Modern Vespa

Test riding a px I not long got and I noticed the speed is showing lower than the speed I'm doing. It will show 25mph but I reckon I'm doing 35.

We've all been there. There are lies, damn lies, and Vespa speedos.

I know they are out by a couple of mph give or take but this one is out by around 10mph

That's actually pretty good for a Vespa speedo.

Yeah, but don't they normally read high, not low?

Unfortunately the Vespa speedometers have huge discrepancies. My PX150 shows about 10mph above what I am actually doing. My P200E speedometer shows the opposite 10MPH below the real speed. I started relying on GPS reading.

Often PX ones are exactly correct in the middle near 40mph. Yet way under at 20mph and way over by 60mph. About as useful as a stopped clock.

I've never had one what's low by 10 mph normally it's out by a couple. I will fit my phone on it to get the speed then mark it on the clock

According to Steve at Speedoking, P series speedos are 5-8? mph lower from the factory. But with old speedos many things can cause inaccuracy; worn or kinked cable, old lube and grime, chewed up gear.

i've always taken a lot of pride of having original, complete, working Veglia and VDO speedometers on my bikes. I love the early split window odometer models.

That being said, I pay about as much attention to the MPH/KMH needle as i do the markings on the selector side of the headset. . . . going down the road.

Have you disconnected the drive at the speedo and put a few drops of oil on the cable? Ideally remove it at the hub then you can flush the cable with clean oil. Works for me on lots of classics that were either slow or swinging erratically ( getting stuck then freed).

My VNA Allstate's starts at 10mph. That's where the needle sits when bottomed out. So I already know it'll be at least 10mph slower. I rarely look at the needle though. Just go along with whatever the traffic is doing,

Mine has been on 20 for the past 20years

I had the hub off to find it was clogged up so I cleaned it up and sprayed it today I will put it all back together tomorrow. The speedo plaster gear was no good as well.

that would do it, for sure

Vespa speedo gears will deform like that (or worse) if you just think about them too hard.

I've never understood the logic behind the design.

if it weren't easy to deform it might lock the front wheel....

That's legit. Still seems like they erred more than a bit on the side of caution, though.

When you rebuild the front wheel, make sure to install the wheel first, and the plastic cog last. Otherwise you'll have to replace the cog again.

They made the cog fragile because other parts on the speedo circuit (speedo itself, cable, front hub) are more expensive and hard to repair. If something goes wrong with any of the other parts, the cog is the sacrificial lamb that keeps the other parts intact.

I've put the hub back on after cleaning it up and spraying it and I installed the plastic cog and cable. I span the front wheel around to see if the it's working on the clock but there's no movement on the clock. It's doing my head in now 😆 I will have it apart tomorrow again.

Spinning by hand might not be enough to show

Yeah, typically you have to spin it with your foot while you keep an eye on the speedo, or drive off to pick up enough speed to move the needle.

Ok i will take it out for a spin hopefully it's working

I've did a little test run and it's not working. I've taken the cog out and found it's abit damaged. I put a drill on the end of the cable to see if the clock moves with it does. The cable seems ok and the clock works. That's two cogs it's damaged now. I've replaced a couple of the years and I've never had this problem

You might be doing up the little bolt too tight. Plenty of white grease. Put a long matchstick in the gear to check it works. Leave the bolt loose until the cable is in.

I saw a video from Scooter West. They install the cog first, the wiggle the wheel hub in to feel it mesh.

I've done it both ways but still don't get much mileage out of the plastic gear.

Tested mine out of curiosity when I managed to master technology of the cell phone and found a GPS app and said at 49mph I was doing 59mph made me happy but my Chinese thing called a Lambretta Lampshade whatever the model is said 60 mph and was doing 45mph 😊