Factory 250f's

Zycki11
Posts
5809
Joined
4/1/2008
Location
Ankeny, IA US
4/1/2018 9:34am
I thought this was interesting. PC kawi is running a 13/48 combo, Troy Lee KTM is running 13/48, Star is running 13/47. Those are some big horses them 250f's are cranking out to carry those combos
|
mattyhamz2
Posts
10850
Joined
7/6/2015
Location
So Cal, CA US
Fantasy
760th
4/1/2018 9:45am
Easier when you have factory transmissions also
Zycki11
Posts
5809
Joined
4/1/2008
Location
Ankeny, IA US
4/1/2018 10:43am
mattyhamz2 wrote:
Easier when you have factory transmissions also
Of course, although the factory transmission is generally more spread out. But the fact that the Yamaha team is running 13/47 is insane
walent215
Posts
2409
Joined
12/6/2014
Location
Ridgecrest, CA US
4/1/2018 11:06am
mattyhamz2 wrote:
Easier when you have factory transmissions also
Zycki11 wrote:
Of course, although the factory transmission is generally more spread out. But the fact that the Yamaha team is running 13/47 is insane
That is pretty impressive actually...id be curious to know what Geico runs considering they start out with the " weaker" motor
Jrewing
Posts
2866
Joined
1/4/2014
Location
AU
4/1/2018 2:16pm Edited Date/Time 4/1/2018 2:17pm
I'd say it's to help run one gear longer and shift less, but it surely helps to have the ponies to do it

The Shop

level
Posts
6185
Joined
8/27/2006
Location
Acworth, GA US
4/1/2018 3:05pm Edited Date/Time 4/1/2018 3:08pm
It’s a supercross setup only I’m sure where you rarely get into higher gears and if I remember right that combo would allow more bottom end in a higher gear. Also you are not running wide open in third gear for very long in supercross so that would allow for it to pull faster in a higher gear. I bet the whole race is second and third gear.
RCF
Posts
546
Joined
4/1/2008
Location
PA US
4/1/2018 3:16pm
Ktm stock is 14/51. 3.64 so 13/48 3.69. It's actually lower
4/1/2018 3:42pm
Zycki11 wrote:
I thought this was interesting. PC kawi is running a 13/48 combo, Troy Lee KTM is running 13/48, Star is running 13/47. Those are some big...
I thought this was interesting. PC kawi is running a 13/48 combo, Troy Lee KTM is running 13/48, Star is running 13/47. Those are some big horses them 250f's are cranking out to carry those combos
Let's do some basics here...I swear people should have paid attention in high school physics.

A stock yz250f on my dyno cranks out around 40 hp and 20lb ft.
Same for a kx250f (actually kawis' hate my dyno or like magazine dynos...it's always usually a bit shy of 40 and around 19.5lb ft)

On my dyno our best effort ktm is in excess of 50 and 24 lbft, yamaha similar torque numbers and a tick off peak hp, kx similar to yamaha etc.

stock ktm gearing 14:51 - ratio is 3.64
stock yz250f gearing is 13:50 ratio is 3.84

Now - this doesn't account for internal gearing - both stock bikes could be IDENTICAL at the tire in ratio depending on internal ratios - which a factory transmission CAN change - but often wont need to. The factory services ktm 250 trans is std ratios...

When making more power you have some options. Keep the gearing you have and get more acceleration - or reduce teeth on the back and trade some of the additional pull you COULD have had - for more width in usable power. AKA less shifting.

So - lets assume the factory yz250f makes 20 percent more torque (the only number that matters for acceleration) That puts it around 24 lb ft - lets be really generous and say its 25 and stock is 20.

You could then re gear the bike 20 percent TALLER and have the SAME pull stock has but HUGE width to power.
What is a 20 percent change?

3.84*.8 = 3.072

Working backwards - 13*3.072 = 39 tooth rear or 39/13 = 3.072.
Going to a 47 from a 50 is a 5 percent change in final drive ratio.
So if the team IS making 20 percent more torque - you would have 15 percent more pull - and 5 percent more width than a stock bike - assuming stock internal ratios. Commonly mis understood - changing sprocket teeth DOESN'T"T change gear drops. When you shift - you will drop an identical amount of RPM using a 50 or 47 rear tooth sprocket.

The funny part I laugh at with privateers and excuses from riders - assuming you have a decent built bike - you shouldn't be more than 10 percent off a factory effort in torque or hp. When you do all the math behind what that means in real world differences of acceleration - it's hardly anything. It's actually an argument against mod engines for amateurs and budget allocation on lower budget efforts.

That 10 percent is best made up with lots of chassis and suspension testing - where most privateers are more likely to be 40-50 percent off a factory effort.

The BIG difference from a factory effort is in RPM. A top team will run well over 15k for sx - I'd guess 16-16.5 on some teams based off what I hear.

