Tire To Gear Ratio Questions

[Jacob Ochs]

So I have the 2.8l v6 making around 120hp and a ax-5 transmission, I have a rear dana 35 and front dana 30 both with 4.10 ratio, I want to run 33-35 inch tires when I put on my lift, should I upgrade my gears or jut leave them at the 4.10? Thanks for all the help so far guys!

[Eagle]

I assume you mean 4.10 ratio.

 

The 2.8L V6 was rated at 115 horsepower, not 120, and the rating was probably optimistic. My personal feeling is that you simply shouldn't even consider tires as big as 33" or 35" with the 2.8L, but it depends a bit on how you plan to use it. For trail only, it might be tolerable. For regular street driving, you'll regret it.

 

I'll assume the factory tire size for your vehicle was probably 215/75-15. With 4.10 gears and the 5-speed, at 65 MPH in top gear the engine would be turning at 2512 RPM. 65 MPH in fourth gear would be 3349 RPM.

 

You can't get gears any deeper than 4.88 for the Dana 30, so let's look at 4.88 gears with 35" tires. 65 MPH in top gear would turn the engine at 2375 RPM, and 65 MPH in fourth gear would be 3167 RPM. In other words, your final drive ratio would be higher (lower RPM) than stock gearing.

 

33" tires would be marginally better. At 65 MPH with 4.88 gears top gear with 33" tires would be 2526 RPM, and fourth gear would be turning 3368 RPM. Basically equal to your factory gearing and tire size.

 

If you leave the stock 4.10 gearing, with 33" tires 65 MPH would be 2122 RPM and fourth gear would be 2829 RPM.

[onlyinajeep726]

I'd consider an engine swap before I started with bigger tires on a 2.8 equipped MJ.  A 3.4 would be a good upgrade in both power and reliability.  Then pushing 33's wouldn't be so bad.  But, that's just my suggestion. 

[mnkyboy]

I ran 33s with 4.88s and a 2.5l. It did pretty well, I could tell the truck was happier with 4.88 and 31s though.

 

Right now I'm in the precess of going to 5.38s and 35s.

 

I did run for quite a while on 3.55s and 33s, it was terrible but it did go down the road.

[onlyinajeep726]

I'll take a 2.5 over a 2.8 any day.

[jpnjim]

Depends on what you plan to do with it,

but it will probably be pretty gutless either way.

 

I wouldn't sink the money for a 4.88 swap if it wasn't going to be much of an improvement over the 4.10s you have now.

 

If you were lucky enough to find a set of factory 4.56 axles cheap, I'd probably do that,

but for all the $$$ a 4.88 r&p swap is going to cost,

you probably still won't be happy with the results.

 

How is it now for power?

What size tires are you running?

[Incommando]

http://www.grimmjeeper.com/gears.html

 

Plug in your numbers there and play with combo's.

 

Power is not the issue gearing is IMHO. Many early Taco's got by on 33's & 35's with less horsepower than the 2.8's claimed HP.( I think torque is the more relevant number anyway but that is another issue altogether) Those taco's (even before they were called Tacoma's) had much greater gearing options available and they still suffered at some point due to the compromises that had to be made regarding street versus trail performance. I assume by wanting to run 33-35" tires on a D35 you mean to use it for looks only anyway so I would be biased towards realistic street ability at that point. If you had a stick with a low first gear of at least 4-something and some pretty low gears like 5.38's you may be able to make such a combo livable. 

[Jacob Ochs]

Okay yes this is simply for looks probably won't ever see much off road, I was going to get 33' now because 35 seems to big for me, I have a manual, I seem to get great power to what I know I can easily burn the rubber off my tires now (being the 17 year ok that I am) idk what size they are but they're 27 inches high, I really don't have the time or money for a 4.0 high output swap I have one in my garage but I don't know how nor want to cut the firewall to fit the engine it seems like a big headache, I just put new carriers in both the D30 and 35 with all new spider and side gears and I'm hoping with 4.10 ill be able to run 33 inch tires decently!

[wvzj]

Good luck with that. I know the 2.8 I had was gutless with 215's.

[onlyinajeep726]

Okay yes this is simply for looks probably won't ever see much off road, I was going to get 33' now because 35 seems to big for me, I have a manual, I seem to get great power to what I know I can easily burn the rubber off my tires now (being the 17 year ok that I am) idk what size they are but they're 27 inches high, I really don't have the time or money for a 4.0 high output swap I have one in my garage but I don't know how nor want to cut the firewall to fit the engine it seems like a big headache, I just put new carriers in both the D30 and 35 with all new spider and side gears and I'm hoping with 4.10 ill be able to run 33 inch tires decently!

 

A 4.0 swap isn't that bad, but it does take some time.

[Jacob Ochs]

Okay yes this is simply for looks probably won't ever see much off road, I was going to get 33' now because 35 seems to big for me, I have a manual, I seem to get great power to what I know I can easily burn the rubber off my tires now (being the 17 year ok that I am) idk what size they are but they're 27 inches high, I really don't have the time or money for a 4.0 high output swap I have one in my garage but I don't know how nor want to cut the firewall to fit the engine it seems like a big headache, I just put new carriers in both the D30 and 35 with all new spider and side gears and I'm hoping with 4.10 ill be able to run 33 inch tires decently!

 

A 4.0 swap isn't that bad, but it does take some time.

 

Did you run into any problems?

[onlyinajeep726]

Overall, not really.  I have everything photographed in my build thread and what I don't have posted, I have in my photobucket.  It's tedious, but not hard IMO.  But I will say this much, if you or anyone reading plans to a do a swap like this, regardless if it's an '86 or not, a donor XJ/MJ will be a very good thing to have.  That's what persuaded me to do the swap on mine.