It's a gear ratio thing, not a HP thing. It's more like the sprockets on a 10 speed bike, The larger the rear sprocket, the easier it is to pedal uphill, but the smaller ones make you go faster. The person pedalling isn't getting any stronger, just like the motor itself doesn't produce any more or less HP, It's just how it makes it's way to the ground, and the chassis DYNO, where the HP is measured.

 

I used to love doing burnouts in my bigwheel. I had the Hulk Green Machine.

That mother was BAD!

 

Larger wheels will rob you of power and time, if they didn't you'd see them on the majority of race cars in motorsports.

 

I actually thought with a 20 inch tire you would be faster on the top end but not the bottom end.

 

its all rotational mass.

 

I got that wrong, actually it's not the size of the wheel that will change your effective gear ratio but the diameter of the tire and wheel combination.

Take a stock GT's 17" wheels that come with 235/55's (27.17" diameter), put a 245/45 drag radial (25.68" diameter)on the rear, effectively changing the gear ratio from 3.55 to 3.75.

 

I must be a bit older than you because that thing wasn't out in my childhood days.Yellow mag wheels were just becoming popular for your BMX when I was a kid.

We just had the standard bigwheel unfortunately.

 

OK here we go again......

First off I really dislike these type of threads.....

Most of every comment in this thread is based on truth, but may have a slant that may makethem subjective.

Misconceptions posted in THIS thread:
Taller tire increase traction... NOPE! Taller tires cause less torque at tire/ground contact point! Not the issue here because OP is wearing shorter tires!
20" have less side wall flex... Measureable? How much side wall flex in relation to rotational does one this stock 17" tires have?

Why do people demand to compare street tires to drag tires? Try taking a corner on you dragster tires! (At the same tire pressure you would run at the strip)Now comparing drag radials, again how much side wall flex does one think they REALLY have? Some yes, but again is it measurable to the naked eye? They are usually wide and soft therefore increasing traction like that! Anyone ever seen a 235x55x17 or a 235x50x18drag radial? Yes they may exist be they are NOT the norm!

Again are 20" tire and rim combo the best drag racing combination? No.
Just because someone bolts on a set of 20" wheels and tires, Will they automaticly run slower ET? NO!
If the increase in traction overcomes the decrease in torque due to the highly speculated 'rotational mass' the new 20" WILL give one a lower ET!
Almost ANYONE who hasbolted on a 20" combo has noticed better traction! Granted in some combos this better traction maybe the resultfrom less torque gettting to the pavement BUT that is NOT the case 100% of the time!
If we could measure the forcein relation totraction, this is where a larger foot print would show why some claim 20" could be better than stock 17" or 18" combos.

Sorry, but I'm tired of uninformed people thatclaim things they know nothing about regarding this issue! (not to be take as EVERYONE who has a different opinion as I are uninformed!!)

 

Dude did you eat your grape nuts this morning?[sm=love.gif]

 

Moose, I apologize for attacking you over you comments, I took it as the threadwas childish,on top of that I had a few extra brewski's that day. On the other hand, my daughter can spin the wheels on her Barbie Jeep power wheels pretty easy too, and the diameter of the wheels on that are much smaller than the big wheel, LOL

As far as all the info on the thread, 05SDI has made some valid points. Back to my original thread, I'm still looking for some numbers before and after on this issue. So if anyone has some dyno numbers let me know.