285's or 305's for my 2008 JKU Rubicon?

J

JJJK

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Hello,

I am new to the wrangler forum (my first post!), and was wondering if I can have your opinion. I have a 2008 JKU Rubicon and my 255's need to be replaced. I am going with the BFGoodrich KO2. I want to upgrade my tire size and love how the 305's look. I understand I need new rims (looking at vision rims due to cost) for the bigger tires and not that interested in wheel spacers.

Don't know to go with the 285's or 305's. I have heard because my Jeep is 2008, the 305's might be hard on other components of my Jeep. I want to avoid that at all costs. I don't want to get into other problems. I would love to go with the 305's. Is it safe to do so? The Jeep hasn't been offrode, probably continue highway driven as there is no off roading opportunities in my area anyway. Just wondering if I can have your opinion.

Thanks for your time,

Jamie
 
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This is my 2009 when I had just a teraflex leveling kit. The wheels are pro-comp, and the tires are 285 70 r17. I had a bit of rubbing on the air dam before the leveling kit.

Unfortunately we have the 3.8 engine, and while it's not as bad as it's made out to be, it is a bit underpowered. I have a manual transmission so it's not as bad for me, but the automatic trans that came with these was... functional... but unimpressive.

so it depends on what "305" you are talking about. if 305 70 17, that is around 33.8 inches, getting a bit big for us. If 305 75 17s then you are talking 35" tires and I would highly suggest not doing that if you don't want to regear.
 
Thanks for your reply Macguyver. I am looking at the 305/65/R17 BF Goodrich KO2...I also have manual transmission. Should I stay away from the 305 as I don't want to re-gear or would it even matter. It is either the 305/65/R17 or the 285/70/R17...
 
Thanks!

Here is the site I use to judge tire size stuff. https://tiresize.com/calculator/
If you dig around there is a ton of great tools in there.

I wouldn't go much over 33".

That being said, 305 65 17s are almost an inch (about 2 cm) wider than the 285 70 17s, but almost the exact same height. Remember that in tire size, ALL of the numbers are important. On the site compare 305 65 17s to 305 75 17s to see what I mean.

Personally I really like the size I got. No need to regear, though you have to do a program on the computer to get the speedometer correct. With manual trans you don't have to worry about shift points so it's more about just knowing your speed. They also don't stick out too far from the fenders, just a couple cm. The 305s would stick out farther and have a higher chance of rubbing, especially if the suspension is stock.
 
305 is a bit of an oddball size. I think the tire selection is a lot better in 285 as well, so that's probably what I'd go with.

The narrower 285 will also perform excellent in the rain and snow compared to a wider 305.
 
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I have 305/70-17s on mine. Let me tell you with the 3.8/auto trans combo it's gutless as heck at hiway speed. The trans is constantly searching back and forth cause there's not enough power to stay in the higher gear. I'm in the process of figuring out what gears I'm going to install.

Long story short.......do 285s. 🤣
 
I just put 285/70 on my ‘09 JK with 1.25 inch spacers and factory wheels. They are barely past the fenders. With new wheels changing your back spacing at least 1.25” you will not have rubbing and the engine power loss with your manual trans will barely be noticed. As far as the speedometer goes, with the 255s my speedo was faster than gps speed. Now 55 on dash is 55 on gps.
 
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MacGuyver said:
Thanks!

Here is the site I use to judge tire size stuff. https://tiresize.com/calculator/
If you dig around there is a ton of great tools in there.

I wouldn't go much over 33".

That being said, 305 65 17s are almost an inch (about 2 cm) wider than the 285 70 17s, but almost the exact same height. Remember that in tire size, ALL of the numbers are important. On the site compare 305 65 17s to 305 75 17s to see what I mean.

Personally I really like the size I got. No need to regear, though you have to do a program on the computer to get the speedometer correct. With manual trans you don't have to worry about shift points so it's more about just knowing your speed. They also don't stick out too far from the fenders, just a couple cm. The 305s would stick out farther and have a higher chance of rubbing, especially if the suspension is stock.
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Thanks MacGuyver for your reply. I am learning alot from great posts from you and others. I will check out the tiresize website. I have seen others with 35" and 37" inch tires. For your engine to handle these tires, I assume modifications to your engine have to be made to handle the extra weight of these tires or is it just re-gearing. Thanks again!
 
Chris said:
305 is a bit of an oddball size. I think the tire selection is a lot better in 285 as well, so that's probably what I'd go with.

The narrower 285 will also perform excellent in the rain and snow compared to a wider 305.
Click to expand...

Hi Chris,

Thanks for your reply. Even though I wanted to go with the larger tires, I am going to go with the 285's BF Goodrich KO2's based on your reply and others. Learning alot here Thanks..
 
JJJK said:
Hi Chris,

Thanks for your reply. Even though I wanted to go with the larger tires, I am going to go with the 285's BF Goodrich KO2's based on your reply and others. Learning alot here Thanks..
Click to expand...

That's a great choice if you ask me (y)
 
Not a problem.

Also as a heads up, just because you see someone do something to their Jeep, 37" tires for example doesn't mean it's a good idea. It might be for that person but not for you. Or it may just be a bad idea... angry eyes for example. :ROFLMAO:

Another thing to keep in mind is that the bigger the change you make from stock, the more likely it is that other things will have to be changed as well.
I currently have a 2.5 inch teraflex lift and I'm right on the border of needing to change other things to compensate for the changes that have been made. Adjustable track bar or long arm suspension kinda stuff.

As far as the 3.8, there isn't much you can do to increase the power without very expensive mods. At least that I'm aware of, regearing is the typical way larger tires are compensated for.
Along those lines I highly suggest staying away from the K&N "more power!!" air filters. ProjectFarm, a youtuber, tested them and they are only a little better than no filter at all. Dust and more go right through.
 
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