Kalkhoff Agattu C8 Impulse - one for the hills!

10mph

Esteemed Pedelecer
Dec 13, 2010
349
0
England
Kalkhoff Agattu C8 Impulse - one for the hills!

In short: The new 8 speed Agattu Impulse is definitely better than my 3 speed Agattu with the Panasonic motor on hills, and gives a slightly faster overall average speed on mixed terrain circuit. I am strong enough only to need the higher gears, but an infirm rider looking for just very light pedalling exercise would probably make more use of the lowest gears at lower speeds. It has a neat, light battery which will give excellent range, and ought to provide a 5 year service life. The rest of the bike looks and feels like it will last forever. The comfortable, upright riding position and the low step-through frame suits me perfectly. If I were younger, I might choose a more streamlined riding position, but at the age of 70 I much prefer to sit up so reducing the strain on the body, and the motor easily overcomes any wind resistance.

Background: one year's experience with a Kalkhoff Agattu C3 (Panasonic)
Before describing my test rides of the new Agattu Impuse I will describe my one year's experience of ebiking in order to explain what I need out of an ebike, and the baseline I am judging the new bike against.

One year ago I was experiencing my first ride on my brand new Kalkhoff Agattu which I had chosen because of the reputation of the brand and its Panasonic crank drive for reliability and hill climbing.

The hills I sometimes encounter have slopes up to 13%. However, a lot of my use of the bike in measuring road race running courses is on flatter terrain, and here I just need to be able to comfortably keep up the ideal measuring speed of 10 mph over long distances. I do occasional spurts at higher speed when my desired measuring line takes me across the path of traffic. To save money I chose the 3 speed version for my first e-bike. I had test ridden it on a hill averaging 12%. See Nightingale Lane Test

Ordered in a January Sale, it cost around £1400 with the 25.2v 18Ah Li-ion battery providing 453Wh of energy, which proves to be enough for over 80 miles, if I am frugal in low assist using around 5.5Wh per mile. On maximum assist the range very comfortable exceeds my requirement of 30 miles (enough to measure a hilly marathon) and should continue to do so as the battery degrades. Indeed, to judge from my first year experience this battery is going to last 5 years see my post.

In my travels around the country to measure races I have only ever encountered one hill I could not ride up - in Newborough Forest in Anglesey, where in one place the sandy trail was so steep I had to get help from a fit runner who was showing me the route to push the bike up. I was tired out with riding over sand dunes on a very hot day last summer. Such extremely steep and rough slopes are very much an exception for me.

Kalkhoff Agattu C8 Impulse

As I have explained above, my 3 speed Panasonic Agattu suits me very well. Nevertheless I was curious about how the new “Impulse” system would compare, and I also wanted to try a bike with more gears. So I read with great interest the announcement by 50cycles the arrival of 2012 model Agattu C8 bikes for sale in the UK and their availability for testing. See http://www.50cycles.com/kalkhoff-impulse-ebike-introduction.htm

Last Tuesday I was lucky enough to receive the new Impulse on loan for a few days of testing. Here it is in front of my 3 speed Agattu. The frame has changed slightly with a wider down tube at the front, but with neater welds. Painted white the tube appears wider than it really is: 17.5 cm circumference compared with 15 cm for my bike.

With the battery case being elegantly curved to hug the back mudguard, the overall length of the bike is reduced by 2 cm to 189 cm. The Li-ion battery, 36V 15Ah, is very slightly lighter than the 25V 18Ah battery on my Panasonic Agattu, yet holds 540Wh of energy: some 19% more. A nice improvement is the 3 amp charger which improves the charge time from 10 hours to around 5 or 6 hours. There is a socket on the battery so you can plug in the charger and charge with the battery in situ on the bike.

This page from 50cycles website give more information on the new Impulse system and here is a Kakhoff flyer on the Impulse features(pdf).


I will upload my test data in a second post here.
 

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10mph

Esteemed Pedelecer
Dec 13, 2010
349
0
England
Agattu Impulse C8 Test Data

10 mile circuit with 13% hill

Below I show a typical fastest ride around a 10 mile circuit on my Panasonic Agattu in maximum assist. The overall average speed was 14.6 mph and on the 300m steepest section of the hill which averages 11% and has 100m at 13%, one can see that average about 4.5 mph in bottom gear.

The total climb from 0 miles to the hill top at 3.2 miles is 80m (260 feet). In the steepest section it climbs 33m in 300m

For my first test ride with the Agattu Impulse was over this same circuit I was somewhat tired, having been out for a long ride on the Panasonic the day before. However I managed 15 mph average and more importantly my speed up the hill (in 5th gear) was 5.5 mph, a useful 22% faster than my Panasonic Agattu.


8 Hill Repetitions

My next test was two days later when I was still rather tired after a day on my feet in London and another day spent measuring a hilly race at Highclere castle. I did repetitions of the 300m section of the 13% hill. In the following plot you see my speed against time (not distance). I used each gear in turn from low to high. Before each climb I had a stop to recover from my efforts: short before the first rides, but increasing as I tired over the 8 climbs. The actual climb is highlighted by the red rectangles. The average speed being given on the y-axis and the duration on the x-axis.

