Modern Vespa

Someone has to raise the reflag and is about time I come forward. Look, scooterhelp gearing chart looks awesome, it has a great database but I wholeheartedly disagree with the final results. I just don't know if the equation is done manually or automatically but the values are not adding up.

Here is the background. I have been testing my scooters over, and over and over with redundancy of speed measurement and other instruments, two tachs, 3 GPS simultaneously, all my instruments are in sync. What I mean with that is all my GPS are reading simultaneously the same speed and my tachs are spot on within 10-30 rpms of each other. The problem is when I bring my data and compare it with scoolerhelp gear charts, it just doesn't add up.. never!!! it doesn't matter if I even try not just the gear set that precisely correspond my vespa, it doesn't even match even doing a combination (up or down).

This forum has been great, lots of smart people, I keep learning every day but hear me out, go out grab a tach, grab a GPS and test it. I have been doing it and none of my scooters speed/rpms match. I wholeheartedly think that the final values needs to be revised, I really do, no offense, I am not reinventing the wheel all I am saying is that the data shown it doesn't add up to me and I am measuring everything with redundant equipment and staying at a specific speed/rpms to ensure I get steady values.

If you ever used the chart and you think your numbers were off please share. I am absolutely not taking anyone serious if you tell me that you are reading off your scooter speedometer because that is NOT accurate.

My P200E was reading 5000 rpm at 50 MPH (GPS)
My 2005 PX150 reads 50@6250, 55@6850 and 60@7400 rpms (GPS)

^^ That is just the tip of the iceberg, is just a simplistic measurement, I have more, way more that I have been collecting. If you give me the choice between:
1) Believing my GPS and Tach
or
2) Believing the final speed result on the scooter help final speed/rpms

I'dd pick the first one. I just don't think 4 test equipments are wrong (two GPS and two tachs from reputable companies). What I truly think is that the data on the charts needs to be revised , that is all!!. I have seen that data for many years but it wasn't until a few years ago when I started gathering my equipment is when I started to find out that the data put on the charts does not equate. Am I wrong? if so how? if the equipment wrong? how so? what speed is showing on the charts? GPS? speedometer? It doesn't add up folks, not to me.

It is a good chart for comparing ratios though.

The gearing chart doesn't take into consideration 2 HUGE factors: wind resistance and friction.

Never in a million years will it be accurate, it's just a theoretical calculation to choose approximately acting gearing.

That's already huge benefit to be able choose the gears you'd want and see how it'll act.

It's like you said, it's great for seeing gear ratios.

^^ I understand your consideration. When I tested my scooters here in the flat deserts I take my time to look at the gauges, I stare at the gauges for a couple of seconds of predetermined increments, ie: at 40 mph.. then at 50 mph .. then at 60mph and so on. The same thing I do with the RPMS, at 5000 rpms, 6000 rpms, etc. I watch my CHT. Yes the wind will slow you down(obviously) but the charts are set (equations).

Wholeheartedly I just feel like they haven't been revised/updated. I would agree, it is a great tool for gear ratios.

It's not just slow you down… it's everything… let's take the PX for example… it's 108kg dry weight, then there's the riders weight. The surface areas of the bike + rider….?

And it's not just the friction of the floor and wheel, it's the friction of all moving components… from the piston all the way to the clutch to driveshaft…

I'm not sure who will have a calculator to calculate the piston size, frictional forces inside the engine, plus the weight of everything…

Maybe their tire size dimensions are off.

Does everyone know their exact engine characteristics? X hp @ Y rpm.

Just asking.

Aero dynamics
TS=Cx(HP^1/3) 30.2      for a large cruiser
31.79    for a medium sport bike
32.99    for a small sport bike
Maybe 30 for a Vespa
Using Sticky's info classic Lambretta comes out at 30

^^ This is what I am talking about. I looked into it dozen of times. I punched my numbers not just the pre-set assumed factory specs but I also tried combinations.

https://www.scooterhelp.com/tuning/vespa.gear.calc.html

I think it is a combination of things but I wouldn't rule out the tire dimensions. I know the website mentions the standard 10" by 3.5". I run various tires but they are all the standard 10" by 3.5. Today I made sure the tire pressure was also set correctly because I also check that.

