Rear end gear ratios - anyone have a calculator spread sheet for looking at speeds?

[Cornerz]

So I’m about to order a new set of rear gear and pinion. The current 3.55 ratio is too long for my track- on a warm day, I’m in 3rd for all except one slow speed corner in 2nd. So I’m hoping to look at where my RPMs are going to be at my current apex speeds with different gear sets.
Have any of you already built a calculator that can save me from doing all the math?
Trying to decide between 3.73, 3.91(3.92) and 4.11, and want to see what speeds I’ll end up with at given RPMs and what RPM I’ll end up with at given speeds and trans gears.

 

[mwjscn]

Vehicle speed calculator with engine/road speed graph for each gear

Input gearbox ratios and tyre size to calculate potential maximum speed in each gear, with a graph to show road speed against engine speed throughout the rev range and show gear change points. Useful to see how changing wheel and tyre sizes will effect the performance of your car.

legacypic.uk

You can open the link up in a few tabs if you want to compare different gears simultaneously.

 

[Cornerz]

Vehicle speed calculator with engine/road speed graph for each gear

Input gearbox ratios and tyre size to calculate potential maximum speed in each gear, with a graph to show road speed against engine speed throughout the rev range and show gear change points. Useful to see how changing wheel and tyre sizes will effect the performance of your car.

legacypic.uk

You can open the link up in a few tabs if you want to compare different gears simultaneously.

Thanks. I’ve found a couple online since I posted. I’m going to build a spread sheet from there I think unless someone has one already built.

 

[EF1]

I have one pm me an email and I will send

 

[Cornerz]

I have one pm me an email and I will send

Awesome. PM on the way

 

[EF1]

which transmission are you running?

 

[Cornerz]

which transmission are you running

Original TR-3650.

 

[EF1]

Spreadsheet sent. It has MT 82 ratios in it. Just copy and paste ratios for the TR-3650 from page 2 into the ratio cells on page 1. I built it when trying to decide which transmission and gears to use when my MT82 died a horrible death.

 

[67GTA]

So I’m about to order a new set of rear gear and pinion. The current 3.55 ratio is too long for my track- on a warm day, I’m in 3rd for all except one slow speed corner in 2nd. So I’m hoping to look at where my RPMs are going to be at my current apex speeds with different gear sets.
Have any of you already built a calculator that can save me from doing all the math?
Trying to decide between 3.73, 3.91(3.92) and 4.11, and want to see what speeds I’ll end up with at given RPMs and what RPM I’ll end up with at given speeds and trans gears.

Looks like you’re considering non-Ford Performance gear sets based on the ratios. The usual recommendation is to stick with the FP gears because aftermarket tend to whine or make more noise than the FP. The real reason for this is FP uses a different manufacturing process on their gears than the aftermarket, which require different setup methods and patterns. If I remember correctly, FP uses a newer 2-cut face-hobbed process on the 8.8” gears, while all aftermarket use a traditional 5-cut face-milled process. It’s important to understand which one you have, and setup accordingly.

If you stick with the Ford gears, you can typically reassemble with the same pinion and differential shims that were in there from the factory and be very close if not right on the money. Otherwise, it’s very important to take the time to verify which setup process is needed.

 

[Cornerz]

Looks like you’re considering non-Ford Performance gear sets based on the ratios. The usual recommendation is to stick with the FP gears because aftermarket tend to whine or make more noise than the FP. The real reason for this is FP uses a different manufacturing process on their gears than the aftermarket, which require different setup methods and patterns. If I remember correctly, FP uses a newer 2-cut face-hobbed process on the 8.8” gears, while all aftermarket use a traditional 5-cut face-milled process. It’s important to understand which one you have, and setup accordingly.

If you stick with the Ford gears, you can typically reassemble with the same pinion and differential shims that were in there from the factory and be very close if not right on the money. Otherwise, it’s very important to take the time to verify which setup process is needed.

Yes. I’ll be doing a full setup on it. I’ve got some experienced local help here, but it’s worth noting for anyone else not familiar with setting up new rear end gears that there is way more to it than just unbolting and reinstalling the parts. I need to refurb the diff clutches as well due to excessive axle backlash due to clutch wear. I don’t think the 3.73 is going to get me where I want to be, so I’ll need to get the pinion height and backlash correctly set. Luckily it’s not my first time, instead it will be my second! lol.

 

[Mad Hatter]

What diameter tires are you running?? I found the 315/30-18's make the 3.73 a little short on the MT82 gears. But it will depend on your track and power levels. In my case I really only use 3rd, 4th and 5th, and that's with a Calimer stage 3 that is a little taller then stock.

 

[EF1]

The calculator I sent uses wheel height in the calculation. You enter wheel diameter in inches. I don’t use metrics.

 

[EF1]

Clarification. Overall tire diameter.

 

[Dave_W]

If you already have rpm data for your track, you can use the ratios between current and proposed gears to find new rpm. For instance, 3.73 is 1.0507 shorter than 3.55 (simply 3.73 divided by 3.55), if you're at 6000 rpm at the end of a straight with the 3.55, you'll be at 6304 rpm with the 3.73 (if you're at the same speed).

However, with the shorter gears you may be able to accelerate harder; in theory, you could back-of-napkin estimate the acceleration G by using difference between corner exit mph and top speed over the time between those events (gives average mph gained per second - convert units into ft/sec gained per second, then divide by 32ft/sec/sec (1G) to find acceleration G) then multiply that by the R&P change ratio (1.0507 above) to find the new acceleration G. You can then apply that acceleration rate over the distance between corner exit and braking point to find the new top speed at the end of the straight (and difference in time to travel that distance), given the same corner exit speed.

Buying a new R&P set gives one the option to have "prep" work done to it before installation. What are folks opions on 1) cryo treating, and 2) REM polishing, for ring & pinion gears?

 

[biggsy]

Here is another one to throw in the mix. I like This because You can simulate your shift points and compare between ratios and tire sizes on the same graph

Gearing Analyzer with Shift Tracer

Enter gear ratios, tire and diff ratio to analyze RPM vs velocity at shift points with tracer

www.blocklayer.com

 

[blacksheep-1]

Fyi...

Thread 'Gear installation' https://trackmustangsonline.com/threads/gear-installation.18062/

 

[Cornerz]

Fyi...

Thread 'Gear installation' https://trackmustangsonline.com/threads/gear-installation.18062/

Thanks Blacksheep. That’s great! After some review of the spreadsheet and my min/max corner speeds, I think I’ve finally decided on the FRP 4.10 gear set and their rebuild kit for the diff clutches. As much of a pain as it will be to pull the rear end completely out of the car, I think you are right - it’s the only way I’ll be able to get the measurements correct. I can’t see doing it under the car on stands.

 

[blacksheep-1]

Thanks Blacksheep. That’s great! After some review of the spreadsheet and my min/max corner speeds, I think I’ve finally decided on the FRP 4.10 gear set and their rebuild kit for the diff clutches. As much of a pain as it will be to pull the rear end completely out of the car, I think you are right - it’s the only way I’ll be able to get the measurements correct. I can’t see doing it under the car on stands.

I did the one in my F150 in the truck, but once you remove the spare, you can actually sit back there comfortably.

 

[EF1]

I rebuilt the rear in mine last summer complete with a Detroit True Track and 4.10 Ford Performance gears without removing it from the car. It can be done, but in hindsight it would have been easier and quicker to remove the whole housing. There is a lot of back and forth when setting up gears and it would have been easier on the ground where gravity works with you instead of against you.