We can reliably go to 15 on some builds but past that is playing with a money pit. It takes cubic dollars to chase RPM - and lots of testing. That's not even accounting for making good usable power at that RPM.

So a private effort at 14k - vs a 15.5k motor that pulls properly that high - is night and day in on track performance for a host of additional reasons.

At the ultra high rpms - case integrity becomes a problem - valve train stability and life is a challenge - and piston/rod durability is of serious importance. I personally think timing chains are a massive weak link in performance at those speeds as well.

So im not "all that impressed" by running a 13:47.

on a ktm a 13:48 is nothing far off a 14:51


And to anyone who ever wonders why a stock 250f and stock 450 at a local track in the hands of a good local rider turn similar times - and the 450 isnt just WAY faster feeling - it's all final gear ratios. a stock 250f vs a stock 450 in 3d gear can be 30 percent different in final drive ratio - aka knocking off 30 percent of torque at the tire for acceleration of the 450 - but trading it for 30 percent more width - aka why you don't shift a 450 much.






es337
Posts
1086
Joined
4/13/2012
Location
MD US
4/1/2018 4:39pm
Let's do some basics here...I swear people should have paid attention in high school physics. A stock yz250f on my dyno cranks out around 40 hp...
Let's do some basics here...I swear people should have paid attention in high school physics.

A stock yz250f on my dyno cranks out around 40 hp and 20lb ft.
Same for a kx250f (actually kawis' hate my dyno or like magazine dynos...it's always usually a bit shy of 40 and around 19.5lb ft)

On my dyno our best effort ktm is in excess of 50 and 24 lbft, yamaha similar torque numbers and a tick off peak hp, kx similar to yamaha etc.

stock ktm gearing 14:51 - ratio is 3.64
stock yz250f gearing is 13:50 ratio is 3.84

Now - this doesn't account for internal gearing - both stock bikes could be IDENTICAL at the tire in ratio depending on internal ratios - which a factory transmission CAN change - but often wont need to. The factory services ktm 250 trans is std ratios...

When making more power you have some options. Keep the gearing you have and get more acceleration - or reduce teeth on the back and trade some of the additional pull you COULD have had - for more width in usable power. AKA less shifting.

So - lets assume the factory yz250f makes 20 percent more torque (the only number that matters for acceleration) That puts it around 24 lb ft - lets be really generous and say its 25 and stock is 20.

You could then re gear the bike 20 percent TALLER and have the SAME pull stock has but HUGE width to power.
What is a 20 percent change?

3.84*.8 = 3.072

Working backwards - 13*3.072 = 39 tooth rear or 39/13 = 3.072.
Going to a 47 from a 50 is a 5 percent change in final drive ratio.
So if the team IS making 20 percent more torque - you would have 15 percent more pull - and 5 percent more width than a stock bike - assuming stock internal ratios. Commonly mis understood - changing sprocket teeth DOESN'T"T change gear drops. When you shift - you will drop an identical amount of RPM using a 50 or 47 rear tooth sprocket.

The funny part I laugh at with privateers and excuses from riders - assuming you have a decent built bike - you shouldn't be more than 10 percent off a factory effort in torque or hp. When you do all the math behind what that means in real world differences of acceleration - it's hardly anything. It's actually an argument against mod engines for amateurs and budget allocation on lower budget efforts.

That 10 percent is best made up with lots of chassis and suspension testing - where most privateers are more likely to be 40-50 percent off a factory effort.

The BIG difference from a factory effort is in RPM. A top team will run well over 15k for sx - I'd guess 16-16.5 on some teams based off what I hear.

We can reliably go to 15 on some builds but past that is playing with a money pit. It takes cubic dollars to chase RPM - and lots of testing. That's not even accounting for making good usable power at that RPM.

So a private effort at 14k - vs a 15.5k motor that pulls properly that high - is night and day in on track performance for a host of additional reasons.

At the ultra high rpms - case integrity becomes a problem - valve train stability and life is a challenge - and piston/rod durability is of serious importance. I personally think timing chains are a massive weak link in performance at those speeds as well.

So im not "all that impressed" by running a 13:47.

on a ktm a 13:48 is nothing far off a 14:51


And to anyone who ever wonders why a stock 250f and stock 450 at a local track in the hands of a good local rider turn similar times - and the 450 isnt just WAY faster feeling - it's all final gear ratios. a stock 250f vs a stock 450 in 3d gear can be 30 percent different in final drive ratio - aka knocking off 30 percent of torque at the tire for acceleration of the 450 - but trading it for 30 percent more width - aka why you don't shift a 450 much.






