The numbers behind Ironman drafting

Triathlon Forum
1

Using numbers from Ironman New Zealand, I found the peak period of athletes exiting the swim was between 1:10 and 1:15 with 215 athletes. This is a rate of 1.16 seconds per athlete. Scaling this for a course of 2200 athletes, such as many North America events, and you have 0.80 seconds seperation between swimmers coming out of the water.

Once on the bike, assuming 18mph speed, the riders will now be seperated by 21 feet. However, if they hit an uphill or some wind and slow down to 12mph, they are seperated by 14 feet. If each bike is 5 feet long, then the air gap (wheel to wheel) is 16 feet and 9 feet respectively.

A 7 meter long draft zone is 23 feet. These numbers show that riders must ride in 2 columns to fit on the course at 18mph, and 3 columns at 12 mph.

Looking at other rider groups, the 2 columns are required @18mph for swimmers exiting from 1 hour to 1:15, 2 columns @ 12mph from :55 - 1:20. 3 colums of riders are required at 12mph for swimmers exiting from 1:05-1:15.

Why did I bother with these calculations? Because one of the least enjoyable aspects of IMNZ for me was having to spend the first 60 or so miles trying to avoid drafting, while simultaneously trying to ride on the (left hand) side of the road as required (the course was not closed to traffic). As you can see, it is not possible for all the riders to ride single file. Trying to hold an even pace and stay out of the draft zone is very challenging, and compounded by the fact that bigger riders like me go slow uphill and fast downhill, so we are always jockying back and forth with the smaller people.

As I think about IMAZ coming up for me next year, I can see from these numbers that it will be much worse. If they do not close Beeline HWY (which has a wide shoulder, but traffic flows at 70mhp), there will not be enough room for the riders. My hope and best guess is that it will be closed, and riders will be allowed to ride 3 abreast without penalty as long as they keep the legal seperation. If you say 2meters/bike, 3 bikes take a pretty wide road.

I guess the best thing is to improve my swim by 15 minutes so it won’t be an issue.

2

I agree, we rode from Tempe BP over and up the Beeline this morning on our way to Fountain Hills. To the Shea intersection it is only 20 or so miles. They could clean up the shoulder and give us one lane and you could ride 3 but where are they going to do with the next 8 miles? Shea is somewhat busy and taking us up a little farther down the beeline to the McDowell Resi rode not the answer. Going 8 miles up shea (if they close all of the south bound lanes) will add some hills. They could always loop us around and up the 18% hill on Golden Eagle :slight_smile:

It will be interesting to see the final course. I think that they will most likely close all of the beeline from Shea to McDowell.

Its really a shame that they cant take us through Rio Verde and up 9 mile hill to Pima and keep it a 1 lap out-and-back.

3

Dan,

You’re applying static parameters to a dynamic situation. In the actual race, there’s a lot of position shifting going on as slow swimmers who ride fast pass fast swimmers who ride slow. Hills complicate things because they slow the process and because of different abilities of athletes to climb or descend.

At mass start events the first portion of the course is crowded and hopefully the Officials will allow sufficient time for riders to disperse before issuing penalties. Normally this takes a few miles to occur. The object is not to get everyone riding at a fixed distance and at the same speed but rather for the race dynamics to occur within the rules.

Larry

4

I was actually doing a similar estimate of the Clermont Sprint series race just yesterday. Too odd…

I figured it was damn near impossible to avoid drafting on a 12 mile bike course after a 400 meter swim done by 800 people, even with 3 minutes of separation. This is one reason (safety is the best one) why the number of participants should be limited. Otherwise, the drafting rules should be amended to allow drafting in races which are clearly oversubscribed. Of course, if you do that, the safety problem is exacerbated. :slight_smile:

Having said all that, I have miraculously survived 97 races with no penalties. I’ve deserved them in a couple of the sprint races though and one Olympic distance race. Sooner or later…

-Robert

5

Thanks for trying to clarify this Larry, but I don’t understand how assuming a more dynamic situation helps matters. In fact, rather than needing three lanes for riders, you actully need 4 if you allow for passing. Using a highway analogy, you have the slow lane, the middle lane, and the fast lane. The slow and middle guys can move left to pass, but the fast lane guys are blocked unless there is a 4th lane for them to pass in.

