to run some kind of tensioner. I did that on my CT200U (last pic).

https://rcfminibikes.com/product/rcf-universal-engine-block-mount-adjustable-chain-tensioner/

I'm running one of those now for a tensioner on my DB30 and it works great. Much better than the stock style setup, which was always a headache. You can see it installed in the attached pics.
 

Attachments

Last edited:

SAS289

Well-Known Member
#9
You can calculate the theoretical highest and lowest ratios. I've seen multiple sources stating the ratio range as 2.7:1 to 0.9:1 so I will use those plus 15 and 70 tooth sprockets for an example.

70/15=4.67 (rounded), 4.67:1 ratio
4.67x2.7=12.61 (rounded) Highest ratio (AKA: lowest gearing): 12.61:1
4.67x0.9=4.20 (rounded) Lowest ratio (AKA: highest gearing): 4.20:1
From there you would use the 4.2:1 for the sprockets in the speed calc. Use a 10 tooth and a 42 tooth in the speed calc to represent that ratio and plug the other numbers in to get an appx top speed. And you have to use reasonable RPM numbers. You can't assume the engine will get to the chosen RPM under load at top speed.
 
#10
From there you would use the 4.2:1 for the sprockets in the speed calc. Use a 10 tooth and a 42 tooth in the speed calc to represent that ratio and plug the other numbers in to get an appx top speed. And you have to use reasonable RPM numbers. You can't assume the engine will get to the chosen RPM under load at top speed.
Agreed. I wasn't concerning myself with top speed. Note that I said "theoretical highest and lowest ratios" because I don't know whether the engine would be capable of sufficient RPM for the CVT to up-shift all the way.
 

Minimichael

Well-Known Member
#11
How do you apply a fixed gear calculator to a variable ratio CVT?
The TAV 30 ratio to the sprocket varies. The Comet asymmetric systems achieve slight "overdrive," their ratio range being from about 3.2: 1 through around .83:1.
It's true, I hadn't noticed the detail about the torque converter. Just saw jackshaft and thought the link might help... Lot of smart people in this room.

Here's another link!
https://www.bmikarts.com/Go-Kart-Gear-Ratio-Calculator-Jackshaft-Setup
 
Top