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Full Version: GEARING VS. TYRE RE. RPM OR POWER.
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Syncromad Wrote:14" syncro with standard 0,85 4th, does 4600rpm @ 120, 15" 215 wheels drops this approx 300 rpm, 0,82 5th in place of 4th drops another 250 rpm,

1. This is true speed via GPS I suppose Stu? What is the diff ratios of the 2.1/ wbx6/ 1.6td and 16" busses?
2. The 0.85 is the std 4th gear rato and 0.82 is the 5th gear from the 5cylinder busses. Is there anything else to give a higher ratio (lower numeric value)?
3.1. The std 14" (195/70) tyres is approximately 628mm(or 24") in diameter,
3.2. And the 215/80/15" upgrade is 709mm /28" wich increases ground clearance and add more driveability to open road cruising.
3.3. What is the size of the 16" tyre then? I'll guess 29"(6.5*16")

So, please post your RPM to corrected speed, what tyre size you have and driveline so that there is a place to compare for future referenceHuh[/quote]
Hi Bennie
You cant unfortunately regard your rev counter as being accurate as swell.
Unless you have had it recently checked and set.
They have an adjustment on them that will make a difference as much as 800rpm.
And now with them being over 20 years old i am sure most of them are not accurate.
The main final drive ratios you got were: 6.17 (16 inch diesel) 5.43 ( most of SA but 14 diesel and 16 petrol in europe)
4.86 (europe 2.1 petrol)
Then you got the others: 4.57 5.83
Tire sizes also vary from manufacturer to manufacturer. Just because it is a 215 80 15 dosent mean it is 28 inch.
My DFG mud tires i used to always use 235 85 16 are 31.5 inch new whereas the
235 85 16 i now use is just over 32inch.
Inflation on a tire will also affect all the above.
Russel
YesRussel, once again you have so much info, it makes me feel like a bean counter again. I know tyres are not all equal, some say 30" on the sidewall but is closer to 29" while others are over it and the pressures inflated also effect rolling circumference.
Never new 'bout the rev counter also having differences and variations.

Anyway, I'm running wranglers 215/80R15, got the 0.82 higher 5th gear and getting 109kmh @ 4,000rpm, 100kmh @ 3650rpm and get an good 136kmh @ 5,000rpm.
Above is GPS speed and have tested the odometer with the road mile markers to be underreading by 9% while the speedo underreads with 3% or so.
Bennie what is your gearbox code.
Russel
There is also the Upgrade 0.76 4th gear ratio with a the teeth a bit coarser than the fine gears as these gears are available for the V6 2Wd Busses
We are actually fitting a .76 gear in a Baywindow Autovilla ATM
I use a 0.7 4th gear, can't remember the third right now for my
Personal tdi installations. These gears have much courser teeth on them.
You need the extra strength with the tdi. Standard 3rd and 4th don't last,
The torque eats them and then can destroy more in your gearbox.
Russel
I use 1.18 3rd and 0,70 4th albin gears in my Tdi.
There is a gap between 3rd and 4th but with the Tdi torgue no big problem.
In the pictures installed the albin gears and you can see the huge deference between them and the original ones next to them

[Image: IMGP8345.JPG]
Thanks all, this input is very interesting and the knowledge shared will help a lot. Bus1988, what revs are you running then on the 0.7 gear? What wheel combo you have? I suggest it runs quite low @ 100kmh, giving great drivability with the tdi install. What engines are in the bus?
Pierre, was it an aftermarket 0.76 gear that was made up for the V6 busses?
Russel, what tdi engine has a higher rev limit or can run at over 3500rpm constantly in a bus without too much strain?
I am on 205/80/16, 5.43 diff and i have 100 km/h at 2750 rpms and 120 km/h at 3300 rpms (That's for me the maximum cruising speed with this setup)
You can run a tdi at 3800 with the side affects being low fuel economy and
Shortened engine life. It won't just blow up. But then it is pointless fitting a tdi.
I am using a 0.7 with 6.17 diff and 235 85 16 tires. In town I stay in 3rd doing 60km/H at 2300 rpm at 120 km in 4th it is 3100rpm.
I have a 1000rpm drop from 3rd to 4th.
You don't want to have your revs to low as then you drive on torque
And this is what eats gearboxes.
Russel
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