Talk me out of 315 cooper STT's with stock gears, also fitment and RPM?'s.

[nicholas]

I know this is generally frowned upon without regearing and especially with a true 35"+ tire, but hear me out.

Here are some of the things I have been thinking about.

1-I wheeled my old Z71 with 35's for 6 years before repenting and buying my dream rig (LC). I really like the way 35's feel and perform offroad. I also liked being able to travel at a lower RPM on the freeway also though it did suck driving up long mountain grades like parley's canyon, powder mountain's road etc-with 3.73 gears! Although shorter grades weren't bothersome. I usually drive slower than most people. The 285's just seem a tad smaller than what I am used to and the 315 seems like it would be a good fit for the LX.

My LX will be my DD here soon so in regard to lowering my overall RPM for a given speed on the freeway. According to an online calculator 315's would only lower my RPM from 2200 to 2087 while maintaining the same speed. While this would theoretically increase my MPG or allow me to drive a bit faster than normal, say ~70MPH instead of 60-65, and maintain the same MPG, I would have to guess that any gains would be negated by a)Increased weight/rolling resistance, b)definitely lower city MPG and 3)bogging down up mountain grades.

I will be living in the midwest for at least 2 more years, 5 years max, so mountain grades and high elevation are virtually a non-issue.

In the event that I end up going to a progam out west (Grand Junction, CO , Oregon, or Spokane, WA) in 2 years, I would hope that the supercharger "might" help a little on the mountain grades and high elevation for the remaining life of the tire or until I have the funds to regear/lock the 3rds. Besides forced induction lowers your effective gear ratio right?


2- Spare tire fitment:
I won't have the flow for a rear bumper/swingout for several years, so I would like to fit a 315 cooper in the stock spare location. I have been searching and it appears that there is a rumor that a cooper will fit with the crank lift mod, but I have yet to find proof.

According to cooper's site it appears that the 315's are actually only 34.47" Diameter and 11.92" section, so roughly 1.4" taller and 0.6" wider than the 285 I have under there right now which doesn't seem like a whole lot, but that is an increase of 5.5" in overall circumference.

I need to go measure the 285 spare in situ, but I have not done the crank mod yet so I don't know how much clearance that will make+/-. IIRC the 285 barely fits but perhaps there are some areas that could be trimmed (sheetmetal etc).

I usually like to throw the spare in the cargo area on wheeling trips so I wouldn't be concerned about dragging it on trails; I'm more or less concerned about have a place to store it when I am commuting around town/road trips.


3-I might have to get some 850's up front and or a spacer to clear the 315's especially for trails, but I definitely won't be seeing any rubicon-esque trails anytime soon.

4-Lastly, I live in an apartment with a 1 car garage that is already packed to the gills so the only way I can clear this move with the is to sell the 285's I have since I don't have room to store 5 extra tires. Ideally I'd get another set of stock 80 wheels and have a set of 285's and 315's but I definitely don't have the room and I will be moving around a lot in the next 2.5 years. So here is a shameless plug for my tires:

https://forum.ih8mud.com/sale-tires-wheels/268483-5-285-75r16-cooper-stts-75%-tread-central-ia.html


So what do you wise elders think?

What are the thoughts of anyone that has ran a similar setup?

I figured I would test out the waters here before I do something I might regret. I am being tempted by some 315's here locally, which makes this a tough decision.

Thanks in advance!

 

[UCBerzerkeley]

what about 295/75? stands 33.6" tall, sort of in between

 

[bpassmore]

Well, I ran my 315s for a while. The acceleration didn't take a hit, but my braking did. big time. Keep that in mind. It is a good size, but my mileage dropped from 15 on avg to 13 on avg.....

take or leave it....

 

[akarilo]

Go for it; especially with a blower! Don't think you'll regret it a bit.

 

[Nay]

Dude, I ran 35" trxus for almost two years in Colorado on stock gears. They mate up better RPM wise with OD off than 33's do. 33's sucked every bit as bad as 35's did, I could feel no real difference onroad between the two because the altitude induced power loss is so bad anyway that the power to weight ratio is your biggest killer.

The biggest problem I had was being undergeared for high elevation rock crawling, and it was starting to cause some damage to my rig because I needed momentum in spots where you really need to crawl.

