Why don't people use GT3 pulleys and belts?

In Germany I found them here:

Seems like they have quite a wide length selection

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That link has 3 pitch. They have 5 pitch too.

I Will consider testing those. They are NOT cheap

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Oh yeah damn it my bad. Thanks for posting the correct one.

too me the GT3 and HTD profile look the same, both are round. So whats the big fuss about them? Or better put, why can the GT3 carry more torque

I tried to use HTD3 on my first build

The main problem has nothing to do with torque transfer, but with alignment. Since the tooth is smaller, you have less margin to to get thing out of roundness or your belt will skip

For this same reason you can’t run them loose like HTD5, Boosted use them, never held one in my hand, but from vídeos the belt tension they use is way higher than I am able to use on my HTD5 setup

In resume, everything have to be perfect in your drive train for them to work, your pulleys as perfect centered as possible, your motor mount to have as little flex as possible, and ideally have a bearing inside the wheel pulley to help with that

A positive point is that they have less loses since the rubber is thinner and takes less energy to flex and because of that the board “CAN” free roll better. I highlighted the can since that only happens if your construction is solid, if it’s not, you have to run the belt tension really high to avoid teeth skipping and the lower rolling resistance will not happen

I’m my opinion is not worth, specially from those who are starting that generally use cheaper components since it will be a pain to get it working ok when your pulley may not be perfect and your motor mount flexing under load like a lot of the cheaper one that are sold

HTD5 can tolerate all that much better


Did you mix up HTD3 and GT3?

They are not - look at my image above. The HTD at the bottom is completely round while the GT3 has a different shape.

I only used HTD3, Which is almost the same as GT3, the latter has a more oval shaped tooth profile that according to gates improves the torque transfer capacity a little bit, but the problems with alignment will be the same for both

As previously discussed in this topic we are talking about 5mm pitch but the tooth shapes HTD vs GT3. GT3 does not mean 3mm pitch (so has nothing to do with HTD3) but is simply the name of the tooth shape.

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Oh sorry for that, completely my mistake

Is the GT2 that is equivalent to HTD3 right?

According to @TowerCrisis the evolution was: HTD then GT2 as an improvement and then the current GT3 shape. All of these come in various pitch sizes.

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For what it’s worth I’ve been using GT3 since my first build and all is good…


Man tells us how you made it fit your wheels etc.

Alright, I’m going to include an extensive write-up here and put it in an edit in the original post for any newcomers.


Here are some direct comparisons followed by interpretations of the data.

General Lifetime:

Durability This is the general lifetime testing of the different belts. Each test was conducted with the same pitch, pulley sizes, speeds, and torque. It concluded upon belt replacement was necessary, or until enough data was collected (no need to go further, in the case of GT). The baseline for these tests was the HTD performance, set at 100%. These tests were conducted at speeds and pulley sizes that result in accelerated belt wear, which will be explained further down this post. GT 5M has nearly 190% the lifespan of HTD 5M.

Tooth Jump:

Tooth%20Jump These results are not particularly favorable for GT 5mm pitch, at least upon first glance. HTD and GT seem to be very similar in the 5mm pitch, however it is important to see that this test was only tested up to 2300 RPM, while we typically run our motors around 6000 rpm. This results in much worse tooth skip, as it is far beyond the specifications of the tooth profiles. This higher rpm with higher torques is where GT shines greatest, and as you can see GT and HTD profiles begin to diverge as installation tension decreases. We run our tension somewhere in the 2-3 lb range. Some with idlers as low as 0 or 1 lb of tension.

Operating Belt Tension:

Belt%20Tension Here is the exact maximum belt specification for the tension on the taut side. For explanation’s sake, I’m going to divide numbers by 2, so the belt width is equal to 12.7mm, which is close to our use case. HTD 5M is rated at 51 lbs of tension. GT is is rated at 80 lbs. Please note that this is independant of ratcheting or pulley size, this is only the maximum allowable tension on the belt.

Minimum Pulley Size Per RPM Unit: Pulley%20Size

This is fairly straightforward. A 22 tooth HTD 5M pulley is rated to operate at 1160 RPM. This is over 5 times less than the 6000 rpm we operate at. A 22 tooth GT 5M pulley is rated to operate at 2000 RPM. Again, we are far out of spec, but by much less. This is 3 times less than the 6000 rpm we operate at. Unfortunately, both will experience accelerated wear, but HTD will suffer much worse.

