A class bike build advice

[MTABike]

I recently bought a bike to prepare for speedweek and perhaps bub next year.  Starting with a 2005 Yamaha R6. I plan to run in the 650cc A-BG class.
I'm starting to plan out my chassis and have a couple of questions:

Which wheels and why? 
Seems like most people who are starting with a modern sportbike and even a lot who aren't are running stock style wheels (17" mags)
My initial thoughts are to run a narrow front wire wheel and as big and narrow of a solid rear rim as I can find tires for.   From the reading I've done it seems like maybe the ease of finding speed rated tires is choosing a lot of peoples wheels and tires for them.  Is this correct? With an inline 4 tearing a wide hole in the air is my front tire even really going to make much of a difference?

Rear suspension?
Should I run it and why or why not?  One of the things that drew me out to Bonneville in the first place is the stripped down rigid naked bikes I kept running across. I would love to build in this style, but if rear suspension is going to help go faster, I'm all for it. The general idea I have for this chassis is to keep it as low as possible with a water tank where a reasonable swingarm pivot would normally be between the engine and rear wheel.

Wheelbase.

Where do I start as far as coming up with a reasonable wheelbase for a bike of this type. my plan is to mock up the wheels, motor, and forks with cardboard versions of the components I plan to run between the engine and wheel and see where I'm at. Stock wheelbase is around 55". In my head it seems like 72"-84" might work.  I'm 6'4" and would like to have a bike for once that doesn't make me look like I stole it from a kid.

I'm sure that I'll have lots more questions as this progresses but some advice on these topics would help me progress! Thank you very much and I look forward to your responses.

~Scott

[55chevr]

Get the rule book for where  you are planning to race ... My bike is 72" wheelbase and rigid ... a bit rough on the body at Maxton but no problem at Bonneville and Loring ... the reason for sport bike stuff is cheap and available ... tires are no problem to get ... and the stuff works.

[55chevr]

I used an S1W Buell donor bike ... nice wheels / front end ...

[MTABike]

I have a copy of of the 2010 SCTA book.  Have been studying it quite thouroughly. Your bike looks great.

[wobblywalrus]

The tubeless tires on mags are somewhat safer than tube types on wire wheels.  Lighter, too. 

[MTABike]

Thank you for the advice so far guys.  I suppose I should have waited till after WoS to ask since anyone who can be is on the salt.  Any tips on front end setup?  Inverted fork that I have now vs a narrower coventional telescoping front with narrower front mag? I'm pretty sure if I use my current forks that it will require new tripple trees to get the trail right with more rake.

[MTABike]

Last night some buddies helped with a rough mockup so I could get a more specific idea of what goes where while I prepare to build the frame jig and frame.

Rough numbers
Rake: 35 degrees
Wheelbase: 78"
Seat height: 24"

the parts


with "rider"



Wondered if anyone has more advice or guidance.  I personally think that the back wheel should come closer to the rider in order to keep the amount of ballast down.  Seems like I can tuck my head in better than I thought I would be able to.
Thank you,
Scott

[Stan Back]

I always thought it was a good idea to attach the rear wheel.

[wobblywalrus]

What engine does it use?

[Stainless1]

I always thought it was a good idea to attach the rear wheel.

Roadsters ya, bikes sometimes...

It looks like you have raised yourself up into the wind unnecessarily, A bike, think a little more outside the norm.  The low seat position is good, the high gas tank is bad.... 
You can always add ballast in front of the wheel, the more room you have to hide stuff from the wind behind the engine and you the faster you will go. 
Just my thoughts, good visuals... stare at the pictures, play a little and take more.

[55chevr]

Rake: 35 degrees --- perfect
Wheelbase: 78" --- good ( mine is 75 - works well - very stable at 150 )
Seat height: 24 --- good -

[octane]

Hi Scott
You say I'll run in the 650cc A-BG class.
What kind of blower/turbo set-up do you have in mind ?

.. With an inline 4 tearing a wide hole in the air is my front tire even really going to make much of a difference?

Here's something to have fun and play around with
concerning frontal area/drag/HP
that I used for my little supercharged Indian:

Go to : DRAG LOSS CALCULATOR
( and scroll down for 'calculator')



For calculating the frontal area I took a pic from the front
with markings for each 10 cm. ( This is what the bike looked like back then.
It's a bit different today )




...then made a 10 x 10 cm grit
( Arms tucked in more, on this pic )


...and calculated the area.
That came to 0.3355 sq. meter ----> 3.605 sq. feet.
As the parts further back from the grit-line appears smaller than they are,
so I adjusted it up to 3.9 sq. feet

I set the cd to 0.9, based on a know figure for another bike
and punched the figures into the drag loss calculator
Don't forget to ad to the total weight of rider: helmet, leathers, boot, gloves

cd----------------------.9
frontal area-------------3.9 sq. ft.
weight------------------539 lbs.
speed-------------------100 mph

 Horsepower needed....: 24.9

...............

cd----------------------.9
frontal area-------------3.9 sq. ft.
weight------------------539 lbs.
speed-------------------120 mph

 Horsepower needed....: 42.3


Good luck with your bike !

[dw230]

The late Cliff Gullet had a sports store in Bozeman, Yamaha bikes, snow mobiles, water craft, etc. His brother, I'm sorry  - his name escapes me right now, runs the shop now I believe. They are experienced salt racers. I am sure you could get some good input from them.

Anyone remember the store?

DW

[Buickguy3]

  Dan
That would be Team-Bozeman.com. They are the Yamaha dealer.
  Doug

[bak189]

Lars, those leathers certainly fit you a lot better then they did me.....especially now, I just got to loose weight...oh, sure