46mm vs 88mm for TTs

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rides4beer
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by rides4beer

So I did my first race this past weekend, duathlon with a 14 mile bike portion. I was passed by four people on the bike portion (caught two of them on the second run), all four were on full aero TT setups, tucked, helmet, skinsuit, 88mm/disc combos. I had a blast at the race and of course now I need to go faster.

First and foremost, I will improve my position, already have a set of aerobars that will be going on and I will adjust my fit and start training for that position. I have a San Remo speedsuit that is coming as part of my team kit. I have a mediocre aero helmet that I might upgrade for something better, we'll see.

But since this is "Everything wheels", let's talk wheels. I already have a set of 46mm LB wheels, aero optimized (105% rule) with 23mm GP4Ks. All of the studies you see are comparing deep wheels to box section wheels, so of course the time savings are very impressive. But looking at the two studies below, going from 45s to 90s only saves 15-22sec over a 40k TT. Most of the TTs I'll be doing here are shorter, so even less time savings.

I'm thinking that I might be better off just racing with my 46's, maybe swapping some latex tubes and Conti TT tires for race day for better rolling resistance.

Yes, I'm talking myself out of spending money and just want someone to back me up. :lol:

http://flocycling.blogspot.com/2016/06/ ... l-flo.html

https://www.williamscycling.com/Aerodynamics_ep_61.html

alcatraz
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by alcatraz

46mm hits a sweet spot for racing with drafting.

If you can't draft then try a set of 88mm wheels running gp5000 tubeless. That will be quite competitive. Don't forget to match rim width with your weight and road quality.

Forget the disc wheel. The difference to an 88 is small and the disc is crazy heavy and unsuitable for training rides, also a pita to inflate especially roadside.

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rides4beer
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by rides4beer

alcatraz wrote:
Wed Apr 03, 2019 3:00 pm
46mm hits a sweet spot for racing with drafting.

If you can't draft then try a set of 88mm wheels running gp5000 tubeless. That will be quite competitive. Don't forget to match rim width with your weight and road quality.

Forget the disc wheel. The difference to an 88 is small and the disc is crazy heavy and unsuitable for training rides, also a pita to inflate especially roadside.
Some are draft legal, some are no-draft. I was reading that the disc is really only needed if you're sustaining over 27mph, I'm around 22 right now on this TT course (hopefully that will improve with some aero changes). Not sure if I want to mess with tubeless yet, we'll see.

AJS914
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by AJS914

Yes, I'm talking myself out of spending money and just want someone to back me up. :lol:
I agree with your analysis. What are you going to save 10 seconds in your type of events? When that 10 seconds becomes meaningful then think about buying some new wheels. Until then, work on everything else - bike, positioning, clothing, shave legs, etc.

I was also thinking, what percentage of drag is accounted for by the front wheel versus the rear? I would assume the majority of the benefit so you could always keep your eye out for a used 88mm front wheel.

rides4beer
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by rides4beer

AJS914 wrote:
Wed Apr 03, 2019 5:14 pm
Yes, I'm talking myself out of spending money and just want someone to back me up. :lol:
I agree with your analysis. What are you going to save 10 seconds in your type of events? When that 10 seconds becomes meaningful then think about buying some new wheels. Until then, work on everything else - bike, positioning, clothing, shave legs, etc.

I was also thinking, what percentage of drag is accounted for by the front wheel versus the rear? I would assume the majority of the benefit so you could always keep your eye out for a used 88mm front wheel.
Yup, that's exactly what I'm thinking, work on my position, and everything else, including just my overall bike fitness, I've only been riding for about six months. Now that the weather is getting better and we have more light in the evening, my team does a training ride once a week, and there's another fast group ride that I'll be doing each week, that'll help over just my normal rides (which I try to get in a fair amount of climbing and do some sprints, etc., but nothing structured).

I've also read that the front is the more important piece of that part of the aero puzzle, which makes sense.

