Dirtbikes w/street tyres

[Lowe119]

How well do the motocross bikes do against roadbikes in the same classes? I saw a couple racing at BFR last year and it seemed like they did well.  
I am just thinking about how hard would it be to take my dirtbike and put it on the track. I'm not too serious about it, but I was wondering what everyone's thoughts are on the subject....
Is there anything the road riders don't like about them on the track? Are they at a big disadvantage? Does it take a ton of modifications - tyres, gears, suspension, plastic?

[251am]

 I talked to a fella running a CR250 at BHF. He was having a blast. What are you thinking of converting? This guy was running 15/30 gearing.

[EM JAY]

   I ran with a few at BHF and they usually beat me, >:( I raced an MZ.  I dont think there is a problem with them on the track?   8)

[Lowe119]

I only have a KDX 200, so it's not as nice as the CR250s. But if I could dice with some people (and maybe get some wood), it might be an option.
What classes do they ride in? Supersingles? Ultra Lightweight Sportsman? GP Singles? It's not a road bike so it can't be in supersport or superbike, right?

[Nate R]

Generally, the wheels and front rotor(s) are replaced with street sized ones, and a bigger rotor.

Outside of that, just suspension.

[EM JAY]

   They usta run in Supersingles and I'm not sure of the sportsman classes?  Those classes no longer exist so now its combined into Ultra Lt. Wt. Superbike I think...

[Zac]

Here is a dirt bike with street tires (110/90-18 cheng shin on back and 90/90-21 dunlop 401 Harley tire on front, no other mods)



This was in an ASMA Vintage race.  I had the bike there to run the Supermoto race.  I took it out in a beginner track day session and ran faster than some of the beginners on 600s, with gearing that limited me to about 85 MPH (I was pulling fifth as I was still leaned over coming onto the straight).  Elaine usually runs her '72 Honda CL450 in the Vintage races, but because it is a pre-'93 class, she's usually out classed. I figured I could hang with her on the CR, and we ended up having a good race going back and forth quite a bit.  I had better acceleration and braking, she had better corner speed and a little more top speed.  Here's where she came around my outside off the start in turn 1:



So - a 250 motocross bike with street tires can keep up with a 30 year old, 30 hp bike.  

I'm currently building up a CR500 motard bike.  Basically: 17" wheels, 320mm rotor and 4 piston caliper, and lowered suspension, geared to the moon.  The motards are legal in any SuperBike class (singles are allowed unlimited frames), GP classes, Thunderbike, and GT classes.  What would you want to run?  ULWSB, and maybe LWSB, LWGP, GTL, and Thunderbike.

-z.

[Zac]

The road racers shouldn't have a problem with the motards on the track.  More entires means more competition.   :)  Motards do pretty well on tight, twisty tracks.  I had some good dicing with them on my MZ this year.  But as soon as the track straightened out, the power of my MZ really came on, and they had to play catch up in the corners.   ;D  Give it a try.  Cheap way to race, and you'll have fun.

[MZGirl]

The road racers shouldn't have a problem with the motards on the track.  More entires means more competition.   :)  Motards do pretty well on tight, twisty tracks.  I had some good dicing with them on my MZ this year.  But as soon as the track straightened out, the power of my MZ really came on, and they had to play catch up in the corners.   ;D  Give it a try.  Cheap way to race, and you'll have fun.

Sorry, that was from me.  Some idiot didn't logout on our home computer.   >:(   ;)

[Lowe119]

I don't see a belly pan on the pics....  ??? :-/ Do you need one for the tranny oil? Or is that just for engine oil. I'm pretty handy with fiberglass, so that won't be a problem, though. (it's my first 2-stroke)
So what kind of tyres? Metzlers?
Now I'm a little interested.  :P ;D

[Zac]

Per CCS rules 2-strokes do not need a bellypan.  That old Honda CL would for a CCS race.  For 2004 AHRMA changed their rules to require bellypans on both 4-strokes and 2-strokes, but the two stroke belly pans only need to hold some crazy small amount like 0.5 liter.  Most of the 2-strokes in CCS (250s, old RZs) are not running fluid retaining pans, unless they have an AMA legal lower.

Belly pans are a pain on the motorcross bikes because you can't use a motocross style stand anymore.

-z.

[Jeff]

Shane Myers ran his husky last year at BHF quite a bit, and at Gateway as well.  Off the line, he gapped people by hundreds of yards, and in the infield, he was as fast or faster than most.  However, on the straights, he would top out well before the bumble-bee's following him, so they would catch up or pass him.  It was really good racing...

As for mods??  Big bucks in wheels, suspension.  That's about it...

The only issue I have with Motards is if they get out on the track with 600+ inline 4's, or big twins.  They don't have the top speed, and pose a hazard on the straights.

I believe a guy was killed in 2002 at Daytona (if I recall correctly) during a practice while on a motard.  He was topped out on the straight, 3 riders came up behind him, one went left, one went right and the 3rd didn't have a chance to react.  Right down the middle and punted him to death (literally).  (I may be wrong on the facts, again, this is memory).