Your experience with tire sizes vs performance

[goffoz]

So its time to put new tires on the 2wd 7passenger, 2.1 powered van.
Its a 1989 all stock GL with 14"alloys. with 195/75's
We do alot of freeway hill driving here...you know straight up the hill for 3 or 4 miles on 50 or 80 in N.Cal towards Lake Tahoe.
It always seems to me that the engine is overgeared in 4th and under geared in 3rd. just not happy in either gear and max speed is about 50mph. I can accelerate in 3rd. can't hold it in 4th.
What I'd like to find is a tire diameter that will let me hold a higher 3rd gear speed.. but still be driveable in 4th on lesser inclines. and flat ground.

Has anyone else found a really sweet tire ratio for the stock 2.1wbx that they like better than the stock wheels..remember this is for hill country
..long grades climbing 1000ft. or more at a time
Seems to me a inch more diameter would be good..but I'm guessing

[Phishman068]

My 225/70/16s do exactly that, but I've never seen it as a benefit. I suppose that in that particular situation it would suffice. I can do 60mph nicely in 3rd, spinning 4000-4200 Rpms, making lots of power. However, hit a hill in 4th if your going less than 65 and you'll be downshifting.
Perhaps a size or two down from mine would be nice for your needs.

[goffoz]

[Phishman068]

They are bfgs and I believe around 29" tall. Specs exist online.
I now have a zetec powering it, and don't really like going past 60 in third. I drove it the same way and speed before my wbxer blew. Though, perhaps that had something to do with it....

[CaptTurbo]

Instead of looking for bigger tires or wheels you might look into buying 10 Cent's exhaust system. I think he's selling them through RMW now. I hope to buy one for my van one day but I'm in body restore mode now and I have to budget for such lovely things. It's on my wish list for sure.

The system I'm talking about is stainless steel and said to give a generous torque increase which will put you up those grades without the down shifts.

[Robw_z]

I have a 1990 2wd manual trans non camper with the stock 2.1- I ran 27" BFG's on my 14" alloys for over a year, but got sick of having low power in stop and go driving, and trouble climbing up hills. After debating for months, I went with 195/75/14 BFG's.

The power increase in stop and go driving has been very nice, and even more pronounced than that is greatly increased hill climbing ability. I live in Idaho and go up significant passes firly frequently. So yes I am saying I have the same tire size as you currently have but am happy. Your discontent is probably justified but if you experienced 27" tires for a year like I did you may find the grass to be greener on the other side (I hope I'm not somehow coming off as a jerk ).

Remember that while a larger tire diameter does translate mathematically to lower RPMs across the board, but that also means the engine has more trouble pushing you along at those RPMs. 195/75/14 is a 25.5" diameter tire, and a 27" tire is usually actually more like 26.8", a 1.3" difference.

I really stressed my tire decision because they are so expensive. Basically I think larger tire diameters are an improvement, regardless of what size of rim they are on, but only if you have added HP which you can only practically get through an upgraded WBX or an engine conversion.

YMMV.

-Rob

[goffoz]

[1621]

No doubt the tire size change will make a difference, though NorCal mountain grades will suffer. Open flatland will be nicer though, certainly on the high speed freeways like 80.

I'd recommend looking at the Derek Drew Gear Ratio calculator (do a search here and find the link in Jon_Slider's thread). While you're not changing gears per say, you are regearing in a sense with the bigger tires. The chart is set up perfectly for you as it will show you where your power bands are at given speeds. There's a provision for you to input tire size data to give you a sense of how it will impact your drive.

I recently regeared my 2wd Westy due to non-optimal power delivery resulting from a larger tire size (28") and weight of the van + five occupants and our gear (5500 lbs.). And this is with a 1.8T moving us along. I wasn't willing to compromise on tire size, and my wife won't allow me to ditch our three sons at the base of each mountain grade, so I changed the ring and pinion for one that improves our power ratio, albeit reducing our theoretical top speed. So while a lot of folks talk about horsepower and torque figures, choosing the optimal gearing is as important, if not more so - and that includes tire size selection. Definitely check out Derek Drew's calculator before making your decision.
_________________
'85 Westy

[goffoz]

[goffoz]