Comparing bananas and lemons - Part 3 : Speed

 

Yes I know, I seem to be plugging Enfield’s in the previous posts (and the ‘busa) but hey, you do the math and see for yourself!

Anyway, I found this “speed trap” formula, given weight and power, for estimating quarter mile times and speeds - It’s surprisingly accurate:

http://www.stealth316.com/2-calc-hp-et-mph.htm

I used the Patrick Hale formulas and the numbers come to within a few percent of real world test reports that are found on the net.

Speeds in KM/h

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Hero Honda CD100	7.5	110	185	6.225	94.24	24.73
Pulsar DTSI 220	21	148	223	17.43	124.46	18.68
Karizma ZMR	17.6	159	234	14.608	115.56	20.13
CBR 250	26.4	162	237	21.912	131.55	17.66
Honda CB750	67	218	293	55.61	166.79	13.89
Suzuki Hayabusa	190	242	317	157.7	229.23	10.08

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Diesel bullet	7.5	185	260	5.625	81.46	28.66
Std 500	22	185	260	16	115.02	20.23
Std 350	18	180	255	12	105.27	22.12
Lightning 535	26	185	260	20	123.80	18.78
Enfield CL500	27.2	185	260	21.2	126.21	18.41
ACE Fireball	42	185	260	36	150.31	15.44
Constellation	51	190	265	45	160.78	14.42
Interceptor	56	190	265	50	166.47	13.92

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
BSA Goldstar	42	175	250	36	152.26	15.23
Velocette Venom	41	177	252	35	150.46	15.42
Triumph 650 twin	46	180	255	40	156.62	14.81
Norton 650SS	49	198	273	43	156.84	14.79
Vincent 1000	55	227	302	49	158.38	14.64

Model	HP	Dry wt	Wt+75KG	RWHP	QM spd	QM time
Jawa 250	12	135	210	9	102.07	22.82
Yezdi Roadking	16	135	210	13	115.24	20.19
Jawa 350	23	168	243	20	126.60	18.36
Yamaha RX100	11.5	103	178	8.5	105.78	22.01
Yamaha RX135	14	103	178	11	115.17	20.20
Suzuki Shogun	13.8	104	179	10.8	114.27	20.36
Yamaha RD350	30.5	143	218	26.5	143.98	16.12
Maico 760	43	115	190	34.4	164.21	14.12

Conclusions?

Most bikes will top out after ¼ mile, so common claims of top speeds are greatly exaggerated.

These formulas seem to bear out real world experience -from personal experience, I know that my L 535 tops out at around 125 kph, and Jawa 250 at 100 kph or so, and the figures for the RX100 and DTSI 220 also seem to be on the money. Some also agree with gearing and tire-circumference calculations as seen on www.gearingcommander.com


It is well likely that some of the more powerful bikes with continue to accelerate beyond the quarter mile mark, since they are not yet at peak power RPM, but most of the smaller bikes are maxed out here.

Claims of 144 km/h for the DTSI 220  as per the advertisements (as the worlds fastest Indian) and excess of 160 km/h for the CBR 250R are quite unbelievable.

One key point is that a bike has to be geared such that it hits the top speed at peak power RPM in top gear.Peak power RPM and peak RPM are two different things entirely. 

On the road, in top gear, no bike will cross its peak power RPM - it stands to reason - If the bike is geared to reach top speed after or before peak power, the engine it rotating too fast or too slow, and producing less power than it could. Neither is ideal.

Bikes like the Hayabusa may differ in this regard because they are often rev limited and under geared - Meaning if it were allowed, it could rev higher than the limit and produce more power.


Many manufacturers will slyly use redline RPMs, calculate top speed based on the gearing, and put that in the specifications. Speedometers are notoriously inaccurate, even digital ones. Civilian GPS units seem to have anecdotal evidence of gross inaccuracy. Radar guns are also suspect.

The only accurate way to measure top speed that I can think of, is to record a video while driving full tilt, between two milestones. Road milestones will probably be accurate to within a couple of meters, and the timer in handy cams is digital, and has no measurable timing error. 

So take that "How fast does your bike go?" thread on your motorcycle forum with a tablespoon or two of salt. Even a camera shot of a speedometer is not valid evidence.

Let's go on and look at efficiencies in the next part of this series

Comparing bananas and lemons - Part 4 : Efficiency

Lets look at mileage figures now – We will use kmpl * hp as the metric for both engine and wheel horsepower values respectively, so we have engine efficiency and vehicle efficiency

Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Hero Honda CD100	7.5	6.225	75.00	0.466	0.562
Pulsar DTSI 220	21	17.43	40.00	0.697	0.84
Karizma ZMR	17.6	14.608	45.00	0.657	0.792
CBR 250	26.4	21.912	30.00	0.657	0.792
Honda CB750	67	55.61	14.36	0.798	0.962
Suzuki Hayabusa	190	157.7	13.6	2.144	2.58
Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Diesel bullet	7.5	5.625	40.00	0.225	0.3
Std 500	22	16	28.00	0.448	0.616
Std 350	18	12	35.00	0.42	0.63
Lightning 535	26	20	24.00	0.48	0.624
Enfield CL500	27.2	21.2	28.00	0.593	0.761
ACE Fireball bullet	37	31	28.72	0.890	1.062
Enfield Interceptor	56	50	16.41	0.820	0.918
Model	HP	RWHP	KMPL	Wheel Eff	Eng Eff
Jawa 250	12	9	35.00	0.315	0.42
Yezdi Roadking	16	13	35.00	0.455	0.56
Yamaha RX100	11.5	8.5	35.00	0.297	0.40
Yamaha RX135	14	11	35.00	0.385	0.49
Suzuki Shogun	13.8	10.8	35.00	0.378	0.48
Yamaha RD350	30.5	26.5	16.00	0.424	0.49
Maico 760	43	34.4	8.00	0.275	0.34

These numbers are self explanatory – no doubt it’s a meaningless metric because km/l is not measured while running at peak power, but the relative numbers between bikes will remain more or less similar.

The Hayabusa makes amazing amounts of power for a liter of petrol, and the Fireball impresses too, despite being based on an antiquated OHV Enfield engine

Summary

• New technology is not always better, whatever metric you choose - except for real…
• …rocket science (Hayabusa class bikes) , which will win hands down on any contest, except where rockets cannot be ridden.
• The legendary Brit super bikes are still way ahead of today's "hoi polloi" bikes.
• Two strokes are generally very bad on almost all metric.
• There is no substitute for wheel horsepower, raw displacement, or a skinny rider!
• The RD350 is a winner when it comes to two strokes, but even it pales in front of the Maico 760
• Enfield's are a class apart on what they do best - pull like a tractor.
• If you ride Enfield's, get a Fireball, it's as close to rocket science as you can get while maintaining its pedigree.