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Zwift on a budget / speed sensor only
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I am interested in beginning Zwift now that the weather is beginning to limit outdoor riding and I'm getting tired of re-watching the same Youtube videos while on the trainer, However, I do not have a smart trainer, power meter, or designated set up space. Instead, I would be backing the car out of the garage and setting up my fluid trainer and computer for each workout. The only thing I am missing to get started is an appropriate bluetooth / ANT+ speed sensor.

I am interested in hearing feedback from others who are currently on Zwift using just a speed sensor versus power meter and/or smart trainer. What has been your experience so far with the speed sensor, things you have liked and disliked? What speed sensor would you recommend?

I do all my workouts early in the morning so I would not anticipate doing any group rides or races. Just hoping to change up the way I spend my time on the trainer and make it more engaging/productive.
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Re: Zwift on a budget / speed sensor only [Dallcro] [ In reply to ]
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When I first started using Zwift, I used just a speed sensor and zPower(that's what zwift calls turning speed to power). The speed sensor isn't really that important as long as it's consistent and accurate, and I feel like most of them are. I used the wahoo one. The more important element is the type of trainer you have and whether or not Zwift has a power curve for it. You can check here under classic trainers: https://zwift.com/hardware#ready

I would say that training with zPower works fine, the only caveat being that you need to be consistent in your setup (ie tire pressure, tension tightness, etc) so that your using consistent readings.

edit: I would also add, in addition to the speed sensor, you need an ANT dongle for your computer (you didn't say if you had one or not), this enables the speed sensor on the bike to communicate with the computer/zwift.
Last edited by: MRid: Sep 23, 18 5:06
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Re: Zwift on a budget / speed sensor only [Dallcro] [ In reply to ]
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Sometimes I forget to charge my power meter head unit and it shuts down mid zwift ride. I just switch over to the speed sensor and it's close enough that I can continue. All the functionality works great. I think you may need to be in tune with your level of exertion and be mindful of that. Maybe look at your heart rate a little more. All that said, accuracy will likely depend on the quality of your trainer and if zwift has it in it's list. I have a Kinetic Road Machine.

I have a garmin speed sensor on the rear hub. I like it because it communicates with my 920. It doesn't need a wire and or head unit because it communicates directly with my watch.

This is the Ant + dongle I use on my laptop https://www.amazon.com/...garmin+ant+stick+usb

This is the speed sensor and cadence sensor combo I had prior to my power meter setup https://www.amazon.com/...in+speed+sensor+bike
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Re: Zwift on a budget / speed sensor only [Dallcro] [ In reply to ]
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I used Trainerroad with their virtual power for a year before investing in a power meter and didn't have any complaints. Zwift should be pretty similar. It depends on the trainer, but a good fluid trainer should be pretty consistent in power numbers if you stay on top of using the same tire pressure and screw it down the same number of turns each time. I like the Wahoo RPM Speed sensor, pick up the Cadence sensor too if you can swing it.
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Re: Zwift on a budget / speed sensor only [Sikedsyko] [ In reply to ]
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I just ordered the Wahoo speed sensor, ant + stick and cable from MEC. I have an older Taxc Flow (2004?). I'm curious to compare power readings.

It's a Good life if you don't Weaken!
My Mom 1922-2004
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Re: Zwift on a budget / speed sensor only [Dallcro] [ In reply to ]
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I would say it depends on which trainer you have; not only if it is zPower compatible but what peoples' experiences with it are. Even better, borrow a power meter for a day if you can and test your trainer for drift as it heats up.

I was using speed sensor only with a Cyclops Fluid2 trainer and it was challenging and frustrating. This was on Zwift as well as Trainerroad. I ended up getting a Stages power meter and immediately saw why. The issue was resistance drift as the trainer warmed up. As an example, here are two ramp tests, one with speed sensor and one with stages:





In the second one, you can see I held speed pretty much constant, but as the trainer heated up the resistance increased from ~100 watts to over 350 in 20 minutes of riding. Power starts to level out after a while of hard riding, but the drift makes virtual power difficult for trainerroad intervals, and infuriating for riding on Zwift!

Definitely not saying all trainers are like this, or even all Fluid2s are, but mine was not very good at all for virtual power, and it would be good to know how yours responds.
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Re: Zwift on a budget / speed sensor only [brando] [ In reply to ]
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Wow your Fluid2 is terrible!

I no longer have a Fluid2, but when I was using mine with a powertap wheel at least 7 years ago, the readings from my speed sensor + HRM + powermeter all were super rock steady and super repeatable at all efforts, at all times. The speed power correlation was so exact that it would distinguish power reliably even with 0.5mph differences (the power for 22.0 mph would NEVER come out equal to 22.5, for example.) And the HR data correlated extremely well, within the expected constraints of HR variability.

If you're not doing something wonky, and holding say 20mph steady on the speed sensor and your powermeter reads a 100 watt variance before and after warmup, I would say there's a 100% you have a defective Fluid2 trainer.
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Re: Zwift on a budget / speed sensor only [Dallcro] [ In reply to ]
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I have been using Zwift since the Beta including: ~2 years on a cheap fluid trainer using only a Garmin speed sensor, 8 months on the same cheap trainer with a power meter on the bike, 6 months with a PM and new smart trainer.

