Vado SL 5.0 - power setting to compensate for bike weight

[John in CA]

I regularly ride my SL 5.0 with a friend who is on an 18lb. road bike. We typically ride up (and then down) a very steep mountain--3,500 vertical feet in 12 miles. I couldn't do it without my Vado, and even using the motor, it's hard work and a great workout. I'm sure my friend works harder than I do, but we were wondering by how much. Is there a way to calculate what power setting on the Vado will compensate for the weight of the bike, and the difference in the weight of the Vado and my friend's 18lb bike? I weigh about 215lb. I'm sure the lowest gear on my friend's road bike is an important variable, and I don't have that information. Perhaps there is a rough estimate for a Vado setting that "neutralizes" the 18lb difference between the Vado (35lb) and the road bike (18lb).

Thanks for any insights.

 

[Stefan Mikes]

I might think the main difference between you two is the leg power and body weight You did not say what the body weight of your friend was.
What is the approximate speed he does the climb at? I might come up with a theoretical calculation.

 

[Jeremy McCreary]

Can't help with the Vado power settings, but here's how to quantify the extra power you're losing to extra total weight. Once you have that number in Watts, the Vado gurus can help you dial in the compensating assist.

The 3 main resistances in cycling on smooth pavement are air, rolling, and slope. Only the latter 2 depend on weight, and total weight W (bike+rider+cargo) is what counts. Unlike air resistance, neither depends on speed.

Recall that weight is a downward force given by

W = M g,

where W is in Newtons, M is the mass reported by a scale in kg, and g = 9.81 m/s² is the acceleration of gravity.

To a good approximation on grades up to ~15% or so, the slope resistance you're fighting is

Rs = W s / 100%

where Rs is in Newtons, and s is the percent grade.

The rolling resistance is

Rr = W Cr,

where Rr is in Newtons, and Cr is the coefficient of rolling resistance. Wilson and Schmidt, Bicycling Science, gives Cr = 0.006 for a typical commuter and Cr = 0.004 for a typical touring road bike. The latter seems reasonable for you and your friend.

So the total weight-dependent resistance is

Rw = Rs + Rr = W (s + Cr),

In effect, your rolling resistance is equivalent to adding a constant 0.4% grade to every part of every ride.

The power in Watts lost to Rw is

Pw = Rw Vg = W (s + Cr) Vg,

where Vg is your ground speed in m/s.

So when you (subscript 1) and your friend (subscipt 2) are riding up the same grade at the same speed on similar tires against the same air resistance, the extra power loss due to your greater total weight alone is just

Pw1 - Pw2 = (W1 - W2) (s + Cr) Vg

Again, once you have this number in Watts, the Vado gurus can help you dial in the compensating assist.

 

[fooferdoggie]

if he had a power meter it would be easy. not sure How it could be done without one. even then you could match watts output and then go from there. maybe just have him ride your bike and play with assist till it feels the same for him?

 

[Stefan Mikes]

Can't help with the Vado power settings, but here's how to quantify the extra power you're losing to extra total weight. Once you have that number in Watts, the Vado gurus can help you dial in the compensating assist.

The 3 main resistances in cycling on smooth pavement are air, rolling, and slope. Only the latter 2 depend on weight, and total weight W (bike+rider+cargo) is what counts. Unlike air resistance, neither depends on speed.

Recall that weight is a downward force given by

W = M g,

where W is in Newtons, M is the mass reported by a scale in kg, and g = 9.81 m/s² is the acceleration of gravity.

To a good approximation on grades up to ~15% or so, the slope resistance you're fighting is

Rs = W s / 100%

where Rs is in Newtons, and s is the percent grade.

The rolling resistance is

Rr = W Cr,

where Rr is in Newtons, and Cr is the coefficient of rolling resistance. Wilson and Schmidt, Bicycling Science, gives Cr = 0.006 for a typical commuter and Cr = 0.004 for a typical touring road bike. The latter seems reasonable for you and your friend.

