BM Open wheel cars

[xxguitarist]

It seems that BM allows all formula cars that are not otherwise classed (CM and FM cars), but the class is basically exclusively D sports racer types.

Modified class B (BM)
All Formula Cars or Sports Racers compliant under the current Club RacingGCR Sections 9.1.1.A.1 a-h or 9.1.8.D.1 A-H, unless specifically classed else- where, with the following exceptions:

Why don't we see any formula cars running nationally? Aero, weight, motor restrictions?

Thanks for the input!

[DavidC.]

It seems that BM allows all formula cars that are not otherwise classed (CM and FM cars), but the class is basically exclusively D sports racer types.



Why don't we see any formula cars running nationally? Aero, weight, motor restrictions?

Thanks for the input!

Im on the waitlist even though I know I won’t be as competitive this year. Next year, hopefully aero and motor upgrade will make me more competitive.

[David Ferguson]

Back with I was running Solo II, the hot B-Mod cars were Water-cooled SuperVees. or old Formula Atlantics. They were pretty quick.

The DSR advantage for autocrossing, is that they often were built with a narrow track to keep the weight down, and a narrow track with low weight can be an advantage in autocrossing.

[Jim Garry]

The formula cars allowed in BMod follow the Formula Atlantic rules. Those cars are pretty ungainly for BMod compared to the narrow, short sportsracers that do run. They are usually much heavier too due to their engine size.

From the rulebook:

1. Turbocharged and supercharged engines are not permitted.
2. May use any automobile-based 2v/cyl engine up to 1300 cc, any 2-stroke motor up to 900 cc, any 4v/cyl or more engine up to 1005 cc.
Minimum weight with driver (lbs.):........................................... ..............1020

3. May use any 2v/cyl automobile-based production engines up to 1615 cc.
Minimum Weight with driver (lbs.):........................................... .............1110

4. May use any 4v/cyl or more engine up to 1615 cc. May use any 2-stroke up to 1300 cc or Mazda 12A rotary with any porting and any carbure*tion. May use fuel injection without weight penalty as required by the GCR.
• Minimum weight with driver (lbs.):........................................... .................1180
5. May use any engine up to 3000 cc.
Minimum weight with driver (lbs.):........................................... ..............1285

6. Minimum rim width:............................................ .................................................n one
7. Maximum allowed rim width (in.):............................................ ..........................15

Motorcycle engines allow cars to be light. FAs don’t use motorcycle engines. F2000 is allowed at only 1090 but the engine is down on power compared to a modern bike engine.

However a few years ago the allowance was opened up so that an original FA was not required and new chassis were built according to those rules, but much smaller. So the class is seeing home built formula cars, or converted formula cars, that are much smaller and lighter and running with a motorcycle engine. However they have to run the FA aero requirements which are somewhat more restrictive than those for the sports racer specs. But one of these cars did win a National Championship a few years ago.

[CM/FFdriver]

Does FB fit in the BM category, Motorcycle engine just not the full body of the DSR

Ben

[xxguitarist]

DavidC, Hope you're able to make it in. It filled fast this year! What is your car?

Jim,
My reading of the rules seems to indicate that solo has exceptions of:

B. Minimum wheelbase of 80” (203.2 cm).
9. Minimum width for all cars shall be no less than 57” as measured at thenarrowest end of the car at the tire outer sidewalls with a minimum 14psi of tire pressure.

So the car could be modified (?) to reduce either width or wheelbase as desired?
Or does this segment refer back to the GCR dimensional requirements for FA?

Reading the rules, like you posted..

2. May use any automobile-based 2v/cyl engine up to 1300 cc, any 2-stroke motor up to 900 cc, any 4v/cyl or more engine up to 1005 cc.
Minimum weight with driver (lbs.):........................................... ..............1020

Is it not allowed to convert a formula to motorcycle power under 1005cc?

[Jim Garry]

Does FB fit in the BM category, Motorcycle engine just not the full body of the DSR

Ben

Yes but with FA aero

[Jim Garry]

My reading of the rules seems to indicate that solo has exceptions of:


So the car could be modified (?) to reduce either width or wheelbase as desired?

