Longer chainstay = more speed

[Osiris]

Some time ago, I mentioned in another thread that while the Vendetta V20 is by no means slow, nothing about it's performance struck me as all that impressive. In coast down and power/speed tests, it proved to be almost identical to my Bacchetta CA2. No matter, I thought, because if I just wanted to go as fast as possible, I could dust off my rarely ridden M5 CHR or M1 Lowracer, which are in an entirely different league when it comes to top speed.

But then I saw photos of several V20's being raced on the track, and noticed that their booms were much more horizontal than mine, resulting in a correspondingly higher bottom brackets and a much more aerodynamic posture. I bought a size Large chainstay from someone else on the forum, hoping this might help me to coax some extra speed out of the V20. The bike was at the shop at the time having a Di2 system installed, so it was a convenient time to have them replace the existing 19.5" chainstay with the new one, which looked about six inches longer.

The bike looked dramatically different once the surgery was completed. The bottom bracket was now 31.5" above the floor, compared to only 26" before, according to measurements taken by the shop tech.

Before:

After: https://photos.smugmug.com/Sports/Bicycling/i-Tm8cM3L/0/8c939f44/XL/DSCN0213-XL.jpg

I've only done two rides since the change, but the test results are extremely encouraging. On coast down tests, the higher BB resulted in a whopping 2 mph increase in top speed, and on a 1 mile flat section, it was substantially faster than before at similar power levels. It's hard to be more precise because my power output this time was about 15 watts less than before, while the speed was higher. Unfortunately we've also had lots of wind in the area over the past few weeks, so I'll need to do a lot more testing in calmer weather to confirm these results.

The only downside is that the handlebars are now so much lower that I've had to reduce the reach so that the tops of my thighs don't bump into them when pedaling. This created too much bend at the elbows, so I ordered a curved slider. Installed with the curve pointing up, I should be able to push the handlebars forward and still maintain adequate clearance for my thighs.

I'll have more to report once I get everything set up properly.

 

[DavidCH]

I'll have more to report

I'm interested how you get on. I was told that having a larger chainstay would make the bike less stable. I think cruzbike do 3 lengths of chain stays.

 

[BJ686]

Looks nice! I've also wondered if raising the bottom bracket a bit might also provide the ability to produce more power since it places the body in a slightly more closed position.

Now you just need some deep carbon wheels for all-out aero!

 

[Osiris]

I'm interested how you get on. I was told that having a larger chainstay would make the bike less stable. I think cruzbike do 3 lengths of chain stays.

I honestly didn't notice any difference in handling. One of the things I loved most about the V20 is it's superb ability to negotiate sharp turns in a very controlled manner, and I'm happy to say that hasn't diminished a bit. One other observation made by Larry Oslund was that a shorter chainstay makes it easier to climb hills, but I didn't see any difference there either. It could be that it makes a noticeable difference on longer and/or steeper climbs than those I encounter on my favorite routes, however. Larry certainly has a lot more experience to draw on than I do.

 

[Osiris]

Looks nice! I've also wondered if raising the bottom bracket a bit might also provide the ability to produce more power since it places the body in a slightly more closed position.

It's possible, but I'll need a lot more tests to determine that. By coincidence, both the V20's seat height and BB height are exactly the same as they are on my M5 CHR. The big difference of course is the arms positions. The M5 uses a tiller that places your hands close together and presses your arms against your torso for maximum aerodynamic advantage. The V20 has a wide handlebar that places the rider's arms far out into the wind stream, creating more drag. How much more is anyone's guess, but the reason I so seldom ride the M5 is because it's tiller handlebar makes the front end extremely unstable.

Now you just need some deep carbon wheels for all-out aero!

I was considering that, but when I looked at the wind tunnel results published on this forum, I noticed that "aero wheels" only accounted for a small reduction in drag. Now I understand why I noticed no performance increase on my CA2 when I swapped the stock aluminum wheels out for a full dish rear wheel and a deep dish front wheel. If I were racing, a 10 watt decrease in drag would certainly matter, but for general street duty I just don't see the point of it. They certainly do look cool, though.

 

[Osiris]

After doing several coast down tests on the same Strava segment, it looks like the Large chainstay resulted in a net speed gain of 1.5 mph. Improvements in power to speed ratio are much harder to ascertain. Not only has this area been plagued by windy weather, but when holding 25 mph traveling in a direction perpendicular to the wind, I'm seeing differences in power output as great as 20 watts. The most consistent results were obtained on two segments of a paved trail which I know to be perfectly flat, where I managed to sustain 25 mph with 240-250 watts. That's a big improvement over the dismal results I'd gotten with the short chainstay, which required something like 270 watts at 25 mph. An indoor test track would be ideal for such tests, but unfortunately I don't have access to one, so road/trail data will have to suffice for now.