Tl:dr?
4/1/2018 5:20pm Edited Date/Time 4/1/2018 5:20pm
Zycki11 wrote:
I thought this was interesting. PC kawi is running a 13/48 combo, Troy Lee KTM is running 13/48, Star is running 13/47. Those are some big...
I thought this was interesting. PC kawi is running a 13/48 combo, Troy Lee KTM is running 13/48, Star is running 13/47. Those are some big horses them 250f's are cranking out to carry those combos
Let's do some basics here...I swear people should have paid attention in high school physics. A stock yz250f on my dyno cranks out around 40 hp...
Let's do some basics here...I swear people should have paid attention in high school physics.

A stock yz250f on my dyno cranks out around 40 hp and 20lb ft.
Same for a kx250f (actually kawis' hate my dyno or like magazine dynos...it's always usually a bit shy of 40 and around 19.5lb ft)

On my dyno our best effort ktm is in excess of 50 and 24 lbft, yamaha similar torque numbers and a tick off peak hp, kx similar to yamaha etc.

stock ktm gearing 14:51 - ratio is 3.64
stock yz250f gearing is 13:50 ratio is 3.84

Now - this doesn't account for internal gearing - both stock bikes could be IDENTICAL at the tire in ratio depending on internal ratios - which a factory transmission CAN change - but often wont need to. The factory services ktm 250 trans is std ratios...

When making more power you have some options. Keep the gearing you have and get more acceleration - or reduce teeth on the back and trade some of the additional pull you COULD have had - for more width in usable power. AKA less shifting.

So - lets assume the factory yz250f makes 20 percent more torque (the only number that matters for acceleration) That puts it around 24 lb ft - lets be really generous and say its 25 and stock is 20.

You could then re gear the bike 20 percent TALLER and have the SAME pull stock has but HUGE width to power.
What is a 20 percent change?

3.84*.8 = 3.072

Working backwards - 13*3.072 = 39 tooth rear or 39/13 = 3.072.
Going to a 47 from a 50 is a 5 percent change in final drive ratio.
So if the team IS making 20 percent more torque - you would have 15 percent more pull - and 5 percent more width than a stock bike - assuming stock internal ratios. Commonly mis understood - changing sprocket teeth DOESN'T"T change gear drops. When you shift - you will drop an identical amount of RPM using a 50 or 47 rear tooth sprocket.

The funny part I laugh at with privateers and excuses from riders - assuming you have a decent built bike - you shouldn't be more than 10 percent off a factory effort in torque or hp. When you do all the math behind what that means in real world differences of acceleration - it's hardly anything. It's actually an argument against mod engines for amateurs and budget allocation on lower budget efforts.

That 10 percent is best made up with lots of chassis and suspension testing - where most privateers are more likely to be 40-50 percent off a factory effort.

The BIG difference from a factory effort is in RPM. A top team will run well over 15k for sx - I'd guess 16-16.5 on some teams based off what I hear.

We can reliably go to 15 on some builds but past that is playing with a money pit. It takes cubic dollars to chase RPM - and lots of testing. That's not even accounting for making good usable power at that RPM.

So a private effort at 14k - vs a 15.5k motor that pulls properly that high - is night and day in on track performance for a host of additional reasons.

At the ultra high rpms - case integrity becomes a problem - valve train stability and life is a challenge - and piston/rod durability is of serious importance. I personally think timing chains are a massive weak link in performance at those speeds as well.

So im not "all that impressed" by running a 13:47.

on a ktm a 13:48 is nothing far off a 14:51


And to anyone who ever wonders why a stock 250f and stock 450 at a local track in the hands of a good local rider turn similar times - and the 450 isnt just WAY faster feeling - it's all final gear ratios. a stock 250f vs a stock 450 in 3d gear can be 30 percent different in final drive ratio - aka knocking off 30 percent of torque at the tire for acceleration of the 450 - but trading it for 30 percent more width - aka why you don't shift a 450 much.






Listen man, I don't know what that means. But I do know that 4 strokes ruined this sport. CHANGE MY MIND
Zycki11
Posts
5809
Joined
4/1/2008
Location
Ankeny, IA US
4/1/2018 7:47pm
Isn't the entire point of this thread about the ability to maintain a specific ratio while running a different setup? I still find it amazing that the factory bikes are able to do that. And yes, I understand the engine gap is much tighter from a well built motor guy to factory compared to the chassis. It's the ability to have the power and spread it out that makes the factory motor plants so good. On the flip side, the suspension/chassis setup is a whole new world and one that takes tons and tons of time. Prime example, Cooper Webb's bike to me looks like shit. On the flip side, Andersons bike seems to be planted everywhere.
Mit12
Posts
1977
Joined
6/23/2014
Location
Lake Havasu City, AZ US
4/1/2018 10:30pm
The gearing is actually lower geared than stock. I tooth on the counter shaft is equal to almost 4 teeth on the rear. A stock bike would pull this gearing better than stock gearing.
mxer807
Posts
133
Joined
12/16/2017
Location
Lake Elsinore, CA US
4/1/2018 11:03pm
Those 250f’s probably have Close to stock 450 hp.

Post a reply to: Factory 250f's

The Latest