Yes. But who wants to take an historic FA car and cut it up?

Reading the rules, like you posted..

Is it not allowed to convert a formula to motorcycle power under 1005cc?

Yes and again no one has wanted to destroy an FA car. Too much value would be lost for what? Just take a bit of the money you would have spent and buy/build your own BMod Solo car.

[xxguitarist]

Yes. But who wants to take an historic FA car and cut it up?


Yes and again no one has wanted to destroy an FA car. Too much value would be lost for what? Just take a bit of the money you would have spent and buy/build your own BMod Solo car.

Jim,
I appreciate all the input.
This makes sense. Is it correct that BM has no requirements like CM on having a manufacturer tag?
If so, then one could start from scratch, or use bits and pieces of say a damaged FF frame, so long as they stayed within the dimensional and weight requirements?

Andrew (Black RX8 in DSP at NER)

[xxguitarist]

While we are discussing the FA aero, I did some digging in the GCR- july 2018. I'm not finding a complete description of the aero device requirements. I'm sure there's more to it, but I'm not finding it... Can someone direct me to the right section?

9.1.1. Formula Atlantic (FA) Specifications GCR - 194


Bodywork:1. No part of the bodywork and aerodynamic devices shall exceed in height a horizontal plane 90cm(35.4”) above the ground. The safety roll bar/roll cage and the engine air box are not included inthis height restriction. Measurements are to be made as raced with driver on-board.
2. The overall maximum width of the bodywork behind the front wheels shall not exceed 130cm(51.18 inches). The maximum width of any aerodynamic device situated behind the rear wheels,including the rear wing, shall not exceed 110cm (43.307 inches).
3. The bodywork ahead of the front wheels may be extended to an overall maximum width of 150cm(59.055 inches) provided it does not extend beyond the outside of the front tires. Flexible ormovable aerodynamic skirts are prohibited. No part of the body or suspended part of the car shallextend more than 1cm (0.394 inches) below the horizontal plane forming the bottom of the tub orchassis floor (both static or in motion).
4. Any part of the bodywork ahead of the front wheels exceeding an overall width of 110cm (43.307inches) shall not extend above the height of the front wheel rims.
5. Any specific part of the car which has an aerodynamic influence on the stability of the vehicleshall be mounted on the entirely sprung part of the car and shall be firmly fixed while the car is inmotion. Aerodynamic devices, including wings and end plates, shall not extend to the rear morethan one meter (39.4 inches) from the centerline of the rear wheel hubs.
6. Neither the safety roll bar nor any of the units associated with the functioning of the engine ortransmission shall have an aerodynamic effect by creating a vertical thrust.

7. The leading edge of an airfoil fixed to the front of the car shall not be sharp. Minimum radius --0.5cm (0.2 inches).

[DavidC.]

DavidC, Hope you're able to make it in. It filled fast this year! What is your car?

Jim

Van Diemen RF84 currently with an old ‘93 Honda CBR 900 motor.

[Jnovak]

Here are a few pics of a Bmod I designed and built for a customer. It is based on our Blade F600 but with a GSXR1000 race motor and shocks. I do not have pictures of the car with the Blade body with front and rear wings fitted. Wi!l find them on my other computer and post them soon.

[Jim Garry]

Jim,
I appreciate all the input.
This makes sense. Is it correct that BM has no requirements like CM on having a manufacturer tag?
If so, then one could start from scratch, or use bits and pieces of say a damaged FF frame, so long as they stayed within the dimensional and weight requirements?

Andrew (Black RX8 in DSP at NER)

Correct

[Lynn]

From the 2018 Solo Rule Book:


F . Aerodynamic restrictions for Formula Atlantic (all open-wheel in BM) shall follow the current Club Racing GCR Formula Atlantic Preparation Rules with the following Solo® allowances:

1. Wings and all other aerodynamic devices front and rear may match but shall not exceed sports racer P2 GCR maximum height (45.25” per P2 GCR 9.1.8.D.D.2 ).