Now, my 5.29's are way better, but it's still a dog, big time. I would take your supercharged 80 on stock gears over my naturally aspirated on 5.29's any day of the week for road use here. Not so for hardcore offroad use, but this will not force you to regear even if you come to GJC.

Having said that, you'll end up wanting to regear if you move here, the SC + gears = , but want and need are two very different things.

 

[jfz80]

1) Do it (is there a ? there) just keep an eye on tire weight as part of your consideration. I hear the Toyo Mt's are a pretty heavy tire and this may affect your decisions; i think the cooper is almost identical tread but not as heavy. If the price is right and they are local, id jump on it.

2)Look at getting a Q78 spare perhaps, as it will fit and if you do the spare tire winch mod then it should fit above the bottom of the frame rails. (search blarsen if needed)

3) You might. 850 or even J's (which would want to be paired w/ L shocks). Without a lot of wheeling you may be just fine. Id get them and see if you rub before adding spacers.

4)Sell the tires, use the funds for the extra gas I tried the whole two sets of tires things and it was never practical. The AT's are on when you want to go wheeling and your too tired to swap to them when youve got the MT's and your just doing numerous short trips. I end up swapping tires at 6:30 morning of a trail ride.

You got the S/C so i think youll be fine and not too disappointed in performance, as mentioned braking takes a bigger hit. Plus it sounds like you have eventual plans to regear and lock at some point.

I ran/run 315's and 35's and now 37's on stock gears and only the S/C and 3'' exhaust for performance improvements and havent felt the need to throw down 2 grand on gears yet. Sure its in the plan, but intill then im satisfied w/ the performance.

 

[Nay]

Also, check into the 35x10.5x16 SSR for a spare, Very narrow and not quite as tall as a Q78.

In fact, why don't you come down to Denver and buy my almost new 315 Toyo MT's and 35x10.5 never used SSR spare so I can move up to 37's?

Here's a shot of the SSR next to a 35" trxus.

 

[khoopes]

I have 285's on my stock 93' and it only gets about 12mpg with AT's. Not good.

What is the stock gear ratio on these FZJ's?

Is the Supercharger worth the money performance wise?

I am looking at another cruiser with 315's on it and this is a good thread.

Kris

 

[nicholas]

I have 285's on my stock 93' and it only gets about 12mpg with AT's. Not good.

What is the stock gear ratio on these FZJ's?

Is the Supercharger worth the money performance wise?

I am looking at another cruiser with 315's on it and this is a good thread.

Kris

Stock ratio is 4:10.

I thought the s/c was worth the money for my purposes, but there differing opinions out there. Do a search for "supercharger owners thread" for a pretty thorough debate about it.

 

[Box Rocket]

I've been running 315's with stock gearing on my truck the entire time I've owned it, and that's at ~4500' above sea level. I haven't really had too many complaints. It can be a dog on some of the long canyon climbs but other than that I don't worry about it. For crying out loud, I was used to my heavy 2F powered FJ40 on 37's with 4.88's and that was slow. So I can easily deal with my 80 with 35's and stock gearing.

I wouldn't think twice about it. If you go with a smaller tire now, you'll just want to go bigger later and you'll have spent good money after bad. Get the tires now and address gearing later if you think you need to. Then you're not wasting anything.

 

[nicholas]

FWIW, I actually did go with the 315's, but I've only driven maybe 60 miles since I've had them so I can't really say how I like them yet.

One data point I do have is that my transmission temp went up to 150* while going up a fairly steep 1/4 mile hill @2-4psi boost and ~35 mph. Usually my temps are much lower than that around town.

You can tell that the trans is definitely under a little bit more load with the 35's vs 33's.

 

[khoopes]

I think the additional RPM in part of the tranny generates more heat. Also I have not been able to tell if the torque converter locks up in 3rd gear on the FZJ80. I have a Turbo 4Runner on 31's and it blinks the trans temp light sometimes because I run it in 3rd gear with the 4:10's. Someone here mentioned running the Cruiser in 3rd.

 

[orionkhan]

FWIW, I actually did go with the 315's, but I've only driven maybe 60 miles since I've had them so I can't really say how I like them yet.