Like I was telling a buddy of mine that is also here on the forum I think there is not a lot of combined proven/tested data compiled. This gearing chart has been the "go to" place and it looks fantastic, sort of Microsoft excel product where you input numbers and it gives you the final result. I just think that when the chart was created there was not proven RPM/GPS compiled data. I am not complaining, I am just making my observation, I personally used the chart to sort of "gauge" my gear ratios but when comparing my actual collected data (specific speed, specific rpm ) times 3 scooters it doesn't add up. it is a few mPH off and I find it significant.

I am tempted to tear my scooter apart and count the teeth of the pinion, the clutch gear and measure the tires diameter for a complete revamp.

As it turns out my 05 PX 2005 purchased in the USA comes with a clutch gear with 20 teeth. I was convinced since day one that things did not add up to the charts on scooter help. Even using the 21 gear still doesn't add up but I am glad I am bringing this topic/discussion to a fresh start .

Having purchased my 05 PX150 back in 2012 with 3200 miles on the clock I am inclined to say that it has the original clutch (20 teeth). Is it possible that someone before me went and changed from a 21 teeth to a 20 teeth? is possible but unlikely.

With so many people out there with PX on stock gearing and no Tach or GPS to verify information is hard to gauge/compare. Lots of people posting stuff based on speedometer reading. My speedometer reads average 10 mph above so it is a terrible source that is why I do Tachometer, GPS and today I went and counted the teeth. It was a 20 on the clutch and 68 on the big gear.

I have been complaining over the years on the short gearing, a lot of great people came to the rescue with their feedback, suggestions, recommendation, ideas and I appreciated it.

In summary, don't assume your PX150 comes with a standard 21/68. Go and verify the stuff yourself (count the gears), grab a GPS/tach and compare, I am so glad I did. Right now I am going to install a used clutch that I have with a 22 teeth clutch gear. I tried the 23 and it doesn't go in. Doing my math I should see an increase of 11% and I am looking forward to it.

So I did the 22 teeth clutch gear from an older scooter and I removed the 20 teeth cosa style that was on my PX150. I changed nothing else and I am reporting an increase of 5mph in 4th gear at the same given rpms.

Acceleration suffered but it is also partially my fault as I did not soak the clutch packs enough and the clutch was slipping a hair from what I can perceive. I did manage to beat the previous top speed and achieve 2 mph more at 600 rpms less. My CHT is now roughly 40 degrees cooler at compared to before.

Personally after doing all the testing I don't ever recommend anyone running a 20 teeth ever again specially if you are planning on doing any road trip. Not only it is inadequate but also will make your CHT go up trying to achieve a reasonable cruising speed.

I got my new best of 66 mph (GPS) at 7600 rpms in 4th with the 22 teeth. I couple of days ago I was doing 64 mph at 8000 rpm and on another day I reached 8170 rpms but I did not had the GPS. This is on a new Malossi sport(2 piston rings 177cc aluminum kit, 26/26 carb and SIP SR3.

This is a great kit if you have the right gearing. I am going to buy a Cosa clutch style 21 teeth and re-do the test. This current clutch feels stiff and was slightly slipping. Here are two runs that I just did, very consistent one of the other.

Ohh how i LOVE gearing..

Did you try other calculators?
Eg the .fr version

I'd say it's impossible to make gearing decisions solely on charts. They can be helpful, but there is no substitute to your ass on the seat to give you real feedback. A good example is the 200 gearing. The chart doesn't reveal 3rd to 4th shifting being less than snappy.

I only have experience riding 2 engines; a 187 with a 22/68 gear ratio and a 200 with the stock gearing. When looking at charts, I have 2 points of comparison. Beyond that, setting up a gearbox comes down to trial and error and success depends a lot on rider preference.

This thread is a perfect example of what George Box was referring to when he wrote, "All models are wrong. Some models are useful."

Taking a look at my own tools for this stuff, for my P200 I calculate an overall 4th gear ratio of 4.71 versus 4.69 on ScooterHelp. That translates to one MPH at 6K RPM's in 4th gear (I calc 64MPH vs sh's 65MPH).

Depending on who you ask, a 3.5x10 is either 1307mm or 1357mm in diameter. I use 1357 myself, because it matches my observations. If you use 1307, you'll estimate a speed that's 2 MPH slower (62 vs. 64 MPH)

For anyone who's not already building and/or running their own suite of engineering tools, that math is going to be just fine for solving basic questions like, "Will a short 4th be enough to close the gap from 3rd to 4th?"