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dgasmd
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by dgasmd

For the distance you mentioned, I’d stick with what you have. I used to do duathlons many years ago and was always amazed how much time people wasted in the transitions, which more than completely negated their “aero equipment gains”. Work on eliminating most of your transition time. Youll get far more gains there and improving your running than anywhere else

RussellS
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by RussellS

I'm guessing, with a whole lot of certainty, that the riders who passed you were on full time trial bikes. Whereas you are on a road bike with bolt on aero/triathalon handlebars. Their position is why they were faster on the bike. Their aero wheels were mere seconds advantage. 1 second is equal to 10-20 feet? In a triathalon, for the bike portion anyway, if a rider is within 10-20 feet of you, then you are tied. They gained all their time and speed from being lower and flatter than you by using their time trial bike position. Despite what many people yip and yap about, the rider accounts for almost all of the aeroness or lack on a bicycle. Your torso and head are 10-20-50 times more surface area than the wheels and frame combined. Maximize your body's aeroness and then play with the bike and wheels if you want.

rides4beer
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by rides4beer

dgasmd wrote:
Wed Apr 03, 2019 7:11 pm
For the distance you mentioned, I’d stick with what you have. I used to do duathlons many years ago and was always amazed how much time people wasted in the transitions, which more than completely negated their “aero equipment gains”. Work on eliminating most of your transition time. Youll get far more gains there and improving your running than anywhere else
I'm sure I have room for improvement, but I was really impressed with how smoothly my transitions went, especially considering I hadn't practiced at all! lol I'm a runner recently turned cyclist, so my runs were pretty strong, even tho my running volume has been down since I've been spending most of my time on the bike :lol: I think I can make some aero improvements, and of course just keep increasing my bike fitness, and should be able to get into the top 3 next year (small local race, 150 or so people, I was 5th overall).

RussellS wrote:
Wed Apr 03, 2019 9:14 pm
I'm guessing, with a whole lot of certainty, that the riders who passed you were on full time trial bikes. Whereas you are on a road bike with bolt on aero/triathalon handlebars. Their position is why they were faster on the bike. Their aero wheels were mere seconds advantage. 1 second is equal to 10-20 feet? In a triathalon, for the bike portion anyway, if a rider is within 10-20 feet of you, then you are tied. They gained all their time and speed from being lower and flatter than you by using their time trial bike position. Despite what many people yip and yap about, the rider accounts for almost all of the aeroness or lack on a bicycle. Your torso and head are 10-20-50 times more surface area than the wheels and frame combined. Maximize your body's aeroness and then play with the bike and wheels if you want.
Yup, they were on full time trial bikes, I was on my road bike, which is technically an aero bike, but with regular drop bars, not even bolt on aero bars. So I'm sure I have some decent gains to be made just with a set of bolt ons and working on my position. I didn't even have my 46mm wheels for the race, since they're getting the hubs replaced at the moment, so I was on my alloys.

Jugi
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by Jugi

Deep wheels are fun (when it’s not terribly windy). Go have fun.

wintershade
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by wintershade

rides4beer wrote:
Wed Apr 03, 2019 4:52 pm
alcatraz wrote:
Wed Apr 03, 2019 3:00 pm
46mm hits a sweet spot for racing with drafting.

If you can't draft then try a set of 88mm wheels running gp5000 tubeless. That will be quite competitive. Don't forget to match rim width with your weight and road quality.

Forget the disc wheel. The difference to an 88 is small and the disc is crazy heavy and unsuitable for training rides, also a pita to inflate especially roadside.
Some are draft legal, some are no-draft. I was reading that the disc is really only needed if you're sustaining over 27mph, I'm around 22 right now on this TT course (hopefully that will improve with some aero changes). Not sure if I want to mess with tubeless yet, we'll see.
The answer according to the aeroweenies over at Slowtwitch will tell you a disc is always faster in any sort of non-drafting sitution, even on hilly courses. And contrary to popular belief, the slower you are, the more a disc actually helps you.

See my somewhat tongue in cheek thread on "how fast do you need to be to credibly ride a disc": https://forum.slowtwitch.com/forum/Slow ... c#p6717280

Some other poster said, and I agree, there is more time to be gained by focusing on speed in transitions, etc., but if you have the money, pretty much nothing will make you faster than a disc wheel. But the 10 seconds don't matter, until they matter.