So the total weight-dependent resistance is

Rw = Rs + Rr = W (s + Cr),

In effect, your rolling resistance is equivalent to adding a constant 0.4% grade to every part of every ride.

The power in Watts lost to Rw is

Pw = Rw Vg = W (s + Cr) Vg,

where Vg is your ground speed in m/s.

So when you (subscript 1) and your friend (subscipt 2) are riding up the same grade at the same speed on similar tires against the same air resistance, the extra power loss due to your greater total weight is just

Pw1 - Pw2 = (W1 - W2) (s + Cr) Vg

Again, once you have this number in Watts, the Vado gurus can help you dial in the compensating assist.

Jeremy, all good and thank you! This is why I asked how much John's friend weighed and at what speed they were expected to climb. You could also have got rid of the rolling assistance in the simplified equation, assuming both were the same.

After we can determine the power demand for both riders, I could be able to specify the relevant assistance for John

P.S. If John's Vado SL 5.0 were the Mastermind version, I would just recommend increasing the assistance with MicroTune until the speed of both riders equalized...

 

[mschwett]

I regularly ride my SL 5.0 with a friend who is on an 18lb. road bike. We typically ride up (and then down) a very steep mountain--3,500 vertical feet in 12 miles. I couldn't do it without my Vado, and even using the motor, it's hard work and a great workout. I'm sure my friend works harder than I do, but we were wondering by how much. Is there a way to calculate what power setting on the Vado will compensate for the weight of the bike, and the difference in the weight of the Vado and my friend's 18lb bike? I weigh about 215lb. I'm sure the lowest gear on my friend's road bike is an important variable, and I don't have that information. Perhaps there is a rough estimate for a Vado setting that "neutralizes" the 18lb difference between the Vado (35lb) and the road bike (18lb).

Thanks for any insights.

this question gets asked a lot... and nobody ever likes the answer!

we do need to know how hard you're pedaling, since the amount of work it requires to lift 18lb up a mountain is fixed, but the assistance supplied by the vado SL is proportional to your pedaling input. also not clear exactly how steep the climb is - but let's say it's a sustained 3,500 foot climb at 10%, which is very steep, and pretty unusual for a california road, but possible! at 10% it would take 6.6 miles to go up 3,500 feet, so that's pretty close assuming your 12 miles is a round trip.

here's how much power it takes to carry you and a road bike up that mountain at 5mph - 260 watts.

then let's say you wanted to ride the vado UNPOWERED up that same climb. we'll add 17lb.

it now takes 277w. the difference will be almost completely proportional to weight - the effects of friction and drag are meaningless at these speeds. it's ALL about gravity!!

so, in this particular case, you'd need 18 watts of effective power from the motor to equalize these scenarios. the motor is around 80% efficient, so the power supplied to the motor needs to be 20 watts. in our example, you were pedaling at 260 watts to go that fast, so there really is no assist setting which would produce so little power. a setting of 5/5 would still be too much, but in my experience super low settings like that just produce no power at all - the motor is not designed to go that "slow" as it were.

let's change it around a bit to get closer to what your output probably is. changing the grade to 6% (typical sustained grade of california hill climbs) reduces your contribution on the road bike to get 5mph down to 161w, and you need another 12w (15w at the battery?) to equalize the weight. the 15w is around 10% of your output, so with the vado SL's 2.0x power factor (remember we're using the actual power draw, not the output) that's an assist ratio of 5% still. one caveat here is that the efficiency of the SL motor is likely MUCH MUCH lower than 80% when it's spinning so slow. i've seen charts that show 50%, which would bring the needed setting closer to 10% than 5%.

the conclusion is that based on weight alone, there is no setting low enough to compensate only for the weight of the bike, and nothing more. with a lighter rider and a bigger difference in bike weight, you start to get there. a real world example of this is a local hill (much shorter than yours, but fairly steep in sections) that i rode on my creo sl around 50 times - 25 powered, 25 unpowered, and then another 50 times on my s-works aethos (14lb bike), and the theoretical results very closely matched the predicted results if enough rides were averaged out to neutralize the effects of wind and other random stuff.

your question also didn't really ask about the other differences between the bikes, which jeremy covered, but again, at these speeds and such steep grades, the difference between tires and drivetrain and all that are really really minor. if you use the same tools to look at FLAT ground at speeds above 20mph, you'll find massive differences in power needed to propel a road bike vs a MTB, for example, with bikes like the vado and sl in between.

