User Login    
 + Register
  • Main navigation
Main Menu
Login
Username:

Password:


Lost Password?

Register now!
Fast Search
Slow Search

Advanced Search
Google Ad

Browsing this Thread:   1 Anonymous Users



(1) 2 »


rev210
Re: Tyre Size and Horsepower
#15
Not too shy to talk
Joined:
2006/7/7 17:10
Group:
Registered Users
Posts: 36
Offline
it's a gearing change so to speak.

A dyno usually doesn't show any power change, if you take into account the error margin on the readings.

Dyno's are a good general tuning aid. The 'look at my power graph' manner that most people go and get the tuned based on, overlooks the best a dyno really has to offer.

For instance you can 'time' the accelleration across the graph to determine intertia or gearing benifits in comparison. It's a very handy thing to do, it tells you more about how fast your car is than the power curve.Although it still doesn't account for everything (like aerodynamics /weight etc.) Most people have no clue about this fact including 99% of workshops who own a dyno (perhaps I'm being harsh). Somewhere in the whole dyno fad people forgot what they wanted more power 'for'.

Next time you go to tune your car on a dyno get a time axis on some of those graphs. You can see what all that lovely extra power is really doing or check out the gains from the new light weight flywheel or carbon fibre tail shaft. You can even see the reason why fattening up the power curve at the expense of a little top end is a good move, especially when you have poor ratio spacing in your gear box.

Posted on: 2006/8/9 12:16
Transfer the post to other applications Transfer


R-fastmotorsport
Re: Tyre Size and Horsepower
#14
Home away from home
Joined:
2004/2/29 11:00
From Sydney , NSW
Group:
Registered Users
Posts: 923
Offline
Sorry to end the argument but no difference at all - been there, done that with the A14. Used 13" wheels against 15" wheels and the diff was 0.2 rwhp on 2 different occassions. As previous replies have stated, the curve just moves in relation to rpm. Same curve, same output, just located at higher/lower rpm. Yes tractive effort changes slightly due to mechanical advantage but HP is "you got what you got"
Cheers

Posted on: 2006/8/9 8:45
Transfer the post to other applications Transfer


BUNDY351
Re: Tyre Size and Horsepower
#13
Home away from home
Joined:
2006/1/22 11:26
From Flinders View, QLD
Group:
Registered Users
Posts: 672
Offline
Sorry to come in a little late. But I am interested to know if one was to increase the size of the rim/tyre this may increase the weight of the rim/tyre. In doing this would it not take a little more HP to turn the increased mass of the rim/tyre combination. You may loose a little HP initially but it should not matter up in the RPM. Personally I reccon leave the DYNO for the number chasers and and let your quarter mile times do the talking.

Posted on: 2006/8/9 8:08
Transfer the post to other applications Transfer


Datsun1000
Re: Tyre Size and Horsepower
#12
Just can't stay away
Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
Posts: 149
Offline
I told them not to bring it up aging unless the can find a form of proof,

and now they are trying to change the argement to save face.

they also also as a side not believe dyno and real road rear wheel horspower differs.

Posted on: 2006/8/9 7:25
Transfer the post to other applications Transfer


Mildman
Re: Tyre Size and Horsepower
#11
No life (a.k.a. DattoMaster)
Joined:
2003/9/2 6:01
From SE Melbourne
Group:
Registered Users
Posts: 3195
Offline
Ask them if they think what gear the car is in makes a difference on to the overal power results of a dyno.

Then ask if they think the diff ratio makes a difference to rwhp.

Then ask them to show you the mathematical formula that demonstrates these relationship

Power = torque * rpm is all there is to it.

Where is tyre size in this equation, where is gear ratio in this equation.

Get them to give you a different mathematical equation for power - and when they do, quickly take that equation down to the patent office so that later you can collect your nobel prize.

It's as simple as the mathematics - if they can refute your formula P=T*rpm/5252 then they have an argument - otherwise direct them to their arsehole and their elbow and see if they can tell the difference!

