Scooterotica

We have all heard the stories of 100mph scooters that cruise motorways at 80mph and still return 60mpg on near standard engines, is there a formula that allows you to work out how much bhp/torque you will need to get these speeds.
I did read somewhere you would need 35+bhp to get 100mph but that was on a aprilia site and bikes have 6 gears to keep the revs up

stick with fairy tale books , not many if any , genuine 100mph scooters out there , especially on the road

To double your speed you need 800% more power - So roughly speaking, a genuine 30hp could get you up to 90mph (depending on bulk!), but you'd need 40hp for that next 10mph.

So you can see, after 20hp (80mph) you're looking at lots of expensive modification for little gain in top speed unless you do something significant with weight and aerodynamics.

"Cruising" at 80 mph sounds nice but it would take a very expensive engine to do that. You could always fashion a clip on aerodynamic fairing out of plastic or something. That should be good for at least 5 mph. A tuner in the 60's got 111 mph out of a home tuned SX200 at Monza by doing that.

It's stating the obvious really but tuning is very much a case of ever diminishing returns.

A better carb, exhaust and a mild porting and the improvement over standard is very obvious, doesn't cost the earth and won't compromise reliablity or fuel consumption too much.

Go much further (like buying an RB) and you'll start to break everything else in the engine since it was all designed to work at much lower stress levels and is probably half knackered anyway as its decades old. That means far more expense. It'll also drink fuel like a 70s muscle car.

My mildly tuned Jet will nearly touch 70 on a good day. My mates RB will do 85 in the same ideal conditions but each one of those 15 miles per hour has come at a big price.

i think the 20bhp 17lb of torque is plenty for road use. having been riding my ts1 this weekend for the first time since rebuild torque is the answer to most of our woes on the road.

mbd welded and lowered the exhaust port for extra torque and with a 240cc it now pulls away in 2nd as it used to in 1st with an li 150 box and 17/46 sprockets. it still revs out too.

im no expert just a disatisfied consumer but i have been hunting for the answer for yonks.

i think the answer is the most cc you can get on a plated barrel to avoid the wear, biggest bore and longest stroke to get the same 20bhp 17lb of torque. that way there is power through the range rather than a peak of power giving the same ouput but half the rev range.

rt kit with 71mm piston and 64mm alpha crank is the answer in my opinion. some say they are expensive but they are not if you save going through a dozen other kits before you get there. add a 30mm mikuni with a filter and >44mm< clubman.

so a question for those that do understand the gobledy gook: how is the top speed affected by torque as apposed to bhp?

All good posts so far. And all pretty realistic. The weight and drag are pretty critical as are the gearboxes. A close ratio box helps the motor climb up. How fast do those 125cc gp bikes do? 148mph or something the other day..they must make around 48/50hp. So there is a good example.
Nick, yes the cubes help..but with the lambretta the issue is port area rather than cc. We need a rethink on that.

sitting at 70/80 all day would mean motorway driving, wheres the fun in that ?

You'd get that dress all messy Johnny thats for sure

tony, im still favouring big cc tractor engines that pull anywhere in the rev range. low tune BIG cc.

i know the modern thought is high revs multi port but thats with a zillian speed gearbox that does not need the clutch to go up and down the gears with power valves ect.

tuned scooters go further away from what is needed on the road (in my opinion.... ) as they get harder to ride and need to be revved.

this is ok when at a rally where you we have a different mindset because we think we are the ace face/barry sheen but in leafy french villages there is nothing worse than a noisy chavtastic revvy lambretta.

6LDA 28B is looking to make the lambretta a daily usible scooter that can be used as a motorway/a road mile muncher. the reality is if you want to go somewhere far away then you have to use motorways and a roads....... he already owns or has had bikes that will eat any scooter so I know he hasnt got a race scooter fantasy.

There seems to be more than one definition of fast, a. white knuckle exceleration fast and b. get from a to b in a short amount of time without too much stress, fuel stops or racket fast.

6LDA 28B is looking for option b. (he drives a volvo )

so if you could make a 400cc standard ported lambretta then that would be ideal. 2x 12bhp = 24bhp but thats not an option so im thinking big cc and just a touch of tuning to give good power and torque at 70mph which is where 6LDA 28B and our complaining crew like to be sitting, at 7000 rpm so the fan is cooling enough but not screaming.

i had my road race ts1 with kegra pipe flat out in the outside lane a good few times (when i was 12 stone) in the days when I rode with my ex on a motorbike everywhere. her gpz speedo would be saying 90 so 80 - 85 was realistic. i cant say it was 100% pleasant but we would do luton to wembley at that speed in the outside or middle lane start to finish quite regularly. only 25 miles each way so bearable.

i dont think i want to do it again though, 70 all day is fine and even my humble jet200 (225 rubbish mugello) will do it just if i ride flat to the bars. so 70 - 75 is not unrealistic with a big cc race tour or similar kit.

going from 225 to 240 is more than noticeable so in future i will not be p1551ing about with anything less than 250 - 260

i know you know you stuff tony but i have come to accept that i dont like "tuned" engines as much as i like big engines.

i am the same with bikes, lazy vfr v4 s or triumph triples are my thing. i always gave my mates a run for their money on their gsxrs purely because the grunty bikes were so easy to ride which compensated for my s**t riding style

if 6LDA 28B and most of our chums want to race/play racing then we opt for enduro as there is no scooter in the world that compares to that amout of fun and power in the rawest of conditions.....with the added bonus that you get to see me injure myself on every outing