The climb times and average powers were:
Gear 1: 188 seconds - 207 watts
Gear 2: 158 seconds – 245 watts
Gear 3: 142 seconds – 273 watts
Gear 4: 140 seconds – 277 watts
Gear 5: 134 seconds – 290 watts
Gear 6: 122 seconds – 318 watts
Gear 7: 130 seconds – 299 watts
Gear 8: 168 seconds – 231 watts

The climb in Gear 6 was fastest at 6mph, the same speed that I had obtained in gear 5 during my initial test 3 days before. The average power I calculated from the time, the 33m height rise, and the total weight rider+bike 120kg. (eg power = 33*9.81*120/122 = 318 watts). This is the “useful” power into the road. The power at the crank wheel end of the chain might be about 10-15% higher when one allows for the rolling resistance of the bike and the rear gears hub and drive chain efficiency.

I was conscious that I was definitely tired when doing these reps with only short periods of recovery. So when well rested 6 hours after a lunch time ride I went out to the hill again, selected 5th gear which I thought would be close to optimum, and managed to climb averaging 9 mph. From the climb time 80 seconds I calculate 486 watts.

With an optimistic assumption for the amount of power from my own pedalling delivered to the road of 120 watts, I calculate that the Impulse motor is capable of bursts 360 watts for at least 80 seconds delivered into the road. If the overall efficiency is 75% then it would be drawing about 500 watts electrical power from the battery. At the end of the sequence of 8 climbs above I felt the motor casing with my cold hands and found it slightly warm – not hot: not much energy is being converted to heat in the motor.

Gear ratios

The crank has 38 teeth, the rear sprocket 21 teeth.

I measured the gearing of the Agattu Impulse by wheeling the bike forward for 1 full rotation of the pedals. Dividing the distance by pi, I obtained the following results:
Gear 1: 26 inch
Gear 2: 32 inch
Gear 3: 37 inch
Gear 4: 41 inch
Gear 5: 46.5 inch
Gear 6: 60 inch
Gear 7: 69 inch
Gear 8: 76 inch

For comparison, my 3 speed Agattu Panasonic is
Gear 1: 44 inch
Gear 2: 60 inch
Gear 3: 81 inch
See http://www.pedelecs.co.uk/forum/electric-bicycles/8218-agattu-gears-where-do-i-connect-ammeter.html

For me, with hills not exceeding 13% gradient gears 1 to 4 on the Impulse would get very little use, even for starting up on a slope. The lower gears could however definitely be of value in the future if I were to encounter steeper hills, or if my leg strength/power output were to deteriorate.

With my present riding strength it would be interesting to have an option changing the crank wheel – rear sprocket ratio of 38/21. Perhaps 38/18, which would for me at least, bring gears 2 and 3 into more frequent use, and would have the beneficial result of reducing cadence in gear 8 at 15.5 mph from the present 65 per minute to 55. Such change should be possible without making the bike illegal, since the assist cut-off speed is presumably governed by the road speed sensor which is installed on the rear wheel.
 

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yselmike

Pedelecer
Sep 6, 2011
129
0
purmerend
I had a walk in town today[ Purmerend ]saw my first Flyer outside a bakers and 20 meters down the road a new impulse8
the kalkhoff looked really cool.
 

funkylyn

Esteemed Pedelecer
Feb 22, 2011
3,172
26
South Shields, Tyne & Wear
Absolutely excellent review.
So, are you going to be treating yourself to a new bike then ? :D

Lynda :)
 

swinnerton

Pedelecer
Aug 1, 2008
29
0
Hi...loved reading your review...my wife and I have just taken delivery of 2 Agattu Impulses to replace Proconects which we've had for over three years. Apart from the usual punctures and routine maintenance they have been excellent and never let us down...batteries still show 5 lights ! We spend a month in Provence every year and the hill top villages are well suited to les velos electrique .We were looking forward to putting a few miles on our new toys this week but woke up this morning to snow !
Regards
Gerry
 

tillson

Esteemed Pedelecer
May 29, 2008
5,145
3,001
Thank you for the well written and interesting review of the Impulse system 10MPH.
 

indalo

Banned
Sep 13, 2009
1,380
1
Herts & Spain
Ditto Tillson's post and I'd be interested to hear a longer-term report on this model in times to come. I have said this before and I don't mind repeating it; IF someone has a need for an electrically-assisted bicycle, then the Agattu is all the ebike that most people will ever need....apart from those for whom it is patently unsuitable!

Indalo
 

Tim

Esteemed Pedelecer
Nov 1, 2006
770
78
London
Great review! Thank you very much, we're very lucky and grateful that you were able to give it such a thorough test. The bike you tested, a Kalkhoff Agattu C8 Impulse 50cm step-thru model, will now be on permanent display and test ride duty in our Richmond showroom.
 

jhruk

Esteemed Pedelecer
May 13, 2009
315
67
Ditto Tillson's post and I'd be interested to hear a longer-term report on this model in times to come. I have said this before and I don't mind repeating it; IF someone has a need for an electrically-assisted bicycle, then the Agattu is all the ebike that most people will ever need....apart from those for whom it is patently unsuitable!

