Spidermax Files: The Dr. Colt Conversion

Optimizing the Piaggio MASTER 500cc CVT part VII

2015-05-27 3 years with the D. Pulley sliders
2014-02-24 2 years with the Dr. Pulley sliders
2012-10-25 the 19 gram 2.5 mm mod is just great

2012-09-01 500 km with the 19 gram 2.5 mm mod

2012-08-23 changed to a 2.5 mm washer for some extra acceleration
2012-08-19 comments about my 19 gram slider mod
2012-07-16 new test with four 19 gram sliders and the standard 2mm washer
2012-07-04 5000 km with the Dr. Colt Conversion and the switch to a 2.5 mm washer
2012-03-17 Dr. Colt 1000 km results and first conclusion.
2012-02-15 Some thoughts about the bad Dr. Pulley photo faking.
2012-02-14  Dr. Colt steep hill climbing test
2012-02-13  Dr. Colt high speed test
2012-02-09 installation Dr. Pulley sliders
2012-02-03 initial post

If you have been a good boy (or girl) and have read through my blog you might remember that before I started my "let´s see how many rollers we can remove conversions" I was thinking of getting light Dr.Pulley sliders and see how they would work out. Sadly Dr. Pulley sliders have to be mail ordered from overseas and even that proves a challenge because of the limited weights at that time and virtually no dealers.

Now some years later and with 2 sets of the once reliable Piaggio rollers failing horrible it is time to look for safe alternatives. As it happens I stumbled across a Dr.Pulley seller in Germany who has a lot of different weight sliders from the original 21 gram down to 14 gram and you can even  order 13 gram.

After some considerations I decided against the 8x13 gram and will see how my favorite Colt Conversion works with Dr. Pulley sliders.
I ordered the 2517 8-21 for the quite steep price of 45 Euros ($60) plus a moderate 3.50 for shipping.

This will be a long-term test to see if they are as good and reliable (37000 km) as the original Piaggio rollers once were. (In case you are not familiar, nearly every European scooter has an engine made by Piaggio and the OEM parts like belt and rollers are also all from Piaggio.)


Installed 4 of the 8 Dr. Pulley 21 gram sliders in a Colt Conversion setup at 56250 km. Since these sliders have to stay in the exact position during the assembly of the pulley halves I kept pressure via the fingers on the pressure plate and the pulley halve while sliding in.

When I am over the cold, I will let you know about the first impressions, but the solo test ride showed a bit different characteristic to the Colt Conversion. It felt like a tiny hesitation and then a bit more pronounced acceleration. For the "does it work?" test, it is a clear YES in the tested low to medium speed.

The Dr.Colt Conversion is between the Mustang and the Colt Conversion.
It reaches rpm max earlier but you are still able to have V-max if you want under ideal conditions (slight downhill and tailwind).
If the Piaggio rollers would be still have tho original quality I would rather stick with them.

 In the uphill hairpin turns the D. Pulley sliders did OK, but not quite as agile as the Colt Conversion with the standard rollers. There was never a squealing or belt flapping but I would have liked 500 rpm more. So it was mostly in the mid to lower 3000 rpm band up the hairpins. If more power was needed the response was quick enough.
If you could get Dr. Pulley 21 gram rollers, I think that would be the better choice.
I will check if after initial wear in phase the characteristic changes.

Some thoughts about the bad Dr. Pulley  photo faking:

Dr. Pulley has some convincing pictures to claim why the slider is better than the roller.
But on a closer look you see that they are using some bad photo-shopping.
if the pressure plate would be as high and as far to the center of the weight as in the photo below, the Dr Pulley slider would be on the edge of the slider ramp with the possibility to flip
also the pressure plate sits on the pulley, so the weight should be in bottom  position

the pressure plate (silver thingy on top) is much higher out of the pulley and is much too short  as compared to the real life or the photo above

If we put the roller in the same position as the slider there is no way the edge of the pressure plate can harm the roller, but then again the pulley is in rest position, so the rollers should be at the bottom and the pressure plate should be further down. to keep in contact with the rollers!
this is what the pulley actually looks in rest or low rpm
2012-03-17 Dr. Colt 1000 km results 
Since a couple days I have a new rear tire and I could finally put the Dr.Pulley sliders through the paces.
It is not a Colt conversion, not even near.
The acceleration is more like the Mustang Conversion (6 rollers), more dynamic than the factory setup but much less explosive than the Colt conversion. In the hairpin turns in the mountains it is OK but far from the quirky handling and instant response I am used to.
In high speed situations above 120 km/h the RPM are too high and it can reach RPM max depending on the situation below 150 km/h.

So far the Dr. Colt Conversion with four 21g sliders are a disappointment compared to Colt Conversion with four 21g rollers.
I will see if I can make modifications to get the quick response back.

2012-07-04 Dr. Colt 5000 km results 
I was not too happy with the 4 roller (slider) setup. I missed the explosive acceleration I had with the simple rollers. I tried to install the Dr. Pulley sliders the wrong way since somebody posted that he did it by accident and had higher RPM and a better acceleration. It did not make any difference in my setup.
About 1000 km ago I switched from the standard 2 mm distance washer in the driving pulley to a 2.5 mm washer and except for a still tiny hesitation I have now the acceleration from the Colt Conversion.
This setup works also better with the new area we moved, where the allowed V-max is 100 km/h and I have much more hills and some of them with over 20%.
Funny thing is my gas consumption went down a bit even the engine runs a bit higher than with the 2 mm washer.

Right now I have nearly no internet so pictures and updates will be delayed.
The Dr. Pulley sliders show after 5000 km no wear at all.

