"125 & 250 Gp" thread in "Motorbike Chat"
How long before they go 4 stroke and how long before a 250cc 4 stroke engine produces the same BPH as a 250 2 stroke ...

How long before they go 4 stroke and how long before a 250cc 4 stroke engine produces the same BPH as a 250 2 stroke engine given that significant develompent of 2 stroke engines ceased some years ago and unlikely to resume?

Does make you wonder what direction they will take.

400 4Ts to replace the 250 class? Would allow race reps to fit into the Japanese street bike market nicely.

But what for the 125s? Maybe 200 or 250 4Ts?

Never, it's not possible.

Don't talk wet boy!
250 2 stroke engines of the early 70's didn't produce as much power as a modern 250F MX bike. And for the majority of that time, both were being developed. In 20yrs time, 2 stroke technology will have been stagnent for 30yrs whereas 4strokes will have gone from strength to strength. whilst I accept the fundamental power advantage the design has, the advantage is slipping.......

True...but you'd still need 400bhp / litre diesels before the 2ts would have to worry.

Assuming MotoGP stays 800cc (750 would have made more sense but lopping a pot off Honda's V5 made 792, what a coincidence) then rechristening the class MotoGP1 would allow 400cc and 200cc bikes to run as MotoGP2 and 3.

Seems fair enough to me.

They could even do it as 400 twins and 200 singles to keep a modular approach which may reduce development costs. Superdreams anyone?

As for bhp if the MGP bikes now are putting out 240bhp that would be 300bhp/litre, or 75bhp from a 250 4T if you assume a linear relationship to capacity. Anyone know how that compares to current 250GP smokers?

---

Never break more than one law at a time, and never carry more grass than you are willing to eat.

I imagine Eddie will know better but the figures of 85-90 horsepower seems to stick in my head for a 250 two stroke.

---

"Its easier to make a fast bike reliable than a reliable bike fast" Soichiro Honda.

Here is the data for the very ugly factory KTM250

Engine Type
two cylinder, 2-stroke
Displacement (cc)
249.6
Bore x Stroke (mm)
2 x 54 / 54.5
Performance
approx. 110 HP / 13.000 rpm
Torque
62 Nm / 12.200 rpm
Compression ratio
9:1
Transmission
6 gears
Carburetor
2 x Keihin 39
Cooling
Liquid cooled
Lubrication
Mixture lubrication
Ignition
CDI

Frame
Aluminium twin spar frame
Suspension front / rear
Öhlins
Brakes front / rear
Brembo Steeldisc
Rims front / rear
Marchesini
Fuel capacity
approx. 23 liters
Weight
101 kg






This is the spec for the Joe public Honda RS250

(sorry the tables don't seem to work)


SPECIFICATIONSPECIFICATIONMODELRS250RTYPEMR02
LENGTH × WIDTH × HEIGHT1954×640×1090mm
WHEELBASE1340mm
GROUND CLEARANCE110mm
SEAT HEIGHT785mm
CASTERANGLE22° 30'
WEIGHT (SEMI DRY)101kg
ENGINELIQUID-COOLED 2-STROKE CRANKCASE REED VALVE 75° V-TWIN
DISPLACEMENT249cm3
BORE AND STROKE54×54.5mm
MAX. POWER OUTPUT67.7kw/12500rpm92PS/12500rpm (UNLEADED HIGH-OCTANE FUEL)MAX.
TORQUE52.3N•m/12000rpm5.33kgf-m/12000rpm (UNLEADED HIGH-OCTANE FUEL)
CARBURETORKEIHIN PJ38 THROTTLE SENSOR-EQUIPPED POWER JET CONTROLCARBURETOR × 2
IGNITION DIGITAL CDI
TRANSMISSION6-SPEED
CLUTCH DRY MULTIPLATE
FUEL TANK CAPACITY21 LITERS
ENGINE OIL CAPACITY0.5 LITERS
FRAME TYPEALUMINUM TWIN-SPAR
BRAKE296mm DUAL FLOATING DISK WITH 4-PISTON CALIPER198mm single disk with single piston caliper
WHEEL3.50-17 6-SPOKE 'U' SECTION CAST MAGNESIUM5.50-17 8-SPOKE 'U' SECTION CAST MAGNESIUM
SUSPENSIONFULLY ADJUSTABLE 41mm INVERTED TELESCOPIC FORKREMOTE RESERVOIR DAMPER

Mmm, so quite a lot of difference in power then.
It was a while ago that I read about them as I think the article was about a TZ250B in about 1992 or so

---

"Its easier to make a fast bike reliable than a reliable bike fast" Soichiro Honda.

Oi!!! I hadn't finished!

I reckon that your figures were about right though.

2002 Yamaha TZ250

General informationModel:Yamaha TZ 250
Year:2002
Displacement:249.00 ccm (15.19 cubic inches)
Engine type:V2Stroke:2Power:86.90 HP (63.4 kW)) @ 12250 RPMTorque:50.00 Nm (5.1 kgf-m or 36.9 ft.lbs) @ 11750 RPMCompression:8.2:1
Bore x stroke:56.0 x 50.7 mm (2.2 x 2.0 inches)
Cooling system:Liquid
Dry weight:104.0 kg (229.3 pounds)
Seat height:773 mm (30.4 inches) If adjustable, lowest setting.
Overall height:1,077 mm (42.4 inches)
Overall length:1,957 mm (77.0 inches)
Overall width:650 mm (25.6 inches)
Ground clearance:119 mm (4.7 inches)
Wheelbase:1,345 mm (53.0 inches)Chassis and dimensions
Front suspension travel:110 mm (4.3 inches)
Rear suspension travel:113 mm (4.4 inches)
Front tyre dimensions:120/60-R17
Rear tyre dimensions:165/55-R17
Front brakes:Dual disc
Front brakes diameter:298 mm (11.7 inches)
Rear brakes:Single disc
Rear brakes diameter:185 mm (7.3 inches)Speed and acceleration
Power/weight ratio:0.8356 HP/kg

If I recall rightly - Max Onion Bhajis last Chesterfield Aprilia was the first 250 to kick out over 100hp. That was absolutely ages ago in racing terms...

An equivalent 4t would really need to be 500cc at least, and I think the costs and development would rule it out for 80% of the teams currently involved.

Why mess with a working formula?

Simple answer to that one...


Honda don't like it

---

"Its easier to make a fast bike reliable than a reliable bike fast" Soichiro Honda.

Julian and Toby were discussing the proposed changes on Eurosport yesterday. They mentioned that Honda only built eleven TZ250s in the last year and don't want to build any more. Only Aprilia and KTM want to carry on with the 250s. Something to do with their not liking the idea put forward of a 620-640cc IL4 4T formula to replace the 250s.

Its no surprise aprilia dont like it, is it? i think all four of the jap manufactors would play ball though, maybe kawazaki could win something... hehe

---

CBT - Done / Theory - Done / DAS Booked

Hondas never built a single TZ250

---

"Its easier to make a fast bike reliable than a reliable bike fast" Soichiro Honda.