Emulating Improved Roadholding

This is two of our committee members working out what their next move will be. It didn’t take them long to work it out.

Story by Rob Carmichael with the assistance of Doug Fraser

“EMULATOR”- IT SOUNDS LIKE A JOB DESCRIPTION FOR SOMEONE WHO DOES EMU IMPERSONATIONS FOR A LIVING!

Those of you who know the ups and downs of motorcycle forks will know what an Emulator is, but if you are like me when I started on this project, you wouldn’t have a clue what an Emulator was or whether they actually do improve a bike’s roadholding. Fortunately for me, an experienced motorcycling mate very graciously offered to help me to find out.

‘Emulators’ (AKA fork damping valves) are hydraulic valves that make old style damping rod forks of yesteryear perform like well-tuned modern cartridge forks – they ‘emulate’ (i.e. try to match or excel) them. The valves sit on top of the damping rods and are held in place by the main springs. This makes them simple to install and they can be either pre-tuned for a specific model bike, or be self-tuneable by the rider to suit conditions and rider preferences. At least that’s what the manufacturers say, but are these devices as good as they claim? Read on.

DFX Fork Damper Valves for Honda GB500TT: https://www.dfxparts.com.au/

PRODUCT SELECTION AND INSTALLATION

I’m not even sure what prompted me to try Emulators as my Honda GB500TT already handles and rides well, but there was an expectation (probably from enthusiastic advertising) that my bike’s roadholding could be ‘transformed’ by these devices. For example: “You will see vast improvement in how the bike holds a line through corners……”

There are various valve brands with models for different purposes (off-road/on-road/ competition) and at different price points. I chose a pair of non-adjustable fork valves that had been specifically pre-tuned for the Honda GB500TT. These valves were manufactured and sold by DFX Parts Pty Ltd, Performance Motorcycle Suspension, an Australian motorcycle engineering company based in Maroochydore, Queensland.

At $250 per pair this gadget was closer to the top end of the price spectrum, but this product claims certain advantages over the others on the market, such as: no need to calibrate the valves in-situ as they are pre-tuned to suit particular models and this results in easy installation; and importantly, the fact that DFX is one of few valves that provide controlled damping on both fork compression and rebound strokes. To quote Glenn Corbet founder of DFX: “I had tried just about every combo of spring rate, oil, more/less preload, but nothing can compensate for rebound damping, which is only found in ‘cartridge’ forks.

Until now, that is.”

DFX provided good documentation on installation and technical back-up. In its simplest form the installation process would go like this:

• Secure the bike with the forks on full decompression and remove the top caps from the legs; • From the fork legs remove shims, spacer tubes and springs, leaving the damper tubes in-situ; • Using an extended magnetic or claw gripping tool, positively locate the Emulator on top of the damping tube in each fork leg with the locknut facing up; • With the aid of a syringe and a measuring tool, add Fork Oil to the specified air gap level (1400 mm). Motul 10 w is recommended by DFX; • Reinstate the springs to seat on the emulators, and spacer tubes and shims on top of the springs, and tighten the fork leg top caps to the correct tension; • Test compression and rebound strokes for striction, check fork alignment and recheck tension on all fasteners.

But as the GB had been using Motul 15 w we decided to also drain the forks and fill with fresh Motul 10 w fork oil during the installation which was relatively straight forward. I only encountered a problem when rebuilding the forks.

Initially I was unable to simultaneously apply sufficient downward pressure and clockwise turning force to engage the external thread on the fork caps with the internal threads of the fork tubes. This problem was caused by the increase in preload caused by the location of the valves underneath the springs. The problem was eventually overcome by carefully aligning the points where the two threads engaged.

We were then ready to test the bike for improved roadholding.

PERFORMANCE TESTING AND EVALUATION

This is what Glenn Corbet says you can expect when you install DFX damping valves: “Your bike will feel more stable. It will soak up bumps (and especially the big ones like potholes) in a more efficient way………You also don’t get that pogo-stick rebound that wants to throw you off the seat, and your bike will suddenly stick to the corner lines you choose instead of drifting…... if your suspension isn’t working well you aren’t achieving optimal braking and grip levels”.

Directly after installation I did a quick test ride and the bike seemed to be both more planted and more subtle at the same time, with reduced front end dive under hard braking, and reduced rebound over large bumps while being more compliant with small surface undulations. These fleeting initial impressions align with the claims made by DFX about their product, but being the customer my view may be biased to justify my financial outlay. What was needed was an independent, 3rd party evaluation, so I approached BSA doyen and bike builder extraordinaire Doug Fraser who lives close by. One of Doug’s daughters owns a Honda GB400 so Doug was able to do a direct A/B comparison of the standard OEM suspension set up on the GB400 against the upgraded suspension on the GB500, which consisted of standard OEM springs and tuned DFX damping valves in the front forks and IKON shocks at the rear (see photo of the two bikes on p3).

Doug took both bikes on a test ride over the same inner suburban route, consisting of traffic humps, and other traffic calming furniture, cobbled bluestone laneways, and street surfaces subject to undulation, surface slumping, potholes, etc. Doug reported that the suspension setup on the GB500 was superior to that on the GB400, both front and rear, so part of the overall improvement was due to the superiority of the IKONs over the GB400’s OEM rear shocks. But rebound damping

Honda GB500 in front and GB400 at rear just before testing.

on the GB500 front forks was noticeably better. It was particularly evident when crashing over large bumps like double-decker speed humps or performing hard front brake application – no “pogo-sticking”. Doug’s independent findings agreed with my initial impressions and though not quite what you might call “transformational”, they were consistent with the maker’s claims.

To conclude, DFX says this about roadholding: “Brakes, Tyres, Suspension: the holy trinity of motorcycle handling performance. But the best tyres and best brakes in the world aren’t doing their job if your suspension isn’t keeping your wheels on the ground.” True, you can only improve your road bike’s roadholding by increasing the amount of time that the tyres’ contact patches stay in contact with the road surface and DFX damping valves appear to do just that.

So, especially for the benefit of VJMC members with Japanese bikes made before cartridge type damping units became standard issue, fork damping valves appear to emulate the performance of cartridge units, and this justifies use of the term ‘Emulator’, with no connection to emus whatsoever!