Modern Vespa

Will a 3.5 inch tire on a 10 inch rim from a large frame bike fit on a small frame vespa ?

Front?

Rear?


Comments?

I dunno... maybe with 3.5 your tire can friction with rear shock/exhaust
Ask to Jimmyb he has 3.5x10" on his ET3

you're supposed to run 3.0" by 10" on a smallframe. I think because there's not enough clearance to run 3.5"S side to side. The tire can run on the fork / engine.

so, what do you need to make it work? some kit?

that's a good question...i'm not entirely sure.

The question also arises : does Jimmy run 3.5 tires on a 3.0 rim? or 3.5 rims as well?

Understand that running a non-spec tire width affects your gearing, and will actually give you a higher top speed.

Consider a P200 ..your theoretical speed at 6000rpm with a 3.5 stock tire is 65mph. With a 4" rear tire it's 69mph. Your power doesn't change, so whether or not the engine can push your fat ass up that high is a different story, but the gearing ratios change.

-Eric

my v90 has 3.5. but, i have not taken it apart to see what is different. it is a can of worms i am putting off.

well, i can think of 2 ways it would be :

1) a 3" rim + a 3.5" tire
2) a 3.5" rim and 3.5" tire


On P-series, all a 4" rear tire kit is is a shim that you put inbetween the two halves to convert the rim. Being that there's already a production 3.5" rim out there, i don't see why you would need to shim a 3" one ...but i've never bothered to do that stuff before so it's all new to me.

Forgive my idiocy, but I always thought that a 3.5" x 8" wheel and tire measurement meant that the wheel had an 8" diameter, and a 3.5 inch width, side to side (i.e. between the two sides of the rim). Obviously, with the tire installed the overall diameter would increase according to the height of the sidewall.

How would width affect speed with respect to gearing (apart from greater rolling resistance/friction from a bigger contact patch, perhaps)? An increased diameter, sure, would mean that more distance is travelled per rotation (as the overall circumference is greater) but how would the width of the tire affect anything (apart from handing, force required to turn in and response, etc.)?

I'm a wee bit confused -- am I missing something? Is the 3.5", in fact, not a width measurement? Is it the radius of the rim from the hub or something?

The reason I ask is that one day I'd like to convert my 8" Super 150 to 10" wheels for better handing and safety. Any extra top speed (if there's enough grunt for it) would just be gravy, and the loss in acceleration doesn't bother me...

All stock Vespa rims are 2.10 not 3 or 3.5. Smallframe rims are the same as large frame rims. 3.5 tires on smallframes will rub the stock exhaust and the the cylinder cover in the rear. You can trim the cylinder cover and a different exhuast will help too (poini,pinasco). As for the front some tires rub more than others. A washer behind the rim will help off-set most tires enough.

i have standard size for smallframes

10 series rims w/3-10 rubber

the guy before must have tried 3.5 cause theres weird wear on the rear swing arm.

it is of my opinion that the tire size should stay stock

i really like the way my smally rides

I agree with Jimmy run the 3X10. Just run better tires.

Thanks Matt ..i had forgotten that.


Phaetn - your questioning is based on the fact that you're thinking of the tire AT REST versus IN MOTION.

Think about a tire as it's mounted on the bike. As the engine spins faster, it spreads out such that the DIAMETER of the tire increases.

The wider the tire, the more it's thrown outward, the larger it's diameter is.

At least, this is how it was explained to me.... regardless of the physics involved, i pulled the results from the scooterhelp.com's gearing calculator ( it's in the tuning section ). Compare the speeds of a P200 w/ stock 3.5" tires versys a P200 with a 4" wheel to get the numbers i posted.

-Eric

Thanks for the reply, Eric.

Unless scooter/motorcyle tires are way different than car tires (and I appreciate there are design differences because of speed ratings, lean angles, etc., rather than just camber adjustments and toe-in and toe-out settings in a car that affect grip in various attitudes) I don't really buy the whole tire deformation thing at speed seriously increasing the diameter enough to affect overall velocity by that degree.

I used to do a fair amount of car racing on the track and it just doesn't seem intuitively right to me (albeit the slicks I raced on were very low profile compared to a scooter tire -- still they were MUCH wider -- on the rear they were up to 255/40/17s, if memory serves, though they may well have been wider -- it's been about a decade since I raced); I had them spinning round at a car speed of up to ~240km/h at Watkins Glen and have never once heard of anyone talking about the kind of deformation that would cause such a velocity difference. Again, I appreciate the tire construction is very different (they were Z rated, not J rated! ).

Even if it a scooter tire did go somewhat oblong (remembering that the contact patch has the effect of the weight of the scooter and rider on it), that might still result in roughly the same circumference, just not a round shape; secondly, would a 1/2" extra width seriously weaken things that much across the tire?