One data point I do have is that my transmission temp went up to 150* while going up a fairly steep 1/4 mile hill @2-4psi boost and ~35 mph. Usually my temps are much lower than that around town.

You can tell that the trans is definitely under a little bit more load with the 35's vs 33's.

What did you do to address the spare tire issue?

 

[billmiranda]

I am running stock gears, 3" lift (OME of course) and 35" tires.
I have only (as others stated above) really noticed a difference in braking. I can still run my 97 80 series at speeds over 80 mph indicated.. which is 88 true as it seems that the 35s I have make a 10% reading difference across the board.. Speedometer reads 10% lower than stock. This is based on both police radar and GPS readings.

The tranny is heating up uphill because of the additional leverage needed to turn those tires and the torque converter is struggling to maintain speed.

Get a nice tranny cooler (additional, not inplace-of), get a true flush in there and run synth fluids. If all else fails.. tere is a place out west that sells performance converters for the 80.. can't remember the name off-hand but I can look for it.

 

[billmiranda]

Also... instead of regearing front and rear... would it bee economically feasible to put in a transfer case doubler?... that way you keep your stock gears and great economy, while being about to drop gearing at the flick of a lever?.. not sure.. haven't looked into it much as my truck keeps me happy but I may want to turn it into more of a trail vehicle.

 

[Tools R Us]

...
The tranny is heating up uphill because of the additional leverage needed to turn those tires and the torque converter is struggling to maintain speed.

Get a nice tranny cooler (additional, not inplace-of), get a true flush in there and run synth fluids. If all else fails.. tere is a place out west that sells performance converters for the 80.. can't remember the name off-hand but I can look for it.

150F is well within normal operating temps, on the cool side in fact. I wouldn't worry until temps were consistently in the 200F range. The stock trans cooler setup works well, a bunch of locals run big tires and don't have trans heating issues even when climbing mountains at 100F+ ambient.

 

[96r50]

Slight hijack: Kevin, is there a minimum/maximum recommended temperature range for ATF? I'm actually more concerned with the low end temperature range, as it can take a while for the transmission to warm up (according to my gauge).

 

[Tools R Us]

Slight hijack: Kevin, is there a minimum/maximum recommended temperature range for ATF? I'm actually more concerned with the low end temperature range, as it can take a while for the transmission to warm up (according to my gauge).

Somewhere I have the results from a wear study done on auto trans, need to find and post it. IIRC the wear numbers were higher at 120F than 200F, with the sweet spot being 150-180F. This is why most systems run the fluid through the air cooler first, then the water cooler (radiator), the radiator helps to heat the fluid, get the trans up to temp in cold weather.

One of the problems with a cool running unit is, they are much less efficient at evaporating out moisture. Moisture in the oil converts to acids and other contaminants, so the best plan is to change fluid more often to combat this.

 

[nicholas]

What did you do to address the spare tire issue?

See below




As for the Temp data points. It appears that 150* isn't as high as I thought it was, as Kevin mentioned. Although I can definitely feel the tranny working hard at low speeds if I'm not in low gear while driving up steep inclines.

I actually felt what I thought was a my tranny slipping on two occasions. Turns out my transmission was overfilled by about a quart or so :whoops:from my last flush I did. I drained it and now things seem to be fine.

Honestly 35's aren't as big of a deal with stock gears as I thought they would be. I actually really like the lower RPM range at highway speeds. It kind of sucks with stop and go driving, but nothing to worry too much about.

 

[matt49]

do you have the info for a performance converter for the 80?

much appreciated

I am running stock gears, 3" lift (OME of course) and 35" tires.
I have only (as others stated above) really noticed a difference in braking. I can still run my 97 80 series at speeds over 80 mph indicated.. which is 88 true as it seems that the 35s I have make a 10% reading difference across the board.. Speedometer reads 10% lower than stock. This is based on both police radar and GPS readings.

The tranny is heating up uphill because of the additional leverage needed to turn those tires and the torque converter is struggling to maintain speed.

Get a nice tranny cooler (additional, not inplace-of), get a true flush in there and run synth fluids. If all else fails.. tere is a place out west that sells performance converters for the 80.. can't remember the name off-hand but I can look for it.