Motorcyle Fork Low Friction/Wear Surface

[jkdmag]

Hoping for an explanation as to the advantages of low friction/wear surfaces on motorcycle fork legs. Current basic designs have PTFE coated bushes working with either hard chromed steel or aluminum in an oil environment.

Claims are made for significant improvement in wear and friction performance for the aluminum components by hard anodizing, and similar improvements to the steel components by substituting other coating for the chrome layer, eg TiN or DLC.

Given the low friction/wear properties of PTFE and hard chrome, why would there be any improvement to be gained by the changes to the alternative surface treatments as listed above.

 

[coatingengineer]

Hello. Sounds like you have yet to see "failure mode", yourself, using conventional surface treatments like hard chrome. Nevertheless, there may be some advantages. Specifically, in boundary lubrication (e.g. oil environments), PTFE can serve you well in overcoming static friction and periodic dry intervals. Also, depending on "PV-WEAR" (applied pressure x rub velocity), surface treatments like hard anodizing (with PTFE seal) may significantly extend aluminum life. No chemistry between oil and PTFE; degradation is not an issue.

William Gunnar Naschak

http://www.IndustrialCoatingsWorld.com

http://www.nationalsurfacesolutions.com

 

[jkdmag]

Would any friction reduction from the increased harness of anodized aluminium, when sliding against a PTFE coated bush, be worth the cost of the anodizing. Also, if PTFE coatings offer excellent low friction properties, why would these coated bushes wear the untreated aluminium to any significant extent.

Again, is hard chrome coated with DLC or TiN that much superior to simple hard chrome in terms of friction, when rubbing against PTFE coated bushes.

Are the claims being made for these surface treatments worth the cost or just sales hype.

 

[coatingengineer]

Friction is a system-dependent parameter, a function of material, counter-face, hardness, temperature, load, surface finish, distance and rate of travel. If you (or the industry) have seen no wear or performance compromise, there's no sense in pursuing "the better mousetrap". Stick with what you have.

Here, I'll try to answer your questions. First, the harder the base material (i.e. resistance to plastic deformation) the more effective the lubrication. Second, wear life will increase by coating the aluminum with hard anodize with Teflon seal, though friction, comparatively speaking, will increase. You will have to determine which is more important: lower friction or better wear-life.

The same rules apply (slightly higher friction vs. longer wear-life) when considering other forms of dry lubrication, such as the diamond-like coatings. Chrome and TiN are so close in hardness, I can't imagine combining the two, or giving up chrome, unless you're looking at it from an environmental, heavy metal standpoint: Cr(VI).

In short, surface treatments you've described, with a PTFE counter-face, can be excellent ways to extend the life of a "system". Whether that includes motorcycle forks is something I can't answer. Though I think you have, already.

Hope this helps. Best wishes.

William Gunnar Naschak

http://www.IndustrialCoatingsWorld.com

http://www.nationalsurfacesolutions.com

 

[jkdmag]

Thanks coatingengineer, if I understand your comments correctly the friction/wear performance of (1) PTFE coated bush against chrome and (2) PTFE coated bush against aluminium are the equal of that available from the alternatives I have listed.

This would support my suspicion that the "significant friction and wear advantages" claimed by various sections of the motorcycle industry for these expensive surface treatments is not justified.

 

[coatingengineer]

Glad to help. It'd be interesting to know if those significant friction and wear advantages are measured, quantified. Or, maybe others from your industry have testimonials.

William Gunnar Naschak

http://www.IndustrialCoatingsWorld.com

http://www.nationalsurfacesolutions.com

 

[jkdmag]

The lack of quantified "performance improvement" is the reason for my questions. I have been unable to find any comparative performance measurements, just opinions from both the product suppliers and positive endorsement from customers that has paid out $200-$500, depending on the coating, hardly a science based validation.

Most people have the coating applied during a fork rebuild that would usually include bush replacement, which might have a more significant affect of the friction performance. Interesting also that there have been reported instances where the OEM hard anodizing has had to be replaced due to failure, which raises the question as to the quality of the OEM anodizing and perhaps even its value in this application.

My own limited understanding of the friction/wear properties of stell/aluminium rubbing against PTFE coated bushes has made me skeptical of the unsubstantiated claims, hence my questions.