 

[Stefan Mikes]

there is no setting low enough to compensate only for the weight of the bike

However, a substantial weight difference -- and especially their leg power! -- between two different riders could be compensated

 

[mschwett]

However, a substantial weight difference -- and especially their leg power! -- between two different riders could be compensated

absolutely and let's not also forget that at such slow speeds, even the human effort is unlikely to be efficient with the gearing commonly found on a road bike or a vado. my guess is the hill isn't quite as steep and the speeds not quite as low as my example.

 

[John in CA]

Wow.... thanks guys.

Jeremy... it's been 60+ years since I took high school physics, so I must confess that I didn't follow any of that. (That is physics, right?)

I'm not sure what my friend weighs, but let's say 210lb. As for speed, it varies of course, but I'd say between 5-10mph. I'm 76. My friend is 77 and a life-long biker, with very strong legs. He's willing to push harder than I am.

My bike is 2021 Vado SL 5.0, so no Mastermind. I have my power settings at 40/40, 60/60 and 80/80. For a short section of the ride, 40/40 is enough help. At 60/60, I can keep up with my friend for most of the ride, but there are sections where I have to go to 80/80. For other sections, 80/80 is too much assistance and I overtake him. The closer we get to the summit, the more help I need/want. I aim to work hard without being out of breath or having my quads burn. I have a Range Extender

There are several website that discuss the grade of our ride: Mt. Diablo State Park, Walnut Creek, CA. It seems the average grade is 5.6-6.5%. It is 12 miles one way, 24 miles round-trip. (We park and start the ride 1.5m outside the park.) Here are a couple of sites describing the ride:

Mount Diablo (North Gate Road climb) - Bay Area Mountain Bike Rides

bayarearides.com

Climbing Mt. Diablo - Northgate, CA by bike - cycling data and info

Cycling the most popular bike climb in the Bay Area - Mt. Diablo's North Gate Road - View route map, streetviews, images, slideshows, videos and more for this cycling route to the top of Mt. Diablo - Northgate, CA, USA. All the info (difficulty, distance, altitude gained, elevation, average...

pjammcycling.com

Later today I can post screen shots of the Specialized app (the new one) Ride Data. Maybe that will help you "bike geniuses" guide me.

Many thanks!

John

 

[Stefan Mikes]

John,

There is no need to discuss the difference in the total system weight of you and your friend. It is not significant by percentage. He must be stronger than you.

On my gravel group rides I used 60/60% SL assistance to match average riders (not by any means weak ones!), and to catch up with strong riders I needed SL 80/80%, with occasional bursts to Turbo. That's it.

 

[John in CA]

Thank you, Stefan.

My friend is definitely stronger than I am. And he is willing to push harder and longer than I am.

It seems there is no simple way to determine a power setting that will make a 35 lb bike feel like an 18 lb bike. Too many variables. I'll continue loving my SL 5.0 and perhaps try some different power level combinations.

 

[mschwett]

Wow.... thanks guys.

Jeremy... it's been 60+ years since I took high school physics, so I must confess that I didn't follow any of that. (That is physics, right?)

I'm not sure what my friend weighs, but let's say 210lb. As for speed, it varies of course, but I'd say between 5-10mph. I'm 76. My friend is 77 and a life-long biker, with very strong legs. He's willing to push harder than I am.

