Outer Limits 4x4 Board

my bro wants to stick 36-37inch tyres on his 75series he wants to know what it does to the gearing and what ever, he's got 33's on now but it could be already colaborated for 35's because thats wat used to be on b4 we bought it.
any info would help

cheers flynn

the ratio`s will be pretty much gone it would be hard to take even in 4wd low

if its not turbo'd he won't like it at all

i've got 35's on my patrol ute turbo'd and intercooled standard gearing
works well for me ... have crawler gears for off road tho

36-37s ... would definately look at diff ratios

To run those tires he'll want crawlers for offroad, so all he has to do is to get the ones that have an 8% reduction in high...

Would you get the same corrective gearing result from crawler gears with the high range ratio reduced, as you would with a lower diff ratio?

rOd wrote:Would you get the same corrective gearing result from crawler gears with the high range ratio reduced, as you would with a lower diff ratio?

Crawler gears effectively reduce the ratio on LOW range only.

If you get diff raitos done.. the change will affect both the high and low range which makes the vehicle more usable on the butimen with big tyres.

Unless you like driving a slug to and from the offroad spots and engage the low range (with crawler gearings) then it should be okay.

TOM

Some of the crawler type gears will also lower your high range gearing.

This is for the best anyway of you are running bigger rubber..

Stew

The answer lies in a Chev conversion

Try this...
http://www.trekoutfitters.com/Instructions/index.htm
(further down the page)
It may only help if you know what gear's are already installed.

Doing a physical speedo check (found on some freeways) could give you a bit of an idea whether your bro's gearing is already up or down.


Hardy

When I put the 35's on the Mav' I was surprised at how much it shagged the gearing. More prodominantly on road, particularly hills (obviously), but still offorad too. The car "runs away", compared with previously, when going down steep hills and goes faster when crawling along rocks.

Numerically, its apparently a 16% differential, which is quite significant. On road, the speedo indicates 100km/h, but I'm doing 116km/h. Offroad, when I'm crawling along rocks or going down hills, I'm going 16% faster than before.

Its worth going to the trouble (and expense) of having gearing changed to compensate, at least partly, for increased wheel size. My 4.11's are being changed over for 4.6's. I should get the car back today, I'm looking forward to seeing the difference.

bigbluemav wrote:When I put the 35's on the Mav' I was surprised at how much it shagged the gearing. More prodominantly on road, particularly hills (obviously), but still offorad too. The car "runs away", compared with previously, when going down steep hills and goes faster when crawling along rocks.

Numerically, its apparently a 16% differential, which is quite significant. On road, the speedo indicates 100km/h, but I'm doing 116km/h. Offroad, when I'm crawling along rocks or going down hills, I'm going 16% faster than before.

Its worth going to the trouble (and expense) of having gearing changed to compensate, at least partly, for increased wheel size. My 4.11's are being changed over for 4.6's. I should get the car back today, I'm looking forward to seeing the difference.

Gearing issues aside, it will also impact negativly on your brakes, by increasing the tyre diameter you are also increasing the leverage on the brakes on all 4 wheels.
Dave, my mechanic mate was saying only last week how he noticed a huge improvment in brake performance when he went from 35"s down to 33"s, he has a patrol so it is fairly heavy to start with.
Peter.

What was the question again??????

. . . . I am too busy trying to keep an eye out for anything that I need to brake for anywhere in the next km and looking for a 10km patch of clear road to overtake someone in my GU (turbo diesel coil cab running 4.625s) that runs 37's on the road to remember what the question was . . .

Then there's the financial considerations - a 37" tyre is often substantially more than an equivalent 35" and my already laughable fuel consumption has gone out the window. If my car wasn't leased and I couldn't package everything, it would cost an absolute fortune to keep it on the road.

Oh and finally, to get the rig sitting high enough to clear rubber of that size, say goodbye to any decent handling.

All that aside, my car certainly looks cool sitting on top of the new tread

I just did a little article for our club mag. This may help with the effect of larger tyres to the diff ratio.

old tyre size divided by new tyre size multiplied by current diff ratio equals effective diff ratio after fitting the new rubber.

Good Point Droopypete

In relation to brakes I recently installed DBA Gold slotted, drilled rotors and they have improved brake performance of the vehicle.

Also, I drive the thing like I'm driving a diesel powered, 6" lifted vehicle with no sway bars and tyres that have 10" sidewalls. It ain't no sprts car!!