Both 669 and 725 are from the 30 series. In some cases, the cart comes with one of these belts but many dealers recommend using the other one. It creates much confusion among the go-kart owners.
So, 669 vs 725 belt – which one should you choose?
The 669 belt has a length of 669 mm while the 725 model is 725 mm long. The 725 belt is compatible with a wider range of go-karts than the 669 belt. This belt also has better stability, durability, and less slippage risk than a 669 belt. On the other hand, a 669 belt provides a higher stall speed for a smoother launch of the cart.
To know more about their differences, keep reading and make an informed buying decision.
669 Vs 725 Belt: Quick Comparison
First, have a look at the main differences between 669 and 725 belts from the table. After that, we will go into an in-depth discussion.
| Feature | 669 belt | 725 belt |
| Length | 669 mm | 725 mm |
| Width | ¾ inches | ¾ inches |
| Thickness | 2 inches | 2 inches |
| Compatibility | Limited range such as Mid XRX and Blazer 200 | Wide range such as Mudhead Karts, and HammerHead 80T |
| Stall speed | More efficient | Less efficient |
| Tire Slippage | More | Less |
| Wear & Tear | More | Less |
669 Vs 725 Belt: In-depth Comparison
While comparing two belts from the same series, you have to consider their compatibility, stall speed, slippage, and durability. Here is the in-depth discussion between 669 belts and 725 belts for a better understanding.
Size:
The length of the 669 belt is 669 mm or 26.34 inches whereas the length of a 725 belt is 725 mm or 28.5 inches. So, the 725 is around 2 inches longer than a 669 belt. Both belts are 3/4″ in width and around 2 inches thick.
If you are unsure about the belt size, first determine the torque belt converter size for your go-kart.
Compatibility:
The 725 belt is compatible with a wider range of go-karts than the 669 belt due to its length.
The 669 belt is only compatible with a few mid-sized TrailMaster Karts, for example, Mid XRX and Blazer 200.
On the other hand, big carts are recommended to pair with a 725 belt for maximum efficiency. For example, Mudhead Karts, and HammerHead 80T.
Some manufacturers recommend pairing 725 belts with some mini-karts and mid-sized carts as well. For example, Trailmaster MB200 Mini Bike with bearing and bushing style driver and Mid XRS.
The belt may not bog your predator down during acceleration but may cause many problems in the cart.
Stall Speed:
The stall speed of a 725 belt is lower than the stall speed of a 669 torque converter belt.
The stall speed of a torque converter is the engine speed at which the torque converter starts to transfer power to the transmission from the engine. A good stall speed ensures an efficient launching of the car.
Belts with shorter diameters provide higher stall speeds. Due to its less surface area, it creates less friction. Also, due to the minimal slackness, it can transfer energy more efficiently.
As the 669 belt provides higher stall speed, it will ensure better launching efficiency of your cart. Due to the lower stall speed, with a 725 belt, the cart will feel lazier when you start driving.
Tire Slippage:
A go-kart with a 669 is prone to more slippage than a cart with a 725 torque converter belt.
As I have mentioned previously, a belt with a shorter diameter has a higher stall speed. However, this also comes with the drawback of a more tire slippage tendency. As the cart is launching at a higher speed, the cart will have less traction on the road. The tire will get less control and slip more often.
So, if the 669 belt is short for your cart, your car would be completely miserable on the road.
Wear & Tear:
A 669 belt is more prone to wear and tear than a 725 torque converter belt. As it provides more speed while stalling, it also creates more heat. Also, due to the less slackness, it comes in the pulley exposure more forcefully. Due to the excessive heat and force, this belt also wears out sooner.
So, let’s say you buy two torque converter belts from the same brand. The 725 belt will more likely to last longer than a 669 belt.
That’s all of their comparison. Like 669 and 725, the difference between 428 chains and 40 is also a famous discussion among go-kart owners. You should know about it too.
669 Vs 725 Belt: Which One Should You Choose?
Choose a 669 if you are concerned about having a belt that will provide you with more stall speed. This is a better belt choice when you race very often and will provide you with a smoother start.
On the contrary, if you are concerned about stability and less slippage while driving, choose a 725 belt. It is also suitable for you if you are concerned about the durability of the belt.
However, when it comes to compatibility, you should always choose the belt recommended by the dealer. Because you should never experiment with any of your vehicles without knowing the full scenario.
Here’s an example. If you want a transmission on your Predator, learn if it’s possible to install a transmission on the Predator. After that, go for the procedure.
Another thing, make sure to install the belt on your go-kart properly to avoid any problems. The following video might help with the process.
Frequently Asked Questions (FAQs):
Are Torque Converters Good For Go-Karts?
Yes, torque converters are a good clutch type for go-karts. It provides your go-karts with a more efficient gear ratio aligned with the engine RPM. It also increases the power output going to the go-kart wheel. So you will get the benefit, especially with low-torque conditions.
What Is The Difference Between Asymmetric And Symmetric Belts?
The teeth of a symmetric belt are evenly angled. Whereas, in the asymmetric belt, the angle is different on each side. You will find an even angle of 15o on both sides of the symmetric torque converter belt. While for the asymmetric belt, one side is 18.5 degrees angled and the other side is angled 2.5 degrees.
What Is A 30-Series Torque Converter?
The 30-series torque converter is a series of go-kart belts for 2 to 4-cycle engines with 8 HP power. 30-series torque converter belts are ¾ inches wide. And for this series, drive clutches of both 6″ or 7″ diameter are available. Two popular belt models of this series are the 669 and 725.
Conclusion
Here goes my verdict on the 669 vs 725 belt. I hope it clarifies your confusion about the 30 series torque converter sizes.
Now you can make an informed decision and ensure better performance from your go-kart. However, it is still better to consult your dealer about your confusion.
Let’s end today’s discussion here. Have a great day!