Of course eventually things spread out, but my experience is it takes much more than a few miles. The middle pack will have fast riders move up ahead and slow riders move back, but the middle pack also overtakes slow riders that swim fast and is joined by slow swimmers that ride fast. Realize that I am also assuming a perfect distribution of riders over that period of time; in the real world you will have peaks even larger.

If the officials know that the course is such that you can’t avoid drafting for the first X miles, they should allow a modified draft zone during that section. Otherwise those who try to follow the rules are frustrated to no end.

Based on these numbers and my previous experience, unless I hear total road closures I think my long rides should include intervals for the first 20 miles minimum. Instead of riding 220W steady, I need to go up to 300W for passing in 15 seconds, and then drop down to 140W for when I am passed and forced back, and keep switching between the two every minute or so. Steady tempo is out the window.

6

Couple of things

  1. I’m a largish bloke too so I know the problems with hills. Swim faster, that’s what I do (1:02) so it’s less of a problem :slight_smile:

  2. I ride slowly so I’m not the one worried about the drafting thing. I just stay left (here in NZ) and try not to get in anyone elses way :frowning:

  3. IMNZ only had about 1200 starters so the gaps should be bigger :slight_smile:

  4. Race IM in NZ and reduce your problems with drafting! Yipee (Oh yeah, spend more of your greenbacks when you’re here, we like the way they feel in our wallets!

7

I did a half Ironman yesterday with supposedly 700 individuals and an unknown number of teams. Five waves at 5 minute intervals. The bike started flat for the first three miles and then a long hill, with rollers for the next ten miles. The bike was an out and back course. I started in the last wave, which also had the team swimmers. The bike stayed crowded through the first 18-20 miles! I was pleasantly surprised that most everybody was not taking advantage of it, with the exception of one individual. After watching this guy for over 20 minutes, I think he finally got tagged by a course marshal on a motorcycle, the first marshal of the race that I saw. Still though, I had to work hard to avoid drafting. Totally blew off worryiing about it on the hills when everyone bunched up. At one point, I had to sit up on my bars and coast when one really tall guy came up slowly on my left to pass and pinned me behind a slower rider in front of me (this was after the turn around). Also, after having passed the turn around, I observed two large clogs of riders going the other way, at least 20 riders in each group, no pace lines or anything, but rather strange given that is was 20-25 miles into the bike course. Bottom line? I believe in your numbers 100%. I expect to live those numbers at IMC with over 2000 participants and an anticipated swim time of 67-68 minutes.

8

Thanks for trying to clarify this Larry, but I don’t understand how assuming a more dynamic situation helps matters. In fact, rather than needing three lanes for riders, you actully need 4 if you allow for passing. Using a highway analogy, you have the slow lane, the middle lane, and the fast lane. The slow and middle guys can move left to pass, but the fast lane guys are blocked unless there is a 4th lane for them to pass in.

The field isn’t going to line up like floats in a parade - at least not until there’s a long flat stretch a ways into the course. In a sense you do have multiple lanes when there’s a lot of passing going on. And for 15 seconds the passers take up significatly less space than if they’re all moving in formation at a fixed speed. Those things would be extremely difficult to calculate. But it is a significant couterpoint to measurement based solely on bike length and following distance.

If the officials know that the course is such that you can’t avoid drafting for the first X miles, they should allow a modified draft zone during that section. Otherwise those who try to follow the rules are frustrated to no end.

Crowding the course at the beggining of the bike segment is an inherent evil of the mass swim start. If Officials were using that to issue huge numbers of penalties early in the race, you’d hear a lot more complaints. Instead people complain about the drafting that does occur. The only way to effectively remove the problem is with wave starts. Personally I feel that mass starts are part of the Ironman cool.

Larry

9

The only way to effectively remove the problem is with wave starts. Personally I feel that mass starts are part of the Ironman cool.

Actually even wave starts don’t really help things that much, because the faster riders (me) also frequently catch up with the faster swimmers (not me) and all of the slower riders from the previous waves. It’s not really an ideal solution either. In the Gulf Coast 1/2 IM last month I was passing so many people that it took until about mile 40 out of 56 before the field really spread out. However, I do like having people in front of me going somewhat slower, as it’s a nice incentive to keep up my 22mph average. (Did I mention I swim slow?) In a way the mass starts are better, because the substantially faster swimmers are typically fast bikers too, so the field spreads quickly rather than a wave, where at least half the people in front of me coming out of the water will be going 16-18mph. I don’t have a preference…the only drafters that annoy me are the packs of 15-20 that blow past everyone in an obvious peleton. EVERYONE gets stuck every once in a while with that one person out of 1700 who decides to pass at the wrong time, becomes a wheelsucker for a minute or two, etc.