Having thought more about it, I think the answer must be that the 4" widths are just a slightly higher profile tire, and hence a greater diameter overall. That would explain why the Scooterhelp calculator shows the difference between a 3.5" width and 4" width in first gear at 1,000 RPM reported as 4mph and 5mph, respectively even when there would be next to no rotational force involved (as opposed to say, at 65 mph). That said, the numbers are identical in second and third at 1,000 RPM, and also in KM/h in first at 1,000, so rounding (a PUN!!) errors must be involved in the table results. Nevertheless, that difference between 4 and 5 mph in first shows something's up with diameter even at that low speed.

In scooter tires we just don't take the profile into account, but only look at the rim size (10") and don't worry about the sidewall height since the increase probably still wouldn't rub. In cars it's expressed as the second number and reflects a ratio of the tire's width (e.g. in a 255/40/17 the sidewall height is 40% of the tire's width of 255, mounted on a 17" rim). In scooter tires we just talk about rim size and width (10" x 4") but the profile isn't mentioned. It makes sense that it gets bigger as the tire gets wider (as happens in cars), but proportionally it's still the same (50% of the width or whatever).

My $0.02, but I'd be happy to be proven wrong.

EDIT:
Looking back over the post, my apologies for the diatribe, and hopefully I don't sound too pedantic... I just like thinking through this stuff... I've been spending my holidays with a 2 and 4 year old all day for weeks and I need to think about something other than juice, snacks, and naps.

I'm seriously thinking of getting [redacted]'s VBC 10" rim and gather since it's not stainless or chromed there aren't issues about casting/cracking, etc. to worry about. That way I wouldn't have to worry about a fork/hub conversion with attendant new drums and pads, though it would look a little funky (all that extra interior rim with the same size hub).

Stumbled upon this old post and took couple of pictures to clear up the difference between 3.00-10 and 3.50-10 Michelin S83 tires.

Here are the two sitting side by side. See the difference?


Becomes lot more obvious when put on the ground side by side


Added width also comes with higher profile. I already have a 1mm spacer between the rear hub but still had a slight rub on the cylinder cowl on my Primavera. Also on hard braking the front wheel rubbed some paint off inside the lower part of the fender due to the higher profile.

Summing it up: Fit 3.00-10 tires on the smallies and leave the 3.50-10 tires for the lardys.

You can fit the wider profile but you need to watch for rub on the clutch cover, etc. Like you mentioned, you can also space it away from the hub a bit if needed. Some brands have different profiles than others.

If you like the fatter look but not the added height / gearing effect, I've run 90/90's on a smallie with no issue. I actually had them left over from a gearing experiment on my old p200, and when my 3.5x10's went bald I decided to go for it.

That's right.

Even if a tire can spin freely on the stand, it has to be taken into consideration that places flex when pushed hard. This is the reason I'm not comfortable with running larger tires on my smallies. Making the adaptation right takes a lot of work and is not worth it in my opinion.

My smallframe came with a 3.5 tire on the front for some unknown reason. I didn't run it like that, but it didn't seem to rub on anything when I was wheeling it around. The split rim was also wider. The smallframe split rims I have are the same narrow width on each side, but the front spit rim it came with has a wide side and a narrow side.

I believe smallies should have the wide and narrow halves on rims. At least all of mine have had them like in this sip image of original rim.
https://www.sip-scootershop.com/en/product/rim-piaggio_81001000

Front does not rub with 3.50-10 when rolling around, but might make a slight rub on the fender when bottoming out the front suspension on tight braking.

Wanted to run 3.5 on my small frame…

I still like the look of it, seems more balanced looking

But when I realised that it would rub on the engine swing arm, it put an end to the idea…

Apparently the SIP engine cases will fit the 3.5, but didn't think about the front bottoming out…

Stiffer front shock would sort it out?

Dunno, since smallies suspension is pretty much all the way bottomed out when braking hard due to it's geometry.

With anti-dive kit 3.50 should be no problem on the front.

Hmm, yes you're right, I'm misremembering. It was actually the odd wheel that had two wide halves and the smallframe had a wide half and a narrow half. I have no idea where that odd wheel came from.

Maybe two wide halves rigged together? If it had two holes for the valve, this would be the case.

I just checked that and it doesn't seem to be the case. It has no stampings or identification markings on it either. The other normal rim has the Piaggio crest stamped into it.

Yeah have the anti dive kit ready to install…

Once the engine is ready

Wide rim looks like Cosa. They were like this from the factory...

Also SS180 & GS160 have the wider symmetrical rims. You can see here how it looks like a standard rim installed backwards.