Why Not Use A Tungsten Flywheel For Flat Track Racing?

[nicholastanguma]

Purpose built flat track race bikes use super heavy flywheels in order to achieve the very specific torque and traction specifications required for successful FT racing. As far as I know, the diameters of these flywheels are somewhere in the range of an enormous 7 inches to reach such weight.

When Harley-Davidson was attempting to make their liquid cooled 750cc v-twin into a competitive FT racer they found themselves flummoxed by the fact that particular street production mill's cases simply didn't have enough room in them for a 7 inch diameter flywheel. The engine could be tuned to make race level power, but the street production sized flywheel just wouldn't allow for that power to be made at the rear wheel in the very specific way that creates successful FT racing.

So I got to thinking: why not simply employ a smaller diameter flywheel of something super heavy, such as tungsten?

Or is weight alone not the only issue at play--perhaps the rotational forces of a 7 inch flywheel diameter are also somehow important?

[PackardV8]

I’m told that making the rear wheel into a big flywheel became so common in US flat-track that AMA Pro Racing has now set a maximum wheel weight. In response, teams do what they can to lighten the hub part of the weight so they can locate more weight at the rim, sometimes even utilizing an inner tube.

[n2omike]

Rotational inertia has more to do with where the located... than the weight itself. The further the mass is from the axis of rotation, the more of an affect it has. The highest rotational inertia for a given weight is a hoop... where all the mass is at a maximum distance from the axis of rotation. A spinning disk would have less, as much of the weight is closer to the axis. Larger diameter is king.

Tungsten has an extremely high hardness and is difficult to machine. A tungsten flywheel would be very expensive to produce, but not impossible.

[Truckedup]

40 years ago when Honda was chasing Harley , Honda was behind until they realized the 45 degree Harley 315-405 degree V twin firing order gave more traction ....So now it's heavy inner tubes,,,Amazing simple innovation

[billet]

Tungsten has an extremely high hardness and is difficult to machine. A tungsten flywheel would be very expensive to produce, but not impossible.

Not flat track racing but dirt late model racing: A few years ago the trick of the week was to add weight to the LR axle tube and or the LR wheel. I know for a fact that least one high profile driver/team made 2" wheel spacers (LM's have wide five pattern wheels so the lug pattern is roughly 10.5" diameter so the spacer ends up being almost 12" in diameter). They purchased enough tungsten to make 4 wheel spacers, the material alone was 20K.

We now have a weight rule on the hub, wheel and tire assembly of around 40#, but nobody checks it anymore

[hoffman900]

AMA Flat Track racers were using a heavy rear wheel, which I also believed helped with handling balance issues, let alone better traction. There is a weight limit now as mentioned above. I do believe they use heavy iron rotors though.

Issue 129 of Race Engine Technology did a deep dive dossier of Vance and Hines work on developing / modifying the "new" Harley XG750R engine for AMA Production Twins and a modified version with an aftermarket head for Super Twins racing. They did specifically talk about increasing MOI but not increasing weight on the crankshafts, and they did have trouble with breaking them. Ultimately, they use a modified production crank in both, with tungsten pucks bolted to them to increase MOI, but machining the rest of the crank to take total weight out. This is the way to do it as you don't need a whole crank made out of tungsten. They also use Tungsten pucks on the outside edge of flywheel as well, which is how they tune it for different tracks.

Formula 1 engine manufacturers has been using tungsten as a bolt on counter weight for at least 20 years now to reduce counterweight size (which allows you to lower the engine and shrink some other things down). Lots of pictures online of these types of cranks.

Here is how Honda did it in the mid 2000s:

8DDA5EAE-88E8-4E59-A5C9-6C82B2F71E8D.jpeg

[nicholastanguma]

AMA Flat Track racers were using a heavy rear wheel, which I also believed helped with handling balance issues, let alone better traction. There is a weight limit now as mentioned above. I do believe they use heavy iron rotors though.

Issue 129 of Race Engine Technology did a deep dive dossier of Vance and Hines work on developing / modifying the "new" Harley XG750R engine for AMA Production Twins and a modified version with an aftermarket head for Super Twins racing. They did specifically talk about increasing MOI but not increasing weight on the crankshafts, and they did have trouble with breaking them. Ultimately, they use a modified production crank in both, with tungsten pucks bolted to them to increase MOI, but machining the rest of the crank to take total weight out. This is the way to do it as you don't need a whole crank made out of tungsten. They also use Tungsten pucks on the outside edge of flywheel as well, which is how they tune it for different tracks.

Formula 1 engine manufacturers has been using tungsten as a bolt on counter weight for at least 20 years now to reduce counterweight size (which allows you to lower the engine and shrink some other things down). Lots of pictures online of these types of cranks.

Here is how Honda did it in the mid 2000s:

8DDA5EAE-88E8-4E59-A5C9-6C82B2F71E8D.jpeg

Terrific, thanks for posting!

