Bornco

Hi,

I'm curious about your modified bike. What do you think made it faster for you than your CoMotion and Santana, and are you faster with your 38's than a narrower tire? How much effect do you think the 650 wheels have?

I've been thinking about running 32's instead of our 28's, but I was pretty sure we'd be slower. Any info you have would be appreciated.

Thanks,

Jack

waynesulak

Why 38mm tires? Below is a summary of my understanding of tire rolling resistance:

There are two schools of thoughts on tires. One long held view is that the higher the pressure in a tire the less rolling resistance and the faster the tire. This is borne out by many tests of tires on a drum apparatus that can accurately measure rolling resistance under controlled conditions. As I understand it, an inflatable tire deforms around its contact patch it absorbs some energy. The higher the pressure the smaller the contacts patch and the less energy is absorbed resulting in a faster tire. The desire to have high pressures leads to narrower tires which can hold more pressure than a wider tire made with the same materials. When testing all tires at the same pressure the faster tires are thought to be those with the most flexible sidewalls because those tires take less energy to deform around the contact patch.

The second school of thought feels that a smooth steel drum does not accurately test a tire real world rolling resistance over an uneven surface. The purpose of an inflatable tire is to absorb road irregularities so that the entire mass of bike and rider does not have to be lifted over each bump. Lifting the mass of the bike even a very small distance uses energy and reduces speed. Testing tires on a smooth steel drum ignores the road irregularities which can be significant on a rough road. The tests performed by this group are on real roads but lack the controlled conditions of the steel drum tests. This leads many to doubt their results because they can be affected by rider position, wind, temperature and other factors.

We ride on fairly rough roads and I started riding a tandem with tires at 120 to 130 psi and then went to 32mm high quality tires at 90-100 psi and found them faster. Now we ride 38mm tires at 70-75 psi which I think are slightly faster on our roads and as a bonus more comfortable. For our team the added comfort also seems to help us keep the power up after a few hours in the saddle.

I believe that any high quality flexible tire is fast regardless of its width. Tire construction is the most important factor and there are cheap slow tires of all widths. On rough roads the difference is small when comparing good tires. While I do believe wide tires can be faster, on good roads I am not sure there is much of a difference. To put it all in perspective a little wind or a little stronger riders will outweigh the difference in tires. I think speed is mostly determined by the motors so I wouldn’t sweat the tires too much.

Other Modifications:

We are a moderately powered 280 lb team that likes a flexible frame. Our desire to try a more flexible frame led to the choice to ride a steel Santana because its design allowed me to calculate and test frame stiffness. Ultimately this led to the removal of the lateral tube. Liking flexible frames puts into a very very small minority of tandem riders. We arrived to that view by riding thousands of miles on tandems of varying stiffness so we know what we like. I don’t think flexible frames are for everyone but we seem to have an easier time staying on top of a gear when climbing.

Below is a picture of our bike with 40+mm tires mounted. I went down to 38mm due to tire clearance issues.

Wayne

tandem rider

Interesting. Thanks for posting!

2frmMI

Wayne: What rims/hubs/#spokes etc., on your 650Bs?

zonatandem

Have had a steel tandem frame break at 50,000 miles and again at 56,000 miles. Sold that tandem with 64,000 miles on the odo.
While most folks will not put that many miles on a tandem it shows that material fatigue can happen.
Have put 56,000 and 57,000 miles on 2 other steel tandems.
Have also broken an experimental steel fork at 13,000 miles.
Our mantra is that after 50,000-some miles perhaps it is not a bad idea to design another tandem for ourselves.
Been riding full carbon (Zona) tandem for the last 10 years and still extremely happy with our choice.
Buy the best you can afford . . . watcha gonna do, wait 'til you get older?
Pedal on TWOgether!
Rudy and Kay/zonatandem

Bornco

Thanks, great info!! I think we'll give some 32's a try.

We're fairly new to tandeming and have only ridden our bike, which is a Santana Arriva from the early 90's. My wife loves it and doesn't want to try anything else, I on the other hand, would love to test a few other bikes. I appreciate you taking the time to explain the changes to your Santana, sounds like you aren't afraid to think outside the box and have found the perfect bike for your team. I like the paint job!!

Jack

waynesulak

Thanks we are very happy with it. I would like to try a carbon bike with wide tires but don't want to spend the money to commission a one prototype by a builder that doesn't usually build that type of bike.

When looking for 32mm tires we found the choices few for fast flexible tires. Maybe others can give you some ideas.

waynesulak

It is a Santana so hubs are Hadley. Found them very high quality with easy maintenance. Mid range in weight
Spokes 14/15/14 double butted - 36 per wheel with brass nipples
Rims - Started with Synergy but Velocity had a bad batch and replaced them under warranty with A23 - 431 grams.
Total wheel set weight 1149 rear + 891 front = 2,040

2frmMI

Velocityusa.com only shows A23 in 700c. Do they make them in 650b but not show them on the web?

waynesulak

They are a nonstandard offering commissioned by Longleaf Bicycles available in 32 and 36 hole drillings. This is a lightweight "tubless ready" rim. That means it is difficult to mount tires because the diameter is on the large size compared to some rims.

Most people seem to use the Synergy 650B rim.

https://www.longleafbicycles.com/