Mountain Bike Fork Oil Substitute (5wt, 10wt And All The Other Variants of Oil)

The forks in your bike move up and down when it faces collisions. The oil inside the fork then moves around and provides the damping and consistency.

This consistency comes from the viscosity of the fork oil. There are other types of fluids that can provide you with the same viscosity. 

So, what are the mountain bike fork oil substitutes (5wt, 10wt and all the other variants of oil)?

For fork oil substitute you can use Automatic Transmission Fluid (ATF). On the scale of fork oil’s viscosity, it would be 7.5 wt. Another option is to use hydraulic oil. For 5wt you can use ISO 15 or 22 hydraulic oil. As for 10wt, ISO 32 hydraulic oil would be a closer match. 

Wanna learn more about the alternatives? Then keep reading our piece till the end.

Let’s begin!

Fork Oil Alternatives

Understanding the differences in forks like 100mm vs 120mm travel forks can be challenging. But so is finding a substitute for fork oil for your mountain bike. 

The weight measurement of fork oil is quite complicated. What’s even more troublesome is that different brands have different weight measurements of them.

Mountain Bike Fork Oil Substitute (5wt, 10wt And All The Other Variants of Oil)


To find an appropriate fork oil you’d need to know more about your bike. Your bike model, the consistency you need in your suspension gear, things like that.

Here’s a video by Partzilla that explains how you can choose the weight of your fork oil-

Considering all that, sometimes finding the right fork oil is difficult. So you’ll need an alternative. Let’s say such a situation arises and you can’t find fork oil in the market.

But you desperately need it or at least an alternative for it. We may not be able to help you find the fork oil. But we can help you prepare an alternative.

Automatic Transmission Fluid

Automatic transmission fluid is the best alternative for fork oil. In fact, there’re many people who use ATF from the beginning instead of fork oil.

Before the fork oil, only ATF was available. So, it has quite a history of being used as the fork oil. It has shear-resistant and anti-foaming properties.

So, it’s safer than other possible alternatives. Alternative transmission fluid has about the same weight as 10 wt fork oil. If you compare the weight of fork oil to ATF, it would be 7.5wt. 

Which can be a good alternative option for 5 wt or 10 wt fork oil. Some people also mix engine oil with ATF to use as the fork oil alternative. 

Mountain Bike Fork Oil Substitute (5wt, 10wt And All The Other Variants of Oil)


You cannot pick just any brand of ATF. I’ve found that there are certain ATFs that don’t work particularly well with forks. That’s why getting the right brand of ATF is important.

Here are some of my go-to Automatic transmission fluids as fork oil substitutes: 

Although it’s a good substitute, it ain’t perfect. ATF is outlined for torque converts. Its job is to provide lubricant to the torque converter elements. For example turbine, stater, clutch assembly, etc.

Thus it’s usually used for four-wheeled vehicles. So it can be said that it’s more suited for four-wheeled vehicles than motorbikes. But it is still the best alternative after the fork oil. 

Hydraulic Oil

Hydraulic oil is another common alternative option for fork oil. Fork oil is basically hydraulic oil. So, it’s safe. But there are some differences between them.

Fork oil comes with additional additives which prevent the foaming of oil. So the suspension damping would be worse than what fork oil delivers. 

There’re also some additional additives included to them that are not present in hydraulic oil. But it has additives that protect the seals. It also has antioxidants.

So, it has good tolerance against high temperatures. If you plan on using hydraulic oil you must use the right weight. Especially the viscosity. 

Mountain Bike Fork Oil Substitute (5wt, 10wt And All The Other Variants of Oil)


It usually has 100 ISO viscosity(SAE 30). But the grades could be different depending just like motor oils. So, better check the viscosity index first. 

If you compare them with fork oil, you’d know what viscosity hydraulic oil you’d need. For 5 wt fork oil, you’d need ISO 15 hydraulic oil. 

ISO 22 hydraulic oil would also do the work. If it’s for 10wt fork oil then go for ISO 32 hydraulic oil. These are the closest match you can find for changing fork oil.

Other Options

Your best alternative option after fork oil is ATF and Hydraulic oil. If you can’t find any of these oils then you have a few more options. But know that, these options should be avoided if you can.

It might sound a bit funny, but you can use peanut butter or jelly. Since their consistency will be thicker than usual lubricant oil.

As you’re using a substitute for fork oil it can’t be of low consistency. That’s why you’ve to avoid using any kind of normal lubricant oil. 

Some also suggest using motor oil or engine oil as a substitute. But unless you’re using the perfect weight substitute don’t go for it. 

Engine oil and fork oil have different weight measurements. For example, a 5wt engine oil is equivalent to 40wt of fork oil. So, you can only use engine oil if you can figure out the equivalent weight.

Otherwise, using motor oil or engine oil is a flat no. Also, you better discuss the situation with a professional first. If the choice is wrong your bike can be damaged. So, is your riding skill.

Final Tip

Fork oil is an essential element of your motorbike. Its task is to provide consistency. Consistent rebounds and consistent dampening when the temperature falls and rises.

It’s the perfect component that your motorbike suspension needs. There’s no perfect alternative for it other than fork oil itself. 

Although it can be a little expensive, you should stick with the old option. Unless your fork oil is leaking.

Don’t try to change the brand either. Because different brands follow different consistency for fork oil. The 5wt fork oil that you use and the 5wt fork oil from another brand won’t be the same.

I’ve personally tried the fork oils of many brands. But time and time again I go back to the Maxima fork oils. They are super easy to use and work really well. 

Here are some of the options of the Maxima fork oils: 

So, unless it’s absolutely necessary don’t look for alternatives. And even if you do, try to make your choice between ATF or hydraulic oil. And if you’re confused about it talk to someone knowledgeable about this.


Have some more questions? This segment might help-

How to tell if the fork seal has a leak?

Take a clean cloth and wipe the lower side of the forks with it. Now, take a small ride on your bike and check the forks again. If you see oil around the lower part of the forks then it’s leaking. You’d need a seal replacement soon.

How often do I have to change the fork seal?

Changing the fork seal should be done every two years. Or let’s say once you’ve ridden your motorbike for 40 hours. The fork seal wears out even if you clean them regularly and starts to leak. So after every 40 hours of ride, change the fork seal and the fork oil.

What happens if fork seals have a leak?

Riding with a bad fork seal can be dangerous. The leaked oil from the fork seal can reach the brake calipers. So you may have trouble with stopping or decelerating the bike. It also causes an unbalanced ride and poor shock absorption. So, leaky seals should be replaced.

Final Words

That’s all about mountain bike fork oil substitute (5wt, 10wt and all the other variants of oil). Now you know your other options and the requirement for using them.

But make a double check before you change the fork oil. Using the wrong substitute can cause you more money and a lot more hassle.

Safe riding!

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