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This is probably a dumb question, but while riding my recently completed AF conversion, I noticed it seems to lack a little top end speed. I am running a 1990 engine, which is lower geard and close ratio gearbox, but I realized the cr 250 is running a 19" rear wheel. So in my mind that would be the same as going up in teeth on the rear sprocket, hence gaining alot of lowend and torque while at the same time losing speed. Is that right? If so, what is the difference in running a 14/51 with and 18" rear wheel, and the same gearing while running a 19" rear? Just curious. I could just be all in my head too as the conversion feels so much smaller than the old steelie. Jason.

The 89-90 motors dont have shit for top end, I run 14/46 on my 89 bottom end.

I know what you mean, but do you think the larger rear wheel would slow it down even more?

It's so small a difference I don't think you'd notice.

JBaze wrote:I know what you mean, but do you think the larger rear wheel would slow it down even more?

Larger rear wheel would give more top end, less bottom.

JBaze wrote:If so, what is the difference in running a 14/51 with and 18" rear wheel, and the same gearing while running a 19" rear? Just curious. I could just be all in my head too as the conversion feels so much smaller than the old steelie. Jason.

Depends on the tire size.

MojoScojo wrote: Depends on the tire size.

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We have the winner.....

Mad Dog wrote:

JBaze wrote:I know what you mean, but do you think the larger rear wheel would slow it down even more?

Larger rear wheel would give more top end, less bottom.

How could that happen? If you run a larger rear sprocket, you lose top gain bottom. I would think the same principal would apply to the rear wheel as well. Also the rear tire on the bike right now is a 110/90-19. I am not looking to win any drags or anything, when I was messing around with bike today I noticed the different sized wheels and was just curious.

and what size tire was on the other bike?

JBaze wrote:[How could that happen? If you run a larger rear sprocket, you lose top gain bottom. I would think the same principal would apply to the rear wheel as well.

When you add a bigger rear sprocket, you gain mechanical advantage due to the increased difference in tooth count between the front and rear sprockets. You lose speed in the process.

When you go to a larger rear tire, you lose mechanical advantage due to the larger circumfrence of contact with the road. You gain speed in the process.

AlisoBob wrote:

JBaze wrote:[How could that happen? If you run a larger rear sprocket, you lose top gain bottom. I would think the same principal would apply to the rear wheel as well.

When you add a bigger rear sprocket, you gain mechanical advantage due to the increased difference in tooth count between the front and rear sprockets. You lose speed in the process.

When you go to a larger rear tire, you lose mechanical advantage due to the larger circumfrence of contact with the road. You gain speed in the process.

Ok, I see said the blind man! If I think about something long enough, I wind confusing myself right out of action. The tire on the old bike was a 120/100-18 also.

Yup, it's like a lifted 4x4. You put bigger tires on it, it's gonna lose bottom end torque and gain top speed. That's why folks regear to lower ring and pinions (higher numerically) like if stock is 4.33 they go to 5.13's etc..

JBaze wrote:

AlisoBob wrote:

JBaze wrote:[How could that happen? If you run a larger rear sprocket, you lose top gain bottom. I would think the same principal would apply to the rear wheel as well.

When you add a bigger rear sprocket, you gain mechanical advantage due to the increased difference in tooth count between the front and rear sprockets. You lose speed in the process.

When you go to a larger rear tire, you lose mechanical advantage due to the larger circumfrence of contact with the road. You gain speed in the process.

Ok, I see said the blind man! If I think about something long enough, I wind confusing myself right out of action. The tire on the old bike was a 120/100-18 also.

It's not really the wheel but the overall circumference of the tire, which is what everyone is saying.
19's generally have a lower profile than 18's.
Afterall, it still needs to clear the ender.

Notice this chart.

http://www.motorcycle-karttires.com/gla ... ookupID=17

Two of the 19's are actually smaller than the 110/100 x 18.

Do you really think you can tell the difference in the top speed, on a dirt bike on uneven terrain?

What it affects more is the attitude of the bike, acceleration, handling, absorbtion etc.

Mad Dog wrote:

JBaze wrote:

AlisoBob wrote: When you add a bigger rear sprocket, you gain mechanical advantage due to the increased difference in tooth count between the front and rear sprockets. You lose speed in the process.

When you go to a larger rear tire, you lose mechanical advantage due to the larger circumfrence of contact with the road. You gain speed in the process.

Ok, I see said the blind man! If I think about something long enough, I wind confusing myself right out of action. The tire on the old bike was a 120/100-18 also.

It's not really the wheel but the overall circumference of the tire, which is what everyone is saying.
19's generally have a lower profile than 18's.
Afterall, it still needs to clear the ender.

Notice this chart.

http://www.motorcycle-karttires.com/gla ... ookupID=17

Two of the 19's are actually smaller than the 110/100 x 18.

Do you really think you can tell the difference in the top speed, on a dirt bike on uneven terrain?

What it affects more is the attitude of the bike, acceleration, handling, absorbtion etc.

Thats what I'm saying, I haven't spent more than a few minutes in the saddle of my conversion. Until I rode it I hadn't ridden an alum. framed bike. So I have no basis for comparison. I am used to the steel framed 500's, so riding the conversion bike for me is a completly new experience. So like in my first post it's more than likely in my head. Back in my motocross days I went from an 87 to a 90 model and felt like I was going slower than on my 87, when in actuallity, I was going alot faster. Just do to the improved ergonomics and handling. So that is probably what is happening here. Because this "new" bike just feels like it flows under me, as oposed to haveing to really ride it to make it go fast. Does that make sense?

The first time I rode my A/F at Jawbone, I thought the tranny broke on trail SC102.

I always ride it in 4th ( on my steelie) and on my A/F I " couldnt" get it to shift up into 5th.

I was in 5th , dumb shit.

Same gearing, same trail, riding one whole gear up....

A/F's are fast and smooth...... Set up correctly.

AlisoBob wrote:The first time I rode my A/F at Jawbone, I thought the tranny broke on trail SC102.

I always ride it in 4th ( on my steelie) and on my A/F I " couldnt" get it to shift up into 5th.

I was in 5th , dumb shit.

Same gearing, same trail, riding one whole gear up....

A/F's are fast and smooth...... Set up correctly.

Well in theory the outer tire dia is suppose to be the same. Its just that the 19 sidewall is narrower for less sidewall flex.

iggys-amsoil wrote:Well in theory the outer tire dia is suppose to be the same. Its just that the 19 sidewall is narrower for less sidewall flex.

Thats why I run 18" on the af`s in dirt

Yup......

18's and 20's