2012-07-16 new test: four 19 gram sliders standard washer

The 2.5 mm washer setup started to develop a little squealing Sea Lion after a while.  I guess that after 60000 km the pulley had lost a bit of material so that with the 2.5 mm washer only part of the belt was engaged in lower rpm. Since I did not like that, I am trying something else.
I took my 4 unused D. Pulley sliders and got the inserts out.
Let me tell you that material of the slider is quite soft and easy to manipulate compared to the original Piaggio roller material.
I drilled 4 holes in each insert and have now 75 gram for 4 sliders compared to 84 gram before.
We moved to an are where we have lots of mountains and the most of the time 80 to max 100 km/h is the maximum. So I need a setup what works best with 2 people under these conditions.
The first tests look quite promising...

2012-08-19 comments about my 19 gram slider mod

After over 1000 km I can tell you that the Spidermax has a near perfect acceleration for the mountains where I live now.
There is sometimes still a bit too much hesitation for my taste, so I will put the original rollers back in and compare it to the original colt conversion to see how they are comparing.
Remember this setup is optimized for a 120 km/h max and steep mountains.
My gas consumption did not change noticeable.
The occasional little squeal did not go away and may be wear related since the belt is now since over 25000 km installed. It also can be that a bit of oil from the slow leaking gear box seal behind the driven pulley finds it way onto the belt. 

2012-08-23 changed to a 2.5 mm washer for some extra acceleration

To drive my insanity a step further I changed form the 2 mm washer to the 2.5 mm to get some extra rpm. The engine started to sound a bit like a turbine again when going WOT. We just love it.
Stay tuned for an update...

2012-09-01 500 km with the 19 gram 2.5 mm mod

So far I have nothing to complain. Keep in mind that the bike is tested in hilly to very steep grade mountains and always with 2 persons with and often with some additional load (grocery). The combined weight of everything should be 5% under the 400 kg margin.
The Spidermax slingshots into roundabouts (nearly no traffic lights were we live) and I often have to go from WOT to a more moderate throttle setting. The acceleration up hill to pass traffic is very good and so far the only thing I would like to tweak is the little torque hole in the 4000 rpm band, but that might not be possible.
Over all this looks looks like the optimal setting and possible acceleration for my area.

2012-10-25 the 19 gram 2.5 mm mod is just great

It is just awesome how the Spidermax behaves with this mod. There is never the feeling you need more acceleration or more speed. So far the RPM limiter has not kicked in - but I was not over 130 km/h so far. I am over 65000 km and it is just fun to race the 650cc bikes from the start up until 80 km/h. 

2014-02-24 2 years with the Dr. Pulley sliders

Well the last 2 years I was at a location where I could get only internet with my mobile phone at high prices and low speed. Also we got 2 dogs who loved to get with us in the car so my beloved Spidermax had a lot o no riding time and I was barely on the net, hence the big gap in my blog posting.
We also moved again, this time out of the mountains back to the coast and into an area where it is only slightly hilly.
The Malaguti Spidermax has now around 73000 km and the Dr. Pulley sliders are working flawless.


2015-05-27 3 years with the Dr. Pulley sliders

Well the last year I was at a location (Lanzarote) where I put less than 1000 km on the Spidermax. It is not fun to riden in 30 to 50 km/g crosswinds with high dust content. The Dr.Colt 4x19 gram and a 2.5mm washer is now 15.000 km and 3 years in service without any problem. After the initial 5000 km with the 21 gram sliders, i put them aside and installed the remaining 4 sliders in what were modified to 19 gram.
Now with my new Spidermax RS I installed the 4 sliders with 5000 km already on them.
Since it is mostly flat here in Valencia, Spain the 4x21 gram setup with the original washer works very well.

the sliders with 5000 km - a bit dirt, minor abrasions but no noticeable wear


  1. Would a dry graphite lubricant be any benefit to: smoothing engagement & operation and adding extra life to the rollers?

  2. no, the roller life is only determined by the plastic material and that from Piaggio is now terrible. Since the high rpm the lubricant would just move out of the pulley and into the belt area, so that is a no no.
    Right now use rollers from Malossi or Polini if they have the right dimensions, or go with the much more expensive D. Pulley who have a wear resistant nylon component.

  3. Hi , Joe !
    I too am very interested for this new rollers .
    Please, give a info about all 8 rollers setup : what is the reply ?
    8 rollers of 21 gr : acceleration ? consumer ? max speed ? or is just a new way to steal money ? I think your photo's are wrong. This roller pushes the plate, at the tip, and not as you represented. I think that the acceleration is greater when the roller rotates, about 80 km / h and up. You confirm this?
    Ciao joe, and congratulation for your very nice blog.
    See you also on my forum.

  4. Hi Sloper, long time no hear. I stop by in your forum a sew times a year to see whats going on in Italy and the Spidermax.
    I did not try the Dr. Pulley sliders in anything other than the 4 roller (slider) setup. For me the rollers worked better, the sliders are not so fast reacting. The main difference is in the starting acceleration. 80 km/h and above there is no difference for me to the rollers. The main price difference is because of the much higher quality material Dr. Puller uses and the different shape.
    If you happy with the Piaggio rollers , stick with them. For me in my Colt setup they fail within a few 1000 km, so I needed some more reliable quality.
    As to the photos, the plate gets pushed by the huge flat spot on the sliders (I think that might be the reason for the delayed acceleration)

  5. Hallo,

    ich wollte mich mal für den Tip bedanken einfach vier Rollen draussen zu lassen. Mein Fuoco brüllt und beschleunigt besser. Ich werde jetzt aber trotzdem ab und zu kontrollieren und prüfen. Hab auch noch ein paar Dr.Pulleys die ich auch mal im Russian Roulette Modus versuchen werde.

    Greetings to Gran Canaria !!

  6. Hi!

    Could You send any contact of You? Email or phone number?
    I need some help about GT500 electrical problem.

    Thank You!


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