As for speed sensor I found it was extremely poorly calibrated but did not prove problematic for my overall experience. I used a Garmin speed sensor and it was very consistent so for training and making progress. Even for group rides and workouts the speed sensor worked great. I would recommend the Garmin if you have an ANT+ dongle as I never had dropouts which would be incredibly irritating. The only downside is that the 'virtual watts' won't be accurate so if you switch to PM on the road then everything needs to be re-calibrated. This really doesn't matter though as if you ever get a PM for racing you can use it Zwift as well. You will see a lot online about PM being much better than speed sensors which is true but only if you are also using power in the rest of your riding or are seriously racing in Zwift.

The difference between the smart trainer and cheap fluid unit is significant but not all good. The 'simulated gradient' feels really really unnatural even when the trainer difficulty is turned way down. They have calibrated the gradient based on relative difference felt by a 75kg at 10km/hr which means the changes in slope between say 0-5% hit you alot harder than they would on the road. 10%+ gradients feel like a wall The ability to use Erg mode is nice(ish) but I often find I fight the trainer because it tries to drops resistance as your cadence increases causing a further increase in cadence and if you slow you cadence to then more resistance kicks in you feel the jolt. I feel like a yo-yo around the target where as I would rather just turn off erg and hit the targets. That is to say using a fluid-trainer won't negatively effect your Zwift experience relative to a high end smart trainer.
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Re: Zwift on a budget / speed sensor only [lightheir] [ In reply to ]
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Same here. I had a CycleOps Jet Fluid Pro and the thing was so consistent that a powermeter never really changed my indoors training. Targeting "240W" instead of "27.5km/h" is functionally the same. Within a tenth of a km/h, it was consistent ride to ride.

ZONE3 - We Last Longer
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Re: Zwift on a budget / speed sensor only [scott8888] [ In reply to ]
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scott8888 wrote:
The difference between the smart trainer and cheap fluid unit is significant but not all good. .


How is the draft feel when latching on? The resistance back off like on the road or does it yoyo also like the hills being unrealistic?

I hear complaints of Zwift races requiring ungodly high power even in the peloton on a flat. Which is crap. Real world even on rollers a big enough group just sucks you along.

Also, are the descents still 100mph weird?

Thinking of trying it, but a few oddities keeping me from buying in.
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Re: Zwift on a budget / speed sensor only [burnthesheep] [ In reply to ]
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You have hit on one of the major misconceptions of how 'smart' smart trainers are. Basically they aren't smart enough for what you are talking about.

The current generation of trainers and trainer apps do not adjust resistance based on speed/wind resistance. They only measure training and work out virtual speed so you can not feel the difference while drafting nor is their a realistic feedback between trainer resistance and increases in speed (you shift for resistance changes the same way you would on a traditional magnetic trainer). So you don't feel anything you just see it on screen which.

This also why gradient difference don't feel real because speed isn't taken into play. In the real world it takes a steep gradient before gravity takes over from wind resistance as the dominant force you feel. So at ~20mph slopes of less than about 5% can be pretty subtly especially if you have decent momentum. Often in the real world you lose a bit of speed but that change in air resistance is enough to overcome the additional gravity. Because Zwift can't simulate the feedback of wind resistance the changes in gradient are equivalent to what you would feel when trying to accelerate from a dead stop at that gradient. And there is no question trying to start on a 10% hill is a hell of lot harder than riding over a 10% hill. Zwift and the others would argue the hill start situation is still 'real life' but it just doesn't feel natural.

As for the descents most trainers can't simulate them and so there is no difference between a flat road and a negative gradient that you can feel. Your virtual rider will accelerate accordingly but its not as though you will spin out. From a training standpoint I like this as your training isn't interrupted by descents but it again really changes the way climbing feels relative to the real world.

As a final note I do understand it is technically possible to have a trainer which does respond its resistance dynamically with speed, drafting, etc. However this level of data transfer requires a solid/cord connection between the trainer and the computer running the software and can't be done wirelessly. Other than the newest Kurt Kinetic trainers most trains lack the USB connections required to make the system work. So in the near future we may see trainers that are much more capable at simulating real world feel.
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Re: Zwift on a budget / speed sensor only [scott8888] [ In reply to ]
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scott8888 wrote:
You have hit on one of the major misconceptions of how 'smart' smart trainers are. Basically they aren't smart enough for what you are talking about.

I really appreciate that feeback!

You could be saving me lots of money. I was under the incorrect assumption that it would do that for you. A primary driver for me wanting one.

I wonder if Zwift would ever partner with things like Wii/Switch, Xbox, Playstation to get a little more computing power behind it in terms of graphics, routes, and improving the experience.

I gather the cost/month is probably already on par with subscriptions to online play services for those boxes.
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Re: Zwift on a budget / speed sensor only [lightheir] [ In reply to ]
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LOL, I'm happy to know that other Fluid2s are solid and reliable! I sent my original Fluid2 back to Cyclops last winter, and this is new replacement. It has a much better feel than the old one, so I may continue to put up with it, or I might see about getting something else. Thanks for your reply.
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Re: Zwift on a budget / speed sensor only [brando] [ In reply to ]
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Thank you everyone for the responses. Maybe I should step up to some P1pedals and go from there....
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Re: Zwift on a budget / speed sensor only [burnthesheep] [ In reply to ]
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You are not buying in. You rent by the month, so you can stop payments.
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