2. Front wing width may match but shall not exceed overall front width as measured at the tires. Front wing elements may not extend behind the front wheel centerline.

3. Rear wing width shall not exceed the Club Racing FA specs with the exception that endplate gurney lips are not included. Endplate Gurney lips shall not exceed 7 cm (2.756”) additional width per side and shall not deviate more than 10° from vertical. No part of the entire rear wing assembly, including wing elements and end plates, shall extend more than 1 m (39.37”) to the rear of the rear wheel centerline.
a. Except for cars meeting the dimensions of subsection F.3.b herein, the rear wing element assembly maximum plan view fore-aft dimension shall not exceed 70 cm (27.56”).
b. For cars 66” wide or more at the rear tires and which also meet a weight of 1180 lbs, the fore-aft dimension of the rear wing element assembly plan view shall not exceed 90 cm (35.43”).

4. Side pod or other parts not considered chassis are not required to attach or stay above a line situated 1 cm (0.4”) above the chassis bottom (this is an exception to GCR 9.1.1.A.1.g.10).

5. Flexible ground sealing is permitted on cars 66” wide or more at the rear tires and which also meet a weight of 1180 lbs.

[xxguitarist]

Lynn,
Thank you for your contributions.
It is seeming like the wings may not be fully detailed, but have a set of requirements for their legal adjusting and location?
I found this, which also includes better versions of the swift drawings:
http://f2000championshipseries.com/p...0-%20Print.pdf


What I haven't found is hard rules on the total area, element count, and angle of mounting (and relatively less significant things like chord depth, profile, etc)

Is this because all FA cars came with the same aero package, and it is not intended to be able to be reproduced by an individual or team?

[CM/FFdriver]

I'm thinking in two ways

1. being an OLD DSR chassis with some old shcool suspension geometry if this is true? and then cost of a DSR chassis.

2. A newer FB chassis with newer suspension geometry is this true? and then the cost.

maybe 3 ways

I always thought about AM and there homebuilt chassis and how bad or good the suspension geometry is and if you know of a chassis with 90" length and 70" width with very good or proven suspension geometry, put big fat tires and lots of wing front and rear, Go...!

Ben

[Jim Garry]

You have to consult the FA rules in the GCR.

[Jim Garry]

A recommendation ...

Do yourself a huge favor and stop asking questions for now, and start reading. You really don't know if we're giving you the right answers. And we may be leaving things out that you need to know

Download the Solo Rules and the GCR. In the Solo Rules read section 18 and also Appendix A, the Modified subsection.

Then read the FA rules in the GCR which are referenced by the Solo Rules.

Then ask questions if you're not sure.

[xxguitarist]

Jim,
I'm not seeking to be spoon fed, and I appreciate the help, however I am having trouble finding the true definition of FA wings.

I have posted quotes from GCR appendix on FA aero (post #10)

I also had already reviewed the solo rules section related to open wheel cars in BM, the same as Lynn posted.

I have found side plate templates for a Swift (FA?) end plate here, provided as a scan of some painters tape:
https://www.scca.com/pages/technical...-and-downloads

I have read section 18 & the appendix related to BM. I see in section 18 that there is a square footage of wing specified, but that is for "Specials" or AM cars by my understanding.

In the appendix, I see references to FA spec, with allowances for additional gurney lips.

I am sure I am missing something, so the help that you & others offer is valued.

[David Ferguson]

It sounds like you've found the right sections of the GCR. You can see the rear wings can be at most 110 cm wide, and must be no higher than 35.4". I don't see a restriction on number of elements, but there is a limit to how far behind the rear axle centerline the wing can extend (39.4"). Old FA wings had a very large chord, but more modern cars use a shorter chord and more elements.

There is a limitation on the front body work (ie, wing) width (150 cm), and this may be no higher than the height of the front wheel rims. Also there is a minimum radius for the leading edge of the bodywork.