Posted on: 2006/8/9 7:07
_________________
Mildman, Datsunless
Transfer the post to other applications Transfer


Datsun1000
Re: Tyre Size and Horsepower
#10
Just can't stay away
Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
Posts: 149
Offline
I have been argeing with one of them for an hour now and they still will not admit that tyre size does not effect rear wheel horsepower

Posted on: 2006/8/9 6:22
Transfer the post to other applications Transfer


L18_B110
Re: Tyre Size and Horsepower
#9
No life (a.k.a. DattoMaster)
Joined:
2002/8/6 2:24
From Brisbane, Australia
Group:
Registered Users
Posts: 3792
Offline
@'s a PITA!

the dyno doesn't care what car is on it, or what tyre its got. the dyno simply measures the force seen at the rollers (torque or tractive effort), multiplies that by the roller speed, divides it by a constant (5252 for imperial bhp) and then it has the bhp figure.

no adjustment is needed to the dyno if you change tyre size. eg a 10% larger tyre would produce 10% less torque measured by the roller, but the roller will also be going 10% faster, so the mathematical equation power = torque * rpm / 5252 remains unchanged. The dyno will give the same power output no matter what tyre you put on a car.

Posted on: 2006/8/9 5:14
_________________
"if you're not on the edge, you're just taking up space"
Transfer the post to other applications Transfer


Datsun1000
Re: Tyre Size and Horsepower
#8
Just can't stay away
Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
Posts: 149
Offline
Quote:

L18_B110 wrote:
Quote:

Datsun1000 wrote:
Hi Guys,

Can tyre size affect rear wheel horsepower?

The basis of the question

If you put a car on a Dyno and perform a run and then chage the tyre size up to a larger overall size, will the rear wheel horsepower change.
excluding the very small fraction of a friction increase by the larger tyres.

Cheers Guys,

A link to proof or actual mathmatical proof for a yes or no answer would be appeciated.


no, tyre diametre will not affect bhp on a dyno. tyre diametre is just another form of gearing. and gears are torque multipliers. a taller tyre (or gear) will mean less torque (tractive effort) at the wheels, but they will be turning at a proportionately higher speed, so no net change to the power. eg change to a 10% larger tyre will make 10% less torque, but it will be going 10% faster at the same time, so it all balances out.

power = torque * speed / a constant



Below is what the retorted with

@ says:
so your saying that bigger tires need computer adjustment to multiply the torque change?
# says:
no that is not what is being said
@ says:
that is exactly what was said "torque multiplier"
@ says:
you need to change to settings on the dyno to adjust for the change in ratio
@ says:
so the ratio DOES make a difference
@ says:
otherise you wouldnt need to tell the computer the difference in gear ratios

Posted on: 2006/8/9 4:16
Transfer the post to other applications Transfer


L18_B110
Re: Tyre Size and Horsepower
#7
No life (a.k.a. DattoMaster)
Joined:
2002/8/6 2:24
From Brisbane, Australia
Group:
Registered Users
Posts: 3792
Offline
Quote:

Datsun1000 wrote:
Hi Guys,

Can tyre size affect rear wheel horsepower?

The basis of the question

If you put a car on a Dyno and perform a run and then chage the tyre size up to a larger overall size, will the rear wheel horsepower change.
excluding the very small fraction of a friction increase by the larger tyres.

Cheers Guys,

A link to proof or actual mathmatical proof for a yes or no answer would be appeciated.


no, tyre diametre will not affect bhp on a dyno. tyre diametre is just another form of gearing. and gears are torque multipliers. a taller tyre (or gear) will mean less torque (tractive effort) at the wheels, but they will be turning at a proportionately higher speed, so no net change to the power. eg change to a 10% larger tyre will make 10% less torque, but it will be going 10% faster at the same time, so it all balances out.

power = torque * speed / a constant


Posted on: 2006/8/9 3:58
_________________
"if you're not on the edge, you're just taking up space"
Transfer the post to other applications Transfer


Datsun1000
Re: Tyre Size and Horsepower
#6
Just can't stay away
Joined:
2003/8/20 3:55
From Melbourne
Group:
Registered Users
Posts: 149
Offline
This is my belief that a lager tyer size will use the horsepower for higher top end speed and a smaller tyer size wilol use it for acceleration.

However i am after some way to prove this as it has been an ongoing argument with 2 of my friends that are adament that a larger tyre size will reduce rear wheel horspower.

id like to prove it without going down and putting a car on a dyno. and then changing the tyre size

Posted on: 2006/8/9 3:55
Transfer the post to other applications Transfer



(1) 2 »



You can view topic.
You cannot start a new topic.
You cannot reply to posts.
You cannot edit your posts.
You cannot delete your posts.
You cannot add new polls.
You cannot vote in polls.
You cannot attach files to posts.
You cannot post without approval.

[Advanced Search]