Ah that old horse chesnut once again. Gear Ratios...

[Paul Y]

Not sure how many times this has been discussed, how many times the formula has been posted or indeed how many have theorised on the potential rear end ratio but I am sure it is more than the amount of mince pies I will consume over the Chrimbo period.

Problem is what looks good on the calculator can very quickly become a nightmare on the road.

Therefore a suggestion.

Would it not be a good idea for a sticky post to be created in which we could add what we use and our thoughts on its suitabilty?

Obviously we would need to include tyre size,type of gearbox (manual or auto) standard or OD, engine type and power and intended use. Type and weight of vehicle and amount of lead in the drivers foot...

In that way we could get some real world experiance to add to the calculators tale and still go and order the 4.88's......

I would offer to kick it off but the reason that I am posting this is I have just spent the past 3 hours trying to work out what ratio I should use in the Pumpkin.

Was on a 3.50 but am going to go to a 3.25 for a bit more in the first 2 gears and a little longer legs to help with the fuel consumption, but as it is still all in bits in the garage I can not comment.

Anyway, Just a thought. Any takers??

P.

[stueeee]

Obviously we would need to include tyre size,type of gearbox (manual or auto) standard or OD, engine type and power and intended use. Type and weight of vehicle and amount of lead in the drivers foot...

Blimey! A good idea, but more variables than you can shake a stick at. How about expressing it in weight of vehicle and MPH/1000 RPM in the gears and some idea of what motor is up front. As you've identified with your car, it's about ratio spread as well as overall gearing. when I got my truck with a TH350 auto box in it, the first was a bit high for traffic whereas the direct top seemed way too low @ 23.5 MPH/1000 I'll have to see if I've gone to the opposite extreme with a new box with a .68 (34.6 MPH/1000) 5th gear!

Stuart.

[langysrodshop]

Paul there is gear ratio info in the tech archives or am i wasting my time ???

[Paul Y]

Paul there is gear ratio info in the tech archives or am i wasting my time ???

Steve,

No you are not wasting your time and it is this that I used. However...

These do not tell the whole story, as what looks good on the calculator might not work so well in real life and visa versa.

The thought was for us to have a reference point that correlated the calculator with the real world, sort of like this.

Approx Vehicle weight -3500lb Chevy

Engine details -Big Block 500hp, 550lbft

Gearbox -DNE 5 speed

Gearbox final drive ratio -1-1

Axle Ratio -3.50-1

Tyre diameter -29"

RPM@ 70mph -2860rpm

Comments

With the DNE box 1st gear is too short and does not take advantage of the torque whilst I would like to drop 200rpm in top help with fuel consumption.

In the 1/8th I have to change into 3rd just before crossing the line.

Am looking at changing to a 3.25 gear to give 1st gear a bit more legs, help with the rpm @70mph and drop a bit of time of the 1/8th.

Now I am not saying this is perfect and could probably be put into a spread sheet to make it all line up but what do you think?

P.

[langysrodshop]

The only problem i see Paul is the amount of variables.
Start a post and see what happens.

[Mart]

Redoxide posted a link to a pretty useful table for diff ratio's and tyre sizes recently.
Anyone know where it is??
Mart.

[langysrodshop]

In the Tech Archives.

Redoxide posted a link to a pretty useful table for diff ratio's and tyre sizes recently.
Anyone know where it is??
Mart.

[Adam]

TIRE HEIGHT X RPM X 0.002975 / REAR RATIO = SPEED.

You want to be aiming for about 23 mph per 1000 rpm for a nice driving all round street car.

I should save a copy of this as it's asked most weeks.

[kapri]

Is there anything in Tech archives about this ?

[Paul Y]

Ok, I think either I am not making myself clear or, or, or well something else.

Yes. There are lots of posts on how to work out the rear end ratio but that does not tell the whole story.

What I was trying to establish was a kind of "had a 3.89 and it was ok but swapped it over for a 3.50 and now the car drives much better as it has more mid range sort of thing"

Or even " In my T with a 350/350 combo I use a 2.90 and it is fantastic because I get great acceleration and good crusing"

The reason I brought this up is that I asked on an Americian Chevy site for comments and came back with exactly this type of reply which is a lot more useful than the old 23mph per thousand answer (not that it is not important but there is more to it than that)

And, something else I found was the rule of 10. Not heard it before but apparently the combined first gear, axle and tyre height should give you a 10-1 ratio for optimum performance.

Anyway, rambling now but is there any mileage in this or should I just shut up?

P.

[langysrodshop]

I think the problem is Paul that different strokes for different folks, A guy that lived in Scotland may need good cruising gears as he has a long way to go whereas a local guy might prefer 4.11's for that instant hit.

Like i said earlier post it and wait for the replys.

[Paul Y]

Think you are right Steve but where to post it?

Tech? Discussion? Club house? For Sale??

In the new spirit of the site I think that 'we' should look at haveing stickies for thing that get asked on a regular basis etc. Not saying this is one of them if there is no interest but....

Anyway, where do you want me to post it Mr Moderator??

P.

[kapri]

Paul, the biggest failing I see in gearing is people getting it wrong because they are comparing the cruising 'note' to that of their daily. I've been more than happy with the 22/1000 set up on my V8 powered motor . In those powered by 4's it is a bit more tricky and depends on the amount of torque versus weight ratios.

I think that most rodders don't even consider gearing they just fit 'A 'jag rear or 'A' volvo axle or the rear axle that came in the donor motor with no consideration for overall gearing or performance.

Cheap tuning if you get the gearing right.

Tech would be the best section, after all you'll get those that are interested in such things posting. If there's enough good posts it'll get added into Tech Archive !! LOL

[langysrodshop]

Tech Discussion Paul.
The problem with stickys is that they take up valuable discussion space, That's why we have the archives. If the post is good it will get in.

Think you are right Steve but where to post it?

Tech? Discussion? Club house? For Sale??

In the new spirit of the site I think that 'we' should look at haveing stickies for thing that get asked on a regular basis etc. Not saying this is one of them if there is no interest but....

Anyway, where do you want me to post it Mr Moderator??

P.