Tuesday, February 18, 2020

Plan 2020 - Wheels

Track Wheels

Other than the rider's position (meaning the aero drag of the actual rider), the biggest aero improvements can be made on wheels.

Track wheels are different from road wheels

First, they have to be secured using a nut and bolt type system. They cannot use a quick release skewer.

The rear dropouts are horizontal, meaning you can move the hub fore and aft. Most road dropouts are vertical so no horizontal movement - you need much less force to hold a wheel in place in a vertical drop out versus a horizontal one. Because of that, although there are front wheel skewer adapters, in the rear it's generally best to have a very strong nut-bolt system, else the wheel will move under pressure, usually shifting sideways so that the tire rubs the frame. Alternatively some dropout screws, designed to limit axle movement within the dropout, will keep the wheel from moving. With such bolts a rider might opt to use a lighter nut-bolt system.

Second, track wheels have two threaded sections on the rear wheel, one for a single cog, with a reverse thread on top of that for a reverse thread lockring. The cog screws on normally, and when you pedal your pedaling action tightens the cog. Believe it or not, it's possible to unscrew that cog, if you backpedal hard, or skip and skid the rear wheel while backpedaling. Therefore the reverse thread locking is critical - it prevents back pressure from unscrewing the cog. It actually tightens if you manage to start unscrewing the cog. Also, for safety reasons, it's illegal to use a hub that doesn't have a reverse threaded lockring.

Although old fashioned road freewheel hubs are threaded the same as a track cog, the lack of a reverse lockring bit means you can't use a simple road freewheel hub on the track. Rear track hubs are unique.

Rear track wheels are also very narrow, 120mm from outside the locknut to outside the locknut. Rear road wheels are much wider, 135+mm. So you can't use a road rear wheel for track without a lot of work. You'd need to narrow it up and add that reverse lockring thread.

Front wheels are easy. They are the same width at the axle as a road hub, 100mm, and with a track adapter skewer, you can use pretty much any road front wheel on the track. There aren't any extraordinary forces on the front wheel so no issues using a skewer adapter system that clamps with a force similar to a quick release skewer.

Rolling resistance, comfort, and rigidity

Since trackies aren't worried about comfort, you can get away with quite narrow tires. Narrow tires are generally more aero, so I'll need to get a few 19mm and 21mm tires.

Also, since tracks are relatively smooth, and tire deflection is wasted energy, track riders tend to ride with a lot of air pressure in the tires. No need for big, cushy riding tires. They'd only absorb some sprint energy better utilized to driving the bike forward.

Likewise, because tracks tend to be sheltered a bit, control in crosswinds is less critical. U shaped rims aren't as critical, and in fact, for indoor tracks, many riders will use a disc front wheel, something completely unmanageable if riding out on the road.

Apparently, and I've yet to verify this, lateral stiffness is a thing, with significant G-forces acting on the rider on the banking. My early T-Town memories don't seem to reflect this but I was probably going too slow.

Wheel Aerodynamics

I did some extensive research on track racing wheel aerodynamics. This basically meant watching countless track videos on YouTube while riding the trainer. It also involved perusing some of the time trial forums to see exactly what people are using, what they've found to work.

I also wanted to work within the experiences I had, meaning riding in some wind (2020 Nationals is at an outdoors track), front disc wheels (I had a 24" front once), and my budget. I love cross-tailwinds with my tall wheels because I can fly. I figure the same applies for the track, but I'll get about 80 meters of flying on the longest of straights before I'm turning again. I know front disc wheels are hard to control. And my budget it limited.

Remember that the front wheel is responsible for about 2/3 of the aero drag of the wheels. It also has a massive effect on handling, since it acts as a lever to turn the bars. The rear wheel is less important, but it affects handling very little. On the road my approach has been to use the tallest rear wheel available (90mm for the Stingers) with the tallest front wheel I can handle in moderate wind (75mm for the Stingers). In really windy conditions I'll use a shorter front wheel to improve control, dropping to a 45mm front wheel or even a non-aero 26?mm wheel.

With that in mind this is what I've gathered, with a "Wanted" list for each section.

Disc Wheels

The fastest wheels are lenticular (lens shaped) disc wheels, meaning they're a bit wider at the hub than at the rim. Viewed from above they're sort of lens shaped, like a flatter contact lens. These sail best when in an indirect headwind and they sail really well in a cross-tailwind.