Looks like you would have plenty of area to play -- perhaps you were expecting the FA rules to be more restrictive for more items like the FC rules.

[griceiv]

Jim,
I'm not seeking to be spoon fed, and I appreciate the help, however I am having trouble finding the true definition of FA wings.

I have posted quotes from GCR appendix on FA aero (post #10)

I also had already reviewed the solo rules section related to open wheel cars in BM, the same as Lynn posted.

I have found side plate templates for a Swift (FA?) end plate here, provided as a scan of some painters tape:
https://www.scca.com/pages/technical...-and-downloads

I have read section 18 & the appendix related to BM. I see in section 18 that there is a square footage of wing specified, but that is for "Specials" or AM cars by my understanding.

In the appendix, I see references to FA spec, with allowances for additional gurney lips.

I am sure I am missing something, so the help that you & others offer is valued.

you are getting confused by the swift 016 specific allowances. Ignore all of the 016 specs and focus on the actual FA rules.

[Jim Garry]

Last two responses are excellent.

I meant no insult in my response. Should have taken more time in constructing it.

[xxguitarist]

Thank you all for the input.

David, You're correct, I was expecting a much more restrictive rule set as usual in SP, SM, etc solo classes- spoilers may be this tall, follow profile of car, etc and SM is strictly limited to 8 sq ft area, etc.

I went through and compiled the list of requirements from GCR, then edited it with the solo allowances. There definitely seems to be quite a bit of room to experiment.


Jim, no worries :-)

[TedV]

I had looked at a Formula Jedi chassis as a base for BM car. They aren't the best crash protection for hill climbs and meeting trees, but are fine for assaulting cones in autocross. DSR footprint and skinny. Kinda like what Jay posted but from England.

[lowside67]

It seems that BM allows all formula cars that are not otherwise classed (CM and FM cars), but the class is basically exclusively D sports racer types.

Why don't we see any formula cars running nationally? Aero, weight, motor restrictions?

Thanks for the input!

In my opinion, this is easily answered - autocross heavily favours smaller cars - narrower and shorter wheelbase. The current class leaders are mostly either purpose built or based off early 78” wheelbase Legrand sports racers which have been stretched to meet the 80” minimum. On the other hand most modern FC/FB cars have WB exceeding 100” - a massive and likely insurmountable detriment.

Finally, the aero rules have changed in recent years and now provide for some parity between sports racer and formula car designs but historically dramatically favoured sports racers.

Short of purpose built or hacking up a car, I would wager it is impossible to find something open wheel that is small enough physically to be worth trying to build against the incumbent sports racers. But that’s just my $0.02.

-Mark

[-pru-]

A few photos from 2013 Solo Nationals which Dan Cyr won BM with an open wheel car (car #65 below)...

[lowside67]

So essentially an AM car with BM legal wings and drivetrain? I would love to know what chassis that car started with.

Cheers
Mark

[-pru-]

So essentially an AM car with BM legal wings and drivetrain? I would love to know what chassis that car started with.

Cheers
Mark

Yep, folks that see the #65 car call it "AM-lite" or "7/8-AM"

Via owner Dan Cyr:

Originally pocket rocket
Danny Collins out of Colorado
Three chassis made

Take care,

[-pru-]

This popped up on my FaceBook feed today: X1 Racer

[OneWayOut]

This popped up on my FaceBook feed today: X1 Racer

"Exact pricing to be confirmed upon completion of the prototype."

#lolz

[phantomjock]

Sweet looking, Very low production rate, however.
Go-fast 260 KPH - they say.
Lower cost than FF - they say.
Is this the Formula Miata - from a previous discussion?

Cheers - Jim

[chrisw52]

This popped up on my FaceBook feed today: X1 Racer

neat looking car, but a mono shock in front.

[lowside67]

I have always operated on the understanding that BM has largely been won by Legrands given that they are one of the only 80" WB sports racers that are available.

With that said, according to this site, Tom Ellam's Cheetah which dominated the field at last year's nationals has a 90" WB and is 64" wide.