My bike is 2021 Vado SL 5.0, so no Mastermind. I have my power settings at 40/40, 60/60 and 80/80. For a short section of the ride, 40/40 is enough help. At 60/60, I can keep up with my friend for most of the ride, but there are sections where I have to go to 80/80. For other sections, 80/80 is too much assistance and I overtake him. The closer we get to the summit, the more help I need/want. I aim to work hard without being out of breath or having my quads burn. I have a Range Extender

There are several website that discuss the grade of our ride: Mt. Diablo State Park, Walnut Creek, CA. It seems the average grade is 5.6-6.5%. It is 12 miles one way, 24 miles round-trip. (We park and start the ride 1.5m outside the park.) Here are a couple of sites describing the ride:

Mount Diablo (North Gate Road climb) - Bay Area Mountain Bike Rides

bayarearides.com

Climbing Mt. Diablo - Northgate, CA by bike - cycling data and info

Cycling the most popular bike climb in the Bay Area - Mt. Diablo's North Gate Road - View route map, streetviews, images, slideshows, videos and more for this cycling route to the top of Mt. Diablo - Northgate, CA, USA. All the info (difficulty, distance, altitude gained, elevation, average...

pjammcycling.com

Later today I can post screen shots of the Specialized app (the new one) Ride Data. Maybe that will help you "bike geniuses" guide me.

Many thanks!

John

yeah, i figured you were talking about diablo. i've climbed that mountain on a bike, it's a great ride. the grade really does average around 6% but depending on which route you take there are some 8-10% stretches. and let's not talk about the very top lol.

but in any case, the answer to your question is pretty simple - the bike represents a 7% weight penalty, which is really all that matters at those very slow climbing speeds. to get 7% more power on an SL bike you need an assist setting 4%. as i said, it doesn't really go that low lol.

this is why i said nobody likes the answer to this question...

 

[John in CA]

@mschwett ..... yikes! You got that right! A power setting of 4% is essentially no assist at all. What this tells me is that my friend is a hell of a lot stronger than I thought, and way, way stronger than I am. His road bike does have a very low gear, including a small front chain ring, but still....

Yes, I am talking about Mt. Diablo, north gate entrance. It's a great ride, with incredible views on a clear day, and more bikes than cars on weekdays. I'm just grateful for my SL 5.0 which gives me access to this ride while still giving me a great workout and a nice reward on the way down. (On every ride, my friend and I see these young guys, dressed in spandex from head to toe, riding incredible road bikes. We'll be trudging up the hill, and they go flying by at 15-20 mph. We remind ourselves that they are half our age and maybe half our weight. Ha.)

 

[mschwett]

i did diablo from south gate earlier this year. it's really a beautiful and unique ride - about the same amount of climbing as going up mt tam, which is much closer to me, but without any downs and back ups, and the scenery is quite different. tam is heavily forested, taking you through redwoods and windy shadowed roads and then you pop out on top for incredible views. diablo just sort of gradually unfolds with views of meadows and rolling hills and the horizon in many directions.

i do think you'll find the gearing make a difference in your OWN power production. it's really very hard to be efficient pedaling so slow, and it's super hard on the knees. two data points: which gearing do you have on your vado, and what is your average speed for a steady climbing section? i had to significantly shorten the shortest gear on my creo sl to get an efficient climbing cadence on most of our local hills and mountains, although i was trying to do it with little or no power, which drops the speed even further.

this is the bike i last rode up there, you can see i left it in the gear it was in most of the way LOL. it is a distant cousin of your vado and my creo. the bike weighs 14lb, i weigh about 180, and i went slow. like you, i really think the SL bikes are incredible for allowing a lot of cycling experiences that would otherwise be left to the very young or very fit, while preserving the ability to work as hard as you feel up to.

 

[John in CA]

@mschwett .... yeah, the south gate ride is gorgeous. I really like that it's got a fairly level section in the middle, compared to the north gate "all up" ride. I have not done Mt. Tam, but I'd like to sometime.

Beautiful bike! Is that an S-Works Aethos? Do I see a Garmin Varia radar? I just got one and love it. I use the app on my iPhone to see approaching cars--very helpful and reduces how often I look in my rearview mirror.

