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:
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.
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
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