Outer Limits 4x4 Board

Dave and i have been talking, and neither of us are sure how to work it out, or if it can be.

If you have.......

gearbox with a first of 3.5
low range of 4.7
diff ratio of 4.8

then you have a low range of about 78:1

now if you are running a 28 inch tyre the truck is going to crawl slower than if the same truck was running a 44. Is there away to workout the crawl ratio inrelation to the distance traveled? the over all crawl ratio of the truck and the different charteristics of the truck in a percentage of distance lost verse over all crawl ratio change?

question 2.

a hilux with 4.88 and 33's is said to be of factory ratio, if a hilux is fitted with 35's and 5.29's it is also said to be close to factory ratio. On paper the final drive works out to be different but add into the equation the fact that in theroy both ratios are factory, how do you work out the total distance of the rolling radius of the tyre in relation to the crawl ratio and why do two trucks, in theory with stock ratios, crawl and preform differently. Although the crawl ratio and tyre size are different the "over all" ratio would in theory be the same.


NICK AND DAVE

POS wrote::shock:

thats what we thought.


NICK

Dave & Nick we are starting to worry about you 2. Dave don't let him convert you.

NICK wrote:

POS wrote::shock:

thats what we thought.


NICK

Yeah its a good one!

Have you asked SAM???

I do remember reading about the same thing in a yankie mag but i can't find it and i can't remember the ratio as i didn't really care at that point of time!

It shouldn't be too hard to work out!

All the Mechanical engineers out there should be able to do this with their eyes closed!

convert me? im not the one that lives in sydney for the sole reason of mardigras


NICK

Factoring the gearing effect of different tyre sizes is simple cause the circumference of the tyre is proportinal to the diameter so if you want to compare different gearing with different tyre sizes just divide the overall gearing by the tyre size that that gearing is running to get an overall number that can be compared.

BUT for the life of me I carnt work out what you are actualling asking so I dont know if I have answered anything??

Sam

POS wrote:

NICK wrote:

POS wrote::shock:

thats what we thought.


NICK

Yeah its a good one!

Have you asked SAM???

I do remember reading about the same thing in a yankie mag but i can't find it and i can't remember the ratio as i didn't really care at that point of time!

It shouldn't be too hard to work out!

All the Mechanical engineers out there should be able to do this with their eyes closed!

it is one of those things that makes you go mmmmmmmmmmmm. there has to be an equation that will work it out.

eg, what diff gears do you need?

well it is the old ratio div. tyre size x new tyre size= new ratio

4.56/31x33=4.85

the above equation shows changing a 31 up to a 33, requires a 4.88 ratio to allow for the extra rolling dia.

NICK

Strange Rover wrote:Factoring the gearing effect of different tyre sizes is simple cause the circumference of the tyre is proportinal to the diameter so if you want to compare different gearing with different tyre sizes just divide the overall gearing by the tyre size that that gearing is running to get an overall number that can be compared.

BUT for the life of me I carnt work out what you are actualling asking so I dont know if I have answered anything??

Sam

yeah we know that, but thats not what we asked.


mmmmmmm maybe try this,

if you have a 35 tyre and then fit a 39, what effect does this have on the crawl ratio of 80.1 at the ground. We realise the crawl ratio the axle remains the same, but effect on driven speed and distance changes in relation to tyre size.

NICK

OK so instead of talking about overall gear ratio talk about distance travelled per 1000 revolutions of engine (use a thousand to make the numbers big enough)

so with 75:1 and 35in tyres you get



1000 x 3.14 x 35 / 75 = 1465 inches per 1000 revolutions of motor


Hows that??

Sam

yeap that is what i had, you need to take pie into the equation, and thats as far as we got.


Is there now anyway to convert distance traveled back to and "overall" ratio?


NICK

Strange Rover wrote:OK so instead of talking about overall gear ratio talk about distance travelled per 1000 revolutions of engine (use a thousand to make the numbers big enough)

so with 75:1 and 35in tyres you get



1000 x 3.14 x 35 / 75 = 1465 inches per 1000 revolutions of motor


Hows that??

