Dr pulley sliders confusion - LX 50 2T
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Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Sun Jun 28, 2020 9:12 am quote
Hi all, a few questions about sliders if I may:

Question 1:

The stock rollers for a vespa LX 50 2T are 7.5 gram and are 19x15mm in size.

I see on http://www.drpulley.info/ that you need to minus 10% of that weight for the sliders which takes the slider weight to 6.75 grams however I also read on sip-scooter.com that you need to either add or subtract only a gram.

This is somewhat confusing.

I also can't seem to find any in 19x15mm, only 19x15.5mm.

What should I do?

Question 2:

I assume that adding these will put a bit more stress on the belt.
Is it wise to replace the stock belt with a kevlar belt at the same time?

Can anyone recommend a specific one?
Enthusiast
Derbi Boulevard 125 4t
Joined: 05 Feb 2020
Posts: 56
Location: Lithuania
Sun Jun 28, 2020 10:37 am quote
On my 125 scooter i actually found best performance with 0.7-1g heavier sliders compared to stock rollers.
Enthusiast
GTS 300 ABS, 2018
Joined: 07 Jun 2020
Posts: 52
Location: Finland
Sun Jun 28, 2020 11:08 am quote
Don`t know much about slider weight optimizing, but we have had this Kevlar belt discussion also in Finnish forum. So far we (veterans) have more or less decided to leave them for true racers and money men. Sliders will not increase the engine torque.

Correct size of 50 cc Vespa weights is 19x15.5. Search no more.
Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Sun Jun 28, 2020 11:03 pm quote
kaukari wrote:
Correct size of 50 cc Vespa weights is 19x15.5. Search no more.
Thanks kaukari, I couldnt find it in the vespa manual either.

After upjetting my main to a 58 I find that the acceleration is already pretty quick with the stock rollers so was thinking that 1 gram heavier would be a sensible bet also.

I shall report back after I replace them.
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Sun Jun 28, 2020 11:47 pm quote
As has been said the stock are 15.5 same as Dr. Pulley.

Conventional wisdom says 10-15% lighter so for 7.5g that gives you a spread of 6.4 to 6.8g so 6.5g fits the bill which is 1g lighter as per your SIP reference.

1915/6-6.5


NB had you gone with SuperdaveOZ that would be short for this guy!



https://www.youtube.com/watch?v=6GMSYjsnxpE
Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Mon Jun 29, 2020 12:18 am quote
waspmike wrote:
As has been said the stock are 15.5 same as Dr. Pulley.

Conventional wisdom says 10-15% lighter so for 7.5g that gives you a spread of 6.4 to 6.8g so 6.5g fits the bill which is 1g lighter as per your SIP reference.

1915/6-6.5
Why 1 gram lighter as opposed to heavier?
waspmike wrote:
NB had you gone with SuperdaveOZ that would be short for this guy!

Thanks I had not seen that before!
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Mon Jun 29, 2020 1:16 am quote
SuperDaveAU wrote:
Why 1 gram lighter as opposed to heavier?
I don't have my book of formulas at hand but the force exerted by spinning objects is something like: weight x distance from the centre x the square of the rpm.

So the idea being that the lighter the weight the faster it has to spin to develop enough force to overcome the spring in order change CVT gearing. This means that because the engine is spinning faster it is developing more HP (up to a point) but it will use more fuel, which is why the stock set up is conservative.

So more rpm with lighter weights is the same as lower rpm with heavier weights except at lower rpm you have less HP. ( like trying to uphill in high gear)

Which way you tune depends on what you are trying to achieve.
Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Mon Jun 29, 2020 1:20 am quote
I thought that:

lighter weights = quicker torque off the line but lower top speed
heavier weights = lower torque, but more top speed.

with the stock weights (7.5gram) and a 58 jet I can get up a hill at 30mph no problems and have a top speed of a little over 40 mph.

I would like to keep to top speed (or increase it) and don't want to lose the ability to climb the hill at 30 mph.
Enthusiast
GTS 300 ABS, 2018
Joined: 07 Jun 2020
Posts: 52
Location: Finland
Mon Jun 29, 2020 2:59 pm quote
Sounds logical. I improved my daughters Primavera 50 cc hill climbing by changing 6.5 g rollers to 5.7 g. No loss at top end, but is a bit lowder. Girl was happy and only that counts.
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Mon Jun 29, 2020 6:02 pm quote
SuperDaveAU wrote:
lighter weights = ................. lower top speed
A common misnomer. At extremes maybe yes but not if done properly.

The lighter weights allow the engine to rev more so more HP. More HP = more top speed.
More revs means the weights develop more force to move the drive pulley. ^2 of the rpm, remember?
There are published account on 50cc groups where the reduction of weights actually increased top speed.
Bear in mind we are talking in the order of 5mph or less.
Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Mon Jun 29, 2020 11:50 pm quote
waspmike wrote:
SuperDaveAU wrote:
lighter weights = ................. lower top speed
A common misnomer. At extremes maybe yes but not if done properly.

The lighter weights allow the engine to rev more so more HP. More HP = more top speed.
More revs means the weights develop more force to move the drive pulley. ^2 of the rpm, remember?
There are published account on 50cc groups where the reduction of weights actually increased top speed.
Bear in mind we are talking in the order of 5mph or less.
Ahh brilliant, in that case I shall go lighter.

Sip only have 5, 5.5, 6 & 7 gram available in that size though.

Which weight would you recommend?
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Tue Jun 30, 2020 2:09 am quote
Having a brain fart today.

Last edited by waspmike on Sun Jul 05, 2020 12:23 am; edited 3 times in total
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Tue Jun 30, 2020 2:10 am quote
https://www.sip-scootershop.com/en/products/variator+rollers+dr+pulley+_sr1915565


Get them from Dr. Pulley.info?
Hooked
Vespa LX 50 2T (2011)
Joined: 01 Apr 2010
Posts: 226
Location: South-West London, UK
Tue Jun 30, 2020 2:18 am quote
waspmike wrote:
https://www.sip-scootershop.com/en/products/variator+rollers+dr+pulley+_sr1915565


Get them from Dr. Pulley.info?
Could do.
These ones with the flaps look different though..
https://drpulley.shopnix.de/TechPulley-FR-sliding-rolls-Dr-Pulley-SR/Size-19x15-5mm-6x/TechPulley-Sliding-roll-SR1915/6-6-5::1399.html
Ossessionato
LXV 150 3v ie. Midnight Blue (Sold)
Joined: 06 Dec 2010
Posts: 3363
Location: Bangkok
Sun Jul 05, 2020 12:19 am quote
Spin off from Dr.Pulley? A way to circumvent patents?

There is also one called Flying Roller with the same wing idea but less plastic.





http://modernvespa.com/forum/topic106919
Enthusiast
GTS 300 ABS, 2018
Joined: 07 Jun 2020
Posts: 52
Location: Finland
Sun Jul 05, 2020 12:57 am quote
Flying Rollers sound so good and wonderfully dangerous. I am so excited...
Sponsor
Granturismo 218
Joined: 04 Feb 2013
Posts: 6137
Location: NWAOK
Sun Jul 05, 2020 5:47 am quote
6-6.5 gram rollers will do what you are looking for, and they are a lot more reliable than Dr. Pulley sliders.
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