10

It may be difficult to simulate all of the dynamics of a group of riders, but it is not difficult to calculate that a group of ~375 bikers leaving over 5 minutes is an average of 0.8 seconds/rider, that their speed of 18mph is equal to 26.4 feet per second, which gives 21 feet per rider, that the draft zone including the bike is about 28 feet, and therefore, under the BEST circumstances you will need a second lane for riders. If they are not “lined up” then you simply have a higher concentration at various peaks, which requires even more lanes (although at 18mph the second lane is not totaly used yet). Maybe a traffic engineer has a simulation program that can estimate exactly how many lanes you need, but it is not less than 2 initially and that is best case assumptions.

I don’t think wave starts will help much due to the increased dynamics; I think what I would like is for race directors to admit this up front and allow for it officially, assuming they can’t practically widen the road. Just saying that they expect riders to be 2-3 deep for the first 50 miles or whatever, so slow riders keep left but don’t worry about the 15 seconds passing rule.

To pass a rider moving 18mph in 15 seconds from behind their draft zone, I would have to be traveling 19.27 mph. So effectively, anyone traveling between 18 and 19.27mph cannot pass this “18mph pack” without drafting or speeding up. Speeding up is okay for a couple of riders, but if the draft-zone spaced pack is over a mile long it could be a long time before you get a break. Of course hills may give you an opportunity to pass but if you are a bigger guy you just wind up moving back further.

11

Your numbers speak to a very simple but at the same time complex problem - The no drafting rules are great but at certain times and in certain places they are asking athletes to do something that is physically impossible to achieve. I have been saying this for many years. It’s one of the reasons why the ITU did away with the rules. You can’t have 60+ worldclass triathletes all exit the swim within 20 seconds or so and then have them not draft on a one lane road as they all cyclce along at the same speed.

I am not advocating drafting in age-group or Ironman events. However, this get-tough on drafting strategy does not work either as it leaves a bad taste in people’s mouths when they are given a penalty or worse a DQ for something that was not completely their fault.

12

In a big IM race it can take the mid to front of the pack in 40 to 50 K to sort itself out and people to settle in “where they are supposed to be” Furthermore, you often have the pro-women caught up in this and they can be either unfairly penalizd or legally benefit from the situation. However, you look at it, it’s risky for them and has a direct impact on the dynamics of their race and how it unfolds. I believe that this is why the exempted the Pro women from the blocking penalty at IMH last year - to give them the left side of the road to pass, be passed and have their own race.

13

The solution is not to allow drafting, but to increase wave time increments and/or reduce the number of entrants to safe levels. (something not being done)

-Robert

14

It’s one of these things that has been talked about for 10 years but nothing has been done about it likley because the possible solutions are either unpalatable or will be costly.

15

I don’t think wave starts will help much due to the increased dynamics; I think what I would like is for race directors to admit this up front and allow for it officially, assuming they can’t practically widen the road. Just saying that they expect riders to be 2-3 deep for the first 50 miles or whatever, so slow riders keep left but don’t worry about the 15 seconds passing rule.

Where wave starts are used they make all the difference in the world when they’re well tuned. I’ve seen dramatic examples of this at 2 major events here in California. On event puts over 2,000 athletes on a 26 mile out and back course with automobile traffic. The downside is that it takes nearly 2 hours to get everyone started at the latter event.

Mass start is another issue. For the most part the early course crowding is an inherent problem that is easier to live with than to fix. Penalty assignment usually isn’t up to the RD; it’s a judgement call on the part of the Officials. The Officials that I know all race and aren’t prone to take a “shooting fish in a barrel” approach by issuing penalties for behavior that is totally unavoidable. I think that Officials should be able to make that call rather than just saying that the first 50 miles is a “free” zone.

Larry

16

there is no simple solution or fix to this problem and I think it’s only going to get worse. Courses are becoming smaller, more loops or 1 lane instead of 2, and races are expanding. 2,200 people at IMAZ, yep there is going to be a fair bit of drafting in the first 50k, no way around it. if you get 2 lanes the left should be for passing the right should be for riding (now if people would just drive like that, I digress). You could get several people side by side and not in a long line that way. pro women can ride in left lane for the first 60k -70k then have to utilize the right lane as well. I