Sam

so for example

1000x 3.14 x 44/ 75 = 1842 inches per 1000 revolutions of the axle, so the ratio of distance traveled has now changed and is 500 inch more, in reality altering the "overall" ratio.

NICK

sam, when we take 1000 into the equation is it revs of the motor or axle?




NICK

the 1000 is for the 1000 revolutions of the motor.

Once you take the tyre size into account you can no longer talk about overall ratio cause now its a distance and the overall ratio doesent make any sence.

What you could do is say the the tyre size changes the gear ratio relative to a basic tyre size (say a 35in tyre)

So if you have 75:1 and 35s then the overall ratio is

75 x 35 / 35 = 75:1

Now if you had 44s then

75 x 35 / 44 = 60:1

Which means your overall comes back to 60:1 compared to a guy that had the same ratio and was running 35s.


Sam

Strange Rover wrote:the 1000 is for the 1000 revolutions of the motor.

Once you take the tyre size into account you can no longer talk about overall ratio cause now its a distance and the overall ratio doesent make any sence.

What you could do is say the the tyre size changes the gear ratio relative to a basic tyre size (say a 35in tyre)

So if you have 75:1 and 35s then the overall ratio is

75 x 35 / 35 = 75:1

Now if you had 44s then

75 x 35 / 44 = 60:1

Which means your overall comes back to 60:1 compared to a guy that had the same ratio and was running 35s.


Sam

After all that it seems so simple, we new you would know and that was exactly what we wanted to know.


Now what do you think the ideal crawl ratio and tyre size combo is in relation to the above statement?

dont forget that torque at the wheel doesnt reduce by the same amount compared to circumference, becasue the radius is the leverage that the gearing is working against

35", loaded radius = 17", circumference = 107"
44", loaded radius = 20", circumference = 126"

so even though the distance travelled is different by 15% the reduction is torque at the wheel is only 15%

aw shnitz, forget i said anything
my brain hurts

if you could work out what you are actually asking, maybe people could help you!

the ratio will be he same no matter what size tyre u have, and is therefore pointless in this respect.

but the ratio of the distance travelled to rpm of the motor would be what you are looking at right?
but what are you actually asking?

oh so you mean the ratio at the axle never changes


so what rpm would a truck at 75.1 need to be doing to travel 8763 inches on 35's compared to the same truck on 49's in the same amount of time.


NICK

you do not specifiy the rpm or time for the 35's to compare to?

ok, on 35's the rear axel would have to rotate 79.7 times,
on 44's the axel only needs to rotate 63.4 times

so with 75:1,
the engine need to rotate 5977.5 times on 35's
and 4755 on 44's.

so lets say u do the distance at 1500 rpm on the 35s, which would take 3.98 minutes on 35's.
to do it in the same time on 44's it would be doing 1194 RPM

napsta wrote:you do not specifiy the rpm or time for the 35's to compare to?

ok, on 35's the rear axel would have to rotate 79.7 times,
on 44's the axel only needs to rotate 63.4 times

so with 75:1,
the engine need to rotate 5977.5 times on 35's
and 4755 on 44's.

so lets say u do the distance at 1500 rpm on the 35s, which would take 3.98 minutes on 35's.
to do it in the same time on 44's it would be doing 1194 RPM

and both would take the same amount of time? take into account the fact that they were racing, they would be dead even side by side giving the fact that they would be doing the same distance and speed on a different tyre ratio distance.

nick

HA HA NICK
from all that do you how no what you were asking about.
and do you no the answer to that question.

Nick don't forget to take in acount tire pressure it alters the distance traveled

83 lux wrote:HA HA NICK
from all that do you how no what you were asking about.
and do you no the answer to that question.

well now that i have got the answer to my first few questions, i will ask another, why is it you always get words back to front and leave afew out off every sentence?


NICK

Mate i could sorta work out your question but i have no idea what SCOOT just asked!

www.4lo.com might help.
ruff, this might interest you for the site as well.
shane