Renn 575 Disc: Initial Thoughts

In a attempts to gain “free speed”, if there is such a thing, I decided to purchase a disc wheel with the notion that a company called Renn makes a very good product much less expensive than some of the more popular brands (HED, Zipp, etc). Found a good deal online and finally purchased a Renn 575 Disc Rear Wheel. Aero helmet will be next, but only when I find a good deal or a used one because, well, I’ve spent quite a bit of money on gear and race fees this year – will probably wait until winter to purchase.

Bike Set-up

Specialized Transition Comp w/Ultegra set-up. Renn 575 Disc rear wheel. Normal wheel up front – Mavic Cosmic Elite.

Maiden Voyage

The ride was smooth, much smoother than normal. Material in the disc seems to absorb road vibration and noise very well. In fact, I rather enjoyed it, though at times I wondered if the tire was flat because of how different it felt and sounded.

Speaking of sound, I was surprised to not hear the common whir of the disc. Mind you, it was there, it’s just that when down in aero, the rush of wind over powers the sound of the disc cutting through the air. Only could I hear it if I tilted my head so that my ear aligned. But it seems many other people heard because, as I flew past, they would look – normally they would not.

Performance-wise whether there is a benefit is difficult to say. I did a loop I normally do, but since I look at averages rather than actual numbers, I am not entirely sure. My average speed for this loop seems about the same. Again, still not sure. Making a comparison on performance is even tougher because I did this ride on legs still tired from running a marathon only days earlier. So although I have not ridden in several days, my legs felt a bit sluggish, though again, it’s hard to say because the wheel seemed to be “heavier”.

Speaking of heavy, the wheel at times seems heavy. Going up Sagamore Hill, a hill with average grade I use for repeats when I ride mornings, the wheel seemed heavy. My average pace up the hill *seemed* slower. It’s times like this when I wish I were a number junky, because then I’d know exactly where it stood compared to without the disc. But it seemed slower going up the hill. And since it seemed slower, I tried to exert more energy.

Down hills and flats is where the wheel seemed to gain performance. Although it wasn’t entirely noticeable, when searching for positive results, I could find them – but again, often when you go searching for something, you’ll find it even if it really isn’t there (pure psychology).

This morning there was a nice gradual down hill stretch for a mile that then turns into a fairly flat-to-one or two rollers for another 2 miles where I typically race cars. On good days I could keep up. Today I had to brake at times so that I didn’t overtake the car in front. I felt fast, but not all that different than normal. Again, if I were a number junky, I might be able to tell you I was .5 mph quicker. Or not. Don’t know. But I’m guessing I was a touch quicker, merely because of two thoughts: First, I had to let up on the pressure on the pedals so that I didn’t pass a car, which is really cool by the way. Second, the wind was stiff nearly the entire ride. But there was no wind. Thing is, I was creating my own wind. I think I was going just a touch faster so that I had even more wind to cut through. And because it was a touch faster, I noticed it.

Initial Summary

I really don’t know if the Renn disc is faster. I think it’s way too early to tell. From my first ride, I’m guessing the wheel *is* faster; however, it’s not all-around faster. The wheel seems faster on the flats but mainly on the downs (hard to tell on the flats), whereas it seems slower on the up, as if the wheel required more work to turn. My guess is that after a few rides, I will gain more muscle to turn the wheel on the hills and flats where, after that, it will be faster to the bottom line (time); but right now I’m not there. So since it is faster on the flats and downs and slower on the ups, my ride this morning was near the same average speed as normal. I expect that to change when my legs are fully recovered from my most recent marathon and when I get a few more rides on the disc to learn the nuances and specialized muscles to work the wheel.

What’s Next?

I’ll add to this thread more thoughts of subsequent rides.


5 Responses to Renn 575 Disc: Initial Thoughts

  1. Brad says:

    I have done Lake Placid in the past and one thing I can tell you is except for the top pros aerodynamics is not the biggest issue. The climbs are many and long the 3 mile climb into a town I forget the name of is painful on many levels. I would look for weight savings over aerodynamics. True sometimes you can get both in a product but that carries a heavy price.

    I will be racing in Lake Placid in 2008 too however unlike you I am simply looking to survive the day (my running is not even close to yours). Unless you are blazing fast on the bike I would consider a set of Nimble Fly wheels over a disc. I have a set on my bike I am using for training and they are very light and fast and I will be using them in Lake Placid too if I can not scrape together the money for the race wheels I really want.

    Anyway see you at the lake,

    P.S. The swim at Placid is the best of any tri I have ever done.

  2. rebecca says:

    Disc wheels are beneficial if you are traveling over 25mph, which doesnt’ usually happen on the uphill. If you do not ride with this average, then you wasted your money. They are heavier than spoked wheels, but more aerodynamic. Good luck.

    • Kelvin says:

      Disc wheels are beneficial at any speed. There is no such thing in physics as an aerodynamic advantage that occurs only at a certain speed. You may find the wattage benefit varies based on speed. The benefit may be relatively higher above X mph, but even at slower speeds there is a wattage benefit from decreased drag.

      The crux of a disc wheel is the weight gain, which is felt more in climbs. To get an exact sense of whether a disc wheel would require analyzing the wattage gain/loss over a course under certain conditions (i.e. wind direction/speed etc.), but for most people, if there’s a fair amount of climbing or wind, the disc won’t help. If the course is flat, not windy, and with relatively few sustained climbs, then the benefit could be significant.

    • Matt says:

      NOT TRUE!
      Aerodynamics play a role at any speed and can actually benefit the slower cyclist as they are on the course for longer and that allows for a greater percentage gain.

  3. Yeah I am really interested in the subject that your talking about. I’ve bookmarked this post and am looking forward to see many more of these posts on this blog.

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