The problem with a front wheel is that it catches massive air, like massive. On a 24" disc wheel I got blown across about 10 feet of road, almost into oncoming traffic, and I was going only 25 mph. With a full size 700c disc wheel, I would image it's only really usable indoors, with zero wind. My online findings seem to confirm this. Therefore a front disc will be for a different year, when Nationals is indoors, or, if conditions are absolutely ideal, for 2020.

Basically I'll see if I can pick up a lenticular front disc for a steal. Otherwise I'll let it go.

For the rear wheel, again, lenticular discs are fastest, but the flat discs (Zipp) are very close. For me I think it'll be virtually indistinguishable. The biggest issue with Zipp rear discs is that the track axle is pretty much nonexistent, unavailable. It's like the unicorn of wheel parts. List price is almost $300 so it blows the budget out of the water.

This meant I was searching primarily for semi-affordable rear disc wheels, like Corima and Fast Forward. If I could pick up a Zipp track disc I'd do that, as long as it was substantially cheaper than a lenticular.

Wanted: Lenticular rear disc. If a cheap Zipp rear disc shows up, so be it. Less expensive lenticular disc front wheel (since it won't be used much, if at all, in 2020).

Budget: $1000 lenticular rear, $650 flat rear, $900 lenticular front. I'd want a second rear wheel, probably a bargain flat disc wheel, as a spare.

Three and Five Spoke Wheels

With front discs being virtually unusable except indoors, I need to have a low spoke count front wheel. The fastest front wheel on the road has been the HED3, previously known as the Specialized TriSpoke. Fortunately for me this wheelset was my secret weapon back before aero wheels were a thing, and I have both a tubular front TriSpoke and a clincher front TriSpoke.

(I have a TriSpoke rear freehub and a 105 freehub fixed gear adapter but I learned that the TriSpoke uses a Dura-Ace freehub so the adapter doesn't work. I'm waiting to use that fixed gear adapter though as it's a unicorn item.)

I looked into 5 spoke front wheels but found that although they were stiffer, they weren't necessarily faster. If it was all about speed, the TriSpoke should work.

The only drawback with the TriSpoke is that it's flexible. How that affects me on the track I'm not sure, but for now the most cost effective approach will be to use the TriSpokes I have now.

Wanted: nothing, but if TriSpoke is too flexible maybe a 5 spoke front wheel.

Budget: nothing

Spoked Front Wheels

The final wheel for my track racing quiver would be a spoked front wheel, like the wheels I use for the road. I have a couple of them so I figured if the TriSpoke wasn't rideable I could use my Stinger7 front wheel.

At the worst I might invest in a Stinger9, a 90mm front wheel. I don't know if it would get me that much extra speed - it probably wouldn't - so the 7 should be a good fallback wheel. It's be fine in a mass start track race since that's what I use in mass start crits.

Plus I can use a 7 in a crit. I'd really want a 7, with the TriSpoke or a front disc my preference on the track.

Front wheels can be secured using a bolt-nut combination that looks like a quick release skewer without the lever. I have one set already, may need to buy another couple fronts. This means I can buy a quick release hub front wheel without worrying about track legality.

Wanted: A second Stinger 7 or a Stinger 9.

Budget: $500

Trainer wheel

Believe it or not I don't have a clincher track rear wheel, meaning one with the fixed gear and the narrow spacing of a track bike. I have two rear track wheels right now, one so bad its hub consists of steel sheets pressed together; I won't use that one. The other is nice, a 32H Suntour Superbe Pro hub wheel. It's laced with a narrow tubular rim right now.

I'd like to get a 24H clincher rim, a cool looking one with stickers on the side (no braking surface), and lace it onto the hub. It'd be 16 spokes on the drive side, cross 2, and 8 spokes radially laced on the non-drive side. I've done this before when building 24H rear wheels for the road and it works great. I just have to work out the spoke lengths for such a build.

This wheel would be my warm up wheel, trainer wheel, and ultra emergency spare rear wheel.

Although I'm not sure why I'd need a spoked clincher front wheel, I have a Eurus front wheel with a new rim, sitting in my inventory for literally 10-12 years. I'll lace over the new rim - it should work as a wheel for rollers, maybe for warm ups, or out-on-the-road experiments.

Wanted: 24H disc brake clincher rim

Budget: $100


I have some wheel shopping to do.

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