Author Topic: Yet another front fork oil question  (Read 576 times)

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Offline ifsson

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  • Country: Czech Republic
Yet another front fork oil question
on: August 01, 2019, 02:22:42 PM
Greetings from Bohemia,
after some 40.000 km on 2013 Crosstourer (manual gear) I started to feel that front fork is quite soft while braking, I'm 85kg and ride alone, no off-road only paved roads. So  I've adjusted rebound to max. Which seemed to solve the symptoms, but didn't really solve the problem - instead of increasing compression I've just eliminated rebound.

So I'm thinking of changing front fork oil, and while doing this I thought about installing hyperpro springs.

However workshop manual states KHL 15-10 fork fluid with 138mm level. Not a lot of information on KHL 15-10 fluid specs, but according to several sources it should have viscosity of 15.3 at 40C. With hyperpro springs I'll get SAE 15W fork oil. There is also not much info on hyperpro fork oils - but generally SAE 15W fork oils of different brands have viscosity of 45 to 55, let's assume average of 50. Hyperpro also states fork level 125mm - so more oil.

And here is the question: simply changing to hyperpro oil with 125mm will give me much stiffer front fork both because of thicker oil and more oil in the forks. In my case of riding only on paved roads, does it makes sense to change the springs at all? Can I actually achieve what I want simply increasing oil viscosity and level?


Offline ifsson

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  • Country: Czech Republic
Re: Yet another front fork oil question
Reply #1 on: September 11, 2019, 06:07:08 PM
Oh my, 185 views and no answer. But as I've tried the setup one way and then another way - I have a comparison and you can have a review

First of all I've created several "sophisticated" tools to cover for Honda tools needed for fork disassembly I'm extremely proud of the fork rod puller tool (MRSP 30$) made from bamboo Asian food stick  :008:. Anyway I was once again quite disappointed with Honda assembly quality of this bike, that was really outstanding on my previous VT600, VTX1300 and VTX1800 bikes. I have a 2013 Crosstourer with 40k km always kept in a garage. And clearly there was oil with some water in one of the forks - hence corrosion inside. Had to clean it.  I assume that it could get inside only during the assembly in the factory. Oil was really dirty, but that was expected.

Then I've changed oil for Motorex SAE15 and used recommended Hyperpro settings i.e. 125mm oil level and most importantly mounting fork 10mm through the clamp. Front suspension became stiffer and bike handling improved. Honestly, after 40k km fron suspension was extremely soft, so almost any change would have been an improvement.

BUT I wanted to reuse oil seals, which was a clear mistake. One of the oil seals was leaking. And as I had to disassemble the fork anyway, I decided to change the springs in both forks - so I ordered Hyperpro spring set. Springs are a bit longer approx 7mm and a bit stiffer. So after mounting springs I do have a subjective feeling of improvement, however I cannot say that it's significant and honestly I cannot say what % of improvement is caused by oil change and level and different fork position, and what % is caused by spring replacement.

But I guess Hyperpro wouldn't be so successful with selling only advice on suspension change and oil for 150 EUR. And yes, 1 liter of included Hyperpro oil is not enough, so keep some of the oil from the forks.

UPD: I see significant improvement in bike being lower - 10mm in the fork is enough to have my whole foot on the ground - which was previously impossible.

I know it's kind of a blasphemy, but I'm really thinking of purchasing KTM Duke 1290 next year. Starting to be disappointed with big X.
Last Edit: September 11, 2019, 06:14:30 PM by ifsson


Offline marcparnes

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Re: Yet another front fork oil question
Reply #2 on: September 12, 2019, 04:55:41 PM
Very creative tools! Nice :-) Interesting how the water could have gotten in there. I really doubt that happened during assembly at the factory. I wonder if it could come from condensation over time. 

Marc Parnes
2018 Goldwing DCT Tour in Red
2020 BMW R1200GS
A Life of Bikes
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