Lastly, I want a 14lb bike, and I want to weigh 180! Haha.

 

[mschwett]

@mschwett .... yeah, the south gate ride is gorgeous. I really like that it's got a fairly level section in the middle, compared to the north gate "all up" ride. I have not done Mt. Tam, but I'd like to sometime.

Beautiful bike! Is that an S-Works Aethos? Do I see a Garmin Varia radar? I just got one and love it. I use the app on my iPhone to see approaching cars--very helpful and reduces how often I look in my rearview mirror.

Lastly, I want a 14lb bike, and I want to weigh 180! Haha.

the garmin varia is a MUST. i almost never ride without it. i use an iphone mini as my "bike computer" and the app i use overlays the garmin radar bar along one side, color coded and with the little car icons moving to and fro. and yes! the bike is an s-works aethos. very understated

 

[John in CA]

the app i use overlays the garmin radar bar along one side, color coded and with the little car icons moving to and fro

I use RideWithGPS and it will add the Garmin radar bar along the side. Since I know where I'm going , I just use RWGPS for ride stats. The iPhone Varia app is a full-screen view of the road behind, and of course gives a nice beep when it detects a car (or bike). Nice. And yes, a MUST.

 

[John in CA]

Mount Diablo:

 

[Jeremy McCreary]

Jeremy... it's been 60+ years since I took high school physics, so I must confess that I didn't follow any of that. (That is physics, right?)

I'm not sure what my friend weighs, but let's say 210lb. As for speed, it varies of course, but I'd say between 5-10mph. I'm 76. My friend is 77 and a life-long biker, with very strong legs. He's willing to push harder than I am.

Understood, but it's not as hard as it might look. The last formula I gave is all you need to get a ballpark estimate of the motor power you need to compensate for your extra total weight. And from various posts here, we now have the necessary data.

The short answer: At 6 mph up a 6% slope, about 17 W.

Showing my work
To end up with power in Watts, easiest to work in metric units. You are rider 1; your friend, rider 2. Technically, the "weights" you gave are actually masses, so I'll rewite the last formula to reflect that:

Pw1 - Pw2 = (M1 - M 2) g (s + Cr) Vg,

where M is total (rider+bike+cargo) mass, g is the acceleration of gravity, s is your average slope, Cr is your coefficient of rolling resistance, and Vg, your average ground speed up the slope. All but the masses are the same for both of you.

Assuming the stated bike masses include all accessories and water,
M1 = 215 + 35 lb = 114 kg
M2 = 210 + 18 lb = 104 kg
M1 - M2 = 114 - 104 = 10 kg

g = 9.81 m/s³
s = 6% / 100% = 0.06
Cr = 0.004
s + Cr = 0.064
Vg = 6 mph = 2.7 m/s

Pw1 - Pw2 = (10 kg) (9.81 m/s²) (0.064) (2.7 m/s) = 17 W

So 17 W is all you need from the Vado motor to compensate for your greater total weight at 6 mph up a 6% slope. At 10 mph up a 10% grade, the extra power would increase to 46 W.

Implications
One important lesson here: Small to moderate differences in weight and rolling resistance translate into pretty small differences in required power on slopes under 5% at speeds under 10 mph.

To be clear, an extra kg can become meaningful on very long rides at higher speeds over steeper terrain. But not so much on typical recreational rides. On the flat, an extra kg means very little at any speed. In that setting, your focus should be on reducing air resistance, not weight.

That said, an extra few kg can make a significant difference in responsiveness — i.e., in acceleration, braking, leaning, steering, and jumping. If you want a really responsive ride, by all means, sweat every kg — especially your own. Otherwise, relax.

 

[John in CA]

@Jeremy McCreary .... thanks again. All of your numbers still intimidate me (haha), but they help me confirm a few things:

1) I will continue to admire my friend's strength and determination in riding up a ~3,900' mountain on a non-electric bike at the age of 77.
2) I will need varying levels of assist for varying grades.
3) I need to lose weight.
4) I will relax and stop worrying about assist levels.