Exact RPM And Torque Ratings:

HTD%20torque GT%20torque

These graphs show the operating RPM and torque ratings. HTD 5M is rated to 75 in lbs of torque at 6000 RPM. GT 5M is rated to 250 in lbs of torque. This means that GT 5M can run at 3 times the torque of HTD 5M. While we are not typically exceeding these, it still means that GT will suffer much less wear over time. Please note that this data is unrelated to pulley size, that data will come next and will show further disparity between HTD and GT.

Exact Torque Ratings Per Pulley Tooth Count:

HTD%20exact%20torque%20and%20lifetime GT%20exact%20torque%20and%20lifetime

I’m going to use the math for 5000 RPM, as it is the closest common value to 6000 rpm between the two graphs. HTD 5M is rated to 11.6 in lbs of torque with an 18T pulley. GT 5M is rated to 25.2 in lbs of torque with the same rpm and pulley.

What is more interesting is the low RPM values. At 100 rpm, HTD is rated to 25.7 in lbs of torqe, while GT is acceptable up to 58.5 in lbs with an 18T pulley. Our intense startup torques far exceed HTD specifications.

However, HTD is already in the “accelerated wear” category all the way up to 28T pulleys at 5000 rpm. HTD suffers from excessive wear from an 18T pulley at any rpm of 1160 and up. GT is acceptable wear at 5000 rpm at any pulley size 18T and up. GT is functional from 200 rpm to 14000 rpm with an 18T pulley. It only suffers from excessive wear from 100 rpm and lower, which we are rarely in when riding. For a visualization, this is when the motor makes a full turn every .6 seconds, which is a very slow creep for us.

We will be exceeding the torque ratings of these, so GT will also suffer accelerated wear, but not nearly to the extent of HTD since it is already going to wear excessively at any torque.

Other Details, Unrelated to Performance:

Ignore this if all you care about is raw performance, only the above information will be relevant to you.

Sound The sound levels are not easily interpreted from this. Decibels are determined on a logarithmic scale, not linear. So 100 dBA is much more than 2x louder than 50 dBA. GT is significantly quieter than HTD.

Idler%20Size We use backside idlers. GT and HTD perform the same here, but the data shows that we are seriously exceeding the spec here lol. Reversed bend radius very negatively affects belt life (given that all other wear factors are already in spec. We use idlers so other factors like belt slippage don’t occur, which is objectively a greater concern for wear).

Totally random thing I found about belt movement that I thought was kinda neat: Interesting%20detail

I found this very interesting. In a tuned pulley setup where they are in line and not twisted of offset at all, the belt will always ride to one side. If you have a precision CNC’d motor mount setup that ensures your pulleys are properly lined up, then you will still suffer from belts moving sideways. It is dependant on the direction the fibers internal to the belt are twisted. S twist is the opposite of Z twist. So if you’re using two of the same belts, they will both move in the same direction, ie: one will move away from your truck and the other towards it. Just thought this was interesting to read about.

TLDR: All Gt profiles are far superior to HTD, particularly in lifespan, torque ratings, and rpm. If you want a quick interpretation of the data, here is a comparison of many profiles: In%20Conclusion




Neat and thorough

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well if i build a board with belt again i guess it is time to switch. but first i will build a direct drive.

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I’ve been using 5mm GT2 for 2 years now


Where do you get them from?

Edit. My usual source has a GT variant of the HTD I normally get. See comparison below. Im no expert on how to read the specs but is this better? Breaking strength is similar but working tension is much higher, what does it mean? I need an engineer. :man_teacher:


Breaking strength doesn’t really matter for our case. The breaking strength of 12mm belt is nearly 850 lbs! We will never reach that kind of tension, you will lose traction before that happens. Notice that the rating is followed by “not representative of the load-carrying capacity” ie: the belt will not operate properly at this tension.

What is a concern though is the working tension. This is how much tension the belt can have in one direction and still mesh properly with a pulley at speed. That specification isn’t complete, the working tension should be affected by many other factors such as belt surface speed, fastest pulley RPM, and pulley size.

A specification of 712N or 454N is meaningless without the corresponding RPM and pulley size.

If you’re having issues with excessively fast belt wear or belt slippage on HTD, a GT belt could solve your problem.

I would recommend buying belts from SDP-SI.com They have many sizes and types of belt, all manufactured by Gates themselves.

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