Hi,
Could anyone running 235/50 18's let me know what tire pressures you're running.
I just bought 18x7.5 rims and 235/50ZR18 BFGoodrich's for the summer and am unsure of the correct pressures or how to calculate them. From what I've read here, it sounds like I should be running higher than factory pressures. Any help would be great!
16274

I suspect you have already seen our collective ignorance on this 'max pressure' thread:
http://www.elementownersclub.com/forums/showthread.php?t=20870

It looks like the max load rating of these tires is comparable to the stock tires, maybe a bit higher, but the max pressure may also be higher. Any advise from the tire dealer?

I've seen tire pressure tests based on fitting a business card a short distance under the edge of the tire. You could also try to look at the contact patch. With stock tires at recommended pressures the patch is roughly square. Since these tires are a bit wider than stock, so I'd expect the proper patch to be a bit shorter than wide.

paulj

Thanks, I'll take a look at the contact area of the tires tomorrow and try to see. What are you looking for when you use the credit card under the tire?

I called BFGoodrich's tech line, they said I needed to call Honda America. I tried Honda, but they were closed for Good Friday, I'll try them back next week.

I did see the tire pressure post. That, and wheel/tire fitment post got me thinking that maybe someone out there has this size on his/her E and arrived at a good pressure.

Right now I just put in a few pounds over the door sticker, I just don't want to burn any more gas or tire than I need to.

Thanks again for your help!

To get a professional opinion I think you'd have to talk with an independent tire shop that specializes in plus sizes. I'm not surprised that the tire manufacturer says check with the car manufacturer. The ideal pressure depends strongly on the weight of the vehicle. Honda will probably say: 'we don't recommend changing tire size'. Corporations don't risk giving opinions that could leave them open to lawsuits.

paulj

Here's a discussion that found by a google search on 'tire pressure plus size', from a 'Sport Compact Car' site:
http://www.sportcompactcarweb.com/tech/0208scc_tires/

I also find references to load/inflation charts that tire dealers are supposed to have. I haven't been able to find any such charts on the web (except for truck/rv sizes). I posted a graph of this data on
http://www.elementownersclub.com/forums/showpost.php?p=252275&postcount=12

I did a search for 'business card' on rec.autos.4x4.

http://groups.google.com/group/rec.autos.4x4/browse_frm/thread/a4a43f29bdaa9ff4/de792e3d8a539abc?q=business+card&rnum=2#de792e3d8a539abc

One regular there, Jerry Bransford, advocates:

The proper tire pressure is that which allows the right amount of tread to be on the road. Too high of a tire pressure causes the tread to 'bulge' which means the tire is only riding on the center of the tread itself. Lower the tire pressure until you can only slip a business card in under the tire edge a maximum of maybe 1/4" to 3/8" to insure it's not inflated at too high (or too low) of a pressure.


I can do this with my Cooper ATR tires, and they are inflated 2-4 psi above recommended. The idea is to lift the edges of the tread off the ground just a bit. Of course when actually moving, the contact area will vary, with some further bulging at high speads, and shift of the contact to one side or the other on turns.

The applicability this test may vary with tires. Jerry is a 'Jeep Geezer' (http://members.cox.net/jerrypb/id17.htm ). Off road tires tend to have square shoulders which make this card test easy. It may be harder to apply to the rounded shoulders of the stock Wranglers. Off road people also lower their tire pressures into the 20's or even 10's for slow speed driving (where heat buildup due to excessive flexing is not a problem).

Another 4x4 tire pressure test focuses on even tire wear. You draw a chalk lines on the tire, and adjust pressure until the chalk wears off evenly across the tire width.
http://groups.google.com/group/rec.autos.4x4/browse_frm/thread/9e71fe08b44ea3f9/b273aa3ca7d33bae?q=business+card&rnum=8#b273aa3ca7d33bae


paulj

Tried the business card test, it's a little hard to tell with the tires more rounded shoulders, but I definitely don't think I have too much air as the card didn't seem to go far.

Still have to try Honda America back, but I'm not holding out much hope that they'll give me a pressure for a wheel/tire combo this far from the stock offering.

Did the rough estimate suggested by the BFGoodrich engineer on sportcompactcar, but it came out to 48.5 F and 46.5 R, yeow, thats higher than the tire's 44 lb. max!

The formula found here in the 'maxpressure' thread:
(OEM Tire Weight Rating / OEM Tire Max Pressure * OEM Recommanded Tire Pressure ) / (Aftermarket Tire Weight Rating / Aftermarket Tire Max Pressure)
Yielded 34 F and 36 R which seems like a reasonable start, maybe a couple pounds low.
Think I'll start here, try the chaulk on the tread, and monitor the wear.

I've been running mine at 34 frt and 36 rear. I tried lower and it was a big difference in the feel.. I would recommend this as the minimum pressure and go from there,Tim

Anyone reading this that needs tires...thats over 1/2 off !!!!!! Tire rack right now is $75 a tire. I paid $152 each and thought I got a good deal!