Bestbikesplit slower on aerobars

I’m slowly trying to make the shift to aerobars ready for an IM race next year. To see what time savings I could make, I put all my data into bestbikesplit and it is telling me I’ll actually be slower.

With everything else the same, these are the times:

Road bike on drops: 6:07 - Best Bike Split
Road bike on aerobars: 6:20 - Best Bike Split
TT bike on aerobars: 6:25 - Best Bike Split

I’ve been told this site is pretty accurate, so why would it be giving me an 18 minute penalty for using a TT bike over drops on a road bike?

I’m not familiar with the site, where does it get the CdA from?

Its using the following values
Your road bike 0.3159
Your TT bike 0.3479

No wonder it thinks the road bike is faster if the CdA is lower

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With the free account, it does all that maths for you and you can’t modify it, this is what it says about the CDA:


These are the two bikes, the TT bike definitely gets a higher CDA but I’ve no idea why.

It is interesting that the climbing CdA is lower for the TT bike.

I think it is the position thats costing you

Road bike in the drops (this likely means bent arms, forearms at almost 90degrees) is going to be more aero than a recreational (upright)position on aero bars.

You’d be better doing some out and back test on both bikes with your real-world riding positions to workout which is faster

Playing with my racing position, if I say I’m a midpack triathlete, I get a CdA of 0.3156 at 0 degrees but if I say I’m advanced I get 0.2756 which is finally better than the road bike. This then works out at a race time of 6 hours, just 7 minutes faster.

I’m sure real world will be different to the maths on here, but I was looking at this and similar things to see if I could work out the cost / time saved benefits before potentially spending any money.

Just base on these figures, if I have to go from no aerobar skills to “advanced” just to save 7 minutes, that means the £1500+ for a new bike isn’t worth it.

I’m going to spend the winter playing with the TT position on my indoor bike to see how it feels and then look at making a decision in the spring. A new bike wouldn’t get any riding before then anyway.

The app has a rough estimate of CDA. It’s the actual CDA you achieve on your bike that matters. On a long ride, maintaining the position that gives you that low CDA becomes very difficult. You can achieve a low CDA body position on a normally set up road bike, but it’s very tough to maintain for any length of time. Aero bars make staying in a low CDA body position much easier. Body position is one of the biggest contributors to overall drag. Specific low drag helmets, bike frames, and wheels can also help.

Body position is number 1
Skinsuit number 2
Helmets, aero socks, shoe covers, wheels and tyres, clean drive train, big chainring to increase drivetrain efficiency come next.
Bike frame is bottom of the list in terms of aero gains, although N+1 and all that.

If I ever get to the position where aero socks will make a significant making a difference then I’ll be very happy but very very surprised!

The comfort level of aerobars is interesting, I’ve heard people complain about the position being hard to hold for long durations but also people say that it is easier to hold. I’ve only done five minute blocks so far which have felt OK but I’ve also been very glad to get back onto the hoods after them. I guess it is a winter of playing to see what I can manage before I make any decisions.

I’ve just heard the GTN show is going to do a video on road vs TT bike in the next week, so that is good timing, I’ll see what they say.

Personally I hate the TT position. I can lock in for 10/15mins or so but more than that I really dislike it. I dont have a TT bike but have a well fitted road bike and clip bars also included in the fit.
I did full distance IM on that and was glad I had the ‘road bike’ option. Even just moving to the drops for a while was nice (I also had muscular problems with my lower back at the time and moving around was a blessing). What I may have lacked in total CDA reduction I am sure I made up for in feeling relatively better at the start of the run.
My main event is 70.3. Plenty of them have hilly profiles. I’m no climber by any stretch of the imagination butr I feel a lot more smug than the TT riders do when theh hills arrive.

It is comments like this that put me off the TT bike. I’m very inflexible and like to move around a lot on the road bike so I’m worried that like you I’ll end up 15 minutes in and having to move to the base bar and then completely blow my position. Did you do much training in the position? My hope would be that if I spent a lot of time in it then I would get used to it.

My target race is IM Barcelona which is pan flat so no worries about hills.

I did some training in that position, not 100miles+ though. Perhaps if I had then I’d have been better on a TT. It’s not like it was targetting a podium or even AG position so I wasn’t squeezing every last bit out of my prep. I wanted to enjoy the training rides as well as the event and I just counld’t see a TT position doing that for me (I’m very flexibble, but I’m 6’4 so there’s a lot of me to bend over!). Myabbe it’s more personal preference on my part. I’m sure there are TT riders here with a different view.

My full distance was IM Kalmar, also a pancake. I’m tall and wide and heavy - I certainly won’t be looking for anything else for another full distance.

If the cost was £100 I’d go for it without worries, it is just the cost and the chance of coming out worse.

I guess I’ll just stick with it over the winter and see how it goes.

Again personal preference but I’ve never regretted not having them. I’ve a nice aero road bike, well fitted and comfortable (and I love it) so with decent bars it’s a pretty good half-way house.

My next bike won’t be a TT either, even though I’m focussing quite seriously on a couple of specific tris this coming year. I’m more intrerested in a gravel to get some more fun in!

I’ve just emailed the company who did my last bike fit to see what they say.

I’m looking to go more towards off road, but after my last IM performance, I know I can do better so I’ve got to scratch this itch before moving on with it.

That’s an expensive itch right there. You know what you need to do…

For six moths said I’d never do another, then started thinking I could do better, then got caught up in the hype of people going and racing this year, and next thing I’d signed up again for next year.

I just need to do it and for it to go right so I can get it out of my system and move on. This is one of the reasons I’m nervous about bikes, I’m a runner and swimmer so the bike is where I can make most improvements, but I’m worried about moving from what I know to something new and having it go wrong.

I’m mostly over thinking it all rather than taking it as it comes which is what I should be doing.

I’d say it’s definiltey worth speakign with the bike fitting place, as you said. I took a lot of guidance from the guy I used. He was great. (Are you in the UK?)

I’ve just booked a fit two weeks today.

I’m in the UK, going to what used to be Rutland Cycles in Nottingham, it is now some long name with Specialized in it since they bought them out.

Cool. Let us know the outcome. Looks like they do the Retail fit, which is what I had.

I grew up in Nottingham as it happens. Am further south now though.

I had my last fit with them and Phil who does them really seems to know his stuff.

They’ve got an offer on Retul at the moment, only £100 for getting it done. He is going to do it on their fixed bike but I can take those numbers to the Kickr and then use them as a start if I get a full TT.

I’ll try to remember to check back when it is done.