[hoffman900]

AMA Flat Track racers were using a heavy rear wheel, which I also believed helped with handling balance issues, let alone better traction. There is a weight limit now as mentioned above. I do believe they use heavy iron rotors though.

Issue 129 of Race Engine Technology did a deep dive dossier of Vance and Hines work on developing / modifying the "new" Harley XG750R engine for AMA Production Twins and a modified version with an aftermarket head for Super Twins racing. They did specifically talk about increasing MOI but not increasing weight on the crankshafts, and they did have trouble with breaking them. Ultimately, they use a modified production crank in both, with tungsten pucks bolted to them to increase MOI, but machining the rest of the crank to take total weight out. This is the way to do it as you don't need a whole crank made out of tungsten. They also use Tungsten pucks on the outside edge of flywheel as well, which is how they tune it for different tracks.

Formula 1 engine manufacturers has been using tungsten as a bolt on counter weight for at least 20 years now to reduce counterweight size (which allows you to lower the engine and shrink some other things down). Lots of pictures online of these types of cranks.

Here is how Honda did it in the mid 2000s:

8DDA5EAE-88E8-4E59-A5C9-6C82B2F71E8D.jpeg

Terrific, thanks for posting!

That same issue of RET they do a deep dive with Ron Shaver. He talks about taking weight out of the crankshafts and not running a flywheel to specifically keep the engine from pushing the car into the corner. Said the Ford crank was originally 8 counterweights, but is down to 6 now and both the Chevy and Ford cranks are in the 43lb range.

[sbcharlie]

On the Yamaha twin flat track bike we weighed the crankshaft and made a bearing support on the outer crankcase cover. We currently building a billet cover to ad more weight and designing it so you can add or remove weight when needed

[pcnsd]

Class C traction and how to deal with it. Anyone remember the brake drag technique? It was once the latest thing.

Kenny Coolbeth brake drag.jpg

Jake Johnson brake drag.jpg

[RAS]

Do you know what Tungsten cost? Grinding it is a long process with expensive equipment. No.

[englertracing]

AMA Flat Track racers were using a heavy rear wheel, which I also believed helped with handling balance issues, let alone better traction. There is a weight limit now as mentioned above. I do believe they use heavy iron rotors though.

Issue 129 of Race Engine Technology did a deep dive dossier of Vance and Hines work on developing / modifying the "new" Harley XG750R engine for AMA Production Twins and a modified version with an aftermarket head for Super Twins racing. They did specifically talk about increasing MOI but not increasing weight on the crankshafts, and they did have trouble with breaking them. Ultimately, they use a modified production crank in both, with tungsten pucks bolted to them to increase MOI, but machining the rest of the crank to take total weight out. This is the way to do it as you don't need a whole crank made out of tungsten. They also use Tungsten pucks on the outside edge of flywheel as well, which is how they tune it for different tracks.

Formula 1 engine manufacturers has been using tungsten as a bolt on counter weight for at least 20 years now to reduce counterweight size (which allows you to lower the engine and shrink some other things down). Lots of pictures online of these types of cranks.

Here is how Honda did it in the mid 2000s:

8DDA5EAE-88E8-4E59-A5C9-6C82B2F71E8D.jpeg

Terrific, thanks for posting!

That same issue of RET they do a deep dive with Ron Shaver. He talks about taking weight out of the crankshafts and not running a flywheel to specifically keep the engine from pushing the car into the corner. Said the Ford crank was originally 8 counterweights, but is down to 6 now and both the Chevy and Ford cranks are in the 43lb range.

900hp sprint cars with gigantic tires......
Vs motorcycle with radiused tires with very little contact patch.

[englertracing]

Tungsten has an extremely high hardness and is difficult to machine. A tungsten flywheel would be very expensive to produce, but not impossible.

Not flat track racing but dirt late model racing: A few years ago the trick of the week was to add weight to the LR axle tube and or the LR wheel. I know for a fact that least one high profile driver/team made 2" wheel spacers (LM's have wide five pattern wheels so the lug pattern is roughly 10.5" diameter so the spacer ends up being almost 12" in diameter). They purchased enough tungsten to make 4 wheel spacers, the material alone was 20K.

We now have a weight rule on the hub, wheel and tire assembly of around 40#, but nobody checks it anymore

Was this a dry slick setup?

If it was a typical setup I'd imagine adding flywheel weight, adjusting throttle linkage progression, adjusting engine power delivery, and suspension tuning would result in a faster car.

[englertracing]

I’m told that making the rear wheel into a big flywheel became so common in US flat-track that AMA Pro Racing has now set a maximum wheel weight. In response, teams do what they can to lighten the hub part of the weight so they can locate more weight at the rim, sometimes even utilizing an inner tube.

A guy I knew had a flat track cr500, told me he filled his swing arm with buckshot, and filled the tire with water.

I asked is the flywheel heavy?
No it's lightened