I've read through many search threads, but haven't found the info I'm seeking. I'm buying an XB the end of this month. The roadtest of the manual trans as many know is quite high in the rpm's at 70 mph. What I'm seeking is some feedback as to what people are experiencing with their oversized tires/wheels. Mainly interested in the 16" & 17" arena. Don't want to risk much larger.

Thank you for your time.

 

you have to make the overall height of the wheel/tire combo taller than stock to reduce rpms at high speed. HOWEVER, know that this will hurt acceleration to give you higher top speed and throw off your odo and speedo.

 

Yesti,
Thank you for such a prompt reply. Yup, having spent 5 years in a dealership, and 15 years on jets....I know the side-effects. Thanks though. Just wonderin' how much the increased circumferences drop the "R's". Still leanin' towards the fun factor of the manual.

Love this site!!!!

 

I don't notice much of a drop in RPM's from going to taller tires 195/65/15 with a little bit of rub on full lock both ways... maybe a drop of 200 rpms going 70 mph .... I liked 205/50/15's when i had them on.

205/50/15 - 23.1 OD Peppier acceleration.
195/65/15 - 25.0 OD Slower acceleration.. but the speedo seems correct.

 

Cool!!! Thanks for the info. That's exactly what I'm lookin' for! I'm doin' all I can to justify getting the manual trans.....getting closer all the time.

Thank You

 

I have two xBs with a 5 speed and I have gotten used to the high rpms at freeway speed.Also letting the engine rev up to atleast 4000 rpm before shifting.I like that it keeps you in the power range when you are in 5th.It makes the car excel faster to pass or to keep your speed steedy without downshifting.

As for your question I dont know sorry.

 

i'd just get an echo/yaris manual transmission. cheap easy and yep.

 

here's your formula

old tire size circumference (divide by) new tire size circumference.

use that multiplier (should be a number less than 1) against RPMs@ speed.

what i dont get is, if your speedo still says 70, your RPM's will still be the same, you'll just be going faster.. you gonna re-calibrate the speedo or get GPS ? sorry but it sounds like a pretty dumb idea *runs to hide*

at 80 the xa/b tachs 4200rpm

with a 5% increase in overal circumference you'll be taching just under 4000rpm

but a 5% difference in tire size is HUGE..

185 65 15 has a circumference of 76.87"
you'd have to run over 5" of sidewall to accomplish your goal, so a 205 65 15 would do it.. but holy crap that's gonna look stooopid on a 5.5" wide wheel.. so now you're factoring in buying wider 6.5" wheels (MINIMUM) but should try and get 7" wide wheels honestly..

205 65 15 OMG balloons anyone?

 

Forget the revs and gas mileage. Get the manual for the same reason I did, it's great fun around town. We still have traffic rotaries around here, and when one is not crowded I shift down and see how fast I can get around. Not really very fast, but it's a lot of fun.

 

^^ hehe when i do that, i come up on 3 wheels

 

he could get 185/70/15's . but man those things will be tall , unstable , ugly , and you will probably rub.

 

Thanks to everyone for the info. Very nifty. Yup Hotbox, there's gonna be a fine line between the plus sizing, and the rub/ugliness.

Thanks!!!

 

Tamago explained this, basically you are changing your 'final gear'. By making the wheel/tire combo physically taller than stock, for each revolution of the tire you are going _that_ much farther, so to go the same distance, the engine has to spin _that_ many less revolutions. of course we are talking fractions here, so the difference is going to be small unless you go extreme, but that will cause other problems...

 

To those with facts and figures, a huge thanks....still lookin' for more. To those with tech tutorials. I'm a 747 tech, I have that covered, thank you. I know your intentions are good.

Thank you all!!!

 

I'm running 215-45r17 Falkiens on Motegi MRMs (+40-42mm offset), and I got a rub at full lock until I pulled out the front inner fender wells. Otherwise no problems.

 

Won't that cause all the kibbles and bits of the suspension and whatnot to be more vulnerable to road wear and tear (moisture, rocks, etc.)? I'm trying to get some 215/40/18's and just wonderin' what it's like (drive and cornering)

 

Yes, you are correct. I just pulled the inner fenders last week, and am currently working on a fix. The only rub spot is on the foward inside portion of the inner fender plastic lining where the tire hits at full lock...that area of the plastic has worn away after 4 months of driving it that way, and now I need to do some trimming and attach a splash guard to my CAI filter.

P.S. I forgot to mention that I am dropped a little over 2" on Tein S-Techs!

 

Your profile doesn't tell us where you live- if it's hilly or mountainous country, then you'll find the relatively low gearing to be an advantage, and may not want to give that up. Lots of econoboxes have very tall 4th and 5th gears, which is probably fine in Florida, not good for climbing the Rockies...

It's not like the revs are absurd, anyway- 3000rpm in 5th at 60mph, 4000rpm at 80mph...

Nifty semi-accurate tire size calculator here-

http://www.miata.net/garage/tirecalc.html

You'd have to run some risk of rubbing in turns to reduce cruising rpms by even 10%.

 

I'm in the midwest. Minnesota, Wisconsin, and sometimes Michigan....relatively flat compared to your beautiful Colorado mountains. I'm a visualist when it comes to mechanical events, it's just a bit high on my comfort level with the rpms.

A bit off topic, I've been to Hong Kong a few times these last couple of months. I need to start shooting pics of all the box variations cruising the streets there. Nissan has a version, and there's another company which slips my memory. Stylin' mini-vans is really a trend there. Pilin' in the entire clan and cruisin'.

 

That would work in theory to lower your RPM's, but the higher rotational mass (and consequently moment of inertia) I think would actually lower your fuel economy around town. Also I am just switching over from a Jeep Wrangler to an xA, so this is my area of expertise. To notice any gains at all from a tire swap you need to change it more than I think is possible on a non-lifted vehicle of any kind. If you wanted to do something to get the revs down like 500 rpm's you'd really have to change your gear ratios, in a Jeep you can regear to do this, but it's usually in the opposite direction (to increase rpm's), but I think you'd need to get a new transmission, do they have a 6-speed that fits? or my personal favorite idea, throw a lift under there and put on some 31's, that'd lower your rpm's at highway speed significantly