Also, after reading my ST thread I'll add, I wish I had followed the ST people's advice and just got a disc plus jet 6 front with a jet 9 rear for training. That's the ticket.

rides4beer
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Location: VA

by rides4beer

wintershade wrote:
Wed Apr 10, 2019 1:19 am
The answer according to the aeroweenies over at Slowtwitch will tell you a disc is always faster in any sort of non-drafting sitution, even on hilly courses. And contrary to popular belief, the slower you are, the more a disc actually helps you.

See my somewhat tongue in cheek thread on "how fast do you need to be to credibly ride a disc": https://forum.slowtwitch.com/forum/Slow ... c#p6717280

Some other poster said, and I agree, there is more time to be gained by focusing on speed in transitions, etc., but if you have the money, pretty much nothing will make you faster than a disc wheel. But the 10 seconds don't matter, until they matter.

Also, after reading my ST thread I'll add, I wish I had followed the ST people's advice and just got a disc plus jet 6 front with a jet 9 rear for training. That's the ticket.
Thanks. My first step is my position, aero bars go on next week, and I get my 46mm wheels back at the same time. My next TT (10 mile), will be with that setup. My club does a TT series through the summer, so I'll get more practice.

Maybe I'll add a disc first, run it with my 46mm front, and then add a deeper front later.

c50jim
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by c50jim

This thread reminds me of my triathlon days back in the 80s and early 90s. My first triathlon was on a road bike with the old brake cables that sprang up out of the levers. That was all we had in 1985. I went through adding various aero bits and pieces and have some at least anecdotal experience with gains from particular changes since each was made separately.

Aero bars were the biggest game changer. IIRC, something in excess of 2 minutes on a 40 km TT when I added the old Scott DH bars (anyone else remember those?).

Disc wheel was also meaningful, good for close to a minute on the tris I did.

Any other changes were so small that I couldn't measure an improvement. That doesn't mean that there was no improvement, just that it was similar to a good/bad day thing.

I did go back to doing TTs in the 2005-2010 era. My younger son was national level competitive and it gave me something to do while I waited for him since he didn't need support in TTs. We used Zipp 303, 404 and 808. Neither my son nor I was particularly fond of the 808s. I only used them once and found that I was focusing on keeping the front wheel straight rather than pedaling harder. My son found the same thing. Neither of us is small - both 185 cm+ and probably 75-80 kilos in those days.

rides4beer
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by rides4beer

c50jim wrote:
Wed Apr 10, 2019 7:19 pm
This thread reminds me of my triathlon days back in the 80s and early 90s. My first triathlon was on a road bike with the old brake cables that sprang up out of the levers. That was all we had in 1985. I went through adding various aero bits and pieces and have some at least anecdotal experience with gains from particular changes since each was made separately.

Aero bars were the biggest game changer. IIRC, something in excess of 2 minutes on a 40 km TT when I added the old Scott DH bars (anyone else remember those?).

Disc wheel was also meaningful, good for close to a minute on the tris I did.

Any other changes were so small that I couldn't measure an improvement. That doesn't mean that there was no improvement, just that it was similar to a good/bad day thing.

I did go back to doing TTs in the 2005-2010 era. My younger son was national level competitive and it gave me something to do while I waited for him since he didn't need support in TTs. We used Zipp 303, 404 and 808. Neither my son nor I was particularly fond of the 808s. I only used them once and found that I was focusing on keeping the front wheel straight rather than pedaling harder. My son found the same thing. Neither of us is small - both 185 cm+ and probably 75-80 kilos in those days.
Good info, thanks! I've only been cycling for about six months, and this was my first TT, so def still learning (while trying to keep the spending reasonable lol). I have a feeling the biggest gains will be the aero bars that I'm putting on next week. With those and some training, I figure I'll be doing pretty good on my 46's. I'm gonna see if I can borrow a disc and do some back to back testing on the TT loop here.

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