If that's correct, that would suggest to me there might be a much larger number of production formula and sportsracers that could be competitive.

I have been looking at the Formula Jedi cars as a base for a BM/hillclimb car: 81" WB, 58" wide at front tires, 62" wide at rear tires, approx 725lbs without driver. That would easily allow for adding some weight via larger wings and still require ballast to get to 1,020lbs for a 1000cc motor.

My preference given the interest in hillclimb is to have the longest and largest car that is not going to be a detriment at autocross for overall stability at higher speed events. I am wondering now if I should actually not be targeting 80" WB but rather 90? I would love to just buy a Stohr WF1 but at 97" WB and 64" wide I am not sure if that's the right call for BM.

-Mark

[David Ferguson]

I would love to just buy a Stohr WF1 but at 97" WB and 64" wide I am not sure if that's the right call for BM.

-Mark

It's the right call. Give it a try. The suspension on a Stohr has really good mechanical grip and I am sure it would be a winning combination.

[xxguitarist]

Quite a crazy year at nationals, especially for BM.. Feel bad for you guys having to run after dark!

In lighter news, car 74/174 was similar to what I had considered. It started life as a FF, and was converted to GSXR 1000cc power. I chatted with the drivers a little, and they were questioning some of their aero effectiveness.
The other non-DSR type car there was something along the lines of a F500/FM car plus aero, with a 2 cyl 2 stroke & CVT.

[lowside67]

I was there as well and was surprised by how little aero the top BM cars really have - the Ellams have just a flat bottom that ends in front of the rear axle and just exits into the mess of rear axles, arms, etc. No diffuser, no anything.

I think these cars are more mechanical grip than is intuitive at these speeds which would seem to support that a formula car could definitely be equally competitive.

-Mark

[Jim Garry]

The wings alone make a good bit of df. I removed mine (another Cheetah) at a local event. Car was still balanced. It accelerated significantly better. But was 2 seconds slower on a 50 sec course.

[lowside67]

The wings alone make a good bit of df. I removed mine (another Cheetah) at a local event. Car was still balanced. It accelerated significantly better. But was 2 seconds slower on a 50 sec course.

Good point - I should have been more clear, I guess I meant aero related to the body. The wing allowance is larger for an open wheel than a sports racer so if the wings are the primary aero device for a BM car, this would seem to suggest an open wheel could be as good or perhaps better.

-Mark

[Jim Garry]

At issue is the design restriction on open wheel car rear wings in BMod. They must conform to FA rules. That puts restrictions on location of the rear wing, size, and aspect ratio. Thus open wheeled cars are limited in rear wing design. This effectively limits their front wings because if made too large the cars will be poorly aero balanced.

Regarding the Ellam car, you may have missed an underbody part that is completely legal.

[lowside67]

At issue is the design restriction on open wheel car rear wings in BMod. They must conform to FA rules. That puts restrictions on location of the rear wing, size, and aspect ratio. Thus open wheeled cars are limited in rear wing design. This effectively limits their front wings because if made too large the cars will be poorly aero balanced.

Regarding the Ellam car, you may have missed an underbody part that is completely legal.

I think you may be surprised by what the FA allowances are:

Rear wing:
Max width = 110cm / 43.307" (per GCR 9.1.1.A.1.g.2 on page 193)
Max plan depth = 70cm / 27.56" (per Solo BM F.3.a on page 203)
Max height = 45.25" (per Solo BM F.1 on page 202)

A 43" x 27" wing assembly is approx 8 sqft.

Front wing:
Max width = width of car assume 64" (per Solo BM 7.F.2 on page 203)
Max depth = unrestricted assume 18" (no rule)
Max height = height of front rim (per GCR 9.1.1.A.1.g.4 on page 193)

A 64" x 18" wing assembly is approx 8 sqft.

According to my calculations, a formula car could have around 16sqft of wing while a sportsracer is limited to 8sqft total.

To me, this is a compelling advantage to a formula car.

-Mark