Project 100 (custom enclosed Honda C90 targets 100 mph vmax and 100 km/L FE)

[Patrick]

Originally Posted by Quasimoto

Unsprung weight is all of the motorcycle that is not supported by the suspension, such as the wheels, brakes, tires, etc. Check it out.

Exactly my point. So where's all the unsprung weight he's adding?

[Quasimoto]

Originally Posted by Quasimoto

Actually, you know not of what you speak. Unsprung weight is all of the motorcycle that is not supported by the suspension, such as the wheels, brakes, tires, etc. Check it out.

wheels, brakes, tires, etc

[Patrick]

Originally Posted by Quasimoto

wheels, brakes, tires, etc

You mean in comparison to the original Honda 90 motorcycle? Then yes, there might be some additional weight there. But it might not be all that much. The rims are aluminum instead of steel, same with the swingarm. The brakes are disks instead of drums and might(?) be lighter or about the same. The big difference is probably the tires.

So why do you believe that the additional unsprung weight, if there is any, will prevent him from reaching his goal? Because of the additional rotating mass that has to be accelerated on every takeoff?

[visionary]

Replies
Quasimoto – to be honest, until you mentioned it, I hadn’t put much thought into “unsprung weight”, although it’s a subject I’m very familiar with. My best guess is that of the 45kg increase only 10kg will be unsprung. The bigger (heavier) tyres and brakes are only about 5kg per end, and it’s a necessary evil as I must improve the spec to make it suitable to use at the higher speeds. But think of this – why will this significantly impair my ability to reach the 100mph target? Unsprung weight will play no part in straightline performance, its major effects will be shown on “ride and handling” and even then the better tyres brakes and dampers should outperform the stock C90 kit.
Patrick – yeah, the “jackshaft” was an unintended consequence, and I acknowledge that it will reduce my driveline efficiency, but its there now and fabrication has finished with reasonable solution, so I’ll stick with it! But if I posted images and weights, I would be interested in how big you think the losses will be. My stock motor gives (supposedly) 7.5hp, and I’m aiming to up this to 10hp to reach the 100mph target – would another 0.5hp cover the losses?
On the starter thing – I bought the “electric start” version of the C90 already, and I plan to keep the original charging system and battery on the revamped vehicle.

Thanks to both of you for your input! Let me have more, particularly on the aero and body design side. This project is all about how you can take a low power vehicle with a modest top speed and make a “fast & frugal” motorcycle – and aero is the key!

[Patrick]

Originally Posted by visionary

My stock motor gives (supposedly) 7.5hp, and I’m aiming to up this to 10hp to reach the 100mph target – would another 0.5hp cover the losses?

I don't know how much the losses would be, but I'm sure that industrial pillow blocks soak up at least some power. Here's a site with some parts that might help you boost your engine's power output: POWROLL PRODUCTS FOR THE HONDA CT, CL, SL, ATC, S90

[Quasimoto]

Originally Posted by Patrick

You mean in comparison to the original Honda 90 motorcycle? Then yes, there might be some additional weight there. But it might not be all that much. The rims are aluminum instead of steel, same with the swingarm. The brakes are disks instead of drums and might(?) be lighter or about the same. The big difference is probably the tires.

So why do you believe that the additional unsprung weight, if there is any, will prevent him from reaching his goal? Because of the additional rotating mass that has to be accelerated on every takeoff?

Exactly, even with the proper gearing; that small motor will be straining against the additional rotational mass of the large rotors, wheels, and tires.

[Patrick]

The top speed of the motorcycle is what, about 50 mph? So if you gear it to a new top speed of 100 mph your acceleration will be much worse. Add in the additional weight and it will probably be a real dog off the line. Also, first gear is going to be way too tall, so you will probably be slipping the clutch a lot. You might want to throw some kevlar clutch plates in there when you have the engine apart for the hopup so that you don't keep frying the clutch. Barnett Performance Products INDIVIDUAL KEVLAR FRICTION PLATES from RJ SPORT & CYCLE Honda CT90~q=fitaa9013zzisidaa5zz~r=bidaa140zz~

[Quasimoto]

[QUOTE=visionary;258784]Replies
Quasimoto – to be honest, until you mentioned it, I hadn’t put much thought into “unsprung weight”, although it’s a subject I’m very familiar with. My best guess is that of the 45kg increase only 10kg will be unsprung. The bigger (heavier) tyres and brakes are only about 5kg per end, and it’s a necessary evil as I must improve the spec to make it suitable to use at the higher speeds. But think of this – why will this significantly impair my ability to reach the 100mph target? Unsprung weight will play no part in straightline performance, its major effects will be shown on “ride and handling” and even then the better tyres brakes and dampers should outperform the stock C90 kit.

Since the total unsprung weight includes the lower fork legs, front fender, brakes, rotors, axle, wheel, tire; the rear swing arm, brakes, rotors, axle, wheel, and tire; It would be my guess that the total increase would be closer to 36kg unsprung. But of course I don't have the parts to weigh, so am only guessing.

[jkv357]

Originally Posted by Patrick

The top speed of the motorcycle is what, about 50 mph? So if you gear it to a new top speed of 100 mph your acceleration will be much worse. Add in the additional weight and it will probably be a real dog off the line. Also, first gear is going to be way too tall, so you will probably be slipping the clutch a lot. (SNIP)

Getting both reasonable (usable) acceleration and a 100 MPH top-speed at the same time is going to be difficult. Especially with added weight.

I don't know that you would even have the necessary amount of power (with full streamlining) to achieve 100 MPH from that engine without significant modifications - even with proper gearing.

[Patrick]

You could try a Trail 90 (CT90) engine with the dual-range gearbox. It's supposed to have a 1.89:1 ratio to the countershaft when in low range. Then you could gear up the final drive to 2X and achieve the 100 mph top speed while in high range (1:1 ratio). Supposedly these are shiftable "on the fly." You would have an 8-speed gearbox, in effect.