 

[jond]

On my V2 the boom was perfectly horizontal with chain stay large

the v20 slightly angled with large chainstay. No I didn’t get taller different geometry

The V2 was faster. Albeit a lighter build. Sram red v ultegra. And of course I was younger. Lol. Same wheels and power meter numbers.

You just have to pay attention to the great work all scientific done by cruzbike in the wind tunnel and Lazza O he of the many wheels.

Sometimes I wish I was as tall .

Until I go to the carnival and they won’t let Larry ride lol.

Hard to beat packages are hard to beat.

Really glad you are seeing the speed. Go fast go safe

 

[Osiris]

I spoke about this with Thom Ohlinger, who designs racing recumbents and trains bent racers, including our very own Larry Oslund. His reply was as follows:

"I've found that the higher the bb to the seat pan, the faster. It's relative to height, but nobody knows how high is too high. My dual 451 was 11" seat to bb and it was a rocket. And, the higher bb helps your power as the seat leans back. If we had that wind tunnel we could keep raising the bb until the bike got slower. Arnold (of Raptobike) has a very high bb and says his bike is very fast. So, 10" is a good, fast, safe no number. 11" or more if you're tall. JB is 6'6" and builds his at 11". But who knows, 12 or 13 might be faster."

 

[MrSteve]

The corollary to a higher bottom bracket or its position relative to your hip socket is the angle of the seat back.
(Er, in my experience.)
For example, Larry Oslund has modified his stock seat with a sculpted foam wedge in the lumbar (lower back) area.
This wedge effectively decreases his seat angle and helps his aerodynamics as well as providing Mr. Oslund with comfort.

Corroborating all this is the fact that my Sofrider V1, modified with both a very high bottom bracket and a very reclined
seat is, for me, more aerodynamic than my Vendetta V1.5!
My Vendetta climbs very, very well and is faster overall, by a large margin, than my Sofrider.

My Sofrider spanks my Vendetta downhill, in headwinds and on level ground because of the science, the physics
of aerodynamics is undeniable.

 

[LarryOz]

Some time ago, I mentioned in another thread that while the Vendetta V20 is by no means slow, nothing about it's performance struck me as all that impressive. In coast down and power/speed tests, it proved to be almost identical to my Bacchetta CA2. No matter, I thought, because if I just wanted to go as fast as possible, I could dust off my rarely ridden M5 CHR or M1 Lowracer, which are in an entirely different league when it comes to top speed.

But then I saw photos of several V20's being raced on the track, and noticed that their booms were much more horizontal than mine, resulting in a correspondingly higher bottom brackets and a much more aerodynamic posture. I bought a size Large chainstay from someone else on the forum, hoping this might help me to coax some extra speed out of the V20. The bike was at the shop at the time having a Di2 system installed, so it was a convenient time to have them replace the existing 19.5" chainstay with the new one, which looked about six inches longer.

The bike looked dramatically different once the surgery was completed. The bottom bracket was now 31.5" above the floor, compared to only 26" before, according to measurements taken by the shop tech.

Glad you are getting it dialed in! I knew you would.
By the way - I installed the longer chainstay on my V20 (My boom was dead flat) and I ended up slower. My feet were just too high for my shoulders and created more drag. Each person has to fine tune the bike to exactly what is best for them.

Now you need to come up to the Charlotte Motor Speedway next Wed.week and do a 10 Mile TT with me and Jeffrey! https://cmstimetrialseries.racesonline.com/

 

[Osiris]

Glad you are getting it dialed in! I knew you would.
By the way - I installed the longer chainstay on my V20 (My boom was dead flat) and I ended up slower. My feet were just too high for my shoulders and created more drag. Each person has to fine tune the bike to exactly what is best for them.

My boom is almost flat, but it made me faster!

Now you need to come up to the Charlotte Motor Speedway next Wed.week and do a 10 Mile TT with me and Jeffrey! https://cmstimetrialseries.racesonline.com/

Hahaha, I only wish I could! 10 miles is a long way to go on a recumbent, but maybe day I'll be up to it.

 

[Dave Arnold]

My boom is almost flat, but it made me faster!

Hahaha, I only wish I could! 10 miles is a long way to go on a recumbent, but maybe day I'll be up to it.

I really like those wheels!

