Thoughts - not low profile stuff.

Website · Post by **CovKid** » 11 Mar 2012, 09:10

Just thinking out loud here. At the moment I run on 15" merc steel wheels but the tyre size (overall diameter) isn't much bigger (if any) than when I ran on 14" wheels. I have a 5-speed box and even at virtually stock, 1st is only ever any good when stone cold, 2nd being a better bet to pull away. I can sit in 4th quite comfortably at even 30mph so I figure if I go up a tyre size (plenty of room in my arches for sprinter tyres) I should start to see a more usable gearbox and even gain a few MPG on a run. That sound logical?

Post by **Titus A Duxass** » 11 Mar 2012, 09:46

Sounds logical.

I run 215/65 16 on mine with a standard, slightly restricted, JX.
These are about 5% oversize, the JX just handles it, if I removed the "cat" it would have no problems.

First is more useable and motorway cruising is quieter at 115 - 120 kmh.

The fuel consumption hasn't changed much.

Website · Post by **CovKid** » 19 Mar 2012, 15:16

Thanks Titus. My reasoning can't be far off the mark then.

Post by **ringo** » 19 Mar 2012, 16:43

I went 8% over stock when I fitted the AAZ and it made all the difference to first - I think the only question you need to ask is "how far can I go"

Ringo

Post by **jamesandtheopenroad** » 19 Mar 2012, 17:25

I've got 195/65 14's on mine. First is fine to pull away in, but I'm sure I read somewhere that it's actually slightly less economical with urban driving because you have to use more power to pull away with. That and when you get to a hill, you have to change down sooner into 4th.

I could be talking rubber-ish tho.

Sorry, bad pun.

Post by **andisnewsyncro** » 19 Mar 2012, 18:05

jamesandtheopenroad wrote:I've got 195/65 14's on mine. First is fine to pull away in, but I'm sure I read somewhere that it's actually slightly less economical with urban driving because you have to use more power to pull away with. That and when you get to a hill, you have to change down sooner into 4th.

I could be talking rubber-ish tho.

Sorry, bad pun.

That's considerably smaller rolling radius than standard 185R14

If it's any help, when I swapped from 185R14 to 195R15 on the Syncro 2.1DJ, the gearbox felt much better mid range and the mpg is marginally higher. Cruising speed is very comfy with a bit left in reserve. I knew it was a big change in the radius but thought it worth a try, that was 3 years ago

Website · Post by **CovKid** » 19 Mar 2012, 20:46

All useful stuff. I'm just finding that even with 15" wheels, 1st is virtually redundant on mine so going to 70's might ease the problem a little. I can live with speedo being a little out. Its a quick van for a 1.9 but would be nice to get better use out of 1st and 5th.

Post by **maxstu** » 26 Apr 2012, 16:14

Im running 195/70/15 on Mercs alloy with a 5mm spacers. That size wheel/tyre combination fairly matches original spec of 185/82/14. However, Im concerned my fuel economy is getting afffected. Normally I get 18mpg on gas, and with a following wind 20mpg on long runs at 60mph.

Since fitting alloys now getting 15 and 17mpg respectively. Plus she feels slightly sluggish on inclines. Ive checked all running/rolling gear, brakes are free (new) and bearing set correctly without coming to any conclusion except the alloys/tyres weigh plenty more than standard steelies.

This weekend intend to give her a full service to see if plugs, leads filters etc are combined culprits. and check the LPG set up too.

If no difference found will change back to steel wheels and run her for a few weeks to test.

Anyone else suffering from similar fuel economy issues?

Post by **andisnewsyncro** » 26 Apr 2012, 18:21

All I can think is that it's a pressure issue, although I would have thought there's not a massive difference in the sizes you've mentioned. It can depend on tyre brand - some are better than others, Is this absolutely the ONLY thing you've changed that's made your economy drop? How are you gauging your MPG?

Post by **maxstu** » 26 Apr 2012, 18:44

andisnewsyncro wrote:All I can think is that it's a pressure issue, although I would have thought there's not a massive difference in the sizes you've mentioned. It can depend on tyre brand - some are better than others, Is this absolutely the ONLY thing you've changed that's made your economy drop? How are you gauging your MPG?

Tyres are brand new Matador C rated. Front psi 38-40 and rear 45-47. ve got a small gas tank which takes 32ltrs. Fill it up run 30-50 miles then refill til safety valve cuts off supply from nozzle. Then simple maths. Miles divided by litres used then x 4.5 equals mpg.

Here she is...

Club 80-90 Forums