Thoughts on Final Drive Ratios

I've been playing with a gear calculator toying with the final drive on my Lancia Beta Coupe. (YES JVL, we're almost ready LOL) I have the hologation papers from the factory effort and if i'm doing this right, those cars max'd out just shy of 70 mph. This sound right?

I'm aware that these would get changed for differnt conditions, etc. Perhaps with the European rally not having the lengths of straights they wanted the pull out of each corner. I'm interested in the collective more experienced opinions.

Thanks

Dan

Zagato78 Wrote:
-------------------------------------------------------
> I've been playing with a gear calculator toying
> with the final drive on my Lancia Beta Coupe.
> (YES JVL, we're almost ready LOL) I have the
> hologation papers from the factory effort and if
> i'm doing this right, those cars max'd out just
> shy of 70 mph. This sound right?

No you're making some big mistake somewhere.
Post what you are doing DETAILS MAN DETAILS!!!

>
> I'm aware that these would get changed for
> differnt conditions, etc. Perhaps with the
> European rally not having the lengths of straights
> they wanted the pull out of each corner. I'm
> interested in the collective more experienced
> opinions.

Sure they change final drives and everybody had extra gearsets aavailable for specialty rallies like Safari, but who can say what you're doing wrong since we don't know what you're assuming, and what you know.

Here's some info tho:
In the mid 80s the GpB Audi works car were geared for about 115mph when they did our woods at Olympus.
We asked, and I confirmed it in conversations with Arne Hertz.

The GpA Lancias were geared for under 120, again we asked the mechanics while sharing a ciggie with them--a crazy friend was asking in his crazy bicycle racer Italian, and the mechanics were all happy that somebody was talking to them, and I understand Italian enough the answer "185".

My Saab with a rev limit of 7100 and Michelin 16/62 x 15 will do about 105-ish and the gearkit I use is what they used on virtually all events in the 70s with the 96.

Saab 99's gearkit is so close to the Saab 96 the only differences depend on how much you rev it. And the 99/900 motor is strong so it can be revved higher.

I ran into the co-driver of the man who made the gearkits for the factory Skoda 1.3 Favorits back in the early 90s, and he said, the the guy who made the kits, Janne Sellholm, later confirmed, the cars would do "140km and not a skvat above", so there you have a case of overall top speed traded for acc thru the gears.
That's all you can do when you have little motors, but damn they sounded wicked.

So POST you DATA and lets see if we can fingure out where you went astray.

>
> Thanks
>
> Dan
Smoooochies!

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Here are the ratios as per the Fia paperwork

13 inches wheels
Assuming 7000 redline(production redline)

1st 3.5
2nd 2.467
3rd 1.895
4th 1.522
5th 1.280

Final 3.929

This is where i screwed up, miss translated the reverse gear 3.071 for the final drive. With the 3.929 the top end comes to 54mph LOL, yeah i'm doing something wrong.

Dan

I screwed up the tire diameter(duh!) with that gearing, and a tire diamter of 22 inches, i'm seeing 91 miles an hour.

Playing around the tire diameters is making a big difference. I never appreciated how big an effect that is.

Dan

Now what will the speed be with a 62cm or a 65cm tire?

---

Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

Zagato78 Wrote:
-------------------------------------------------------
> Here are the ratios as per the Fia paperwork
>
> 13 inches wheels
>Assuming 7000 redline(production redline)
Jeeeeezs H. Khrist, son, NO Fiat can possibly rev so LOW!!!!!
I certainly never been in a Fiat that revs less than 7600 STOCK and we're talking rally cars, son!!!!!
8000 minimum!
>
> 1st 3.5
> 2nd 2.467
> 3rd 1.895
> 4th 1.522
> 5th 1.280
>
> Final 3.929
>

You serious with those ratios???
That 5th is 5.01:1 overall

> This is where i screwed up, miss translated the
> reverse gear 3.071 for the final drive. With the
> 3.929 the top end comes to 54mph LOL, yeah i'm
> doing something wrong.
>
> Dan

Tires are the easiest way to screw yourself.
That's why I'm making sure that the Gp5 guys in the Volvos and the Xratties get somewhat shorter final drives from the stock 3.64 to 3.9 or 4.3.
When you add the tall tires, which gears you UP, the TOTAL change is around 11% shorter than a streeet car.
See?
Final drive gears you shorter by 18% (4.3) but the tires we use costs us 8% cuase they're tall at 24.5" vs street cars 24.3"--more or less.

Gotta run top the Pharmacy for the baby then down to machine shop but I'll look at your figures later and add a more realistic 8000 rpm limit!!

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.



Edited 1 time(s). Last edit at 04/14/2007 11:39AM by john vanlandingham.

John,

Yes i was being a tad conservative with 7k LOL, my street car is never shited before 8k either.

That 5th gear was the factory set, the street box that i have will have the following gears, for now.

1st 3.5
2nd 2.235
3rd 1.522
4th 1.152
5th .925

Final drive 4.214

Another thought, adding a LSD, does that drag on the system warrant rethinking the gearing or is the effect minimal enough to overcome with engine power?
Just random babbling to increase my overall understanding. The gearing and math thing is kinda new to me. LOL

Dan