 

[super slim]

I think that the OLD Oompa-Loompa of the East (Larry O), is correct and if the knees max. height is higher than the shoulders, then slow times, as he has done MANY tests with chain-stays and crank lengths on his secret test track!!!!

Is Larrie's back arch support of the flattish Cruzbike seat, a secret weapon, allowing the pedal loads to go into the hips, instead of the shoulders, if using the shaped comfortable Thor seat!

 

[Osiris]

I think that the OLD Oompa-Loompa of the East (Larry O), is correct and if the knees max. height is higher than the shoulders, then slow times, as he has done MANY tests with chain-stays and crank lengths on his secret test track!!!!

Max knee height should always be above shoulder height for best aerodynamics. This is true even on relatively slow recumbents like my Bacchetta CA2, which have a much more upright seat than the V20. For reference:

Jason Perez:

Maria Parker:

Larry Oslund himself:

 

[LarryOz]

I think that the OLD Oompa-Loompa of the East (Larry O), is correct and if the knees max. height is higher than the shoulders, then slow times, as he has done MANY tests with chain-stays and crank lengths on his secret test track!!!!

Is Larrie's back arch support of the flattish Cruzbike seat, a secret weapon, allowing the pedal loads to go into the hips, instead of the shoulders, if using the shaped comfortable Thor seat!

We are all different sizes and for me, putting my boom level increased my drag. I was really surprised. I did a bunch of coast down testing with different chain-stays and picked what worked best foe me.
No secrets here! haha. It definitely might help "lock" me in better, especially on a flatter bike. I think higher cadence is even better and will result in you ability to hold higher power for longer periods without cumbersome load on your legs. I look back to 2015 when I was the strongest and I was always training around 100rpm. The last year or 2 I seemed to get slower and slower. Maybe it is my age! haha I am now training closer to 110rpm, and will try and race my TT's at 105-110. (Most of the top end Time Trial'ers seem to ride at about 105) That is the secret weapon!

 

[DavidCH]

I have a vendetta. My cranks are 155mm , I have a medium chainstay 19" and my knees at the highest position are just over 3 inches over my shoulders.

The only way I can lower my knee height are to use centrally cleated shoes or a change of seat. So after that experiment perhaps the idea of a longer chainstay are marginal. So kind of curious what is the optimum knee height relative to shoulders is?

If I were to have a longer chainstay with the BB being higher , the knees would be 5 inches higher than my shoulders however, the crank is in a more closed position so I expect that I could apply more power. I can see this could be a costly exercise just to gain 5 watts. Now if I could make myself believe that a chainstay and seat update could give me 20 extra watts of power with a lower CDA with a change of shoes that might be quite a worthy transition and certainly would not be marginal.

So... cda could be lower if free wheeling on a descent. However the Thor seat's cda is greater that the V20's. Going uphill would certainly be a benefit having the extra power. The roadies ... not many... catch me on hills. That power/cda transition would be worthy.

What do you say?
(I know... I'm not going to find out unless I spend the money... looks like next years budget for sure)

 

[Gary123]

I'm also thinking of going to Central cleat (shoe mod). Should raise feet about 2 in. Hoping for better cda and more power. I ride catalyst pedals on mb and love them.

 

[cranky cyclist]

Catalyst pedals don't work well for me. I would love the mid foot position with cleats and a big pedal such as the catalyst. I have used the Catalyst pedals when on the trainer and definitely feel more power. My feet slip off when on tough hills and I have a hard time when starting out. I may try the use of toe clips to hold my heels in position. Someone has used toe clips in the heel position and reports that it works for him.

 

[Osiris]

I have a vendetta. My cranks are 155mm , I have a medium chainstay 19" and my knees at the highest position are just over 3 inches over my shoulders.

The only way I can lower my knee height are to use centrally cleated shoes or a change of seat. So after that experiment perhaps the idea of a longer chainstay are marginal. So kind of curious what is the optimum knee height relative to shoulders is?

If I were to have a longer chainstay with the BB being higher , the knees would be 5 inches higher than my shoulders

Something isn't making sense here. Going to a longer chainstay will only raise your feet. But how can raising (or lowering) your feet change your knee height relative to your shoulders?

 

[DavidCH]

Something isn't making sense here. Going to a longer chainstay will only raise your feet. But how can raising (or lowering) your feet change your knee height relative to your shoulders?

Well you know better than me because you have done it. Now that you have said that... it's given me the idea that each knee goes through a different loci of points depending on chainstay. I still suspect the knees will go higher with a higher bottom bearing.