I didn't build my own tools because I don't trust the online options. I built my own tools to consolidate the various models I like to use, plus having them in spreadsheets allows me to save them for each scoot and refer back when necessary (like just now, when I looked up my P200 motor's gear ratios).

This circumference thing. Depending on what tyre pressures you like and how fat the rider is, changes the radius, which changes everything.
The working radius is the hub centre nut to the tarmac, with the rider and on, no stand and feet up. As it would be when riding (hard to measure). When using this radius dimension and calculating the circumference the gear calculator speed becomes exactly correct.

^^ Thanks for your inputs and feedback guys. I started having hesitations from the very beginning. Recently I took my time to remove the clutch just to verify the clutch cog because things never added up. Indeed I was correct, I had a shorter 20/68 on my 05 PX150. I used the charts many times, all the configurations and things never added up, the chart and the comments of the late EFL being a 21/68 wasn't correct. I used the two GPSs and 2 tachs simultaneously and I recorded increments(speed and rpms).

I came to the conclusion that the charts from scooter help are useful on gear ratios and as a vague reference but they are not accurate. Credits to the inventor of the charts, my wild guess is that a GPS was not used and also a tire circumference can make a difference. the problem that we have on this forum is that not that many people actually use the GPS. A lot of people read out of the speedometer and that gives you a complete false sense of speed. Many people will tell you" I can cruise all day at 60-65 mph". 60-65 mph on my speedometer is actually 51-55 GPS.

Last week I ordered a 21 Clutch Cog. I already did the testing on the 20/68, 22/68 and now I have a 21/68 on hand but not installed. My initial impression on the 20 vs the 22 cog is that 20 is way too short and runs out of steam too quick in the city and is not good at all for hwy. The 22 cog is slightly less peppy on acceleration but brings your CHT down significantly. You can cruise much better on the hwy with the 22 cog. I got the 20/28 at 8170 rpms but only 64 mph on a Malossi aluminum 177. I can do 66mph on the 22/68 at 7600 rpms.

I have no doubt in my mind that the 21 cog will fill in the gap between top end speed and great acceleration.

Scooterhelp is outdated on almost everything. It's OK as a starting point…

Try this if you haven't already…

http://gearingcalc.free.fr/

I have seen the French version. It is neat, I only understand a couple of words but I haven't spent much time on it messing with the numbers. I am sort of creating my own charts based on the data that I have.

One thing very interesting that I found though is the fact that there is also a percentage error even using your own GPS and tach. Let me explain:

Let's just say that a 05 PX150 does 60mph@6000mph in 4th (this is just an example). So based on this you would pick an additional 1mph per 100 rpms right? so far so good, but, what I found during my recent testing (60-70 combined passes) is that in real testing my 05 PX150 would do 8100 rpms but only achieve 64 mph on the stock 20 cog clutch so now watch this:

8100 rpms divided by 64= 1mph per 126 rpms. When you are tucked down trying to go from 64 to 65 mph you will see 64 mph at 7975 rpms but you might not see the 65 mph even when you are at 8200 rpms.

What I am trying to say is that even 1 mph can cover 126 rpms down or 126 rpms up on the tachometer. The other day I was trying to get my personal best record on the PX 150 and I was tucked down and I was at 66 mph and the rpms kept going up slowly but I never saw the 67 mph. I went easily over 200 rpms above from when I achieve my 66 MPH but I never saw 67 mph. That is exactly what I was trying to explain you.

Next time you drive your car look at your tachometer and your speed. Your tach increments are most likely 200 rpms per line on the tachometer. When you are on the hwy you are ie. at 75 mph at 3000rpms but 3000 is like 2920rpm or is like 3060 rpms but you are just seeing a fat tach needle hovering above the 3000 rpms. That is what happened to me when I did the speed/rpms testing, you could be reading 66 mph but your tach could be at 7975 rpms and at 8200 and still be reading 66 mph.

To prove what I am saying I would have to record the numbers on slow motion.

i like that one mostly because it gives the tooth count so I can plug them into my spreadsheet.

I also put in the power output curve, wind resistance and incline.

Is your clutch slipping? That'd do that.