Hi all,
I am finding that my 5 speed, '75 Spider will pull down about 25 MPG on my daily 90 mile commute.
I would really like to get a bit more mileage and drop the cruising RPM's to somewhere in the mid 2K range.
If the manuals I read are correct, than the stock rear axle ratio is 4.3/1.
I have seen another ring and pinion set that has a 3.9/1 ratio.
Has anyone used these? And if so, did the fuel economy improve?
Is it worth it?
Thanks again.
Rear axle ratio change?
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RoyBatty
- Posts: 852
- Joined: Sat Aug 28, 2010 11:44 pm
- Your car is a: 1975 124 Spider - 1971 124 Sport Coupe
- Location: Locust Grove, VA
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narfire
- Posts: 3959
- Joined: Sat Dec 27, 2008 2:14 am
- Your car is a: 1980 124 spider
- Location: Naramata B.C.
Re: Rear axle ratio change?
For reference,I'm getting about 11 kilometers per liter with the stock FI and 13 inch tires. That works out,if my math is correct, to about 26 mp us gallon or 31 miles per imperial gallon. My commute is 35 klicks of mostly 40-50 miles per hour.
100 kph or about 61 mph,I'm turning about 32-3300 rpm.
100 kph or about 61 mph,I'm turning about 32-3300 rpm.
80 FI spider
72 work in progress
2017 Golf R ( APR Stg. 1)
2018 F350 crew long box
72 work in progress
2017 Golf R ( APR Stg. 1)
2018 F350 crew long box
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Tobi
Re: Rear axle ratio change?
Looking at the avatar, it will be hard to find much taller tires.So Cal Mark wrote:just put on taller tires
I would get a Toyota Prius
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Daniel
Re: Rear axle ratio change?
The ring and pinion from a automatic is 3.58 to 1 less likely to be abused as well when buying a used one .
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RoyBatty
- Posts: 852
- Joined: Sat Aug 28, 2010 11:44 pm
- Your car is a: 1975 124 Spider - 1971 124 Sport Coupe
- Location: Locust Grove, VA
Re: Rear axle ratio change?
Thanks Narfire,
Do you know your rear axle ratio?
Considering how I am using the car mainly on long straight stretches of two lane country roads and highways, How is it not worth it to change the rear axle ratio to a better number for cruising?
Not to argue, but it would seem that the engine would benefit from not having to spin up to the higher revs for the cruising stretches.
Also in my experience driving this car in the last several weeks, the engine seems to have plenty of bottom end grunt to handle the change.
I do enjoy a twisty foothill road here in the Amador County Wine country, but I am not driving the car in hill climbs.
Do you know your rear axle ratio?
Considering how I am using the car mainly on long straight stretches of two lane country roads and highways, How is it not worth it to change the rear axle ratio to a better number for cruising?
Not to argue, but it would seem that the engine would benefit from not having to spin up to the higher revs for the cruising stretches.
Also in my experience driving this car in the last several weeks, the engine seems to have plenty of bottom end grunt to handle the change.
I do enjoy a twisty foothill road here in the Amador County Wine country, but I am not driving the car in hill climbs.
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majicwrench
Re: Rear axle ratio change?
Engine was designed to run pretty high RPMs and you are doing no damage by doing so. You may--may---pick up a tiny amount of fuel mileage. So "worth it" is entirely up to you.
My 72, I do not know the ratio, but I know it is not the easiest to get rolling in 1st gear and I would not want to make that any worse.
THe biggest improvements in mileage will come from proper tuning, proper air in tires, keeping speed reasonable.
Again, "worth it" is your decision.
My 72, I do not know the ratio, but I know it is not the easiest to get rolling in 1st gear and I would not want to make that any worse.
THe biggest improvements in mileage will come from proper tuning, proper air in tires, keeping speed reasonable.
Again, "worth it" is your decision.