another Tire/speed thread

[LH Drive]

I was reading about how tire size does'nt matter when it comes to acceleration on another thread. It seams that a taller tire will cover more ground on the same engine drivetrain rotation as to having a smaller tire, say 29" vs 32". I understand it would work out similar to having an overdrive at highway speeds but it does bog you down going up hills. Will having taller tires add more stress to your 2 1/4 lump? As my daily driver I don't see much hwy speed as I keep my LR inside city limits. Its the stop and go lights that has me wondering if mounting 29" tires will be better for my purpose. By accident i ended up with 265/75R16's on my Series, they are very close to 32" tall. It feels like my LR has trouble turning them from take off. I usually have to tinker with my choke till the engine warms up even though it's not winter anymore. I've checked other engine parts and replaced thing that were not broken. Replaced my carb with a webber 34ich thinking this would solve my problem. Installed new points, coil, dist. cap, plugs and wires. Got a faster start and better idle but still the same problem overall. Maybe my Rover seams to think because of my taller tires that im always going up hill and wants to bog down. I even have some kind of long headders on my Turner 8:1, 2.1/4 petro engine that came with my LR. I'm happy with my gas pedal responce and it will do a small burn out in 1st gear on pavment. I don't drive it like its stollen as every break down usually sets me back somehow. Think i'm getting a low MPG driving it compared to other series owners i've read, about 10-11 mpg and somewhere around 14-15 on the Hwy I don't see much. I don't smell fuel like when you run rich and the engine does'nt smoke. I recently snapped a rear axle shaft on the carrier side leaving a stop light. I felt this was due to my larger tires. Has anyone ran smaller tires then upgraded to larger tires on the same truck and noticed any difference?

[Tim Smith]

It sounds like you've got something out of tune. I'm running 33s and have no problems accelerating from a stop. In fact, if the truck is rolling, I've been known to just pop it into 2nd and go. From your description it sounds like you are missing some low end torque.

My style of driving is that once the truck is rolling in the slightest, I just drop the clutch and go. I hate swapping clutches so I tend to avoid clutch slipping as much as possible.

As for your mileage, I also think yours sounds awful low. I'm still not sure but I think I'm getting closer to 18 mpg. Just started my account (http://mpgtune.com/user-profile.php?userId=1419) at mpgtune.com so I'll start getting some solid numbers to reference going forward.

I'm running the Weber 34ICH, with tight valves and well adjusted ignition. Lately I've tended to run my tires at high pressures. About 32 in the front and 27+ in the rear. I used to run about 26 front and 23 rear which was much smoother (and probably safer) but fuel prices have pushed my pressures up a bit.

I'd give it a good tune up and see if you can't get your acceleration and mpg's up a bit. :thumb-up:

[I Leak Oil]

Yes, taller tires affect acceleration, overall speed, fuel mileage, add stress to the driveline, etc. The taller the tire the more of an affect it has. The rim size itself has no affect on these factors but the tire size does. This subject has been beat to death on various forums and many sites even have different calulators to play with to determine what gearing and tire sizes will give you.
Jason T.

[Blueboy]

265/75R16's on my Series



as a side note - that is the OEM size on D90s which as you probably know had a V8.

Jaime

[ArlowCT]

I have run 31"s, 32"s and 29"s on my truck and Have found that the 29"s are the best in my mind. They are really about 30.5" tall and the truck runs great with them. Good power pulling away, great turning radius, and great stopping. Everyone always takes about how quick can you get them going but when you only have drum brakes it also helps having a lighter tire when it comes to stopping.

I also do alot of off roading and have found that the smaller tires help me more times than they hold me back. Also have have not broken anything with the small tires. When running the bigger tires I went through 3 trans, 3 overdrives, 2 rear pumpkins, and 1 halfshaft (I was young and dumb but was also driving alot of miles).

As for the power and fuel mileage with your engine you should be doing better. I have the same weber on a 2.25 with a 9:1 head and get about 17MPG on the highway. I had a set of those headers sitting around and decided to put them in one day. I didn't every make it out to the main road before I turned around, drove home and took them off. Headers work real well with high flow and high horsepower, both not strong points of the rover lump. I would try switching back to the original manifold and seeing how you like it.

Good luck.:thumb-up: