On the dyno, knobblies tires show less HP than a smooth dyno tire. The heavier the tire, and the softer the knobblies, the worse it gets. If you run the knobblies on the dyno you will see that the tires sometimes bounce or even deforms under acceleration. This produces skew HP figures in the dyno. The motor itself does not make more or less HP with the different tires, it’s purely the way they put the power on the dyno roller that causes the "wrong" figures.

For example. If you go the FMH's web site and you look at the dyno run of the YFZ450, the stock knobblies show 10 HP less than dyno tires on the same bike.

To get more accurate figures, smooth dyno tires are a must.

 

one reason the new ds's are slightly faster is the rear end. its lighter - they shaved a few lbs. off rotating axle mass, going to an aluminum sprocket hub, the wheel hubs are a little bit thinner, and the swingarm is shorter giving more traction to boot.

 

that guys 720 put out 65 hp from the dyno sheet he showed me said his tires started doing what freeze said and hit his heel guards. but i'm not sure i would put tomuch into that dyno.

 

[quote]
Originally posted by: TheOz
You are safe to make some good bottom and mid power with a little top end and overrev with the HMF and proper rejet. The only danger zone is the intake porting: you can mess one up easier than you can help one! It would be best to have someone that has dyno'ed dozens of different intake configurations do your intake.

Freez: correct, the horsepower doesn't "magically drop" on the bike by running knobbies. The dyno numbers just show lower and very erratic. Don't trust dyno runs made with knobby tires. In fact, don't trust dyno runs that can't give you crate stock dyno numbers on the same dyno.

Hightower: very good point- less rotating mass may very well be the reason for a horsepower or two.

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i just saw a article in dirtwheels that showed a sidewinder chain and sprocket swap to 520, said it could show a couple hp.

 

I put zero stock in anything dirtwheels has to say about anything. they are one big commercial.

 

oh he got 65 out of it? i never actually saw the sheet but i was right there when he was on the dyno and the guy running the computer thought it was 62, i guess it looked a little different on the printout. His tires were not rubbing the heelplates on that run at all it was on an earlier run when they rubbed on the heelplates because they were rubbing behind the dyno rollers on the metal as well. he was using Razrs i was amazed at how much they expanded.

 

i did see the print out but not sure on the tire rub just going by what he said nice thing for him it was with a stock carb.

 

yeah i was fairly impressed with his numbers.

 

Really? A mild stock bore on gas should make 65hp. While a good one should make 70hp. At 715cc, it should be more like 76hp.

Do you know what other stockish DS650's were putting out on that dyno? Just curious to see what kind of numbers are really there out on the West Coast.

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