ATF in forks

[gills]

I've just changed the fork seals on my bike and put in ATF rather than fork oil. The front end was a bit too firm for me when I got the bike, so I was interested to go back to standard spec, hence going for ATF rather than fork oil. I don't know what had been in, but it looked like a medium weight fork oil when I drained it out - certainly thicker than the new ATF.

The ATF has certainly made the ride much smoother and more comfortable. The handling is not quite as sharp on a smooth surface, but on the roads I tend to ride on (mostly B or unclassifieds) it's actually holding the road better through the corners. What are others experiences with ATF/fork oil? Which do you prefer?

[rj2para (Bisto)]

I have 7w in mine as it was handy, but Skyhook I think has a blend closer to 10w. Sky?

I think mine is a bit soft so I may go firmer next time or even look to improve the springs.

ATF was new to me so Google came to hand uncovering an interesting thread.

www.thumpertalk.com/forum/archive/index.php/t-507141.html

[skyhook]

Nice find there rj,

As for fork oil i used a mix of 5w with 10w so should work out a 50/50 mix as 7.5 but that is on the yam.

My thinking there was 5w was a bit to soft and 10w being a bit to stif and 7.5 seems to work out spot on for my rideing.

ATF looks like it's upto the job so next time might give it a try

[76offset]

Interesting to hear peoples' experiences with fork stiffness. I mainly ride on terrible bumpy roadsds on the IoW and last service time I drained, rinsed out and refilled to correct measured level with bog std. ATF which was an improvement on the discoloured slurry that came out. I can't help thinking though that a synthetic multigrade, I think to try 0w15 if I can find it. That should make it thin when cold and thicker when warm, and I've seen it claimed synth oils are more stable than mineral with temp change - Have to suck it and see ! Rick.

[McF]

Nov 18, 2011 11:00:47 GMT 1 76offset said:

That should make it thin when cold and thicker when warm, and I've seen it claimed synth oils are more stable than mineral with temp change

Assuming a winter low temperature on IoW as -5C (probably in the daft hours of the morning and you're not going to be riding with high performance expectations.
and a summer high of 30C
That's only 35C temperature parameter and still quite low in the range for engine oils which are designed to be used at temperatures in excess of 90C and are graded at 100C (ie the higher number is the viscosity at 100C)

Scraping my memories from many years ago, I believe the viscous properties behave on an exponential curve (shaped like this - ignore the numbers it's just an example)

Imagine that temperature is the bottom axis and viscosity is the side axis.
At lower temperatures a lot of increase only produces a small amount of increase in viscosity. As the oil gets hotter eg over 70C it gets thicker quicker with small increases in temperature

[gothitjulie]

Currently using 10W since the summer, feels OK, pretty stable but a bit fierce when I hit a high speed bump, but I can live with it.

Before that I used ATF, found it fine especially in winter, but I won't be riding all through this winter (spinal surgery start of January) so trying the 10W.

[skyhook]

I might add that the book says use 5w but i find this a bit to soft as the yam did dive a bit at front end on heavy brakeing.

So with a mate of mine who dose a bit with bikes we mixed our own and seems to work realy well, but will look into ATF.

[76offset]

This is a very late response McF, I appreciated your post with the viscosity graph, thankyou, and I take your point. If I understand you correctly you think the multigrade effect of a very thin syn oil will be ineffective at lower temps i.e zero +/ - 10deg. (I wonder if anyone has any data?) By way of interest I remember being surprised to see a recommendation to dilute lub. oil with paraffin for Briggs Stratton engines (official) in arctic conditions, so many things are possible !