Indalo
atob magazine have tested the Agattu C8 Impulse in their latest (April – No.89) edition - I’ve just read it as a subscriber to the exacteditions version. If you don’t already subscribe I see they are now offering a free pdf download of the whole magazine if you register on their site, although the April edition doesn’t appear on there yet.
 

flecc

Member
Oct 25, 2006
43,913
19,990
Many thanks for an excellent and highly detailed review 10mph. I've felt confident the new Impulse system would acquit itself well and I'm not disappointed.
 

10mph

Esteemed Pedelecer
Dec 13, 2010
349
0
England
Thanks to all for the comments, and jhruk thanks for the link to the A to B magazine review. I will keep my eyes peeled for a free download of issue no 89. I had searched on Google for an English language review of the Agattu Impulse and not found one. There are various reports in German, but I am limited to using Google translate so can't get an exact account of what is being said.

I have just reposted a profile of the steepest section of the 13% hill which I used in my test rides.

The 300 metre section of the hill which I used for the 8 hill repetitions was from the 25 metre to the 325 metre points on this profile.
 

tillson

Esteemed Pedelecer
May 29, 2008
5,145
3,001
A to B seemed to like this bike in their review. The battery capacity and range are also impressive. I'm sure that it will sell well.
 

Tim

Esteemed Pedelecer
Nov 1, 2006
770
78
London
A to B seemed to like this bike in their review. The battery capacity and range are also impressive. I'm sure that it will sell well.
We have a couple of model variations available to test ride in both Richmond and Loughborough. Agattu C8 Impulse 50cm (step-thru) and Agattu C11 Impulse 55cm (crossbar), with an Agattu C8 HS Impulse (crossbar with hydraulic brakes, which we hear has been the best seller in Germany this season) to follow soon. Kalkhoff have just completed a massive production run on these models, so there'll be more to come. There are some XXLs in stock too - in all black



I really should do a ride report of the C11 soon, I've been using it all the time this Spring, it really gallops along, very lively.
 

tillson

Esteemed Pedelecer
May 29, 2008
5,145
3,001
We have a couple of model variations available to test ride in both Richmond and Loughborough. Agattu C8 Impulse 50cm (step-thru) and Agattu C11 Impulse 55cm (crossbar), with an Agattu C8 HS Impulse (crossbar with hydraulic brakes, which we hear has been the best seller in Germany this season) to follow soon. Kalkhoff have just completed a massive production run on these models, so there'll be more to come. There are some XXLs in stock too - in all black



I really should do a ride report of the C11 soon, I've been using it all the time this Spring, it really gallops along, very lively.
I'm tempted to drop in the next time that I am in Loughborough and have a little go. It could leave me with a dilemma.
 

NRG

Esteemed Pedelecer
Oct 6, 2009
2,593
10
Lovely looking bike Tim, do you do trade in's!
 

eddieo

Banned
Jul 7, 2008
5,070
5
These bikes have not been without problems, I suggest anyone who is serious, have a read over on German Pedelec forum. New Panasonic drive better and Bosch better weight, performance and more modern looking...

one chap with both impulse and bosch bike commented that range of impulse was worse even with bigger 11Ah battery (on same leisure route)

Lets not get carried away with the hype....you really need to try the different drives and see what is what
 
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flecc

Member
Oct 25, 2006
43,913
19,990
I prefer the Impulse transmission to the Panasonic one. Like the Bosch, it's motor drives the chainwheel, doing away with the problems relating to the small motor sprocket and jockey wheel(s). Better with hub gears even and very much better with derailleurs.

The 11 Ah battery is the small Impulse option which 50cycles aren't offering anyway, they are bringing them all in with the 15 Ah one.
 

tangent

Esteemed Pedelecer
Mar 7, 2010
299
0
Thanks you for posting a very informative review.

As an owner of a Panasonic system bike, I do like the idea of separating power assistance from cadence. I am curious about the power restriction though. How is the speed actually measured if not by cadence? e.g. is it measured using a sensor/magnet combination on the rear wheel, or some other mechanism? The other question I have is how is the power reduced as the cutoff limit is approached? Is it in steps and if so, at what speed does the power step down start? Does the power reduction seem very sudden, or is it gentle like the Panasonic system?

One other question! How does the motor noise compare with the Panasonic based Agattu?
 
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flecc

Member
Oct 25, 2006
43,913
19,990
Pending 10mph responding, the speed control is by a magnetic sensor on the rear wheel. No quoted figures for the power phase down, but this chart if accurate indicates it's from roughly 12 mph and gentle (click to enlarge):

Impulse power gradient.jpg
 

tangent

Esteemed Pedelecer
Mar 7, 2010
299
0
That power assist curve does look gentle. Possibly a bit too gentle if it starts to power down at only 12mph. Still better than a sudden plummet though. I wonder what the curve would look like if the magnet on the rear wheel were to fall off?